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

Upwelling 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 (pCO(2)) in upwelling regions before and after typhoons remain unclear. Sea surface pCO(2) 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 pCO(2) values were 325.1 +/- 18.3 and 322.9 +/- 17.4 mu atm on the shelf break and middle shelf, respectively, before the typhoon. After the typhoon, the surface pCO(2) values dropped to 315.5 +/- 15.9 and 305.7 +/- 7.2 mu atm 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. Plain Language Summary The variations in pCO(2) are highly dynamic in upwelling regions. During typhoon invasion, assessing pCO(2) variations in upwelling regions becomes more challenging. We conducted pCO(2) observations in the shelf break and middle shelf of the sECS before and after Typhoon "Maria." Before the typhoon, surface pCO(2) values were 325.1 +/- 18.3 and 322.9 +/- 17.4 mu atm in the shelf break and middle shelf, respectively. After the typhoon, the surface pCO(2) values dropped slightly to 315.5 +/- 15.9 and 305.7 +/- 7.2 mu atm, respectively. The pCO(2) of subsurface water should increase owing to heating in the warm surface layer and is expected to decrease owing to biological uptake and mixing during the upwelling process. The contribution of the three controlling factors (temperature change, net biological activities, and mixing) in the variation of pCO(2) was the same in the two upwelling regions before and after the typhoon. As the atmospheric pCO(2) (392.2 mu atm) was higher than the water pCO(2), the two upwelling regions acted as sinks for the atmospheric pCO2 during our study period. Our study provides a better understanding regarding the dynamics of pCO(2) in upwelling regions before and after the typhoon.