Decadal Variation And Major Controls Of Carbon Sink In The North Pacific

Ocean is one of the major sinks of the anthropogenic CO2,and the sequestration rate of CO2 by the ocean is increasing with the increase of anthropogenic CO2 emission.The North Pacific is the largest ocean in the Northern Hemisphere and it is affected greatly by human activities,which might have an important impact to the global ocean carbon cycle and export productivity.This study focuses on the decadal variation and major controls of carbon sink in the North Pacific based on the sea surface CO2 partial pressure((pCO2)sw)and other parameters over the past 30 years.(pCO2)sw shows great spatial variation in the North Pacific,with the overall characteristics of low-latitude area>high-latitude area>middle-latitude area.In the lowlatitude zone,both(pCO2)sw and its increasing rate are higher than that of atmospheric pCO2((pCO2)air);in the middle-latitude zone,(pCO2)sw is lower than(pCO2)air and they show similar increasing rates;in the high-latitude zone,both(pCO2)sw and it’s increasing rate are lower than(pCO2air.Distributions of air-sea CO2 fluxes in the North Pacific vary spatially.Generally,the low-latitude area is the source of CO2,while the middle and high-latitude areas are sinks.Strong carbon source is in the central and eastern equatorial Pacific between 5°S-5°N,and strong carbon sink is in the western and central Pacific between 35°～45°N.The highest carbon sink is located in the Northwestern Pacific east of Japan.There is also spatial difference in the seasonal and decadal variations of air sea CO2 fluxes in the North Pacific.In the low-latitude zone,the maximum and minimum carbon sources ocurr in summer and winter,respectively,which is mainly influenced by vertical mixing on(pCO2)sw.In the middle and high-latitude zones,the maximum and minimum carbon sinks are in winter/spring and summer/autumn,respectively.The seasonal variation of carbon sink in the middle-latitude zone are mainly controlled by sea surface temperature and wind speed;the seasonal variation of carbon sink in the high-latitude area is mainly regulated by(pCO2)sw.During 1988 to 2019,the North Pacific is generally a sink of atmospheric CO2.The average air-sea CO2 flux in the North Pacific is estimated to be-0.22 PgC yr-1,with an increasing rate of-0.0025 PgC yr-1.The increasing carbon source in the low-latitude zone is mainly affected by the increase of wind speed and faster increasing rate of(pCO2)sw than(pCO2)air,with the latter is the major controlling factor.The increasing carbon sink in the middle and high-latitude areas are mainly caused by the slower increasing rate of(pCO2)sw than(pCO2)air,and the increase of wind speed.