PP32B-01
Study on Mg/Sr paleo-thermometer in speleothem: Mg source effect
The partitioning coefficient (KMg) of Mg/Ca between cave dripwater and calcite is a temperature (T) dependent, whereas KSr of Sr/Ca has little T influence. Using Sr/Ca variation in a stalagmite to normalize Mg/Ca variation for removal of Mg source change in dripwater, Mg/Sr in stalagmites may be a proxy of paleo- temperature. One of the assumptions for this paleo-temperature indicator requires that Mg/Sr ratio in the source water should remain constant through time. We have investigated Mg/Ca and Sr/Ca ratios in cavewaters and modern calcite deposits in Western Guizhou, China for verifying the assumptions. Cavewater samples from Zhengjia, Shijiangjun and Zhijin Caves in central western Guizhou, China have average Mg/Sr ratios of 1278± 411, 1155± 207 and 14.0± 2.7, respectively. The modern speleothem deposits from the caves exhibit the same feature: high Mg/Sr ratios in samples from Zhengjia and Shijiangjun Caves, and low in samples from Zhijin Cave. This is mainly because high Mg/Ca in dolomite limestone in the area of Zhengjia and Shijiangjun Caves. The above results show that bed-rock compositions affect the Mg/Sr ratios of the cave water. In a stalagmite from Shijiangjun Cave, the Mg2+ concentration sharply increased while the Sr2+ concentration strongly decreased in the upper 6-cm part where high detrital content of CaCO3 deposition appeared. The large variations and high values of Mg/Sr ratios in this part of the stalagmite do not represent either the temperature effect on CaCO3 deposition or influence of bed-rock composition. Instead, such variations may reflect the changes in overlying environment caused by climate variability and human activity. This means that Mg/Sr ratio in source water experienced large changes when the overlying conditions changed. The Mg/Sr in such a stalagmite cannot be used for paleo-temperature reconstruction. Based on the measurements of Mg/Ca and Sr/Ca ratios in both waters and modern carbonates from Zhijin Cave, we have calculated the partitioning coefficients for Mg/Ca and Sr/Ca between calcite and water. The KSr value ranges from 0.04 to 0.134, averaging 0.073± 0.035. The average KMg value is 0.021±0.010. The values provide us the fundamental data for using Mg/Sr ratio as a proxy of paleoclimate reconstruction.
PP32B-02
The Initiation of the Southern Central Great Barrier Reef: Multiproxy Study on Periplatform Sediments From ODP Site 1195 on the Marion Plateau (NE Australia)
The sediments deposited at ODP Site 1195 (Marion Plateau, NE Australia) record synchronous shifts in their chemistry, mineralogy, grain size and colour at 6 meters below sea floor. These significant changes are interpreted to reflect the onset of the southern province of the Great Barrier Reef (GBR). An increased deposition of carbonate-rich sediments of neritic origin, coincident with a decline in both sedimentation rate and terrigenous input, is attributed to inshore trapping of materials by the reefs. Based on an age model combining magnetostratigraphic and biostratigraphic data, we propose that the southern province of the GBR initiated between 560 and 670 kyr B.P. Our best estimate concurs with previous studies reporting an age between 500 and 930 kyr B.P., albeit constraining more tightly these earlier age estimates. However, it does not support research placing the birth of the GBR in Marine Isotope Stage 11 (about 400 kyr B.P.), nor the recent theory of a worldwide modern reef development at that time.
PP32B-03
Southern Ocean Multi-Decadally Resolved Sea Surface and Intemediate Water Multi Proxy Reconstructions Spanning the A2 Antarctic Warm Event at ODP Site 1233
Southern Ocean circumpolar dynamics are hypothesized to play an active role in the climate system through their influence on atmospheric carbon dioxide levels, the global thermocline and the ocean overturning circulation. It is increasingly clear that Southern Ocean millennial scale sea surface temperatures show a pattern similar to what is observed in Antarctic ice cores, suggesting southern dynamics play an active part in these events. The full nature and role of these changes cannot be fully understood until higher resolution records are available capturing Southern Westerly Wind (SWW) and Antarctic Intermediate Water signals (AAIW) detailing the timing, rate and amplitude of these events. Here we present a multi-decadal foraminiferal multiproxy reconstruction spanning the A2 Antarctic warm event (here ~44-48 kyr BP, MIS 3) from the region in the southeast Pacific where the SWW and the Antarctic Circumpolar Current (ACC) intersect with the South American continent and freshly formed AAIW is monitored at depth. Ocean Drilling Program (ODP) Site 1233 (41°00'S, 74°27'W, 838m, sedimentation rate ~1.5-2.2 m/kyr) from the Chilean slope monitors simultaneously AAIW and sea surface water properties that are strongly influenced by the climate signals of the large scale atmospheric (SWW) and oceanic systems (ACC). We use a combined foraminiferal approach of planktic, G. bulloides, and benthic, U. peregrina, oxygen isotopes (temperature plus δ18Owater) and G. bulloides Mg/Ca (temperature). This allows us to 1.) establish a sea surface temperature (SST) signal derived from foraminifera that is easily compared to the benthic record 2.) reconstruct the δ18Owater using the same foraminiferal species for determining both temperature and δ18Oforam and 3.) assess the high frequency variability in the sea surface temperature and rate of changes. The Mg/Ca SST reconstruction shows a 2-3°C variability in both high and low frequency. We find that >50% of the amplitude in the planktic δ18O record is caused by changes in δ18Owater, much of which is probably related to local fresh water fluxes, due to the fluctuations of the Patagonian ice sheet. The high resolution Mg/Ca SST reconstruction mirrors the lower resolution alkenone-derived SST from site 1233 spanning A2 and is correlated to the changes in benthic foraminiferal δ18O, approximately with the same magnitude, indicating a broad scale change involving the major circumpolar dynamical systems.
PP32B-04
Late Miocene Washhouse Climate due to Temporary Closure of Panama Seaway
Tectonic processes have played an important role in driving long-term climatic change. It has been shown that the final closure of the Central American Seaway (CAS) in the Pliocene caused a major reorganization of ocean and atmospheric circulation. A comparable tectonic situation existed in the time interval between ~ 10.9 and 8.3 Ma, when the CAS was temporarily closed. To study the effects of such a major paleogeographic change on continental climate, we reconstructed an 8 million-year proxy record of European precipitation and runoff variations for the Middle to Late Miocene (5.3 to 13 Ma, temporal resolution ~ 60 kyr), based on the ecophysiological structure of herpetological (amphibians and reptiles) assemblages. Our data provide strong evidence of a washhouse climate in mid latitudes, characterized by a several-fold increase in the continental runoff induced by up to more than 200% increase in precipitation relative to recent. We interpret the washhouse climate in terms of a weakened Azores High due to a reversed oceanic northward heat transport upon closure of the CAS. The two intervals of washhouse climate (between 10.2-9.8 Ma and 9.0 -8.5 Ma) occur in warm periods, while the in-between interval (from 9.7 to 9.2 Ma) with a reduced hydrological cycle occurs in a globally cool period when the Atlantic Meridional Overturning Circulation (AMOC) was weaker. The transition between the washhouse and the cool climate may well have been fuelled by the enhanced atmospheric moisture transport into high latitudes and promoted by increasing amplitudes of obliquity variations. The reduced European hydrological cycle in the cool interval caused a severe biotic crisis, including the extinction of hominoids in Europe. Our data corroborate results from coupled ocean-atmosphere-land models predicting significant increases in the hydrological cycle in response to global warming.
PP32B-05
Ancient dirt DNA
In the past two decades, ancient DNA research has progressed from the retrieval of small fragments of mitochondrial DNA from a few late Holocene specimens, to large-scale studies of ancient populations, phenotypically important nuclear loci, and even whole genomic studies of extinct species. However, the field is still regularly marred by erroneous reports, which underestimate the extent of contamination within laboratories and samples themselves. An improved understanding of these processes and the effects of damage on ancient DNA templates has started to provide a more robust basis for research. Recent methodological advances have included the discoveries of DNA preserved in ancient sediments, coprolites, and fossil ice (Ancient Dirt DNA). These findings promise to make possible the reconstructions of entire ecosystems through time and allow for studies of past population genetics in cases where fossils are rare. The advantages and pitfalls connected to the Ancient Dirt DNA approach will be discussed as will recently obtained data relating to Greenland environmental history, long-term bacterial survival and the first human migration into the Americas.
PP32B-06 INVITED
Uncovering the Mysteries of Lacustrine Haptophytes Using Fossil DNA
Certain haptophyte algae produce alkenones which are indispensable biomarkers used in paleoclimate studies. Sedimentary alkenones record past water temperatures experienced by the algae via the unsaturation index (UK37), as well as capturing a snapshot of the source water hydrogen isotope composition (used to reconstruct hydrological changes) and carbon isotope composition (used to reconstruct partial pressure of CO2). In these ways, alkenones have been exploited for paleoclimate reconstructions from ocean sediments. Paleoclimatologists and organic geochemists are now beginning to discover alkenones in sediments from lakes around the globe. However, unlike in the oceans, the exact haptophytes responsible for producing lacustrine alkenones are unknown and may be specific to different lakes. To effectively use alkenones for isotopic and temperature reconstruction from lake sediments, the identity (and potential temporal variability) of the producer organisms must be understood. Using 18S rDNA we have previously shown that the surface sediments of four lakes in southwestern Greenland, as well as 1000 year old sediment from one of these lakes, all depict the presence of the same haptophyte taxa. Here, we report higher-resolution paleogenomic results from the Holocene sediments of Lake E in southwestern Greenland, which indicate that there has not been any discernable change in the haptophyte population (as inferred from 18S rDNA) within the lake after their appearance 5500 years ago. This differs from the significant shifts in haptophyte taxa which have been reported from the sediment record of Ace Lake, Antarctica (likely due to Lake E having had a more stable environmental history than Ace Lake) and validates the application of a single UK37-temperature calibration to the entire sediment record of Lake E. We also report the results of the first global survey of lacustrine haptophytes. We compare haptophyte 18S rDNA sequences from lake sediments from Greenland, Tibet, Spain, Great Britain, North America, Europe and Antarctica. This approach utilizes sedimentary DNA to answer questions that traditional algal culturing techniques have been unable to address, providing the first phylogenetic map of lacustrine haptophytes and revealing some of the challenges faced in developing lacustrine alkenones as a continental paleoclimate proxy.
PP32B-07 INVITED
A Qualitative and Quantitative Comparison of Sedimentary Palynomorphs, Lipid Biomarkers and Fossil DNA: Which Tool Provides the Most Detailed Paleoecological and Paleoenvironmental Information?
In recent years, it was shown that Holocene planktonic taxa could be identified at the species-level based on their preserved fossil genetic signatures (fossil DNA) in either cold and/or sulfidic lacustrine and marine settings. Many of those species are not known to leave morphologically recognizable remains and thus most likely would have escaped microscopic determination and enumeration. In addition, fossil DNA analysis also revealed past planktonic taxa for which no specific lipid biomarkers are known. However, the best, and yet unexplored, approach to validate fossil DNA as paleoenvironmental tool would be based on a direct qualitative and quantitative comparison of each of the above described proxies. In an up to 2700-year-old record of undisturbed sulfidic sediments from the Small Meromictic Basin in Ellis Fjord, Antarctica, we compared the quantitative and qualitative distribution of fossil ribosomal DNA of phototrophic algae like diatoms, dinoflagellates and past chemocline bacteria (green sulfur bacteria) with the distribution of their fossil lipid biomarkers: highly branched isoprenoids, dinosterol and carotenoids. For dinoflagellates, we performed a comparative microscopic (palynological) analysis of fossil dinocysts whereas comparative diatom microfossil data was available from the literature. We will discuss important new insights about the cell-specific fate of fossil DNA and the additional paleoenvironmental information which was revealed from the fossil DNA analysis.
PP32B-08
Contributions to bulk sedimentary nitrogen isotope variability in the Eastern Equatorial Pacific
The surface waters of the Eastern Equatorial Pacific contain a standing nitrate pool due to iron limitation. As a consequence, nitrogen isotopes records from sediments underlying the Eastern Equatorial Pacific have been interpreted as an archive of relative nitrate utilization in the upwelling region and thus, a potential record of changing Fe availability. The nitrogen isotopic composition of the upwelled nitrate was assumed to be constant on glacial-interglacial timescales. However, some proportion of the nitrate in the Eastern Equatorial Pacific passes through the oxygen minimum zone of the Eastern Tropical South Pacific. Active water column denitrification in the oxygen minimum likely imparts a large isotopic signature upon the advecting nitrate pool. Here, a high resolution, well-dated sedimentary N isotope record from Eastern Equatorial Pacific site ODP 1240 is compared to records from the Eastern Pacific margins where variation in sedimentary 15N/14N is primarily attributed to changes in regional denitrification rates. Similarity in the magnitude and timing of the N isotope variations suggest that the large-scale glacial-interglacial pattern observed in the sedimentary 15N/14N of Eastern Equatorial Pacific sediments reflects variation in regional denitrification rates rather than large-scale changes in demand for nutrients driven by fluctuating availability of iron. Underlying the glacial- scale variations in the Eastern Equatorial Pacific is a longer timescale shift in sedimentary 15N/14N that cannot be directly attributed to regional changes in denitrification rate. This shift may reflect an important biogeochemical change within the Equatorial Pacific however, diagenetic artifacts must first be ruled out.