Coupled climate and subarctic Pacific nutrient upwelling over the last 850,000 years

Highlights

• Increased Bering Sea sea ice caused expansion of intermediate water in glacials.

• Intermediate water expansion inhibited deep water nutrient supply to surface waters.

• Region contributed to global ocean-air CO₂ exchange on glacial timescales.

• Tight correlation between subarctic nutrient upwelling and global CO₂.

Abstract

High latitude deep water upwelling has the potential to control global climate over glacial timescales through the biological pump and ocean-atmosphere CO₂ exchange. However, there is currently a lack of continuous long nutrient upwelling records with which to assess this mechanism. Here we present geochemical proxy records for nutrient upwelling and glacial North Pacific Intermediate Water (GNPIW) formation in the Bering Sea over the past 850 kyr, which demonstrates that glacial periods were characterised by reduced nutrient upwelling, when global atmospheric CO₂ and temperature were also lowered. We suggest that glacial expansion of sea ice in the Bering Sea, and the simultaneous expansion of low nutrient GNPIW, inhibited vertical mixing and nutrient supply across the subarctic Pacific Ocean. Our findings lend support to the suggestion that high latitude sea ice and the resultant intermediate water formation, modulated deep water upwelling and ocean-atmosphere CO₂ exchange on glacial-interglacial timescales.