14. Data Report: Early and Mid-Pleistocene (MIS 65-11) Summer Sea-Surface Temperature, Foraminiferal Fragmentation, and Ice-Rafted Debris Records from the Subantarctic (ODP Leg 177 Site 1090)1

Sabine Becquey2, 3 and Rainer Gersonde2


Pleistocene summer sea-surface temperatures (SSSTs) have been reconstructed from planktonic foraminifers on a composite core section recovered from the Subantarctic Zone of the Southern Ocean, applying the modern analog technique (MAT) (Fig. F1). The composite consists of core PS2489-2 and a Pleistocene splice recovered from five holes drilled at Ocean Drilling Program (ODP) Leg 177 Site 1090 and represents the past 1.83 m.y. Core PS2489-2 documents a late and mid-Pleistocene record ranging from marine isotope Stage (MIS) 14 to MIS 1. Data and results obtained from core PS2489-2, including an age model based on stable isotope measurements and 14C-AMS (accelerator mass spectrometry) datings as well as records of MAT-derived SSST, species abundance distribution of selected foraminifers, foraminiferal fragmentation, and ice-rafted debris (IRD) are presented and discussed in Becquey and Gersonde (in press). The data on stable isotope measurements, species abundance distribution, SSST, IRD, and fragmentation ratio obtained from sections recovered at Site 1090 between 10.83 and 44.54 meters composite depth (mcd), representing a period between MIS 65 and MIS 11, are presented in this report. The upper portion (MIS 11-14) of this record overlaps that obtained from core PS2489-2, allowing an accurate splice of both records. The data are also archived in the on-line PANGAEA information system at the Alfred Wegener Institute (AWI) for Polar and Marine Research, Bremerhaven Germany (www.pangaea.de).

Scientific interpretation of the Site 1090 data is presented in Becquey and Gersonde (2002) and can be summarized as follows. The record, which documents hydrographic variability in the present Subantarctic Zone of the Southern Ocean during the past 1.83 m.y. is characterized by two main periods connected by a transitional interval (Fig. F2). Between 1.83 Ma (MIS 65) and 0.87 Ma (MIS 22), the SSST estimates display minor glacial-interglacial variability ranging between 3 and 5C. This indicates that isotherms characteristic for the present Polar Front Zone (PFZ) were shifted to the north by ~7 in latitude and governed the area of the present central Subantarctic Zone during most of the early Pleistocene. This northward shift of the present PFZ isotherms may have affected the atmospheric circulation and reduced or even prevented warm-water advection from the Indian into the South Atlantic Ocean via the Agulhas Current system. The northward expansion of the Antarctic cold-water realm may have influenced the coastal upwelling regime off southwest Africa and the low-latitude climate. During the transitional period spanning from 0.87 Ma (MIS 22) to 0.43 Ma (MIS 12), glacial periods were the coldest during the Pleistocene, with temperatures corresponding to those at the present Polar Front. Interglacial SSSTs reach values that are close to present temperatures at the Subantarctic Front, which results in a slight steepening of the glacial-interglacial SSST gradient ranging between 3 and 10C. The SSST variability shows increasing 100-k.y.-dominated climatic cyclicity, which is in response to a major increase in the ice volume around the mid-Pleistocene Revolution (MPR). The SSST record obtained for the past 0.43 m.y. (since MIS 12) exhibits strong fluctuations between glacial and interglacial periods. Only during the climatic optima (MIS 11.3, 9.3, 7.5, 7.1, 5.5, and the early Holocene), does the SSST exceed present-day temperatures. The distinct meridional shifts of the Antarctic Circumpolar Current (ACC) frontal zone systems are governed by a 100-k.y.-dominated cyclicity.

The mid-Brunhes dissolution event, as well as the enhanced carbonate preservation at the MPR, appears to be part of long-term carbonate preservation oscillations of global extension. The presence in the foraminiferal fragmentation ratio of 404- and 100-k.y. cyclicities during the early Pleistocene might be indicative for an involvement of the global carbon cycle.

1Becquey S., and Gersonde, R., 2003. Data report: Early and mid-Pleistocene (MIS 65-11) summer sea-surface temperature, foraminiferal fragmentation, and ice-rafted debris records from the Subantarctic (ODP Leg 177 Site 1090). In Gersonde, R., Hodell, D.A., and Blum, P. (Eds.), Proc. ODP, Sci. Results, 177 [Online]. Available from World Wide Web: <http://www-odp.tamu.edu/publications/177_SR/chap_14/chap_14.htm>. [Cited YYYY-MM-DD]

2Alfred-Wegener Institute for Polar and Marine Research, Columbusstrasse, 27515 Bremerhaven, Germany. Correspondence author: becquey@usal.es

3Present address: University of Salamance, Faculty of Sciences, Department of Geology, 37008 Salamance, Spain.

Initial receipt: 16 January 2002
Acceptance: 6 November 2002
Web publication: 3 February 2003
Ms 177SR-117