Diester-Haass, Liselotte and Zahn-Knoll, Reiner (1996) Eocene-Oligocene transition in the Southern Ocean: History of water mass circulation and biological productivity. Geology, 24 (2). pp. 163-166. DOI 10.1130/0091-7613(1996)024<0163:EOTITS>2.3.CO;2.

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Abstract

High-resolution records of carbon and oxygen isotopes and benthic foraminiferal accumulation
rates for the Eocene-Oligocene section at Ocean Drilling Program Site 689(Maud Rise, Weddell Sea; paleodepth about 1500 m) were used to infer variations in paleoproductivity in relation to changes in climate and ventilation of the deeper-water column. The benthic foraminiferal abundance and isotope records show short-term fluctuations at periodicities of 100 and 400 ka, implying orbitally driven climatic variations.
Both records suggest that intermediate-depth water chemistry and primary productivity
changed in response to climate. During the Eocene, productivity increased during cold
periods and during cold-to-warm transitions, possibly as a result of increased upwelling of
nutrient-rich waters. In the Oligocene, in contrast, productivity maxima occurred during
intervals of low d18O values (presumably warmer periods), when a proto–polar front moved
to the south of the location of Site 689. This profound transition in climate-productivity
patterns occurred around 37 Ma, coeval with rapid changes toward increasing variability
of the oxygen and carbon isotope and benthic abundance records and toward larger-amplitude
d18O fluctuations. Therefore, we infer that, at this time, temperature fluctuations
increased and a proto–polar front formed in conjunction with the first distinct pulsations
in size of the Antarctic ice sheet. We speculate that this major change might have resulted from an initial opening of the Drake Passage at 37 Ma, at least for surface- and intermediate-water circulation.

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