PP11A-0199
Simulated Modes Of Variability In the Permian (251 Ma): The North Panthalassic Oscillation
An Arctic Oscillation-type variability is found and investigated in two multi-millennia fully coupled climate simulations of the Permian/Triassic (251Ma) period using the Community Climate System Model, Version 3 (CCSM3). We refer to this mode of variability as the North Panthalassic Oscillation (NPO) and diagnose its character in both Permian experiments. The first simulation is a realistic representation of the Permian/Triassic boundary where CO2 levels are set to 10 times present day values. The NPO in this experiment manifests in the western Panthalassic Ocean (akin to the Pacific Ocean). The second simulation represents a much colder Permian world where CO2 levels are set to present day values. In this experiment, the NPO demonstrates its ability to change its maximum variance location from eastern Panthalassa (akin to the Atlantic Ocean) to western Panthalassa, by the end of the simulation. The NPO's ability to flip dominance location is influenced by sea ice expansion into eastern Panthalassa and subsequent changes in baroclinicity and storm tracks. Tropical precipitation is also shown to play a smaller role in the cold case where the mid-latitude connection to the tropics is stronger.
PP11A-0200
Closure of the Indonesian Seaway during the middle to late Miocene (13.2-5.8 Ma): Early history of the Western Pacific Warm Pool
We document the waxing and waning of a ‘proto-Western Pacific Warm Pool' and Equatorial Undercurrent (EUC) based on a study of multi-species planktic foraminiferal isotope ratios and census data spanning the 13.2-5.8 Ma interval at ODP Site 806 in the western equatorial Pacific (WEP). We hypothesize that the presence or absence of a proto-warm pool in the WEP, caused by the progressive tectonic constriction of the Indonesian Seaway and modulated by sea level fluctuations, created El Ni~{n}o/La Ni~{n}a-like alternations of hydrographic conditions across the equatorial Pacific during the late Miocene. This hypothesis is supported by the general antithetical relationship observed between carbonate productivity and preservation in the western and eastern equatorial Pacific, a phenomenon caused by these alternating ocean-climate states in the modern ocean. The two-step development and intensification of a proto-warm pool 11.6-9.6 Ma coincides with ice sheet expansion associated with Miocene isotope events Mi5 and Mi6, resulting in a cumulative sea level fall of 50 m and production of Northern Component Water. It also marks the initiation of a more modern equatorial current system as La Ni~{n}a-like conditions became established across the tropical Pacific. This situation sustained carbonate and silica productivity in the eastern equatorial Pacific (EEP) at a time when carbonate preservation sharply declined in the Caribbean. Proto-warm pool weakening after 10 Ma may have contributed to the nadir of a similar ‘carbonate crash' in the EEP. Decay of the proto-warm pool and resultant El Ni~{n}o-like conditions brought higher productivity to the WEP, particularly 9.0-8.8 Ma coincident with a major perturbation in tropical nannofossil assemblages. This interval of increased productivity records the initial phase of the widespread ‘biogenic bloom'. Resurgence of a later proto-warm pool in the WEP 6.5-6.1 Ma may have spurred renewed La Ni~{n}a-like conditions, which contributed to a strong late phase of the ‘biogenic bloom' in the EEP.
PP11A-0201
Circulation Through the Central American Seaway During the Miocene Carbonate Crash
Changes in deep sea circulation in the Caribbean Basin were investigated in order to determine the cause of the carbonate crash in the middle to late Miocene and the impact of the shoaling of the Central American Seaway (CAS) on larger scale circulation patterns. Gateway events, such as the shoaling of the CAS, have long been associated with the reorganization of ocean circulation and dramatic climate events. The distribution of water masses in the Caribbean region was evaluated using Nd isotopes from fossil fish teeth from three ODP sites: Site 998 in the northern Caribbean Basin (3179 m water depth), Site 999 in the southern Caribbean (2897 m), and Site 846 from the eastern equatorial Pacific (3296 m). Prior to the carbonate crash in the Caribbean (14 to 12 Ma) εNd values increased from -6 to ~-3, while carbonate mass accumulation rates \(MARs\) decreased. During the crash interval εNd values were highly variable within the Caribbean basin with values ranging between -4.4 and 0; the highest values correlate with intervals of greatest dissolution. As carbonate MARs increased following the crash εNd values in the Caribbean began to decrease, reaching a value of ~-6 by 9 Ma. The carbonate crash in the eastern equatorial Pacific lags the Caribbean crash by about 0.5 Ma. Prior to the crash εNd values at Site 846 increased from -4 to -2. They then remained relatively steady during the crash. The radiogenic Nd values in the Caribbean basin are much higher than any values recorded in the Atlantic throughout the Cenozoic. The possibility that these values are altered by ash diagenesis in the Caribbean has been evaluated, but there is no correlation between intervals of ash deposition and radiogenic εNd values. However, these radiogenic values are similar to values reported for Pacific intermediate and shallow waters during the Miocene. It appears that corrosive, intermediate Pacific waters were gradually introduced into the Caribbean prior to the crash, while pulses of almost exclusively shallow to intermediate Pacific waters filled the Caribbean during the crash. This inflow of Pacific waters through the CAS has been predicted by several GCMs investigating the affects of CAS sill depths and the location of the ITCZ on Northern Component Water (NCW) production and flow directions through the CAS. Periods of enhanced NCW production correlate with intervals of more intense dissolution in the Caribbean, suggesting that aging of the water along the conveyor belt flow path from the North Atlantic to the Pacific creates more corrosive Pacific Deep Water, which then contributes to North Pacific Intermediate Water and Pacific Central Water. These corrosive waters flow southward producing more radiogenic εNd values and carbonate dissolution in the equatorial Pacific and Caribbean Basin. Shoaling of the CAS and a decrease in NCW combine to limit the flow of radiogenic, corrosive waters into the Caribbean. This reduction in Pacific throughflow is documented by the decreasing εNd values beginning at ~10 Ma at Site 998 and continues until ~5Ma as documented by εNd data from a ferromanganese crust located in the Straits of Florida.
PP11A-0202
Temporal and Spatial Changes in Bottom-Water Oxygenation in the Japan Sea During the Late Quaternary : The Effects on the Benthic Foraminiferal Assemblages
Late Quaternary hemipelagic sediments in the Japan Sea are characterized by alternating beds of light and dark layers which are synchronous basin-wide and considered to be reflections of bottom-water oxygenation during the depositions (Oba et al., 1991; Tada et al., 1999). In this study, benthic foraminiferal assemblages are analyzed to understand temporal and spatial variations of sea-floor environments during times of dark layer formation for the last 160ka, based on the 3 cores IMAGES MD01-2407 and D-GC-6 recovered at the same position (water depth 932m) in the southeastern Japan Sea, and KR05-09, PC-1 (water depth 1792m) in the northeastern Japan Sea. The dark layers in these cores are classified into six types by dominant species of benthic foraminifera and benthic foraminiferal abundance mainly in the core MD01-2407 (Usami et al., 2007), as follows: Barren-type (almost absent of benthic foraminifera), Angulogerina-type (abundant Angulogerina ikebei), mixture-type (relatively high species diversity and equitability), Islandiella-type (abundant Islandiella norcrossi), Eilohedra-type (abundant Eilohedra nipponica), Brizalina-type (abundant Brizalina pacifica). In the core KR05-09, PC-1, to the contrary, benthic faunas are adopted only three types, barren-type, mixture-type and Brizalina-type. In particular, most of the dark layers from MIS3 to 5b are barren-type, suggesting more severe oxygen depletion in benthic ecosystem of the northeastern Japan Sea. Oba, T., Kato, M., Kitazato, H., Koizumi, I., Omura, A., Sasaki, T., Takayama, T., 1991. Paleoenvironmental changes in the Japan Sea during the last 85,000 years. Paleoceanography 6, 499-518. Tada, R., Irino, T., Koizumi, I., 1999. Land-ocean linkages over orbital and millennial timescales recorded in late Quaternary sediments of the Japan Sea. Paleoceanography 14 (2), 236-247. Usami, K., Ohi, T., Hasegawa, S., 2007. Foraminiferal response to late Quaternary climate variability in the Japan Sea : Concerning low oxygen environment and productivity. 9th International Conference on Paleoceanography [ Shanghai, China ], Abstracts (in press).
PP11A-0203
Ice free Arctic Ocean, an Early Holocene analogue.
Extensive systems of wave generated beach ridges along the North Greenland coasts show that these areas once saw seasonally open water. In addition to beach ridges, large amounts of striated boulders in and on the marine sediments from the same period also indicate that the ocean was open enough for ice bergs to drift along the shore and drop their loads. Presently the North Greenland coastline is permanently beleaguered by pack ice, and ice bergs are very rare and locked up in the sea ice. Predictions of the rapidly decreasing sea ice in the Arctic Ocean generally point to this area as the last to become ice free in summer. We therefore suggest that the occurrence of wave generated shores and abundant ice berg dropped boulders indicate that the Arctic Ocean was nearly free of sea ice in the summer at the time when they were formed. The beach ridges occur as isostatically raised "staircases", and C14-dated curves for relative sea level change show that they were formed in the Early Holocene. A large set of samples of molluscs from beach ridges and marine sediments were collected in the summer of 2007, and are presently being dated to give a precise dating of the ice free interval. Preliminary results indicate that it fell within the interval from c. 8.5 to c. 6 ka – being progressively shorter from south to north. We therefore conclude that for a priod in the Early Holocene, probably for a millenium or more, the Arctic Ocean was free of sea ice at least for shorter periods in the summer. This may serve as an analogue to the predicted "greenhouse situation" expected to appear within our century.
PP11A-0204
Effects of Mountain Height on the Atlantic and Pacific Thermohaline Circulations
Geological evidence indicates that mountain uplift, such as those in southern Asia and western North America, occurred on large scales during the middle and late Cenozoic. Models have shown that mountain uplift is associated with changes in monsoon due to alteration of wind patterns and shifting of areas of high precipitation. These changes are accompanied by drier conditions in the continental interiors, as seen in the central Asian desert, and SST decreases over the western Indian Ocean. In our experiments, we use a low-resolution, fully- coupled GFDL ocean-atmosphere-land surface model to investigate the effects of mountain height on the deeper ocean and focus on the thermohaline circulation of the Atlantic and Pacific Oceans. The series of experiments consists of the global orography being fixed at a certain fraction of the present day values (control case), ranging from 0% (ie flat orography) up to 140%. Land distribution and initial conditions are kept the same for all experiments. Depending on the mountain heights, the model in each experiment is integrated for 1000-2000 years. Results show that, in the extreme case of flat orography, there is a complete switch-over from a strong meridional overturning in the Atlantic to one in the Pacific. Moreover, the Pacific overturning, which reaches an equilibrium state within 800 years, is much stronger than that of the Atlantic in the control case (27Sv compared to 19Sv). The Pacific overturning is accompanied by deep downwelling, especially in the northwest Pacific, and a stronger Kuroshio current. Heat exchange between the atmosphere and ocean appears to be important to the maintenance of the Pacific overturning. As mountain height is increased, the maximum Pacific overturning strength attainable is reduced gradually. The scenario in which mountain height is set to 50% of that in the control case represents a threshold whereby strong overturning in the Atlantic starts to develop and after which there is no longer significant activity in the Pacific.
PP11A-0205
Improving the Accuracy of Core Location and Recovery Estimates Through the Integration of Core Data, Wireline Logs and Drilling Parameters: an Example From IODP Expedition 310, Tahiti Sea Level
In palaeoclimate and sea-level studies accurate depth positioning of core pieces is critical in assessing the usefulness of a specific drill site. The location and amounts of core recovered during a drilling program can often place severe constraints on the subsequent applications of core measurements. The principle objectives of Expedition 310 are to establish the course of postglacial sea level rise at Tahiti in the South Pacific, to define sea surface temperature (SST) variations for the region over the period 20 to10 ka, and to analyse the impact of sea level changes on reef growth and geometry. Average conventionally-calculated core recovery for the 37 boreholes drilled during this expedition is 57.47 percent, although for an individual borehole core recovery is highly variable. Depth inaccuracies increase as recovery falls below 100 percent as, by convention, core is placed at the top of the core barrel run from which it was recovered. Careful integration of datasets can improve the positioning of core. The Expedition 310 logging programme included the collection of high resolution optical and acoustic images. Visual correlation of the recovered core with these image logs provides an extremely effective method of integrating these datasets. Comparison of drilling parameters (rate of drilling, pullback pressure and torque on bit) with the downhole logs indicates a clear correlation between these datasets and allows the logging data to be accurately matched to the drilling data. The final integrated depths comprise the underlying framework for all subsequent scientific analyses of recovered core employing interpretations based on depth. There are two principle outcomes of the integration process: (i) Accurate depth positioning can be achieved. In coral reefs where regions of high porosity and large void spaces are common, without careful integration of discrete core pieces with continuous records of the nature of the borehole, large depth errors can result and propagate through analyses. (ii) Core recoveries can be accurately estimated. Estimates based on core alone cannot take into consideration meso or macro scale porosities. Utilising continuous geophysical measurements allows areas of high porosity to be identified and incorporated into the calculation of recovery percentages.
PP11A-0206
Improving the Depth-Time Fit of Holocene Climate Proxy Measures by Increasing Coherence with a Reference Time-Series
An accurate assessment of historical local Holocene data is important in making future climate predictions. Holocene climate is often obtained through proxy measures such as diatoms or pollen using radiocarbon dating. Wiggle Match Dating (WMD) uses an iterative least squares approach to tune a core with a large amount of 14C dates to the 14C calibration curve. This poster will present a new method of tuning a time series with when only a modest number of 14C dates are available. The method presented uses the multitaper spectral estimation, and it specifically makes use of a multitaper spectral coherence tuning technique. Holocene climate reconstructions are often based on a simple depth-time fit such as a linear interpolation, splines, or low order polynomials. Many of these models make use of only a small number of 14C dates, each of which is a point estimate with a significant variance. This technique attempts to tune the 14C dates to a reference series, such as tree rings, varves, or the radiocarbon calibration curve. The amount of 14C in the atmosphere is not constant, and a significant source of variance is solar activity. A decrease in solar activity coincides with an increase in cosmogenic isotope production, and an increase in cosmogenic isotope production coincides with a decrease in temperature. The method presented uses multitaper coherence estimates and adjusts the phase of the time series to line up significant line components with that of the reference series in attempt to obtain a better depth-time fit then the original model. Given recent concerns and demonstrations of the variation in estimated dates from radiocarbon labs, methods to confirm and tune the depth-time fit can aid climate reconstructions by improving and serving to confirm the accuracy of the underlying depth-time fit. Climate reconstructions can then be made on the improved depth-time fit. This poster presents a run though of this process using Chauvin Lake in the Canadian prairies and Mt. Barr Cirque Lake located in British Columbia as examples.
PP11A-0207
Chydorid Ephippia – a Promising Tool for Climate Reconstruction
Ephippium analysis, a recent palaeolimnological method, uses the two reproduction strategies of littoral water fleas of the family Chydoridae (chydorids) to estimate the past length of open-water season in cold-temperate lakes. In northern lakes chydorids reproduce asexually during most of the open-water season until the oncoming winter triggers sexual reproduction. This results in the appearance of males and sexual females, and after fertilization, the formation of a modified female shell (carapace), the ephippium, which protects the resting eggs. Chitinous chydorid remains, including ephippia, preserve well in lake sediments and can be identified to species level. In a mild climate (long open-water season) the period of asexual reproduction is long compared to the period of sexual reproduction, resulting in a higher proportion of shells of asexual females being deposited in sediments than in cold climates where the proportion of ephippia (shells of sexual females) increases. Surface sediment samples were collected from 90 Finnish lakes. The lakes are situated along a transect across Finland where the average open-water season varies from 213 days in the south to 137 days in the north and where annual temperatures vary from +5° C to -2° C, respectively. We tested with statistical methods the relationship between the present ephippium proportions and the present climate normals (1970 – 2000). The preliminary results indicate a clear increase of ephippium proportions from N 60º to N 70º. The linear correlation is highest between ephippium proportion and June temperature (-0.84***). The aim of the study is to provide a model for climate reconstructions on the basis of the analysed data to be applied on past sediments
PP11A-0208
Evidence of Lacustrine Bedforms in Lake Champlain, Vermont
High resolution CHIRP seismic profiles reveal the presence of two large lacustrine sediment drifts (Drifts A and B) located in Lake Champlain's Juniper Deep. Both drifts are positive features composed of highly laminated sediments overlying trough-filling acoustically-transparent sediment. Both drifts are oriented approximately north-south and are parallel to a steep ridge along the eastern shore of the basin. Drift A, located at the bottom of a structural trough, is classified as a confined, elongate drift that transitions northward to become a system of mudwaves. Drift B is perched atop a structural high to the west of Drift A and is classified as a detached elongate drift. Bottom current depositional control was inferred from the orientations of the bedforms and modern lake circulation patterns. Sediment thicknesses and volume estimates were used to create isopach maps and 3-dimensional images detailing drift evolution. Sediment cores were taken at the crest and at the edges of the drifts. Drift source, deposition, and evolution will be discussed in the context of the regional history of the Lake Champlain Valley.
PP11A-0209
Paleoclimatic record of the late Quaternary from a gravity core sediment of Lake Hovsgol in northern Mongolia
Gravity core sediment (HS 7) from Lake Hovsgol(Mongolia) is divided into three sedimentary units on the basis of sediments texture, water contents, occurrence of fossils and sediment color. Unit 1(27¢¦128§¯) is generally massive and is crudely stratified. Ostracods are well preserved over the all interval of Unit1, but diatoms are not well preserved. At Unit2(9¢¦27§¯), mud content is slightly low and lamination is well developed. It is dark greenish gray in the upper part, and dark greenish gray is alternating with light brownish gray in the lower part. Diatom contents increase towards the top and ostracods fragments disappear at the top of Unit 2. Unit3(0¢¦9§¯) is laminated mud in olive gray color. Diatom contents are high but ostracods are not observed in this unit. According to 14C age dating results, we assumed that Unit1 is Pleistocene sediment, Unit2 is sediment of a transitional stage and Unit 3 is Holocene sediment. Chemical composition of trace elements from ostracods show variations through Unit1, especially showing a distinct change at 95¢¦100§¯ interval. It matches to the distribution of ostracod at this interval. Contents of ostracod decrease at the interval and contents of Cytherissa lacustris decrease, but Limnocythere inopinata increase. It was interpreted that warm air was supplied to Lake Hovsgol after LGM(Last Glacial Maximum), causing ice melting. Consequently the bottom environment of Lake Hovsgol experienced some changes as the lake level increased little bit. At the top of Unit 1 appear a lots of pyrite which are arranged in line, and diatoms occure but ostracods are not observed toward the top of Unit 2, and lamination is developed in Unit 2. It means the bottom environment of Lake Hovsgol changed to anoxic condition. At that time, plenty of water was supplied into the lake, resulting in water stratification and cutting off oxygen supply to the bottom of Lake Hovsgol. It made the lake level rise higher, so that the bottom environment changed from oxidation to reduction environment. Finally, the habitation condition of ostracod was destroyed and ostracods couldn't survive there after the end the Pleistocene. This change is more distinctive than that at 95¢¦100§¯ interval. It was probably caused by the effect of decreasing effect of Siberia air mass which was dry and cold, and by increasing warm and humid air mass. So an inflow of warm and humid air mass into the region of Lake Hovsgol incurred ice melting and higher precipitation. It seems that strengthening of East Asian monsoon brought on that climate change. Positive value of ¥ä13C of Unit3 is most of due to the lake water DIC equilibrated with the atmospheric carbon value and increased the photosynthesis after LGM in late Pleistocene.
PP11A-0210
Ground Penetrating Radar, Magnetic and Compositional Analysis of Sediment Cores and Surface Samples: The Relationships Between Lacustrine Sediments and Holocene Lake- Level and Climate Change at Deming Lake, Minnesota, USA
Deming Lake is a small (<1 square km), deep (about 17m), meromictic kettle lake situated near the prairie- forest boundary, in Itasca State Park, MN. Because of the lake's location and morphology, the accumulated sediments comprise a high-resolution record of limnological and ecological changes in response to Holocene climate variations. We used a shore perpendicular transect of three cores (located in littoral, mid-slope, and profundal settings) and ground penetrating radar (GPR) profiles to investigate Holocene lake-level variability at Deming. Cores were sampled continuously at a 1-2 cm resolution and sediment composition (in terms of percent organic matter, carbonate material, and minerogenic residue) was determined via loss on ignition (LOI). Isothermal remanent magnetization (IRM) and anhysteretic remanent magnetization (ARM) were used as proxies of magnetic mineral concentration and grain size. Four lithostratigraphic units were identified and correlated between cores based on these analyses. Changes in GPR facies corroborate the correlation between the two shallow cores. In order to inform our interpretation of down-core variations in magnetic properties and LOI values in terms of variations in lake depth, a suite of over 70 modern sediment samples were collected from the basin and analyzed. LOI compositional variability across the basin was high, with no clear trends related to depth or distance from shore. A sharp decrease in minerogenic content was observed at depths consistent with a predicted wave-base of 0.5 m, but aside from this trend it appears the steep slopes of much of the basin promote gravity driven slumping and mixing of sediments at depth. In the profundal sediments IRM values are routinely 5% higher than in the slope and littoral environments, while ARM/IRM ratios indicate an increase in magnetic grain size with water depth. We infer that an increase in coarse organic material in the shallow-water cores of Deming records a period of aridity (associated with a decrease lake-level less than 2m based on GPR profiles) and/or increased water clarity during the regionally expansive mid-Holocene dry period. We do not see clear evidence of late-Holocene lake level change of a significant magnitude (i.e. >1m). While remanence measurements (especially IRM) often correlate with the LOI residue, interference in the IRM resulting from the dissolution of magnetic minerals casts uncertainty into the reliability of our magnetic measurements as a signal of climate driven limnological change. Additional measurements must be performed before definite interpretations about the lake-level changes at Deming can be made. We suggest that future studies look more closely at the near-shore record (water depths <1m), as our results indicate shoreline migration in response to moisture balance fluctuations during the last 1000 years (as recorded at numerous sites in the great plains and upper Midwest) may have been subtle.
PP11A-0211
Basement and Stratigraphic Characteristics around Kansai International Airport (KIX), Osaka sedimentary basin, Japan - Integrated Analysis of Geophysical Data -
Osaka sedimentary basin in the southwest Japan, includes Osaka Bay and Osaka Plain. Several urban areas are situated around the bay. The basin is surrounded by many active faults. Detailed underground structure plays important role to seismic hazard for urban areas. The basin consists of granitic basement and overlaying thick unconsolidated sediment called as the gOsaka Grouph. Several marine clay layers of the Osaka Group are key layer for stratigraphy and are useful for interpretation of seismic profiles in the basin because marine clay layer is continuous and indicate wide distribution. The bottom of marine clay layer is confirmed clearly in the seismic profile due to high acoustic impedance between clay and coarse sediments. Many detail geological and geophysical information have been accumulated as the results of various survey after the 1995 Kobe Earthquake. These survey revealed underground structure and stratigraphy of Osaka Group of northwestern part of the basin. On the contrary, there are few subsurface information in the southeastern part of the basin. Several survey for estimation of seismic hazard, were carried out in the southeastern part of the basin. In the view point of the stratigraphy, Kansai International Airport (KIX) plays significant role. New second runway was opened at 2nd Aug. 2007. Before constructing the KIX airport, many geological and geophysical surveys have been performed. Accumulated data are basic information of stratigraphy and sedimentary environment in the southern part of the basin. Gravity and tremor surveys were carried out to estimate underground structure beneath the second runway before opening the runway. Deep borehole to basement is drilling in the second runway. The information derived by this borehole provides remarkable information. Recent deep borehole information will modify previous results. Thus, we summarized previous study to compare new results. In this study, we summarized information derived form geophysical surveys. The basement configuration were inferred form compiled result of gravity, tremor and seismic surveys. The seismic profiles around KIX were attempted to re-interpretation. In the poster, we will discuss characteristic of the local sub-basin with the basement configuration and interoperated seismic profiles.
PP11A-0212
Precessional and Sea Level Induced Hydrological Changes in the Mediterranean Sea During the Messinian Salinity Crisis
The Messinian Salinity Crisis (MSC) occurred nearly 6 million years ago when tectonic uplift closed the straits connecting the Mediterranean Sea (MS) with the Atlantic Ocean. High rates of evaporation and diminishing water input led to a 1500-2500 m drop in MS level and the deposition of a thick layer of evaporites (Hsu et al, 1973). Cyclic patterns in evaporite deposition during the MSC have been correlated with variations in precession. It is important to model both sea level induced climatic changes and precessional changes to see how they feedback on the hydrological cycle and therefore the desiccation process during this remarkable event. In this study, experiments were conducted using the National Center for Atmospheric Research (NCAR) Community Atmosphere Model (CAM 3.1) configured with a Slab Ocean Model (SOM). We attempted to break down the series of events that occurred during the MSC to isolate the effect of each separate component on the atmosphere. In all experiments the horizontal ocean heat transport is turned off to represent the isolation of the MS from the Atlantic Ocean. The first experiment simulated the beginning of the MSC when a substantial sea level lowering occurred and extremely dry conditions led to deposition of the "Lower Evaporite" layer. In this experiment the level of the MS is reduced by 1500 m and water is removed from the basin. Lowering the sea level of the MS results in anomalous cooling of more than 2 K in the North Pacific. This agrees with proxy data that indicates extensive glaciation just after the initiation of the MSC. Another experiment simulated the end of the MSC during the Lago-Mare event when water is believed to have existed at the bottom of the desiccated sea. In our Lago-Mare experiment, the sea level is reduced up to 1500 m but water remains in the basin. Our Lago-Mare simulation results in anomalous wintertime warming of more than 10 K over the MS. Anomalous heating drives local changes in the wind field that leads to convergence at the northern margin of the basin. This yields a topographically induced precipitation anomaly of more than 1500 mm yr-1 over the Alps when water remains at the bottom of the basin. This result supports geological evidence of wetter conditions in the peripheral mountains that are believed to have led to more humid conditions during the Lago-Mare event. New results simulating the influence of the precessional cycle on the climate of the desiccated basin in both scenarios will be presented. Precessional variations, which influence the hydrological cycle, may play a key role in the desiccation process.
PP11A-0213
Reconstruction of the pressure pattern over Japan using two-point pressure/temperature datasets
The temperature and pressure differences between Tokyo and Nagasaki were applied for reconstruction of the past climate conditions. January and July in each year since the 1820fs were divided into several types characterized by sea level pressure patterns. The findings indicated that the warming after 1900 (after the decline of the so-called Little Ice Age) and again after 1960 can at least partly be attributed to a increase in frequency of warm circulation types at the cost of cold types. The different nature of the shift in circulation types around 1900 and 1960 suggest that the mechanisms behind these warmings are of a different nature.
PP11A-0214
Calibration of meteorological conditions with tree ring chemistry: high-resolution stable isotope evidence from robotically micromilled cellulose
Stable isotope values of tree ring cellulose record variation in humidity, soil moisture and stable isotope values of precipitation. We refine and constrain this hypothesis by examining tree ring cellulose from the northeastern United States. Cottonwood trees ( Populus deltoides) from Green Lake State Park (GLSP) in central New York State were robotically micromilled to recover discrete high resolution aliquots of cellulose that represent as little as two weeks growth. Cellulose δ13C, δ18O and δD values were compared to instrumental meteorological records, including temperature, precipitation (amount and isotope value), and humidity to evaluate the integrity with which tree cellulose records atmospheric conditions. Trees from GLSP were selected because they are adjacent to our precipitation collection site and our long carbonate-based climate record recovered from Green Lake sediment that has been calibrated with a century of meteorological data. A detailed cellulose-based record can extend our calibration of lake sediment back beyond the century long meteorological record. Thus, by fine-tuning the carbonate record using tree data an accurate climate record dating back millennia can be generated. Correlations between meteorological, carbonate sediment and tree ring records provides a more robust model for interpretation of climate variability using tree ring and carbonate isotope values. Aliquots of cellulose were recovered using a computer-controlled robotic micromilling device at a spatial resolution of ~0.5mm. Ring widths of our cottonwood trees were up to 7mm, permitting high-resolution sampling. δ13C, δ18O and δD values were obtained from each of the 410 collected samples resulting in a continuous record from 1944-2006. Substantial inter- and intra-seasonal variability is apparent in δ13C values that vary by up to 2 permil seasonally and 5 permil over our 62-year tree record. Time-series wavelet analysis of isotope and meteorological data demonstrate a strong solar-climate influence, with δ13C lagging behind solar activity by 5-6 years. Lake sediment carbonate δ13C values lag behind tree cellulose δ13C value, interpreted to represent the time required for decay of cellulose and incorporation into the lake's dissolved inorganic carbon reservoir. A significant decrease in δ13C beginning in the early-mid 1980's is attributed to lower SO2 concentrations in the atmosphere (known to interfere with leaf stomata) related to declining steel production. Oxygen values conflate a number of variables, including water sources, temperature and moisture stress resulting in considerable intra-seasonal variability. δ18O values vary by 6 permil over the life of the tree. A record of δD values will likewise be presented.
PP11A-0215
Precipitation Fluctuation In The Past 5000 Years In The Northern Vietnam Inferred From Stalagmite Geochemical Data
We present geochemical proxy records of 2 stalagmites, S14-4 and S14-B collected respectively from the inner and outer chambers of the cave S14, located at Son La province, northern Vietnam, over the past 5000 years. The stalagmite S14-4 provides a serial δ18O record from 5000-350 yrs B.P. High growth rate and depleted δ18O values suggest a relatively wet condition at the beginning of mid Holocene. After a transition period at 4000-3000 yrs B.P., a dry interval in the late Holocene is revealed. Three obvious hiatuses recorded in the stalagmite S14-B were dated as 4800-4200, 3200-2750, and 2150-1750 yrs B.P. These discontinuities coincide with the periods of low δ18O values of S14-4, which implies that there were 3 centennial-scale dry events. High uranium concentration of 2-12 ppm at the windows of 4200-3200 yrs B.P. of S14-4 and 4200-2150 yrs B.P. of S14-B indicates a strongly chemical weathered outcome. Events of the Medieval Warm Period and Little Ice Age can also be recognized in δ18O records.
PP11A-0216
New Measurements from Old Boreholes: A Look at Interaction Between Surface Air Temperature and Ground Surface Temperature
We recently logged new field measurements of several boreholes throughout the Midwest, including North Dakota, South Dakota, and Nebraska. We then compared these new measurements against measurements previously obtained. Our comparisons included inverse modeling of past and recent measurements as well as climate modeling based on past surface air temperatures obtained from the weather stations. The data show a good correlation between climate warming in the last century and ground surface warming. Of particular importance is that cooling of air temperatures beginning in the mid 1990s reflects in the ground surface temperatures. The boreholes included in the study consist of three boreholes located in north central North Dakota, including two deeper than 200 meters. Two boreholes in the southwestern part of South Dakota, and two from southeastern South Dakota, all approximately 180 meters deep. Also included, were two boreholes (135 meters and over 200 meters deep) located in southwestern Nebraska, and two boreholes in the panhandle of Nebraska, each over 100 meters deep. We obtained historical surface air temperature from climate stations located near the boreholes, both from the United States Historical Climatology Network and from the Western Regional Climate Center.
PP11A-0217
Sediment fabric types reveal Late Neogene precessional forcing in Guaymas Basin, Gulf of California
The North Pacific Subtropical High (NPSH) annual migration drives west coast seasonal upwelling and gives impetus to the Trade Winds, creating a coastal OMZ and enhancing preservation. Modern observations and palaeoclimate records show that NPSH migration varies on interannual to millennial timescales. In modern Guaymas Basin, a restricted basin situated at the wet/dry Subtropical divide, varved deposition results from dry- season diatom productivity and wet-season terrestrial flux. High-resolution logging of 75 percent laminated, 63 m, continuous piston core MD02-2515 and 6 m kasten core MD02-2517 has identified eight sediment fabric types. Based on observed climate and supported by climate proxies (discrete and continuous X-ray fluorescence, magnetic susceptibility, biogenic silica, total organic carbon), these types are interpreted as the result of climatic conditions produced by variations in NPSH migration. Measurement of varve thickness and detailed correlation with nearby radiocarbon dated core JPC-56 (Keigwin, 2002) gives an age range of 0-36kyr. Systematic variations in the predominance of one or more sediment types reveal precessional forcing, which drives a 5000-year oscillation of millennial- and centennial-scale wet/dry cycles, with significant non-laminated intervals occurring every 5000 years.
PP11A-0218
Tropical sea Surface Temperature and Salinity Variability During Deglaciation Inferred From A new Tahitian Coral Oxygen Isotope and Sr/Ca Record
We investigate tropical sea surface temperature (SST) variability during the last deglaciation from a subfossil Porites coral. Since this species is still growing in the same location today, this analysis allows for a direct comparison between modern and prehistoric behavior as deglaciation proceeded. The coral sample was recovered during IODP Leg 310 drilling of offshore fossil reefs (sample 310 11A 6R 1W 27,0-40,0). Stratigraphic evidence and mean δ18O values suggest that the coral grew as sea level began to rise just following the last glacial maximum; these inferences will be confirmed with U-series dating now in progress. Exploration for diagenetic features using SEM and thin sections has allowed us to identify the parts of the coral slab most suitable for paleoclimate analysis. To reconstruct sea surface conditions during this time, we measured δ18O and Sr/Ca at 0.5mm resolution; annual density banding indicates that our record spans roughly 15 years with an annual growth rate of 9-15 mm/yr. Mean oxygen isotope values fall about 2‰ heavier than a modern coral from neighboring Moorea. Assuming an ice volume correction of 0.8-1.0‰, our δ18O results suggest that cooler SSTs were probably accompanied by regional seawater δ18O increases, as a paleotemperature interpretation of the isotopic results yields values around 5- 6oC, larger than expected. Modern Sr/Ca calibration data are planned to allow us to use Sr/Ca to partition the temperature and seawater isotope components of this signal, and replication of both Sr/Ca and δ18O will allow us to assess additional uncertainties. The annual cycle of coral δ18O is comparable or slightly reduced from the modern, although differences in site exposure may partly account for the difference we observe. We will compare our temperature inferences with additional data and with coupled model results.
PP11A-0219
Glacial and Interglacial Climate Variability in Guaymas Basin (Gulf of California) from a Varved Record
To test for interaction between long and short climate cycles it is necessary to reconstruct records of interannual to decadal variability over sufficiently long time periods. Marine varved sediments are one of the few archives with the necessary resolution. The latest Quaternary in sediment core MD02-2515 (65m, 7 to 38 kyr) from the Gulf of California is predominantly varved with few bioturbated intervals (e.g. the Younger Dryas). The Guaymas Basin allows reconstruction not only of regional upwelling and precipitation but also of ocean circulation in the North Pacific (intermediate water) and equatorial Pacific (subsurface water). The material is therefore ideally suited to test for interaction between all scales of climate variability, from orbital scales (glacial/interglacial) via millennial (D/O cycles) to interannual oscillations (ENSO). A varve age model has been compiled, supported by correlation of delta15Norg data with the GISP-record, allowing estimation of biogenic and lithogenic fluxes at annual to near annual resolution. During the last glacial the rates of opal, TOC and lithogenic material were 2-3 times higher than during the Holocene, indicating that total mass fluxes control the export production of carbon. Dysoxia in the basin is mainly controlled by regional productivity (as opposed to intermediate water circulation) as seen from a strong correlation between opal and delta13C in benthic foraminifers. The distribution pattern of opal does not correlate with typical North Atlantic patterns (e.g. D/O cycles). Annual resolution records of opal content and delta15N in laminated intervals from the last glacial, Bolling/Allerod, and Holocene all show ENSO-like variability but there is no consistent change in strength or frequency.
PP11A-0220
Paleoenvironmental Reconstruction of a Glacial-age Sediment Core From Baldwin Lake, Southern California: Evidence for Multi-timescale Climate Variability
A detailed multi-proxy sedimentological and high-resolution thin-section image analysis was conducted on a glacial-age (20,000-65,000 calendar years BP) 14-meter sediment core from Baldwin Lake, Southern California. The results are used to investigate the difference in depositional environment and process between the core's two predominant sediment units: massive versus laminated/semi-laminated sediments. Massive sediments produce typically high magnetic susceptibility, low total organic matter, and high mean grain-size values. An analysis of thin-sections from the massive sediments reveal a heterogeneous sediment fabric lacking any distinct structures. Laminated and semi-laminated sediments produce generally low magnetic susceptibility, high total organic matter, and low mean-grain-size values. Thin-sections from laminated sediments reveal very diffuse cm-scale laminae couplets of alternating light and dark layers. There are, however, two laminated sections, which deviate from the latter characterization. These two "anomalous" sections contain highly variable magnetic susceptibility, low total organic matter, and variable mean grain-size values. Based on the data above, four lacustrine facies are proposed: (L1) organic-poor, massive, medium-to coarse-silts with high magnetic susceptibility represent deposition in a playa lake environment; (L2) organic-rich, massive and semi-laminated, fine-to medium-silts with high magnetic susceptibility represent deposition in a shallow lake with highly variable lake levels; (L3) organic-poor, semi-laminated to laminated, fine-to coarse-silts with highly variable magnetic susceptibility represent a persistent shallow lake environment; and, (L4) organic-rich, semi-laminated to laminated fine-to medium silts with low magnetic susceptibility represent deposition in a deep lake environment. At the facies scale, the lake's hydrologic state appears related to hemispheric climate patterns based on a comparison to the GISP2 oxygen isotope record. To investigate the finer-scale (sub-centennial) variability, a gray- scale digital image analysis of the sediment thin-sections was pursued assuming a constant sedimentation age model between dates. The image analysis shows a high degree of variability within both massive and laminated sediments. Wavelet analysis and wavelet spectrum of the gray-scale data in the massive, semi-laminated, and laminated sediments reveal a fairly dominant multi-decadal scale signal (10-100 yrs). A weaker sub-decadal signal (2-7 yrs) is present for all sediment types, but only the laminated sediments show this sub-decadal signal consistently. Temporal variability in the wavelet spectrum for the massive and some laminated sediments argues for a non-stationary climate regime during the last glacial period. Tentatively, we assign sub-decadal variability to ENSO. The dominant multi-decadal scale signals may be linked to complex ocean-atmosphere dynamics such as the PDO and AMO. These results suggest that both ENSO and the PDO influenced glacial climate in Southern California. However, our data also suggest that these systems were non-stationary through time.
PP11A-0221
Age Constraints On Interglacial Sediments Beneath The Former Center Of The LIS Using OSL And U-Th Dating
The main rivers of the Hudson and James Bay lowlands expose an extensive sedimentary record consisting of several glacial units locally interbedded with pre-Holocene nonglacial sediments. The presence of nonglacial sediments near the former geographic center of the Laurentide Ice Sheet (LIS) is significant because it implies a large reduction of ice volume or a completely ice-free episode (i.e. interglacial). Distinguishing between these two scenarios has been a recurrent problem in the lowlands because of the lack of reliable ages on these deposits. Radiocarbon dating of these deposits routinely yielded infinite ages while thermoluminescence dating gave ages requiring unrealistic paleogeographic reconstructions. Here we use three different methods to date an extensive pre-Holocene nonglacial unit that crops out along the Nottaway River and Harricana River in northwestern Québec. This unit consists primarily of an accumulation of abundant compressed wood fragments and organic-rich clays of about 5 m in thickness along the Nottaway River, while fluvial sands comprising abundant wood fragments and organic matter of about 3 m in thickness are exposed along the Harricana. Along both rivers, these sediments lie below several glacial and glaciolacustrine units. Radiocarbon dating of two wood fragments yielded infinite ages of 55.2 ka and 54.8 ka on the Nottaway and Harricana rivers, respectively. Uranium-Thorium (U-Th) dating was carried out on four samples of compressed wood logs of the Nottaway River. Because living wood does not contain significant Uranium concentrations in its structure, the Uranium measured in fossil wood samples likely originates from diagenetic uptake. The calculated U-Th age can thus be considered as a minimal age, given that the system remains closed after this uptake phase. Reproducible results were obtained from the four samples which yielded U-Th ages ranging between 100 and 110 kyr, with an average age of 106.3 ± 2 ka, thereby suggesting a single phase of Uranium uptake during burial or early diagenesis. Optical luminescence dating of the wood-bearing fluvial sands on the Harricana River also support the antiquity of the nonglacial unit, and preliminary measurements suggest and an IRSL age of 131 ± 2 ka. Additional U-Th and OSL analyses are currently being processed on other samples in order to reinforce correlations between the two sectors investigated. Consequently, the application of different dating methods suggests that pre-Holocene organic- bearing sediments in the study area belong to the last interglacial (Sangamonian; marine isotopic stage 5e). This is consistent with the paleoecological content of this unit, which suggests deposition under climate conditions roughly similar to today. Our results suggests that only one ice-free interval is recorded in the sequences of the James Bay lowlands of Québec, indicating that the following glacial advances and partial ice retreat events took place throughout the course of the last glacial cycle. This represents the first time that pre-Holocene organic- bearing sediments are dated reliably in the Hudson-James Bay lowlands, thereby providing important constraints for paleogeographic reconstructions of the LIS.
PP11A-0222
Glacial age precipitation and temperature estimates for the tropical Guatemalan highlands
The Sierra Cuchumatanes of Western Guatemala supported a large ice cap of approximately 44 square km area, and a group of 5-6 small valley glaciers during the local last glacial maximum (LLGM). We propose that a temperature reduction during the Guatemalan LLGM was between -4.5 degrees C and -6.0 degrees C from present accompanied by precipitation totals that fall between 80-100% of present day levels. Our new field work on moraine limits expands upon previous reconnaissance-level studies. Here we present a comprehensive reconstruction of the Guatemalan glacial geomorphology on a high limestone plateau; including delineations between morphologically different moraine sequences, boundaries of sub-glacial till deposits and locations of dry moraine dammed lakes. The glacial geologic map was produced via field mapping and GPS surveying, coupled with aerial photographic analysis. A 50m digital elevation model (DEM) created for the mapping portion was employed as input for a physically based GIS mass-balance model, developed by Plummer and Phillips (2003). The mass-balance model data was calculated for varying precipitation, temperature, environmental lapse rates, cloudiness, wind speed and humidity. A sensitivity analysis using variations in temperature and precipitation provided constraints on Guatemalan highland paleoclimate. Although the ages of the glaciations are unconstrained, a qualitative assessment of moraine morphology suggests correlation with the LLGM (20 – 17.5 ka) moraines of Mexico.
PP11A-0223
Pb Isotopes from Paleogene Fe-Mn Oxide Coatings from the Southern Ocean as a Proxy for Deep Water Circulation and Weathering Intensity.
Pb isotopes extracted from Fe-Mn oxide coatings on bulk sediment are investigated as proxies for seawater Pb isotopes on Cenozoic time scales. Previous studies investigating long-term variations in weathering inputs and circulation patterns used Pb isotopes derived from Fe-Mn crust, but these crusts grow very slowly, are difficult to date, and have limited spatial resolution. Due to the slow growth rates they record a signal that is averaged over ~ 104-105 years, limiting the application to studies of long term changes. Initial results suggest that Pb isotopes extracted from Fe-Mn oxide coatings may be a proxy for more rapid variations in weathering and circulation. Comparison between the Pb isotopic values derived from these coatings and from fossil fish teeth for ~25 Ma old samples from ODP Site 1090 on the Aghulus Ridge (Southern Ocean) shows similar values, although there is a small systematic offset when plotted in 207Pb/204Pb vs. 206Pb/204Pb and 208Pb/204Pb vs.206Pb/204Pb space. This may be due to initial Pb concentrations in the hydroxyapatite of fossil fish teeth. Initial data from oxide coatings indicate a well-defined inverse correlation between values for εNd compared to 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb for samples ranging from 15-45 Ma at ODP Site 1090. Previous studies argue that the Nd isotopic variations at this site are largely driven by circulation, specifically the opening of Drake Passage followed by the influx of North Atlantic waters in response to development of the Antarctic Circumpolar Current (ACC) (Scher and Martin 2004, 2006 and in review). This correlation between the two isotopic systems suggests the Pb isotopic record is also dominated by a circulation signal. A 207Pb/204Pb vs. 206Pb/204Pb plot illustrates that Pb isotopic values varied over this interval as a function of the relative influx of Atlantic and Pacific waters, with the introduction of less radiogenic Pacific values indicating opening of Drake Passage, followed by the introduction of more radiogenic Atlantic waters. It is intriguing that Atlantic Pb signals are carried as far as the Southern Oceans given the short residence time of Pb (50-200yrs). Increased variability of Pb isotopic data and a decreased correlation to ε Nd values from 20 Ma and younger may record variations in more local weathering inputs.
PP11A-0224
Paleoenvironmental changes affected on the diversity explosion and extinction events of the fossil diatom resting spore assemblage across the E/O boundary
The marine diatom genus Chaetoceros is known as a major contributor to primary production in near-shore upwelling regions and coastal areas, where it accounts for 20–25% of the total marine primary production. They produce heavily silicified resting spores which are easily preserved as fossils under nutrient-poor conditions. The diatom resting spores are therefore preserved as significant constituents in fossil marine diatom assemblages providing useful information for reconstructing paleoproductivity and paleoenvironmental changes. However, due to the importance of Chaetoceros in marine primary production, it is crucial to investigate fossil resting spores in upwelling regions. As the result of revising the taxonomy of fossil diatom Chaetoceros resting spores using DSDP 338, 436 and 438, and onland-samples (Newport Beach Section, California) from the late Eocene to the Recent, the Chaetoceros Explosion Event (when there was an increase in diversity and abundance, and a 50% reduction in valve size) across the Eocene/Oligocene (E/O) boundary was clarified. On the other hand, investigation of middle Eocene samples from the Integrated Ocean Drilling Program (IODP) Expedition 302, revealed an Extinction Event across the E/O boundary of diatom resting spores other than Chaetoceros. These two events indicate increased amounts of nutrient supply via upwelling and a change from a stable water column with a constant nutrient supply in the Eocene to an unstable one with sporadic nutrient supply due to increased vertical mixing in the Oligocene. http://www.geocities.jp/restingspace2/
PP11A-0225
Species-selective Aerobic Degradation of Dinoflagellate Cysts - Results of a Natural Exposure Experiment
Organic-walled dinoflagellate cysts undergo species-selective decomposition in oxic environments but are preserved under anoxic conditions. The relative degradation rate of individual species has been assessed during exposure experiments under oxic and anoxic conditions at two sites in the Eastern Mediterranean, namely the Urania and Bannock Basins areas. These areas contain anoxic brine waters and are overlain by oxic intermediate and surface waters. The exposed material consisted of sediments collected from (a) the Namibian shelf, (b) the S1 sapropel and (c) modern eastern Mediterranean. After 15 months of exposure to oxic conditions, sub-samples from the Namibian shelf and the sapropel showed a considerable reduction in cysts concentration compared to their original abundance. Exposure to anoxic conditions did not lead to detectable differences in relation to the initial composition. Our experimental results indicate that Brigantedinium spp. and Echinidinium granulatum are very sensitive to oxygen exposure, whereas Spiniferites spp., Lingulodinium machaerophorum and Echinidinium spp. appear to be moderately sensitive. Nematosphaeropsis labyrinthus, Echinidinium aculeatum, Operculodinium israelianum, and Impagidinium aculeatum are extremely resistant against aerobic decay. The observed changes in the dinocysts assemblages provide clear and straightforward argument that species- selective degradation of dinocysts takes place rapidly under oxic conditions independently from dinocyst production and transport processes. Our results imply that diagenetically induced composition changes have to be taken into account not only during interpretations of fossil records but also (sub) recent dinocyst assemblages.
PP11A-0226
Biotic Response of Tethyan Bathyal Ostracodes Across the Eocene-Oligocene Transition
The fundamental global climate shift from "greenhouse" to "icehouse" conditions during the Eocene-Oligocene transition (EOT) has been variously attributed to the development of oceanic gateways, perturbations in the global carbon cycle, and variations in orbital forcing. This global climate shift is marked by the first significant Cenozoic glaciation of Antarctica and associated with a variety of faunal and floral changes in the marine and terrestrial realms. Establishing the tempo and mode of biotic changes through the EOT can provide insight on both its physico- chemical nature and biotic impact. In the deep-ocean benthic environments, ostracodes provide the only numerically significant metazoan faunal record by virtue of their highly calcified valves, and improved faunal records should provide a productive complement to more established benthic foraminiferal records. Dall'Antonia et al. (2003) found no major faunal changes in ostracode assemblages through the Global Stratotype Section and Point (GSSP) for the Eocene-Oligocene Boundary (i.e., base of the Priabonian stage) in the Massignano Quarry of Italy. However, the stratigraphic congruence of this GSSP with the globally recognized Oi-1 oxygen- isotope shift remains controversial; Van Mourik and Brinkhuis (2005) argue that Oi-1 event significantly postdates the current GSSP on the basis of dinoflagellate biostratigraphy and correlation to other isotopically well- characterized EOT sections. To further explore this issue, we are extending the existing GSSP ostracode faunal record up-section through the adjacent "Massicore" to characterize any biotic responses that may coincide with, and thereby independently test, the predicted position of the Oi-1 event. Preliminary analyses of limited samples show markedly higher ostracode abundances (i.e., valves per gram bulk sediment; insufficient constraints on sedimentation rates preclude calculation of ostracode accumulation rates) above the predicted Oi-1 event. Ongoing faunal analyses of ostracode valves per gram, resampled (abundance-corrected) richness, and community structure will assess potential biotic responses across the predicted position of the Oi-1 event and through the broader EOT.
PP11A-0227
Shaking up an Old Standard: The Paleocene-Eocene Boundary Through the Eyes of DSDP Site 401
Ocean Drilling Program (ODP) Site 690 (Weddell Sea) has been the standard against which all other Paleocene- Eocene Thermal Maximum (PETM) carbon and oxygen isotope records are measured. Deep Sea Drilling Program (DSDP) Site 401 (Bay of Biscay) has a nearly complete record, and despite having a shorter section containing the PETM, contains a detailed record of the carbon isotope excursion (CIE). Site 401 contains no collapse of the carbon isotope gradient between planktic and benthic foraminiferal species, indicating there was no rapid oceanic turnover in the North Atlantic at this time. A negative dip in δ13C is observed prior to the main CIE in Morozovella subbotinae, Acaranina soldadoensis and Subbotina patagonica, and is a potential precursor to the main CIE. Records of δ18O in planktic foraminifera show no recovery to pre- excursion levels at Site 401, indicating the rise in sea surface temperature in the North Atlantic was not a transient event. Additionally, there is a change in habitat of the species A. soldadoensis, which migrates from shallow dwelling to thermocline dwelling and returns to shallow dwelling during the recovery phase of the CIE.
PP11A-0228
The Paleocene-Eocene Thermal Maximum-central east Greenland flood basalts Connection?
Synchronicity of the Paleocene Eocene Thermal Maximum (PETM) at 55.5 Ma and voluminous eruption of the of the central east Greenland (CEG) flood basalts has lead authors to find a causal relationship between these two events. However, age constraints within the thick CEG volcanic succession are spare and often are associated with large uncertainties or based on samples with poor stratigraphic control. Based on new Ar-Ar ages combined with chemostratigraphic relationships within the CEG succession, we constrain the timing of the PETM to a restricted portion of the CEG volcanic stratigraphy with the Geike Plateau Formation. As such the PETM occurs at the height of effusive volcanism and limited pyroclastic activity. The outpouring of large volumes of basaltic magma by fissure-fed eruptions could have contributed large volumes of SO2 to the atmosphere, likely contributing to cooling, rather than global warming as recorded by the PETM. Likewise, there is no evidence for CO2-rich volcanism in CEG flood basalt province at this time to contribute significant greenhouse gases. We suggest that although these two geologic events are synchronous, they may be coincidental.
PP11A-0229
Multiple Export Production and Sulfur Isotope Records over the Paleocene Eocene Thermal Maximum
The Paleocene Eocene Thermal Maximum (PETM) was a global climatic event that occurred 55 million years ago. δ18O values from benthic foraminifera indicate that temperatures rose 4-5oC coeval with a precipitous drop in δ13C values that indicate a new source of carbon rapidly entered the global carbon cycle. Marine barite (BaSO4) was used to evaluate the 1) barite accumulation rate that serves a proxy for export production and 2) the sulfur isotopic composition of seawater that reflects the mass balance of oceanic sulfate (SO42-). Increased barite accumulation rates at the PETM suggest that increased export production and CO2 sequestration was in direct response to the carbon isotope excursion, although not all of the increases are accounted for. High resolution δ34S values are lower but within reasonable range of previously observed values and indicate a decrease in sulfate removal by pyrite deposition.
PP11A-0230
Triggering the Paleocene/Eocene Thermal Maximum: the Kilda Capacitor Hypothesis
The Paleocene/Eocene Thermal Maximum (PETM) may have been triggered by catastrophic expulsion of gas from an anoxic rift-basin great lake or silled ocean basin between Norway and Greenland (Lake Kilda), which formed when kilometre-scale uplift accompanying emplacement of the North Atlantic Igneous Province severed connection with the global ocean. Modern analogues to such basins are meromictic and hence can act as capacitors for methane and carbon dioxide. By analogy with modern African Lake Kivu, carbon dioxide and methane of both organic and hydrothermal origin would have accumulated in the stratified Lake Kilda capacitor until the gas saturation level rose to within a few hundred metres of the lake surface. Lake water overturn may have caused a catastrophic expulsion of up to 100 Gt of gas, in an event analogous to the African Lake Nyos emission. This pulse could have been large enough both to create an initial sharp warming phase by which the atmospheric residence time of methane was extended, allowing the initiation of positive feedback from other slower greenhouse gas release mechanisms, that in turn maintained global warming throughout the PETM.
PP11A-0231
Composition of Eocene Ice-Rafted Debris, Central Arctic Ocean
IODP Expedition 302 drilled a 400-m sediment record which contains physical evidence of ice-rafting in the Eocene and Neogene in the Arctic (Backman et al., 2006; Moran et al., 2006, St. John, in press). An increase in the terrigenous sand abundance occurs above 246 mcd (~46 Ma), with a flux similar to that in the Neogene. Higher resolution sampling in an interval of good recovery from 246-236 mcd shows evidence of cyclic input of IRD and biogenic components that fits with Milankovitch forcing at the obliquity period (Sangiorgi et al., in press). The question remains – what areas of the Arctic were ice-covered at this early stage in the Cenozoic? To address this provenance issue the composition of the terrigenous sands (250 micron fraction) in cores 55-56X is being quantified. Grains in 75 samples are being point-counted and their compositions categorized. Quartz grains are the dominant component (greater than 10,000 grains per gram), with some being hematite-stained, and there are lesser amounts of mafic minerals. No carbonate grains are identified so far in this study. Possible sources areas for Eocene IRD are the Eastern European and Russian Arctic margins. Tracking compositional variations of the IRD over the interval of cyclic deposition, should indicate whether the cyclic IRD deposition was consistently derived from one source region or multiple regions during this time.
PP11A-0232
Equatorial Pacific Reactive Phosphorus Accumulation Rates across the Eocene/Oligocene Transition
Paired benthic foraminiferal stable isotope and trace metal records from ODP Site 1218 in the equatorial Pacific have shown that the Eocence/Oligocene (E/O) transition (~34 Ma) represents a major increase in Antarctic ice accumulation and a rapid deepening of the global calcite compensation depth (CCD) occurring in two steps [e.g., Lear et al., 2000; Lear et al., 2004; Coxall et al., 2005; Palike et al., 2006]. Simultaneous increases in biogenic mass accumulation rates (MARs) around Australia and in the Atlantic Ocean have been interpreted as representing increased productivity and/or organic carbon (C) burial possibly linked to cooling and ice sheet growth [Diester-Hass and Zahn, 2001; Anderson and Delaney, 2005]. Because the global CCD deepens across the transition, there is a need to distinguish organic C burial changes from CCD changes. We are determining reactive phosphorus (P, micromol P cm-2 kyr-1) MARs as an indicator of organic C burial for Site 1218 to help constrain the relative role of productivity during the E/O climatic transition. Reactive phosphorus (the sum of oxide associated, authigenic, and organic P; sequentially extracted from bulk sediment), delivered to the sediment water interface with organic C, is well preserved in oxygenated sediments. Preliminary results show an order of magnitude decrease in reactive P concentrations (from ~100 to ~10 micromol P g-1) across the E/O boundary. This may indicate that absolute organic C burial as well as the ratio of organic C burial to calcite burial may have decreased across the E/O transition in the equatorial Pacific upwelling zone.
PP11A-0233
Provenance Of James Bay Lowlands Glacial Deposits In The Context Of Multiple Ice-flow Events Of The Eastern Sector Of The Laurentide Ice Sheet
Paleoclimate records indicate that the Laurentide Ice Sheet (LIS) was highly dynamic throughout the last glacial cycle. Measurements of glacial striations taken from multi-faceted rock outcrops and tracing of lithological indicators also indicate important reorganizations of the ice divide system of the LIS. The sequence of shifting ice flows for the eastern sector of the LIS consists in several ice movements dating presumably from the ice-dome buildup in the early phases of the last glacial cycle to late deglaciation stages. There is, however, little information on the timing of these ice flow shifts as well as the exact trajectories and extent of the documented ice flow events. Here we focus on the evolution of the Labrador-Quebec ice dome by documenting the provenance of till units of the James Bay lowlands of Quebec. This region preserves a long record of late Pleistocene events and its location near the former geographic center of the LIS makes it particularly important for the study of ice sheet dynamics. Our investigations along the Harricana and Nottaway rivers indicate that the regional stratigraphy consists of at least 4 distinct till units. A 20-m thick varve unit also separates the lower two till units from the two upper ones. This glacial sequence lies on fluvial sands containing abundant compressed wood fragments. Distinguishing ice-flow events in multiple-till sequences is difficult and requires the development of approaches that will lead to a well-constrained interpretation of till provenance. Ice flow directional data of till was obtained through sedimentological methods (till fabrics, measurements of striations on bullet-shaped boulders, etc.), as well as the petrography of clasts, and mineralogic geochemical composition of till matrix. Clast petrological data from the four-till sequence shows variations that suggest an early ice flow towards the northwest, followed by a counterclockwise shift to the west, southwest and then south. This succession of ice flows is also supported by till fabrics. Overall, the ice flow sequence documented here is concordant with the striation record obtained from the surrounding Shield rocks. Of importance here, is the occurrence of the northwestward movement, which is documented for the first time in this part of the lowlands. Geochronological constraints obtained from the organic- bearing unit also indicate that these ice flow rearrangements occurred during the last glacial cycle. The bedrock geology surrounding the James Bay region is also suitable for the application of radiogenic tracers on the glacial deposits. We thus use bulk Sm-Nd isotopes from till matrix and 39Ar/40Ar ages of individual detrital hornblende grains to further distinguish rocks sources and gain additional insights on ice flow trajectories. Geochemical analyses are currently being processed, and the combined Sm-Nd data and 39Ar/40Ar ages should help refining ice flow trajectories. These results will contribute to identify the former locations of ice-accumulation centers and their subsequent migration paths, thereby helping resolving the post-glacial rebound history of the LIS.
PP11A-0234
Dating "Dirty" Carbonates by U-series Isochrones: Insight Into Why Leaching Methods Don't Work
While accurate dating of "dirty" carbonates (carbonates having abundant detritus) using U-series methods would greatly impact the geochronology of difficult to date quaternary samples, robust methods are few in number. We set up a series of experiments using nearly pure carbonates (a calcitic stalagmite and a modern coral) that we physically mixed with variable amounts of USGS standard SDC-1 (mica schist representative of detritus). We dissolved each dirty carbonate mixture with acetic acid followed by leaching the residue with EDTA (to attempt to eliminate sorption). After completely dissolving the residue, the two solutions were spiked and measured for U- Th-Pa isotopes by MC-ICP-MS. Results show that significant amounts of 238U(235U), 234U and 232Th are removed from the mica schist despite the gentle dissolution. The concentrations of all nuclides in both solutions and residues show a linear relationship as a function of detritus/carbonate ratio. However, the linear relationship for isotope activity ratios, except (232Th/238U)A, is much weaker, especially for the residues. The migration direction of 231Pa and 230Th are consistently from the high concentration end member to the lower one; migration of these nuclides is not always the same direction as indicated by the long-lived isotopes (235U, 232Th). In summary, only total sample dissolution (TSD) methods can give an accurate age while leaching methods always are biased by nuclide migration out of the silicate detritus.
PP11A-0235
Uranium Migration In Organic Rich Sediments
Sediments cores from the eastern Mediterranean Sea contain numerous dark-colored layers that are rich in organic carbon, the sapropels. The organic matter traps uranium (U) leading to concentrations of up to 50ppm. Consequently those layers are interesting for U series dating and/or to investigate U as a productivity proxy. The exceptionally high organic carbon concentration of S5 sapropel limits post-depositional oxidation and make this sapropel one among the best preserved. Here we measured U concentrations and activity ratios of 234U/238U, 230Th/234U and for the first time also 231Pa/235U in different sediment cores of the eastern Mediterranean Sea by using gamma spectrometry and mass spectrometry. Compared to a sea water origin of uranium and a closed system evolution we find that measured ratios in the center of S5 are depleted for 234U/238U and elevated for 230Th/234U and 231Pa/235U ratios. Because Th and Pa can be considered immobile the observed systematic deviation from closed system evolution across S5 is not only due to radiogenic 234U migration as previously stated, but also to U (235U and 238U) migration. To constrain effective diffusion coefficients for radiogenic 234U and U we have developed a 1D box model, which accurately fits the measured radionuclide profiles. Thus, U migration has to be taken into account to improve the interpretation of U profiles as a productivity proxy or to establish U series dating of organic rich sediments.
PP11A-0236
εNd Across OAE 2 in the Late Cretaceous at Demerara Rise (ODP Leg 207) and Blake Nose Plateau (ODP Leg 171)
We analyzed Nd isotopes on Late Cretaceous fossil fish teeth and debris and extractions from Fe-Mn oxide coatings from a total of six sites along two paleodepth transects in the western North Atlantic: Demerara Rise Sites 1258, 1260 and 1261, and Blake Nose Sites 1049, 1050 and 1052. Both transects span a range of more than 1000 m and the sites were at middle to upper bathyal paleodepths during the Late Cretaceous. These samples were analyzed to test and better define vertical and horizontal variation in North Atlantic εNd values with particular focus on low background values (-16 to -14) punctuated by a dramatic 8 unit positive excursion across Oceanic Anoxic Event 2 (OAE2) previously observed at Site 1258. Extractions of Nd from dispersed Fe-Mn oxide coatings on black shales and carbonate marls above, within and below the excursion yield isotopic ratios that are consistent with data from fish teeth, indicating that the oxide coatings are robust archives for Nd isotopes in a range of lithologies.Despite the range of depths sampled, all three Demerara Rise sites record similar nonradiogenic background εNd values and a similar magnitude excursion during OAE2, indicating that the water column was well mixed over these depths at this location. In contrast, there appears to be a depth gradient in εNd values in the older samples from Blake Nose that disappears by Campanian-Maastrichtian times. During the Albian-early Cenomanian, the shallowest site (1052) records the least radiogenic εNd values (-5 to -4) observed in our study, whereas the intermediate depth site (1050) records values of -6 to -5 and the deepest site (1049) records values of -6 to -7. All of these values are very radiogenic compared to Cenozoic data from Fe-Mn crusts from the North Atlantic, and seem to imply a component of Pacific water was incorporated into Albian-Cenomanian bottom waters on Blake Nose. Much of the Cenomanian-Campanian is missing in various Blake Nose sites, and we have yet to run samples from the portion of OAE2 recovered in Hole 1050C. However, after this event, εNd values on Blake Nose are distinctly lower and similar at all three sites from the Late Campanian into the Eocene. Further, the εNd values observed (-9 to -8) are consistent with Cenozoic data from Fe-Mn crusts located in the North Atlantic. Together, these data suggest a transition from a stratified water column dominated by Pacific waters at intermediate depths in the Albian- Cenomanian to a well mixed water column with a strong component of North Atlantic water following OAE2 in the Blake Nose region.
PP11A-0237
Oxygen Isotopes of Pedogenic Nitrate: New Paleoproxy for Precipitation in Arid regions.
Pedogenic nitrate is found in most arid and semiarid environments, usually in association ıwith atmospherically derived chloride. While the chloride mass balance techniques have ıbeen used to assess hydrologic recharge rates over time and as a soil chronometer, the use ıof nitrate as a paleoproxy has largely been ignored. This is because nitrate is not a ıconservative in the root zone, it being consumed by plants and microbes that use it as a ısource of fixed N, and nitrate production via by oxidation of ammonium by nitrifying ıbacteria. The accumulation of pedogenic nitrate is thus a two source problem: ıAtmospheric deposition and biologic formation. I will show that the atmospheric ıcomponent of the nitrate budget has a unique 17O composition relative to ımicrobial nitrification. This Δ17O signal is can be used to assess the ratio of ıbiogenic/inorganic nitrate accumulation. This ratio is primarily impacted by the change in ıthe biogenic component which is related to soil moisture/precipitation. Thus soil nitrate ııΔ17O can be used a new paleoproxy for precipitation rates in arid/semi arid ıregions. ı
PP11A-0238
Radiocarbon In Mollusk Shells As Proxy For Peruvian Upwelling: Modern Pre-Bomb Reservoir Effect Correction
Analyses of radiocarbon content in Peruvian pre-bomb mollusk shells revealed short-term changes in vertical mixing and permit calculation of a new regional reservoir effect correction (ΔR) that includes variable confidence intervals to reflect sample time averaging. The rationale of the molluscan proxy is based on the mixing of radiocarbon-depleted deep water with comparatively enriched surface water. As mollusks grow, their radiocarbon content varies with ambient conditions, thus recording upwelling changes through ontogeny. Vertical mixing on the coast of Peru is variable at multiple time scales, often as a result of El Niño/Southern Oscillation (ENSO) activity. Intense upwelling is reflected in low 14 C concentration in shell carbonate while cessations or reductions in upwelling produce increases in radiocarbon. Four pre-bomb mollusk shells were analyzed for radiocarbon content consecutively from hinge to edge at high spatial resolution. Two shells of {Donax} {marincovichi} (formerly {D.} {obesulus}) collected in Puerto Pariñas (4o40'S) and Puerto Salaverry (8o13'S) during 1929 and 1926 and two specimens of {Protothaca} {asperrima} collected in Paracas (13o52'S) during 1948 were analyzed. The number of subsamples per shell varied between ten and nineteen. Additionally, eight shells of {Argopecten} {purpuratus} from Puerto Salaverry, Callao Bay (12o 4' S) and Sechura Bay (5o 45'S) collected in 1908 and 1926 were analyzed at lower spatial resolution. Radiocarbon profiles from {Donax} and {Protothaca} show abrupt and significant changes in radiocarbon content, suggesting rapid upwelling variation during the life of the organisms. Lower resolution analysis of {Argopecten} also shows variable radiocarbon content within the shells associated to upwelling changes. Statistical analysis demonstrated no significant difference in the means of multiple ΔRs obtained from the twelve shells. However, ΔR variance was significantly different between shells. These findings suggest that regional average ΔR for Peru (1908 to 1948) remained relatively constant, but significant short-term variability occurred. Based on the statistical analysis of the data we propose a new ΔR correction of 114 years. The confidence interval of this correction is dependant on the degree of time-averaging in the sample(s) analyzed, thus an equation describing the relationship between sampling and ΔR was constructed.
PP11A-0239
Late Neogene Changes In Atlantic-Pacific Intermediate And Deep-Water δ13C gradients
This study compares intermediate and deep-water δ13C records from the Atlantic/Caribbean (sites 704, 925/926, 982, 1000) and the east Pacific (sites 846, 1236, 1237, 1241) for the time interval from 8.8 to 2.0 Ma. The comparison reflects changes in Atlantic-Pacific nutrient distributions and thus changes in thermohaline circulation. The δ13C gradient between the deep Atlantic and the deep Pacific remained relatively constant from 7-3 Ma and decreased after 3 Ma. At the intermediate water level, Pacific and Atlantic δ13C values were similar prior to 4.2 Ma; the difference increased after 4.2 Ma due to decreasing upper Atlantic nutrient concentrations. The δ13C values between the shallow Atlantic and the eastern Pacific are very similar prior to 8.5 Ma. After 8.5 Ma, the Atlantic-Pacific difference strongly increased until 5.9 Ma. The timing of the observed changes in Atlantic-Pacific δ13C gradients suggest influences from ocean gateway dynamics.
PP11A-0240
Chemostratigraphies of carbon, oxygen and strontium isotopes and oxygen contents across the Precambrian-Cambrian boundary
The Precambrian-Cambrian (PC-C) boundary is one of the most important intervals for evolution of life. However, the scarcity of well-preserved outcrops through the boundary makes it ambiguous to decode change of the surface environment and biological evolution. In south China, strata through the PC-C boundary are continuously exposed and contain many fossils, suitable for study of environmental and biological change. In addition, we conducted excavations at four sites of Three Gorge area to obtain continuous and fresh samples. We measured the delta13C, delta18O and 87Sr/86Sr values of the drill core samples and REE compositions of fresh carbonate rocks, respectively. We identified two positive and two negative isotope excursions of delta13Ccarb within this interval: a moderate increase from 0 to +2 permil and a subsequent dramatic drop to -7 permil at the PC-C boundary, and a continuous increase to +5 permil at the upper part of the Nemakit-Daldynian (ND) stage and the subsequent sharp decrease to -9 permil just below the basal Tommotian unconformity, respectively. The continuous pattern of the delta13C shift is irrespective of lithotype and is comparable to fragmented records of other sections within and outside of the Yangtze Platform, indicating that the profile represents global change of seawater chemistry. A chemostratigraphy of 87Sr/86Sr ratios of the drilled samples also displays a smooth curve and its large positive anomaly just below the PC-C boundary. The estimate of oxygen content of seawater from REE composition of carbonate minerals shows significant decreases around PC-C and ND-Tommotian boundaries, respectively. The combination of chemostratigraphies of delta13C, 87Sr/86Sr and pO2 indicates that the 87Sr/86Sr excursions preceded the delta13C negative excursion at PC-C boundary, and suggests that global regression or formation of the Gondwana supercontinent, evident in increase of influx of continental materials, caused biological depression together with decrease of oxygen content of seawater due to dissolution of methane hydrate.
PP11A-0241
Combined Textural and Stable Isotopic Data as Proxies for the Mid-Cretaceous Paleoclimate: A Case Study of Lacustrine Stromatolites in the Hayang Group, Gyeongsang Basin, SE Korea
Microbial interference of the prevailing sedimentary dynamics during stromatolite growth, records vital biogeochemical information, which reflects the prevailing local paleoclimatic conditions. Most stromatolite studies focus on the use of stable isotopes and other geochemical parameters for paleoclimate reconstructions. The use of textural data as a proxy has hardly been considered. This study documents the simultaneous geochemical and textural changes in Mid-Cretaceous lacustrine stromatolites (Gyeongsang Basin, SE Korea), deposited in a semi arid-arid setting as proxies for determining the paleoclimatic conditions during their growth. Here fibrous calcite/micrite couplets in the Sinyangdong, Hwasan and Banyawol stromatolites constitute the basic growth cycles and can be divided into first-, second and third-order cycles. Second-order cycles show couplets with gradual textural changes from lower fibrous calcite to upper micrite laminae and three different types of micrite are present. There is further textural division in the microbial micrite laminae of the Sinyangdong stromatolites where one micrite type always directly overlies the fibrous calcite and is followed by a second type of micrite. Sometimes, the first type of micrite evolves into the second, and also shows increasing paleosalinity conditions within the cycle (higher δ18O values) such that the end of a cycle shows more saline conditions than the beginning of the next cycle. Consistent enrichments in δ18O and depletion in δ13C values towards micrites within the Sinyangdong and Hwasan stromatolite couplets and a concomitant depletion of both isotopes from fibrous calcite to micrite in the Banyawol sample can be observed. The consistent shifts in these isotopes imprinted in the different textural growth fabrics indicate that paleohydrological changes related to paleoproductivity and paleosalinity fluctuations could play a significant role in the formation of these primary lacustrine carbonates. Textural changes shown by the frequency of the growth cycles also corresponds with oxygen and carbon isotopic values and this appears to have been influenced by climate-related paleohydrological changes.
PP11A-0242
Sedimentary Trace Metal-Organic Interactions as Proxies for Oceanic Redox Conditions
Knowledge of trace-metal partitioning in oceanic sediments (e.g., Fe, Mo, U, Zn) are requisite to the construction of accurate models of geochemical cycling in modern and ancient waters. Factors such as oxygen penetration depth and bottom-water redox; sedimentation rate; and supply of reactants, such as dissolved sulfide, are known to affect metal sequestration in and remobilization from coastal sediments. In addition to these factors, the flux of organic carbon (OC) and the composition of this carbon are also a key in the sequestration of these metals. Currently, however, there is an absence of quantitative information on the mass balance of metals fixed in coastal sediments through direct interactions with OC, how OC remineralization affects this mass balance, and the specific nature of the metal-OC relationship. To address these issues, we have undertaken a field-based study to test the hypothesis that porewater redox conditions are recorded in the concentrations of trace metals bound in the sedimentary OC pool. We have collected sediments from several modern anoxic/euxinic basins: the central Black Sea, the Orca Basin, the Cariaco Basin, and Effingham Inlet (Vancouver Island). These environments vary in terms of dissolved sulfide concentrations and sedimentary iron sulfide geochemistry. Additionally, the sediments are characterized by a range in OC concentrations, and proximity to terrestrial sources. Extractable organic carbon was characterized with gas chromatography, and OC-bound metals are quantified using high-performance liquid chromatography- inductively coupled mass spectrometry. The preliminary results suggest that variations in the ratios of aromatic to saturate hydrocarbons may control the speciation of metals in the organic carbon pool. Bottomwater redox may be one factor controlling this relationship, although it is currently unclear if this is due to variations in metal speciation or the direct involvement of S in the OC-metal reaction mechanism. The results of our analyses will be used to construct an integrated mass balance for metal sequestration-OC reactions during diagenesis. Beyond paleoceanographic reconstructions, our quantitative models for trace metal-OC interactions in modern sediments are critical to address modern environmental concerns, such as trace metal pollution in response to anthropogenic eutrophication and predictions of chemical responses to global warming.
PP11A-0243
Leachable Li and Mg Evidence for Hydrological Changes in the Mono Basin, CA, USA
Hydrology in closed basin lakes, such as Mono Lake of the US western Great Basin, is sensitive to regional climate changes. Lake level history of the Mono Basin has been put into a precise age framework using the paleomagnetic intensity of the Wilson Creek Formation sediments to North Atlantic records, and accordingly Greenland's GISP2 oxygen isotope record (Zimmerman et al., 2006, EPSL, v. 252, pp. 94- 106). This allows correlation of the lake level indicators and Greenland climate at high resolution. The physical evidence for lake level, based on the association of strata in near shore terraces, can be confidently correlated to proxies of lake chemistry preserved in the strata. We have tested the application of leachable Li, following the procedure developed by Bischoff et al. (1997, Quaternary Research, v. 48, pp. 313-325) for Owens Lake. At Owens Lake there is a positive correlation between salinity based on diatoms with leachable Li concentrations. In contrast, at Mono Lake the leachable Li concentration follows the bulk carbonate concentration, generally correlating low lake levels (high salinity) with low leachable Li concentrations. Our preferred explanation for both the carbonate and leachable Li concentrations is based on the fact that the Mono Basin rarely overflows, and therefore precipitation of minerals during evaporation leads to chemical divides (Garrels and Mackenzie., 1967, in "Equilibrium Concepts in Natural Water Systems", W. Stumm, Ed., pp. 222-242). As Li behaves conservatively compared to elements like Ca2+ and Mg2+, it might be expected that the leachable Li would be higher when lake level is lower. However, the host for the Li appears to be Mg-smectite. Therefore, the concentration of leachable Li in the sediment is controlled by the concentration of Mg-smectite, as well as the Li/Mg of the water from which the Mg- smectite precipitated and the Kd of the Li into the Mg-smectite. We are studying the Li and Mg systematics of these samples in order to deconvolve these factors and contribute to paleo-hydrological studies of this and other closed basin lakes.