Effect of submarine groundwater discharge on the coastal ocean inorganic carbon cycle

Abstract

Using radium (Ra) isotopes, we estimate that the average submarine groundwater discharge (SGD) flux (marine plus terrestrial groundwater) into the southwest Florida Shelf (SWFS) was 20 6 10 3 10 7 and 18 6 8 3 10 7 m 3 d 21 in July and October 2009, respectively. The terrestrial groundwater flux was the same order of magnitude as the local river discharge in July 2009. Shelf-water total alkalinity (TAlk) and dissolved inorganic carbon (DIC) concentrations could not be explained by river inputs alone, suggesting a groundwater source. We estimated SGD fluxes of TAlk and DIC using the SGD flux derived from a shelf-water 226 Ra budget and TAlk and DIC concentration differences between the groundwater and seawater. These fluxes were also determined by the observed TAlk : 226 Ra and DIC : 226 Ra relationships in the shelf water, and the 226 Ra flux sustained by SGD. These TAlk and DIC fluxes were 11-71 times more than the combined input of local rivers, suggesting that SGD was the dominant source of TAlk and DIC to the SWFS during 2009. SGD is an important component of the inorganic carbon budget for the coastal ocean.

Evaluation of Water Residence Time, Submarine Groundwater Discharge, and Maximum New Production Supported by Groundwater Borne Nutrients in a Coastal Upwelling Shelf System

“…In this study, the mixing loss is calculated based on the 226/228 Ra excesses and the average water residence time calculated with equations (1) and (2). Therefore, the uncertainties in the SGD estimate mainly stem from the variability of water residence time, the uncertainties of 226 Ra and 228 Ra excess estimates, and the variation of radium activities in groundwater end-member, as suggested in other similar SGD studies (Gonneea et al, 2013;Liu et al, 2012, Q. Liu et al, 2014Rodellas et al, 2017). The uncertainties in estimates of 226 Ra and 228 Ra excesses are mainly from the measurement error and have ranges of 15-20% and 7-12%, respectively (Q. .…”

Controls on the sources and cycling of dissolved inorganic carbon in the Changjiang and Huanghe River estuaries, China: 14C and 13C studies

“…Studies of riverine DIC have concluded that contributions to the riverine DIC pool are mainly from three potential sources: (1) atmospheric CO 2 invasion through air‐river exchange; (2) chemical weathering of carbonate and silicate rocks consuming CO 2 in the soil and atmosphere; (3) CO 2 derived from respiration of OM in both drainage basin soils and river water (Richey et al ; Zhang et al ,b; Raymond et al ; Cai et al ; Goldsmith et al ; Zeng et al ). Studies have also shown that in some cases, groundwater input of DIC derived from weathering or OM respiration could also be an important DIC source in river basin (Liu et al ; Ishikawa et al ). Atmospheric CO 2 invasion through air‐river exchange alone is a relatively small fraction of river DIC as calculated based on Henry's Law.…”

Temporal variations of groundwater tables and implications for submarine groundwater discharge: a 3-decade case study in central Japan

“…The groundwater aquifer in Uozu is sand. Thus, according to Darcy's law, the groundwater flow rate is correlated with the hydraulic gradient (Mulligan and Charette, 2006). The SGD flux is positive for the groundwater table.…”

“…The groundwater flows down a gradient, and SGD occurs wherever a coastal aquifer is connected to the sea (Chen et al, 2005;Zhang and Mandal, 2012). SGD has been recognized as not only an important source of freshwater discharge into the ocean, but also a valuable component of the hydrological cycle between the terrestrial groundwater system and the marine environment (Church, 1996;Taniguchi et al, 2002;Hatta and Zhang, 2013;Liu et al, 2014). The estimation of global SGD varies from 0.2 to 10 % of the river flow (Burnnet et al, 2001).…”