Les diatomees et les evenements climatiques des 150 000 dernieres annees; Applications de fonctions de transfert aux diatomees de l'ocean Austral

International audienc

Southern Ocean Core MD 94–101

News of the international paleoscience community a core project of the international geosphere-biosphere programme IGBPInternational audienceOne of the named Activities in the PAGES Implementation Plan focuses on 'Regional, Educational and Infrastructure Efforts' (REDIE). This reflects a foresighted view among the founders of PAGES that our future legacy should include not only data and scientific understanding, but also human development. The urgent need to establish scientific priorities and devise ways of realizing and coordinating them has taken precedence and REDIE has taken second place-until now. This summer (July 17-24), a formidable group of leading paleo-scientists from around the world will give a summer school entitled "The Dynamics of the Earth System: Processes and Records of Past Climate Change" (see http://phkup0.unibe.ch/summer/). One outcome of discussions between the PAGES IPO and the organizers of the summer school, Thomas Stocker and Andy Lotter, has been a scheme to fund attendance by young scientists from developing countries. START, the 'Global Change System for Analysis, Research and Training', that has responsibilities for capacity buildin

Transfer functions between diatom assemblages and surface hydrology in the southern ocean

International audienc

Glacial–interglacial changes in the accumulation rates of major biogenic components in Southern Indian Ocean sediments

International audienc

A test of (Ge/Si) opal as a paleorecorder of (Ge/Si) seawater

Late Pleistocene variations of germanium to silicon ratios in marine diatom shells from sediment cores, (Ge/Si) opal , are coherent with the global isotope record of glacial to interglacial climate change. These variations are thought to reflect changes in (Ge/Si) seawater driven by climatemodulated alterations in oceanic Ge/Si sources and sinks. However, an important criterion for interpreting (Ge/Si) opal as a monitor of whole ocean (Ge/Si) seawater is that the opal burial ratio be insensitive both to local diatom production and surface ocean silica concentrations (so-called biological fractionation effects) and to differential dissolution artifacts (so-called diagenesis offsets). Here we test these assumptions by comparing model ocean sediment (Ge/Si) opal distributions with data from Holocene and glacial sediments across the high-latitude Indian-Antarctic Ocean siliceous ooze belt. In contrast to the model, the data show no gradients in either Holocene or glacial (Ge/Si) opal values across productivity zones displaying dramatic changes in biosiliceous production, opal burial, and dissolution. This evidence supports the contention that fractionation effects are small and that observed down-core variations in (Ge/Si) opal faithfully record secular changes in (Ge/Si) seawater

Melting history of Antarctica during the past 60,000 years

International audienc

The last deglaciation in the Southern and Northern Hemispheres: A comparison based on oxygen isotope, sea surface temperature estimates, and accelerator 14^{14}C dating from deep-sea sediments

International audienceThe last deglaciation in two deep-sea sediment cores recovered from the Southern Indian Ocean is studied and compared with two records obtained from the North Atlantic. The chronology has been established by accelerator mass spectrometric (AMS) $^{14}$C dating of planktic foraminifers. Climatic changes are inferred based on $\delta^{18}$0 measurements in planktic foraminifers and on sea surface temperatures (SST) obtained by means of faunal and floral transfer functions. In the North Atlantic, the last deglaciation began at about 15 -14.5 ka, Holocene conditions were reached at about 12.5 - 12.0 ka and a cold interval occurred between 11.0 and 10.0 ka (Younger Dryas Event). In the Southern Ocean, the last degiaciation began between 16.5 and 13.0 ka and Holocene temperatures were reached at about 12.0 ka. Both Southern Ocean records present transitory oscillations: Core MD 84-551 (5SOS) exhibits a temporary increase in $\delta^{18}$0 dated at about 10.5 ka (but it is still unresolved if this feature is due to SST changes or other regional causes) while Core MD 84-527 (44°S) is characterized by a cold event at about 11.6 ka (only in the SST records) and a prominent warm optimum between 10.5 and 8.0 ka (in the SST and $\delta^{18}$0 records). More data are needed to determine if there was a time lag between the last degiaciations in both hemispheres and if common transitory oscillations can be recognized