Assessing the effect of strong wind events on the transport of particulate organic carbon in the Changjiang River estuary over the last 40 years

In the context of global climate change, the frequency of strong wind events are increasing. These extreme events have more significantly altered the marine environment than normal events; however, relevant in-situ measurements are usually lacking for such extreme events. In our previous study, we established a method to estimate particulate organic carbon (POC) flux by combining satellite data with a numerical model. Based on this method, this study aimed to quantify the impact of typhoons and strong seasonal winds (with a wind speed of >10.8 m/s) on POC flux and transport outside the Changjiang River estuary (CRE). Wind data in CRE during 2010-2019 revealed that the annual durations of strong winds (849.7 +/- 111.7 h/yr) and typhoons (204.4 +/- 64.5 h/yr) increased by 15.3% and 143.3%, respectively, compared to those during 1980-2009. The seasonal durations of typhoons and strong winds during 2010-2019 increased in autumn and in winter and spring, respectively. Considering northward Typhoon Bolaven as an example, we found that its passage strengthened the southward POC transport and the POC erosion outside CRE. Four scenarios with special wind characteristics were further simulated to analyze the annual effect of strong winds on POC transport. The proportion of northerly winds in strong winds affected the southward POC transport, whereas strong winter winds triggered 23.0% of the southward transport of POC flux. Finally, based on eight groups of numerical simulation experiments, the increasing proportion of northerly winds in strong wind events during 2010-2019 enhanced the southward POC transport and POC erosion by 15.9% and 2.8%, respectively, compared with the transport and erosion during 1980-2009. The increased durations of typhoons in autumn and strong winds in winter are expected to increase the proportion of northerly winds in extreme winds, thus enhancing the southward POC transport in CRE and affecting the southeastern coast of China. The combination of high-spatiotemporal-resolution satellite data and the numerical model provides novel insights into the impact of short-term wind extremes on POC transport in the estuary, with important implications for relevant biogeochemical processes, in particular, carbon cycle, in the coastal ocean.