U.S. Geological Survey and The National Academies; USGS OF-2007-1047, Short Research Paper 024; doi:10.3133/of2007-1047.srp024
Abrupt turnover in calcareous-nannoplankton assemblages across the Paleocene/Eocene Thermal Maximum: implications for surface-water oligotrophy over the Kerguelen Plateau, Southern Indian Ocean Shijun Jiang and Sherwood W. Wise, Jr. Department of Geological Sciences, 108 Carraway Building, Florida State University, Tallahassee, FL 32306-4100, USA (
[email protected];
[email protected])
Abstract Ocean Drilling Program (ODP) Core Section 183-1135A-25R-4 from the Kerguelen Plateau in the Indian Ocean sector of the Southern Ocean represents only the second complete, expanded sequence through the Paleocene/Eocene Thermal Maximum (PETM; ~55 Ma) recovered from Antarctic waters. Calcareous nannoplankton at this site underwent an abrupt, fundamental turnover across the PETM as defined by a carbon isotope excursion. Although Chiasmolithus, Discoaster, and Fasciculithus exponentially increase in abundance at the onset, the former abruptly drops but then rapidly recovers, whereas the latter two taxa show opposite trends due to surface-water oligotrophy. These observations confirm previous results from ODP Site 690 on Maud Rise. The elevated pCO2 that accompanied the PETM caused a shoaling of the lysocline and carbonate compensation depth, leading to intensive dissolution of susceptible holococcoliths and poor preservation of the assemblages. Similarities and contrasts between the results of this study and previous work from open-ocean sites and shelf margins further demonstrate that the response to the PETM was consistent in open-ocean environments, but could be localized on continental shelves where nutrient regimes depend on the local geologic setting and oceanographic conditions. Citation: Jiang, S., and S.W. Wise (2007), Abrupt turnover in calcareous-nannoplankton assemblages across the Paleocene/Eocene Thermal Maximum: implications for surface-water oligotrophy over the Kerguelen Plateau, Southern Indian Ocean, in Antarctica: A Keystone in a Changing World – Online Proceedings of the 10th ISAES, edited by A. K. Cooper and C. R. Raymond et al., USGS Open-File Report 2007-1047, Short Research Paper 024, 5 p.; doi:10.3133/of2007-1047.srp024.
Introduction One of the major paleoclimate discoveries of the scientific Ocean Drilling Program (ODP) was the Paleocene/Eocene Thermal Maximum (PETM) at Maud Rise (ODP Site 690) in the Southern Ocean (SO; Kennett and Stott, 1991; Bralower, 2002). We report here a second such site located half way around the Antarctic continent in the SO at ODP Site 1135 on the Kerguelen Plateau (KP; Fig. 1).
Figure 1. ODP Site 1135 (★) and other reference sites (●) on an ODSN 55-Ma plate reconstruction.
The PETM was a catastrophic, rapid greenhouseforced global warming event ~55 m.y. ago (surface- and bottom-water temperatures rose by ~5oC at high latitudes within 5 μ
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