Using the radium quartet (228Ra, 226Ra, 224Ra, and 223Ra) to estimate water mixing and radium inputs in Loch Etive, Scotland

Hsieh, Yu-Te; Geibert, Walter; van-Beek, Pieter; Ståhl, Henrik; Aleynik, Dmitry; Henderson, Gideon M.

doi:10.4319/lo.2013.58.3.1089

Cited by 11 publications

(5 citation statements)

References 48 publications

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“…The error bars are 1 SD of the average, and provide an estimate of the spatial variation in age rather than an uncertainty associated with the method. In terms of cross-shelf mixing, the age method can be translated to a mixing rate from a regression line between water age and offshore distance (figure not shown; Hsieh et al 2013). For July, this approach yielded a mean cross-shelf rate of 0.028 m s 21 (R 2 5 0.6), which is the same order of magnitude as an estimate from this region derived from long-term mooring data (0.01 m s 21 ; Weisberg et al 2009).…”

Section: Discussionmentioning

confidence: 99%

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

Liu

Charette

Henderson

et al. 2014

Limnology & Oceanography

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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.

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Section: Discussionmentioning

confidence: 99%

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

Liu

Charette

Henderson

et al. 2014

Limnology & Oceanography

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“…Figure 6: Shelf sediment 228 Ra fluxes. Values reported by: Li et al (1979); Moore et al (1987); Moore et al (1995); Cochran(1984);Santschi et al (1979);Rama and Moore (1996);Crotwell and Moore (2003);Hancock et al (2000);Hancock et al (2006);Hsieh et al (2013). Most of the data are summarized inMoore et al (2008).…”

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confidence: 99%

Benthic fluxes of trace metals in the Chukchi Sea and their transport into the Arctic Ocean

et al. 2019

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The Chukchi Sea is a primary site for shelf-ocean exchange in the Arctic region and modifies Pacific-sourced water masses as they transit via the Bering Strait into the Arctic Ocean. The aim of this study was to use radium and trace metal distributions to improve our understanding of biogeochemical cycles in the Bering and Chukchi Seas, and evaluate their potential response to future changes in the Arctic. We investigated the distributions of dissolved and total dissolvable trace metals (Cd, Fe, Ni, Cu, Zn, Mn, Co, and Pb) in the Bering and Chukchi Seas during spring. In addition, the long-lived radium isotopes ( 226 Ra and 228 Ra) were measured as tracers of benthic trace metal inputs. Trace metal concentrations, especially Fe and Mn, were highly elevated in Chukchi shelf waters compared with the open Arctic Ocean and Bering Strait. Trace metal, nutrient, and Ra patterns suggested that Fe, Mn, and Co concentrations were predominantly controlled by reductive benthic inputs, whereas the other trace metals were influenced by biological uptake and release processes. We propose that Fe, Mn, and Co in the Chukchi Sea are supplied from shelf sediments during winter overturning, and we combine the 228 Ra fluxes with the distributions of Fe, Mn, and Co to provide a first estimate of their benthic fluxes in the region. The average benthic flux of 228 Ra was 1.49 x 10 8 atoms m -2 d -1 , which is among the highest rates reported globally. Estimated dissolved Fe (D-Fe) flux from the sediments was 2.5 µmol m -2 d -1 , whereas D-Mn and D-Co fluxes were 8.0 µmol m -2 d -1 and 0.2 µmol m -2 d -1, respectively. The off-shelf transport of D-Fe to the Arctic Ocean is estimated to be about 10-25% of the benthic Fe flux, with the remainder retained on the shelf due to scavenging and/or phytoplankton uptake. Our results highlight the importance of the Chukchi Sea as a major source of the micro-nutrients to the Arctic Ocean, thereby supporting primary production. Long-term changes in factors that affect cross-shelf mixing, such as the observed reduction in ice cover, may therefore enhance shelf nutrient inputs and primary productivity in the Arctic.

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“…Seasonally dynamic stratification is a well‐observed feature of Loch Etive (Hsieh et al, 2013; Stashchuk et al, 2007). Step boundary conditions for the vertical temperature and salinity profiles were adopted to induce stratification and were implemented with surface and bottom values for each parameter specifying the location of the step in the water column at 3 m. Values for the temperature and salinity profiles were informed by conductivity–temperature–depth (CTD) dips conducted during the bathymetric surveys and the results in Dunnery et al (2021) as no CTD data were available that corresponded to the time of the ADCP data.…”

Section: Methodsmentioning

confidence: 99%

“…Seasonally dynamic stratification is a well-observed feature of Loch Etive (Hsieh et al, 2013;Stashchuk et al, 2007).…”

Section: Numerical Modelmentioning

confidence: 99%

Sediment transport and the freshwater modification of tidal hydraulics approaching a fjordic sill: The Falls of Lora, Loch Etive, western Scotland, UK

Armstrong

Howe

Inall

et al. 2023

Earth Surf Processes Landf

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The Falls of Lora (FoL), Loch Etive, illustrates a highly energetic tidal site across a shallow (mean depth = 8 m) fjordic sill. The FoL hydrodynamics have been investigated using an acoustic Doppler current profiler (ADCP), a numerical flow model, water‐level data and meteorological data. Additionally, four bathymetric timeseries datasets (from February 2014, September 2020, November 2021 and June 2022) provided alternative indication of flow variability by monitoring the geometry of submarine sediment bedforms. A correlation of 0.22 (−0.2 < 97.5% confidence interval < 0.2) was found between catchment‐integrated precipitation and residual water height (with effects of tide and atmospheric pressure removed). Residual water height varied by 0.77 m. Artificially increasing the water height by up to 0.6 m at the model's up‐fjord open boundary to emulate the effects of precipitation increased (decreased) peak depth‐averaged flow speed of the ebb (flood) jet by 0.44 m/s (0.34 m/s) whilst modifying residual flow fields around the FoL. The freshwater‐modified residual flow correlated with the westward displacement of a flow transverse sediment ridge observed in two bathymetric surveys conducted after periods of relatively high precipitation. Additionally, in one of the surveys associated with increased precipitation, wavelength stretching in the sediment dunes was observed uniquely at the western approach to the FoL, dominated by the freshwater‐enhanced ebb flow. Increasing the water levels of the up‐fjord boundary from 0.1 to 0.6 m resulted in an increased mean bedload transport of 2.28 × 10−5 m3/s (370% increase) for these dunes dominated by the ebb current. Whereas Loch Etive has an anomalously high freshwater influence on sill flow compared with other Scottish fjords, it is predicted that freshwater inputs are a significant influence on sill hydrodynamics and nearby sediment transport pathways in other fjordic systems.

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Using the radium quartet (²²⁸Ra, ²²⁶Ra, ²²⁴Ra, and ²²³Ra) to estimate water mixing and radium inputs in Loch Etive, Scotland

Cited by 11 publications

References 48 publications

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

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

Benthic fluxes of trace metals in the Chukchi Sea and their transport into the Arctic Ocean

Sediment transport and the freshwater modification of tidal hydraulics approaching a fjordic sill: The Falls of Lora, Loch Etive, western Scotland, UK

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