Pliocene mixed-layer oceanography for Site 1241, using combined Mg/Ca and δ18O analyses of Globigerinoides sacculifer.

Groeneveld, Jeroen, Steph, Silke, Tiedemann, Ralf, Garbe-Schönberg, C.-Dieter, Nürnberg, Dirk and Sturm, Arne (2006) Pliocene mixed-layer oceanography for Site 1241, using combined Mg/Ca and δ18O analyses of Globigerinoides sacculifer. Open Access Proceedings of the Ocean Drilling Program: Scientific Results, 202 . pp. 1-27. DOI 10.2973/

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To reconstruct changes in tropical Pacific surface hydrography, we used samples from Site 1241 (5°50′N, 86°26′W; 2027-m water depth) to establish high-resolution records of Mg/Ca and δ18O for the mixed-layer dwelling planktonic foraminifer Globigerinoides sacculifer for the
Pliocene time interval from 4.8 to 2.4 Ma. An increase in average seasurface temperatures (SSTs) (24.5°–25.5°C) between 4.8 and 3.7 Ma can probably be explained by a southward shift of the Intertropical Convergence
Zone, thereby increasing the influence of the warmer North
Equatorial Countercurrent.
The general global cooling trend, a response to intensification of Northern Hemisphere glaciation (NHG), started at ~3.2 Ma (shown by the δ18Obenthic record) and is paralleled by tropical east Pacific cooling (indicated by SSTMg/Ca). Tropical east Pacific cooling, however, had already commenced by ~3.7 Ma, suggesting that global cooling, probably related to decreasing atmospheric CO2 concentrations, might have started well before intensification of NHG.
Relative changes in local sea-surface salinity (indicated by δ18Osalinity) show a decoupling from global high-latitude processes (shown by the δ18Obenthic record). Long-term regional freshening started with decreasing
SSTMg/Ca at ~3.7 Ma, suggesting that changes in the tropical wind field combined with latitudinal shifts of the tropical rainbelt were related to general decreases in tropical east Pacific SST-controlled δ18Osalinity.
The similarity of Pliocene SSTMg/Ca for G. sacculifer with modern SSTs in the east Pacific, in combination with the early development of a shallow thermocline at Site 1241, gives no direct support to the idea that a permanent El Niño-like Pliocene climate might have existed during
the early Pliocene.

Document Type: Article
Research affiliation: OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-P-OZ Paleo-Oceanography
Kiel University
Refereed: Yes
Open Access Journal?: Yes
DOI etc.: 10.2973/
ISSN: 1096-7451
Date Deposited: 03 Dec 2008 16:52
Last Modified: 23 Jan 2019 13:41

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