¹Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA, 02543, USA
²Department of Earth and Atmospheric Sciences, ES 351, University at Albany-SUNY 1400 Washington Ave., Albany, NY 12222
*Now at Swiss Federal Institute for Snow and Avalanche Research, Fluelastrasse 11, 7260 Davos Dorf, Switzerland (dannenmann@slf.ch)
³Institute of Marine and Coastal Sciences, and Dept. of Geology, Rutgers, The State University, 71 Dudley Road, New Brunswick, NJ 08901-8521
⁴CEREGE-CNRS, Europole Mediterranéen de l'Arbois, Aix- en-Provence Cedex, France

.Abstract.  A detailed record of planktic ?18O from a sediment core in the Sulu Sea, located between the South China Sea and the western Pacific warm pool, reveals that for the past 400 kyr (1kyr=1000 years), ?18O variability on orbital time scales is similar to that caused by changes in ice volume alone.  This result indicates that in the Sulu Sea, temperature-driven changes in planktic ?18O on orbital times scales were generally compensated for by the effect of sea level change on the local freshwater budget, as well as by changes in the tropical hydrologic cycle and their attendant effects on surface water ?18O. Increased rainfall in the some regions of the western tropical Pacific is reminiscent of La Niña conditions.  However, based on a comparison of Sulu Sea and Cariaco Basin records, we argue that the mean tropical climate state was not more La Niña-like than today on broader spatial scales.  Suborbital variability occurred throughout the past 400 kyr, suggesting little sensitivity to ice volume or to glacial-interglacial changes in tropical hydrology. Variations on 4-10kyr time scales appear to be linked to those in the North Atlantic region, suggesting a common forcing of that variability.   Although several recent studies suggest a tropical origin of suborbital variability and we do not rule it out, we suggest that current understanding of high-low latitude linkages is poor, and that  North Atlantic oscillations forced  Sulu Sea salinity variations by modulating the intensity of the East Asian summer monsoon.  We suggest that a North Atlantic origin of that tropical suborbital variability can be reconciled with weak glacial amplification in the tropics if the tropical response is nonlinear.
[PDF file, full text]

East Asian Monsoon Forcing of Suborbital Variability in the Sulu Sea During Marine Isotope Stage 3: Link to Northern Hemisphere Climate

Stefanie Dannenmann^1*, Braddock K. Linsley^1†, Delia W. Oppo², Yair Rosenthal³, Luc Beaufort^4
1Earth and Atmospheric Sciences, University at Albany, State University of New York, Albany, New York, USA
*Now at Swiss Federal Institute for Snow and Avalanche Research, Fluelastrasse 11, 7260 Davos Dorf, Switzerland (dannenmann@slf.ch)
²Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA
³Institute of Marine and Coastal Sciences, and Dept. of Geology, Rutgers, The State University, 71 Dudley Road, New Brunswick, New Jersey, USA
⁴Centre Européen de Recherche et d’Enseignement en Géosciences de l’Environnement (CEREGE), Aix-en-Provence, France
†  Corresponding author

Abstract
We have generated a new high-resolution record of variations in planktonic foraminiferal oxygen isotopes (?18O) and Mg/Ca from a sediment core (IMAGES 97-2141) in the Sulu Sea located in the Philippine archipelago of western tropical Pacific.  This record reveals distinct, suborbital-scale ?18O changes, most notably during Marine Isotope Stage 3 (MIS3) (~30,000 to 60,000 years B.P.). The amplitudes of these ?18O fluctuations (0.4 to 0.7 ‰) exceed that which can be attributed to sea level changes, and must be due to changes in sea surface conditions. In the same interval, variations in planktonic foraminifera Mg/Ca suggest that suborbital surface ocean temperature variations of 1 to 1.5°C in the Sulu Sea were not in phase with ?18O. Combined, this evidence indicates that the MIS3 millennial ?18O events in the Sulu Sea were primarily the result of changes in surface water salinity, which today is directly related to the East Asian Monsoon (EAM) and its influence on the balance between surface water contributions from the South China Sea and Western Pacific Warm Pool (WPWP).  Within dating uncertainties the MIS3 Sulu Sea ?18O suborbital variability indicates that times of fresher surface conditions in the Sulu Sea coincide with similar conditions in the WPWP [Stott et al., 2002] and also coincide with intensifications of the summer EAM as recorded in the U-Th dated Chinese (Hulu Cave) speleothem ?18O record [Wang et al., 2001] and thus by inference with interstadials in the Greenland Ice core records. Combined, these results indicate that pronounced suborbital variability in the summer EAM and Intertropical Convergence Zone (ITCZ) during MIS3 was tightly coupled with climate conditions in the northern high latitudes.
[PDF file, full text]

Decadal Sea Surface Temperature Variability in the Sub-Tropical South Pacific from 1726 to 1997 A.D.

Braddock K. Linsley¹, Gerard M. Wellington², Daniel P. Schrag³

1. Department of Earth and Atmospheric Sciences, ES 351, University at Albany-State University of New York, Albany NY. 12222
2. Department of Biology and Biochemistry, University of Houston, Houston, TX. 77204
3. Laboratory for Geochemical Oceanography, Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA. 02138

Science  v.290, pp. 1145-1148, 10 Nov 2000. [Abstract][Full text, free access]
 NOAA WDC Paleo Archive [abstract, data and figures]

 We present a 271 year record of Sr/Ca variability in a coral from Rarotonga in the South Pacific gyre.  Calibration with monthly sea surface temperature (SST) from satellite and ship measurements made in grid measuring 1° by 1° over the period from 1981 to 1997 indicates that this Sr/Ca record is an excellent proxy for SST.  Comparison with SST from ship measurements made since 1950 in a grid measuring 5° by 5° also shows that the Sr/Ca data accurately record decadal changes in SST. The entire Sr/Ca record back to 1726 shows a distinct pattern of decadal variability with repeated decadal and interdecadal SST regime shifts  greater than 0.75°C. Comparison with decadal climate variability in the North Pacific as represented by the Pacific Decadal Oscillation index (1900-1997) indicates that several of the largest decadal-scale SST variations at Rarotonga are coherent with SST regime shifts in the North Pacific.  This hemispheric symmetry suggests that tropical forcing may be an important factor in at least some of the decadal variability observed in the Pacific Ocean.