Groundwater discharge impacts marine isotope budgets of Li, Mg, Ca, Sr, and Ba

Mayfield, Kimberley K.; Eisenhauer, Anton; Ramos, D. P. Santiago; Higgins, John A.; Horner, Tristan J.; Auro, Maureen E.; Magna, Tomáš; Moosdorf, Nils; Charette, Matthew A.; Gonneea, M. E.; Brady, Carolyn E.; Komar, N.; Peucker‐Ehrenbrink, Bernhard; Paytan, Adina

doi:10.1038/s41467-020-20248-3

Cited by 60 publications

(52 citation statements)

References 37 publications

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“…Many of the trace metals have particular ecological relevance as (micro)nutrients or toxins (Salt et al, 1995;Beck et al, 2010), and their signatures may be recognizable in near-shore STE sediments (Knee and Paytan, 2011). Submarine groundwater discharge is relevant for marine alkaline earth metal composition (Mayfield et al, 2021), a significant source of rare earth elements to the ocean and could be the missing link in the global distribution of Neodynium (Nd), a key proxy for oceanic water-mass mixing (Johannesson and Burdige, 2007;Chevis et al, 2015;Paffrath et al, 2020). Formation of complexes and colloids, sorption on the surface of particles, ion exchange, and changes in speciation are some of the relevant processes that control metal mobility, reactivity and toxicity (Charette and Sholkovitz, 2006;Waska et al, 2019a).…”

Section: Metalsmentioning

confidence: 99%

“…Mixing intensity and processes in STEs will also be controlled by the amount of freshwater discharging (Luijendijk et al, 2020) or the amount of seawater recirculating (Mayfield et al, 2021). Water quality of the incoming freshwater is not known at a global scale, but, as a first crude guess, could be inferred by proxy, e.g., from land-cover (e.g., Arino et al, 2007) or soil (FAOIIASA, ISRIC et al, 2009) datasets.…”

Section: Hydrogeological Modelingmentioning

confidence: 99%

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A State-Of-The-Art Perspective on the Characterization of Subterranean Estuaries at the Regional Scale

et al. 2021

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Subterranean estuaries the, subsurface mixing zones of terrestrial groundwater and seawater, substantially influence solute fluxes to the oceans. Solutes brought by groundwater from land and solutes brought from the sea can undergo biogeochemical reactions. These are often mediated by microbes and controlled by reactions with coastal sediments, and determine the composition of fluids discharging from STEs (i.e., submarine groundwater discharge), which may have consequences showing in coastal ecosystems. While at the local scale (meters), processes have been intensively studied, the impact of subterranean estuary processes on solute fluxes to the coastal ocean remains poorly constrained at the regional scale (kilometers). In the present communication, we review the processes that occur in STEs, focusing mainly on fluid flow and biogeochemical transformations of nitrogen, phosphorus, carbon, sulfur and trace metals. We highlight the spatio-temporal dynamics and measurable manifestations of those processes. The objective of this contribution is to provide a perspective on how tracer studies, geophysical methods, remote sensing and hydrogeological modeling could exploit such manifestations to estimate the regional-scale impact of processes in STEs on solute fluxes to the coastal ocean.

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Section: Metalsmentioning

confidence: 99%

Section: Hydrogeological Modelingmentioning

confidence: 99%

A State-Of-The-Art Perspective on the Characterization of Subterranean Estuaries at the Regional Scale

et al. 2021

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“…For example, quantitative evidence from time-series data have shown the importance of rainfallinduced hydrological transport of OM from inland mangroves to the coastline through cave networks (Coutino et al, 2020). Although karst platforms account for a substantial percentage of certain trace element inputs to the ocean globally (Beck et al, 2013;Gonneea et al, 2014;Mayfield et al, 2021), point-sources of groundwater discharge only represents a (likely small) portion of these inputs. Point-source discharge, however, can influence coral reefs (Crook et al, 2012) and other local ecosystems (Moosdorf et al, 2015) while contributing to the heterogeneity of land-to-sea material fluxes along global coastlines (Luijendijk et al, 2020;Moore and Joye, 2021;Rocha et al, 2021).…”

Section: Evidence For Reduction In Organic Matter Inputs From a Mangrove Habitatmentioning

confidence: 99%

Changes in Organic Matter Deposition Can Impact Benthic Marine Meiofauna in Karst Subterranean Estuaries

Brankovits

Little

Winkler

et al. 2021

Front. Environ. Sci.

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Subsurface mixing of seawater and terrestrial-borne meteoric waters on carbonate landscapes creates karst subterranean estuaries, an area of the coastal aquifer with poorly understood carbon cycling, ecosystem functioning, and impact on submarine groundwater discharge. Caves in karst platforms facilitate water and material exchange between the marine and terrestrial environments, and their internal sedimentation patterns document long-term environmental change. Sediment records from a flooded coastal cave in Cozumel Island (Mexico) document decreasing terrestrial organic matter (OM) deposition within the karst subterranean estuary over the last ∼1,000 years, with older sediment likely exported out of the cave by intense storm events. While stable carbon isotopic values (δ13Corg ranging from −22.5 to −27.1‰) and C:N ratios (ranging from 9.9 to 18.9) indicate that mangrove and other terrestrial detritus surrounding an inland sinkhole are the primarily sedimentary OM supply, an upcore decrease in bulk OM and enrichment of δ13Corg values are observed. These patterns suggest that a reduction in the local mangrove habitat decreased the terrestrial particulate OM input to the cave over time. The benthic foraminiferal community in basal core sediment have higher proportions of infaunal taxa (i.e., Bolivina) and Ammonia, and assemblages shift to increased miliolids and less infaunal taxa at the core-top sediment. The combined results suggest that a decrease in terrestrial OM through time had a concomitant impact on benthic meiofaunal habitats, potentially by impacting dissolved oxygen availability at the microhabitat scale or resource partitioning by foraminifera. The evidence presented here indicates that landscape and watershed level changes can impact ecosystem functioning within adjacent subterranean estuaries.

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“…Globally, average dissolved δ 30 Si values in low-temperature groundwater systems (+0.2 ± 0.8 ‰) are lower than those in rivers (+1.3 ± 0.7 ‰; 1 SD; Frings et al, 2016). Similarly, groundwater fluxes from other key marine weathering proxies such as Mg, Ca and Sr also exhibit distinct isotopic compositions from global riverine averages (Mayfield et al, 2021). The lower δ 30 Si values in some groundwater systems may be due to the greater extent of water-rock interactions compared to surface waters and the dissolution of 30 Si-depleted secondary minerals (Basile-Doelsch et al, 2005;Georg et al, 2009b;Pogge von Strandmann et al, 2014).…”

Section: Introductionmentioning

confidence: 98%

“…organisms such as diatoms and vascular plants (Ding et al, 2008;De La Rocha et al, 1998;Meyerink et al, 2017). Moreover, Si isotopes are not fractionated during congruent mineral dissolution, and there is a narrow range of 30 Si values for the upper continental crust (UCC), i.e.…”

Section: Introductionmentioning

confidence: 99%

The evolution of stable silicon isotopes in a coastal carbonate aquifer on Rottnest Island, Western Australia

Martin

Meredith

Baker

et al. 2021

Hydrol. Earth Syst. Sci.

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Abstract. Dissolved silicon (dSi) is a key nutrient in the oceans, but data regarding Si isotopes in coastal aquifers are not widely available. Here we investigate the Si isotopic composition of 12 fresh and 16 saline groundwater samples from Rottnest Island, Western Australia, which forms part of the world's most extensive aeolianite deposit (the Tamala Limestone formation). In total, two bedrock samples were also collected from Rottnest Island for Si isotope analysis. The δ30Si values of groundwater samples ranged from −0.4 ‰ to +3.6 ‰ with an average +1.6 ‰, and the rock samples were −0.8 ‰ and −0.1 ‰. The increase in δ30Si values in fresh groundwater is attributed to the removal of the lighter Si isotopes into secondary minerals and potentially also adsorption onto Fe (oxy)hydroxides. The positive correlations between δ30Si values and dSi concentrations (ρ = 0.59; p = 0.02) and δ30Si values and Cl, but not dSi and Cl concentrations, are consistent with vertical mixing between the younger fresh groundwater and the deeper groundwater, which have undergone a greater degree of water–rock interactions. This has produced a spatial pattern in δ30Si across the aquifer due to the local hydrogeology, resulting in a correlation between δ30Si and tritium activities when considering all groundwater types (ρ = −0.68; p = 0.0002). In the deeper aquifer, the inverse correlation between dSi and Cl concentrations (ρ = −0.79; p = 0.04) for the more saline groundwater is attributed to groundwater mixing with local seawater that is depleted in dSi (< 3.6 µM). Our results from this well-constrained island aquifer system demonstrate that stable Si isotopes usefully reflect the degree of water–aquifer interactions, which is related to groundwater residence time and local hydrogeology. Our finding that lithogenic Si dissolution occurs in the freshwater lens and the freshwater–seawater transition zone on Rottnest Island appears to supports the recent inclusion of a marine–submarine groundwater discharge term in the global dSi mass balance. Geologically young carbonate aquifers, such as Rottnest Island, may be an important source of dSi in coastal regions with low riverine input and low oceanic dSi concentrations.

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Groundwater discharge impacts marine isotope budgets of Li, Mg, Ca, Sr, and Ba

Cited by 60 publications

References 37 publications

A State-Of-The-Art Perspective on the Characterization of Subterranean Estuaries at the Regional Scale

A State-Of-The-Art Perspective on the Characterization of Subterranean Estuaries at the Regional Scale

Changes in Organic Matter Deposition Can Impact Benthic Marine Meiofauna in Karst Subterranean Estuaries

The evolution of stable silicon isotopes in a coastal carbonate aquifer on Rottnest Island, Western Australia

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