[A-HW32] Material transportation and cycling in aquatic ecosystems; from headwaters to coastal areas

[AHW32-15] Acidic fresh submarine groundwater discharge around mud diapirs in southwestern Taiwan

*Hon-Kit Lui¹, Chen-Tung Arthur Chen¹, Wei-Ping Hou², Rae Chang¹ (1.Department of Oceanography, National Sun Yat-sen University, Kaohsiung 80424, Taiwan, 2.Taiwan Ocean Research Institute, National Applied Research Laboratories, Kaohsiung 80143,Taiwan. )

Keywords:submarine groundwater discharge, SGD, pH, saturation state of calcium carbonate, mud diapirs

Submarine groundwater discharge (SGD) is an important source of nutrients in many coastal regions, yet little information is available on its carbonate chemistry and the controlling factors. Our SGD samples collected around the coast of southwestern Taiwan contain relatively high total alkalinity (TA) and dissolved inorganic carbon (DIC) concentrations, but low in salinity, dissolved oxygen, pH and the saturation state of calcium carbonate (Ω_ara). Of note is that these high-carbon but low-pH SGD samples are largely located in the coasts with mud diapir outcrops, such as in the coasts of Liuqiu Island, Nanwan Bay, and Chaishan Mountain. The Ω_ara, however, is far below saturation, adversely affecting the marine lives with their skeletons or shells made of calcium carbonate (e.g. coral, shellfish). Meanwhile, seawater near submarine volcanoes with depths 370m and 520m off southwestern Taiwan also contain relatively low pH. Data from the Liuqiu Island suggest that the acidic properties of the SGD are a result due to the physical mixing between seawater and high TA and DIC but low pH and Ω_ara fresh groundwater. Such a result is consistent with our data that some lake waters located nearby the mud diapir regions have distinctly high TA but low pH and Ω_ara values, and the reason deserves further investigation.