Deglacial development of (sub) sea surface temperature and salinity in the subarctic northwest Pacific: Implications for upper‐ocean stratification

Abstract

Based on models and proxy data, it has been proposed that salinity‐driven stratification weakened in the subarctic North Pacific during the last deglaciation, which potentially contributed to the deglacial rise in atmospheric carbon dioxide. We present high‐resolution subsurface temperature ( T Mg/Ca ) and subsurface salinity‐approximating (δ 18 O ivc‐sw ) records across the last 20,000 years from the subarctic North Pacific and its marginal seas, derived from combined stable oxygen isotopes and Mg/Ca ratios of the planktonic foraminiferal species Neogloboquadrina pachyderma (sin.). Our results indicate regionally differing changes of subsurface conditions. During the Heinrich Stadial 1 and the Younger Dryas cold phases, our sites were subject to reduced thermal stratification, brine rejection due to sea‐ice formation, and increased advection of low‐salinity water from the Alaskan Stream. In contrast, the Bølling‐Allerød warm phase was characterized by strengthened thermal stratification, stronger sea‐ice melting, and influence of surface waters that were less diluted by the Alaskan Stream. From direct comparison with alkenone‐based sea surface temperature estimates (SST Uk′37 ), we suggest deglacial thermocline changes that were closely related to changes in seasonal contrasts and stratification of the mixed layer. The modern upper‐ocean conditions seem to have developed only since the early Holocene.