PP11C-1396
Centennial to Millennial Scale Variations of Amur River Discharge, Sea-ice Expansion, and Biogenic Carbonate in Marine Sediment of the Central Okhotsk Sea
The Okhotsk Sea is a seasonal sea-ice area that is the lowest latitude in the northern hemisphere. It is very sensitive for climate change such as global warming. Marine bottom sediment is sensitively recording environmental changes of climate and ocean changes in the past around the Okhotsk Sea. In order to understand centennial to millennial scale climate and ocean changes in the Okhotsk Sea, a series of marine sediment cores in the central Okhotsk Sea are obtained by several cruises (MR0604 by RV Mirai, YK07-12 by RV Yokosuka, XP07 by Prof. Khlomov). Age model of the cores was constructed by oxygen isotope stratigraphy, magnetostratigraphy, tephrochronology, and optically stimulated luminescence (OSL) dating since oxygen isotope stage 13. Correlation among the cores by magnetic susceptibility was also very useful for the stratigraphy in the Okhotsk Sea. Variation of sea-ice expansion was reconstructed by ice-rafted debris (IRD) that was obtained by percentage of >63 micrometer fraction, and volume magnetic susceptibility. Sea-ice has expanded during glacial, especially during stadial (cold) events in marine isotope stage 2 (Last glacial maximum) and 4. Sea-ice in the most part of the Okhotsk was seasonal during late Quaternary, but it was expected as perennial sea-ice condition only in the northern part of the sea. Enhanced arctic atmospheric circulation resulting strong wind field over the Okhotsk Sea would be the most important factor for sea-ice expansion in the Okhotsk Sea. Clay mineral assemblages of terrigenous particles show clear difference between warm (interglacial and interstadial events in glacial) and cold (glacial and stadial events in glacial). Illite relative content in fine silt fraction (2 to 32 micron meter in diameter) by X-ray diffraction analysis enriched during cold periods. The variation of illite also corresponded to K content of non- destructive measurement of XRF core scanner (TATSCAN-F2). The variation of illite and K content suggest increase of aeolian dust that is consistent of forcing of enhanced atmospheric circulation during cold periods. On the other hand, smectite relative content increased during warm period, especially interglacial representing the Amur River discharge. Biogenic carbonate enriched during interglacial and interstadials with centennial to millennial scale variations. Abrupt increasing biogenic productivity and/or preservation of carbonate would be related to changes of river runoff and thermohaline circulation. The environment around the Okhotsk Sea is controlled by sub-polar and polar atmospheric circulation, by fresh water input of the Amur river, and by intermediate and deep water formation that relates global and local thermohaline ocean circulation.
PP11C-1397
Inter-core correlation of Okhotsk Sea sediment cores using geomagnetic paleointensity and paleoenvironmental implications
We conducted a paleomagnetic and environmental magnetic study of three piston cores (MR0604-PC5, 6, and 7) taken from the central part of the Okhotsk Sea. Age estimation and inter-core correlation were carried out using relative paleointensity. Then, regional difference of environmental changes was examined based on magnetic properties. Water depths of the coring sites range from about 800 to 1200m. The cores are about 20m long, and composed of diatom bearing silty clay of dark olive gray in color. Oxygen-isotope ratios measured on core PC7 show the average sedimentation rate of about 5 cm/kyr. Paleomagnetic and rock magnetic measurements were done on discrete samples. Magnetic overprint could be removed by alternating field demagnetization of up to 20mT in general. The average inclination of each core is close to the value expected from the geocentric axial dipole at the coring site. Magnetic properties show no sign of magnetite dissolution in reductive diagenesis. These facts indicate that these cores are suitable for relative paleointensity estimation. In this study, ARM was used as a normalizer of relative paleointensity estimation, because normalization with ARM showed smaller coherence between normalized intensity and normalizer than normalization with SIRM. This is probably because relatively large magnetic grain size of these sediments; In the Day plot, data points locate in the lower right part of a PSD region. Depths of the three cores were converted to ages by correlating the normalized intensities with that of ODP Site 983 (Channel et al., 1998). The record of ODP Site 983 was selected as a target curve because its resolution is higher than the Sint-800 stack. The ages of core PC7 derived from relative paleointensity are consistent with the oxygen-isotope stratigraphy. The ages of the bottom of the cores are estimated to be 360 to 540 ka. Inter-core correlation using paleointensity revealed that magnetic property variations are in anti-phase between the northernmost site and other two southern sites. In interglacials, magnetic concentration increases, magnetic grain size increases, and relative abundance of high-coercivity minerals increases at the northernmost site, whereas the opposite occurs at the southern two sites. This contrast could be explained by the idea that the northernmost site was covered with perennial ice in glacial periods, which thawed and provided IRD in interglacials. At the southern two sites, on the other hand, IRD was provided mainly in glacial periods.
PP11C-1398
Coral-based climate reconstructions from a massive Porites coral from a mid-Pacific shallowly submerged atoll: Sabine Bank (Vanuatu)
Sabine Bank (Republic of Vanuatu) is a carbonate bank that is rapidly subsiding (~1-2 mm yr-1) as it descends toward the New Hebrides Trench. Climatologically, Sabine Bank is located at the southern edge of the Western Pacific Warm Pool (WPWP) (≥28°C), and is well located to monitor ENSO- related climate variations in temperature and salinity. Previous work in the Vanuatu region has demonstrated that coral δ18O variability consistently correlates to the Niño-3.4 index. But more importantly, Sabine Bank offers perhaps the most purely open-ocean site from which a coral record has ever been developed. A modern, ~2.5 m long, massive Porites coral head was cored in ~12 m of water in 2006. Skeletal extension rates, estimated from banding discernable from X-radiographs is estimated at ~1.2 cm yr-1. A slab from this coral had has been sampled at ~monthly resolution and analyzed for Sr/Ca. The coral Sr/Ca record generated to date extends back ~70 yrs and exhibits a clear and pronounced climate signal. Coral δ18O determinations have been initiated. Eventually, we expect to have a >200 yr record of climate variability based on paired coral Sr/Ca and δ18O variations. Establishing such "proof of concept" with a modern coral at Sabine Bank is a prerequisite to proposed deep drilling at this location, whose tectonic setting offers a unique opportunity to sample fossil corals representing sea level and paleoclimate for a range of ages from MIS 7 to Present.
PP11C-1399
Towards Seasonality Proxies: Environmental Dependencies of Lamination, C isotopes and Trace Elements in Speleothems from Katerloch Cave, Austria
Katerloch Cave, located at the SE-rim of the European Alps, hosts abundant candle-stick stalagmites. Petrographical studies as well as U-Th dating revealed high growth rates of 0.2 to 1 mm/yr. The stalagmites consist of low-Mg calcite and show a macroscopic lamination of white, porous (inclusion-rich) and translucent, dense laminae. C and O isotope analyses (0.1 mm res.) along the growth axes of several stalagmites reveal a pronounced variability of the δ13C values, while the δ18O values change gradually across laminae. The dense layers coincide with high δ13C values, while the porous layers correspond to low values. Trace element contents also vary on short timescales, whereby high Mg and low Sr and Ba values typically correspond to highδ13C values and translucent, dense laminae. To understand the growth dynamics of speleothems in this cave, as well as the dependencies of the proxies, the cave was monitored for three years. Seasonal variations are manifested in the cave air pCO2 and C isotopes, i.e. a high pCO2 and low δ13C values prevail during the warm season and vice versa. Drip water δ13C values, pH and SICc also vary seasonally and therefore suggest a close relationship between cave air and drip water. In spite of a pronounced seasonal variability of the isotopes in meteoric precipitation the drip water δ18O and δD values are constant year-round. This observation supports effective mixing of the drip waters in the karst aquifer. Modern calcite collected on artificial substrates reflect the observed cave air and drip water isotope patterns and further support speleothem deposition in O isotopic equilibrium. The results suggest that the seasonally variable temperature gradient between the cave interior and exterior determines the intensity of air exchange in Katerloch Cave. Increased air-density contrasts during the cold season result in enhanced cave ventilation, thereby altering the cave air and drip water chemical and stable C isotopic compositions. The speleothems record these seasonally variable compositions. Consequently, the seasonal temperature cycle is the primary factor controlling the speleothem growth dynamics in this cave and drip rate fluctuations modulate the seasonal amplitude of the proxy variables. Translucent, dense laminae form during the cold season when an increased air exchange results in low cave air pCO2, high cave air and drip water δ13C values, higher Mg contents and a higher SICc. These conditions favour a higher degree of lateral coalescence of the calcite crystallites and thus a fabric lacking abundant inclusions and pores. White, porous laminae form during the warm season under opposite conditions. Seasonality is also reflected by the calcite δ13C values, which are mainly controlled by variable CO2 degassing, i.e. by the seasonally variable cave air/drip water pCO2 gradient. In contrast, the calcite δ18O values record inter-annual variations and reflect the isotopic composition of regional precipitation, cave air temperature and to some extent the seasonal distribution of recharge of the aquifer. There is some evidence for prior calcite precipitation affecting the Mg concentrations in the speleothems, whereas the Sr and Ba contents are mainly controlled by the growth rate and crystallization mechanism directly related to the seasonally variable lamination pattern. Understanding of the modern seasonally resolved dependencies of these proxy variables provides the basis for a quantitative assessment of past changes in seasonality in this region.
PP11C-1400
A speleothem-based high resolution reconstruction of climate in Southeastern Brazil over the past 4000 y
Preliminary stable and radiogenic isotopic investigations of speleothem CR1 from Cristal Cave in southeastern Brazil established a high-resolution record of climate change extending to approximately 4100 years before present (y BP). A total of 14 sub-samples were collected from CR1 for U/Th age determination. ICP-MS analysis of those sub-samples yielded very precise ages with analytical errors (2σ) averaging of ± ~13 years. An initial growth rate of .062 mm/yr for the first 2860 years is followed by a rate of .08 mm/yr for the remaining growth period. An average growth rate of ~.066 mm/yr allows for sampling of δ18O at sub-decadal resolution. Preliminary stable isotopic investigations have been done at high-resolution (nearly annual) for the past 125 years and approximately every 65 years prior to that. High- resolution stable oxygen isotope analysis will be performed for the entire duration of the archive in the near future. Initial results show a range of δ18O values from –5.92 per mil to –3.99 per mil. The data show a trend of steadily decreasing values over the past 4000 y BP. The exception to this trend is the last 150 years BP, when some of the least negative values for the record are observed. Variations in speleothem δ18O in southern Brazil have been shown to primarily reflect changes in rainfall δ18O, which in turn reflect changes in rainfall source or rainfall amount (Cruz et al., 2006). In the Brazilian subtropics, δ18O values are often not direct proxies for mean rainfall amount because the "amount effect" is not the primary controlling factor. For this location, δ18O is controlled mainly by moisture source, in particular South American monsoonal versus extratropical sources (Cruz et al., 2005). The relative contribution of monsoonal and extratropical moisture helps to define the amount of rainfall occurring during the summer and winter due to the control exerted on the seasonal balance of precipitation by the mean location and southward extent of Hadley cell convective activity and the South American summer monsoon (Cruz et al., 2005). For example, decreases in δ18O are often interpreted as an decreased contribution of winter versus summer precipitation (Cruz et al., 2005). Thus we interpret the trend observed in CR1 δ18O values as being due to increased summer precipitation and/or an overall increase in total yearly precipitation. The more enriched values of the past 100 years suggest a recent decrease in summer and/or total rainfall.
PP11C-1401
Reconstructing the Late Pleistocene Paleoclimate of Southern Nevada via Speleothem Proxy Records
The Great Basin province of the Southwestern United States is an area marked by evidence of a drastically altered climate in the recent past, as well as a wealth of sites with ecological and anthropological interest. Unfortunately, the region is also subject to a paucity of high-resolution studies necessary to link these elements and piece together its relationships globally. Speleothems, i.e. cave calcite, inherit their oxygen and carbon isotopic ratios from infiltrating meteoric waters and allow for U-series dating methods, permitting them to function as ideal proxies for reconstructing terrestrial climates. A suitable stalagmite was collected from the lower section of Pinnacle Cave, a limestone cavern on the flank of Mount Potosi in Clark Country, Nevada. Growth of the stalagmite initiated at ~19.479 ka and continued until ~15.744 ka. A time series was developed from eleven U-series dates and the isotopic variations within the sample, having a sampling resolution of ~20 years. The oxygen record is characterized by oscillations on both millennial as well as decadal time scales and is marked by a strong negative isotopic excursion at ~18.5 ka. Taken by itself, this large excursion can be interpreted as a significant depression in temperature and/or increase in available moisture over the site, for which evidence is curiously absent from other local records.
PP11C-1402
Centenial-Scale Climate Variability During the Early Deglaciation (19 to 16 ka) Expressed in Speleothem Oxygen Isotopes From the Yucatan Peninsula, Mexico
Speleothems were sampled from multiple caves in Yucatan, Mexico. U/Th ages indicate growth of the stalagmites during the Last Glacial Maximum (LGM) chronozone and into the early deglaciation (~21 to 16 ka). Oxygen and carbon isotopes were measured on calcite samples drilled every 0.5mm along the growth axis of the speleothems. Oxygen isotope values are greatest during the LGM chronozone with a sharp decrease in values at 19 ka. The early deglaciation (19 to 16 ka) is marked by centennial-scale changes in δ18O that are superimposed upon a gradual increase to 16 ka where growth stopped. Centennial- scale variability during this period is similarly expressed in percent reflectance records from the Cariaco Basin, (Peterson et al., 2000), suggesting a regionally coherent pattern of climate change. The δ18O of speleothem calcite during the LGM-to-early deglacial period reflects changes in cave temperature and the δ18O of precipitation. To better understand the controls on the δ18O of precipitation in northern Yucatan we are collecting rainfall samples for δ18O analysis along with temperature and precipitation data. Initial results over a 2.5 year period suggest a correlation between δ18O and rainfall amount.
PP11C-1403
High resolution dust concentration size distributions measurements in the EPICA-DML ice core in different climatic stages
Mineral dust measured in ice cores from Antarctica provides unique information about climate variability in the past more than 800 000 years. Higher dust load in the atmosphere during glacial times is attributed to higher aridity in the source and higher storminess during colder climate. Changes in dust concentration in ice cores emerge from changes in the source and changes of the transport. Dust size distribution data provide the possibility to separate concentration changes in ice cores in those attributed to the source and those attributed to the transport. The low accumulation in almost all ice cores from the Antarctic plateau complicates the measurements of dust concentration and size in seasonal resolution. The EPICA ice core drilled in Dronning Maud Land, an area of relatively high accumulation (recent accumulation rate: 64 kg/(m2year)), provides the unique possibility to obtain dust concentration and size distribution data in subannual resolution even during the last Glacial, when the accumulation was lower by a factor of two. Here we present data from different climatic stages in seasonal resolution. With a simple 1D-transport model we estimate the influence of the transport and the source variability on the dust concentration changes measured in the ice core.
PP11C-1404
Volatility of unevenly sampled fractional Brownian motion: an application to ice core records
The analysis of many natural time series and especially those related to ice core records often suffers from uneven sampling intervals. Here, we introduce a method that allows one to reliably estimate the volatility properties of fractional Brownian motion despite uneven sampling. It is based on the linear correlations of the process which are used to rescale the volatility series. For high-resolution temperature proxy records from Antarctica, we confirm that its volatility properties reveal a strong nonlinear component in the time series for time scales of 1 - 100 kyr. The results suggest that temperature increments appear in clusters of big and small increments --- a big (positive or negative) climate change is most likely followed by a big (positive or negative) climate change and a small climate change is most likely followed by a small climate change.
PP11C-1405
Laboratory Evaluation of the 'Sortable Silt' Paleoflow Proxy
Local resuspension of sediments by deep-sea boundary layers is thought to separate non-cohesive fine particles making up the bed, known as sortable silts, by size, shape and density. Paleoflow speeds have therefore been proposed by others to be knowable from observed particle size distributions of seafloor sediments of a known age, but this approach has not been thoroughly verified under controlled conditions. To examine the relationship between bed grain size and speed of an overlying flow, we conducted experiments in well-constrained, laboratory channel flows with mean flow speeds in the range of 10-70 cm s-1 (corresponding to shear velocities in the range 0.45 to 2.25 cm s-1) over beds of non- cohesive, glass microspheres with characteristic diameters in the range of 13-62 μm. In a given 12-cm deep flow, particles in suspension transport were isokinetically sampled at 11 elevations and assessed with a LISST 100X transmissometer. Mass-weighted, composite size distributions of particles in equilibrium suspension transport and in the residual bed were constructed for comparison with the known size distribution of particles initially making up an 'unsorted' bed. In addition, we made spot measurements of a potentially sorted bed for each flow conditions. Statistically significant differences between initial bed and suspended particle size distributions were found in only 2 of 14 experiments at the 95 percent confidence level, unadjusted for multiple comparisons. The median grain size of particles in suspension decreased with reduced flow speed to a statistically significant degree, but the modal grain size showed little sensitivity to flow intensity. In all cases, so little material entered into suspension transport that the composite size distribution of residual, surficial bed sediment did not differ from its original composition before flow-induced suspension transport and potential sorting. However, direct assessment of bed sediment during and after a single experiment indicated large spatial and temporal variations in central measures and the overall distribution of particle sizes, and thus the potential for local sorting by size. This result indicates complex dynamics of silt sorting in rolling bedload transport and associated development of small-scale bedforms. For the specific experimental conditions examined so far, we conclude that resuspension processes mobilize particles independently of silt size and flow speed. Silt sorting by deep-sea flows, if it exists, is more likely achieved during advective suspension transport from an upstream source, and locally as the result of rolling bedload transport driven by moderate flows at work over millennial time scales.
PP11C-1406
Comparisons of High-Resolution Organic Paleoenvironmental Records in Five Lake Erie Sediment Cores Sampled Over a 21 Year Period
We compared paleoenvironmental records of five sediment cores sampled at 1982, 1988, 1991 (two cores) and 2003 at approximately the same locations from Eastern Basin of Lake Erie to evaluate the effects on paleoenvironmental interpretations from spatial variability, that is the uneven distribution of the sediments, and the temporal variability, that is the diagenetic changes of the sediments. The high sedimentation rates of these cores (1.0cm-1.7cm/year) allow us to reconstruct annual climate changes. The paleoenvironmental proxies include total organic carbon, calcite contents, stable carbon isotopes of organic carbon and calcite, stable nitrogen isotopes, the atomic ratios of carbon and nitrogen, as well as stable oxygen isotopes of calcite. The absolute values of these proxies differ among different cores. By comparing the proxies at corresponding ages and depths, the difference seems mainly due to the uneven sediment distributions and is irrelevant of diagensis. The overall temporal patterns of paleoenvironmental proxies are consistent in multiple cores, providing strong evidence of the reliability of paleoenvironmental reconstruction on decadal scale. However, the year-to-year differences in proxies differ among different cores, questioning the reliability of reconstructing paleoenvironemental changes on annual scale. This study suggests that temporal resolution of paleoenvironmental reconstruction may be much lower compared to sediment rate and the analysis of multiple cores may be required for the studies aiming at a temporal resolution equal to sedimentation rate.
PP11C-1407
Annual-to-decadal resolution speleothem records from Zhijin Cave in the central western Guizhou of China: Changes in climate, environment and human activity during the past 1200 years
A 12.5-cm long stalagmite (ZJD-21) from Zhijin Cave (26.67°N, 105.77°E) in the central western Guizhou was dated by ICPMS 230Th/U method and 210Pb alpha counting method, revealing a growth history of 1200 years. A total of 490 samples (0.25mm sampling interval) were analyzed for oxygen and carbon isotopes. The δ18O values range from -10.60 to -7.56 permil (PDB) with an average of -9.00 permil, whereas the δ13C values range from -10.70 to -5.76 permil (PDB) with an average of - 8.43 permil. From the same cave, an 8-cm long soda-straw (ZJD-9C) was dated by 210Pb alpha counting method, providing a δ18O and δ13C record over the past 180 years. For the overlapping period, the two speleothem records have similar trends and features. The speleothem δ18O records in this monsoonal region can be used as a wet/dry indicator with lighter values reflecting wetter conditions, and vice versa. The speleothem δ13C records may be used for evaluating the vegetation changes above the cave, with heavier values indicating less vegetation coverage and intensity. The δ18O values of ZJD-21 are mostly heavier than the average value (-9.00 ‰) during AD1050-1270, AD1380-1460 and AD1780-1885, indicating drier climates were prevailing during these periods. Wetter climates were dominated during AD1010-1050, AD1460-1780 and AD1885-1960, reflected by the lighter δ18O values. The δ13C records from Zhijin Cave exhibit three intervals when the δ13C was strongly increased, which may be corresponding to deforestation events from AD1170 to AD1240, from AD1460 to AD1510 and since AD1800. These deforestation events were correlated to the population surges in South Song Dynasty, Ming Dynasty and Late Qing Dynasty in the area. After AD1900, all δ13C values are heavier than -6.6 permil, which indicates that the karst-desertification problem has been seriously developing in this region under human impacts.
PP11C-1408
Late Holocene Climate Change in Central Finland (62º-64Nº) Recorded by the Annually Laminated Lake Sediments
The deepest basins of six small lakes (Lake Kalliojarvi, Lake Kortejarvi, Lake Korttajarvi, Lake Kallio- Kourujarvi, Lake Lehmilampi and Lake Vahajarvi) depositing varved sediment in Central and Eastern Finland have been cored through winter ice using piston corers and wedge-shaped freeze coring techniques to obtain continuous sediment sequences extending until the present year. The lakes investigated have almost similar surface area with water depth varying between 10.5 and 12.5 m. So far 2-5 m (covering last 2000- 6000 yrs) of finely laminated sediment from all lakes has been impregnated in low viscosity epoxy resin using the water-acetone-epoxy-exchange technique. Laminae counts and thickness measurements have been made using thin sections or image analysis techniques from scanned X-ray radiographs depending on the varve type. Micro XRF technique was applied to study geochemical variations in high resolution. Our preliminary results (Haltia-Hovi et al. 2007) suggest that Finnish annually laminated sediments are excellent material for studying the past climate change and the impact of solar forcing on sedimentation. Due to their precise time control varved sediments can be correlated with other high resolution climate proxies.
PP11C-1409
Pleistocene/Holocene Paleoclimates of the Appalachian Mountains: High Resolution Insights From Speleothems
Speleothem-based isotopic and trace element records from heavily karstified regions of the Appalachian Mountains of eastern North America can be used to evaluate the timing, magnitude, and forcing mechanisms associated with climate change for at least the past ~600,000 years. U/Th-dated records spanning the Holocene, the Pleistocene-Holocene transition, and a large portion of the last ~300,000 years will be briefly evaluated in the context of other highly-resolved records of hemispheric and global climate change. The main goals of this presentation are to demonstrate 1) the decadal- to centennial-scale resolution of these records, 2) their value for defining cyclical and abrupt, aperiodic shifts in regional moisture, and 3) their role in developing a stronger understanding of tropical-extratropical linkages, especially with regard to changes in moisture transport that have occurred in the Caribbean-Gulf of Mexico-western North Atlantic sector.
PP11C-1410
The Shynchronization of Palaeoclimatic Events in the North Atlantic Region During Greenland Stadial 3
Two high resolution marine sediment cores located 83 km apart in the NE Atlantic have been studied: MD95- 2006 (Barra Fan; 57°01.82 N, 10°03.48 W; 2120m water depth) and MD04-2822 (Rockall Trough; 56°50.54 N, 11°22.96 W; 2344m water depth). The records are anchored to the NGRIP ice core stratigraphy and GICC05 chronology by the presence of geochemically characterized Fugloyarbanki tephra. Replicated sea surface temperature (SST) records show evidence for an abrupt and short-lived warming within Greenland Stadial (GS) 3, to which we tentatively assign an age of ca. 25 ka GICC05 b2k. Post-dating this warming event, but prior to the onset of Heinrich Event (HE) 2, SSTs are warmer than during the early stages of GS-3. Equally, abrupt warming in SSTs post-dating GS-3 coincides with Greenland Interstadial (GIS) 2; both cores resolving the double-warming associated with GIS-2 in Greenland ice-core records. Based on these and other marine palaeoclimate records from the Iberian margin and at the mouth of the Norwegian Channel, we propose a new three-fold event-stratigraphy for GS-3 within the North Atlantic region.
PP11C-1411
Records of Rapid Late Quaternary Environmental Change From Auckland Maar Lakes, New Zealand
High-resolution Late Quaternary paleoclimate archives are preserved in the sedimentary records contained in Auckland maar crater lakes. In particular, Orakei, Onepoto, Pukaki, Hopua and Pupuke maar lakes contain high-resolution sediment records with excellent chronological control for the period from ca 50 ka BP to today. A wide range of proxies have been measured from the maar crater sediments including: pollen and diatom paleoecology, environmental magnetism, grain size, major oxide and trace element geochemistry, total organic carbon, nitrogen and sulphur, plus bulk organic matter stable isotopes. Pollen analysis has been carried out on Onepoto and Pukaki cores that span the last ca 70 and 100 ka respectively in which marked vegetation changes reflect orbital forcing. In particular, reduction of forest and expansion of grass and shrublands coeval with deposition of the Okaia tephra (ca 29 kyr BP) is interpreted as the start of the LGM, after which cool, dry and windy conditions dominated, although our multi-proxy approach indicates that the situation is more complex with warmer/wetter phases punctuating the LGM. Warming commenced ca 17.7 ka BP and is apparent in multiple proxies from the maar lake records. However, the pollen record does not reflect the marked changes displayed in many of the other proxies during the late glacial. Similarly, the Holocene pollen record from Lakes Pupuke and Hopua indicates environmental stability and shows little change throughout the pre-human Holocene though a sustained ca 360 yr long phase of apparently drier conditions between ca 7.9 and 8.2 ka BP is apparent in other proxies. The multi-proxy approach allows us to reliably infer environmental changes in the lakes and catchments. Furthermore, compound-specific carbon and hydrogen isotope analysis of lipid biomarkers extracted from the sediment organic matter and oxygen isotope analysis of diatom silica, sponge spicules and organic matter cellulose are being undertaken to allow us to better understand the paleotemperature and paleohydrological controls on the complex isotopic signal contained in the maar lake sediments.
PP11C-1412
ENSO- and PDO-modulated SST Reconstructions From the Anthropocene Into the Last 2 Millennia: Planktonic Foraminiferal Mg/Ca Evidence at Inter-annual Resolution From San Lázaro Basin (NE Pacific)
On inter-annual time scales, the El Niño / Southern Oscillation (ENSO) climatic phenomenon is the largest driver of change in the ocean-atmosphere system. As such, it is a primary interest to understand how modern global warming has impacted ENSO, and how the marine sedimentary archive records this linkage in the southern California Current (CC). This would allow detailed comparison against other high-resolution archives, such as corals, and an improved ability to interpret past events as potential analogs for the future of ENSO. Furthermore, such reconstructions in recent millennia are crucial, since they record pre- anthropogenic climates under interglacial (warm) boundary conditions that allow us to characterize the nature of modern influence on this system. Here we present sub-decadal reconstructions of sea surface temperature (SST), derived from the Mg/Ca ratio of the shallow-dwelling planktonic foraminifera Globigerinoides ruber. The samples come from San Lázaro Basin in the southern Baja California continental margin (25° N; 112° W), situated beneath the dynamic boundary of the cool eastern Pacific boundary CC of northern origin, and the warm subtropical water masses of southern origin. The bottom of this coastal basin (maximum depth of 540m) is bathed by oxygen-depleted waters that flow over a shallow sill at 370m. High levels of primary production and export of biogenic particles to depth ensue from strong seasonal upwelling processes during spring to early summer. This combination of high sediment production and preservation in an area very sensitive to ENSO impact allows for a high-resolution reconstruction of inter-annual climatic phenomena in this unique eastern boundary current setting. For our highest temporal detail, we examine 2 cores at interannual resolution for the past ~90 years, which we use to validate our proxy against instrumental SSTs. This variability is effectively traced by Mg/Ca in G. ruber, which has an affinity for warmer waters during summer. We then sampled down-core continuously at a temporal resolution between 4-6 years, tracking inter-decadal to centennial variability and capturing the Pacific Decadal Oscillation (PDO), which further enables reconstruction of southern CC response to Northern Hemisphere multi-decadal to centennial anomalies, such as the Little Ice Age and the relatively warmer Medieval Warm Period. Our record shows no significant 20th-century departure relative to earlier centuries, thus resembling a "hockey stick without a blade". We will explore causes for this and other discrepancies, as well as cyclicity with respect to inter-annual climate phenomena.
PP11C-1413
High Resolution Holocene Records of Biogenic Fluxes to the Western Arctic Shelf
Recent changes in the Arctic Ocean ecosystem are occurring on rapid time scales, suggesting that examinations of Holocene paleoceanography require high resolution cores. During Leg 1 of the Healy-Oden Trans Arctic Expedition (HOTRAX), multicore and piston core samples were acquired at sites with average sedimentation rates of 160 cm/kyr (Station 5; 72.7 N, 157.5 W; 415 m water depth) to 348 cm/kyr (Station 8; 72.6 N, 156.9 W; 90 m water depth) during the Holocene. In these very high resolution samples from the Chuckchi Shelf north of Barrow, Alaska, organic C, N, S, total carbonate, biogenic silica and calcite, and C, N isotopes were determined. At Stn. 8 whose record extends into the Pleistocene, organic C shows a near surface maximum (2%) and rapid decrease with depth, and relatively constant concentrations (1.5%) through the mid-Holocene. Organic C decreases to values of ca. 1% in the Holocene-Pleistocene transition; values are quite variable in the late Pleistocene. Nitrogen displays a similar profile, although an increase in the late Pleistocene is largely absent. C:N ratios and C isotopes indicate that organic C is largely supplied by marine productivity through most of the Holocene, although terrestrial sources dominate in the early Holocene-late Pleistocene. Biogenic silica documents large diatom inputs to these sediments in the late and mid Holocene, while biogenic calcite shows very little inputs from calcareous organisms like coccolithophores; however, both of these tracers are not diagenetically stable and their signals are attenuated with time. Total carbonate in these sediments (largely dolomite) increases slightly through the Holocene from 0.1-0.2%, but then abruptly rises to as much as 1% at the Holocene-Pleistocene boundary; it then just as rapidly decreases at the bottom of the core. Interestingly, C/S ratios indicate a substantial freshening of the waters overlying these sediments in the early Holocene, consistent with large riverine inputs over 100s of years. Profiles of these tracers at the shallower Stn. 8 site that only covers the Holocene are very similar, although more variability was found. These high resolution records are invaluable for placing present day observations of changing biological productivity and fluxes in the western Arctic in context.
PP11C-1414
Interannually Laminated Sediment From the Southeastern Weddell Sea: Potential for High-Resolution (Annual-Millennial Scale) and Long-Term (Quaternary-Pliocene) Reconstruction of Glacial History
We present high-resolution data from several gravity cores east of Crary Fan, Antarctica. Here, fine-grained terrigenous sediment accumulated at extremely high glacial sedimentation rates (up to 4 m/ka!). Sediments are laminated, comprising coarse (silty) and fine (muddy) layers of detrital composition. According to AMS14C dating, the records cover a period from 25 to 19 ka and thus represent the last glacial maximum (LGM). In order to find out whether or not the lamination represents interannual stratification and could hence be used as high-resolution chronology, we developed software-based tools to (i) extract gray values at pixel resolution (i.e., 12 values/mm) from x-radiographs, and (ii) to count layers semi-automatically. In core PS1789, for instance, we counted 2430 peaks over 2690 AMS-dated years. Accordingly, there is strong evidence that the lamination represents interannual variability and therefore, the sites from the contourite ridges contain an extremely valuable climate archive for ultrahigh-resolution studies of glacial climate variability in high southern latitudes. Our preliminary interpretation is that a seasonally variable bottom water production was induced by brine injection, which again, initiated density currents that were canalized within the channels. They overspilled the NW levee shoulder and deposited a coarser-grained (siltier) layer during glacial winter, when brine injection was probably enhanced, and a finer-grained (muddier) layer during glacial summer, when brine injection was likely reduced. Apparently, this mechanism operated consistently, producing intense bottom-water in the channels, and creating fine-scale lamination on the ridges over thousands of years during the LGM. Spectral analysis of laminae thickness indicates a novel finding: prominent solar cycles at periods of 80 to 90 years (Gleisberg cycle) and 200 to 220 years (de Vries cycle), revealing a dominant linear response to solar forcing. Seismic investigations reveal that up to 600 m of sediment have been deposited on the sediment ridges since the Late Pliocene. Accordingly, deep drilling would also provide the opportunity to study the long-term glacial history and compare it to the northern hemisphere glaciation.
PP11C-1415
Santa Barbara Water Column Temperature Changes Over the Past 2500 Years as Recorded by Planktonic Foraminiferal Proxies
Santa Barbara Basin planktonic foraminiferal Mg/Ca, δ18O and coiling data are presented from two piston cores spanning the interval from 2500 to 300 calendar years BP. These cores have an average sedimentation rate of 134 cm/kyr and provide a multi-proxy decadal scale record of California Current temperature changes that are directly comparable to previous proxy records from adjacent cores, and help to elucidate the temporal and spatial variability of late Holocene climate anomalies. In addition, AMS 14C chronology allows comparison of the sea surface temperature record to previous terrestrial records of climate change on the California Margin. Santa Barbara Basin Mg/Ca analyses of Globigerina bulloides and Neogloboquadrina pachyderma indicate that during and prior to the Medieval Climate Anomaly (MCA, 1300 to 800 BP), sub-surface and thermoclinal temperatures were 16°C and 10°C, respectively, and cooled approximately 2°C from 2500 to 300 yrs BP. Mg/Ca analyses of Globigerinoides ruber indicate that near-surface waters were also warm during the MCA, reaching peak warm temperatures of 19°C at 1000 BP. Surface water temperatures during the Little Ice Age (LIA; 800 to 300 BP) were between 13 and 15°C, similar to modern cool season temperatures in the region. N. pachyderma coiling data are consistent with the Mg/Ca temperature record, indicating generally cool temperatures prior to 1300 yrs BP, warm temperatures during the MCA and cool temperatures during the LIA. Planktonic foraminiferal δ18O data from these and adjacent cores show higher values during the MCA and lower values during the LIA, indicating a significant salinity effect on foraminiferal δ18O. These data, when compared with terrestrial climate data, suggest that the Medieval Climate Anomaly was characterized by warm dry conditions in the Santa Barbara Basin region, becoming cool and wet during the Little Ice Age.