PP51A-0179
Luminescence From Sediment Within the sea ice of the Arctic Ocean
During the trans-Arctic Ocean HOTRAX'05 expeditions dirty sea ice was collected for luminescence tests at 4 sites from north of Alaska to near the North Pole. Samples were shielded from daylight during collection to permit laboratory analyses of the light-sensitive luminescence from quartz and feldspar grains within these clayey silts and silty clays. Most of the sediment preserved in Arctic Ocean bottom cores is first carried by sea ice. Accurate luminescence dating of bottom cores requires daylight exposure of siliciclastic grains before burial. Therefore, tests for the presence and nature of luminescence within dirty sea ice were carried out. These tests included dual-wavelength TL (thermoluminescence) optical bleaching, multi-aliquot IRSL (infrared-stimulated- luminescence) experiments, and single-aliquot IR (for feldspar response) and post-IR B-PSL (blue-photon- stimulated-luminescence) (for quartz response) experiments. All tests were performed on polymineral 4-11 micron diameter grains. The TL bleaching tests indicate that the TL clock was effectively zeroed for the two samples from the western ocean, but only partly zeroed for the two samples from the central ocean. This variation within TL data is enhanced by use of the more sensitive PSL methods. Apparent ages range among the 4 samples from ca. 400 yr to 1300 yr using a long-bleach IRSL procedure, but are effectively zero using a short-bleach procedure. Age estimates from single-aliquot tests range analogously from ca. 200 yr to 7 kyr using the conventional late- subtraction procedure, but are effectively zero using the early-subtraction method. Therefore relict ages near zero can be measured for sea-ice sediment using appropriate procedures. Thus, the much larger luminescence apparent ages (several kyr) measured (Berger, 2006, Quat. Sci. Rev., v25, p2529) in core tops from across the Arctic Ocean must manifest bottom-current reworking processes (mixing of ‘old' and ‘young' grains in darkness).
PP51A-0180
Radiogenic and U-series isotopes in very low sedimentation rate sediments from Mendeleev Ridge (Arctic Ocean): sources, mineral carriers and stratigraphic implications
Sedimentological and geochemical properties, U-series isotopes, radiogenic isotopes and anthropogenic radionuclides contents were determined on two cores from the Mendeleev Ridge. Excesses in 210Pb over 226Ra activities are observed down to 1.25 cm from core-tops, due to shallow mixing by benthic organisms. Below, 210Pb-activity follows 226Ra-activity in turn controlled by parent 230Th-excess fluctuations in the sediment, except for some 226Ra-diffusion towards the water column from core-top and on both sides of 230Thxs peaks below. Thus, estimating 210Pb-excess requires precise knowledge of 226Ra-supported fraction, i.e., of 230Th- excess and Ra-diffusion. Both cores depict identical grain size, mineralogical, geochemical and isotopic distributions, despite bathymetric difference. This suggests negligible impact of bottom currents, limited scavenging of heavy metals in the lower water column, and a net export of particle reactive U-daughter isotopes (Th, Pa, Pb) produced from the overlying water column. Peaks in 230Thxs and 231Paxs (0-7cm, 17 cm and 30 cm sub-bottom) match high contents in clays and fine carbonates (primarily dolomite), and likely indicate interglacial/interstadial conditions and/or occurrence of turbidity events (e.g., during deglaciations). These peaks correspond to maximum illite supplies, minimum Sr-isotope ratios and epsilon-Nd values in the -10 to -12 range. Interlayered sediments, with high sand but low carbonate contents, minimum clay fluxes (low illite relative contents), minimum 230Th and 231Pa excesses, maximum Sr-isotope ratios, possibly indicate full glacial conditions and significantly reduced sedimentation rates.
PP51A-0181
Beryllium Isotope Dating of Sediment Cores From the Alpha Ridge, Arctic Ocean
Poor preservation of biogenic calcium carbonate and biosilica in Arctic Ocean sediments has led to large problems regarding the establishment of a reliable chronostratigraphy. There are currently two differing sedimentation rate scenarios proposed for the Arctic Ocean. The first suggests sedimentation rates on the order of mm/ka and is based on cores from the Amerasian Basin, whereas the second suggests sedimentation rates on the order of cm/ka mainly derived from Eurasian Basin cores. Here we present dating results from cores HLY0503-09JPC and HLY0503-14JPC retrieved from the Alpha Ridge during the Healy-Oden Trans-Arctic Expedition 2005 (HOTRAX). These cores have been analyzed for seawater-derived beryllium (Be) isotopes in order to establish a chronostratigraphy. The isotopes 10Be and 9Be were extracted simultaneously from sample aliquots by using a leaching procedure. The decrease of 10Be concentration (half-life = 1.51 Million years) with depth in core provides first order sedimentation rates for the sampled cores. To eliminate the dilution effect of beryllium caused by short-term changes in sedimentation rate and grain size variability, the 10Be concentration was normalized to the stable isotope 9Be. The preliminary results show low downcore 10Be concentrations in both cores from the Alpha Ridge. Plotting 10Be against depth suggests an average sedimentation rate of ~2.9 mm/ka for core HLY0503-09JPC and ~2.3 mm/ka for HLY0503- 14JPC. The calculated 10Be/9Be ratios point to even lower average sedimentation rates of ~1.9 mm/ka for core HLY0503-09JPC and ~1.6 mm/ka for HLY0503-14JPC. However, core HLY0503-14JPC shows a pronounced variability of the 10Be concentration as well as for the 10Be/9Be ratio, which results in a large uncertainty of the calculated sedimentation rates. The 10Be concentrations for this core will be compared with the grain size record in order to reduce the scatter of the data. The preliminary beryllium isotope chronostratigraphy supports lower sedimentation rates in the Amerasian Basin compared to the Eurasian Basin. A long-term solid sea ice cover in the Beaufort Gyre may explain the low 10Be concentrations, but does not explain the calculated low sedimentation rates.
PP51A-0182
A High-Resolution Late Pleistocene Sediment Record From the Central Lomonosov Ridge, Arctic Ocean
During the 2005 Healy-Oden Trans-Arctic Expedition (HOTRAX) piston and gravity cores were taken from the central Lomonosov Ridge in a >1000 m deep depression in the ridge morphology forming a local "Intra basin" (Bjork et al., 2007) . Core HLY0503-18TC was retrieved from the deeper parts of this Intra basin at a water depth of 2598 m where sedimentation appears to be focused and accumulation rates, thus, are higher. The core top sediment composition with only some shell material without manganese coating and no gravel clasts suggests a calm depositional environment at this coring site. The uppermost 70 cm of core HLY0503-18TC contains low content of coarse grains (grain size fraction >63 μm) but high abundances of well preserved planktonic and benthic foraminifera and calcareous nannofossils. The planktonic foraminifera assemblage consists of 95- 99% Neogloboquadrina pachyderma (sinistral) in the >150 μm size fraction. Stable isotope measurements performed on N. pachyderma (s) show distinct δ13C minimum values around 40 cm core depths associated in previous studies by e.g. Stein et al. (1994) and Norgaard-Pedersen et al. (1998) with a major meltwater anomaly at the beginning of Termination I. This interval coincides with low number of foraminifera and a reversal in the calcareous nannofossil assemblage from Geophyrocapsa to Emiliana huxleyi (Fornaciari et al., 2006). The total length of this uppermost part of the brown cycle containing abundant foraminifera is more than double compared to what usually is found in the central Arctic Ocean. Nine samples have been submitted for 14C-dating in order to constrain the chronostratigraphy of this, possibly, first high- resolution sediment record from the central Arctic Ocean. References: Bjork, G. et al., 2007, Deep-Sea Research I, 54. Fornaciari, E. etal., 2006, AGU Fall Meet. Suppl., Abstract OS53B-1110. Norgaard-Pedersen, N. et al., 1998, Paleoceanography, 13(2). Stein, R. et al., 1994, Marine Geology, 119.
PP51A-0183
Late Quaternary Paleoceanography of the Mendeleev Ridge, Central Arctic Ocean: Planktonic Foraminiferal Composition and Stable Isotopy
Mendeleev Ridge is located between the two major circulation systems of the Arctic Ocean, the Beaufort Gyre and the Transpolar Drift, thus offering a valuable sedimentary archive for investigating paleoceanographic changes. We perform a detailed investigation of a HOTRAX05 sediment core HLY0503-08JPC (79°35.6'N, 172°30.1'W, 2792 mwd, length 12m) from the Mendeleev Ridge flank that provides millennial to century scale resolution for upper Quaternary sediments. The core has been logged for VIS Diffuse Spectral Reflectance and XRF, u-channeled for paleomagnetic analyses and coninutously sampled at 1cm sample width. The washed >63um sediment fraction is being analyzed for planktonic foraminiferal content and stable isotopic composition. Age constraint for the upper Quaternary record is provided by AMS 14C dates and Amino Acid Racemization measurements from foraminiferal adundance maxima, as well as correlation with established Arctic Ocean stratigraphies. The brown, faunal rich intervals in the upper to middle Quaternary record correspond to interglacials when the influence of circum-arctic ice sheets on processes in the Arctic Ocean was minimal. Grayish, faunal poor intervals reflect glacial/deglacial environments characterized by discharge of icebergs and meltwater. The later part of the LGM contains a pronounced hiatus, possibly related to the ice cover over the basin at that time. We infer that earlier glaciations may also contain hiatuses, which should result in uneven sedimentation rates. Brown intervals are characterized by high biogenic sediment and high stable isotope values in planktonic foraminiferal tests, especially d13C. We presume that these features are related to better ventilation of the halocline from the continental margins at higher sea levels and less ice cover. d18O record displays prominent minima within glacial intervals, which, together with IRD spikes, indicate discharges of icebergs and meltwater from ice sheets at the Arctic periphery. In particular, sharp d18O minima in the penultimate glacial unit probably represent pulsed drainage of proglacial lakes in Eurasia.
PP51A-0184
Late Pleistocene sediment provenance on the Mendeleev Ridge, Arctic Ocean, from XRF Elemental Analysis and Diffuse Spectral Reflectance measurements
During the 2005 Healy-Oden Trans-Arctic Expedition (HOTRAX), core HLY0503-JPC08 was raised from the Mendeleev Ridge at the modern junction of the Beaufort Gyre and the Transpolar Drift. This core with sedimentation rates estimated on the order of 2 cm/ka is well situated to sample variations in sedimentation, and thus circulation patterns during the Quaternary. Some characteristic features such as a distinctive change in lithology and prominent IRD layers provide the basis for correlation with previously developed stratigraphies. This overall correlation is confirmed by 1 cm post-cruise diffuse spectral reflectance measurements generated using a Minolta CM-2600d spectrophotometer. Downcore analysis of principle components extracted from the DSR data indicate an inverse correlation between smectite-chlorite which reaches maxima during interglacial/interstadial intervals when sediment Mn is also high, and illite and goethite which reach maxima during glacial intervals when sediment Mn is low. These glacial-interglacial cycles are also evident in elemental composition measured using a handheld, Innov-X Alpha series XRF analyzer which we employ on Arctic sediment for the first time. Estimates of sediment Mn content inferred by diffuse spectral reflectance agree well with XRF based measurements. We observe three distinct end-members based on physical properties and elemental composition. Low density, fine- grained, glacial sediment exhibit low Mn, low Sr, and high Rb values, and thus a high Rb/Sr ratio. Moderately sandy interglacial sediment exhibits high Mn, high Sr, and low Rb values, while sediment from the transitions in to and out of glacial periods are marked by prominent spikes in density, coarse grains, and Zr concentration. Elevated Rb/Sr ratios during glacial periods may result from the re-suspension of fine-grained sediment previously deposited on the outer shelf during higher sea level, and/or by discharge from proglacial lakes. The increase in grain-size accompanied by lows in the Rb/Sr ratio during interglacial/interstadial conditions provides a proxy for fluvial sediment transport and sea-ice rafting from inner shelf environments. Zr spikes mark IRD events corresponding to ice-sheet instabilities. Because the Zr spikes are generally not associated with elevated Ca, a proxy for detrital carbonate, we infer that these spikes represent predominantly iceberg-rafted sediment of Eurasian origin, whereas three distinct Ca maxima indicate prominent iceberg events originating from the Laurentide ice sheet.
PP51A-0185
Late Pleistocene biomarker records from the central Arctic Ocean (ACEX Hole M0004C and HOTRAX HLY0503-08JPC)
Biomarkers were investigated in late Pleistocene sediments collected from the Integrated Ocean Drilling Program (IODP)-Arctic Coring Expedition (ACEX) Hole M0004C (87°52.1'N, 136°11.3'E) from the Lomonosov Ridge and the 2005 Healy-Oden Trans Arctic Expedition (HOTRAX) HLY0503-08JPC (79°35.6'N, 172°30.1'W) from the Mendeleev Ridge in the central Arctic Ocean. In Hole M0004C, the major biomarkers were long-chain n-alkanes, n-fatty acids, and n-alkan-1-ols, indicating fresh organic matter derived predominantly from higher plants. No concrete evidence for phytoplankton biomarkers was found at the study site. The dominance of terrestrial biomarkers is attributed to the severe degradation of organic matter caused by slow sedimentation in oxygen-rich benthic water and/or low primary production due to permanent sea-ice coverage. Hopane concentrations correlated well with ice-rafted debris (IRD) data, suggesting that they are a tracer of mature sedimentary organic matter and may encode the same information as IRD. High organic carbon content was present in the IRD-rich dark gray layer deposited during MIS-6. The layer contained a significant amount of branched GDGTs, suggesting ice erosion of organic-rich continental soils followed by transportation to the central Arctic by drifting ice. We also present the results from Core HLY0503-08JPC and discuss the correlation with ACEX M0004.
PP51A-0186
Variability in Sediment Supply to the Pleistocene Eastern Arctic Ocean: A Mineralogical Perspective
ODP Leg 151 Hole 910A is located on the Yermak Plateau which is a crucial area for monitoring the Pleistocene variability of Atlantic Water inflow to the Arctic Ocean and the history of glaciations at the Eurasian continental margin. In contrast to other Arctic Ocean records, a well-constrained chronostratigraphy based on stable isotopes, biostratigraphy and magnetostratigraphy allows the identification of glacial-interglacial cycles and a detailed reconstruction of paleoenvironmental conditions in the past 800,000 years. Thus, stable isotope studies revealed that the glacial-interglacial cycles are superimposed by short-term freshwater supply to the Eastern Arctic Ocean on sub-Milankovitch time-scales (Knies et al. in press, Effects of Arctic freshwater forcing on thermohaline circulation during the Pleistocene, Geology). The sources of freshwater and the history of glaciations in the Brunhes Chron prior to the late Pleistocene are virtually unknown. Previous studies on clay mineral assemblages revealed a pronounced variability on various time-scales in the past 150,000 years, reflecting shifts in sediment input between different source areas in response to freshwater input and waxing and waning of ice sheets. Based on these results, the middle to late Pleistocene of Hole 910A has been studied at sub-Milankovitch time-scales to decipher a possible relationship between climate cycles and input of fine sediments from various source areas during the Brunhes Chron. Despite of a strong imprint of local sources on clay mineral sedimentation on the southern Yermak Plateau, a distinct variability has been recognized in the past 800,000 years. The strongest supply from northern Spitsbergen occurred only during the LGM associated with a maximum input of coarse sediments. Previous reconstructions that suggest a pronounced advance of the northern Barents Sea Ice Sheet across the southern Yermak Plateau are refuted since sediments of Hole 910A are normally consolidated in the Middle and Late Pleistocene. The supply of coarse sediments prior to the LGM is moderate indicating that the location was somewhat protected from massive deposition of ice-rafted debris from melting icebergs. Therefore, the clay mineral record of Hole 910A reflects not only supply from local sources but also long-distance transport of fine sediments from source regions located at the Eurasian continental margin. There is apparently a distinct link between climate cycles and the supply from specific source areas. Sequences of sedimentological and clay mineral events are recurrently recorded in Hole 910A indicating that cryosphere variability followed a characteristic pattern at the Northern Barents Sea margin, in particular during deglaciations. Pleistocene clay mineral records are compared along a transect from Yermak Plateau to Lomonosov Ridge to identify events that were of basinwide significance in the Eurasian Arctic.
PP51A-0187
The Holocene Record of the Arctic Oscillation and a Possible Link to Solar Variability
Detailed Fe grain provenance for a 19.9 meter long piston core (HLY02-JPC16) with about 17.5 m of Holocene sediment provides a sub-century scale resolution of the Arctic Oscillation (AO). The presence of Fe grains matched to Russian shelves fluctuates throughout this core, located 125 km north of Alaska in 1300 m water depth. High amounts of these Fe grains indicate a strong positive AO. While century scale fluctuations occur in the influx of Russian ice-rafted grains at this core site, a significant periodicity of about 1500 years exists that is similar to that of Be-10 in the Greenland ice cores. This begs the question as to how the AO might be linked to solar variations, especially such weak ones. The sources of sea ice rafting throughout the Holocene are compared to Modern sea ice samples and there is generally a good match. There is much greater heterogeneity in sources based on Fe grain provenance than other techniques for sourcing sea ice today. While the Laptev Sea is certainly an important sea ice entrainment area, it is by no means the only one and not even the most important over the long term. This distinction lies with northern Canadian sources, especially the Queen Elizabeth Islands facing the Arctic Ocean. The AO plays a major role in mixing sea ice from Russian and North American sources, especially during ++AO events. At these times, not only does the Trans Polar Drift swing closer to North America introducing sea ice from the Russian shelves such as the Laptev Sea to the Beaufort Gyre (BG), but it also aids in dragging some of the BG ice toward Fram Strait. This BG ice is a mix of North American and Russian ice and thus it is not surprising to find sediment from both sources in ice along the drift path of this ice moving toward Fram Strait.
PP51A-0188
Distribution of clay minerals on the Alaskan margin near Barrow Canyon revealed by Diffuse Spectral Reflectance measurements
Sediment clay mineral assemblages provide an excellent means of assessing the provenance of Arctic sediment due to the variety of sediment transport mechanisms at work and the existence of distinct weathering sources from differing bedrock geology. During HOTRAX Leg 1 aboard the USCG Ice breaker Healy (cruise HLY0501), we collected jumbo piston cores on the Alaskan margin near Barrow Canyon which provide detailed Holocene sedimentary records. Measurements of Diffuse Spectral Reflectance (DSR) were collected at 1cm resolution from the split surface of the cores using a Minolta CM-2600d UV/VIS spectrophotometer (400-700nm wavelength range; 10nm resolution; 3mm spot size). To interpret the resulting downcore records, we present a preliminary study using 28 coretop sediment samples collected by the Shelf-Basin Interaction program in 2004 arrayed in four transects across the shelf near Barrow Canyon. The samples were analyzed using an ASD Labspec Pro FR UV/VIS/NIR spectrometer (250-2500nm wavelength range, 2-10nm resolution; 20mm spot size). Our results indicate that the measurements from the two instruments are offset by constant factors, but can be easily compared. To estimate the clay mineralogy of the cores, we decomposed the matrix of DSR measurements from the coretop and downcore samples using principle component analysis and compared the resulting factor score patterns with mineral diffuse spectral reflectance signatures from known samples measured in our lab or available from version 5 of the USGS Digital Spectral Library. The three leading modes extracted by principle component analysis of the downcore samples are applicable to the coretops. We infer that the first principle component mode relates to smectite, the second to chlorite, and the third to a mixture of illite and goethite (herein referred to as illite - goethite). The geographic and bathymetric trends in the coretop data indicate that (1) the smectite and illite - goethite components both increase with depth and reach greater values in the two western transects than in the two eastern transects closest to the coast and Barrow Canyon, (2) the smectite and illite- goethite components are anticorrelated in the two western transects, but not in the two eastern transects, (3) chlorite decreases with depth and is highest in the two transects closest to Barrow Canyon. These results suggest that the chlorite on the Alaskan margin is transported by nearshore currents from the Bering Straight and then by bottom currents flowing through the Barrow Canyon. Accordingly, we interpret downcore chlorite peaks inferred from DSR measurements in our sediment cores as evidence of times of enhanced input of Pacific water to the Alaskan Margin.
PP51A-0189
High Resolution Holocene Paleomagnetic Secular Variation Records From the Alaskan/Chukchi Sea Borderland
Magnetostratigraphy is a powerful dating tool for high latitude paleoceanographic studies. In particular, where datable organic material is scarce and/or reservoir effect is unknown, knowledge of regional paleomagnetic variation (PSV) of the Earth's magnetic field can lead to the setting of a robust chronostratigraphy. Two long piston cores (HLY0501-06JPC and HLY0501-08JPC, hereinafter referred as to cores 8JPC and 6JPC, respectively) from the Alaskan/Chukchi sea borderland were collected on board the USCGC Healy as part of the 2005 Healy- Oden Trans-Arctic Expedition (HOTRAX) in order to establish a pan-Arctic Quaternary stratigraphy. A preliminary age model was derived for core 8JPC with 3 AMS 14C dates performed on pelecypod shells and indicates sedimentation rates greater than 200 cm/ka, whereas CT number, wet bulk density and low-field volumetric magnetic susceptibility allowed the identification of two major sedimentary units within both cores: an upper postglacial unit and a bottom deglacial unit. Here we present new high-resolution paleomagnetic records in order to augment the initial chronology and to correlate the two cores together. The natural remanent magnetization (NRM) was measured on u-channel samples at 1 cm intervals at the new paleomagnetism laboratory of the Institut des sciences de la mer de Rimouski (ISMER). A strong characteristic remanent magnetization has been isolated using progressive alternating field (AF) demagnetization steps between 20 and 70 mT. Component inclinations and declinations were calculated by principal component analysis, revealing that maximum angular deviation values (MAD) are generally lower than 5° and that the inclination of both cores varies around the expected inclination (80.5°) for the latitude of both coring sites based on a geocentric axial dipole (GAD) model. These results suggest that both cores may have preserved coherent PSV. In addition, hysteresis properties measured using a vibrating sample magnetometer (VSM) together with median destructive field values between 10 and 30 mT suggest that low coercivity pseudo single domain (PSD) magnetic grains are the magnetic carriers in the postglacial unit of both cores. The component inclination and declination profiles of both cores will be presented and correlation between them and other emerging paleomagnetic records from the Arctic will be attempted as a first step to construct a regional PSV chronology.
PP51A-0190
Biogenic Tracers Through the Holocene on the Western Arctic Shelf
Present day changes in environmental conditions in the Arctic Ocean are causing substantial alterations in the ecosystem and as a result, fluxes of biogenic matter to the sediments. To place these recent changes in context, high resolution cores (multi- and piston-; up to 17 m in length) covering the Holocene and late Pleistocene were taken as part of the 2005 HOTRAX expedition on the Chukchi shelf north of Barrow, Alaska. These samples were analyzed for Org. C, N, S, biogenic Si, pyrite, mackinawite, and C,N isotopes. At Station JPC-5 (ca. 72.5° N, 157° W; 600 m water depth), highest organic carbon (2%) and nitrogen (0.2%) were found in the upper- most sediment and generally decreased with depth, with the lowest values (ca. 0.8% C and 0.1% N) in the early Holocene. The early Holocene also had very low S concentrations, consistent with low salinity, meltwater conditions. However, there were periods when elevated carbon fluxes occurred in the mid to late Holocene, some of which also had elevated biogenic silica concentrations presumably due to diatom blooms in surface waters. In this respect, atomic C/N ratios ranged from 9-13, consistent with inputs from algal organic matter (as opposed to terrestrial sources that were more prevalent in the early Holocene/late Pleistocene). We are currently making C and N isotope measurements to quantitatively evaluate these sources. These results compare well with cores from the Chukchi shelf taken in 1992 ca. 365 km to the northwest (200 m water depth), and suggest conditions were similar over an area much larger than that covered by just the HOTRAX coring. Processes controlling these biogenic fluxes will be discussed in terms of circulation and source proxies utilized by other HOTRAX participants.
PP51A-0191
Holocene Climate Oscillations in the Eastern Part of the Northwest Passage : A Possible Influence of the Lunar Nodal Cycle
The Arctic climate has undergone dramatic changes over the past four decades. The observations reveal a decrease in sea ice extent and thickness, and a modification of the hydrological cycle. These changes have been attributed mostly to the Northern Hemisphere annular mode (e.g. NAO, AO) coupled with anthropogenic impacts. However, the instrumental climate data for the Arctic only cover the last three decades. In order to improve our understanding of the mechanisms and provide new inputs in the climate simulation experiments, we have collected 4 piston cores (~6 m) for palynological analysis along the main axis of the Northwest Passage, respectively in Lancaster Sound, Barrow, Victoria and Dease straits. Here we present the preliminary results of the 2004-804-009 PC located in Lancaster Sound. This core has been sub-sampled every 10 cm for the analysis of dinoflagellate cysts (dinocyst) assemblages, which allow us to develop transfer functions (best analogue method) in order to reconstruct the sea surface hydrological parameters (sea ice cover, salinity, T °C). Radiocarbon ages indicate that the sequence spans the last 10,323 cal B.P., with a calculated sedimentation rate of 0.57 mm/year. Therefore we can achieve a secular resolution for the reconstruction of climate oscillations. Grain size and geochemical analyses show a prevalence of the fine fraction in the major part of the core, indicating a hemipelagic sedimentation. The base of the core records a higher percentage of sand and CaCO3 and high values of the C/N ratio, which suggest an erosive dynamic with a large inflow of freshwater indicating a terrestrial sedimentation that we associate with the retreat of the Laurentide Ice Sheet in this area. Dinocyst analyses show four different zones. The first zone covers the beginning of the Holocene and shows a maximum abundance of pre-Quaternary palynomorphs with an absence of cysts in the lowermost 40 cm of the core consistent with a glacio-marine environment and high meltwater input. The second zone covers the early to middle Holocene and is dominated by the heterotrophic taxa Brigantedinium sp. and Islandinium minutum. The third zone covers the middle Holocene, where the percentage of autotrophic taxa increases with Spiniferites frigidus/élongatus, Operculodinium centrocarpum, Pentapharsodinium dalei between 4000 and 2000 cal B.P. The fourth zone represents the modern conditions with the dominance of heterotrophic taxa. The increase in the relative abundance of autotrophic taxa between 4000 and 2000 cal B.P. suggests that environmental conditions were more suitable to sustain photosynthetic dinoflagellate populations, probably as a result of an increase of nutrients avaibility, a decrease in the sea ice cover or a combination of both. The G/P (Gonyaulacoid/Peridinioid) ratio records a strong increase of autotrophic taxa between 4500 and 2500 cal B.P. accompanied by an increase of the reconstructed August T °C and a decrease of both the ice cover and summer salinity, suggesting the imprint of the Holocene thermal optimum. Wavelet analysis shows a cyclicity near 1800 year in dinoflagellate percentage as well as in the reconstructed summer salinity and T °C. A similar cycle was recorded in the relative abundance of a brackish palynomorph in sediment core from northern Baffin Bay, near our sampling site. The similarity between both signals could be the result of a sub-harmonic cycle of the 18.6 year nodal, which triggers a strong tidal mixing.
PP51A-0192
Paleoceanographic Variability During the Late Glacial-Early Holocene Transition in the South western Barents Sea.
We have investigated a sediment core from a local depression, Ingoydjupet, at 409 m water depth SW Barents Sea in the northern North Atlantic. This location is at present influenced by Atlantic water masses from the North Cape Current and a fresher water mass from the Norwegian Coastal Current. Both currents are important players in the meridional overturning circulation of the North Atlantic. The radiocarbon chronology of the core yields a centennial scale time resolution enabling a detailed temporal study of the paleoceanographic changes. The core has been analyzed for microfossil distribution of planktonic foraminifera at the > 100 μm fraction, geochemistry and grain size. At ca. 10.700 cal yr BP planktonic foraminifera are introduced. Coarser sedimentary grains including IRD disappear, indicating a marine environment no longer influenced by iceberg rafting. This coincides with the final stages in the deglaciation of the Fennoscandian ice sheet. A continuous planktonic fauna is established at around 10.500 cal yr BP. The fauna has a pronounced dominance of Turborotalita quinqueloba from 10.500 - to 7.000 cal yr BP suggesting a strong continuous influx of Atlantic water into the SW Barents Sea and a close proximity to the Arctic Oceanic Front. A cooling of the surface water is indicated by a strong increase of Neogloboquadrina pachyderma (sin) lasting from 8.700 - 8.400 cal yr BP. Taking the uncertainty in the age model into account, this event relates to the 8.2 ka cold event, which has previously been recognized in the North Atlantic region, including the Barents Sea. The benthic and planktonic δ13C - and δ18O isotope values, measured on Cassidulina neoteretis and T. quinqueloba respectively, show a parallel fluctuation pattern signalling a vertical mixing of the water masses during the late Weichselian – early Holocene transition. The relative differences in both the δ13C and δ18O isotope signal between surface and bottom water masses can be attributed to variations in temperature, salinity and primary production in the photic zone. In addition, analyses of biological silica and CaCO3 show a low production and δ13C measurements indicate a marine origin of the organic matter in the sediment during this time interval.
PP51A-0193
The Holocene in the South-Western Barents Sea: Large Scale Natural Climatic and Oceanographic Variability
Results from a high-resolution multi-proxy study of the Holocene section of the gravity core PSh-5159N from the Ingøydjupet depression in the south-western Barents Sea will be presented. The site is located within the pathway of Atlantic Water that enters the Barents Sea in the North Cape Current. The combined use of planktic and benthic oxygen isotopes, planktic and benthic foraminifer counts, foraminifer SST estimate using the WAPLS method, grain size and XRD data provide an opportunity to detect changes in subsurface and bottom water temperatures, stratification of the water column, and to investigate connections to large-scale movements in the marginal ice zone and front position. Due to a possible hiatus 5-2.5 ka BP, focus will be on the early and the late Holocene. During the earliest phase of the Holocene, 11-9.8 ka BP, the oxygen isotopes reflect low surface salinity. The site was probably covered by sea ice, at least during winter. Summer melting possible introduced a low salinity surface layer, similar to what is seen in the northern Barents Sea today. As the marginal sea ice zone moved further north and eastward, the front followed, and between 9.8-8 ka BP, the front was located close to the site, and along the western Barents Sea margin. Increased advection of Atlantic Water is indicated from 7.7-6.5 ka BP. At this time a clear indication of warmer subsurface water masses are seen, and the signal is seen not only locally at this site, but regionally. The last 2.5 ka BP is characterised by large-scale variability, both in the bottom and subsurface water. Generally warmer bottom water indicates warmer winter conditions than earlier in the Holocene. Somewhat colder conditions are recorded in the subsurface, and at times the front seems to have been located in vicinity of the site. There are also indications of somewhat increased sediment deposition from sea ice, compared to the early Holocene. Trough the Holocene, the gradient between planktic and benthic oxygen isotopes has generally been higher than the present gradient between the subsurface and bottom water, indicating stronger stratification of the water column. Some of the variance of the stratification is probably related to the location of the core of the Atlantic Water in the North Cape Current, and how that would influence the site. The changes in the inflow of Atlantic Water through the Barents Sea Opening are influenced by the regional atmospheric forcing and wind pattern, and the persistence of these over time. Presently, there is also a strong seasonal aspect to the strength of the inflow, and probably this has to be taken into account when making paleoceanographic interpretations from the area.
PP51A-0194
Spatiotemporal environmental changes in the Barents Sea during the Holocene
We analyzed time series of major benthic foraminiferal species, stable isotope and paleotemperature estimates for the reference sediment cores from different oceanographic settings along the SW-NE transect in order to highlight the links of paleoenvironmental changes in the Barents Sea to global variability of climate and meridional overturning circulation. The time resolution based on the oxygen isotope and AMS 14C data is ~100- 400 years. The results are compared with the other time series available in the region. Our foraminiferal records demonstrate a strong dominance of the typical arctic benthic species and subpolar planktic species in the Holocene assemblages, except for the south-western part of the Barents Sea where so-called atlantic benthic species and boreal planktic species are common since ~ 11.2 cal ka. Therefore, foraminiferal assemblages point to a relatively persistant Atlantic water input into the Barents Sea along the Norwegian coast during the last ~ 11.2 ka. However, our faunal mean annual SST estimates for the south-western Barents Sea demonstrate rather pronounced changes from ~ 6° C at the YD/Holocene transition to 13° C in the Early Holocene, i.e. the amplitude of SST changes is much higher than in the northern part of the sea where it did not exceed 2°C. These findings are consistent with spatiotemporal variations of benthic and planktic oxygen isotope ratios, and with an increase in percentage of benthic species indicative to a longer ice free season in the Northern Barents Sea during the strong Atlantic water influx along the continental slope at 7.8 to 6.9 cal ka BP. A pronounced increase in ‘atlantic' and boreal foraminifer abundance in the south-western part of the sea is established at the end of the Early Holocene. Later on, an opportunistic ‘arctic' species dominates the assemblages in several Northern Barents Sea cores thus pointing to a gradual paleoenvironmental deterioration through the Middle to Late Holocene. In total, a set of all available data points to a spatial and temporal heterogeneity of the termal optimum, and Atlantic water input via the southern (surface layer) and northern (subsurface layer) branches into the Barents Sea.
PP51A-0195
The 8200 cal. Year BP Event Reflected in the Arctic Fjord Van Mijenfjorden, Svalbard
Detailed stratigraphic investigations of a high resolution sediment core from the Arctic fjord, Van Mijenfjorden, Svalbard, reveal significant reductions in benthic foraminiferal δ18O of 0.4 ‰ and 0.2-0.3 ‰ dated to respectively ca. 8200 and 8450 cal. yr BP. These reductions, combined with changes in the benthic foraminiferal fauna and IRD, indicate substantial changes in the hydrography of the fjord such as freshening of the bottom water, enhanced sea ice distribution and reduced biogenic production. The age and duration (~100 years) of the youngest event is directly in phase with the 8200 cal. anomaly in the δ18O record GISP2 and NGRIP of the Greenland Ice Sheet. The changes around 8450 cal. yr BP compares well to the timing of the initial freshwater drainage of the proglacial Lake Agassiz. Therefore the proxy record of Van Mijenfjorden lends support to the theory, explaining the 8,200 cal. yr event as a cumulative response to a freshwater forced reduction in the meridional overturning circulation in the North Atlantic. A reduction in the MOC may have changed the oceanic inflow to the fjord towards reduced influence of Atlantic Water and increased dominance of fresher Arctic Water.
PP51A-0196
Water Masses and Brine Formation on the Southwestern Svalbard Margin During the Last 20,000 Years
The western Svalbard shelf and slope area is situated at the northernmost reach of the Atlantic Water before it enters the Arctic Ocean and continues as the Atlantic layer below polar surface waters. On the shelf, the relatively warm water Atlantic water meets with the cold, icy, low saline polar water derived from the polar East Spitsbergen Current, which enters the Barents Sea from the Arctic Ocean. In Storfjorden southwestern Svalbard, wind driven, brine formation takes place during the winter in the innermost, shallow part of the fjord. We have studied two cores from the Storfjorden area on the southwestern shelf taken at 389 m and 1485 m water depth, respectively. The study area is situated close to the boundary between the warm and cold surface water in an area where even small changes in their distributional pattern should be recorded. In addition, the flow of brine exiting the fjord at the bottom of the Storfjorden Trough passes the shelf core site on its way to deeper waters on the slope. In the present study we reconstruct the distribution of the Atlantic Water and polar water and the flow of brine on the southwestern margin of Svalbard during the last ca 20 14C kyr B.P. The purpose of the study is to assess the behavior and interplay of the two water masses under widely different climatic conditions. Furthermore, our purpose is to reconstruct the extent of brine overflow in relation to the shifting surface ocean and climatic conditions. The study period comprises 1) the last glacial maximum (LGM) ca 20-15.5 14C kyr B.P., 2) Heinrich event H1, ca 15.5-13 14C kyr B.P., when numerous icebergs were delivered to the North Atlantic, 3) the warmer Bølling and Allerød Interstades 13-11 14C kyr B.P., 4) the cold Younger Dryas Stade ca 11-10 14C kyr B.P., and 5) the Holocene, including the early Holocene climate optimum, when the climate was warmer than today. The cores were analyzed for benthic and planktic foraminifera, oxygen isotopes, and IRD. The results show that over the last 20 14C kyr B.P., Atlantic Water has been continuously present on the southwestern Svalbard shelf. However, from 15 to 9 14C kyr B.P., comprising Heinrich event H1, the Bølling-Allerød Interstades and the Younger Dryas Stade, it flowed as a subsurface water mass below a layer of polar surface water, which apparently had expanded >1000 km to the south as compared to it present distribution. In the benthic environment, the shift to interglacial conditions occurred at 10 14C kyr B.P. However, due to the continuing presence of a thin upper layer of polar water, surface conditions remained cold until ca 9 14C kyr B.P., when the warm Atlantic Water finally appeared at the surface. A general cooling of the Atlantic surface water took place during the late Holocene from ca 4000 14C years BP. Brine formation and the overflow of brine over the shelf apparently increased during this period.
PP51A-0197
Foraminiferal Record from Firth of Tay, West Antarctica
The Firth of Tay is a small embayment between Joinville and Dundee Islands at the north-east tip of Antarctic Peninsula. This site was sampled during two SHALDRIL operations in 2006 and 2007. A 75 m long, composite, Holocene section was recovered from ~630 m water depth. It has the potential to reveal the best, expanded record of climatic and oceanographic changes on the east side of the Antarctic Peninsula. Foraminiferal investigation of the lower portion of this section (core NBP0602A-8B-KC) is in progress. The first results indicate significant variations in faunal abundances and population structure throughout. They are due to environmental fluctuations affecting the foraminiferal communities and diagenetic processes that took place after deposition. Some diagenetic gypsum was found abundant ~33 mbsf. Between 42 and 54 mbsf some layers rich in organic detritus (plant or shell fragments) were encountered. The calcareous benthic foraminifera are dominated by Globocassidulina biora accompanied by Fursenkoina fusiformis, few Nonionella and Cibicides, while the agglutinated assemblage by Miliammina arenacea, Paratrochammina bartmani, and Portatrochammina. Down to ~33 mbsf, some more fragile Spiroplectammina were also encountered. All these foraminiferal taxa are typical for Recent environments of similar water-depths in the area. The percent of calcareous foraminifera is low (0-20%) and variable between 9 and 42 mbsf, and it is significantly higher (up to ~95%) towards greater core depths. The most diverse, abundant, and best preserved assemblages were encountered near the bottom of the section below 70 mbsf. They are strongly dominated by various calcareous foraminifera typical for open-marine shelf-waters. In the deepest samples, few planktonic Neogloboquadrina pachyderma were also found supporting the most open-water conditions during deposition of the lowest part of the section. Around 54 mbsf, especially abundant benthic foraminiferal assemblages were noted. However, they are suspected to represent mixed populations.
PP51A-0198
Cenozoic oceanic circulation within the South African gateway: indications from seismic stratigraphy
The gateway south of South Africa allows the exchange of water masses between the Indian/Pacific Oceans (warm surface water masses) and the Atlantic (cold deep and bottom water masses). This heat transfers maintains the global conveyor belt. Hence the South African continental margin represents an important gateway, whose detailed evolution is not yet fully understood. The sedimentary structures within this gateway represent an archive of the onset and modifications of paths and intensities of water masses related to the development of both Northern and Southern Hemisphere ice shields. A compilation of the evolution of the oceanic circulation within the South African gateway since the Early Eocene on the basis of seismic reflection data is put forward and discussed. The effect of a proto-AABW can be found in the southern Cape Basin and south of South Africa as early as Early Eocene-Early Oligocene. In the period Early Oligocene-Middle Miocene a current equivalent to AAIW/Agulhas Retroflection leaves its oldest traces identifiable on the eastern Agulhas Plateau. Indications for the Benguela Current can be found in the Cape Basin in Middle Miocene times. With the onset of NADW in the period Middle Miocene-Early Pliocene the branch of AABW flowing through the Agulhas Passage is weakened and finally deflected to the south in Early Pliocene-Holocene times.
PP51A-0199
High-Time Resolution Analysis of Dust in the Dome Fuji Deep Ice Core, Antarctica: Relationship Between Dust and Calcium Ion
Microparticles (dust) in deep ice cores in polar area are well-known as an indicator of terrestrial materials. Dust concentration variations in deep ice cores depend on variations of dust origin areas and atmospheric transport intensity. Iizuka et al. (2004, 2006) reported that the short cycle signals such seasonal to a few years on sodium and calcium ions preserved in Dome Fuji deep ice core. We conducted the high-depth resolution analysis of dust in an deep ice core at Dome Fuji, Antarctica to study for possible paleoclimate indications of seasonal and/or annual climate variations in the Holocene (depth:294.960 m-295.460 m), last glacial maximum (LGM: 540.725 m- 541.250 m) and glacial periods (2203.990 m-2204.500 m: MIS7c-7d). High-resolution analysis of dust was conducted from 2 to 5 mm in thickness in these core samples. Dust concentrations in the ice cores are the lowest in the Holocene samples (mean: 11.9 ppb), secondly in the glacial samples (mean: 41.0 ppb) and the highest in the LGM samples (mean: 387 ppb), respectively. Correlation between dust concentration and non- seasalt (nss)- calcium ion concentration in the cores are the highest in the LGM samples (r=0.91) and secondly in the glacial samples (r=0.82), respectively. But, both @correlation was not unclear (r=0.26) in the Holocene core samples. Nss-calcium ion/dust mass ratios, which were ratios of soluble calcium in terrestrial dust, were 0.133}0.098 (mean}S.D.) in the Holocene samples, 0.067}0.010 in the LGM samples and 0.129}0.032 in the glacial samples, respectively, suggesting that mineral composition of calcium in dust varied in different climate stages. Especially, standard deviation of the ratio was greater in the Holocene samples than other samples, suggesting that mineral composition of calcium in dust changed in seasonal to a few years scale. On the other hand, it is indicated that mineral composition of calcium in dust was relative stabilized in LGM samples, because the fluctuation range of these ratios was smaller in this period than other periods.
PP51A-0200
Evidence for Early Cenozoic glaciation from a record of seawater δ18O at ODP Site 1209: Exploring the paradigm of an ‘ice-free' Middle Eocene
The onset of the Cenozoic ‘greenhouse-icehouse' transition is poorly constrained, with the Middle Eocene often considered the intermediary ‘doubthouse' phase. Most benthic foraminiferal oxygen isotope (δ18O) reconstructions typically assume ‘ice-free' conditions during this period. However, the occurrence of high- frequency sea-level change of tens of meters in the sequence stratigraphic record, is best explained by glacioeustacy [e.g., 1]. To explore the paradigm of an ‘ice-free' Middle Eocene, we discuss a high-resolution record of seawater δ18O from Ocean Drilling Project (ODP) Site 1209 in the northern tropical Pacific Ocean. The new seawater δ18O record for ODP Site 1209 indicates two major glacial episodes occurred at ~44.8 and 42.7 Ma, with excursions of greater than 1‰. The amplitude of these excursions necessitate the presence of ice in the southern and northern polar regions at these times, consistent with other records of seawater δ18O [2] and ice-rafting debris [3,4]). We also evaluate the seawater δ18O-sea-level calibration accounting for potential biases arising from carbonate ion concentration, Cenozoic ice δ18O composition and additional ice storage as a result of glacioeustatic sea level fall. [1] Browning, J., Miller, K., and Pak, D., 1996, Global implications of lower to middle Eocene sequence boundaries on the New Jersey coastal plain: The icehouse cometh, Geology, 24, 639-642. [2] Tripati, A., Backman, J., Elderfield, H. and Ferretti, P., 2005, Eocene bipolar glaciation associated with global carbon cycle changes, Nature 436, 341–346. [3] Moran, K., Backman, J., et al., 2006, The Cenozoic palaeoenvironment of the Arctic Ocean, Nature, 441, 601–605. [4] Shorttle, O., Tripati, A. Eagle, E., Dawber, F., Morton, A., Dowdeswell, J., Atkinson, K., Bahé, Y., Shaw, R., Thanabalasundaram, L., Khadun, E., 2007, Evidence for Northern Hemisphere glaciation back to 44 Ma from ice- rafted debris in the Greenland Sea, Fall AGU Abstract.