Strong Margin Influence on the Arctic Ocean Barium Cycle Revealed by Pan‐Arctic Synthesis

Abstract

Early studies revealed relationships between barium (Ba), particulate organic carbon and silicate, suggesting applications for Ba as a paleoproductivity tracer and as a tracer of modern ocean circulation. But, what controls the distribution of barium (Ba) in the oceans? Here, we investigated the Arctic Ocean Ba cycle through a one‐of‐a‐kind data set containing dissolved (dBa), particulate (pBa), and stable isotope Ba ratio (δ138Ba) data from four Arctic GEOTRACES expeditions conducted in 2015. We hypothesized that margins would be a substantial source of Ba to the Arctic Ocean water column. The dBa, pBa, and δ138Ba distributions all suggest significant modification of inflowing Pacific seawater over the shelves, and the dBa mass balance implies that ∼50% of the dBa inventory (upper 500 m of the Arctic water column) was supplied by nonconservative inputs. Calculated areal dBa fluxes are up to 10 μmol m−2 day−1 on the margin, which is comparable to fluxes described in other regions. Applying this approach to dBa data from the 1994 Arctic Ocean Survey yields similar results. The Canadian Arctic Archipelago did not appear to have a similar margin source; rather, the dBa distribution in this section is consistent with mixing of Arctic Ocean‐derived waters and Baffin Bay‐derived waters. Although we lack enough information to identify the specifics of the shelf sediment Ba source, we suspect that a sedimentary remineralization and terrigenous sources (e.g., submarine groundwater discharge or fluvial particles) are contributors.

Decoupling of Barium and Silicon at the Congo River‐Dominated Southeast Atlantic Margin: Insights From Combined Barium and Silicon Isotopes

“…This work highlights the strong marginal influence on the Ba cycle at the Congo margin (Figure 8), which was also recently observed in other margin regions globally, for example, in the Arctic Ocean (Whitmore et al., 2022) and along the broad Mauritanian shelf (Rahman et al., 2022). Adopting the estimated global freshwater dBa river input (6.6 ± 3.9 Gmol/yr; Rahman et al., 2022), the Congo River dBa flux accounts for 2.5 ± 1.5% of this global estimation.…”

“…Deep seawaters are typically enriched in isotopically light Si and Ba compared to the surface seawaters as a result of remineralization processes and water mass mixing (Bates et al., 2017; De Souza, Reynolds, Johnson, et al., 2012; De Souza, Reynolds, Rickli, et al., 2012; Horner et al., 2015). Apart from biogeochemical processes, both isotopic systems also provide insights into their various sources and sinks in marginal regions (Whitmore et al., 2022; Zhang, Sun, et al., 2020). As such, the combined use of δ 138 Ba and δ 30 Si is proposed to provide new insights into the linkages between Ba and Si cycling.…”

High latitude controls on dissolved barium isotope distributions in the global ocean

“…The strong upwelling of CDW from below, on Figure 1 Simplified global overturning circulation with locations of seawater profile stations of this study (coloured circles). Open squares denote published profiles (Horner et al, 2015;Bates et al, 2017;Whitmore et al, 2022). Produced using Ocean Data View (Schlitzer, 2022).…”

Benthic-pelagic coupling and isotopic fractionation of barium in Kiel Bight, SW Baltic Sea

“…As a consequence of these general observations, numerous studies have attempted to use Ba concentrations and fluxes or barite abundances in sediments as a proxy for marine primary or export productivity (e.g., Nürnberg et al, 1997;Paytan and Griffith, 2007). More recently, isotope measurements of dissolved Ba in seawater from most major ocean basins have highlighted the potential of Ba isotopes to identify and disentangle the processes that contribute to the vertical and horizontal distribution of Ba in the ocean (Horner et al, 2015;Cao et al, 2016;Bates et al, 2017;Hsieh and Henderson, 2017;Bridgestock et al, 2018;Horner and Crockford, 2021;Whitmore et al, 2022). Further research on Ba isotope fractionation during water-solid interactions in different marine systems is, however, required to fully explore the utility of Ba isotopes as a (paleo-)biogeochemical tracer.…”

“…Some of this imbalance could be explained by desorption of isotopically light particulate Ba (with a d 138 Ba ~0.2 ‰ lower than river water) within the estuarine mixing gradient (Bridgestock et al, 2021a). In addition, other Ba sources and sinks, which have not yet been characterized isotopically, could potentially close the oceanic Ba mass balance: Water column studies suggest that another important external flux of Ba to the ocean originates from the seafloor (Rahman et al, 2022;Whitmore et al, 2022). It is well established that marine sediments release Ba to the bottom water via diffusion or advection across the sediment-water interface (McManus et al, 1994;McManus et al, 1998).…”