Air-sea CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; fluxes on the Bering Sea shelf

N R Bates,M A Jeffries,J T Mathis

doi:10.5194/bg-8-1237-2011

Abstract

Abstract. There have been few previous studies of surface seawater CO2 partial pressure (pCO2) variability and air-sea CO2 gas exchange rates for the Bering Sea shelf. In 2008, spring and summertime observations were collected in the Bering Sea shelf as part of the Bering Sea Ecological Study (BEST). Our results indicate that the Bering Sea shelf was close to neutral in terms of CO2 sink-source status in springtime due to relatively small air-sea CO2 gradients (i.e., ΔpCO2 and sea-ice cover. However, by summertime, very low seawater pCO2 values were observed and much of the Bering Sea shelf became strongly undersaturated with respect to atmospheric CO2 concentrations. Thus the Bering Sea shelf transitions seasonally from mostly neutral conditions to a strong oceanic sink for atmospheric CO2 particularly in the "green belt" region of the Bering Sea where there are high rates of phytoplankton primary production (PP)and net community production (NCP). Ocean biological processes dominate the seasonal drawdown of seawater pCO2 for large areas of the Bering Sea shelf, with the effect partly countered by seasonal warming. In small areas of the Bering Sea shelf south of the Pribilof Islands and in the SE Bering Sea, seasonal warming is the dominant influence on seawater pCO2, shifting localized areas of the shelf from minor/neutral CO2 sink status to neutral/minor CO2 source status, in contrast to much of the Bering Sea shelf. Overall, we compute that the Bering Sea shelf CO2 sink in 2008 was 157 ± 35 Tg C yr−1 (Tg = 1012 g C) and thus a strong sink for CO2.

Highlights

The Bering Sea shelf is one of the most productive marine ecosystems in the global ocean
Spring observations of surface seawater pCO2 ranged from ∼180 μatm to ∼520 μatm across the Bering Sea shelf. pCO2 values ranged from ∼ −200 μatm to ∼+130 μatm (Fig. 5) with large spatial variability in the potential for uptake of atmospheric CO2 or release of CO2 from the ocean to the atmosphere
Spring observations in 2008 of surface seawater pCO2 ranged from ∼180 μatm to ∼520 μatm across the Bering Sea shelf but the presence of sea-ice and relatively small pCO2 gradients suggest that much of the Bering Sea shelf was close to neutral in terms of CO2 sink-source status

Summary

Introduction

The Bering Sea shelf is one of the most productive marine ecosystems in the global ocean. On the extensive continental shelf (Fig. 1), seasonally high rates of pelagic phytoplankton primary production (PP) supports large populations of marine mammals and seabirds, and coastal fisheries of Alaska. But sporadic blooms of coccolithophores, which are CaCO3-producing phytoplankton (class Prymnesiophyceae) have been observed in the SE Bering Sea shelf (e.g., Stockwell et al, 2001; Broerse et al, 2003; Merico et al, 2004, 2006). In contrast to the shelf, the open ocean regions of the western Bering Sea is much less productive and has been described as a high nutrient, low chlorophyll (HNLC) region (Banse and English, 1999)

Results

Discussion

Conclusion