Factors Controlling the Sea Surface Partial Pressure of Carbon Dioxide in Upwelling Regions: A Case Study of the Southern East China Sea Before and After Typhoon Maria

Abstract

AbstractUpwelling regions, which account for 10%–20% of the global ocean's primary production but occupy only 3% of its area, play an important role in the global ocean carbon cycle. However, controlling factors of the partial pressure of carbon dioxide (pCO2) in upwelling regions before and after typhoons remain unclear. Sea surface pCO2 was measured in two upwelling regions of the southern East China Sea (sECS) before (6–9 July 2018) and after (13–17 July 2018) Typhoon “Maria.” Surface pCO2 values were 325.1 ± 18.3 and 322.9 ± 17.4 μatm on the shelf break and middle shelf, respectively, before the typhoon. After the typhoon, the surface pCO2 values dropped to 315.5 ± 15.9 and 305.7 ± 7.2 μatm on the shelf break and middle shelf, respectively. The analysis shows that factors controlling pCO2 variations are the temperature effect (38% to 40%), net biological activities (−33% to −36%), and mixing (−24%), irrespective of whether the measurements were taken before or after the typhoon. During our study period, the upwelling regions in sECS acted as strong sinks of atmospheric CO2 (−4.2 ± 1.2 to −14.1 ± 1.2 mmol m−2 d−1). We suggested that the temperature change, net biological activities, and mixing during the upwelling process characterized the biogeochemical responses over the sECS.