Millennial-scale deglacial reorganizations of the western Pacific North Equatorial Current inferred from Sulu Sea thermocline reconstructions
Abstract
The North Equatorial Current bifurcation latitude (NECBL) is the dominant control on the strength of the Kuroshio Current and as a result, is a strong control on Japanese, eastern Chinese, Korean, and North Pacific climate. By modulating the strength of the Kuroshio Current, the NECBL also controls thermocline salinity in the lower latitude South China and Sulu Seas by regulating the influx of western Pacific thermocline water to these marginal marine basins. We generated high resolution oxygen isotope (δ18O) and trace metal (Mg/Ca, Cd/Ca, Mn/Ca) records spanning ~20-5 ka using the thermocline-dwelling foraminifera Globorotalia tumida from Sulu Sea sediment core MD97-2141 in order to evaluate thermocline variability in this region. Our data provide one of the few high-resolution records of NECBL variability that extends beyond the instrumental era, capturing the climatically variable transition from the Last Glacial Maximum (LGM) to the Holocene (Termination I). We show thermocline freshening events during the Bølling-Allerød (14.6-12.85 ka) and start of the Holocene that we conclude were driven by southward shifts in the NECBL due to a northward shift in the thermal equator. These freshening events were coeval with larger monsoon driven surface freshening events evident in previously published δ18O and Mg/Ca records from the surface dwelling Globigerinoides ruber in the same core. Surface and thermocline salinity increase during the Younger Dryas Chronozone (12.85-11.65 ka) and from ~9.3-8.4 ka coinciding with major cooling events in the Northern Hemisphere (the Younger Dryas and 9.3 ka event) and apparent weakening of the Atlantic Meridional Overturning Circulation. We interpret these increases in thermocline salinity to result from northward shifts in the NECBL. Modern instrumental records show that the strength of flow through the Sulu Sea and Karimata Strait (southernmost South China Sea), is controlled by the NECBL and strongly influences the temperature and depth of the Indonesian Throughflow (ITF) through the Makassar Strait. Our Sulu Sea thermocline record suggests that shifts in the NECBL during Termination I may have modulated the character of the ITF for extended periods since the LGM and those changes could have propagated downstream to the Indian Ocean and Agulhas Current.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMPP51C1392W
- Keywords:
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- 1616 Climate variability;
- GLOBAL CHANGE;
- 1631 Land/atmosphere interactions;
- GLOBAL CHANGE;
- 3022 Marine sediments: processes and transport;
- MARINE GEOLOGY AND GEOPHYSICS;
- 3036 Ocean drilling;
- MARINE GEOLOGY AND GEOPHYSICS