PP31B-0412
Can d44Ca be a Proxy for Paleoceanography? - A Case Study of Globigerinoides Sacculifer from Western Equatorial Atlantic
The δ 44Ca, δ 18O, and Mg/Ca ratios of fossil Globigerinoides sacculifer over the past 20 ka extracted from a Caribbean core, TT9108-1GC, have been measured in order to examine the possibility of using δ 44Ca as a proxy for paleoceanography. Our results indicate that the δ 44Ca of G. sacculifer varies as a function of sea surface temperature (SST) and sea surface salinity (SSS). The Caribbean Sea SSS, reconstructed by combining the δ 18O and Mg/Ca ratios of G. sacculifer and sea level change data, shows significant fluctuations between 36.5 and 39.5 psu during the last 20 ka. After isolating the temperature effect, the δ 44Ca of G. sacculifer exhibits a positive correlation with SSS, ca 0.27±0.02 ‰ per 1 psu. On the other hand, no significant relationship is observed between δ 44Ca and seawater [CO3 -2]. Moreover, variation of G. sacculifer δ 44Ca can also be explained using a Rayleigh fractionation model. As a function of temperature and salinity, the metabolic rate may influence the utilization of vacuole Ca+2 in G. sacculifer, resulting in different δ 44Ca values. The results of this study are inconsistent with the "rate-controlled fractionation model" of Lemarchand et al. (2004), instead, the results are more in-line with the foraminiferal biomineralization model of Erez (2003), where δ 44Ca reflects the adjustments of temperature, salinity, and pH of seawater isolated in vacuoles during the growth of G. sacculifer.
PP31B-0413
Temperature and Productivity Calibration off Southwest and South Portugal: Planktonic Foraminifera Trace Element Proxies Application
Planktonic foraminiferal trace element ratios (Mg/Ca, Ba/Ca, Cd/Ca) from core-top sediment samples collected along the southwestern and southern Portuguese margin (35.5 - 38.5°N, 7 - 11°W) were determined to assess the latitudinal and longitudinal changes in surface water conditions relatively to the present hydrographic conditions and to calibrate sea surface temperature (SST) and nutrient proxy for this seasonal upwelling region. Three species with different depth habitats, linked to specific hydrographic conditions, were used for this study area. Globigerina bulloides an upper water column species, reflects the modern summer coastal upwelling with cold waters and high primary productivity close to the coast along the southwestern margin. Globigerinoides ruber (white) a surface dwelling species, and Globorotalia inflata a deep dwelling species, which are associated with the Portugal Coastal Countercurrent a winter-time warm current. Both these species show their dominance on the southern margin, where upwelling only occurs occasionally, and offshore of the southwestern coast, outside of the direct influence of coastal upwelling (well stratified surface waters). Preliminary SST results, derived from G. bulloides and G. ruber (white) Mg/Ca, indicate 17°C close to the southwestern margin, that is 3-4°C colder temperatures than found offshore and off the southern margin. This pattern reflects the summer upwelled waters and is in excellent agreement with the modern satellite SST average values. G. inflata reflects similar and colder temperatures of calcification and higher values of the nutrient trace element proxies (Ba/Ca and Cd/Ca) than the other study species at both margins indicating the presence of colder and nutrient-richer sub-superficial waters. The insights gained from this study will be applied to estimate past climate conditions in this particular region and in other upwelling areas.
PP31B-0414
The Mg/Ca of Mixed Layer and Thermocline Dwelling Foraminifera From the Eastern Indian Ocean and Western Pacific
Using multi-core top material from the tropical Eastern Indian Ocean and Western Pacific Ocean, we evaluate the robustness of the Mg/Ca and temperature relationship in a variety of mixed layer (G. ruber (white, sensu stricto), G. sacculifer, and G. bulloides) and thermocline (N. dutertrei, P. obliquiloculata, and G. tumida) dwelling foraminifera species. Preliminary evidence suggests that the Mg/Ca ratio of N. dutertrei and P. obliquiloculata is lower in cores below 1,000m than above 1,000m, possibly indicating preferential dissolution of higher Mg-calcite. The Mg/Ca ratios of G. ruber and G. tumida do not exhibit the same depth dependence. Depth dependent Mg/Ca calibrations are created and tested against existing calibrations. Additionally, the potential for using the Mg/Ca derived temperatures of multiple species to reconstruct water column structure is evaluated using both modern hydrography and downcore records.
PP31B-0415
Salinity and Temperature Reconstruction from Oxygen Isotopes and Mg/Ca in Benthic Foraminifera in the NE Pacific margin for the Late Holocene
Upper intermediate waters in the North Pacific presently show an equal partitioning between the wind driven (<26.5?) and thermohaline circulation (>26.5-27.3?). The ventilated volumes and ages in the upper wind driven layer are related to the wind stress curl and surface buoyancy fluxes in mid to high latitudes in the North Pacific, in contrast to the deeper thermohaline layers that are more effectively ventilated by direct atmosphere-sea exchange during convective formation of Subantarctic mode and Antarctic Intermediate Waters the precursors of Pacific Intermediate Waters (PIW) in the North Pacific. These upper and lower intermediate are clearly identified by its temperature and salinity properties that can be used to trace their sources and mixing paths along isopicnals. A precise characterization of temperature and salinity properties with depth is fundamental in order to characterize and track past changes in sources and mixing paths which will alow to reconstruct the past hydrography of these intermediate water masses. Here we will present results from a calibration based on the combined use of Mg/Ca and oxygen isotopic ratios in benthic foraminifera along a depth transect in the NE Pacific in sediments of late Holocene age to characterize the effects of carbonate saturation and early diagenesis in organic carbon rich sediments on the continental margin of Baja California that will aid us to assess the possibility to reconstruct temperature and salinity trajectories further back in the past in these environments.
PP31B-0416
Mg/Ca of Continental Ostracode Shells
Marine ionic chemistry is thought to remain constant. This, together with the belief that marine calcifiers partition Mg/Ca in a systematic manner as functions of temperature (and Mg/Ca) of water forms the basis of the Mg/Ca thermometer. In continental settings both of these assumptions are usually not true. Continental waters contain a wide variety of solutes in absolute and relative ion concentrations. Hence, waters with identical Mg/Ca may have very different concentrations of Mg and Ca and very different anions. Here we use two examples to focus on the effects of ion chemistry on Mg/Ca partitioning in continental ostracode shells and we ignore the complexities of solute evolution, which can change Mg/Ca over timescales of minutes to millennia. Palacios-Fest and Dettman (2001) conducted a monthly study of ,Cypridopsis vidua at El Yeso Lake in Sonora, Mexico. They established a relation between temperature and average shell Mg/Ca using regression analyses on averaged data. When their Mg/Ca-temperature relation is applied to monthly ,C. vidua data from Page Pond near Cleveland, Ohio, water temperatures of -8 to -1°C are obtained. The observed Mg/Ca ranges for El Yeso Lake (0.31 to 0.46) and Page Pond (0.33 to 0.46) are similar, as are their specific conductivities (700 to 850μS for El Yeso Lake; 400 to 600μS for Page Pond). However, [Ca] is 140-260 mg/L for El Yeso, but only 70-90 mg/L for Page Pond. Page Pond data, in fact, shows a good temperature shell Mg/Ca relation for .C. vidua, but the relation is different from that at El Yeso. Hence, shell Mg/Ca is a multi-valued, family of curves function of temperature and Mg/Ca of water that depends on the [Mg] and [Ca] values in water and perhaps other factors. Our second example comes from sites near Valencia, Spain and involves shell data for ,Cyprideis torosa, an estuarine ostracode that is tolerant of a wide range of salinity and can live in continental waters as long as the carbonate alkalinity to Ca ratio is low. The water bodies near Valencia, Spain, range from 200mg/L to 65g/L with both [Mg] and [Ca] increasing with TDS, but at different rates because of carbonate precipitation. The lowest Mg/Ca was 0.5 in a dilute spring and the highest 6.5 in an evaporation pond with temperature at all sites being similar and highly variable. The observed Mg/Ca of the shells from all sites was generally between 0.005 and 0.025, but at any one site the range was only about 0.01 even at sites with monthly data for a full year, so capturing a wider range of temperature. So, unlike the first example, the low Mg/Ca range at individual sites seems to preclude defining a shell Mg temperature relation. In fact, the data show that very different TDS and different solute Mg/Ca result in a narrow range of shell Mg/Ca, as though ,C. torosa lived at a site with low temperature variability. Of interest, calculation of shell metal distribution coefficients, Kd, shows it goes from 0.025 for the dilute water to 0.005 for saline waters indicating that Kd is TDS dependent at these sites because the solutes all lie on a single solute evolution trend. These examples illustrate what can happen if ionic chemistry and TDS of seawater changes on glacial to interglacial or longer timescales, or if the same thermometer is applied to coastal settings. Palacios-Fest, M.R., and Dettman, D.L., 2001, Geochimica et Cosmochimica Acta, v. 65, p. 2499-2507.
PP31B-0417
Mg/Ca ratio in a coral skeleton as a possible proxy for the skeletal growth rate
Besides Sr/Ca ratio, Mg/Ca ratio in a coral skeleton has been used as a thermometer in the sea surface. Especially, Mg/Ca ratios in corals collected from sub-tropical regions where seasonal variations of sea surface temperature (SST) exceed 3-4uC show good correlation with SST. However, some other corals exhibit influence of vital effects on its Mg/Ca ratios rather than SST. In order to evaluate the behavior of Mg/Ca ratio in a coral skeleton, we cultured corals (Porites spp.) with different growth rate in the thermostated tanks. As a result, Mg/Ca mainly reflected the growth rate rather than temperature with negligible contribution from different species. Then we measured Mg/Ca along a growth axis of a coral core collected from the Java Sea where SST usually varies less then 2uC and compared Mg/Ca variation with skeletal density bands. Consequently, variation of Mg/Ca mostly reflected that of density band, high Mg/Ca occurred with high density band, with little impacts of temperature. As the widths of high and low density bands were almost same on this core, calcification would occur more vigorously during the time when high density band was formed. Ultimately, it is suggested that Mg/Ca ratio in a coral skeleton could have a potential as a proxy for the skeletal growth rate or calcification rate. If skeletal growth rate varies together with SST, Mg/Ca of such a coral would apparently reflect SST.
PP31B-0418
The Search for Eight Glacial Cycles of Deep-Water Temperatures and Global ice Volume From the Southern Hemisphere
It has been recently suggested "a substantial portion of the marine 100-ky cycle that has been object of so much attention over the past quarter of a century is, in reality, a deep-water temperature signal and not an ice volume signal" (Shackleton, 2000). There are currently few records available of deep-water temperature variations during the Pleistocene and most of our understanding is inferred from the oxygen isotopic composition (δ18O) of benthic foraminifera from deep-sea sediments. However, variations in benthic δ18O reflect some combination of local to regional changes in water mass properties (largely deep- water temperature) as well as global changes in seawater δ18O (δ18Osw) resulting from the growth and decay of continental ice. Recent studies suggest that benthic foraminiferal Mg/Ca may be useful in reconstructing deep-water temperature changes, but the application of this method to benthic species has been hampered by a number of unresolved issues, such as uncertainties related to the calibration for benthic Mg at the coldest temperatures. Here we present deep-sea Mg/Ca and δ18O records for the past eight glacial cycles in benthic foraminiferal ( Uvigerina spp.) calcite from a marine sediment core recovered in the mid Southern latitudes. Ocean Drilling Program Site 1123 was retrieved from Chatham Rise, east of New Zealand in the Southwest Pacific Ocean (3290 m water depth). This site lies under the Deep Western Boundary Current (DWBC) that flows into the Pacific Ocean, and is responsible for most of the deep water in that ocean; DWBC strength is directly related to processes occurring around Antarctica. Temperatures derived via pore fluid modeling of the last glacial maximum are available from Site 1123 and represent an important tool to constrain deep-water temperatures estimates using Mg/Ca. In selected time slices, we measured B/Ca ratios in Uvigerina in order to gain information on the deep-water carbonate saturation state and have data of Mg/Ca and B/Ca on planktonic species, which also provides evidence on carbonate saturation state. These results permit preliminary discussion of the magnitude of the deep-water temperature changes during glacial/interglacial transitions and the interglacials themselves. In particular, our deep-water temperature estimates confirm that interglacial stages before 430 ka were characterized by less pronounced warmth - at least in the deeper southern Pacific - than those of the past four climatic cycles, a pattern previously observed in the deuterium record from EPICA Dome C. We examine the relative contributions of deep-water temperature and ice volume to the benthic δ18O signal. The phase relationship between the two signals is tentatively assessed for the middle/late Pleistocene, when different patterns of climate variability have been inferred from marine and ice cores records.
PP31B-0419
Controls on Mg/Ca and Sr/Ca in Planktonic Foraminifera: Results From Culturing Experiments
Culturing experiments were carried out on Globigerinoides ruber (white) and Globigerinella siphonifera, collected from the Gulf of Eilat and grown in seawater (i) at constant salinity but varying temperatures of 18 to 31 degC, (ii) at constant temperature but varying salinities of 32 to 44 psu, (iii) at constant salinity, temperature and dissolved inorganic carbon but varying pH of 7.9 to 8.4. Temperature response of Mg/Ca in cultured G. ruber (with an exponential constant of 11 +/- 2% per degC) agrees well with previous calibrations from core tops and net catches. Mg/Ca in G. ruber shows secondary dependence on salinity (6 +/- 2% per salinity unit). This compares well with the salinity response of Mg/Ca in cultured G. sacculifer (approx. 7% per salinity unit; Nuernberg et al., 1996), implying a similar salinity effect for shallow dwelling species. Mg/Ca in G. ruber shows no dependence on pH at ambient seawater range (8.1 to 8.3; NBS scale), but demonstrates considerable variation below and above the normal range of seawater pH. We observe no significant control of seawater temperature or pH on Sr/Ca in G. ruber. However, there is a significant correlation between Sr/Ca ratios and salinity (approx. 0.016 mmol/mol per salinity unit). Multiple regression analysis on Mg/Ca data of cultured G. ruber gives a calibration equation as a function of temperature and salinity [Mg/Ca = 0.29(+/-0.13)Sal + 0.46(+/- 0.13)Temp - 17.0(+/-5.9), R2=0.96, p=0.05]. Salinity can be independently derived from the regression for Sr/Ca [Sr/Ca = 0.016(+/-0.015)Sal + 0.72(+/-0.55), R2=0.91, p<0.05]. Nuernberg, D. et al., 1996. Assessing the reliability of magnesium in foraminiferal calcite as a proxy for water mass temperatures. Geochimica et Cosmochimica Acta, 60: 803-814.
PP31B-0420
Mg/Ca in Different Size Classes of Planktonic Foraminifera
The ratio of Mg/Ca in the tests of planktonic foraminifers is widely used to reconstruct past sea-surface temperature. However little is known about the effects of biological factors on foraminiferal Mg/Ca. In this study we consider the relationship between test size and Mg/Ca in the planktonic foraminifers Globigerinoides ruber (pink and white), Neogloboquadrina dutertrei and Globorotalia menardii. Foraminifera were picked from modern core-top samples from the Pigmy and Garrison Basins in the northern Gulf of Mexico. Results indicate a positive correlation between Mg/Ca and test size, with a range of 1.0 mmol/mol (2.5°C) from the smallest (150-212μm) to largest (500-600μm) size fractions of G. ruber (pink). N. dutertrei exhibits a negative correlation between Mg/Ca and test size, while G. ruber (white) shows no apparent relationship between test size and Mg/Ca. Changes in depth habitat during the life cycle of some species of planktonic foraminifera may account for the relationship between Mg/Ca and test size observed. This hypothesis is supported by the relationship of oxygen isotope ratios with test size. Given that the range of Mg/Ca values between the smallest and largest size classes within some species exceeds the amplitude of Mg/Ca variability observed in many climate records, it is imperative that Mg/Ca analyses be performed on a narrow size fraction of foraminifera.
PP31B-0421
Mg/Ca Ratios in Planktonic Foraminifera Across a Strong Salinity Gradient in the Mediterranean Sea
The Mediterranean Sea provides an ideal environment to conduct a field study of the effect of salinity on Mg incorporation into planktonic foraminifera. Its semi-enclosed nature results in the development of a considerable gradient (5 psu) in salinity while its west to east alignment leads to relatively small sea surface temperature gradients (a maximum of 8° C in the summer). Eleven box core tops were sampled from across the Mediterranean Sea. Orbulina universa, Globigerinoides ruber (white) and (pink) and Globigerinella siphonifera, were picked and thoroughly cleaned using standard techniques for trace-metal work. Samples were analysed for Mg/Ca, Cd/Ca, U/Ca, Sr/Ca, Fe/Ca, Al/Ca and Mn/Ca. Samples were screened for contamination using Mn/Ca ratios for ferro-manganese crusts and Fe/Ca and Al/Ca for clays. SEM images and sequential dissolution experiments indicated that most samples did not feature inorganic encrusting high-Mg calcite (which has previously been found in some high salinity regions such as the Red Sea). After rejecting samples that failed these screening tests, Mg/Ca ratios in all species are higher, for their calcification temperatures, than seen in previous studies. There is an overall increase in Mg/Ca from west to east and percentage increases per ° C are unusually high. Mg/Ca ratios are particularly high in samples from the high-salinity eastern Mediterranean. We present arguments to suggest that these high values are not the result of nutrient or carbonate ion changes, with both of these variables being similar to those in the open ocean. Correlations of Mg/Ca with salinity are generally more significant than with temperature, with Mg/Ca increases per salinity unit of 15-60% - much higher than suggested in previous culture studies. Our results suggest that salinity may act as a significant secondary control on Mg/Ca ratios in addition to the dominant temperature control. A re-analysis of previous calibrations from other settings also suggests that salinity changes may contribute to the variations seen in the open ocean. We suggest that caution should be used when using Mg/Ca as a palaeotemperature proxy in areas of high salinity, such as the Caribbean, or where large salinity changes have occurred in the past.
PP31B-0422
Culture-based Calibration of the Benthic Foraminiferal Mg/Ca Paleothermometer: Initial Results
The magnesium calcium (Mg/Ca) paleothermometer has become a widely used tool for estimating deep water temperatures. To date, calibrations of the proxy have relied on core-top samples; in such studies, water chemistry and biological factors including food supply often co-vary with temperature, making it difficult to isolate the true Mg/Ca / temperature relationship. A multi-temperature culture experiment was conducted at the Woods Hole Oceanographic Institution from December 2006 through May 2007 in order to study the relationship between Mg/Ca and temperature under controlled conditions. Several species of benthic foraminifera were collected from four locations (the Skagerrak and Gullmar Fjord, Sweden; the Bahamas; and the Charleston Bump, United States; 70 to 800 m water depth), and were grown in microcosms under known, constant physical and chemical conditions at 3.5, 7.0, 14.0, and 21 C. Bulimina species ( B. aculeata and B. marginata) were the most successful, reproducing at 7.0 and 14.0 C and adding chambers at all temperatures. These newly added chambers are the focus of our first Mg/Ca analyses. Because cultured benthic foraminifera are typically lightly calcified, sensitive microanalytical techniques with high spatial resolution are required to measure trace element concentrations in single chambers of cultured specimens. We have explored the use of both secondary ion mass spectrometry and laser ablation inductively coupled mass spectrometry for this application, and present preliminary Mg/Ca data from Bulimina species across the experimental temperature range.
PP31B-0423
Assessing the potential of paired Mg/Ca and d18O to resolve millennial-scale SST variability in the Holocene North Atlantic
The potential of paired Mg/Ca and d18O measurements to resolve 1-2 C SST variability in the Holocene North Atlantic was evaluated in G. bulloides and N. pachyderma (d). Mg/Ca and d18O were measured in core-top samples, down-core series from nearby cores, and across the faunally-defined Younger Dryas/Pre-Boreal climate transition. Both oxidative and reductive cleaning steps were necessary for acceptable picked replicate reproducibility (3.15%). Mg/Ca and d18O were measured in G. bulloides and N. pachyderma (d.) samples from 7 core tops containing post-1950 radiocarbon located across a modern 4 C SST gradient. An exponential fit to Mg/Ca vs. d18O-derived calcification temperature for G. bulloides yielded the relation Mg/Ca=0.93±0.15e(0.07±0.01T). Mg/Ca from N. pachyderma (d.) did not show a relation to calcification temperature in these core top samples, an unexpected result given the comparable d18O measured for each species. This result may reflect sample dissolution during intense trace metal cleaning procedures. Mg/Ca and d18O measurements from G. bulloides from 800-14000 BP were compared between two cores located 68 km apart on the Reykjanes Ridge. While d18O is comparable between the two cores, baseline Mg/Ca from core V23-43 is on average 30% higher than in samples from adjacent core KN158-4-63GGC. Plotting independently calculated Mg/Ca and d18O calcification temperatures along a 1:1 line for both cores shows agreement within 1.5 C (1 sigma) for KN158-4-63GGC, but unrealistically high Mg/Ca-derived temperature for V23-43. The elevated Mg/Ca in V23-43 is reproducible and unlikely a result of contamination. To assess the Mg/Ca-temperature relations across abrupt climate changes that cause large shifts in faunal abundance, down-core Mg/Ca measurements from G. bulloides were compared with lithic grain and faunal assemblage counts during the YD/Pre-boreal transition. Faunal and lithic counts clearly resolve the YD interval in both cores, while Mg/Ca does not. This suggests Mg/Ca from a single species is not a reliable indicator of ocean temperature across climate transitions associated with large shifts in species relative abundance. These comparisons indicate that while existing calibrations may suggest robust Mg/Ca-temperature relation, they do not address all sources of variability in down-core records.
PP31B-0424
Tracing Environmental Variation Over The Past 130 Years In The Barents Sea: Mineral Ratio (Mg/Ca, Sr/Ca, Ba/Ca, And Mn/Ca) Evidence In Shells Of The Circumpolar Greenland Cockle, Serripes groenlandicus
In order to quantify the impacts of human induced climate change on Arctic marine ecosystems it is crucial to establish high-resolution proxies to record regional environmental variability. The Barents Sea region is highly influenced by the annual recession and precession of Arctic sea ice and, as an ecosystem is extremely sensitive to seasonal to decadal climatic changes. Long-lived, sessile, marine bivalves have the potential to provide detailed oceanographic and biological proxy information from the Barents Sea in locations where historic, long- term data logging does not exist. Here, we present preliminary mineral ratio evidence (Mg, Sr, Ba, Mn) for Barents Sea environmental variation from shells of the circumpolar Greenland cockle, Serripes groenlandicus, over the past 130 years from 4 different locations in Norwegian and Russian waters. For all mineral ratios there are clear seasonal trends corresponding with dark winter growth checks on the external surface of each individual. The seasonal patterns of Mg and Sr show progressive change. On average for 9 individuals, Mg/Ca was 10.6 percent greater and Sr/Ca was 5.5 percent lower on the winter checks compared to other values, while Ba/Ca and Mn/Ca ratios show peaks during the middle of the summer growth period. Mineral patterns from the Pechora Sea region are particularly pronounced, which may be related to the influence freshwater from summer river discharge. While the mineral data are initially compelling enough to demonstrate clear seasonal periodicity and inter-annual variation, we believe that a multi-proxy approach to interpreting the information obtained from these bivalves is critical. Therefore, parallel to this study, we are examining external, incremental growth and organic carbon isotopes of shell material from the same collection of bivalves.
PP31B-0425
Evidence of Sr/Ca and Mg/Ca Temperature Invariance in Live Aragonitic Hoeglundina elegans Tests from the Little Bahama Bank
Mg/Ca and Sr/Ca were analyzed from core-top individual Hoeglundina elegans aragonitic tests collected from three continental slope depths within the South Carolina and Little Bahama Bank continental slope environs (220 m to 1084 m). Our study utilized only individuals that labeled with the vital probe CellTracker Green – unlike bulk core-top material often stained with Rose Bengal, which has known inconsistencies in distinguishing live from dead foraminifera. DSr x 10 values were consistently 1.74 $ pm 0.23 across all sampling depths. The analytical error in DSr values (0.7%) determined by ICP-MS between repeated measurements on individual H. elegans tests across all depths was less than analytical error on repeated measurements from standards. Variation in DSr values was not directly explained by a linear temperature relationship (p=0.0003, R2=0.44) over the temperature range of 4.9-11.4°C with a sensitivity of 59.8 μmol/mol/1°C. The standard error by regressing DSr across temperature yields + 3.4°C, which is nearly 3x greater that reported in previous studies. Sr/Ca was more sensitive for calibrating temperature than Mg/Ca in H. elegans. Observed scatter in DSr was too great across individuals of the same size and of different sizes to resolve ontogenetic effects. However, higher DSr values were associated with smaller individuals and warmer/shallower sampling depths. The highest DSr values were observed at the intermediate sampling depth (~600 m). No significant ontogenetic relationship was found across DSr values in different sized individuals due to tighter overall constrained variance; however lower DSr values were observed from several smaller individuals. Several dead tests of H. elegans showed no significant differences in DSr values compared to live specimens cleaned by standard cleaning methods, unlike higher dead than live DMg values observed for the same individuals. There were no significant deviations in DSr across batches cleaned on separate days, unlike the observed sensitivity of DMg across batches. A subset of samples were reductively cleaned (hydrazine solution); and exhibited DMg values within analytical precision of those observed for non-reductively cleaned samples. Therefore, deviations in DMg values resulting from the removal of the reductive cleaning step did not explain analytical errors greater than published values for Mg/Ca or the high variance across same sized individuals. Variation in DMg values across the same cleaning methods and from dead individuals suggests the need for a careful look into how foraminiferal aragonite should be processed. These findings provide evidence that both Mg and Sr in benthic foraminiferal aragonite reflect factors in addition to temperature and pressure that may interfere with absolute temperature calibrations. Funded by NSF OCE 0351029, OCE 0437366, and OCE-0350794.
PP31B-0426
Preliminary Results from the CHEETA Cruise transect: Intercomparison and calibration of Mg/Ca, δ18O, UK37' and TEX86 SST proxies
In July, 2007, a sediment coring and water sampling cruise aboard R/V Oceanus was conducted off the SW Portuguese and NW African margins as part of the CHEETA (Changing Holocene Environments of the Eastern Tropical Atlantic) program. Gravity core and multicore pairs were recovered at 28 stations along a transect from 40°N-15°N paralleling the continental slope. A major goal of the CHEETA program is to utilize multiple inorganic (foraminiferal δ18O, Mg/Ca) and organic (UK37', TEX86) proxies to constrain past variations in surface ocean temperatures in this region. The meridional array of multicore top samples than span a nearly 10°C SST gradient, including several active upwelling sites, provides a means to assess the sensitivity of these different proxies to temperature and other oceanic properties. Surface seawater samples, plankton tows, and suspended particles were also collected at each site to compare in situ results with core-top data. We also examine the fidelity of Mg/Ca and δ18O to resolve seawater δ18O gradients along this transect for three species of planktonic foraminifera (G. ruber (white), G. sacculifer, and G. bulloides). Molecular SST proxies (UK37' and TEX86) are also compared to ambient distributions in the water column. These analyses are used to assess the validity of different SST proxies for reconstruction of past surface ocean conditions in the subtropical and tropical eastern Atlantic.