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abstracts
Evidence for calcification depth change of G. truncatulinoides between deglaciation and the Holocene – or why to be careful in transposing modern observations back in time (YSM POSTER PRIZE)
Caroline Cleroux, Jean Lynch-Stieglitz, Matthew Schmidt, Elsa Cortijo, Jean-Claude Duplessy
Deep-dwelling planktonic foraminifera living in the subsurface ocean can be useful proxy for past thermocline conditions. One species G. truncatulinoides is generally accepted as a recorder of the condition around 200 m depth in the North Atlantic and has been used to reconstruct past upper ocean structure.
Recent δ18O measurements from planktonic and benthic foraminifera in the Florida Straits provide a reconstruction of the entire water column isotopic composition (reflecting the vertical density gradient) over the last 12 ka. We use this reconstruction and δ18O measurements on G. truncatulinoides in a nearby core to track the depth habitat of this species from the last deglaciation to 1.6 ka B.P. Around 9 ka, G. truncatulinoides was calcifying in much shallower water than during the later part of the Holocene. We show by analysing several cores that the downward migration toward its modern habitat is a regional phenomenon over the western tropical Atlantic continental slope. The cause is still unclear but we hypothesize that the shallower habitat may be a response to the presence of glacial melt water or to circulation changes. This study emphasizes the needs for better understanding of the ecology, life cycle and controls on calcification depth for G. truncatulinoides and other planktonic foraminifera that are used to reconstruct the history of the thermocline and upper water column structure.
Caroline Cleroux, Lamont-Doherty Earth Observatory, Columbia University,Route 9W, Palisades, NY 10964, United States, ccleroux@ldeo.columbia.edu
Jean Lynch-Stieglitz, Georgia Institute of Technology, Atlanta, GA 30332, United States
Matthew Schmidt, Texas A&M University, Department of Oceanography, College Station, TX 77843, United States
Elsa Cortijo, CEA/CNRS/UVSQ/IPSL, Laboratoire des Sciences du Climat et de l'Environnement, 91198 Gif sur Yvette, France
Jean-Claude Duplessy, CEA/CNRS/UVSQ/IPSL, Laboratoire des Sciences du Climat et de l'Environnement, Gif sur Yvette, 91198 , France
Session: CCT2: Proxy Development, Calibration and Validation
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