Summer Surface CO2 Dynamics on the Bering Sea and Eastern Chukchi Sea Shelves From 1989 to 2019

By compiling boreal summer (June to October) CO2 measurements from 1989 to 2019 on the Bering and eastern Chukchi Sea shelves, we find that the study areas act as a CO2 sink except when impacted by river runoff and wind-driven upwelling. The CO2 system in this area is seasonally dominated by the biological pump especially in the northern Bering Sea and near Hanna Shoal, while wind-driven upwelling of CO2-rich bottom water can cause episodic outgassing. Seasonal surface Delta fCO(2) (oceanic fCO(2) - air fCO(2)) is dominantly driven by temperature only during periods of weak CO2 outgassing in shallow nearshore areas. However, after comparing the mean summer Delta fCO(2) during the periods of 1989-2013 and 2014-2019, we suggest that temperature does drive long-term, multi-decadal patterns in Delta fCO(2). In the northern Chukchi Sea, rapid warming concurrent with reduced seasonal sea-ice persistence caused the regional summer CO2 sink to decrease. By contrast, increasing primary productivity caused the regional summer CO2 sink on the Bering Sea shelf to increase over time. While additional time series are needed to confirm the seasonal and annual trajectory of CO2 changes and ocean acidification in these dynamic and spatially complex ecosystems, this study provides a meaningful mechanistic analysis of recent changes in inorganic carbonate chemistry. As high-resolution time series of inorganic carbonate parameters lengthen and short-term variations are better constrained in the coming decades, we will have stronger confidence in assessing the mechanisms contributing to long-term changes in the source/sink status of regional sub-Arctic seas.

Automated summary

By compiling CO2 measurements from 1989 to 2019, researchers found that the Bering and eastern Chukchi Sea shelves act as a CO2 sink except under certain conditions. The CO2 system in the area is mainly controlled by the biological pump, with wind-driven upwelling causing episodic outgassing. Temperature is the dominant driver of seasonal surface Delta fCO(2), and long-term patterns in Delta fCO(2) are influenced by temperature as well. Rapid warming in the northern Chukchi Sea has decreased the summer CO2 sink, while increasing primary productivity has increased it on the Bering Sea shelf.