Evolution of Ocean Productivity in the Sub-Tropical West Pacific Ocean Across the Last Deglaciation

摘要

Changes in marine export productivity may have played a prominent role in the atmospheric CO_2 rise and associated warming of the last deglaciation, via their impact on the air-sea partitioning of CO_2. To study the evolution of marine export production in the western subtropical Pacific Ocean during the last deglaciation and the mechanisms governing these changes, ~(230)Th-normalization has been applied on a sediment core retrieved from the Okinawa Trough. The reconstructed export productivity record shows two prominent peaks, centered around 14 and 17 ka. Given that phytoplankton growth at our study site is limited by the availability of nutrients today, elevated macro-nutrient supply must have been responsible for sustaining the two deglacial productivity peaks. Specifically, higher nutrient supply originating from the subpolar gyre via subsurface water advection, with enhanced vertical mixing in the subpolar gyre during early HS1 and enhanced wind-driven upwelling during the B/A, would have fueled phytoplankton productivity and export. In contrast, reduced nutrient supply to the euphotic zone caused by gyre circulation changes would have lead to decreased export production during the Holocene. These observations lend support to a predominant control of nutrient availability on the evolution of the marine carbon cycle in the subtropical west Pacific Ocean across the last deglaciation.