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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 which is the largest US coastal shelf sea. 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 sinksource status in springtime due to relatively small air-sea CO2 gradients (i.e., ÉpCO2) 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 atmosphere 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. 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. We compute that the Bering Sea shelf CO2 sink in 2008 was 157 TgCyr-1 (Tg=1012 g C) and a stronger sink for CO2 than previously demonstrated by other studies. [ABSTRACT FROM AUTHOR]

Winter CO2 flux is an important element to assess when estimating the annual carbon budget on regional and global scales. However, winter observation frequency is limited due to the extreme cold weather in sub-Arctic and Arctic ecosystems. In this study, the continuous monitoring of winter CO2 flux in black spruce forest soil of interior Alaska was performed using NDIR CO2 sensors at 10, 20, and 30cm above the soil surface during the snow-covered period (DOY 357 to 466) of 2006/2007. The atmospheric pressure was divided into four phases: >1000 hPa (HP: high pressure); 985

2 flux. The winter CO2 fluxes were 0.22±0.02, 0.23±0.02, 0.25±0.03, and 0.17±0.02gCO2-C/m² d-1 for the HP, IP, LP, and MP phases, respectively. Wintertime CO2 emission represents 20% of the annual CO2 emissions in this boreal black spruce forest soil. Atmospheric temperature, pressure, and soil temperature correlate at levels of 56, 25, and 31% to winter CO2 flux, respectively, during the snow-covered period of 2006/2007, when snow depth experienced one of its lowest totals of the past 80 years. Atmospheric temperature and soil temperature at 5 cm depth, modulated by atmospheric pressure, were found to be significant factors in determining winter CO2 emission and fluctuation in snowpack. Regional/global process-based carbon cycle models should be reassessed to account for the effect of winter CO2 emissions, regulated by temperature and soil latent-heat flux, in the snow-covered soils of Arctic and sub-Arctic terrestrial ecosystems of the Northern Hemisphere. [ABSTRACT FROM AUTHOR]