Early Deglacial Changes in North Pacific Surface and Deep-Water Circulation -- the Record of C14 Reservoir Ages and Sea Surface Salinities

Near the end of the Last Glacial Maximum, deep and intermediate waters in the subarctic North Pacific had apparent ventilation ages of 3300-3600 yr. 14C reservoir ages of surface waters varied from 1200-1700 yr, if accepting the results of the 14C plateau tuning method (Sarnthein et al., 2007) instead of assuming a constant glacial average value of 570 yr (Broecker and Barker, 2007). With the onset of H1 near 17,500 cal. yr BP (GISP2 record of Meese and Sowers, 1997; Hulu Cave record of Wang et al., 2001) surface water ages in the subarctic northwest Pacific started to drop to 300 yr. This low value suggests the onset of a phase of deep-water convection in the northwest Pacific, which is also reflected by an abrupt 1200-to-1500-yr drop in the ages of both upper deep waters (2300 m w.d.) in the subarctic northwest Pacific and lower deep waters (3600 m w.d.) in the northeast Pacific. The deep penetrating circulation change implies that major portions of the North Pacific Ocean underwent a significant increase in deep and intermediate-water ventilation over H1 times, which differs from previous assumptions. This may have great implications for the "Conveyor Belt" concept and a better understanding of a coeval 190-permil shift in atmospheric 14C. The onset of deep-water formation near 17.5 ka may be linked to a major salinity increase in the subarctic northwest Pacific (up to 36 psu), which in turn may result from a reduced freshwater supply by the Kuroshio Current which collects all major rivers of Southeast Asia and feeds the Pacific subpolar gyre like a rain gully. This freshwater supply strongly decreased around 17.5 ka with the abrupt start of severe Southeast Asian aridity, as documented in the Hulu Cave. Broecker and Barker, 2007, EPSL 256, 90-99. Meese and Sowers, 1997, JGR 102, 26,411-26,423. Sarnthein et al., 2007, AGU Monograph 173, 175-198. Wang et al., 2001, Science 294, 2345-2348.