Deglacial changes in subarctic Pacific surface water hydrography and nutrient dynamics – a fresh perspective from diatom oxygen and silicon stable isotopes

Abstract:

Deglacial variations in upper ocean stratification in high latitudes are generally thought to have played a key role in changing atmospheric CO₂ concentrations. Deglacial destratification especially in the Southern Ocean may have provided a pathway for CO₂ exchange between the deep ocean and the atmosphere, thereby increasing atmospheric CO₂ concentrations e.g. during Heinrich Stadial 1, as recorded in ice cores. During the past decade the subarctic Pacific received increased paleoceanographic attention with the aim to examine its potential for influencing the past nutrient cycle and oceanic release of CO₂ via deep/intermediate-water formation, upwelling as well as associated changes in biogenic productivity. Today, the subarctic Pacific is considered a weak sink for CO₂, despite incomplete nutrient utilization in surface waters. Accordingly, changes in subarctic Pacific upper ocean stratification and/or biological nutrient utilization and export production have the potential to effectively influence the oceanic-atmospheric gas exchange.

Here, we present diatom oxygen and silicon isotope records from the North-East Pacific (Core SO202-27-6, Alaskan Gyre) and the North-West Pacific (Core MD01-2416, Western Subarctic Gyre), to investigate the development of surface water hydrography and silicic acid utilization in the open subarctic Pacific over the last glacial-interglacial transition. Diatom isotope records are interpreted in combination with new records e.g. on subsurface water development, export production, sea surface temperature (alkenone-based) and sea ice. The obtained results enable a fresh perspective on the relationship between subarctic Pacific and North Atlantic climate development and provide new information on the role of the subarctic Pacific during the last deglacial atmospheric CO₂ development.