PP13A-0577 1340h
Atmospheric Circulation and Climate Variability over the Last 200 Years from Talos Dome (East Antarctica) Dust Record
Aeolian dust concentration and size distribution measurements performed on the first 30 m of the Talos Dome (East Antarctica, 72°48'S, 159°06'E) firn core, drilled during the 1996 PNRA-ITASE (Programma Nazionale di Ricerche in Antartide-International Trans-Antarctic Scienticic Expedition) traverse, provide a record of recent climatic and atmospheric history over the East Antarctic sector facing the Ross Sea-Oates Coast (Southern Ocean). Talos Dome (2316 m a.s.l.) is located in the Northern Victoria Land at the topoghraphic summit of a dome (Frezzotti et al., 1998). More than 500 samples analyzed from 1.5 to 30 m allowed to obtain a record of atmospheric mineral dust at high temporal resolution (sub-annual) for the last ~200 years. The average dust concentration and size distribution levels, as well as their variability, are higher from early 1800 to the mid-1900 with respect to the most recent part of the record, with a sharp decrease occurring around 1950-55. The concentration and size distribution of microparticles almost covary over the period investigated, high dust concentrations being generally associated to coarser dust and vice versa. Moreover, average modal value of the volume (mass) background dust size distribution and total dust concentration are slightly higher that typical Holocene values for other East Antarctic sites (Delmonte et al., 2004). These evidences suggest that mixing of fine-grained atmospheric dust from long-range transport with more local sources such as the rock outcrops of the Northern Victoria Land, for example, cannot be excluded. A possible local contribution for dust was also suggested by Maggi and Petit (1998) from earlier dust investigations on a firn core drilled in the Northern Victoria Land close to the Transantarctic Mountains (Hercules Nev 73°06'S; 165°27'E). Interestingly, the dust concentration and size distribution profiles are embedded by clear cycles having periodicity of 7-8 years on average overall the 200 years of the record. The magnitude of these variations is a factor of 10 to 100 for the concentration and a factor 3 for the mode. Assuming the arrivals of coarse (fine) -grained dust having high (low) concentration directly related to the easier (more difficult) penetration of troposphere air masses to Talos Dome and hence to the pattern of meridional wind, our data evidence that a modulation of the atmospheric circulation at these timescales does exist. This periodicity corresponds to the time taken by the Antarctic Circumpolar Wave (White and Peterson, 1996) to encircle the Southern Ocean. We hypothesize the cyclic pattern observed as linked to the circumpolar propagation of ocean-sea ice-atmosphere anomalies in the Southern Ocean, imprinted particularly in the Ross Sea region, modulating the atmospheric circulation pattern at interannual timescale and finally the atmospheric dust advection to the site. The Talos Dome dust record, therefore, can be considered as first-order indicator capable to mirror the past Southern Ocean-atmosphere coupled mode of variability.
PP13A-0578 1340h
Relationship Between Holocene Sediment Accumulation and Lake-Volume Change in a Small Coastal Lake in Southwestern Australia
Change in lithology in a 180-cm-long lake-center core from Lake Thetis, Western Australia serves as a proxy for change in lake volume during the Holocene. Lake Thetis is located on the coastal plain 245 km north of Perth, 1.25 km inland from the Indian Ocean. It occupies a sinkhole in middle Holocene limestone. The 300-m-diameter, steep-sided, ~2-m-deep lake has a 5-m-wide marginal terrace covered by relict and living stromatolites and a bottom covered by a thick, red-purple microbial mat. Lake elevation is not monitored, but changes noted over a 25-year period of up to 0.5 m have alternately exposed and submerged the stromatolite terrace. No hydrological study has been done to determine if the lake has a subterranean connection to the sea. Limited measurements of salinity and pH are similar to or greater than those of seawater. The laminated sediment from the core is divided into three intervals based on texture. From 0 to 45 cm, the core consists of uncompacted, red-purple, organic-rich muddy sand. Very fine-grained carbonate sand forms 50% of the sediment. This interval also contains five, lighter-colored bands, where carbonate sand forms up to 90% of the sediment. From 45 to 130 cm, the core consists of laminated red-brown, muddy, very fine sand and light-red-brown, slightly muddy medium- to fine-grained sand. The frequency of medium- to fine-grained sand layers decreases, but the layer thickness increases, upward. Carbonate grains in the thickest layers are coated with iron-oxide minerals. From 130 to 180 cm, the core consists of alternating red-brown mud, light-gray-purple mud, sandy mud, and muddy very fine sand. The carbonate sand is mostly derived from erosion of the stromatolite terrace, with minor eolian contribution from coastal-plain dunes. Therefore, the mud-dominated basal unit accumulated during a time of high lake elevation, when stromatolites were submerged and actively forming. The middle sand-dominated interval accumulated during a time of low lake elevation, when the emergent stromatolite terrace was actively eroding. The layers containing oxide-coated grains might have formed during periods of prolonged exposure. The uppermost interval accumulated under conditions similar to the modern, where lake elevation varies slightly about the slope break of the terrace. Significant climate and sea-level changes have occurred in this area since the middle Holocene, but current data are insufficient to determine which might be the dominant driver of volume change in Lake Thetis.
PP13A-0579 1340h
An Equatorial Harmonic of the Holocene 1500 Year Cycle: Cyclic Geochemical Variability in Lake Edward, Uganda-Congo
The "1500-year cycle" in the late Pleistocene and Holocene climate of the North Atlantic is well-documented. Several studies from subtropical sites in the Atlantic have shown a relatively direct relationship between millennial-scale climate events in the northern subtropics and the North Atlantic that may be explained by latitudinal shifts in the Intertropical Convergence Zone. In contrast, the effects of this millennial-scale variability on equatorial and south tropical latitudes are poorly constrained. The large East African rift lakes span 5o N to 14o S and combine high climatic sensitivity characteristic of closed basin lakes with high sedimentation rates, making them ideal for high-resolution paleoclimate analysis. Analyses of the stable isotopic and chemical composition of calcite in Lake Edward, situated on the equator at the eastern edge of the Congo basin, have documented a ~725 year cycle in the lake's water balance during the mid- to late Holocene. By filtering the 725-year period in Lake Edward and the Holocene1500 year period in the North Atlantic, we show that drought in equatorial Africa occurs during both the cold and warm phases of the North Atlantic's 1500 year cycle. This relationship can be explained by either latitudinal displacement of the ITCZ away from its equatorial mean position, resulting in equatorial drought, or by changes in rainfall intensity along the ITCZ. Our results per se cannot explain the causes of millennial-scale global climate variability. However, the 725-year cycle present in equatorial African climate has also been recognized in marine records from the Indian Ocean and South China Seas, suggesting teleconnections between millennial-scale climate variability in African rainfall and the Indo-Pacific, and hence, the heart of the ENSO system. This suggests that the tropics at the very least could serve an important role in transmitting, if not causing, millennial-scale climate change. Regardless, our results highlight the importance of understanding how regional climate systems respond to global climate perturbations, and further demonstrate that the 1,500-year climate cycle is felt at equatorial latitudes during at least the Holocene.
PP13A-0580 1340h
Particle Analysis and Event Detection Results of the ELSA-HL2-Core Sequence 133-68 kyr BP (Drymaar west of Hoher List, West-Germany)
Particle-size distribution histograms and statistical particle parameters of the ELSA-HL2-core sequence 66-41 m (Drymaar west of Hoher List, Eifel, Germany) are generated by using the `RADIUS particle analysis method' (RADIUS: Rapid Particle Analysis of Digital Images by Ultra-High-Resolution Scanning of Thin Sections). On the basis of these numerical datasets, sedimentation events were detected automatically by an implemented pattern identification module. The basis of the core section (66-65 m) is composed by ash- and tuff layers. During the posteruptive phase of the maar, the slopes were stabilized by rearrangements of material into the basin. In addition, homogeneous silt layers represent loess events. At a depth of 62 m annual laminated sediments (varves) point at normal lake sedimentation conditions. The section 53 - 41 m is dominated by loess deposits, which are sporadically disconnected by laminated layers. All together 78.7 % of the core sequence is undisturbed. The detected sedimentation events (ashes and turbidites) and loess sequences are basis for time correlations (,tuning') on the ELSA-HL2-core. Thus the whole sequence represents the period 133-68 kyr. The Eemian (126-116 ky) is characterized by annual laminated, organic rich sediments. The end of the Eemian respectively the beginning of stadial C25 is represented by high entries of loess over a short period.
PP13A-0581 1340h
A Multiproxy Record of Marine Isotope Stage 11 (MIS 11) in the South China Sea (IMAGES-Core MD972142)
A growing amount of evidence suggests that the tropics play an important role in the global climate system through their influence on the global heat and moisture budgets. Slight variations in sea surface temperature of the tropical oceans can influence the global climate through atmospheric teleconnections as demonstrated by the El Nino-Southern Oscillation phenomenon. The modern surface circulation in the South China Sea is strongly influenced by the East Asian monsoon system. The fact that the surface layers of the ocean respond "immediately" to changes in surface wind field allows a test of model predictions of changes in the monsoon system over glacial-interglacial cycles, as variations in the upper water structure are recorded by the isotopic composition of different foraminiferal species. Furthermore, the Asian monsoon controls seasonal winds, precipitation, land vegetation, volume and mineralogy of continental run-off, and flux of wind blown dust. Thus, the sediments in the South China Sea provide not only Quaternary paleoceanographic records, but also a record of variations in Southeast Asian continental climate. Here we present a comparison of multiproxy records from MIS 1-6 with records from MIS 10-12 from the southeastern South China Sea. First results show a clear glacial-interglacial signal in most measured parameters. Strongly increased TOC and heavier $\delta$ $^{13}$C$_{org}$ values were observed during the glacials compared to interglacials. To explain the observed changes in $\delta$ $^{13}$C$_{org}$ with variations in terrestrial input would require a massive change in the relative amount of terrestrial input in connection with a major shift toward C4 plants in the land vegetation. It seems more plausible to explain the increased TOC as an effect of increased marine productivity during glacial conditions. An increased difference in stable oxygen isotopes between the foraminifers {\it G. ruber} and {\it N. dutertrei} during interglacial compared to glacial conditions is interpreted as a result of weaker mixing of the upper water masses, likely due to a decrease in winter monsoon intensity. Conversely, the intensified winter monsoon under glacial conditions led to stronger mixing and an increased primary productivity reflected in stable carbon isotopes of the different foraminifer species as well as the TOC and $\delta$ $^{13}$C$_{org}$-records. Fluctuations in carbonate concentration and major elements primarily reflect variations in the input of terrigenous material. The sodium and phosphorus content reflect variations in weathering intensity. Partly contradictory data of opal, phosphorus and TOC data further emphasize the importance of an improved understanding of upper water hydrographic variations. Glacial-interglacial variations in Manganese content suggest fluctuations in the oxygenation of the deep-water masses, possibly related to the semi-enclosed nature of the basin during glacial times.
PP13A-0582 1340h
Using high-resolution radiocarbon and trace-element variation in speleothems to investigate the climate-system during the last deglaciation
Significant fluctuations in the atmospheric concentration of radiocarbon ($\Delta$$^{14}$C) have been observed at decadal to millennial timescales and attributed to changes in terrestrial or solar magnetic fields, and/or changes in the carbon cycle, particularly ocean circulation. Previously, we presented a continuous record of atmospheric radiocarbon ($^{14}$C) from 45 to 11 ka based on TIMS U, Th and Pa measurements and AMS $^{14}$C ages of a stalagmite (GB-89-24-1) from a cave on Grand Bahama (Beck {\it et al}, 2001). This record revealed elevated $\Delta$$^{14}$C for the duration of growth and a general decline in $\Delta$$^{14}$C between 26 and 11 ka, from $\sim$ 700 to $\sim$ 100 $\permil$, which was considered too large to be solely a result of reduced production via increased shielding by the Earth's magnetic field and was probably related to redistribution of $^{14}$ during a mode of ocean circulation much different to the present day. Here, we focus on efforts to reproduce and explain the millennial and sub-millennial variations that are superimposed on the general decreasing trend from 26 to 11 ka. We present $ > $200 new AMS $^{14}$C ages from additional Bahamas samples that confirm the millennial-scale fluctuations of $\Delta$$^{14}$C $ > $ 100 $\permil$ during the last deglaciation recorded in the stalagmite GB-89-24-1. Robust chronologies for the additional stalagmites have been obtained using MC-ICPMS U and Th isotope measurements with precisions comparable to AMS 14C measurements for similar sample sizes. Comparison of high-resolution laser-ablation trace-element profiles between different samples has significantly improved our ability to constrain age models and, at the same time, provide climate information. The profiles of $\delta$$^{18}$O, $\delta$$^{13}$C, Sr, Mg, Ba and U variations are likely to be indicative of the changing climate and/or recharge. Changes in $^{14}$C coincide with abrupt shifts in climate as recorded in the Greenland ice cores ($\delta$$^{18}$O) for the last glacial period and deglaciation. We explore the implications of the speleothem $^{14}$C record by comparison with records of $^{231}$Pa/$^{230}$Th, Cd/Ca, $\delta$$^{13}$C and SST from various high-resolution cores from the North Atlantic for last deglaciation. During the last deglaciation, rapid reduction in $\Delta$$^{14}$C occurred at times of inferred warming in Greenland, increases in North Atlantic Deep Water (NADW) formation and abrupt shifts in sea surface temperatures in the Atlantic. One of the most dramatic shifts occurs at $\sim$ 14.5 ka and is correlated with the Bolling transition. We also suggest that atmospheric $\Delta$$^{14}$C levels were enhanced during periods of reduced thermohaline circulation related to Heinrich events 1, 2 and the Younger Dryas.
http://www.ggy.bris.ac.uk/research/karst/radiocarbon.htm
PP13A-0583 1340h
Speleothem Records of Precipitation in the West Pacific Warm Pool
The El Nino-Southern Oscillation demonstrates that changes in the strength and location of deep convection in the West Pacific Warm Pool (WPWP) have a large impact on global climate patterns. However, the relationship between WPWP convection and global climate change on lower frequency timescales is poorly constrained by available proxy records. A recent field expedition to Gunung Buda National Park, located in Northern Borneo (4§N, 114§W), yielded dozens of stalagmites from a variety of caves. The stalagmites range in length from 5cm to 2m in length and several thousand years to $ > $700,000 years in age, as determined by multi-collector ICPMS U/Th ages, with many samples capturing Marine Isotope Stage 3, the deglaciation, and the Holocene. Preliminary data from a sample that spans the last 26ky includes d18O and Mg/Ca values that capture the transition from glacial to Holocene conditions, implying drier LGM conditions relative to present. A down-core greyscale profile from the same stalagmite demonstrates that climatic changes may also be recorded in the speleothem's optical properties. High-resolution, paired optical (fluorescence and reflected light) and geochemical (Mg/Ca, Sr/Ca, and d18O) measurements help to build an interpretive framework for the optical variability and demonstrate the potential of using fast, non-destructive optical techniques for climate reconstruction in the Gunung Buda stalagmites. Rainwater and cave dripwater samples collected at Gunung Buda and nearby Mulu National Park are used to constrain spatial and temporal variability in the relationship between climate variability, cave dripwater chemistry, and stalagmite geochemistry. In addition to this rainwater-dripwater-stalagmite calibration effort, we are constructing an ultra-high-resolution geochemical timeseries of the upper-most section of fast-growing stalagmites to calibrate against local and regional-scale instrumental records of climate variability.
PP13A-0584 1340h
Major Hydrologic Shift around 7-8 ka and Cyclic Events during the Holocene in the Northeastern Atlantic (52N, 21W)
The study of a box-core (SU90-I-10) located in the northeastern Atlantic Ocean (52N, 21W) in the North Atlantic Drift pathway (East Thulean seamount), reveals a quite stable Holocene climate, contrasting with the usual cooling observed around 6ka at more northern latitudes. On the contrary, a clear temperature jump (about + 2 degrees) is identified around 6.6-7.8 ka. It could be related to an intensification of the Northward penetration of the surface currents (North Atlantic Drift), which could have influenced the central western Europe climate, where a similar behavior has already been observed at the same time. Seasonnal contrasts were intensified after this main hydrological shift, especially during the summer seasons. The typical 1-2 ky cooling events already observed elsewhere through the Holocene, in the northeastern Atlantic are clearly recorded too. Finally, the tephra abundance increased according to a shorter cyclicity (about 1 ky ): these Icelandic-derived inputs coming from the northern Atlantic regions could reflect cyclic phases of intensified southward sea-ice transport, that could be linked to the solar activity variability.
PP13A-0585 1340h
Documentation of Carbonate Platform Drowning During MIS 4 in the Huon Gulf, Papua New Guinea
In 2001 we used the ROV Jason to collect material from the tops of a series of carbonate platforms in the Huon Gulf, Papua New Guinea. The Huon Gulf represents an actively subsiding foreland basin that is the result of the collision of the South Bismarck plate with the northern Australian continental margin. Galewsky et al. (1996) modeled the coral reef development and suggested that the coral reefs are able to keep up with subsidence at a rate comparable with the subsidence rate, but that they would drown during major sea level rises. Wallace (2002) further constrained the simple model to include the all of the nine platforms we identified. We collected coral samples from the tops of the platforms because the model indicated that these corals should represent reef growth just prior to drowning. We measured the U-Th-(Pa) isotopic composition of eight distinct pieces of coral from the -250 m platform, the shallowest and best-preserved of the nine identified platforms. Corals measured represent four different species/genera: Galaxia astreata, Porites, Favia and Stylophora. Three of these four corals tend to have broad growth ranges, from 0-60 m water depth; Favia is the exception and grows in shallower water (0-20m). Three samples were clearly diagenetically altered showing either anomalously low uranium concentration or high 232Th. The remaining five produced the following ages: 57.7 (+/- 1.5) ka, 60.1 (+/- 0.4) ka (231Pa age of this sample: 59.5 (+/- 1.1) ka), 62.1 (+/- 0.9) ka, 65.9 (+/- 0.87) ka, and 67.4 (+/- 0.8) ka. All of the samples have d234U initial values within error of modern seawater and a check for protactinium concordancy on one sample passed, which suggests these are reliable 230Th ages. Sedimentary analyses of the samples indicate a clear signature of coral drowning, characterized by a vertical transition from corals typical of deep, fore-reef slope settings (30-60 m) to thick crusts of coralline algae indicative of deeper fore-reef slope setting (60-100 m). Uncalibrated C-14 ages for two samples of the algal crusts are 30.5 (+/- 0.4) KyrBP and 39.6 (+/-1.1) KyrBP. During this period of coral and algal growth, Greenland ice core data indicate millennial-scale climate change events, known as Dansgaard-Oeschger cycles, in the North Atlantic (Stuvier and Grootes, 2000). Coral data from Papua New Guinea link sea level rises of 10-15 m and 1000-2000 years duration to those events (Chappell, 2002). Our data are consistent with the coral drowning due to these millennial scale sea-level changes and/or to long-term subsidence. Galewsky et al., (1996) Geology v. 24, 819-822; L. Wallace (2002) PhD Thesis University of California; Stuvier and Grootes (2000) Quaternary Research v.3, 39-55; Chappell (2002) Quaternary Science Reviews, v.21, 1229-1240.
PP13A-0586 1340h
Caribbean Climate Reconstructions Using Coral Skeletal Geochemistry: Initial Results From Puerto Rico
The Northern Caribbean Sea influences many Atlantic climate processes, including: the North Atlantic Oscillation, Tropical Atlantic Variability, Meridional Overturning Circulation, the varying influence of the Pacific El Nino-Southern Oscillation, and air-sea interactions in the Western Hemisphere Warm Pool. Understanding of decadal- to multidecadal-scale Atlantic climate variability has been inhibited by the temporal limits of the instrumental record. Climate-sensitive geochemical variations in corals have the potential to extend our knowledge of climate variability back in time, although currently very few continuous records of Atlantic climate variability from corals have been published. Coral cores from La Parguera, Puerto Rico were collected during August 2004 to reconstruct ocean conditions in the northern Caribbean over the past 200-300 years. The goals of this project are three-fold: 1) describe the thermal and hydrologic variations in the surface waters of the northern Caribbean, 2) investigate the nature of the relationships between climatic conditions in the Caribbean and other regions including the tropical Pacific and North America, 3) explore the possible changes in the proportion of North Atlantic versus South Atlantic waters entering the Caribbean and determine the effects (if any) on the density characteristics of the waters leaving the Caribbean, which contribute a substantial proportion of the water in the Gulf Stream. Acquisition of geochemical data representing surface temperature (Sr/Ca, ($\delta^{18}$O), hydrologic variations ($\delta^{18}$O), and ocean mixing ($^{13}$C) is in progress. Newly collected elemental ratio data are compared with instrumental records of local to regional sea surface conditions and are used to reconstruct sea surface temperature.
PP13A-0587 1340h
Last Interglacial sea-surface temperature recorded in Porites corals obtained from Hateruma, Japan.
The Last Interglacial fossil Porites corals were obtained from uplifted reef complex at the Hateruma island, Japan. The preservation condition was excellent and the samples were used to investigate paleoceanographic environments in the Western Pacific region. We present the analytical results of d18O and d13C to reconstruct the past hydrological settings in this region. The island is located in the Kuroshio pass and hence d18O could tells us the changes in the ocean circulation pattern and/or precipitation changes in the Western Pacific. More than 4 large Porites coral heads of which growth rates ranged from 8mm/yr to 13mm/yr were analyzed for stable isotopes. Longer than 10 years records were recovered from each corals and the results were compared to the previously reported the present coral samples from the same reef setting in the Ishigaki Island located nearby. Seasonal variations in the d18O for the fossil corals are greater than those from the Ishigaki corals suggested that the insolation seasonality enhancements in the northern hemisphere during the Last Interglacial were recorded in the coral stable isotope data. This is consistent with the result reported previously from the fossil corals in the Yonaguni island (Suzuki et al., 2001). The record from Hateruma corals suggested possible variations in the sea water d18O due mainly to the fluctuations in the flux of the seawater in this region by the Kuroshio current.
PP13A-0588 1340h
High Resolution Paleoclimate Records From Fossil Corals Recovered From Drowned Reefs Around Hawaii
Marine Isotope Stage (MIS) 11 (423-362 ka) was the longest sustained warm interval during the past 500 ky and has been implicated in the "turn on" of major reef provinces around the world (ie. Great Barrier Reef). Reconstructions of the oxygen isotopic composition of seawater (O18Osw) and apparent ice volume indicate that peak sea-level conditions may have lasted until as late as 370 ka (Shackleton, 2000, Lea et al., 2000). Despite these advances little is known about short term climate variability during this unique interglacial episode. The submerged fossil coral reef terraces around Hawaii represent a unique and untapped archive of past mean background climate, in addition to seasonal and interannual climate variability in the North Pacific Subtropical Gyre (NPG) over the past 500 ky. These terraces initiated during the highstands and continued growing through periods of eustatic ice sheet growth, as island subsidence (2-3 m/ky) and falling sea levels kept similar pace, and stable shoreline conditions prevailed. Coral reef growth terminated during the major deglaciations as rapid sea-level rise and subsidence combined to submerge the reefs below the photic zone. In 2001, several massive fossil Porites corals were collected using the ROV Tiburon during the Monterey Bay Aquarium Research Institute's (MBARI) expedition to Hawaii. Sampling for the current project focused on two deep marine plunge pools on the East side of Kohala Volcano, Hawaii. Fossil samples were selected for isotopic analysis based on general appearance and the presence of annual growth bands in x-ray photographs. Each sample passed preliminary x-ray diffraction scans, showing that diagenetic alteration to calcite in the skeleton is $ < $2%. Corals were micro-sampled along major growth axes, and analyzed to quantify their oxygen and carbon isotopic composition. One set of samples, from Plunge Pool 1,were dated at 377 ka using U/Th ratios, and another set from nearby Pool 2 is of unknown age, but likely also grew during MIS 11. Though O18O in Porites corals is affected by sea surface temperature (SST) and O18Osw, O18O of precipitation in Hawaii is relatively high, and seasonal rainfall should not affect O18Osw greatly. Modern samples (P. evermanni and P. lobata) recorded seasonal SST cycles of 2.45oC and 2.03oC, 96% and 80% as large as that reported for a 1o x 1o grid by Levitus (2.54oC). Fossil samples from Plunge Pool 1 recorded a similar seasonal SST range, while those of Pool 2 suggest reduced seasonality (1.3oC) in MIS 11 compared to today. Phasing of the O18O and O13C cycles in the fossil samples is similar to that of the modern samples, indicating similar environmental and biological factors during the two periods. To estimate the average SST during the time the fossil corals grew, residual O18O for each specimen was calculated from the average O18O values by 1) correcting for extension rate effects, 2) subtracting the 'O18Osw between 377 ka and today, and 3) subtracting the average O18O of the modern Porites lobata sample. Pool 1 sample O18O residuals indicate that SST was 3oC cooler, while Pool 2 samples indicate 5oC cooler during MIS 11 compared to today. Further study will include use of Sr/Ca ratios as another SST proxy, and time series analyses of interannual variability in the records.
PP13A-0589 1340h
PAST RADIOCARBON PROFILES FROM DEEP-SEA CORALS IN THE NORTH ATLANTIC
Deep-sea corals are an excellent archive of ocean history since their aragonitic, uranium-rich skeletons are well suited to U-Th dating. This independent dating technique means that 14C is no longer needed for chronometry and can be used to reconstruct radiocarbon profiles of the water column. We have many thousands of coral individuals ranging in depth from 1000 - 2500 m and the first 100 U-Th dates show a bias towards ages of the last glacial and deglaciation. These samples are ideally suited to monitoring the variable depth of the contact between Northern and Southern sourced waters. Initial radiocarbon data exhibit D14C gradients with depth that are large compared to the smooth profile observed in the modern ocean. Samples from one depth (~1750m) but with ages spanning Heinrich 1 through to the Younger Dryas not only reflect the events seen in global records, but also demonstrate transient deep-sea circulation changes. These transient D14C excursions are observed to occur abruptly, even within the lifetime of one coral (~100 years). In addition, these samples allow us to investigate the controls on the atmospheric 14C/12C record, namely the interplay between the production rate of 14C and its removal by ocean circulation. Combining this radiocarbon data with passive tracers of the mixing ratio of Northern to Southern sourced water would allow us to calculate ventilation rates for the deep ocean. Ultimately, we aim to reconstruct ventilation rates for the NW Atlantic through the last glacial and deglaciation.
PP13A-0590 1340h
Radiocarbon and Cd/Ca in Deep-sea Coral Desmophyllum cristagalli: A Modern Calibration of Cd/Ca and a Record From the Younger Dryas
Here we report our latest radiocarbon and Cd/Ca results from a deep-sea coral that captures a very short event in the deep ocean during the Younger Dryas. Our Younger Dryas D. cristagalli sample was dredged from 1069-1235m near the Azores and previously U/Th dated using the method of Cheng et al. (2000) to 11,980+/-120 yr BP. Adkins et al. (2000) demonstrated that deep-sea coral radiocarbon reflects the radiocarbon of the seawater in which they grow. AMS radiocarbon ages in the Younger Dryas coral range from 10,900 to 10,400 14C yr. With a total span of 5cm and assuming an aragonite accumulation rate of 1mm/yr, this coral individual lived approximately 50yr. Thus, the range in 14C age must result from conditions other than coral growth. Along the direction of coral growth the radiocarbon age is oldest at the base, reaches its youngest age in the middle, and returns to an older age at the top. This age reversal reveals the competing influence of radiocarbon enriched and depleted water. Radiocarbon depleted water could be produced by slowing the rate of deep-water formation and/or by increasing the relative proportion of southern source water at the site. In order to resolve the deep-water formation rate from mixing, we measure Cd/Ca as a nutrient proxy by isotope dilution ICP-MS. Previous studies have shown that Cd/Ca in foraminifera and surface corals reflects the Cd/Ca of the water in which the organism grew. A straightforward Cd/Ca calibration has proven elusive in the case of D. cristagalli. Modern D. cristagalli Cd/Ca ratios may yet trend with water Cd/Ca, but several of our modern corals have unexplained high Cd/Ca and high variability. Our results show that Cd/Ca ratios do not vary with the coral banding structure but do vary systematically with coral growth, reaching a maximum value at or near the top of the coral. Cd/Ca in the Younger Dryas sample increases from about 0.25 to 0.65micromol/mol, significantly larger than the range of the modern samples measured to date. If this is indicative of the water in which it grew, it reflects the increasing influence of high Cd southern source water toward over the lifetime of this coral and is qualitatively consistent with the radiocarbon record. The changing signal could be caused by a either moving a front of 14C depleted water a short distance, implying that there were 2 water masses with vastly different radiocarbon signature coexisting in close proximity to each other, or by moving a front of 14C depleted water a significant distance, implying that there was a large shift in the relative proportions of NADW and AAIW bathing this site during the Younger Dryas.
PP13A-0591 1340h
Extreme Cooling of Slopewaters East of the USA and Canada During the Holocene
Detailed sea surface temperature records from the slopewaters east of the USA and Canada indicate that substantial, near-monotonic cooling of 4-10 degC began ~10,000 years ago and continues unabated to the present. That SST records from the Northeast Atlantic and air temperature records from Central Greenland indicate only moderate (~1-3 degC) cooling during the Holocene suggests that ocean-atmosphere dynamics acted to magnify the cooling we observe on the western side of the Atlantic, where the slopewaters are characterized by the interaction between cold, fresh Labrador Current waters and warm, salty Gulf Stream waters. Several hypotheses are advanced to explain these observations. (i) Holocene cooling of the slopewater system was forced by decreasing summer and mean annual insolation at high northern latitudes, and increasing mean annual and winter meridional insolation gradients between 20-65 N. (ii) An equatorward shift occurred in the mean position of the Gulf Stream from 45-50 N (west of 45 W) 11 kyr ago to its present position at 40 N. (iii) The subpolar gyre strengthened in response to stronger westerlies forced by a larger meridional temperatue gradient. An invigorated subpolar gyre transported more cold, fresh arctic water southward in the Labrador Current, cooling the Mid-Atlantic region at least as far south as Cape Hatteras. (iv) Colder SSTs and stronger westerlies over the Labrador Sea increased convection and the production of LSW, amplifying cooling of NW Atlantic slopewaters and acting as a positive feedback (on additional cooling). (v) Positive sea ice anomalies in the Labrador Sea and negative sea ice anomalies in the Greenland Sea resulted from the invigorated subpolar gyre circulation (as observed during the positive phase of the NAO) and amplified cooling of NW Atlantic slopewaters relative to the NE Atlantic. Lastly, we speculate that North Atlantic climate evolution during the Holocene was analogous to an extended positive phase of the NAO and that cooling of the NW Atlantic slopewaters is an important prelude to the expansion of perennial ice in Northeastern Canada at the start of the next glacial period.
PP13A-0592 1340h
High-Resolution Holocene SST Changes in the Northeastern Arabian Sea Reveal a Complex Monsoon History
Sediments off Pakistan provide biological and sedimentological evidence of past changes in the Indian monsoon system. We measured planktonic foraminiferal oxygen isotopes and alkenones in a complete laminated Holocene sequence from the Arabian Sea oxygen minimum zone. Our age model is based on varve stratigraphy and 44 AMS-$^{14}$C ages. Significant SST changes of up to $\sim$ $3\deg$C suggest a more complex monsoon history during the Holocene than previously thought. A gradual, long-term warming trend occurs between 9 and 6 ka BP reaching a thermal maximum of about $27\deg$C at $\sim$ 6 ka BP. After 6 ka BP temperatures decrease to $25.5\deg$C with superimposed centennial variations. The unusual SST trend is difficult to explain with the classical model of a mid-Holocene summer monsoon wind maximum as reported in the western Arabian Sea, which would cool the surface ocean. A warmer and more humid winter monsoon possibly caused by mid-Holocene Himalayan glaciation may have contributed to the warming in the Arabian Sea. A prominent $\delta$$^{18}$O change at 4.2 ka BP further amplified by the SST record is coherent with the greatest historically recorded drought in western Asia and tropical Africa.
PP13A-0593 1340h
A New Climato-Stratigraphic Scheme of MIS5e for the Northern High-Latitude
Multiproxy analyses of sediment cores from the Nordic seas allow to define last interglacial climate intervals into: (1) the deglaciation of MIS6 (T2); (2) the ensuing warm peak interglacial (PI) period with a water mass configuration similar to MIS1; (3) the time of climate deterioration with increasing ice volume and surface water cooling. T2 is characterized by a recurring appearance of the low-latitude planktic foraminifera Beella megastoma which was associated with cold surface waters, meltwater input and reduced deep-going vertical convection. Across the Nordic seas, up to three such events are identified between 129 and 124 ka. At the end of T2 B. megastoma vanished from the Nordic seas together with icebergs while increased subpolar foraminiferal abundance verify the existence of modern-like thermohaline circulation (THC) between 124 and 118 ka. However, surface water temperatures began already to decline notably before iceberg activity recurred (2-3 kyrs earlier), indicating unstable climate conditions during the interglacial-glacial transition. Despite climate boundary conditions were similar in MIS1 and MIS5e, major discrepancies remain. These are found for the terminations as well as for the PIs. Although O-isotopes in planktic foraminifers and Greenland ice infer warmer conditions in MIS5e, other ocean proxies from the Nordic seas support a much more vigorous THC for MIS1, altogether emphasizing the variable modes of an interglacial ocean-atmosphere circulation regime at high latitudes.
PP13A-0594 1340h
Multiproxy deglacial record of climate change in central Florida from fresh water ostracodes using paired Mg/Ca, Sr/Ca, and O-18.
An 11.28 m core collected in Tampa Bay, FL reveals lacustrine sediments during the deglacial warming. Mg/Ca, Sr/Ca and O-18 were measured on two species of brackish water ostracodes. Our interpretation is that variations in Sr/Ca reflect changes in water chemistry and Mg/Ca variations reflect changes in both water temperature and chemistry. Applying Sr distribution coefficients results in virtually identical records of (Sr/Ca)$_ {water}$ for both species. (Sr/Ca)$_{water}$ is relatively constant from 20 to 14.1 ka, increases by a factor of two from 14.1 to 12.5 ka. High Sr/Ca values imply increased salinity due to higher evaporation during drier climates and vice-versa. The major trend in Mg/Ca for both species is a doubling of Mg/Ca starting at 13.8 ka with a relative maximum at 12.5 ka. Reliable Mg distribution coefficients as a function of temperature do not exist for these species so we can only infer relative temperature changes. There is a 2.0\permil decrease in O-18 from 13.7 to 11.5 ka. The overall scenario depicted by these three proxies is a relatively cool and wet climate during the Bolling/Allerod from 14.3 to 13.8 ka, changing to a warmer and drier climate during the Younger Dryas, with the driest and warmest period centered at 12.6 ka. These results will be compared with pollen data from the same core. This contrasts with high latitude pollen and ice core data indicating a cold Younger Dryas. These results support the observation that western tropical Atlantic SST was out-of phase with Greenland climate during the deglaciation.
PP13A-0595 1340h
High-Resolution Pollen Record of Deglacial Climate Variability in Central Florida
Pollen evidence from lacustrine sediments in Tampa Bay, Florida document considerable climatic variability superimposed on deglacial warming in the subtropics. Nine radiocarbon dates on well-preserved mollusk shells provide a reliable chronology of continuous sedimentation from 20 ka to 11.5 ka; examination of pollen assemblages from 2 cm increments within the lacustrine unit provide temporal resolution averaging one sample every 45 years. During the glacial maximum, much drier and cooler than modern conditions are indicated by pollen assemblages enriched in Chenopodiaceae, {\it Carya}, Poaceae and {\it Ambrosia}. Increased abundance of {\it Pinus} pollen between 17.4 ka and 15 ka indicates the existence of warmer, wetter conditions in the interval including Heinrich Event 1. After a reversion to drier, cooler conditions at about 15 ka, {\it Pinus} pollen abundance increased again at 14 ka. Combined with the near loss of {\it Carya} pollen, these data suggest attainment of nearly modern climatic conditions during the Bolling-Allerod (14-13 ka). However, variability within the Bolling-Allerod is documented by shifts to deglacial-equivalent vegetation during the Older Dryas (13.4-13.6 ka). The Younger Dryas (12.9-11.6 ka) is characterized by two distinct phases: from 12.9-11.9 ka, the increased abundance of Chenopodiaceae and {\it Quercus} mark drier, possibly cooler conditions comparable to those of the deglacial (17.4 - 14 ka). From 11.9-11.5 ka, strong dominance of herbaceous Chenopodiaceae is similar to full-glacial conditions, indicating much drier, possibly cooler conditions. Comparison of these paleoclimatic patterns with marine records from Orca Basin in the Gulf of Mexico indicate close temporal correspondence in warming of atmospheric and sea-surface temperatures. Pollen evidence also suggests that significant warming began around 17.4 ka, before the onset of Heinrich Event 1, as has been documented at other sites in the North Atlantic Ocean and Europe. This record of deglacial atmospheric temperature and moisture variability provides an opportunity to evaluate the relative influences of meltwater flows, thermohaline circulation, and atmospheric circulation on climate variability in the subtropical Atlantic Ocean.
PP13A-0596 1340h
Millennial-scale paleoclimatic and -oceanographic variability of the western tropical South Atlantic during the last glacial
One focus of recent paleoclimate research is the interaction between high and low latitudes during abrupt climate changes. In particular, there is a lack of understanding of mechanisms originating in the tropics. Here we present results from sediment cores of the northeast Brazilian continental slope, based on foraminiferal stable isotopes and magnesium/calcium ratios, alkenone and X-ray fluorescence analyses, suggesting mechanisms of interhemispheric exchange of climate variations. The North Atlantic Bond Cycles and Dansgaard/Oeschger cycles are closely mirrored in our benthic carbon records, suggesting deep ocean conditions of the western tropical South Atlantic are primarily controlled by NADW production variability. Surface ocean and thermocline oxygen isotopes, however, are related to more complex interactions of regional changes in temperature, salinity and upper ocean stratification. Furthermore, our thermocline oxygen isotopes may represent an imprint of South Atlantic Central water oxygen isotopes. Sea surface temperatures (SST), as indicated by alkenones and magnesium/calcium ratios, show warming during some Heinrich events and Dansgaard/Oeschger cycles, but cooling during others. In context of the "seasaw theory", this suggests the western tropical South Atlantic is part of a transition area between the North and South Atlantic, being influenced by northern hemisphere cooling during some stadials and by southern hemisphere warming during others. Different amplitudes of SST variability in the alkenone and magnesium/calcium records point to different sedimentation or preservation conditions of these proxies. Bulk sediment titanium/calcium (Ti/Ca) ratios point to variations in precipitation on the adjacent South American continent, probably caused by repeated southward displacements of the Intertropical Convergence Zone. Pollen records from the same region and contrasting Ti/Ca records from the Cariaco Basin underline this suggestion. Ti/Ca ratios show a pattern similar to the GISP2 oxygen isotope record, suggesting also a strong coupling of tropical and high northern latitudes via the atmosphere.
PP13A-0597 1340h
Millennial-scale variabilities of subsurface temperature and thermocline depth in the Sea of Okhotsk during the late Quaternary
The Sea of Okhotsk is characterized by an extended seasonal sea-ice cover and is considered as a possible source area of the North Pacific Intermediate Water (NPIW). Therefore, the reconstruction of past sea surface temperature (SST) and subsurface structures in the Sea of Okhotsk is indispensable for the study of the past variations in the NPIW formation and of the detailed climate changes in the Northwest Pacific. We measured the concentration of alkenones in the Sea of Okhotsk surface sediments to understand the distribution of the marine biomarkers. We also produced the detailed oxygen isotopes of planktonic and benthic foraminifers and alkenone SSTs for a core XP98-PC1 (51°00'N, 152°00'E, 1107m water depth) with high sedimentation rate (~10 cm/kyr), which was collected from the slope off Kamchatka Peninsula in the Sea of Okhotsk. Alkenones are detected in the entire Okhotsk Sea including the northwestern continental shelf. The concentrations of alkenones are not shown a systematic distribution pattern in the Sea of Okhotsk. Calculated alkenone SSTs in the Sea of Okhotsk represent summer to autumn SST in the 0-20 m interval, based on the comparison of the modern SST profiles at the each site. The alkenone records indicated that the SSTs were almost constant throughout the Holocene at approximately 8.5°C at the site of core XP98-PC1. Alkenone SSTs are also lowered by 2°C at the early deglaciation and a similar warm SST were detected in the glacial periods in the Okhotsk Sea. Oxygen isotopes of planktonic foraminifera (Grobigerina bulloides and Neogloboquadrina pachyderma), however, showed the short-term fluctuations during the last 70 kyrs. Because the average depth habitat of N. pachyderma was estimated for ~100 m in the southern Okhotsk Sea (Bauch et al., 2002), the planktonic oxygen isotope variabilities were mainly caused by a rapid change in subsurface temperatures due to thermocline depth oscillation. During the Holocene, the subsurface temperature variability may correspond to the Polar Circulation Index (PCI) in the Greenland ice core (GISP2) (Mayewski et al., 1997) and the regional sea level changes (Razjigaeva et al., 2004). Warmer subsurface temperature in the Sea of Okhotsk may correspond to the warmer climate signals of PCI and high sea level stand. Therefore the millennial scale oscillations of subsurface temperature and thermocline depth were periodically occurred in the Sea of Okhotsk.
PP13A-0598 1340h
High-Resolution Records of Deglaciation on the California Margin: Rapid Warming as Recorded in Surface and Intermediate Waters
We present results from cores in Santa Barbara Basin that reside within (MD02-2503; 569 m) and above (MD02-2504; 441 m) the modern oxygen minimum zone (OMZ). These cores provide a high-resolution marine sediment deglacial record of surface and intermediate water processes. Oxygen isotopic values of benthic and planktonic foraminifera indicate a two-step deglaciation (including Terminations IA and B). During the deglacial period, oxygen isotopic values decrease by 3.2 per mil in planktonic species, indicating an 8-$9\deg$C warming assuming a 1.0 per mil ice volume effect. Benthic species record a 1.95 per mil d18O decrease across the deglacial, interpreted as a 3-$4\deg$C warming at intermediate depths. d18O values of both planktonic and benthic species indicate that surface and intermediate waters warmed synchronously, ~2ka prior to Termination IA, following an episode of cooling from 18-17 ka. This record adds to increasing reports of "Pre Bolling warming" around the globe and indicates the influence of Antarctic warming on surface and intermediate waters on the California margin. In addition to recording the timing of deglacial warming at high resolution, comparison of the two intermediate depth cores provides insights into OMZ processes during the glacial termination. Preservation of laminations and dysoxic benthic foraminiferal assemblages indicate that the OMZ extended to above the sill depth during Bolling-Allerod chronozone (B/A). Bolivina tumida, a benthic species associated with anoxia and methane-rich environments, dominates the assemblage at both the shallow and deep sites during the B/A. Planktonic foraminifera record decreased d13C values during the B/A, indicating a perturbation in the surface water DIC reservoir during this time.The B/A exhibited pronounced expansion of the OMZ around the North Pacific, typically attributed to changes in productivity and ventilation. Records from Santa Barbara Basin indicate the combined influence of water column methane oxidation, ventilation and/or productivity in OMZ expansion during the Bolling-Allerod.
PP13A-0599 1340h
Timing of Late Quaternary sea surface temperature change: Evidence from high-resolution {\it Globigerina bulloides} Mg/Ca records from the California Margin
The role of the Pacific Ocean in climate evolution remains a fundamental question in paleoceanography of the late Quaternary. High-resolution sedimentary sections from the California margin provide a valuable opportunity to address the mechanisms of how heat is transmitted through the extra-tropical Pacific by closely examining the phasing of sea surface temperature relative to ice volume changes in a region far removed from the direct effects of continental ice sheets. We present high-resolution {\it Globigerina bulloides} Mg/Ca records from two sites on the central California Margin. ODP Site 1017E (off Point Conception, California; 955 m) provides a millennial-scale sea surface temperature record to 60 kyr; MD2504 (Santa Barbara Basin; 440 m) provides a centennial-scale record through the Last Glacial Maximum. These records, together with oxygen isotopic data, provide a window into the timing of sea surface temperature change on the deglacial as well as during short-term climate events in Marine Isotope Stage 3. At Site 1017E temperature oscillations in MIS3 were synchronous with $\delta^{18}$O and had an amplitude of as much as $6\deg$C, on average $2\deg$C larger than those inferred by $\delta^{18}$O. Comparison between the Mg/Ca records from the two sites indicates that within the resolution of the age models, the amplitude and timing of SST changes were equivalent between Santa Barbara Basin and Point Conception, suggesting that there was not a strong local overprint on temperature change along the California margin. Mg/Ca records indicate that full glacial sea surface temperatures were approximately $8\deg$C. Both sites show a prominent pre-Bolling temperature oscillation of 2-$3\deg$C, followed by an abrupt glacial-interglacial temperature change of 7-$8\deg$C that occurred synchronously with $\delta^{18}$O.
PP13A-0600 1340h
MILLENNIAL-SCALE CLIMATE VARIABILITY IN THE SUBTROPICAL ATLANTIC DURING THE MIDDLE PLEISTOCENE
We are generating Globigerinoides ruber (white, ss) oxygen isotope and Mg/Ca records from ODP Site 1058 to assess relative climate stability in subtropical northwestern Atlantic during the mid Pleistocene, Marine Isotope Stages (MIS) 11-22. Currently, our records span MIS 11 (a portion only) through MIS 15 with a temporal resolution of about 800-1000 years. The paired Mg/Ca and d18O records allow us to reconstruct fluctuations of sea surface temperatures (SST) and the regional oxygen isotopic composition of surface water on millennial time scales during one of the most extreme glacial-interglacial transitions of the Pleistocene. Our ultimate goal is to test the hypothesis that relative climate stability is linked to the extent of continental glaciation (ice volume). The d18O record displays rapid, high amplitude variability during glacial MIS 12 and the MIS 12 to MIS 11 deglaciation. The Mg/Ca results show that the long-term trends in the temperature record follow the general glacial-interglacial pattern implying SST changes concurrent with large-scale climate change. Portions of the Mg/Ca record generated at higher resolution reveal SST variability similar in timing to variability observed in the d18O record, particularly during MIS 13 and the MIS 13/12 transition. The total amplitude of SST changes implied by the Mg/Ca data is ~6°C, with absolute temperatures ranging from about 24 to 30°C. The current records show that this site is sensitive to millennial-scale variability during the extreme glacial MIS 12 and the MIS 12/11 deglaciation, but not in the older portion of the oxygen is record (MIS 14) thus far generated. Ultimately, the entire record will show if other glacial extremes such as MIS 16 contains similarly high variability, which would further support the hypothesis that ice sheet size plays an important role in determining the amplitude of millennial-scale climate change.
PP13A-0601 1340h
Primary Productivity Changes in the subtropical western North Atlantic During Marine Isotope Stages 11-12: Inferences from Benthic Foraminifera
The time interval referred to as Marine Isotope Stage 11 (MIS 11, ~423 to 362 ka) is characterized by a configuration of earth's orbit similar to that of the Holocene, and is therefore a good analog for our current interglacial. MIS 11 was probably the warmest and longest interglacial of the last 500 kyrs, characterized by sea level possibly 20m higher than today and a maximum in NADW production. In contrast, during MIS 12, sea level was about 140m below present, and the production of NADW was severely reduced. We have examined benthic foraminiferal assemblages in sediments from ODP Site 1058 (Blake Outer Ridge, 3000m water depth), and Site 1063 (Bermuda Rise, 4584m water depth) spanning the MIS 11-12 time interval at a time resolution of 500 to 3000 years. At both sites the glacial-interglacial transition is accompanied by changes in faunal composition; however, bottom environmental conditions appear to have undergone the most dramatic change at Site 1058. Here, infaunal taxa indicative of organic carbon-rich sediments dominate during glacial MIS 12, and are replaced during MIS 11 by epifaunal species indicative of oligotrophic environments. The beginning of the MIS 12 and MIS 10 glaciation is characterized by large, rapid increases in the relative and absolute abundances of {\it Epistominella exigua} both at Site 1058 and Site 1063. In the modern ocean, this species inhabits seasonally deposited aggregates of phytodetritus produced during spring plankton blooms, thus suggesting an increase in surface ocean primary productivity at these times.