Untangling biogeochemical processes from the impact of ocean circulation: First insight on the Mediterranean dissolved barium dynamics

Jullion, Loïc; Jacquet, Stéphanie; Tanhua, Toste

doi:10.1002/2016gb005489

Cited by 19 publications

(16 citation statements)

References 59 publications

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“…High particulate iron and aluminum concentrations were also observed at these stations Menzel et al, 2017Menzel et al, , 2018. Enrichment in 226 Ra has indeed been observed in hydrothermal system plumes at mid-ocean ridge (Kadko, 1996;Kadko and Moore, 1988;Kipp et al, 2017;Rudnicki and Elderfield, 1992). Moreover, the 226 Ra enrichments are accompanied by slight Ba enrichments, which may support the hydrothermal origin hypothesis, since hydrothermal venting at mid-ocean Ridge constitutes the second major external source of Ba to the ocean (Edmond et al, 1979).…”

Section: Ra Inputs and Their Relationship With Bamentioning

confidence: 54%

The <sup>226</sup>Ra–Ba relationship in the North Atlantic during GEOTRACES-GA01

et al. 2018

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Abstract. We report detailed sections of radium-226 (226Ra, T1∕2 =  1602 years) activities and barium (Ba) concentrations determined in the North Atlantic (Portugal–Greenland–Canada) in the framework of the international GEOTRACES program (GA01 section – GEOVIDE project, May–July 2014). Dissolved 226Ra and Ba are strongly correlated along the section, a pattern that may reflect their similar chemical behavior. Because 226Ra and Ba have been widely used as tracers of water masses and ocean mixing, we investigated their behavior more thoroughly in this crucial region for thermohaline circulation, taking advantage of the contrasting biogeochemical patterns existing along the GA01 section. We used an optimum multiparameter (OMP) analysis to distinguish the relative importance of physical transport (water mass mixing) from nonconservative processes (sedimentary, river or hydrothermal inputs, uptake by particles and dissolved–particulate dynamics) on the 226Ra and Ba distributions in the North Atlantic. Results show that the measured 226Ra and Ba concentrations can be explained by conservative mixing for 58 and 65 % of the samples, respectively, notably at intermediate depth, away from the ocean interfaces. 226Ra and Ba can thus be considered conservative tracers of water mass transport in the ocean interior on the space scales considered here, namely, on the order of a few thousand kilometers. However, regions in which 226Ra and Ba displayed nonconservative behavior and in some cases decoupled behaviors were also identified, mostly at the ocean boundaries (seafloor, continental margins and surface waters). Elevated 226Ra and Ba concentrations found in deepwater in the West European Basin suggest that lower Northeast Atlantic Deep Water (NEADWl) accumulates 226Ra and Ba from sediment diffusion and/or particle dissolution during transport. In the upper 1500 m of the West European Basin, deficiencies in 226Ra and Ba are likely explained by their incorporation in planktonic calcareous and siliceous shells, or in barite (BaSO4) by substitution or adsorption mechanisms. Finally, because Ba and 226Ra display different source terms (mostly deep-sea sediments for 226Ra and rivers for Ba), strong decoupling between 226Ra and Ba were observed at the land–ocean boundaries. This is especially true in the shallow stations near the coasts of Greenland and Newfoundland where high 226Ra ∕ Ba ratios at depth reflect the diffusion of 226Ra from sediment and low 226Ra ∕ Ba ratios in the upper water column reflect the input of Ba associated with meteoric waters.

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Section: Ra Inputs and Their Relationship With Bamentioning

confidence: 54%

The <sup>226</sup>Ra–Ba relationship in the North Atlantic during GEOTRACES-GA01

et al. 2018

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“…There is a strong positive correlation between dissolved barium (Ba d ) and silicic acid throughout the global ocean, and a similar trend between Ba d and alkalinity (e.g. Hoppema et al, 2010;Jacquet et al, 2005;Jacquet et al, 2007;Jacquet et al, 2008;Jeandel et al, 1996;Jullion et al, 2017;Thomas et al, 2011), likely a result of relatively deep release of Ba during particulate organic matter remineralization, coupled with large scale ocean circulation (Bates et al, 2017;Horner et al, 2015;Jeandel et al, 1996;Lea, 1993). Water column, sediment trap, and core top studies have also revealed a relationship between excess barium in the particulate phase ( total barium corrected for lithogenic input, Ba xs ) and particulate organic carbon (POC) .…”

Section: Introductionmentioning

confidence: 99%

Oceanic fronts control the distribution of dissolved barium in the Southern Ocean

et al. 2018

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The globally-observed relationship between oceanic barium and the macronutrient silicic acid results from the shared influence of large-scale ocean circulation and mixing on the two elements, and the inherent link between barium and organic matter formation and dissolution. A detailed examination of deviations from barium-silicon correlations can reveal variations in non-conservative processes within the marine barium cycle. Here, we present a high-resolution dataset of dissolved barium and macronutrients from the Drake Passage and the Scotia and Weddell Seas. Our new results highlight the influence of Southern Ocean frontal zones on barium cycling and the deviations of barium and macronutrient distributions as a result of spatial variations in phytoplankton assemblages and in barite formation processes. These new data also reinforce findings that water mass mixing and ocean circulation, in particular the location of oxygen minima, play a key role in barium distribution. Our findings have implications for the use of sedimentary barium as a proxy for export production, which may be complicated by physical water circulation changes or shifts in plankton community structure.

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“…Similarly, Jullion et al (2017) -by using a parametric OMP analyses as applied in the Mediterranean Sea -also reported quantification of the nonconservative component of the Ba signal and suggested that the Ba negative anomalies potentially reflected Ba subtraction during barite formation occurring during POC remineralization. The winter deep convection in the Labrador Sea may also potentially explain these relatively deep Ba anomalies by transporting negative Ba and 226 Ra anomalies waters toward the deep sea, as was observed in the Mediterranean Sea (Jullion et al, 2017). With the exception of the acantharian skeletons that may impact the dissolved 226 Ra / Ba ratios in the upper 200 m, the removal of 226 Ra and Ba that takes place deeper in the water column or that involves other processes (e.g., barite precipitation) does not seem to significantly affect the dissolved 226 Ra / Ba ratios.…”

Section: High Particulate Excess Ba (Bamentioning

confidence: 90%

Answer to Referee 2

Roy¹

2018

Preprint

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We report detailed sections of radium-226 (226 Ra, 3028 E. Le Roy et al.: The 226 Ra-Ba relationship in the North Atlantic during GEOTRACES-GA01 shallow stations near the coasts of Greenland and Newfoundland where high 226 Ra / Ba ratios at depth reflect the diffusion of 226 Ra from sediment and low 226 Ra / Ba ratios in the upper water column reflect the input of Ba associated with meteoric waters.

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Untangling biogeochemical processes from the impact of ocean circulation: First insight on the Mediterranean dissolved barium dynamics

Abstract: International audienc

Cited by 19 publications

References 59 publications

The <sup>226</sup>Ra–Ba relationship in the North Atlantic during GEOTRACES-GA01

The <sup>226</sup>Ra–Ba relationship in the North Atlantic during GEOTRACES-GA01

Oceanic fronts control the distribution of dissolved barium in the Southern Ocean

Answer to Referee 2

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Untangling biogeochemical processes from the impact of ocean circulation: First insight on the Mediterranean dissolved barium dynamics

Abstract: International audienc

Cited by 19 publications

References 59 publications

The &lt;sup&gt;226&lt;/sup&gt;Ra–Ba relationship in the North Atlantic during GEOTRACES-GA01

The &lt;sup&gt;226&lt;/sup&gt;Ra–Ba relationship in the North Atlantic during GEOTRACES-GA01

Oceanic fronts control the distribution of dissolved barium in the Southern Ocean

Answer to Referee 2

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The <sup>226</sup>Ra–Ba relationship in the North Atlantic during GEOTRACES-GA01

The <sup>226</sup>Ra–Ba relationship in the North Atlantic during GEOTRACES-GA01