PP11B-1375
Stable isotope evidence for multidecadal climate variations in the northeastern United States during the past 250 years
Instrumental data show that sea surface temperatures in the Atlantic and Pacific Oceans have a significant effect on the wet/dry climate over the conterminous United States. However, a few high-resolution paleoclimate records have been recovered to extend this effect to a longer time-frame. In this study, we present a ~2-year resolution stable isotope record for authigenic calcite from a freeze core at White Lake in northern New Jersey. The ~250 year chronology was controlled by 210Pb and 137Cs analyses and one calibrated AMS-14C date on terrestrial plant macrofossils. The δ18OVPDB data show high values fluctuating between -7.5‰ and -5.5‰ with a slight decreasing trend at 1780-1840 AD, a negative shift to low values fluctuating between -8‰ and -6‰ at 1840 AD, and a positive abrupt shift to large amplitude oscillations between -5.5‰ and -8‰ at 1920 AD. Based on the comparison with meteorological data, the δ18O values appear to reflect the climatic effective moisture, with higher values corresponding to drier climate. Over the last ~250 years, the δ18O data show a dry period at 1780-1840 AD, a wet period at 1840-1920 AD, and an unstable climate since 1920 AD. The δ13CVPDB data show a constant value of -2‰ at 1780-1840 AD, a negative shift with fluctuations between -2‰ and -3‰ at 1840-1920 AD, and an abrupt shift to a decreasing trend from -1‰ to -5‰ with large fluctuations after 1920 AD. This abrupt shift is consistent with the lithology change from a marl section to a laminated section at 1920 AD. The δ13C values likely reflect the land-use change (farming-related deforestation and reforestation) since the European settlement. Overall, the corresponding changes in our δ18O dataset and in the salinity record from Chesapeake Bay delineate a regional moisture history in the northeastern USA for the last 250 years. The climate transition from dry to wet intervals at the end of the Little Ice Age (around 1840 AD) reflects the atmosphere circulation change from more zonal flow to meridional flow in the northeastern USA. The climate transition around 1840 AD was also documented in the North Pacific region reflecting the intensification of Aleutian Low, and in the western Pacific Ocean reflecting a weakening trade wind. This suggests a possible climate teleconnection between the Atlantic and Pacific basins in the 1840s. The abrupt shift of δ18O values around 1920 AD could imply that the regional climate changed from stable to highly variable climates. The observed moisture pattern from our data could be influenced by the atmosphere circulation changes in the northeastern US, which could be ultimately linked to oceanic factors such as Atlantic Multidecadal Oscillation, and Pacific Decadal Oscillation.
PP11B-1376
North Atlantic Climate Variability During the Late Holocene Recorded in Biochemical Varves in Diss Mere, Norfolk, UK?
Sedimentary records preserving annually resolvable proxy data are a powerful tool for paleoclimate reconstruction. We present the first demonstratively sub-decadal UK record of late Holocene (5200-2500 Calendar yrs BP) environmentally mediated lake primary productivity constructed from thicknesses of biochemical varves deposited in Diss Mere, UK. A SEM based study of the sediment fabric reveals that while Diss Mere's varves visually appear to be a regular alternation of millimeter-scale dark, organic carbon and pale, calcite-rich couplets, they actually contain up to six individual laminae which are primarily the product of in situ lake biological processes during the warm season. Changes in the thickness of the dark and pale "halves" of Diss Mere's varves are controlled by diatom productivity during spring, and calcite precipitation during summer, respectively. Spectral analysis of these seasonal thickness variations reveals coherent variability operating on Atlantic Multidecadal Oscillation (AMO) and North Atlantic Oscillation (NAO) timescales (around 65, 40-30, 20, 8-6.5, 5-2 yrs), indicating that lake productivity in the late Holocene was probably strongly dependent on regional climate conditions.
PP11B-1377
A stable isotopic record of late Holocene climate change in Nicaragua
Radiocarbon dated sediments from a closed-basin lake in the Pacific region of Nicaragua record regional moisture balance changes during the late Holocene, from ~1600 cal yr BP to the present. The oldest date from the sediment core indicates that Lago El Gancho, a shallow depression formed within landslide deposits (i.e., debris flows) flanking the adjacent Volcán Mombacho, began filling by at least ~1700 cal yr BP. Oxygen isotope values of ostracod carbonate within the Lago El Gancho sediment core progressively decreased between ~1500 and 700 cal yr BP, suggesting increasing lake water levels and greater moisture availability. Oxygen isotope values increased abruptly at 700 cal yr BP, indicating reduced lake levels, and increased further after ~425 cal yr BP, coincident with the onset of Little Ice Age cooling. This transition is consistent with other records from Central and northern South America suggesting that conditions throughout the region were drier during that time.
PP11B-1378
East African climate fluctuations over the last 1400 years recorded in southeastern Mediterranean sediments
The southeastern Mediterranean Sea sedimentary history of the late Holocene was influenced by distinctive changes in Nile River sediment discharge and Saharan dust influx. We present high-resolution XRF element data of a marine sediment core of the southeastern Levantine Sea (GeoTü SL112, 32° 44.52´ N, 34° 39.02´ E, water depth: 892 m) spanning the last 1400 years. We suggest a strong relationship between humidity changes in east Africa and the corresponding sedimentological response in the Levantine Sea. The Fe record of our Levantine Sea sediment record shows a remarkable similarity with the lake level record of Lake Naivasha (Kenya) (Verschuren et al., Nature, 2000) and the pre-colonial drought history of Lake Malawi (east Africa). Several intervals of enhanced Saharan dust flux as indicated by high Fe values in the Levantine Sea core coincide with well-known droughts in equatorial east Africa and Lake Naivasha lowstands. Frequency analysis suggests that solar variability has been a major influence in these climate fluctuations. The Fe record of our core, which we interpret as Saharan dust influx to the southeast Levantine Sea, is dominated by cyclicities of approximately 90 and 200 years, known as the Gleissberg and Suess cycles. The most pronounced periods of decreased dust accumulation in the southeast Levantine Sea occurred at about 1.1 kyr BP, 0.7 kyr BP, 0.55 kyr BP, 0.3 kyr BP and 0.1 kyr BP, coincident with the solar minima of Oort, Wolf, Spoerer, Maunder and Dalton.
PP11B-1379
A Sub-annual-resolution record of East African Climate from Lake Malawi for the Past ~1200 Years
There are few high-resolution climate records available for the tropics; this situation is particularly acute in Africa. We present a sub-annual-resolution record of East African climate for the past ~1200 years, based analyses of varved sections of three replicate cores taken as part of the Lake Malawi Scientific Drilling Project. The varves consist of alternating couplets of clastic and diatomaceous material. We have undertaken x-ray fluorescence core scanning at 0.2 mm resolution, which provides six to ten analyses of the sedimentary composition (Fe, Mn, Ti, Si, Ca, K, ...) within each varve couplet. Changes in these elements have been correlated to the seasonal variations that form the light and dark varves. A chronology was developed by comparison of elemental profiles, x-radiographs and optical images from the three cores. Time series analyses provide evidence of the changing influence of sub-decadal climate cycles. Changes in varve thicknesses also show variation in sedimentation rates. In these sediments, the ratio of incoherent to coherent scattering closely follows total organic carbon and Si:Ti variability is dominated by changes in biogenic silica. 'BSi' and 'TOC' strongly co-vary on sub-decadal timescales until 1890. However, after that time TOC variability no longer corresponds to changes in BSi, which itself shows much less variability. This is consistent with a change in algal assemblage, with a switch away from a diatom- dominated system at that time, consistent with recent biomarker studies that suggest a shift in dominant algal groups in the late 19th Century.
PP11B-1380
Lake Challa (Kenya/Tanzania) sediments, a varved climate archive of environmental variability in equatorial East Africa of the last 25.000 years
Recently, an increasing number of climate records from low-latitude regions underscore the importance of tropical atmospheric processes in the global climate system. Nevertheless, the regional synchrony of temperature and humidity variations, as well as teleconnecting mechanisms between high and low latitudes are still poorly understood. The EuroCLIMATE project CHALLACEA aims to provide a continuous high- resolution multi-proxy record of temperature and moisture-balance variability in equatorial East Africa from the Last Glacial Maximum (25 ka BP) to the present. Lake Challa is a crater lake located about 40 km east of Mt. Kilimanjaro at an altitude of 880 m a.s.l. It is a freshwater lake whose water column is stratified during most of the year. It is fed by subsurface inflow which derives mainly from percolation of precipitation falling in the montane forest zone higher up the mountain. Within the lake form lacustrine deposits which predominantly consist of autochthonous components (carbonate, biogenic silica, organic matter). The present study focuses on microfacies analyses and isotope measurements. Fine laminations are preserved over wide parts of a 22 m long sediment profile. Microfacies analyses reveal that the light/dark couplets represent true calcite varves. The darker layers contain organic matter and endogenic calcite. Sediment trap studies show that these layers form during the warm season (Nov to Mar) when water temperatures are high and the lake is biological productive. The light layers consist predominantly of diatom frustules. They accumulate in the sediment trap between June and October. By counting and measuring the thickness of the varves on thin sections, we establish a varve record that currently covers the last 1500 years. Stable isotope analyses on bulk carbonates will complement this record and give further insights into the hydrological variability of the region and enhance our knowledge of climate change in the highly sensitive climate region of the Mt. Kilimanjaro area.
PP11B-1381
The Thermal History of the East African Rift Lakes Region Since the Last Glacial Maximum Using TEX86 Paleothermometry
We present preliminary results from a study using the TEX86 temperature proxy from sediments of East African Rift Lakes (including Lakes Turkana, Albert, and Malawi) to reconstruct the thermal history of tropical Africa for the last ~ 20,000 years at a subcentennial to multicentennial resolution. The TEX86 proxy, based on tetraether membrane lipids produced by lacustrine Crenarchaeota, has been shown to be successful at recording lake surface temperatures of some large lakes, including Lakes Malawi and Tanganyika, while providing unreasonable surface temperatures for lakes that receive a large input of soil material. The East African Rift Lakes are climatically sensitive, with the majority of water loss due to evaporation rather than outflow. Thus, they are useful for paleoclimate studies, being sensitive to even small changes in aridity. Temperature records from the northern and central basins of Lake Malawi agree well and fall within modern surface lake temperatures. A 2.5°C cooling is evident during the Younger Dryas in the northern basin record, with no response seen in the central basin. We are currently investigating mechanisms to explain why both records show a gradual cooling of 3°C during the late Holocene. Lake Albert shows an intriguing two-step cooling during the Younger Dryas, reaching temperatures 2.5°C lower than temperatures preceding or following this interval. The temperature record of Lake Turkana shows an interesting ~ 500 year cyclicity of low temperatures punctuated by abrupt warming events. Lakes Turkana and Albert show TEX86 paleotemperatures considerably lower (8°C cooler in Lake Albert and ~ 4°C cooler in Lake Turkana) than modern surface water temperatures. Although these records appear to fall in the range of temporal variability, these temperature discrepancies may indicate varying Crenarcheotal populations between lakes or other influencing factors.
PP11B-1382
Lake Challa (Mt. Kilimanjaro) sediments as recorder of present and past seasonality in equatorial East Africa
In discussions on the impact of global warming on moisture balance and human water resources, natural archives of past hydrological variability in tropical regions are attracting increasing attention. The EuroCLIMATE project CHALLACEA studies the sediment archive of Lake Challa, a 4.5 km² and ~94 m deep crater lake located on the lower eastern slope of Mt. Kilimanjaro with the aim to produce a continuous, high-resolution and multi-proxy reconstruction of past temperature and moisture-balance variability in equatorial East Africa over the past 25,000 years. Lake Challa is a freshwater lake with a water budget controlled mostly by sub-surface in- and outflow and lake-surface evaporation. Accordingly, microscopic thin-section investigation of sediment composition reveals an overall dominance of autochthonous components (diatom frustules, calcite, and organic matter). First results from an ongoing sediment trap study point to distinct seasonality in sediment input: calcite and organic matter accumulate during the warm southern hemisphere summer months (November - March), whereas the principal diatom blooms occur during the cool and windy period between June and October. Here we present the results of physical and chemical investigations of the lake water column between September 1999 and November 2007, which document the concomitant seasonal changes in lake mixing/stratification and related element cycling. High-resolution μXRF profiles of these elements in the laminated sediments of Lake Challa thus also show marked seasonal cycles, as well as longer-term variability. In particular, variability in the Mn/Fe ratio along the top 15 cm of the sediment record is interpreted to reflect changes in lake stratification during the last ~100 years. This proxy record is evaluated in comparison with records of historical weather variability in East Africa, and of potentially influencing parameters such as the El Niño Southern Oscillation and the Indian Ocean Dipole. Eventually these exercises may contribute to high-resolution reconstruction of tropical East African climate variability over the last 25,000 years.
PP11B-1383
On the Provenance of Freshwater Pulses in the Gulf of Mexico During the Last Deglaciation: the Contribution of Associated Terrigenous Inputs
The clay mineralogy and grain-size of sediments deposited during the deglaciation in the Orca basin (Gulf of Mexico) show that three different sedimentary regimes took place during that period : the early deglaciation (20 to 13 ka) is characterized by (1) a terrigenous-dominated sedimentation, reflecting the high detrital contribution of the illite and chlorite-rich Great lakes area towards the Gulf of Mexico, interrupted by (2) repetitive fine-grained smectite-rich events (SR) originating from the northwestern Mississippi River watershed area, whereas the last part of the record (after 13 ka) shows a reduced detrital vs. carbonated sedimentation and an additional contribution from a kaolinite and illite-rich southern province. The comparison of the respective timing of the SR with the Laurentide ice-sheet meltwater history -recorded in d18O of planctonic foraminifera from the Gulf of Mexico- and with the modelled chronology of deglacial drainage reveals that the SR occur simultaneously with the major meltwater floods. The comparison of potential source areas for the SR detrital supply (based on recently published clay mineral distribution maps on land) and the Laurentide margin evolution (as depicted by continental studies) provides additional constrains on the dominant melting areas. In addition, the mineralogical characteristics of the peculiar meltwater episode associated with the Heinrich-1 cold climatic event help pinpoint its provenance (Great Lakes area vs. northwestern Mississippi province). The decreased contribution of terrigenous supply associated with changing provenance after 13 ka suggest strong modifications of both the continental hydrography in relation with the Lake Agassiz history and of the connection between the Orca basin and the Mississippi delta due to rising sea-level. This study shows that combining clay mineralogy and grain-size characteristics of sediments deposited in the Orca basin offers a unique opportunity to link the reconstructed continental glacial history, the modelled drainage patterns, and the marine record of meltwater flows in the Gulf of Mexico.
PP11B-1384
Comparison of Radiocarbon Ages for Multiproxy Paleoclimate Reconstruction of the Great Salt Lake, Utah
Multiproxy paleoclimate reconstructions from high sedimentation-rate systems offer promising opportunities to deconvolve multiple aspects climate system response to past forcing. However, the time-equivalence of proxies must be established before such reconstructions can be usefully interpreted. Differences in source ages, transport pathways, and surface residence times for substrates may lead to differences in lag times between proxy formation and deposition, compromising comparative analysis of data from multiple proxies. We used multi-substrate radiocarbon dating to investigate the potential for multi-proxy reconstruction of Holocene changes in the volume of the Great Salt Lake (GSL), Utah, based on the stable isotope composition of organic and inorganic substrates in lake sediment cores. Among potential substrates for this work are normal alkanes of vascular higher plant and algal origin, fossil cysts of lake-dwelling brine shrimp (Artemia), and micritic aragonite. Radiocarbon ages for all organic substrates (alkanes, cysts) sampled at any given core depth are concordant within analytical uncertainty and are similar to ages determined on land-plant debris and filamentous algae isolated from the sediment. Inorganic carbonate, in contrast, is depleted in 14C compare to the organic proxies, giving ages that were apparently 2000 to 3000 years older, likely due to winnowing and re-deposition of carbonate at the core site. These results suggest that the maximum temporal resolution achievable through analysis of mineral substrates is on the order of several millennia. Although the limited precision of the radiocarbon analysis precludes precise determination of the maximum potential resolution of organic-proxy based climate reconstructions, the relatively high sedimentation rates (50--150 cm/kyr) and age-equivalence of the substrates analyzed implies that sub- centennial scale resolution should be achievable throughout much of the Holocene portion of the GSL sedimentary record.
PP11B-1385
Change in Mediterranean Hydrologic Cycle at Time of Heinrich Events From a High Resolution Multiproxy Record of the Last 50 kyr
Clay mineralogy, pollen record and pollen-based reconstructions were performed over the last climatic cycle on the Site ODP 976 (Alboran Sea, Western Mediterranean). These proxies show that several droughts occurred during the past 50 kyr. Enhanced contribution of wind-blown palygorskite and development of the semi-arid vegetation (Artemisia rich) occurs during the North Atlantic Cold climatic events (Heinrich events). The peculiar clay mineral association and the presence of Argania pollen grains pinpoint Western Morocco as a major source for wind-blown particles during the Heinrich events. Clay mineral and pollen associations indicate the development of semi-desert environment and the intensification of winds favoring dust erosion and transport from Sahara toward the Alboran Sea during the North Atlantic Heinrich events. Quantitative climate reconstructions performed on the ODP976 pollen record have yielded the reconstruction of ombrothermic diagrams for past key periods. They reveal that annual precipitations regime in the west Mediterranean area were rather different during Heinrich events than today with drastic drought during the whole year. As a comparison, the reconstructed Holocene and stadials annual climatic cycles are very similar to present-day distribution, with dry conditions restricted to summertime. During these cold climatic events, the drastic fall in both precipitations and temperatures suggest cold and arid continental conditions in the West Mediterranean area. These regions were suffering from reduced precipitations not only during winter but also during spring and fall usually experiencing wet conditions. Such a major modification, with repetitive cold and dry-conditions in both winter and spring, should have deeply affected the development of temperate forest -sensitive to precipitation amount- and of the Mediterranean forest which lives under warm-dry summer and mild-humid winter conditions. These clay- and pollen-based reconstructions imply atmospheric conditions close to the present day positive situation of the North Atlantic Oscillation (NAO) during these droughts that resulted in high-pressure stability over the west Mediterranean and favored meridian wind transport from the South.
PP11B-1386
High Resolution ITRAX Analysis of Les Echets (France) Sedimentary Sequence: Linking Geochemical, Biological and Physical Proxies
We present a 30 m long, high-resolution, independently-dated multi-proxy lake sediment record from Les Echets in south-central France which covers the later part of Marine Isotope Stage (MIS) 3 and MIS 2 (40 and 16 ka BP). The sediments in the lower part of the studied sequence are composed of alternating organic rich and minerogenic layers, while the upper part consists predominantly of silt and clay. Organic geochemical, geophysical and biological environmental indicators (grain size, mineral magnetic parameters, TOC, TN, LOI, stable carbon isotopes, rock eval, biogenic silica, and diatom assemblages) show alternating phases of higher and low lake organic productivity which are interpreted as a response to DO climate variability. XRF is a well-established analytical tool that has recently taken a new direction with the introduction of core scanning systems. The ITRAX XRF core scanning system is non-destructive, acquires continuous data for a broad range of elements in situ as well as generates radiographic images. The Les Echets sequence was analysed using the ITRAX at 1 mm resolution. The radiographic images show significant changes that were not revealed by lithostratigraphic descriptions. Distinct, dense layers are associated with changes in elemental intensities which would have been missed using traditional sub-sampling techniques. The high resolution elemental profiles show associations between certain elements (Rb, Si, Ti and K; Sr and Ca) which can be linked to lake productivity and catchment erosion and by extension, paleoclimatic changes.
PP11B-1387
Laminated glacial sediments from the southwestern Black Sea: a preliminary study
Glacial lacustrine Black Sea sediments recovered off northwestern Anatolia are characterized by continuous mm-scale lamination of predominantly detrital origin. We analyzed a sequence of ca. 500 years within the Last Glacial Maximum (LGM) anchored between two calibrated radiocarbon dates in order to investigate the nature of the lamination that potentially reflects seasonal changes in sedimentation. Results of optical and scanning electron microscopy and image-based layer counting combined with the radiocarbon chronology suggest that the light/fine and dark/coarse layer couplets may have been deposited in an annual cycle. We further propose that the light/fine laminae represent the fall and winter season, while dark/coarse laminae form during the spring thawing likely associated with non-calcifying phytoplankton blooms. To understand a potential relationship between the flux of clastic material, the supply of detrital carbonates, and general trends in grain sizes, we compare the varve thickness, μXRF element intensity, and the magnetic susceptibility records. Presenting results of these high-resolution measurements not on a linearly interpolated time scale but on a constructed 'varve year' time axis allows a detail study of inter-annual and decadal scale changes in runoff-related terrigenous supply. On the millennial time-scales, concentration of detrital carbonates at our site can be positively correlated to the relative precipitation changes in NW Anatolia. Outcome of our exercise suggests that this relation is valid also for the short-term variability. As the older part of the glacial Black Sea sequence has satisfactory AMS14C age control, our study will be extended to ~26 cal ka BP. The interannual variability within millennial-scale hemispheric cooling events, particularly the Heinrich Event 2 (centered at ca. 23.5 cal ka BP) may improve our comprehension of short- term climate dynamics.
PP11B-1388
60 ky high resolution record of the environmental change from Sediments of Lake Biwa, Japan
Lake Biwa is the largest freshwater lake in Japan, measuring 22.6 km wide by 68 km long and having a maximum depth of 104 m. In 2007, we carried out seismic survey and piston coring operation in northern part of Lake Biwa. We implemented with 10-KHz acoustic sonar equipment with maximum resolution of 6 cm and maximum acoustic penetration depth of 20 m. We cruised the 18 transverse lines which intervals are about 1.85 km. These reflecting data differed according to location, and showed 10 geologic layers. Most of them will be correlated with tephra layers. We recovered piston cores at six localities having different sedimentation rates. Analyses of the core samples are ongoing in various disciplines. We present initial results from lithological description, measurements of magnetic susceptibility and tephrostratigraphic correlation of the core sediments with the seismic data. After the constructing the age-depth model of core sediments, we discover successive sedimentary change due to the depth, and spatial and temporary distribution of sedimentary supply change related with lake level change and climatic change during about 60ka.
PP11B-1389
Late Quaternary paleoclimate from the sedimentary facies analysis of nine gravity cores at the Lake Hovsgol in northern Mongolia
Twenty gravity cores have been collected from Lake Hovsgol in northern Mongolia. The nine gravity cores were scrutinized to interpret the late Quaternary paleoclimate in terms of sedimentary facies. Sedimentary texture including grain size variation, sedimentary structures, mineral composition, microfossils, bulk color index by spectrophotometer, and age dating by A.M.S radiocarbon are analyzed from the core sediments of the lake bottom. Sedimentary facies of the lake sediments are divided into total 12 facies as 8 Pleistocene facies and 4 Holocene faices. Md Facies was accumulated by high primary productivity at Holocene because of input of much organic nutrient from the surrounding soil. Mld Facies was characterized by black lamination indicating a lake level rise or highstand at early Holocene. Sp Facies was accumulated by plant-rich fine sand and mud at early Holocene, which was accumulated in the coastal swampy environment accompanied with a lake level rise. Sl Facies is alternation of finely laminated fine sand and mud at late Holocene. Mwl Facies is weakly laminated mud at the late deglacial time. Swl Facies was accumulated at the deglacial period. During the period sand was supplied at the early stage and mud was accumulated later reflecting increasing temperature and precipitation. Ml Facies is well laminated sandy mud of the deglacial time. Msl Facies is structureless fine sandy mud at LGM. Sr Facies is also LGM sediment, when the lake level was lower 100 m than that of the present. Sr Facies is sand and mud rhythmite containing lots of sand size particles. Cr Facies is silt and clay rhythmite similar to Sr Facies. Mp Facies is plant-rich fine sand and mud at LGM. Mt Facies is fine sand and mud turbidite accumulated on a steep slope of the lake shore at LGM. The Lake Hovsgol level at LGM was 100m below than the present level and was a small closed lake that stratification was not formed. Coarse sediments were transported with ice sheet, and were accumulated with ostracods which had been dwelled in the lake bottom. Coarser grains were deposited at the northern part of the lake more than at the southern part because ice sheet was located in the northern part. After LGM, the lake environment changed to warmer climate, and inflow by ice melting caused the lake level rise. Following the lake level rise, lake stratification occurred from the coastal environment. Sand contents decreased and carbonate mud began to accumulate at the southern end of the lake while the lake became an open environment. At Holocene, the environment around Lake Hovsgol changed into the present one, and the diatom and clastic mud were mainly deposited in the lake bottom. But during Holocene the shallow coastal area has been transgressed into a coastal swampy environment due to lake level rise. As the lake level continually rose, clastic sand grains, diatom and ostracods kept accumulating. The black lamination structures were formed, indicating an anoxic environment in the lake bottom by the lake level rise or lake level highstand at early Holocene. A.M.S. radiocarbon age data suggests a similar pattern of climatic change with the previous global data (i.e. oxygen isotopic composition from Dongge Cave, China). However, this early interpretation needs further study in the future. In conclusion, the sedimentary facies of the bottom sediments of Lake Hovsgol have been controlled by changes of lake level, depositional position at the lake, and bottom topography.
PP11B-1390
Using Active Tectonics to Extend the Ultra-High-Resolution Global Climate Record from Santa Barbara Basin Back to ~1.2 Ma
Santa Barbara Basin continues to provide one of the highest-resolution climate records of the late Quaternary being studied from the world's oceans. Its unique geologic, tectonic, and oceanographic setting has resulted in a small well-defined bathymetric basin that has proven highly sensitive for recording detailed changes in global climate and ocean fluctuations. Sedimentation rates within depocenters are remarkably uniform, maintaining a rate of ~1 m/kyr over time spans of 1 yr to 1 Myr. Unfortunately, ODP Site 893, the longest available drill record (200 mbsf), only extends to ~160 ka. Detailed mapping of high- resolution multichannel seismic (MCS) reflection and chirp data, and stratigraphic correlation with existing well data indicate that continuous Quaternary strata deposited in the deep paleobathymetric basin were subsequently uplifted, folded, and in places eroded across various young, active fault-related fold structures. These older strata were mapped in 3D to seafloor outcrop, where they are now accessible to piston coring. In 2005, we were able to systematically recover substantial sections of these older sequences back to ~700 ka. Oxygen isotopic and other data confirm the presence of millennial and sub-millennial-scale climatic oscillations similar to those that mark the latest Quaternary. This includes abrupt decadal-scale warming events, climate flickering, superimposition of fine-scale oscillations on glacial-interglacial transitions, and---in the oldest core recovered to date---a remarkably periodic (~1200 yr) millennial-scale climate oscillation never before observed owing to the previous lack of paleoclimate records of sufficient age and resolution. In November 2008, a high-resolution MCS site survey and piston coring cruise will further extend this sampling record back to ~1.2 Ma to test if the basin's sensitivity to global high-frequency climatic oscillations extends back through the Mid-Pleistocene Transition (~800 ka to 1.2 Ma) and to confirm the viability of proposed deeper coring by the Integrated Ocean Drilling Program to recover a continuous ultra- high-resolution global climate record.
PP11B-1391
Lake Hazar: a potential high-resolution 150 ka record of climate and tectonic interactions in Anatolia
Over the last decade, a tremendous number of researches on climate and tectonic interactions have
converged on Turkey, mostly on the NAF (North Anatolian Fault) near Istanbul. For example, the Marmara
Sea has been the focus of an increasing number of international drilling projects, as the marine sediments of
this region provide long-term climate and tectonic reconstructions. Comparatively, the EAF (East Anatolian
Fault) is far from the sea and is few documented in terms of geological records (i.e. Lake Van is away from
the NAF trend). However, like for the NAF, the EAF has a relative simple structure (strike-slip faulting) leading
to large surface rupturing earthquakes (100 km -Ms > 7). In the south-east region, a remarkable example
of land structure is the Sincik/Hazar-Hazar/Palu fault segments interrupted by an exceptional large (20 km)
and deep (212 m) sedimentary basin (Lake Hazar). This natural archive provides a unique
chronostratigraphic sequence on the south-eastern Anatolian plate boundary. According to Cetin et al. 2003,
the lake record could spend the last 150 ka; this interpretation is confirmed by a new seismic survey and by
the study of the first sediment cores collected in the lake in 2007. Our results show that the proximal lake
basin is characterized by a continuous sedimentary sequence of ~80 m that could be valuably drilled.
The first five meters of lake sediments show series of thin distinct seismo-turbidites preserved between
climatically induced sediments. A high resolution radiocarbon age modelling (one radiocarbon date every 200
yr) validate the continuity of the record, making this lake a new valuable high-resolution continental record
for the south-east Anatolian region. This important new natural record has never been deeply cored by
scientific community. As a clue, this lake would be a good candidate for an ICDP deep drilling project aiming
to get the most extensive chronologies of climate and tectonic in south east Anatolia.
http://www.astro.oma.be/SEISMO/CYCLE/SeismicCycleSite/Introduction.html
PP11B-1392
Using Ground Penetrating Radar to Determine Coring Locations in two Colorado Subalpine Lakes
Lake sediment studies provide much data for reconstructing past environmental conditions. These data are collected from sediment cores retrieved from various locations in a lake. Deciding where to core is extremely important yet often difficult decision, and may be essential to the success of the project. The use of ground penetrating radar (GPR) survey transects across a lake basin can aid in determining optimal coring locations by providing information regarding depth to bedrock, thickness of sediment units, and basin morphological features. We have recently used GPR in two lake sediment studies in Colorado: at South Mesa Lake, Grand Mesa, Colorado in 2007; and at Lake Edith in the Colorado Front Range in 2008. At South Mesa Lake, sixty GPR reflection transects were established at approximately 10 meter intervals across the lake ranging from 65 to 150 meters in length, using 270 and 400 MHz antennae; at Lake Edith, 25 transects were established at approximately 10 meter intervals using the 400MHz antenna. These transects ranged in length from 25 meters to 220 meters. Coring locations at both lakes were determined based on analysis of reflections present in GPR profile images and bathymetric maps created from the profiles. GPR data showed features of complex basin morphology that were not otherwise evident, and the presence of potential depositional hiatuses in shallower basins. Selecting core locations without the benefit of the GPR analysis could have resulted in significantly shorter and/or less continuous cores. The longest cores collected were 12 meters obtained from South Mesa Lake, and 9.23 meters retrieved from Lake Edith. Results of particle size analysis, and determinations of bulk density and organic matter will be compared with GPR data to interpret significant radar reflection strata. Sediment and pollen analysis is proceeding on cores from both lakes and the results from these two lakes are expected to yield high resolution, comparative studies of past environmental changes from Colorado's western slope and the Front Range.
PP11B-1393
Centennial Variability in Winter Climate and Water Column Oxygenation During Mediterranean Sapropel S1
Eastern Mediterranean sapropels have been intensively studied as part of the oceanographic response to climate variability on orbital timescales, but the potential of laminated sapropel intervals for more highly resolved climate reconstruction remains underexploited. Even the highest resolution discrete sample series have been shown to alias short term variability in bottom water oxygenation, a key tracer of regional winter climate. Here we present trace elemental profiles of a laminated S1 sapropel, measured by Laser Ablation ICP-MS scanning of resin embedded sediment at <100µm resolution. The profiles reveal persistent centennial scale oscillations in the accumulation of V, Mo and U, interpreted to record variable oxygenation of the Eastern Mediterranean water column during S1. The results question existing theories about the stability of the 'sapropel state' and provide a new archive of centennial-scale winter climate variability in the wider European region.
PP11B-1394
A New Micro-Analytical Technique for the Identification of Tephra Layers in Sediments
Accurate dating and correlation of paleoclimatic records is key to understanding the often abrupt and complex climate changes that have occurred since the Last Termination. Tephrochronology uses material emitted during volcanic eruptions as isochronous markers for linking paleoclimatic records. Cryptotephra (i.e., those tephra not visible to the naked eye) layers can be as little as one to two shards thick while the shards themselves can be smaller than 10 m. The methods used to locate cryptotephra are often time consuming and laborious (e.g., sieving and point counting, density separation techniques) and in some cases may not be applicable (e.g., magnetic susceptibility of tephra may not differ from the sediment). XRF is a well-established analytical tool that has recently taken a new direction with the introduction of core scanning systems. The ITRAX XRF core scanning system is non-destructive, can acquire continuous data for a broad range of elements in situ in both marine and lacustrine sediments as well as take radiographic images. We test the possibility of screening sediment cores to flag the potential location of cryptotephra layers thereby eliminating lengthy laboratory work and saving on often precious sample. The method was tested by seeding a sediment core with tephra shards in layers of increasing thickness and then scanning the core with the ITRAX. The method was then further tested on sequences from two different sites: Hässeldala Port in Southern Sweden where up to 5 different cryptotephra have been detected and Lake Pechora from Russia which has several visible tephra layers. We show that using the ITRAX it is possible to locate most tephra layers without using any sample and within a minimal amount of time (a 1 m core can be analyzed reasonably in 12 hours and it requires essentially no sample preparation). While no quantitative data are generated with this method, major elemental changes are detectable and can be a starting point for identifying different tephra and their sources.
PP11B-1395
Centennial-Scale Nannoplankton Productivity Changes in the Mid-latitude North Atlantic During Marine Isotope Stages 11-12: Evidence From IODP Site 1313
High-resolution nannoplankton records from sediment cores recovered at Integrated Ocean Drilling Program Site U1313 reveal past changes in surface water conditions during Marine Isotope Stages (MIS) 11-12. Samples were spiked with microbeads for collection of quantitative assemblage data and calculation of coccoliths per gram of sediment, which is an estimate of nannoplankton productivity. These data are compared to oxygen and carbon isotopes, total lithics (>315 μm), and high-resolution X-ray fluorescence measurements. Nannoplankton productivity correlates well with the δ18O and calcium data, showing a gradual decrease in productivity during MIS 12, followed by a relatively rapid increase during Termination V, with generally higher levels in MIS 11. Gephyrocapsids dominate the assemblage throughout the studied interval. Gephyrocapsa oceanica, typically considered a warm-water species, is abundant during MIS 12. Some intervals of higher abundance are associated with lithic peaks, and could relate to decreased salinity from melting ice. Gephyrocapsa caribbeanica, typically a cold-water species, is also abundant during the studied interval, but only loosely correlated to inferred temperature. A transition from abundant large gephyrocapsids (>4 μm) during MIS 12 to small forms (<2.5 μm) occurs during Termination V. Small gephyrocapsids have been linked to both upwelling conditions and warmer temperatures. High abundance of the lower photic zone species Florisphaera profunda is typically interpreted as evidence for increased surface water stratification. The abundance of F. profunda fluctuates significantly during MIS 12, with the highest abundance (~4%) occurring just before the onset of Termination V. The studied interval also includes the biostratigraphically important last (common) occurrence of Pseudoemiliania lacunosa at 20.76 c-mcd (451.93 ka) during MIS 12. These results correlate well with other published nannoplankton data for the Atlantic basin, suggesting a change from cool, intermittently stratified surface waters during MIS 12 to warmer surface waters in MIS 11.