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Fresh and saline submarine groundwater discharge as sources of carbon and nutrients to the Japan Sea
Journal article   Open access   Peer reviewed

Fresh and saline submarine groundwater discharge as sources of carbon and nutrients to the Japan Sea

Alex Cabral, Ryo Sugimoto, Makoto Taniguchi, Douglas Tait, Toshimi Nakajima, Hisami Honda and Isaac R. Santos
Marine chemistry, Vol.249, 104209
20/02/2023
DOI: https://doi.org/10.1016/j.marchem.2023.104209
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Fresh and saline submarine groundwater discharge as sources of carbon and nutrients to the Japan Sea 9.09 MBDownloadView
Published (Version of record)CC BY-NC-ND V4.0,  Open Access
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Fresh and saline submarine groundwater discharge as sources of carbon and nutrients to the Japan SeaView
Published (Version of record)CC BY-NC-ND V4.0,  Open

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Abstract

SGD River Bay Radium isotopes DIC DOC DIN Phosphate Chlorophyll
Submarine groundwater discharge (SGD) is an important pathway for carbon and nutrients to the coastal ocean, sometimes exceeding river inputs. SGD fluxes can have implications for long-term carbon storage, ocean acidification and nutrient dynamics. Here, we used radium (223Ra and 226Ra) isotopes to quantify SGD-derived fluxes of dissolved inorganic (DIC) and organic (DOC) carbon, nitrate (NO3−), nitrite (NO2−), ammonium (NH4+) and phosphate (PO43−) in a spring-fed coastal bay in the Japan Sea. The average coastal water residence times using 223Ra/226Ra ratios was 32.5 ± 17.9 days. Fresh and saline SGD were estimated using a radium mixing model with short- and long-lived isotopes. The volume of fresh SGD entering the bay (4.6 ± 4.6 cm day−1) was more than twice that of the volume of saline SGD (1.9 ± 2.1 cm day−1). Fresh SGD (mmol m2 day−1) was the main source of DOC (2.7 ± 2.6), DIC (13.9 ± 13.7), PO43− (0.3 ± 0.3) and NO3− (6.6 ± 6.5) to the coastal ocean, whereas saline SGD was the main source of NH4+ (0.2 ± 0.2). Total SGD-derived carbon and nutrient fluxes were between 4 and 7 and 2–16 times greater than local river inputs. Positive correlations between chlorophyll-a, 226Ra and δ13C-DIC indicate that SGD significantly (p < 0.05) enhances primary productivity nearshore. Overall, fresh SGD of nitrogen and carbon to seawater drove chlorophyll-a, decreased DIC/Alkalinity ratios, and modified the carbonate biogeochemistry of the coastal ocean.

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