OS11A-0180
Surface water saturation state and calcareous nannoplankton production across the Paleocene-Eocene Thermal Maximum
The release of massive amounts of carbon to the ocean-atmosphere system at the Paleocene-Eocene Thermal Maximum (PETM, approximately 55 Ma) has particular relevance today because of the devastating effects that rising atmospheric CO2 and surface water acidification may cause to calcifying organisms such as coccolithophores and corals. Widespread carbonate dissolution at the onset of the PETM is striking evidence for deep ocean acidification at this time. Here, we address whether ocean acidification also affected the production of biogenic carbonate in surface waters. By the novel combination of nannofossil abundance counts and taxon- specific Sr/Ca data we have reconstructed original calcareous nannoplankton production at the Ocean Drilling Program (ODP) Sites 690 (Southern Ocean) and 1209 (paleoequatorial Pacific) and the New Jersey shelf site ODP Leg 174X drillhole at Bass River. Nannoplankton production records at all three sites are decoupled from changes in bottom water chemistry with no evidence for interruption of carbonate production by phytoplankton on geological timescales, even at high latitudes which we would expect to be sensitive to surface water acidification. Therefore, although we cannot rule out that calcification could have been inhibited for less than 1000 years at the event onset, we can conclude that there was no long-term detrimental impact on the surface water calcifying community.
OS11A-0181
Effects of Geologically Short-Lived Surface Water Perturbations on the Calcareous Nannoplankton as Exemplified by the Paleocene-Eocene Thermal Maximum and Cretaceous Oceanic Anoxic Event OAE1d
Calcareous nannoplankton are obligate photoautotrophs restricted to the photic zone in the open ocean. Disruptions to the chemical and physical structure of the surface water mass constitute the most important environmental stresses forcing evolutionary changes. Surface-water environmental perturbations in ancient oceans provide opportunities to test the effects of these stresses on ancient plankton communities. Here we present data from the Paleocene-Eocene Thermal Maximum (PETM) at 55 Ma and mid-Cretaceous (late Albian) oceanic anoxic event (OAE) 1d at 98 Ma, and compare changes in nannoplankton communities, including extinctions and originations (taxonomic turnover) and temporary assemblage shifts, with the extent and rate of change in environmental variables including temperature, thermal stratification, carbon export and alkalinity. In the case of the PETM, high rates of taxonomic turnover affected both oligotrophic and mesotrophic species. These taxa were relatively minor parts of the total assemblages, however, and the numerically abundant species were not affected permanently. The event is associated with a wholesale assemblage shift, including common and rare taxa, that varies from one oceanic setting to another. Highest rates of turnover and assemblage shift occurred during intervals when the rate of change of environmental variables including temperature, stratification and carbon export is highest. Relatively minor perturbations in the structure of the upper surface water mass, such as that associated with OAE1d, led to selective extinction of morphologically specialized oligotrophic taxa that were dependent upon maintaining a fixed position in a stable, stratified water column. These taxa were relatively rare components of the late Albian assemblages. In addition, the environmental changes associated with the anoxic event were coincident with originations and extinctions of less specialized clades undergoing adaptive radiation. These examples suggest that geologically brief perturbations of the upper water column affect only rare taxa permanently, while the more common calcareous nannoplankton exhibit a remarkable resilience to the effects of all but the most extreme short-lived disruptions of the surface water mass.
OS11A-0182
Organic Walled Dinoflagellate Cysts and the Middle Eocene Climatic Optimum (MECO): Preliminary results from ODP leg 120, Kerguelen Plateau.
The Middle Eocene (~ 50-35 Ma) is generally considered as a period of gradual cooling in Earth's transition from the greenhouse into the icehouse. Recently however, oxygen-isotope based studies showed a ~ 600 kyr episode of warming in the Southern Ocean at ~ 41.5 Ma, termed the Middle Eocene Climatic Optimum (MECO). Documentation of potential biotic change during the MECO is very limited. To evaluate if the MECO exhibited a response in algal communities we are currently studying remains of dinoflagellates, i.e. their cysts. Here we present preliminary results from a pelagic ooze from the Indian sector of the Southern Ocean (ODP leg 120 site 748B, Kerguelen Plateau), which comprise the first Eocene well-preserved open ocean dinocyst assemblages ever encountered. Preceding the MECO event, a typical Southern Oceanic offshore community flourished. In contrast, during the MECO, an increasingly cosmopolitan assemblage persisted. Furthermore, low-salinity tolerant species were present in a number of pulses. Remarkably, two huge abundance peaks (acmes) of the cosmopolitan marker Thalassiphora pelagica occurred. According to benthic oxygen isotopes, the first acme occurred during a phase of initial cooling just prior to the MECO. The second acme occurred just after rapid cooling that apparently terminated the MECO. Such acmes are generally considered to reflect strongly stratified water masses. After the MECO, the endemic open oceanic community reappeared. Our preliminary results strongly suggest that, at least in the Southern Ocean, major oceanographic and biotic reorganizations took place during this period of climate change. In order to elucidate the further constraints of the MECO-event, dinocyst-specific stable carbon isotopes and TEX paleo-thermometry will be applied.
OS11A-0183
Benthic Foraminiferal Response to Reduced Oceanic Acidification and Global Warming During the Miocene Monterey Excursion, Congo Fan, Southeastern Atlantic
The Early-Middle Miocene was a period of global warming and increased carbon burial as evidenced by the Monterey global positive carbon isotope shift from 18 - 14 Ma (Vincent and Berger 1985), which culminated in the deposition of massive carbonates and has been linked to recorded atmospheric CO2 lows at this time. We have collected the first ever record of benthic δ18O and δ13C from the Miocene of the Congo Fan, and report on the benthic foraminiferal response to these isotopic shifts from BP wells spanning the Early-Middle Miocene (21 - 14 Ma). Oligocene sediments from the Congo Fan consist almost entirely of agglutinated foraminifera due to deposition below a locally raised CCD. During the Early Miocene a gradual and persistent increase in the percentage of calcareous foraminifera is mirrored by our record of increasing benthic δ13C (from Cibicidoides spp.) at this site, suggesting reduced bottom-water acidification and a lowering of the CCD. Faunas record well- oxygenated bottom waters (~1000 m paleodepth) from 21 - 16 Ma. A dramatic shift in the shallow infaunal morphogroup at ~16 Ma (high abundances in Bulimina elongata, Brizalina aff. barbata, Uvigerina aff. carapitana) records lower oxygen and a probable expansion and strengthening of the oxygen minimum zone lasting for at least 1 my. This is coincident with cooling in this location, adding evidence for raised colder bottom-waters. We postulate that global cooling at this time (e.g. Zachos et al. 2001) was responsible for increasing the strength of the polar front, and in turn strengthening offshore winds at this location affecting an increase in upwelling and surface water productivity.
OS11A-0184
Late Paleocene- Early Eocene paleoenvironments in the Southwest Pacific (ODP Leg 189): Revised Stratigraphy of an Antarctic PETM Record.
The Late Paleocene and Early Eocene (~60 ¡V 50 Ma) were characterized by globally warm climates. Superimposed on this general warmth, several episodes of further warming occurred (so-called hyperthermals), including the Paleocene-Eocene thermal maximum (PETM, ~55 Ma) and Eocene thermal maximum 2 (ETM2, ~53 Ma). While the PETM is by now well documented from Northern Hemisphere, and some equatorial locations, southern high-latitude records are still rare. Here we present high-resolution palynological, XRF, bulk organic stable carbon isotope (ƒÔ13CTOC), and TEX86 palaeothermometry data across Upper Paleocene through Lower Eocene pro-deltaic deposits from the Southwest Pacific Ocean, at ~65¢XS palaeolatitude (ODP Site 1172). Based on a revised integrated biomagnetostratigraphic age model and ƒÔ13CTOC stratigraphy, we identify the southernmost marginal marine PETM ever encountered. Moreover, there is every indication that ETM2 was recovered as well at Site 1172. Despite a high latitude source of the surface waters at this site, the PETM is marked by the characteristic acme of representatives of the (sub) tropical dinoflagellate cyst (dinocyst) Apectodinium, confirming the truly global nature of this PETM event. TEX86 values indicate that surface ocean temperatures rose from ~23¢XC to ~30¢XC during the PETM at Site 1172, hence by a similar magnitude as recorded in other PETM successions globally. Before and after the CIE, mass abundances of low salinity tolerant dinocysts are recorded, taken as indicative of increased runoff. These trends are analogous to those recorded at northern high latitudes, indicating a similar climate response at both polar regions during the PETM. Yet, some distinct differences are apparent, and are discussed.
OS11A-0185
Response To The Paleocene-Eocene Thermal Maximum Of Calcareous Nannofossils: Observations On Composition, Preservation And Calcification In Sediments From ODP Reference Cores
Studies on a climate extreme as the Paleocene-Eocene Thermal Maximum (PETM, ~ 55 myrs ago) have shown the effects of these critical conditions on global biogeochemical cycles and ecosystem, including the marine and terrestrial biota. A prominent negative shift (~ 3 ‰) in marine δ13C, the Carbon Isotope Excursion (CIE) reflects the input of a large amount of isotopically depleted carbon in the ocean- atmosphere system. Studies of the few complete deep-sea sections recovered to date have shown how global climate, atmospheric CO2 levels, marine carbonate chemistry and continental weathering were dynamically related during the PETM. Together, these changes should have strongly influenced the calcifying organisms living in the surface (photic zone) of the oceans. For this reason, recent investigations have focus on the planktonic community response to the shifts in oceanic environments during the PETM, specifically the response of calcifying microplankton to higher CO2 and lower pH, as well as the possible role of plankton in drawing down CO2. Calcareous nannofossils seem to play an important role in these interrelated mechanisms. For this reason we have performed detailed micropaleontologic analysis (using a SEM) of calcareous nannofossil assemblages in selected samples from selected Paleocene/Eocene deep-sea sediment cores with the purpose of documenting possible influence on assemblage composition and preservation. The sediments studied in detail are from ODP Site 1263 (from Southern East Atlantic, Walvis Ridge) that has been chosen as representative of one of the few complete PETM deep-sea cores. Comparative analyses were performed in few selected samples from sections located at different latitudes in the Atlantic and Pacific oceans (ODP Site 929, paleo-equatorial Atlantic, Ceara Rise; ODP Site 689, high-latitude Southern Atlantic, Maud Rise; ODP Sites 1215 and 1221, Eastern equatorial Pacific; ODP Site 1209, central Pacific, Shatsky Rise). This study documents the different ‘behavior' of nannofossils through the different phases of the PETM, at the onset of CIE, within the CIE, and during the recovery interval, and reveals the presence of peculiar morphotypes of Fasciculithus and Discoaster as probably related to the anomalous amount of carbon in the ocean- atmosphere system. Although the anomalous geochemical conditions seems to have had some influence on the nannofossil assemblage composition, it results that local productivity and overall post depositional (diagenetic) conditions were the major controlling factors on nannofossils
OS11A-0186
Proving the Ocean Nourishment Concept
Vast regions of the sea are barren because of a lack of essential nutrients. Ocean Nourishment is the concept of injecting nutrients into the photic zone of the ocean to store carbon and increase the base of the marine food web. It is elaborated in Jones & Young (1997). The first step in demonstrating this concept is to see if the limiting nutrients can be recognised and provided to the oligotrophic ocean. To this end water samples from three sites were collected in ultraclean polycarbonate culture bottles and enriched with various mixtures of nutrients. They were then placed in a water bath and subjected to natural sunlight for a number of days. Fluorescence levels were measured daily. Previously Thomas (1969) carried out enrichment experiments in and out of high nutrient water in the North Pacific and again Thomas (1970) cultured on the deck of his ship nutrient poor waters in the Pacific. He found nitrogen was the most important limiting nutrient in the poor waters but that micronutrients produced growth in the nutrient rich waters. Ryther and Dunstan (1971) in the Atlantic cultured coastal water with only nitrogen and phosphorus separately. The addition of nitrogen without phosphate produced growth in all cases. To increase the geographic coverage of enrichment experiments, samples were collected off Morocco twice, in the Tasman Sea and in the Sulu Sea. The samples enriched with different concentrations of urea (typically 10 microM) and phosphorous. An increase concentration of chlorophyll is the result of growth of phytoplankton exceeding death and grazing by zooplankton. At five sites an increase of chlorophyll was observed in the macronutrient enriched bottles over that in the control. At the sixth site the control grew at much the same rate as the enriched sample possibly due to contamination by the fluorometer. The maximum chlorophyll level was observed after 4 or 5 days. Replicate samples showed different levels of chlorophyll growths. It was concluded that there were sufficient micronutrients present to support some additional photosynthesis at the sites investigated. These results suggest that it will be practical to nourish broad regions of the ocean to increase primary production. References Jones, I. S. F. and H. E. Young (1997) Engineering a large sustainable world fishery.Environmental Conservation, 24, 99-104. Ryther, J.H. and W. M.Dunstan (1971) Nitrogen, Phosphorus and Eutrophication in the coastal marine environment, Science, 171, 1008-1013. Thomas, W H (1970) Effect of Ammonium and Nitrate Concentration on Chlorophyll increase in Natural Tropical Pacific Phytoplankton Populations, Limnology and Oceanography, 15, 386-394. Thomas, W.H., (1969). Phytoplankton nutrient enrichment experiments off Baja California and in the eastern equatorial Pacific Ocean. J. Fish Res. Bd. Can., 26: 1133-1145. Acknowledgement A Eddington made a number of the obsevations. The Ocean Nourishment Corporation Pty Ltd funded some of the reearch. http://www.otg.usyd.edu.au
OS11A-0187
Coupled Biodiversity And Climate Evolution Through The Phanerozoic Eon
The recent discovery of two prominent extinction cycles throughout the Phanerozoic has caught the attention of many, initiating research into the causes of these periodic biodiversity anomalies in areas such as climate and cosmic forcing. The fossil record however, is dominated by marine fossil taxa, comprising more than four-fifths of the total Phanerozoic genera. It is therefore sensible to search for causes that are most likely to effect change in marine biodiversity, such as the 18O/16O composition of seawater. The δ18O composition of the ancient oceans has been used as an indicator of high and low sea surface evaporation and ocean temperature. This study notes a prominent cycle within δ18O estimates that corresponds to a recently discovered extinction cycle (Rohde and Muller, 2005). The coincidence of these two cycles suggests that marine ocean temperature or salinity may have been an influential driving force for Phanerozoic biodiversity.
OS11A-0188
Is the Middle Eocene Climatic Optimum (MECO) recorded in the central-western Tethys?
We have established the carbonate content (%) and the stable oxygen and carbon isotope composition of the bulk carbonates in 535 samples from the Alano di Piave section, located in the Venetian southern Alps, NE Italy. The biomagnetostratigraphic data allow us to establish a sound chronology that indicates that the Alano section extends from the upper part of the Chron C18r (ca. 39.3 Ma) to the base of Chron C16r (ca. 36.5 Ma). Our records show a marked long-term and high-frequency variability. In particular, isotope reveal an interval of striking variability between 13.60 and 25.30 m levels, in which is comprehended a sapropel-like interval. Major and distinct shifts in both δ13C and δ18O records are present within this interval. Specifically, a negative shift in δ18O values (ca. 1.2-1.3 \‰) mirrors an articulated change in δ13C values. A rapid negative shift of the δ13C values of ca. 0.7-0.8 \‰ is followed by a pronounced positive shift in correspondence with the onset of the sapropel-like interval. This positive δ 13C excursion precedes a short-lived δ13C negative excursion that leads a second rapid δ13C increase. This prominent perturbation in the global carbon cycle terminates abruptly when the carbonate content, δ13C and δ18O values simultaneously return to more stable conditions, albeit the δ13C curve shows a post-event interval of instability around the "stable" condition beyond the termination of the event. This isotope excursion interval, here referred to as Chron C18r/C18n event, is well constrained in time occuring from the upper Chron C18r (ca. 40.3 Ma) to the upper Chron C18n.1r (ca. 39,6 Ma). Interestingly, this event correlates exactly with the positive ca. 0.6 \‰ δ13C positive excursion recorded by Jovane et al. (2007) in the Contessa Highway section. In agreement with Jovane et al. (2007), we correlate this positive δ13C excursion with the MECO event of Bohaty & Zachos (2003) in the Southern Ocean. These results suggest that the interval of time between 40.35 and 39.6 Ma is characterized by a strong climatic instability, with a warming that significantly interrupts the overall cooling trend of the Middle Eocene. The pronounced changes of the δ13C values, in bulk carbonates and the coeval oscillations in global CCD (Tripati et al, 2005) strongly suggest that the carbon cycle played an important role in driving the climatic evolution in the doubthouse world of the terminal part of the Middle Eocene.
OS11A-0189
Distribution of Living Coccolithophores North of the Canary Islands: Vertical, Seasonal and Interannual Variations
Coccolithophores are unicellular gold-brown algae covered with small calcium carbonate plates and production and burial of these organisms play an important role in the global carbon cycle. In order to assess their role, cell density and taxonomic composition of living associations were analyzed along an East-West temperature and productivity gradient in the North Atlantic Eastern Boundary Current. Water samples were taken from 9 different water depth levels (0-200m) at three locations near the mooring stations LP1 (29°45.7N, 17° 57.3W), JGOFS Time-series Station ESTOC (29°10.0N, 15°30.0W) and EBC2 (28°42.5, 13°9.3W) during several seasonal cruises from September 1995 to July 1998. Samples were filtered onto Nucleopore® membranes in order to determine coccolithophore cell densities and taxonomic composition of the assemblages. In addition, in situ CTD and fluorometer measurements were done and samples for nutrient and oxygen content were collected from the same water depth levels at all stations. Maximum total coccolithophore cell densities usually occurred in the upper photic zone above the deep chlorophyll maximum that was generally located between 50m and 125m water depth. A strong gradient in total coccolithophore cell densities was found during winter between the open ocean location LP1 with 20'000-40'000 cells/l and the near-shore location EBC2 with a maximum of 160'000 cells/l. During summer, a much weaker gradient occurred with 25'000 cells/l at LP1 and ~80'000 cells/l at EBC2. During spring (April), the cell density gradient was reversed with low cell densities at the near-shore location. In contrast, the strongest gradient in sea surface temperature and salinity occurred during late summer (September) with 24°C and 37.1 at station LP1 and 20.2°C and 36.5 at station EBC2. The weakest gradient was found during winter (January) with 19.5°C and 36.8 at station LP1 and 19.1°C and 36.7 at station EBC2. Four coccolithophore species dominated almost all assemblages analyzed. The most abundant species living in the upper photic zone (0- 100m)was Gephyocapsa ericsonii followed by Emiliania huxelyi and Umbellosphaera tenuis. Florisphaera profunda was the most abundant species below the deep chlorophyll maximum.
OS11A-0190
Active pCO2-Control of Seawater Culture Systems for Laboratory-Based Biogeochemical Experimentation Investigating Global Ocean Acidification
The large-scale effects of anthropogenic CO2 rise and global ocean acidification on calcifying and photosynthetic organisms are not well understood. This ongoing uncertainty fundamentally limits our ability to fully understand global carbon cycling. Field-based studies are limited to the current environmental chemistries observed throughout the world's oceans – a prohibitively resource-intensive platform for manipulative experimentation. Moreover, complex carbonate system equilibria decoupled from the atmosphere are difficult to poise and maintain in laboratory seawater-based experiments lasting longer than a few hours or days. This severely limits the scope of biogeochemical experimentation for simulating past or future ocean chemistries. To address these experimental shortcomings we developed a novel system for the stringent control of pCO2 in culture aeration and seawater. A custom CO2 scrubbing system was designed which removes > 99.8% of atmospheric CO2 at 3-4 L min-1 aeration rate. High precision mass flow controllers integrated with a modular programmable process controller precisely mix high-purity (99.95%) compressed CO2 with the preconditioned CO2-free air stream for aeration into the culture system. Long-term maintenance of experimental CO2 is within ± 2 μatm when operating between 150- 2000 μatm pCO2. The system, in its current configuration, has the ability to simultaneously manipulate and maintain 3 separate carbonate chemistries using aeration pCO2 and seawater alkalinity in independent 400-L seawater reservoirs. Future system expansion can easily maintain 5 or more separate chemistries. The goal of this research is to develop stringent control of seawater carbonate system chemistries for the deep- sea benthic foraminifera cultures housed at the University of South Carolina Arnold School of Public Health. Current experiments are investigating trace metal foraminiferal paleoproxy signatures that appear correlated with [CO32-] very near calcite saturation. Our system's control of equilibrium pCO2 allows precise maintenance of the culture's carbonate system chemistry very near, above and below calcite saturation, while maintaining realistic values for alkalinity and dissolved inorganic carbon. This research was funded by the University of South Carolina Arnold School of Public Health and the National Science Foundation - OCE 0647891.
OS11A-0191
Effects of Hydrogen Peroxide on Coral Photosynthesis and Calcification
The widely-observed decline of coral reefs is considered to be caused by changes in the environment by natural and anthropogenic activities. As one important factor, the run-off of various matters from human activities to the coastal seawater poses stresses to the corals by degrading the quality of the seawater. In Okinawa, Japan, red- soil running off from the developed land has been a major environmental issue since 1980s. Hydrogen peroxide (HOOH), a strong active oxygen species, is one of the photochemically formed chemicals in the red-soil-polluted seawater. Recent photochemical studies of seawater showed that HOOH photo-formation was faster in the red- soil-polluted seawater than clean seawater. We studied the effects of HOOH on corals by studying the changes in coral carbon metabolisms such as photosynthesis and calcification, which are indicators of the physiological state of a coral colony. The corals were exposed to various concentrations of HOOH (0, 0.3, 3 μM). Two massive coral species of Porites sp. and Goniastrea aspera and one branch coral of Galaxea facicularis were used for the exposure experiments. The control experiments showed that when no HOOH was added, metabolisms of each coral colony were relatively stable. On the other hand, when HOOH was added to the seawater, we observed obvious changes in the coral metabolisms in all the coral species. When 0.3 μM HOOH was added, photosynthesis decreased by 14% and calcification decreased by 17% within 3 days, compared with the control. When 3 μM HOOH was added, photosynthesis decreased by 21% and calcification decreased by 41% within 3 days, compared with the control. Our study showed that higher concentrations of HOOH posed more stress to the coral colonies.
OS11A-0192
Using Carbon and Nitrogen Stable Isotopes and Trace Metal Concentrations in Zooplankton to Determine Seasonal and Anthropogenic Influences in the Gulf of Aqaba, Red Sea
The Gulf of Aqaba is a narrow, warm, saline, and oligotrophic gulf surrounded by arid deserts and is connected to the northern Red Sea via the Strait of Tiran. The Gulf of Aqaba is characterized by strong seasonal fluctuations in primary production and phytoplankton biomass (Genin et al 1995, Lindell and Post 1995). Primary production in the gulf is unusually high compared with other warm oligotrophic seas under similar nutrient conditions. This study investigates the relative influence of anthropogenic or terrestrial nutrient sources and metal pollution to seasonal and biological variation in zooplankton. Surface zooplankton samples were collected every month during 2004 from one offshore station and ten coastal stations along the northern tip of the Gulf of Aqaba. Samples were separated into three size fractions and analyzed for δ13C (TOC), δ15N, wt.% inorganic carbon (IC), C/N ratios and elemental concentrations of 17 metals (Li, Cd, Pb, U, Mg, Al, P, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr). The results showed that trace metals were highly variable between all months and locations. Site-specific differences were not statistically significant, but monthly differences were observed in 11 elements, suggesting that seasonal effects dominate metal concentrations in zooplankton. Results from the C, N isotopes reveal that calcifying organisms are significantly more abundant in smaller size fractions, and that there is a trophic level difference in δ15N values that is not present in the δ13C values. In addition, δ13C values record a small but significant difference between the northern and port sites versus the southern sites, suggesting that the northern and port sites are more anthropogenically impacted. However, the δ13C, δ15N, and C/N all show highly significant seasonal variations, which are probably the dominant factor influencing zooplankton in the Gulf of Aqaba.
OS11A-0193
Reconstructing Radiocarbon Variability in the Bismark Sea for the Past 50 years
We present a surface ocean radiocarbon time series derived from a Porites colony which grew near Rabaul, Papua New Guinea. The record covers about 50 years of growth, from the 1940s to 1998, and has been sampled with seasonal resolution (4 samples per year). The coral survived the September 19, 1994 eruption of the Tavurvur vent at Rabaul, which can be seen in X-radiographs of the core. The record features a 170 permil increase in Ä14C starting in the 1960s and tapering off since the 1980s. This increase is relatively large, as compared with other South Pacific coral sites. The record reflects interannual radiocarbon variations with amplitudes between 10 and 20 permil before and after the introduction of "bomb" carbon. Data from the 1940s and early 1950s show a tight clustering of radiocarbon values with Ä14C = -56.5±1.0 permil (29 measurements). The radiocarbon data are examined in terms of regional surface ocean circulation and compared with other coral records from the region.
OS11A-0194
Foraminifera From Atarctic Glaciers: its Distribution Related to Environmental Factors
The present investigation is an attempt to understand which abiotic parameters of the bottom water (depth, salinity, temperature, conductivity and density) might be the controlling factor to describe recent foraminifera fauna associated to glaciers environments from two antarctic islands (King George and Elephant islands). The principal component analyses (PCA) of the environmental data reveals a marked environmental gradient, with 90.1% of the cumulative percentage variation explained by the first two principal components. The coefficients of the linear combinations of environmental variables show temperature and conductivity factors as the largest positive loadings on PC1, and high negative for density, salinity and depth. The PC2 axis is characterized by positive loadings for all variables, showing the strongest positive loading for conductivity on this axis. A plot of PC1 versus PC2 scores reveals 4 distinct groups: Group I includes G5, G6, G7, G8, and G11 stations with negative scores on both principal components, suggest lower temperature and conductivity with high values salinity, density from deeper sites. Group II includes G10 and G12 stations that have negative scores on PC1 and positive scores on PC2, reflecting deeper environments with low temperature and conductivity and intermediate salinity. Group III includes G2 and G9 stations which have positive scores on PC1 and negative scores on PC2 and they have high temperature and conductivity in shallow environments with low salinity and density values. Group IV includes G13, G14 and G15 stations with positive scores on both principal components reflecting environments with intermediate depths and lower salinities. The most ecologically meaningful pattern obtained in the Multi-Dimentional Scaling (MDS) ordination of the data by foraminiferal species reveals three facies (A, B and C). The assemblage associated with MDS A is dominated by Hemisphaerammina bradyi (3.16%, average relative abundance) and Quinqueloculina patagonica (2.67%) from one of the shallowest sites. MDS B is associated to Globocassidulina biora (53.92%), Globocassidulina subglobosa (7.53%), Psammosphaera fusca (5.95%), Buccella peruviana (4.62%), Quinqueloculina seminulum (2.55%) and Miliammina arenacea (2.19%) and is related to sites deeper than 25 meters with lower temperatures and higher salinities. MDS C contains Portatrochammina antarctica (4.86%), Bolivina pseudopunctata (2.31%), Cassidulinoides parkerianus (2.07%) and Hippocrepinella hirudinea (1.82%) characteristic of higher temperature environments. Our data suggest that the main controlling factors of the twelve dominate species are temperature and depth.
OS11A-0195
Response of Sea Surface Temperature and Chlorophyll-a Concentration to Sahara dust storms over the eastern subtropical Atlantic
Satellite retrievals of MODIS aerosol optical thickness (AOT), TMI sea surface temperature (SST) and SeaWiFS chlorophyll-a (Chl-a) concentrations are analyzed jointly to investigate the impact of Saharan dust on SST and primary productivity on the eastern subtropical Atlantic. For that purpose, SST and Chl-a weekly anomaly fields are investigated with respect to their evolution before, during and after intra-seasonal storm events during the period 2000 through 2004. The talk will focus on strong dust outbreaks during 2003 and 2004 between Cape Verde and Canary Islands, during which SST decreases locally under regions of high AOT concentrations by 0.2 to 1.6 °{C}. Using the forcing efficiencies results from Li et al. (2004) and Yoon et al. (2005), reduction of solar irradiance associated with the dust events amounts to 60 W/m2. Based on a simple mixed layer assumption, the observed SST response is consistent with this reduced surface heating due to AOT concentrations. The Chl-a fields show that in several occasions its concentration increases after strong dust events. However, those occasions seem to happen primarily during spring, while in other seasons, other processes seems to impact productivity more strongly than the dust-induced fertilization. Likewise we find also most evidences of dust-induced surface cooling during spring, while during summer and fall internal ocean processes seems to dominate the evolution of SST.
OS11A-0196
Strontium Isotope Dating of Metalliferous Sediment in the SW Pacific Basin
A 2 million km2 region virtually devoid of sediment was identified in the remote SW Pacific Basin during the TUIM- 3 2005 drill site survey cruise. This region, termed the "South Pacific Bare Zone", comprises ocean floor dating back to the Late Cretaceous. Within the Bare Zone, a small (1km2) abyssal valley containing sediment to a depth of 24 m was sampled using a large diameter piston core (MV0502-15JC, 31 ° 42.194'S, 143 ° 30.331'W), leading to recovery of 8.35 m of metalliferous sediment at 5082 m water depth. Fish-teeth Sr-isotope stratigraphy reveals a continuous record of sedimentation from 31 Ma to present at this site. The fish teeth age-depth profile and INAA geochemistry reveal an exponentially decreasing hydrothermal flux, with sedimentation rates approaching 0.05 mm/kyr after 20 Ma. The source of hydrothermal activity at this site was likely the Pacific- Farallon Ridge, which went extinct at 20 Ma. A second piston core (MV0502-16JC; 28 ° 05.151'S, 140 ° 14.140'W) was collected near MacDonald Seamounts located on the southeastern end of the Cook-Austral island chain outside the Bare Zone and recovered 10.5 m of hydrothermal sediment and biogenic ooze. The lower 65 cm of the core consists of a coccolith ooze. From 10 mbsf depth to 1.5 mbsf depth, the core contians reddish black zeolitic clay, while the upper 1.5 mbsf contains biogenic ooze associated with abundant Late Pleistocene foraminifera remains. Concordant nannofossil and fish teeth ages at the base of the core (27-28 Ma), and Pleistocene ages near the top of the core reinforce the validity of the Sr fish teeth method for dating hydrothermal cores. These independent records suggest that regional hydrothermal activity during the Oligocene may have been related to a series of late Eocene/early Oligocene ridge jumps, propagating rifts and seafloor spreading centers that accompanied large-scale plate tectonic reorganization of South Pacific seafloor.
OS11A-0197
Radiogeochemical Properties and Cycling at the Caribbean National Forest El Verde Research Station and Surrounding Region on the Island of Puerto Rico
From 1964 through the early 1970's the Atomic Energy Commission conducted a series of experiments at The El Verde Research Station in Puerto Rico. Among these experiments included several involving the use of Cs-137 and other anthropogenic radionuclides. Radiological tests on the trees and vegetation were conducted in a small section of rainforest to study mineral cycling and metabolism. Studies on fauna and water movement were also conducted. In 2003 an investigation of long-term radiogeochemical cycling at the El Verde Research Station was launched. Results from radiogeochemical analysis of sediments and soils collected from El Verde Research Station, nearby streams, as well as the estuary of Coco Beach in the municipality of Rio Grande, Puerto Rico are presented. Cs-137 activities range from below detection limits to 0.4 Bq/g. Ancillary data obtained from grain size, X-ray diffraction, ICP-OES analyses are also discussed. Understanding the current environmental health of study region's ecosystem is vital, given the fact that this area serves as one of the largest sources of potable water for more than 13 municipalities of Puerto Rico.
OS11A-0198
Validating a Biogeochemical Watershed Disturbance and Climate Change Proxy: Tampa Bay. FL
The Tampa Bay estuary and watershed have been impacted in the past century by residential and industrial development activities that have resulted in pollutant release via runoff and wastewater discharges. Mangrove forest loss, mining activities, accidental spills and nutrient loading have also decreased water quality in this aquatic environment. The primary goal of this project is to provide historical water quality and climate information by determining biogeochemical properties of oyster shells and sediments collected from various locations throughout the Tampa Bay region including ancient Native American shell mounds. Biogeochemical properties of shells collected from these middens will provide insight regarding historical water quality of Tampa Bay. It is expected that a pristine, pre-Columbian baseline may be revealed from the midden shells, and changes in the biogeochemical record may be demonstrated over the recent past from the industrial age to modern day on a seasonal and yearly scale. In order to achieve the goal of this project, midden shells and sediments will be collected and compared from three stations in Tampa Bay that range from undisturbed to severely impacted; Emerson Point, Weedon Island, and Bayboro Harbor, respectively. Water and sediment samples have also been examined to provide additional information regarding radiogeochemical properties of the three study sites. Sediments will be dated using gamma spectrometry techniques (U/Th series). Standard ICP-OES methods are being utilized to determine concentrations of trace, minor and major elements in the oyster and sediment samples. This project is part of a larger on-going investigation. If successful, this investigation will ultimately yield a high-resolution tool for establishing the history of terrestrial land use and climate change.