期刊名称：Journal of Advances in Modeling Earth Systems
电子版ISSN：1942-2466
出版年度：2021
卷号：13
期号：2
页码：e2019MS002028
DOI：10.1029/2019MS002028
出版社：John Wiley & Sons, Ltd.
摘要：Climate change will affect both the mean state and seasonality of marine physical and biogeochemical properties, with important implications for the oceanic sink of atmospheric CO 2 . Here, we investigate the seasonal cycle of the air‐sea exchange of CO 2 and pCO 2, sw (surface seawater pCO 2 ) and their long term changes using the CMIP6 submission of the NASA‐GISS modelE (GISS‐E2.1‐G). In comparison to the CMIP5 submission (GISS‐E2‐R), we find that on the global scale, the seasonal cycles of the CO 2 flux and NPP have improved, while the seasonal cycles of dissolved inorganic carbon (DIC), alkalinity, and macronutrients have deteriorated. Moreover, for all ocean biogeochemistry fields, changes in skill between E2.1‐G and E2‐R display large regional variability. For E2.1‐G, we find similar modeled and observed CO 2 flux seasonal cycles in the subtropical gyres, where seasonal anomalies of pCO 2, sw and the flux are temperature‐driven, and the Southern Ocean, where anomalies are DIC‐driven. Biases in these seasonal cycles are largest in the subpolar and equatorial regions, driven by a combination of biases in temperature, DIC, alkalinity, and wind speed. When comparing the historical simulation to a simulation with an idealized increase in atmospheric pCO 2 , we find that the seasonal amplitudes of the CO 2 flux and pCO 2, sw generally increase. These changes are produced by increases in the sensitivity of pCO 2, sw to its respective drivers. These findings are consistent with the notion that the seasonality of pCO 2, sw is expected to increase due to the increase of atmospheric pCO 2 , with changes in the seasonality of temperature, DIC, and alkalinity having secondary influences. Plain Language Abstract The ocean plays an important role in removing human CO 2 emissions from the atmosphere. The removal varies seasonally, and this variability is expected to change as the ocean's carbon content increases. To predict these changes, models need to accurately simulate seasonal changes of the air‐sea exchange of CO 2 . In this study, we examine the seasonal cycle of the air‐sea exchange of CO 2 in the CMIP6 version of the NASA‐GISS modelE (GISS‐E2.1‐G). We find good agreement between the seasonal cycles in the model and observations in the subtropical latitudes, where seasonal changes are mainly caused by temperature changes, and in the Southern Ocean, where seasonal changes are mainly caused by changes in dissolved inorganic carbon (DIC). Agreement is much poorer in high latitudes and tropical waters, where discrepancies in model wind speed, temperature, DIC, and alkalinity all contribute to differences between the modeled and observed seasonal cycle of air‐sea CO 2 exchange. We further find, under future atmospheric CO 2 increase, that seasonal extremes in the air‐sea exchange of CO 2 increase in most of the ocean. Our findings support the idea that, under increased CO 2 levels, the change in the ocean's ability to take CO 2 from the atmosphere will be seasonally dependent.
