Shelf‐Scale Submarine Groundwater Discharge in the Northern South China Sea and East China Sea and its Geochemical Impacts

Abstract

To evaluate biogeochemical impacts of shelf‐scale submarine groundwater discharge (SGD), the northern South China Sea (NSCS) and the East China Sea (ECS) shelf were chosen for this study. Based on a three end‐member mixing model and a Ra box model, SGD fluxes on NSCS (west and east of the Pearl River Estuary, WPRE and EPRE, respectively) and ECS shelf in winter were estimated to be 3.8–9.5 × 109, 1.4–2.2 × 109 and 0.7–2.2 ×1010 m3 d−1, respectively. Our results were equivalent to the SGD flux to the entire Mediterranean Sea, and were an order of magnitude greater than fluxes to the South Atlantic Bight. SGD associated nutrient fluxes into WPRE, EPRE and ECS were almost in the same order of magnitude, 0.2–2.4 × 103 mol m−1 d−1 for dissolved inorganic nitrogen, 1.2–9.8 mol m−1 d−1 for soluble reactive phosphorus, and 0.4–3.4 × 103 mol m−1 d−1 for dissolved silicate. Moreover, SGD delivered 1.1–2.8 × 104, 0.6–0.9 × 104, 1.7–5.1 × 104 mol m−1 d−1 dissolved inorganic carbon and 1.1–2.7 × 104, 0.5–0.8 × 104, 1.6–4.8 × 104 mol m−1 d−1 total alkalinity to WPRE, EPRE and ECS, respectively. Shelf‐scale SGD is a significant source of nutrients and carbon, and may pose great impacts on regional marine ecosystems.

Spatial and vertical distribution of 129I and 127I in the East China Sea: Inventory, source and transportation

“…The East China Sea (ECS), as a typical ocean marginal sea, contains oceanic input currents, seasonally variable coastal currents and large river inputs. It has been reported that the turnover time of the ECS shelf water was approximately 1.3 yrs and that those of coastal and estuarine waters were much lower, about 30 days (Tan et al, 2018;Wang et al, 2018); these times are significantly lower than that the residence time of 129 I in ocean water. Although the solubility of i 129 Iodine is still highly soluble in estuaries is relatively decreased (Kd: < 200 L kg -1 , Takata et al, 2013) compared to that in the ocean, it is still highly soluble, and it can thus be used to trace the exchange of water masses in marginal seas, even with abundant sediment discharge from rivers.…”

Saltwater Intrusion and Submarine Groundwater Discharge: Acceleration of Biogeochemical Reactions in Changing Coastal Aquifers

“…We encourage similar studies to reconstruct the history of SGD along other coastlines and specifically to evaluate its effect on the receiving waters. Although the measurement of 226 Ra in small samples is time-consuming (Hsieh and Henderson, 2011;Yaala et al, 2019), the 226 Ra/Ca ratios in corals may provide a direct link to the numerous studies of SGD using radium isotopes (Charette et al, 2008;Tan et al, 2018;Tamborski et al, 2020).…”

Transport of Radium and Nutrients Through Eastern South African Beaches

“…The 2:1 line is shown for reference. Data from (b) Patos Lagoon from Windom et al (); from (c) East and South China Seas from Tan et al (); from (d) Wadden Sea from Moore et al (); from (e) North Carolina, South Carolina, and Georgia beaches from Peterson et al () and Table S1; and from (f) Smithtown Bay from Tamborski et al ().…”

“…One primary difference is that the activity of 228 Ra dissolved in most St. Lucia beach porewater is 4 to 40 times lower than the activities measured in other beaches. Numerous studies have shown that the high 228 Ra activities measured in these other upper porewaters are due to the supply of 228 Ra from external sources, namely, groundwater (Moore, , ; Rama & Moore, ; Tan et al, ; Windom et al, ). We therefore argue that the low 228 Ra activities measured in St. Lucia must be due to differences in the groundwater components that flow into this coastal system.…”