PP41B-0542
Water-Column Redistribution of Biogenic Particles in the Central Equatorial Pacific: Evidence From the Spatial and Temporal Variations in Flux and Isotope Compositions of Planktonic Foraminifers in Sediment Traps
The flux of biogenic particles (e.g., carbonates, opal, and organic carbon) exported from the surface to deep oceans plays an important role in controlling the oceanic carbon cycling and the concentration of CO2 in the atmosphere. This flux is assessed by sediment-trap deployment in the modern ocean and by using proxies preserved in the sea-floor sediments for the past oceans. In this study, based on the sediment-trap deployment, we measured the spatial and temporal variations in the flux and isotopic compositions of the calcareous tests of planktonic foraminifers in the central equatorial Pacific. The results show that significant fluxes of the foraminiferal tests collected respectively at 5° south and north of the equator can not be attributed to the export from the overlying surface oceans. Rather, the isotope measurements indicate that these biogenic particles may have a common origin at the equator and are likely to be transported from there by horizontal currents. It seems that the high fluxes of biogenic particles preserved respectively 5° south and north in the sea-floor sediments can not be used to reflect the productivities in the overlying surface oceans. Such redistribution of biogenic particles in the water column is also subject to significant seasonal variations. The results bear implications on not only the quantification of modern-ocean carbon flux, but also the use of the flux and/or isotopic/chemical compositions of foraminifers in sediment cores as a paleoceanographic proxy.
PP41B-0543
Seasonal and annual variation in planktonic foraminiferal fluxes including warm period related El Niño in the northwestern North Pacific
Planktonic foraminifera provide a record of the upper ocean environment through their species assemblage and individual tests. To investigate the relationship between foraminifera and oceanographic conditions and the impact of El Niño on foraminifera, we analyzed foraminiferal fluxes and relative abundances by using sediment trap samples collected biweekly at three sites in the northwestern North Pacific: Site 40N (39 °60'N, 165 °00'E), Site KNOT (43 °58'N, 155 °03'E), and Site 50N (50 °01'N, 165 °02'E) from 1998- 2001, a period that included an El Niño effect. Based on foraminiferal production and assemblage composition, we divided the sampling duration into several periods during which certain characteristic oceanographic properties were observed. These sampling periods were classified into five types (I-V) based upon four factors: 1) the predominant foraminiferal group, 2) total foraminiferal fluxes (TFFs), 3) organic matter (OM) fluxes, and 4) hydrographic conditions, which included sea surface temperature (SST) and thermal structure. Our results suggest that seasonal changes in foraminifera were closely related to water mass properties in addition to SST. If species compositions were the same, then water mass properties were the most important factors affecting the seasonal variation of foraminiferal abundance in the northwestern North Pacific. Although one of the major controlling factors for foraminiferal fluxes is food availability, the controlling factors for each type (types I-V) are different because of specific oceanographic situations, such as phytoplankton blooms, which result in an excess food supply for foraminifera. At Site KNOT in 1998, SST was remarkably high because of El Niño, and high surface temperatures and weak winds would have lowered nutrient supply and intensified water column stratification, resulting in the relatively low fluxes of total foraminifera, N. pachyderma, and G. bulloides, and the high fluxes of N. dutertrei that were observed. The response of foraminifera to El Niño at Site KNOT in 1998 was similar to the response of foraminifera off the coast of Chile during a weak El Niño event in 1991-1992. The impact of El Niño on foraminifera was variable, depending on the strength of the El Niño event and the location, even though some cases showed common patterns of foraminiferal response. At Site KNOT, El Niño conditions affected foraminiferal abundance not only because of higher sea surface temperature, but also through the formation of a stratified water column.
PP41B-0544
Multi-proxy reconstruction of deep sea calcite dissolution from the subtropical South Atlantic Ocean: foraminifer fragmentation, shell weight and Mg/Ca
Tracing post-depositional deep sea calcite dissolution with planktonic foraminifers is challenging because their test structure and composition are often affected by environmental conditions in calcification waters. We attempt to resolve this problem by using a multi-proxy approach on core top sediment samples from a depth transect on the Rio Grande Rise (RGR) where surface ocean parameters are mostly uniform among our sampling locations. We find that we can expand the calibration range of the Globorotalia menardii fragmentation index (MFI) from the tropical Pacific to the subtropical Atlantic. We also demonstrate that the fragmentation trend of Globorotalia truncatulinoides, Neogloboquadrina dutertrei and Neogloboquadrina pachyderma follow both MFI and the drop in bottom water [CO3=]. The drop in Mg/Ca in G. truncatulinoides (a thermocline-dweller commonly found in Quaternary subtropical Atlantic sediments) follows the decrease in bottom water [CO3=] and, thus, supports MFI's dissolution trend. This observation bodes well for developing this tracer as an alternative means of quantifying downcore variations in calcite dissolution. Mg/Ca in G. menardii, another thermocline dweller, is largely insensitive to temperature and reflects mostly post-depositional calcite dissolution. If that also holds true for G. truncatulinoides, we would be able to use its Mg/Ca to assess carbonate dissolution in the glacial sections of Atlantic sediments, where the disappearance of G. menardii prevents the use of MFI. In contrast to all of these proxies, the loss of size normalized shell weight in G. truncatulinoides and Globorotalia inflata follows neither the trend of bottom water [CO3=] nor the other proxies on RGR.
PP41B-0545
Experimental Dissolution of Fine-Fraction Carbonate Sediments From the Paleocene
Pelagic carbonates play a vital role in sequestering CO2 and buffering the oceans through dissolution. The dominant component of deep-sea carbonates is calcareous nannofossils, a group that plays an important role in biostratigraphy, paleoecology and paleoceanography. The composition of assemblages is readily altered by dissolution in the water column, on the seafloor, and within the sediment column. It is therefore necessary to have some understanding of changes in the assemblage composition that may have occurred as well as the dissolution processes involved. Previous studies utilized experiments to constrain the susceptibility of nannofossil taxa during dissolution. While they noted general patterns related to ultrastructure, little is known about how dissolution affects fine-fraction carbonates at the scale of individual crystals of calcite. In this study we use long-term dissolution experiments to recreate dissolution of Paleocene nannofossils from the Indian Ocean in the water through sediment column. This assemblage is diverse and has a range of delicate to robust species and several different calcite morphologies. Detailed observations of subtle changes in the calcite crystals of nannofossils in the SEM reveal information on dissolution processes in pelagic carbonates and the factors that render specific morphologies more susceptible to dissolution. The morphologic alterations of nannofossil species in the light microscope can be used to create a quantitative index for dissolution. This index is based upon etching of rims, the presence of central areas, and the relative abundance of resistant taxa. A quantitative, rather than a subjective, dissolution index will help determine the preservational state of pelagic carbonates from the Paleocene.
PP41B-0546
Considering the effects of diagenesis on the Ca isotope geochemical proxy
The Ca isotopic composition of marine carbonates has been proposed as an indicator of past conditions at the Earth's surface. Some have suggested that Ca isotopes are a proxy for sea surface temperature while others have used Ca isotopes to constrain relative weathering flux through geologic time. Recent results by Fantle and DePaolo (2007) GCA 71(10) suggest that bulk carbonates in some sedimentary columns may experience more reaction than previously thought. In light of this, it is critical to evaluate the fidelity of the proxy by elucidating the effect of diagenetic processes on the Ca isotopic composition of marine carbonates in various geologic settings. The current study uses reactive transport models to constrain the effects of recrystallization during diagenesis on the Ca isotopic composition of marine carbonates. The study considers a sedimentary column in which: (1) advection of a seawater-like fluid dominates the pore fluid chemistry, and (2) a minor component of the bulk sediment reacts at a rate that is different from the bulk sediment. The modeling suggests that, in the former case, the original isotopic composition of marine carbonates can be altered by as much as 0.4‰, given the sorts of recrystallization rates previously suggested by modeling Sr isotopes (e.g. Richter and Liang, 1993, GCA 117(3--4)). However, the sort of enhanced reaction suggested by Fantle and DePaolo (2007) increases the diagenetic effect substantially. In the latter case, Ca isotope variability in bulk sediments may persist even at high recrystallization rates, due to a buffering effect on pore fluid chemistry. At low rates of bulk sediment recrystallization, significant diagenetic alteration can occur when components within the bulk sediment react at faster rates. The implications of the current study are noteworthy. Current calibrations of the Ca isotope-paleotemperature proxy indicate that the relationship between fractionation and temperature of most carbonate-producing organisms in the surface ocean is ~0.02‰/°C. Thus, isotope shifts (0.2‰) due to fairly large temperature changes (10°C) may be erased during diagenesis, complicating the interpretation of paleotemperature. The key to using Ca isotopes as a proxy is selecting suitable sites and appropriate samples, while using modeling techniques to constrain interpretations.
PP41B-0547
A switch from carbonate ocean to silica ocean in the East Sea (Sea of Japan) during the mid- Pleistocene
In this study, we report on the extraordinary CaCO3 preservation in the East Sea (Sea of Japan) during the mid-Pleistocene, which provides a new perspective of carbon cycling as a carbonate ocean. Core 96EBP3 collected from the South Korea Plateau and core MD01-2407 collected from the Oki Ridge show extraordinary downcore variation of CaCO3 contents. CaCO3 contents of core 96EBP3 were measured using UIC coulometer (Model CM5014) and those of core MD01-2407 were converted from CaO measurement using high- resolution major element analysis data determined by an XRF microscanneran (Horiba XGT-2700). The correlation between these two cores was conducted with diverse approaches; radiolarian extinction, warm-water species of radiolaria, and CaCO3 variation. These two cores are in accordance with various features, although core 96EBP3 records some missing ages of MIS 9 and 10. The lower parts of both cores are characterized by extraordinarily high CaCO3 contents up to 50%. The high CaCO3 contents occurred before MIS 11 in both cores. The major constituents of these CaCO3 are coccoliths derived from calcareous nannoplankton. Therefore, these durations of high coccolith dump are quite unique in the East Sea, suggesting that the present-day silica ocean has, periodically in the past, been a carbonate ocean too.
PP41B-0548
Response of Deep Ocean Carbon Cycling to Astronomical Forcing in the Non-Glaciated Eocene ‘Greenhouse' World
Atmospheric carbon dioxide concentrations predicted for 2100 may not have existed on Earth since the early part of the Eocene epoch when global conditions were much warmer and less glaciated than today. Yet our understanding of carbon cycling and climate stability within the Eocene is extremely rudimentary. Here we present the first high-resolution paleoceanographic records across the early to middle Eocene boundary. Our records reveal multiple prominent perturbations to Eocene climate and the carbon cycle. We also observe breakdown in the post-Eocene/Oligocene boundary spatial pattern of astronomical pacing of deep ocean sediment calcium carbonate content. We attribute this divergent response to astronomical forcing to the deglaciated early Eocene climate state.
PP41B-0549
Extraterrestrial 3He Based Age Models for the PETM and ETM-2 Events from ODP Leg 208 Depth Transect Sites
The early Eocene is marked by several short-lived global warming events, or hyperthermals, that were triggered by rapid, massive release of carbon. In each case, the release of carbon acidified the ocean triggering widespread dissolution of seafloor carbonates, thereby producing condensed intervals over much of the deep sea. The amount of time represented in these condensed intervals must be determined in order to reconstruct changes in various biogeochemical and climate parameters including carbonate and clay accumulation rates. Traditional stratigraphic techniques, however, have proved to be inadequate for this purpose. As a solution, a constant flux proxy, extraterrestrial helium-3 (3HeET) is being applied to a number of pelagic early Eocene sections. Here we present 3HeET records of the Paleocene-Eocene Thermal Maximum (PETM) and the second Eocene thermal maxima (ETM-2) from ODP Sites 1262, 1263, 1266, and 1267 located on Walvis Ridge in the South Atlantic (water depths between 2600 and 4800 m). By correcting for long-term changes in the local accretion rate of 3HeET we are able to construct high-resolution age models for both the PETM and ETM-2. Our results confirm a transient rise in carbonate sedimentation rates during the late phase of recovery first reported by Farley & Eltgroth (2003) for the PETM. Additionally, the duration between PETM and ETM-2 has been determined to be ~1.827 Ma by orbital calibration by Westerhold et al. (2007) allowing us to test the constant flux hypothesis.
PP41B-0550
Characterizing the Timing and Scale of Late Paleocene to Early Eocene Carbon Cycle Oscillations, Site 1262, Walvis Ridge
ODP Site 1262, drilled at Walvis Ridge in the S Atlantic, 3600m paleo water depth, provides a continuous record of sedimentation through the Late Paleocene and Early Eocene. The interruption of regularly paced carbon cycle oscillations by transient and extreme climate change events (e.g., the Paleocene Eocene Thermal Maximum (PETM or ETM-1), ETM-2, and ETM-3) allows for in depth study of the interactions between long- and short-term geochemical cycles, perturbations of the global carbon system, and the mechanistic relationship between orbital periodicity and climate variability. Here we present the first stratigraphically continuous, orbital-scale stable isotope and Fe records (obtained by XRF scanning) spanning the entire upper Paleocene and lower Eocene (~52 to 59 Ma). All records shows distinct periodicity. Furthermore, spectral analysis of stable isotope (δ13C, δ18O) and Fe intensity data reveals strong variance in primary orbital bandwidths. Coherence is prominent in eccentricity bands (100kyr, 405kyr), as well as precessional bands (21kyr). Orbital variations in the Fe intensity record, most likely related to carbonate dissolution events, were used to develop an orbitally calibrated age model (Westerhold et al., 2007). Fe intensity cycle peaks are anti-phased with respect to eccentricity controlled δ13C and δ18O cycles in the Atlantic Ocean, and coincide with eccentricity maxima. The data suggest that modulation of the precessional cycle by eccentricity creates a general climate state conducive to periodic shifts in carbon fluxes and reservoir partitioning. Additionally, we will investigate the lead-lag phase relationships between these geochemical and climate parameters.
PP41B-0551
The marine geological record of industrialization
In the far distant future, what traces of our industrialized civilization could a hypothetical alien visitor to the Earth identify our ever having existed by? Popular perception is of landfills being excavated and species extinctions identified. However, localized terrestrial deposits and loss of only a relatively small proportion of species would be fickle candidates for reliable preservation in the geological record. Rather, the imprint of our current civilization will be seen in a global-scale dissolution-preservation event of carbonate in marine sediments, coupled to a pronounced negative carbon isotopic excursion. This is the geological fingerprint of massive carbon release to the oceans and atmosphere in injunction with the rock weathering consequences of a global warming transient. In this contribution I explore the characteristics of the future marine geological record of industrialization and draw parallels with observations recorded in sediments spanning the Paleocene-Eocene Thermal Maximum.
PP41B-0552
Evolution Of The Peru And Equatorial Upwellings Throughout The Last 800 Ka. The Coccolithophore Point Of View.
Here we present the paleoenvironmental study of ODP Sites 1237 and 1238 from the Southeast Pacific ocean. These Sites are located under the Peru and Equatorial upwelling respectively and are mainly affected by the Peru System Currents and Equatorial Countercurrent. In both Sites the coccolithophore assemblage is dominated by "small" Gephyrocapsa, Gephyrocapsa oceanica and Florisphaera profunda because both areas were under the influence of similar paleoenvironmental conditions. Nevertheless, the abundance of the different taxa shows significant and specific differences between both sites. The relative abundance of the coccolith species, coccolith accumulation rate (NAR) and productivity (N ratio) absolute values indicate that the Equatorial assemblage was more productive than that from Peru and allowed us to identify three intervals dated by the identification of calibrated biostratigraphic events and paleomagnetic data. Interval I (0.86-0.45 Ma) and interval III (0.22-0 Ma), which are characterized by high abundance of Florisphaera profunda in relation to the "small" Gephyrocapsa, were related to weak upwelling and weak Trade Winds. These environmental conditions fit with those prevailing today during "El Nino" events. Interval II (0.45-0.22 Ma), characterized by dominant Gephyrocapsa caribbeanica and very abundant "small" Gephyrocapsa and Gephyrocapsa oceanica, was related with well defined upwelling and enhanced Trade Winds, the same features developed during "La Nina" events today. http://oceano.usal.es
PP41B-0553
Coccolithophore Record During the Middle Pleistocene in the North and South Atlantic: Productivity and Dissolution Patterns
The coccolithophore assemblages of ODP Site 1089 (Cape Basin, Atlantic Ocean) and of piston core MD03- 2699, located in the Estremadura promontory (NW of Lisbon), were analyzed. The studied interval ranges from MIS 9 to MIS 13 and includes Mid-Brunhes event (MIS 9 to 11), which is considered one of the warmest during the Pleistocene. This interval is also characterized by generally high carbonate concentrations (and high productivity) with intervals of high dissolution in the deep ocean. The paradox of high carbonate production and high dissolution in certain intervals might be linked to nutrient available, ocean geochemistry, and upwelling. During MIS12 and 13 the assemblages are dominated by {\ it Gephyrocapsa caribbeanica} (a small but robust and well- calcified placolith). {\ it G. oceanica} shows low abundance values during MIS 11, 12 and 13. A light increase of the species is recorded, at ODP Site 1089, during MIS 10. We observed fluctuations in the degree of preservation in the calcareous nannofossil assemblages: interglacial periods are characterized of high to moderate dissolution, glacials by moderate to good calcareous nannofossil preservation. During Terminations IV and V we observed maxima in calcareous nannofossil accumulation, but with moderate preservation, indicating that maxima in calcareous nannofossil production occur during Terminations. The geochemical data from ODP site show that the P/Ti ratio, a paleoproductivity and P mass balance proxy, and Sr concentrations, a nannofossil production proxy, also show peaks during Terminations IV and V—thus, high production from nutrients coincides with high carbonate dissolution. In a coupled biological, chemical, and oceanographic model, low sea levels during glacials result in a basin dominance of the shelf-basin fractionation, with high nutrient delivery to the deep sea and increased carbonate production. Basin production then decreases with the increase of nutrient apportionment to the shelves during higher interglacial sea levels.
PP41B-0554
Coccolithophore response to Abrupt and short-term climate changes in the Gulf of Lions (Western Mediterranean) during the last climatic cycle
Cores PRGL-1 (310 m long) and MD99-2348 (21.5 m long) were recovered in the Gulf of Lions (42.690N; 03.838 E) at 298.48 m water depth, during the PROMESS 1 campaign (SRV Bavenit drilling vessel) and IMAGES V (RV Marion Dufresne, Calypso piston core), respectively. The high sedimentation rates -estimated by robust 14C dating- have given us an excellent opportunity to perform high resolution analyses on these materials. In this study we present data from the last 25 kys. The retrieved sediments consist of silty-clay terrigenous material mixed with a small amount of calcareous microfossils. Quantitative analyses of coccolithophore assemblages allow us to identify significant changes in sea surface temperature in this period. Cold peaks are marked by increases in the proportion of Gephyrocapsa muellerae and large morphotypes of Emiliania huxleyi (>5 m); some of the most significant can be correlated with Heinrich events. The high sedimentation rates observed during most of the studied interval also allow us to identify an overprinted multicentennial scale pattern related to Dansgaard-Oeschger cycles. The combined analyses of coccolithophores and planktonic foraminifers permits to produce a sea surface temperature (SST) record in which sharp fluctuations of around 4º C in amplitude have been detected. These abrupt changes in SST are also linked to changes in surface productivity and in the deep and intermediate water dynamics, probably related with variations in the atmospheric pattern (NAO-like oscillations). PROMESS 1 is funded by the European Community (EVR1-T-40024).