Human activities emit many greenhouse gases and suspended particulates into the atmosphere, causing rapid changes in the global environment. To reduce carbon emissions and slow climate change, as many as 195 countries worldwide have signed the "Paris Agreement." The goal is to be at most 2℃ temperature rise this century, with 1.5℃ as the benchmark. Taiwan has also formulated climate action-related policies and responded to the United Nations Sustainability Development Goals (SDG) and the 2050 Net-Zero Emission goal. Still, ocean acidification and hypoxia have occurred partly because of global warming and the enhancement of the hydrological cycle, which have increased the frequency and intensity of extreme climate events and caused significant impacts on the social environment and economy worldwide. According to the IPCC's sixth assessment report (IPCC AR 6) on climate change and the updated information on climate change in Taiwan, Taiwan will face in the future that the dry season will become drier and the wet season wetter. The number of typhoons will decrease, but the intensity will increase. It is foreseeable that Taiwan's coastal ecosystems will be more severely impacted by climate change, degrading or even changing the functions of the ecosystems.

    Marine scientists worldwide have joined relevant research in the past two decades, but the current knowledge is still insufficient to predict future environmental and ecological changes, especially in tropical oceans. Taiwan spans tropical and subtropical waters. Our team takes geographical advantages and has conducted research in tropical oceans. Our study published in Nature Climate Change in 2017 found that because of global warming, the rate of acidification and hypoxia in the deep water of the Japan Sea in the past 65 years has been faster than that of surface water in the global oceans. This rather unexpected finding was cited in the IPCC AR 6, and we wish to extend the work to other areas of the oceans.

    The seawater around Taiwan has indeed gradually become more acidic along with freshening. As a result, the abundance of phytoplankton, zooplankton, shrimp and crab larvae, fish eggs, and larvae and juveniles in the coastal area decreased significantly when the pH dropped below 7.8. Substantial changes in multiple environmental factors, such as warming and heavy rainfall, have also resulted in changes in the composition of the sword shrimp in southwestern Taiwan waters, a northward shift in its distribution, and a decline in production (annual output from 1,200 to 200 metric tons), as well as increases in oyster pests and diseases. Many deaths and abnormalities caused by acidification and extreme rainfall were reported in southern Taiwan's intertidal coral reef ecosystem. These studies have clearly shown that various ecosystems are affected by acidification, low oxygen, and freshening. The influence of different biogeochemical mechanisms on diverse ecosystems varies accordingly. The resilience of multiple ecosystems needs individual assessment.

    This research will focus on tropical oceans affected by coupling mechanisms between anthropogenic, climate, and various ecosystems. And target (1) quantifying the changes in pH, dissolved oxygen, and salinity (background values) in different water layers in the South China Sea and West Philippine Sea over the past few decades. (2) exploring the anthropogenic effects of nutrients and organic matter in the Dongsha and Xiaoliuqiu waters; correlating natural sources and fluxes and groundwater inflow into the sea with biogeochemical cycles in seawater, seagrass beds, and coral reef ecosystems. (3) discussing the effects of acidification, anoxia, and freshening on marine organisms, coastal fisheries, and recreational services in southwestern Taiwan, and (4) exploring areas around Dongsha Atoll, Guishan Islet, Nanwan, SEATS, Sri Lanka, Tuvalu, and Palau. Through this project, we will provide scientific data on the effects of acidification, hypoxia, and freshening on tropical marine ecosystems and their susceptibility, which can be the basis of formulating our country's management strategies in response to climate change (SDG13 & SDG14) and 2050 net zero emissions.