Improving the inverse modeling of a trace isotope: how precisely can radium-228 fluxes toward the ocean and submarine groundwater discharge be estimated?

Gland, Guillaume Le; Mémery, Laurent; Aumont, Olivier; Resplandy, Laure

doi:10.5194/bg-14-3171-2017

Cited by 14 publications

(17 citation statements)

References 40 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The shelf 228 Ra flux is based on the inverse models using the global seawater 228 Ra database and inventory (Kwon et al, 2014;Le Gland et al, 2017). In the South Atlantic, the average shelf 228 Ra flux is 1.7 ± 0.3 × 10 10 atoms m 2 yr -1 around the Uruguayan and South African continental margins (normalised to shelf area; Charette et al, 2016).…”

Section: Discussionmentioning

confidence: 99%

“…Subsequent downward mixing from the surface can also be used to assess vertical mixing in the upper water column (Charette et al, 2007;Sarmiento et al, 1976;van Beek et al, 2008). Radium-228 has also been used as a conservative tracer to estimate submarine groundwater discharge (SGD) (Windom et al, 2006;Moore et al, 2008;Kwon et al, 2014;Rodellas et al, 2015;Le Gland et al, 2017), river inputs (Vieira et al, 2020), continental shelf (van der Loeff et al, 1995;Charette et al, 2016;Sanial et al 2018;Kipp et al, 2018a) and hydrothermal inputs (Kipp et al, 2018b).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Radium-228-derived ocean mixing and trace element inputs in the South Atlantic

Hsieh¹,

Geibert²,

Woodward³

et al. 2020

Preprint

View full text Add to dashboard Cite

Abstract. Trace elements play important roles as micronutrients in modulating marine productivity in the global ocean. The South Atlantic around 40° S is a prominent region of high productivity and a transition zone between the nitrate-depleted Subtropical Gyre and the iron-limited Southern Ocean. However, the sources and fluxes of trace elements to this region remain unclear. In this study, the distribution of the naturally occurring radioisotope 228Ra in the water column of the South Atlantic (Cape Basin and Argentine Basin) has been investigated along a 40° S zonal transect to estimate ocean mixing and trace element supply to the surface ocean. Ra-228 profiles have been used to determine the horizontal and vertical mixing rates in the near-surface open ocean. In the Argentine Basin, horizontal mixing from the continental shelf to the open ocean shows an eddy diffusion of Kx = 1.7 ± 1.4 (106 cm2 s−1) and an integrated advection velocity w = 0.6 ± 0.3 cm s−1. In the Cape Basin, horizontal mixing is Kx = 2.7 ± 0.8 (107 cm2 s−1) and vertical mixing Kz = 1.0–1.5 cm2 s−1 in the upper 600 m layer. Three different approaches (228Ra-diffusion, 228Ra-advection and 228Ra/TE-ratio) have been applied to estimate the dissolved trace-element fluxes from shelf to open ocean. These approaches bracket the possible range of off-shelf fluxes from the Argentine margin to be: 3.8–22 (× 103) nmol Co m−2 d−1, 7.9–20 (× 104) nmol Fe m−2 d−1 and 2.7–6.5 (× 104) nmol Zn m−2 d−1. Off-shelf fluxes from the Cape margin are: 4.3–6.2 (× 103) nmol Co m−2 d−1, 1.2–3.1 (× 104) nmol Fe m−2 d−1 and 0.9–1.2 (× 104) nmol Zn m−2 d−1. On average, at 40° S in the Atlantic, vertical mixing supplies 0.4–1.2 nmol Co m−2 d−1, 3.6–11 nmol Fe m−2 d−1, and 13–16 nmol Zn m−2 d−1 to the euphotic zone. Compared with atmospheric dust and continental shelf inputs, vertical mixing is a more important source for supplying dissolved trace elements to the surface 40° S Atlantic. It is insufficient, however, to provide the trace elements removed by biological uptake. Other inputs (e.g. particulate, or from winter deep-mixing) are required to balance the trace element budgets in this region.

show abstract

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Radium-228-derived ocean mixing and trace element inputs in the South Atlantic

Hsieh¹,

Geibert²,

Woodward³

et al. 2020

Preprint

View full text Add to dashboard Cite

show abstract

“…The global SGD estimate was further refined to be (4.4 ± 1.2) × 10 13 m 3 yr −1 by considering geographic and salinity effects on radium activities in groundwater end‐member (Cho & Kim, ). A modified 228 Ra inverse model has been recently developed, which leads to an update global SGD estimate of 1.3 – 14.7 × 10 13 m 3 yr −1 (Le Gland et al, ).…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2018

View full text Add to dashboard Cite

The biogeochemical processes in the continental shelf systems are usually extensively influenced by coastal upwelling and submarine groundwater discharge (SGD). Using eastern Hainan upwelling shelf system as an example, this study fully investigates SGD and coastal upwelling and their effects on the coastal nutrient loadings to the mixing layer of eastern Hainan shelf. Based on the spatial distributions of 223Ra and 228Ra, water residence time is estimated to be 16.9 ± 8.9 days. Based on the mass balance models of 226Ra and 228Ra, the total SGD of the eastern Hainan shelf is estimated to be 0.8 × 108 and 1.4 × 108 m3 d−1, respectively. The groundwater borne dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphate (DIP) are estimated to be up to 1121.8 and 20.4 μM m2 d−1. The coastal upwelling delivers 2741.8 μM m2 d−1 DIN and 217.7 μM m2 d−1 DIP into the mixing layer, which are predominant in all the exogenous nutrient inputs. The groundwater borne DIN will support a maximum new production of 7.5 mM C m2 d−1, about up to 24.0% of the total new production in the study area. SGD‐derived nutrient could be significant as a missing DIN to support the new production in the mixing layer of eastern Hainan shelf. The findings contribute to a better understanding of biogeochemical processes under the influences of SGD and coastal upwelling in the study area and other similar coastal upwelling systems.

show abstract

“…Rapaglia et al (2012) applied a location‐allocation model to determine the optimal distribution of samples for field collection. Some authors have also used inverse modeling techniques to obtain an average tracer concentration in large regions with low sampling densities (Kwon et al 2014; Le Gland et al 2017); however, these approaches are rarely applied in small‐scale studies and most of the authors collect a relatively large number of samples to derive average tracer concentrations.…”

Section: Resultsmentioning

confidence: 99%

Conceptual uncertainties in groundwater and porewater fluxes estimated by radon and radium mass balances

Rodellas

Stieglitz

Tamborski

et al. 2021

Limnology & Oceanography

View full text Add to dashboard Cite

Radium isotopes and radon are routinely used as tracers to quantify groundwater and porewater fluxes into coastal and freshwater systems. However, uncertainties associated with the determination of the tracer flux are often poorly addressed and often neglect all the potential errors associated with the conceptualization of the system (i.e., conceptual uncertainties). In this study, we assess the magnitude of some of the key uncertainties related to the determination of the radium and radon inputs supplied by groundwater and porewater fluxes into a waterbody (La Palme Lagoon, France). This uncertainty assessment is addressed through a single model ensemble approach, where a tracer mass balance is run multiple times with variable sets of assumptions and approaches for the key parameters determined through a sensitivity test. In particular, conceptual uncertainties linked to tracer concentration, diffusive fluxes, radon evasion to the atmosphere, and change of tracer inventory over time were considered. The magnitude of porewater fluxes is further constrained using a comparison of independent methods: (1) 224Ra and (2) 222Rn mass balances in overlying waters, (3) a model of 222Rn deficit in sediments, and (4) a fluid‐salt numerical transport model. We demonstrate that conceptual uncertainties are commonly a major source of uncertainty on the estimation of groundwater or porewater fluxes and they need to be taken into account when using tracer mass balances. In the absence of a general framework for assessing these uncertainties, this study provides a practical approach to evaluate key uncertainties associated to radon and radium mass balances.

show abstract

Improving the inverse modeling of a trace isotope: how precisely can radium-228 fluxes toward the ocean and submarine groundwater discharge be estimated?

Cited by 14 publications

References 40 publications

Radium-228-derived ocean mixing and trace element inputs in the South Atlantic

Radium-228-derived ocean mixing and trace element inputs in the South Atlantic

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

Conceptual uncertainties in groundwater and porewater fluxes estimated by radon and radium mass balances

Contact Info

Product

Resources

About