Diatom evidence for the onset of Pliocene cooling from AND-1

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TitleDiatom evidence for the onset of Pliocene cooling from AND-1B, McMurdo Sound, AntarcticaAbstractThe late Pliocene, Â 3.3-3.0. Ma, is the most recent interval of sustained global warmth in the geologic past. This window is the focus of climate reconstruction efforts by the U.S. Geological SurveyÅ› Pliocene Research, Interpretation, and Synoptic Mapping (PRISM) Data/Model Cooperative, and may provide a useful climate analog for the coming century. Reconstructions of past surface ocean conditions proximal to the Antarctic continent are essential to understanding the sensitivity of the cryosphere to this key interval in EarthÅ› climate evolution. An exceptional marine sediment core collected from the southwestern Ross Sea (78^circ S), Antarctica, during ANDRILLÅ› McMurdo Ice Shelf Project preserves evidence of dramatic fluctuations between grounded ice and productive, open ocean conditions during the late Pliocene, reflecting orbitally-paced glacial/interglacial cycling. In this near-shore record, diatom-rich sediments are recovered from interglacial intervals; two of these diatomites, from Â 3.2. Ma and 3.03. Ma, are within the PRISM chronologic window. The diatom assemblages identified in PRISM-age late Pliocene diatom-rich sediments are distinct from those in mid-Pliocene and later Pliocene/Pleistocene intervals recovered from AND-1B, and comprise both extant taxa with well-constrained ecological preferences and a diverse extinct flora, some members of which are previously undescribed from Antarctic sediments. Both units are dominated by Chaetoceros resting spores, an indicator of high productivity and stratification that is present at much lower abundance in materials both older and younger than the PRISM-age sediments. Newly described species of the genus Fragilariopsis, which first appear in the AND-1B record at 3.2. Ma, are the most abundant extinct members of the PRISM-age assemblages. Other extant species with established environmental affinities, such as Fragilariopsis sublinearis, F. curta, Stellarima microtrias, and Thalassiothrix antarctica, are present at lower abundances. Environmental inferences drawn from extant diatom assemblages are in good agreement with those from Chaetoceros resting spores and the Fragilariopsis radiation. All three lines of evidence indicate the onset of late Pliocene cooling in the Ross Sea near-shore environment at 3.2. Ma, with intensification and possible regional persistence of summer sea ice by 3.03. Ma. An important implication of this research is the indication that the Ross Ice Shelf fluctuated dramatically on orbital timescales at a time when nearshore Antarctic conditions were only modestly warmer than present. â"' 2012.AcknowledgementsThe ANDRILL (Antarctic Geologic Drilling) Program is a multinational collaboration between the Antarctic programs of Germany, Italy, New Zealand (AntNZ) and the United States. This study is based upon work supported by the National Science Foundation under Cooperative Agreement No. 0342484 through subawards to both CRR and RBD administered by the ANDRILL Science Management Office at the University of Nebraska-Lincoln and issued through Northern Illinois University, as part of the ANDRILL U.S. Science Support Program. The authors gratefully acknowledge the ANDRILL Program for the award of an ANDRILL Graduate Fellowship to CRR in further support of this work. D. Harwood, J. Barron, C. Sjunneskog, D. Winter, and R. Scherer provided valuable discussion and insights on various elements of diatom-based paleoenvironmental reconstruction. C. Bernhardt and B. Landacre provided advice and support in statistical methodologies. S. Starratt generously provided access to an exceptional light microscope and camera system. This manuscript was improved by early comments from J. Barron and M. Robinson, and by the insightful recommendations of M. Konfirst and two anonymous reviewers. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

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1st AuthorRiesselman, C.AuthorRiesselman, C.Dunbar, R.Year2013JournalPalaeogeography, Palaeoclimatology, PalaeoecologyVolume369Pages136-153DOI10.1016/j.palaeo.2012.10.014URLhttps://www.scopus.com/inward/recor.....ee63aaa0f133628a6dceb154eKeywordsabundancebiostratigraphycoolingdiatomfossil assemblageglacial-interglacial cyclemicropaleontologypaleoclimatepaleogeographyPliocenereconstruction, AntarcticaEast AntarcticaMcMurdo SoundRoss SeaSouthern Ocean, BacillariophytaChaetocerosFragilariopsisFragilariopsis curtaFragilariopsis sublinearisStellarima microtriasThalassiothrix antarctica, rank5Author KeywordsAntarctic Geological Drilling (ANDRILL)AntarcticaDiatomsPlioceneRoss Sea

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TypeArticleCitationRiesselman, C. and Dunbar, R. (2013) Diatom evidence for the onset of Pliocene cooling from AND-1B, McMurdo Sound, Antarctica. Palaeogeography, Palaeoclimatology, Palaeoecology, 369: 136-153 doi:10.1016/j.palaeo.2012.10.014