Unveiled groundwater flushing from the deep seafloor in Suruga Bay

Unveiling the submarine groundwater discharge (SGD) to the sea is an essential part of understanding groundwater flux and its ecological impact on marine ecosystems. Numerous studies have been conducted to estimate the SGD by measuring the chemical parameters, such as radioisotopes and heat flow. However, elucidating the SGD from the deep seafloor has not been efficient or effective. The aim of this study is to show the SGD in Suruga Bay (Japan) at a depth of 100 m, which was found based on the previously conducted simulation modeling using GETFLOWS. Suruga Bay is in relatively close proximity to Mt. Fuji, a volcanic mountain that has a large groundwater reservoir at its base. The observation location was indicated by simulation modeling, and a suggested SDG point was revealed through repeated in situ observations. The results of an incubation experiment conducted to estimate the function of springwater, flushing out from the deep sea bottom, suggest that phosphate-rich groundwater may enhance microbial growth. This may lead to the initiation of a microbial food web in deep coastal waters.