High latitude controls on dissolved barium isotope distributions in the global ocean
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Keywords: barium isotopes, global overturning circulation, high latitude oceans, upper ocean, isotope fractionation, deep ocean mixing
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Abstract
Figures
 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; Hsieh and Henderson, 2017; Bridgestock et al., 2018; Geyman et al., 2019; Whitmore et al., 2022). Produced using Ocean Data View (Schlitzer, 2022). |  Figure 2 Depth profiles of dissolved δ138Ba in the Weddell Sea (green), the Labrador Sea (orange), the Fram Strait (pink), and the low and mid-latitude Atlantic Ocean (black, Bates et al., 2017). Dissolved [Ba] data are from the GEOTRACES intermediate data product 2017 (Schlitzer et al., 2018) and this study. SAMW, Subantarctic Mode Water; AAIW, Antarctic Intermediate Water; CDW, Circumpolar Deep Water; AABW, Antarctic Bottom Water; NADW, North Atlantic Deep Water; LSW, Labrador Sea Water; NEADW, Northeast Atlantic Deep Water; NWABW, Northwest Atlantic Bottom Water; NOW, Northern Overflow Water. Produced using Ocean Data View (Schlitzer, 2022). |  Figure 3 Depth profiles of dissolved δ138Ba in the Pacific Ocean (blue). The depth profile of δ138Ba in the mid-latitude North Pacific (SAFe station, black) is from Geyman et al. (2019). Dissolved [Ba] data are from the GEOTRACES intermediate data product 2017 (Schlitzer et al., 2018) and this study. UCDW, Upper Circumpolar Deep Water; LCDW, Lower Circumpolar Deep Water; NPIW, North Pacific Intermediate Water; NPDW, North Pacific Deep Water; PSIW, Pacific Subpolar Intermediate Water. Produced using Ocean Data View (Schlitzer, 2022). |  Figure 4 Deep ocean mixing line (black dashed line; data from this study) of δ138Ba against 1/[Ba] and results of a regeneration model assuming a pre-formed [Ba] of 35 nmol kg−1 and a δ138Ba value of 0.62 ‰ (grey dashed line). Literature dissolved δ138Ba and [Ba] data (black) are from Horner et al. (2015), Bates et al. (2017), Hsieh and Henderson (2017), Bridgestock et al. (2018), Geyman et al. (2019), and Whitmore et al. (2022). The potential impacts of hydrothermal Ba input in the Atlantic and progressive Ba accumulation in the deep Pacific are denoted by bold light grey arrows. |
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Introduction
Barium (Ba) is a bio-intermediate element in the ocean, whose dissolved concentrations ([Ba]) in the water column have a nutrient-like depth profile with a [Ba] depletion in the upper ocean resulting from removal via marine particles (e.g., barite) and [Ba] enrichment at depth due to particulate matter decomposition and remineralisation (Lea and Boyle, 1991
Lea, D.W., Boyle, E.A. (1991) Barium in planktonic foraminifera. Geochimica et Cosmochimica Acta 55, 3321–3331. https://doi.org/10.1016/0016-7037(91)90491-M
). Recent studies presenting novel dissolved Ba isotope compositions (δ138Ba) have provided additional insights into the processes driving the oceanic cycling of Ba (e.g., Horner et al., 2015Horner, T.J., Kinsley, C.W., Nielsen, S.G. (2015) Barium-isotopic fractionation in seawater mediated by barite cycling and oceanic circulation. Earth and Planetary Science Letters 430, 511–522. https://doi.org/10.1016/j.epsl.2015.07.027
; Cao et al., 2016Cao, Z., Siebert, C., Hathorne, E.C., Dai, M., Frank, M. (2016) Constraining the oceanic barium cycle with stable barium isotopes. Earth and Planetary Science Letters 434, 1–9. https://doi.org/10.1016/j.epsl.2015.11.017
; Hsieh and Henderson, 2017Hsieh, Y.-T., Henderson, G.M. (2017) Barium stable isotopes in the global ocean: Tracer of Ba inputs and utilization. Earth and Planetary Science Letters 473, 269–278. https://doi.org/10.1016/j.epsl.2017.06.024
). In the uppermost water column, Ba isotope fractionation is likely induced by preferential adsorption of the light isotopes onto biogenic particles (Cao et al., 2020Cao, Z., Li, Y., Rao, X., Yu, Y., Hathorne, E.C., Siebert, C., Dai, M., Frank, M. (2020) Constraining barium isotope fractionation in the upper water column of the South China Sea. Geochimica et Cosmochimica Acta 288, 120–137. https://doi.org/10.1016/j.gca.2020.08.008
). Although laboratory experiments of adsorption to silica hydrogel exhibited Ba isotope fractionation in the opposite direction, with heavy Ba isotopes being preferentially adsorbed (van Zuilen et al., 2016van Zuilen, K., Müller, T., Nägler, T.F., Dietzel, M., Küsters, T. (2016) Experimental determination of barium isotope fractionation during diffusion and adsorption processes at low temperatures. Geochimica et Cosmochimica Acta 186, 226–241. https://doi.org/10.1016/j.gca.2016.04.049
), field observations consistently reveal lighter isotope enrichment in surface water particles (Horner et al., 2017Horner, T.J., Pryer, H.V., Nielsen, S.G., Crockford, P.W., Gauglitz, J.M., Wing, B.A., Ricketts, R.D. (2017) Pelagic barite precipitation at micromolar ambient sulfate. Nature Communications 8, 1342. https://doi.org/10.1038/s41467-017-01229-5
; Cao et al., 2020Cao, Z., Li, Y., Rao, X., Yu, Y., Hathorne, E.C., Siebert, C., Dai, M., Frank, M. (2020) Constraining barium isotope fractionation in the upper water column of the South China Sea. Geochimica et Cosmochimica Acta 288, 120–137. https://doi.org/10.1016/j.gca.2020.08.008
). During sinking and decomposition of these particles, barite formation with a preference for the assimilation of light isotopes (von Allmen et al., 2010von Allmen, K., Böttcher, M.E., Samankassou, E., Nägler, T.F. (2010) Barium isotope fractionation in the global barium cycle: First evidence from barium minerals and precipitation experiments. Chemical Geology 277, 70–77. https://doi.org/10.1016/j.chemgeo.2010.07.011
) leads to high dissolved δ138Ba values in subsurface seawater (Horner et al., 2015Horner, T.J., Kinsley, C.W., Nielsen, S.G. (2015) Barium-isotopic fractionation in seawater mediated by barite cycling and oceanic circulation. Earth and Planetary Science Letters 430, 511–522. https://doi.org/10.1016/j.epsl.2015.07.027
; Bates et al., 2017Bates, S.L., Hendry, K.R., Pryer, H.V., Kinsley, C.W., Pyle, K.M., Woodward, E.M.S., Horner, T.J. (2017) Barium isotopes reveal role of ocean circulation on barium cycling in the Atlantic. Geochimica et Cosmochimica Acta 204, 286–299. https://doi.org/10.1016/j.gca.2017.01.043
). In contrast, δ138Ba values of deep waters appear to be mainly controlled by barite dissolution and large scale ocean circulation (Hsieh and Henderson, 2017Hsieh, Y.-T., Henderson, G.M. (2017) Barium stable isotopes in the global ocean: Tracer of Ba inputs and utilization. Earth and Planetary Science Letters 473, 269–278. https://doi.org/10.1016/j.epsl.2017.06.024
).Given that the oceanic residence time of dissolved Ba (∼3.5 to 5 kyr; Rahman et al., 2022
Rahman, S., Shiller, A.M., Anderson, R.F., Charette, M.A., Hayes, C.T., Gilbert, M., Grissom, K.R., Lam, P.J., Ohnemus, D.C., Pavia, F.J., Twining, B.S., Vivancos, S.M. (2022) Dissolved and Particulate Barium Distributions Along the US GEOTRACES North Atlantic and East Pacific Zonal Transects (GA03 and GP16): Global Implications for the Marine Barium Cycle. Global Biogeochemical Cycles 36, e2022GB007330. https://doi.org/10.1029/2022GB007330
) is longer than the global ocean mixing time, but short enough to prevent complete homogenisation, studies have focused on the importance of advection and mixing on determining dissolved δ138Ba within water masses in the deep Atlantic Meridional Overturning Circulation (AMOC; Bates et al., 2017Bates, S.L., Hendry, K.R., Pryer, H.V., Kinsley, C.W., Pyle, K.M., Woodward, E.M.S., Horner, T.J. (2017) Barium isotopes reveal role of ocean circulation on barium cycling in the Atlantic. Geochimica et Cosmochimica Acta 204, 286–299. https://doi.org/10.1016/j.gca.2017.01.043
; Hsieh and Henderson, 2017Hsieh, Y.-T., Henderson, G.M. (2017) Barium stable isotopes in the global ocean: Tracer of Ba inputs and utilization. Earth and Planetary Science Letters 473, 269–278. https://doi.org/10.1016/j.epsl.2017.06.024
). The distribution of deep water δ138Ba is overall consistent with two end member mixing between North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW). However, the lack of δ138Ba data from high latitude regions where these water masses form results in uncertain end member δ138Ba signatures. Additionally, despite several studies in the Atlantic Ocean, the stable Ba isotope distribution in global seawater, in particular in the Indo-Pacific, remains largely unconstrained. The still poor spatial coverage of available data has so far prevented a robust identification of the mechanisms controlling the distribution of dissolved Ba isotopes in the global ocean.Here, we examine the spatial and vertical distribution of δ138Ba and [Ba] in 17 new water depth profiles from the high latitude Atlantic, Pacific and Southern Oceans (Fig. 1). These data reveal how NADW and AABW acquire their respective Ba isotope signatures in the polar and subpolar regions. In combination with previously reported low and mid-latitude δ138Ba profiles (Horner et al., 2015
Horner, T.J., Kinsley, C.W., Nielsen, S.G. (2015) Barium-isotopic fractionation in seawater mediated by barite cycling and oceanic circulation. Earth and Planetary Science Letters 430, 511–522. https://doi.org/10.1016/j.epsl.2015.07.027
; Bates et al., 2017Bates, S.L., Hendry, K.R., Pryer, H.V., Kinsley, C.W., Pyle, K.M., Woodward, E.M.S., Horner, T.J. (2017) Barium isotopes reveal role of ocean circulation on barium cycling in the Atlantic. Geochimica et Cosmochimica Acta 204, 286–299. https://doi.org/10.1016/j.gca.2017.01.043
; Hsieh and Henderson, 2017Hsieh, Y.-T., Henderson, G.M. (2017) Barium stable isotopes in the global ocean: Tracer of Ba inputs and utilization. Earth and Planetary Science Letters 473, 269–278. https://doi.org/10.1016/j.epsl.2017.06.024
; Bridgestock et al., 2018Bridgestock, L., Hsieh, Y.-T., Porcelli, D., Homoky, W.B., Bryan, A., Henderson, G.M. (2018) Controls on the barium isotope compositions of marine sediments. Earth and Planetary Science Letters 481, 101–110. https://doi.org/10.1016/j.epsl.2017.10.019
; Geyman et al., 2019Geyman, B.M., Ptacek, J.L., LaVigne, M., Horner, T.J. (2019) Barium in deep-sea bamboo corals: Phase associations, barium stable isotopes, & prospects for paleoceanography. Earth and Planetary Science Letters 525, 115751. https://doi.org/10.1016/j.epsl.2019.115751
), we are now able to better constrain Ba isotope fractionation in the upper ocean and to obtain a more complete picture of the δ138Ba systematics within the global overturning circulation.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
Horner, T.J., Kinsley, C.W., Nielsen, S.G. (2015) Barium-isotopic fractionation in seawater mediated by barite cycling and oceanic circulation. Earth and Planetary Science Letters 430, 511–522. https://doi.org/10.1016/j.epsl.2015.07.027
; Bates et al., 2017Bates, S.L., Hendry, K.R., Pryer, H.V., Kinsley, C.W., Pyle, K.M., Woodward, E.M.S., Horner, T.J. (2017) Barium isotopes reveal role of ocean circulation on barium cycling in the Atlantic. Geochimica et Cosmochimica Acta 204, 286–299. https://doi.org/10.1016/j.gca.2017.01.043
; Hsieh and Henderson, 2017Hsieh, Y.-T., Henderson, G.M. (2017) Barium stable isotopes in the global ocean: Tracer of Ba inputs and utilization. Earth and Planetary Science Letters 473, 269–278. https://doi.org/10.1016/j.epsl.2017.06.024
; Bridgestock et al., 2018Bridgestock, L., Hsieh, Y.-T., Porcelli, D., Homoky, W.B., Bryan, A., Henderson, G.M. (2018) Controls on the barium isotope compositions of marine sediments. Earth and Planetary Science Letters 481, 101–110. https://doi.org/10.1016/j.epsl.2017.10.019
; Geyman et al., 2019Geyman, B.M., Ptacek, J.L., LaVigne, M., Horner, T.J. (2019) Barium in deep-sea bamboo corals: Phase associations, barium stable isotopes, & prospects for paleoceanography. Earth and Planetary Science Letters 525, 115751. https://doi.org/10.1016/j.epsl.2019.115751
; Whitmore et al., 2022Whitmore, L.M., Shiller, A.M., Horner, T.J., Xiang, Y., Auro, M.E., Bauch, D., Dehairs, F., Lam, P.J., Li, J., Maldonado, M.T., Mears, C., Newton, R., Pasqualini, A., Planquette, H., Rember, R., Thomas, H. (2022) Strong Margin Influence on the Arctic Ocean Barium Cycle Revealed by Pan‐Arctic Synthesis. Journal of Geophysical Research: Oceans 127, e2021JC017417. https://doi.org/10.1029/2021JC017417
). Produced using Ocean Data View (Schlitzer, 2022Schlitzer, R. (2022) Ocean Data View. http://odv.awi.de
).top
Ba Isotope Fractionation in the Upper Ocean
Seawater samples for dissolved [Ba] and δ138Ba were measured at GEOMAR, Kiel, applying methods detailed in Yu et al. (2020)
Yu, Y., Siebert, C., Fietzke, J., Goepfert, T., Hathorne, E., Cao, Z., Frank, M. (2020) The impact of MC-ICP-MS plasma conditions on the accuracy and precision of stable isotope measurements evaluated for barium isotopes. Chemical Geology 549, 119697. https://doi.org/10.1016/j.chemgeo.2020.119697
and the Supplementary Information. The depth profiles of δ138Ba from the Fram Strait, the Labrador Sea and the Weddell Sea are shown together with two low and mid-latitude Atlantic δ138Ba profiles, overlain by [Ba] data in Figure 2. The samples in the surface and subsurface Weddell Sea have relatively high [Ba] (∼90 nmol kg−1) and low δ138Ba (∼0.3 ‰), suggesting that the southward intrusion of Circumpolar Deep Water (CDW) was associated with little Ba depletion and isotope fractionation relative to the AABW end member. Previous studies have suggested that the low availability of light and micronutrients (e.g., iron) limits phytoplankton growth in the upper Weddell Sea despite the large inventory of major nutrients available for phytoplankton growth (Sunda and Huntsman, 1997Sunda, W.G., Huntsman, S.A. (1997) Interrelated influence of iron, light and cell size on marine phytoplankton growth. Nature 390, 389–392. https://doi.org/10.1038/37093
). The minor Ba isotope fractionation in the upper Weddell Sea, as a result of limited barite formation, is consistent with the relatively low productivity of this well known high nutrient low chlorophyll (HNLC) region. The strong upwelling of CDW from below, on the other hand, further diminishes the degree of Ba isotope fractionation, resulting in a homogenous water column δ138Ba signature that is indistinguishable from that of CDW.Figure 2 Depth profiles of dissolved δ138Ba in the Weddell Sea (green), the Labrador Sea (orange), the Fram Strait (pink), and the low and mid-latitude Atlantic Ocean (black, Bates et al., 2017
Bates, S.L., Hendry, K.R., Pryer, H.V., Kinsley, C.W., Pyle, K.M., Woodward, E.M.S., Horner, T.J. (2017) Barium isotopes reveal role of ocean circulation on barium cycling in the Atlantic. Geochimica et Cosmochimica Acta 204, 286–299. https://doi.org/10.1016/j.gca.2017.01.043
). Dissolved [Ba] data are from the GEOTRACES intermediate data product 2017 (Schlitzer et al., 2018Schlitzer, R., Anderson, R.F., Dodas, E.M., Lohan, M., Geibert, W., et al. (2018) The GEOTRACES Intermediate Data Product 2017. Chemical Geology 493, 210–223. https://doi.org/10.1016/j.chemgeo.2018.05.040
) and this study. SAMW, Subantarctic Mode Water; AAIW, Antarctic Intermediate Water; CDW, Circumpolar Deep Water; AABW, Antarctic Bottom Water; NADW, North Atlantic Deep Water; LSW, Labrador Sea Water; NEADW, Northeast Atlantic Deep Water; NWABW, Northwest Atlantic Bottom Water; NOW, Northern Overflow Water. Produced using Ocean Data View (Schlitzer, 2022Schlitzer, R. (2022) Ocean Data View. http://odv.awi.de
).In contrast, the upwelled CDW that moves northwards by Ekman transport undergoes strong Ba isotope fractionation due to high diatom productivity resulting in Ba adsorption to particles in the surface and barite precipitation at intermediate depths (Horner et al., 2015
Horner, T.J., Kinsley, C.W., Nielsen, S.G. (2015) Barium-isotopic fractionation in seawater mediated by barite cycling and oceanic circulation. Earth and Planetary Science Letters 430, 511–522. https://doi.org/10.1016/j.epsl.2015.07.027
; Cao et al., 2016Cao, Z., Siebert, C., Hathorne, E.C., Dai, M., Frank, M. (2016) Constraining the oceanic barium cycle with stable barium isotopes. Earth and Planetary Science Letters 434, 1–9. https://doi.org/10.1016/j.epsl.2015.11.017
). As Subantarctic Mode Water (SAMW) and Antarctic Intermediate Water (AAIW) flow northwards from the Subantarctic Zone, surface and subsurface dissolved δ138Ba values increase from ∼0.3 to ∼0.6 ‰ and ultimately reach high δ138Ba values observed in the Labrador Sea and the Fram Strait (Fig. 2). This meridional upper ocean contrast along the upper limb of the AMOC reflects the combined effects of biologically mediated isotope fractionation at high southern latitudes and the role of large scale ocean circulation.In the tropical and subtropical Pacific Ocean, [Ba] and δ138Ba exhibit larger gradients between the surface and deep waters than those in the Atlantic Ocean (Fig. 3). The stronger Ba depletion (∼30 nmol kg−1) and associated greater Ba isotope fractionation (∼0.62 ‰) likely result from the weak vertical mixing in the North Pacific Gyre (Emery and Dewar, 1982
Emery, W.J., Dewar, J.S. (1982) Mean temperature-salinity, salinity-depth and temperature-depth curves for the North Atlantic and the North Pacific. Progress in Oceanography 11, 219–305. https://doi.org/10.1016/0079-6611(82)90015-5
), allowing more time for Ba removal associated with particle adsorption and barite formation in the upper ocean. In contrast, upper ocean Ba isotope fractionation becomes less pronounced northwards, where [Ba] slightly increases in the sub-Arctic Pacific (Fig. 3). These less fractionated Ba isotope signatures reflect the limited biological productivity of the HNLC region in the upper sub-Arctic Pacific, similar to that of the Weddell Sea.Figure 3 Depth profiles of dissolved δ138Ba in the Pacific Ocean (blue). The depth profile of δ138Ba in the mid-latitude North Pacific (SAFe station, black) is from Geyman et al. (2019)
Geyman, B.M., Ptacek, J.L., LaVigne, M., Horner, T.J. (2019) Barium in deep-sea bamboo corals: Phase associations, barium stable isotopes, & prospects for paleoceanography. Earth and Planetary Science Letters 525, 115751. https://doi.org/10.1016/j.epsl.2019.115751
. Dissolved [Ba] data are from the GEOTRACES intermediate data product 2017 (Schlitzer et al., 2018Schlitzer, R., Anderson, R.F., Dodas, E.M., Lohan, M., Geibert, W., et al. (2018) The GEOTRACES Intermediate Data Product 2017. Chemical Geology 493, 210–223. https://doi.org/10.1016/j.chemgeo.2018.05.040
) and this study. UCDW, Upper Circumpolar Deep Water; LCDW, Lower Circumpolar Deep Water; NPIW, North Pacific Intermediate Water; NPDW, North Pacific Deep Water; PSIW, Pacific Subpolar Intermediate Water. Produced using Ocean Data View (Schlitzer, 2022Schlitzer, R. (2022) Ocean Data View. http://odv.awi.de
).top
Ba Isotope Distribution in the Deep Ocean
The [Ba] and δ138Ba signatures pre-formed in the surface are subducted by deep water formation at high latitudes (e.g., Weddell Sea and Labrador Sea). Due to the vigorous circulation of the Weddell Sea, four depth profiles in the southern and western Weddell Sea (Fig. S-2) are indistinguishable from each other in their δ138Ba values, which defines the end member Ba isotope composition of AABW at 0.26 ± 0.03 ‰. In the Labrador Sea, Labrador Sea Water (LSW), Northeast Atlantic Deep Water (NEADW) and Northwest Atlantic Bottom Water (NWABW) have essentially invariant δ138Ba values and thus define the end member Ba isotope composition of NADW as 0.48 ± 0.05 ‰ (Fig. S-2).
The distinctive Ba isotope signatures of deep waters originating in the Weddell Sea and those in the high latitude North Atlantic (i.e. Nordic Seas and Labrador Sea) constrain the meridional gradient of Ba isotope compositions in the deep ocean. The deep ocean δ138Ba and [Ba] data obtained here are compiled with previously reported profiles in a δ138Ba against 1/[Ba] plot (Fig. 4). The high latitude dissolved δ138Ba and 1/[Ba] data display a linear correlation (black dashed line) suggesting conservative mixing between the Northern Overflow Waters (NOW) with low [Ba] and high δ138Ba and AABW characterised by elevated [Ba] and low δ138Ba. The δ138Ba signature of NADW (0.48 ± 0.05 ‰) in the Labrador Sea is only slightly lower than that of NOW (0.52 ± 0.07 ‰), and a clear δ138Ba-1/[Ba] mixing relationship is observed between NOW, NADW and the waters from the deep subtropical North Atlantic (Fig. 4). This suggests that the pre-formed Ba isotope signature of NOW in the Fram Strait represents the northernmost end member of the global deep ocean mixing trend, which is modified along its pathway to the production sites of NADW due to the entrainment of Lower Deep Water (LDW) at greater depth.
Figure 4 Deep ocean mixing line (black dashed line; data from this study) of δ138Ba against 1/[Ba] and results of a regeneration model assuming a pre-formed [Ba] of 35 nmol kg−1 and a δ138Ba value of 0.62 ‰ (grey dashed line). Literature dissolved δ138Ba and [Ba] data (black) are from Horner et al. (2015)
Horner, T.J., Kinsley, C.W., Nielsen, S.G. (2015) Barium-isotopic fractionation in seawater mediated by barite cycling and oceanic circulation. Earth and Planetary Science Letters 430, 511–522. https://doi.org/10.1016/j.epsl.2015.07.027
, Bates et al. (2017)Bates, S.L., Hendry, K.R., Pryer, H.V., Kinsley, C.W., Pyle, K.M., Woodward, E.M.S., Horner, T.J. (2017) Barium isotopes reveal role of ocean circulation on barium cycling in the Atlantic. Geochimica et Cosmochimica Acta 204, 286–299. https://doi.org/10.1016/j.gca.2017.01.043
, Hsieh and Henderson (2017)Hsieh, Y.-T., Henderson, G.M. (2017) Barium stable isotopes in the global ocean: Tracer of Ba inputs and utilization. Earth and Planetary Science Letters 473, 269–278. https://doi.org/10.1016/j.epsl.2017.06.024
, Bridgestock et al. (2018)Bridgestock, L., Hsieh, Y.-T., Porcelli, D., Homoky, W.B., Bryan, A., Henderson, G.M. (2018) Controls on the barium isotope compositions of marine sediments. Earth and Planetary Science Letters 481, 101–110. https://doi.org/10.1016/j.epsl.2017.10.019
, Geyman et al. (2019)Geyman, B.M., Ptacek, J.L., LaVigne, M., Horner, T.J. (2019) Barium in deep-sea bamboo corals: Phase associations, barium stable isotopes, & prospects for paleoceanography. Earth and Planetary Science Letters 525, 115751. https://doi.org/10.1016/j.epsl.2019.115751
, and Whitmore et al. (2022)Whitmore, L.M., Shiller, A.M., Horner, T.J., Xiang, Y., Auro, M.E., Bauch, D., Dehairs, F., Lam, P.J., Li, J., Maldonado, M.T., Mears, C., Newton, R., Pasqualini, A., Planquette, H., Rember, R., Thomas, H. (2022) Strong Margin Influence on the Arctic Ocean Barium Cycle Revealed by Pan‐Arctic Synthesis. Journal of Geophysical Research: Oceans 127, e2021JC017417. https://doi.org/10.1029/2021JC017417
. The potential impacts of hydrothermal Ba input in the Atlantic and progressive Ba accumulation in the deep Pacific are denoted by bold light grey arrows.It could be argued that the coupled changes in 1/[Ba] and δ138Ba can also be explained by a regeneration model, in which light Ba isotopes are progressively regenerated from sinking particles driving the deep oceans towards a higher [Ba] and lower δ138Ba values. The results of such a model are shown in Figure 4 and the Supplementary Information. As outlined by Bridgestock et al. (2018)
Bridgestock, L., Hsieh, Y.-T., Porcelli, D., Homoky, W.B., Bryan, A., Henderson, G.M. (2018) Controls on the barium isotope compositions of marine sediments. Earth and Planetary Science Letters 481, 101–110. https://doi.org/10.1016/j.epsl.2017.10.019
and Hsieh and Henderson (2017)Hsieh, Y.-T., Henderson, G.M. (2017) Barium stable isotopes in the global ocean: Tracer of Ba inputs and utilization. Earth and Planetary Science Letters 473, 269–278. https://doi.org/10.1016/j.epsl.2017.06.024
, the continuous addition of Ba from sinking particles along the southward flow of deep Atlantic water masses is unlikely to generate significant deviations from the mixing line, confirmed by the similarity with the regeneration model (Fig. 4). In contrast, some low and mid-latitude data clearly deviate towards heavier δ138Ba values, which requires the involvement of a third mixing end member. Hsieh et al. (2021)Hsieh, Y.-T., Bridgestock, L., Scheuermann, P.P., Seyfried Jr., W.E., Henderson, G.M. (2021) Barium isotopes in mid-ocean ridge hydrothermal vent fluids: A source of isotopically heavy Ba to the ocean. Geochimica et Cosmochimica Acta 292, 348–363. https://doi.org/10.1016/j.gca.2020.09.037
presented Ba isotope measurements in several hydrothermal vent fluids and suggested that significant inputs of hydrothermal Ba contribute significant amounts of Ba with high δ138Ba to the deep ocean, which causes deviations from the high latitude end member mixing line and the regeneration model (Fig. 4). By excluding these deep water masses that are potentially influenced by hydrothermal inputs, a conservative mixing model was applied to quantify the variability of dissolved δ138Ba not related to conservative mixing in the low and mid-latitude Atlantic Ocean. However, the lack of deviations of the δ138Ba values from conservative mixing indicates any effects of particle regeneration are within analytical uncertainties and non-conservative contributions originating from biogeochemical cycling are small in this case (Fig. S-3 and the Supplementary Information).In the deep Pacific, water masses below ∼2000 m depth are characterised by light Ba isotope compositions indistinguishable from those of the deep Weddell Sea, though with significantly higher [Ba] (Fig. 4). A higher fraction of regenerated Ba in the deep Pacific would be expected to cause deviations from the observed mixing relationship at higher [Ba] accompanied by slightly elevated δ138Ba values (Fig. 4). The substantially high proportion of regenerated Ba (∼75 %) in the deep Pacific, along with the high Ba ‘utilisation’ (∼70 %) in the upper North Pacific indicated by Hsieh and Henderson (2017)
Hsieh, Y.-T., Henderson, G.M. (2017) Barium stable isotopes in the global ocean: Tracer of Ba inputs and utilization. Earth and Planetary Science Letters 473, 269–278. https://doi.org/10.1016/j.epsl.2017.06.024
, demonstrates that biogeochemical Ba cycling plays a more important role in regulating the deep Pacific δ138Ba signatures than in the Atlantic Ocean. In contrast to the regeneration model, the uniformity of deep water δ138Ba signatures in the Southern Ocean and the North Pacific indicates little or no Ba isotope fractionation during progressive accumulation of Ba along the conveyor belt in the deep Pacific. A homogeneity similar to that of δ138Ba signatures is also observed in the dissolved δ30Si and δ114Cd distribution in the deep Pacific, where both isotope values are indistinguishable from those of the deep Southern Ocean (de Souza et al., 2014de Souza, G.F., Slater, R.D., Dunne, J.P., Sarmiento, J.L. (2014) Deconvolving the controls on the deep ocean’s silicon stable isotope distribution. Earth and Planetary Science Letters 398, 66–76. https://doi.org/10.1016/j.epsl.2014.04.040
; Janssen et al., 2017Janssen, D.J., Abouchami, W., Galer, S.J.G., Cullen, J.T. (2017) Fine-scale spatial and interannual cadmium isotope variability in the subarctic northeast Pacific. Earth and Planetary Science Letters 472, 241–252. https://doi.org/10.1016/j.epsl.2017.04.048
; Xie et al., 2019Xie, R.C., Rehkämper, M., Grasse, P., van de Flierdt, T., Frank, M., Xue, Z. (2019) Isotopic evidence for complex biogeochemical cycling of Cd in the eastern tropical South Pacific. Earth and Planetary Science Letters 512, 134–146. https://doi.org/10.1016/j.epsl.2019.02.001
). Using a simple mass balance calculation developed for stable Cd isotopes by Janssen et al. (2017)Janssen, D.J., Abouchami, W., Galer, S.J.G., Cullen, J.T. (2017) Fine-scale spatial and interannual cadmium isotope variability in the subarctic northeast Pacific. Earth and Planetary Science Letters 472, 241–252. https://doi.org/10.1016/j.epsl.2017.04.048
, the net accumulated Ba originating from dissolution of sinking particles in the deep North Pacific is characterised by an average δ138Ba value of 0.22 ± 0.24 ‰ (Supplementary Information), which is consistent with the deep Pacific δ138Ba signature of 0.25 ± 0.04 ‰. Pacific deep water δ138Ba thus reflects a mixture of biogeochemical Ba cycling and large scale ocean circulation considering its similarity to AABW (0.26 ± 0.03 ‰). This new detailed view of the oceanic Ba cycle will facilitate the use of Ba concentrations and stable isotopes as tracers for ocean circulation globally and for biogeochemical processes in specific regions.top
Acknowledgements
The authors would like to thank Jutta Heinze and Ana Kolevica for their support in the laboratory. Many thanks to the captains, crews, and participants of RV Sonne cruise SO-264, RV Maria S. Merian cruises MSM-39, MSM-45, RV Polarstern cruises PS-80, PS-111, and PS-118 for seawater sampling, particularly Huang Huang. GL acknowledges financial support by the Ocean Frontier Institute through an award from the Canada First Research Excellence Fund. RCX was supported by a German DFG grant (project number 432469432). The China Scholarship Council is acknowledged for financial support of YY during this study.
Editor: Gavin Foster
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References
Bates, S.L., Hendry, K.R., Pryer, H.V., Kinsley, C.W., Pyle, K.M., Woodward, E.M.S., Horner, T.J. (2017) Barium isotopes reveal role of ocean circulation on barium cycling in the Atlantic. Geochimica et Cosmochimica Acta 204, 286–299. https://doi.org/10.1016/j.gca.2017.01.043
Show in context During sinking and decomposition of these particles, barite formation with a preference for the assimilation of light isotopes (von Allmen et al., 2010) leads to high dissolved δ138Ba values in subsurface seawater (Horner et al., 2015; Bates et al., 2017).
View in article
Given that the oceanic residence time of dissolved Ba (∼3.5 to 5 kyr; Rahman et al., 2022) is longer than the global ocean mixing time, but short enough to prevent complete homogenisation, studies have focused on the importance of advection and mixing on determining dissolved δ138Ba within water masses in the deep Atlantic Meridional Overturning Circulation (AMOC; Bates et al., 2017; Hsieh and Henderson, 2017).
View in article
In combination with previously reported low and mid-latitude δ138Ba profiles (Horner et al., 2015; Bates et al., 2017; Hsieh and Henderson, 2017; Bridgestock et al., 2018; Geyman et al., 2019), we are now able to better constrain Ba isotope fractionation in the upper ocean and to obtain a more complete picture of the δ138Ba systematics within the global overturning circulation.
View in article
Open squares denote published profiles (Horner et al., 2015; Bates et al., 2017; Hsieh and Henderson, 2017; Bridgestock et al., 2018; Geyman et al., 2019; Whitmore et al., 2022).
View in article
Depth profiles of dissolved δ138Ba in the Weddell Sea (green), the Labrador Sea (orange), the Fram Strait (pink), and the low and mid-latitude Atlantic Ocean (black, Bates et al., 2017).
View in article
Literature dissolved δ138Ba and [Ba] data (black) are from Horner et al. (2015), Bates et al. (2017), Hsieh and Henderson (2017), Bridgestock et al. (2018), Geyman et al. (2019), and Whitmore et al. (2022).
View in article
Bridgestock, L., Hsieh, Y.-T., Porcelli, D., Homoky, W.B., Bryan, A., Henderson, G.M. (2018) Controls on the barium isotope compositions of marine sediments. Earth and Planetary Science Letters 481, 101–110. https://doi.org/10.1016/j.epsl.2017.10.019
Show in context In combination with previously reported low and mid-latitude δ138Ba profiles (Horner et al., 2015; Bates et al., 2017; Hsieh and Henderson, 2017; Bridgestock et al., 2018; Geyman et al., 2019), we are now able to better constrain Ba isotope fractionation in the upper ocean and to obtain a more complete picture of the δ138Ba systematics within the global overturning circulation.
View in article
Open squares denote published profiles (Horner et al., 2015; Bates et al., 2017; Hsieh and Henderson, 2017; Bridgestock et al., 2018; Geyman et al., 2019; Whitmore et al., 2022).
View in article
Literature dissolved δ138Ba and [Ba] data (black) are from Horner et al. (2015), Bates et al. (2017), Hsieh and Henderson (2017), Bridgestock et al. (2018), Geyman et al. (2019), and Whitmore et al. (2022).
View in article
As outlined by Bridgestock et al. (2018) and Hsieh and Henderson (2017), the continuous addition of Ba from sinking particles along the southward flow of deep Atlantic water masses is unlikely to generate significant deviations from the mixing line, confirmed by the similarity with the regeneration model (Fig. 4).
View in article
Cao, Z., Siebert, C., Hathorne, E.C., Dai, M., Frank, M. (2016) Constraining the oceanic barium cycle with stable barium isotopes. Earth and Planetary Science Letters 434, 1–9. https://doi.org/10.1016/j.epsl.2015.11.017
Show in context Recent studies presenting novel dissolved Ba isotope compositions (δ138Ba) have provided additional insights into the processes driving the oceanic cycling of Ba (e.g., Horner et al., 2015; Cao et al., 2016; Hsieh and Henderson, 2017).
View in article
In contrast, the upwelled CDW that moves northwards by Ekman transport undergoes strong Ba isotope fractionation due to high diatom productivity resulting in Ba adsorption to particles in the surface and barite precipitation at intermediate depths (Horner et al., 2015; Cao et al., 2016).
View in article
Cao, Z., Li, Y., Rao, X., Yu, Y., Hathorne, E.C., Siebert, C., Dai, M., Frank, M. (2020) Constraining barium isotope fractionation in the upper water column of the South China Sea. Geochimica et Cosmochimica Acta 288, 120–137. https://doi.org/10.1016/j.gca.2020.08.008
Show in context In the uppermost water column, Ba isotope fractionation is likely induced by preferential adsorption of the light isotopes onto biogenic particles (Cao et al., 2020).
View in article
Although laboratory experiments of adsorption to silica hydrogel exhibited Ba isotope fractionation in the opposite direction, with heavy Ba isotopes being preferentially adsorbed (van Zuilen et al., 2016), field observations consistently reveal lighter isotope enrichment in surface water particles (Horner et al., 2017; Cao et al., 2020).
View in article
de Souza, G.F., Slater, R.D., Dunne, J.P., Sarmiento, J.L. (2014) Deconvolving the controls on the deep ocean’s silicon stable isotope distribution. Earth and Planetary Science Letters 398, 66–76. https://doi.org/10.1016/j.epsl.2014.04.040
Show in context A homogeneity similar to that of δ138Ba signatures is also observed in the dissolved δ30Si and δ114Cd distribution in the deep Pacific, where both isotope values are indistinguishable from those of the deep Southern Ocean (de Souza et al., 2014; Janssen et al., 2017; Xie et al., 2019).
View in article
Emery, W.J., Dewar, J.S. (1982) Mean temperature-salinity, salinity-depth and temperature-depth curves for the North Atlantic and the North Pacific. Progress in Oceanography 11, 219–305. https://doi.org/10.1016/0079-6611(82)90015-5
Show in context The stronger Ba depletion (∼30 nmol kg−1) and associated greater Ba isotope fractionation (∼0.62 ‰) likely result from the weak vertical mixing in the North Pacific Gyre (Emery and Dewar, 1982), allowing more time for Ba removal associated with particle adsorption and barite formation in the upper ocean.
View in article
Geyman, B.M., Ptacek, J.L., LaVigne, M., Horner, T.J. (2019) Barium in deep-sea bamboo corals: Phase associations, barium stable isotopes, & prospects for paleoceanography. Earth and Planetary Science Letters 525, 115751. https://doi.org/10.1016/j.epsl.2019.115751
Show in context In combination with previously reported low and mid-latitude δ138Ba profiles (Horner et al., 2015; Bates et al., 2017; Hsieh and Henderson, 2017; Bridgestock et al., 2018; Geyman et al., 2019), we are now able to better constrain Ba isotope fractionation in the upper ocean and to obtain a more complete picture of the δ138Ba systematics within the global overturning circulation.
View in article
Open squares denote published profiles (Horner et al., 2015; Bates et al., 2017; Hsieh and Henderson, 2017; Bridgestock et al., 2018; Geyman et al., 2019; Whitmore et al., 2022).
View in article
The depth profile of δ138Ba in the mid-latitude North Pacific (SAFe station, black) is from Geyman et al. (2019).
View in article
Literature dissolved δ138Ba and [Ba] data (black) are from Horner et al. (2015), Bates et al. (2017), Hsieh and Henderson (2017), Bridgestock et al. (2018), Geyman et al. (2019), and Whitmore et al. (2022).
View in article
Horner, T.J., Kinsley, C.W., Nielsen, S.G. (2015) Barium-isotopic fractionation in seawater mediated by barite cycling and oceanic circulation. Earth and Planetary Science Letters 430, 511–522. https://doi.org/10.1016/j.epsl.2015.07.027
Show in context Recent studies presenting novel dissolved Ba isotope compositions (δ138Ba) have provided additional insights into the processes driving the oceanic cycling of Ba (e.g., Horner et al., 2015; Cao et al., 2016; Hsieh and Henderson, 2017).
View in article
During sinking and decomposition of these particles, barite formation with a preference for the assimilation of light isotopes (von Allmen et al., 2010) leads to high dissolved δ138Ba values in subsurface seawater (Horner et al., 2015; Bates et al., 2017).
View in article
In combination with previously reported low and mid-latitude δ138Ba profiles (Horner et al., 2015; Bates et al., 2017; Hsieh and Henderson, 2017; Bridgestock et al., 2018; Geyman et al., 2019), we are now able to better constrain Ba isotope fractionation in the upper ocean and to obtain a more complete picture of the δ138Ba systematics within the global overturning circulation.
View in article
Open squares denote published profiles (Horner et al., 2015; Bates et al., 2017; Hsieh and Henderson, 2017; Bridgestock et al., 2018; Geyman et al., 2019; Whitmore et al., 2022).
View in article
In contrast, the upwelled CDW that moves northwards by Ekman transport undergoes strong Ba isotope fractionation due to high diatom productivity resulting in Ba adsorption to particles in the surface and barite precipitation at intermediate depths (Horner et al., 2015; Cao et al., 2016).
View in article
Literature dissolved δ138Ba and [Ba] data (black) are from Horner et al. (2015), Bates et al. (2017), Hsieh and Henderson (2017), Bridgestock et al. (2018), Geyman et al. (2019), and Whitmore et al. (2022).
View in article
Horner, T.J., Pryer, H.V., Nielsen, S.G., Crockford, P.W., Gauglitz, J.M., Wing, B.A., Ricketts, R.D. (2017) Pelagic barite precipitation at micromolar ambient sulfate. Nature Communications 8, 1342. https://doi.org/10.1038/s41467-017-01229-5
Show in context Although laboratory experiments of adsorption to silica hydrogel exhibited Ba isotope fractionation in the opposite direction, with heavy Ba isotopes being preferentially adsorbed (van Zuilen et al., 2016), field observations consistently reveal lighter isotope enrichment in surface water particles (Horner et al., 2017; Cao et al., 2020).
View in article
Hsieh, Y.-T., Henderson, G.M. (2017) Barium stable isotopes in the global ocean: Tracer of Ba inputs and utilization. Earth and Planetary Science Letters 473, 269–278. https://doi.org/10.1016/j.epsl.2017.06.024
Show in context Recent studies presenting novel dissolved Ba isotope compositions (δ138Ba) have provided additional insights into the processes driving the oceanic cycling of Ba (e.g., Horner et al., 2015; Cao et al., 2016; Hsieh and Henderson, 2017).
View in article
In contrast, δ138Ba values of deep waters appear to be mainly controlled by barite dissolution and large scale ocean circulation (Hsieh and Henderson, 2017).
View in article
Given that the oceanic residence time of dissolved Ba (∼3.5 to 5 kyr; Rahman et al., 2022) is longer than the global ocean mixing time, but short enough to prevent complete homogenisation, studies have focused on the importance of advection and mixing on determining dissolved δ138Ba within water masses in the deep Atlantic Meridional Overturning Circulation (AMOC; Bates et al., 2017; Hsieh and Henderson, 2017).
View in article
In combination with previously reported low and mid-latitude δ138Ba profiles (Horner et al., 2015; Bates et al., 2017; Hsieh and Henderson, 2017; Bridgestock et al., 2018; Geyman et al., 2019), we are now able to better constrain Ba isotope fractionation in the upper ocean and to obtain a more complete picture of the δ138Ba systematics within the global overturning circulation.
View in article
Open squares denote published profiles (Horner et al., 2015; Bates et al., 2017; Hsieh and Henderson, 2017; Bridgestock et al., 2018; Geyman et al., 2019; Whitmore et al., 2022).
View in article
Literature dissolved δ138Ba and [Ba] data (black) are from Horner et al. (2015), Bates et al. (2017), Hsieh and Henderson (2017), Bridgestock et al. (2018), Geyman et al. (2019), and Whitmore et al. (2022).
View in article
As outlined by Bridgestock et al. (2018) and Hsieh and Henderson (2017), the continuous addition of Ba from sinking particles along the southward flow of deep Atlantic water masses is unlikely to generate significant deviations from the mixing line, confirmed by the similarity with the regeneration model (Fig. 4).
View in article
The substantially high proportion of regenerated Ba (∼75 %) in the deep Pacific, along with the high Ba ‘utilisation’ (∼70 %) in the upper North Pacific indicated by Hsieh and Henderson (2017), demonstrates that biogeochemical Ba cycling plays a more important role in regulating the deep Pacific δ138Ba signatures than in the Atlantic Ocean.
View in article
Hsieh, Y.-T., Bridgestock, L., Scheuermann, P.P., Seyfried Jr., W.E., Henderson, G.M. (2021) Barium isotopes in mid-ocean ridge hydrothermal vent fluids: A source of isotopically heavy Ba to the ocean. Geochimica et Cosmochimica Acta 292, 348–363. https://doi.org/10.1016/j.gca.2020.09.037
Show in context Hsieh et al. (2021) presented Ba isotope measurements in several hydrothermal vent fluids and suggested that significant inputs of hydrothermal Ba contribute significant amounts of Ba with high δ138Ba to the deep ocean, which causes deviations from the high latitude end member mixing line and the regeneration model (Fig. 4).
View in article
Janssen, D.J., Abouchami, W., Galer, S.J.G., Cullen, J.T. (2017) Fine-scale spatial and interannual cadmium isotope variability in the subarctic northeast Pacific. Earth and Planetary Science Letters 472, 241–252. https://doi.org/10.1016/j.epsl.2017.04.048
Show in context A homogeneity similar to that of δ138Ba signatures is also observed in the dissolved δ30Si and δ114Cd distribution in the deep Pacific, where both isotope values are indistinguishable from those of the deep Southern Ocean (de Souza et al., 2014; Janssen et al., 2017; Xie et al., 2019).
View in article
Using a simple mass balance calculation developed for stable Cd isotopes by Janssen et al. (2017), the net accumulated Ba originating from dissolution of sinking particles in the deep North Pacific is characterised by an average δ138Ba value of 0.22 ± 0.24 ‰ (Supplementary Information), which is consistent with the deep Pacific δ138Ba signature of 0.25 ± 0.04 ‰.
View in article
Lea, D.W., Boyle, E.A. (1991) Barium in planktonic foraminifera. Geochimica et Cosmochimica Acta 55, 3321–3331. https://doi.org/10.1016/0016-7037(91)90491-M
Show in context Barium (Ba) is a bio-intermediate element in the ocean, whose dissolved concentrations ([Ba]) in the water column have a nutrient-like depth profile with a [Ba] depletion in the upper ocean resulting from removal via marine particles (e.g., barite) and [Ba] enrichment at depth due to particulate matter decomposition and remineralisation (Lea and Boyle, 1991).
View in article
Rahman, S., Shiller, A.M., Anderson, R.F., Charette, M.A., Hayes, C.T., Gilbert, M., Grissom, K.R., Lam, P.J., Ohnemus, D.C., Pavia, F.J., Twining, B.S., Vivancos, S.M. (2022) Dissolved and Particulate Barium Distributions Along the US GEOTRACES North Atlantic and East Pacific Zonal Transects (GA03 and GP16): Global Implications for the Marine Barium Cycle. Global Biogeochemical Cycles 36, e2022GB007330. https://doi.org/10.1029/2022GB007330
Show in context Given that the oceanic residence time of dissolved Ba (∼3.5 to 5 kyr; Rahman et al., 2022) is longer than the global ocean mixing time, but short enough to prevent complete homogenisation, studies have focused on the importance of advection and mixing on determining dissolved δ138Ba within water masses in the deep Atlantic Meridional Overturning Circulation (AMOC; Bates et al., 2017; Hsieh and Henderson, 2017).
View in article
Schlitzer, R. (2022) Ocean Data View. http://odv.awi.de
Show in context Produced using Ocean Data View (Schlitzer, 2022).
View in article
Produced using Ocean Data View (Schlitzer, 2022).
View in article
UCDW, Upper Circumpolar Deep Water; LCDW, Lower Circumpolar Deep Water; NPIW, North Pacific Intermediate Water; NPDW, North Pacific Deep Water; PSIW, Pacific Subpolar Intermediate Water. Produced using Ocean Data View (Schlitzer, 2022).
View in article
Schlitzer, R., Anderson, R.F., Dodas, E.M., Lohan, M., Geibert, W., et al. (2018) The GEOTRACES Intermediate Data Product 2017. Chemical Geology 493, 210–223. https://doi.org/10.1016/j.chemgeo.2018.05.040
Show in context Dissolved [Ba] data are from the GEOTRACES intermediate data product 2017 (Schlitzer et al., 2018) and this study. SAMW, Subantarctic Mode Water; AAIW, Antarctic Intermediate Water; CDW, Circumpolar Deep Water; AABW, Antarctic Bottom Water; NADW, North Atlantic Deep Water; LSW, Labrador Sea Water; NEADW, Northeast Atlantic Deep Water; NWABW, Northwest Atlantic Bottom Water; NOW, Northern Overflow Water.
View in article
Dissolved [Ba] data are from the GEOTRACES intermediate data product 2017 (Schlitzer et al., 2018) and this study.
View in article
Sunda, W.G., Huntsman, S.A. (1997) Interrelated influence of iron, light and cell size on marine phytoplankton growth. Nature 390, 389–392. https://doi.org/10.1038/37093
Show in context Previous studies have suggested that the low availability of light and micronutrients (e.g., iron) limits phytoplankton growth in the upper Weddell Sea despite the large inventory of major nutrients available for phytoplankton growth (Sunda and Huntsman, 1997).
View in article
van Zuilen, K., Müller, T., Nägler, T.F., Dietzel, M., Küsters, T. (2016) Experimental determination of barium isotope fractionation during diffusion and adsorption processes at low temperatures. Geochimica et Cosmochimica Acta 186, 226–241. https://doi.org/10.1016/j.gca.2016.04.049
Show in context Although laboratory experiments of adsorption to silica hydrogel exhibited Ba isotope fractionation in the opposite direction, with heavy Ba isotopes being preferentially adsorbed (van Zuilen et al., 2016), field observations consistently reveal lighter isotope enrichment in surface water particles (Horner et al., 2017; Cao et al., 2020).
View in article
von Allmen, K., Böttcher, M.E., Samankassou, E., Nägler, T.F. (2010) Barium isotope fractionation in the global barium cycle: First evidence from barium minerals and precipitation experiments. Chemical Geology 277, 70–77. https://doi.org/10.1016/j.chemgeo.2010.07.011
Show in context During sinking and decomposition of these particles, barite formation with a preference for the assimilation of light isotopes (von Allmen et al., 2010) leads to high dissolved δ138Ba values in subsurface seawater (Horner et al., 2015; Bates et al., 2017).
View in article
Whitmore, L.M., Shiller, A.M., Horner, T.J., Xiang, Y., Auro, M.E., Bauch, D., Dehairs, F., Lam, P.J., Li, J., Maldonado, M.T., Mears, C., Newton, R., Pasqualini, A., Planquette, H., Rember, R., Thomas, H. (2022) Strong Margin Influence on the Arctic Ocean Barium Cycle Revealed by Pan‐Arctic Synthesis. Journal of Geophysical Research: Oceans 127, e2021JC017417. https://doi.org/10.1029/2021JC017417
Show in context Open squares denote published profiles (Horner et al., 2015; Bates et al., 2017; Hsieh and Henderson, 2017; Bridgestock et al., 2018; Geyman et al., 2019; Whitmore et al., 2022).
View in article
Literature dissolved δ138Ba and [Ba] data (black) are from Horner et al. (2015), Bates et al. (2017), Hsieh and Henderson (2017), Bridgestock et al. (2018), Geyman et al. (2019), and Whitmore et al. (2022).
View in article
Xie, R.C., Rehkämper, M., Grasse, P., van de Flierdt, T., Frank, M., Xue, Z. (2019) Isotopic evidence for complex biogeochemical cycling of Cd in the eastern tropical South Pacific. Earth and Planetary Science Letters 512, 134–146. https://doi.org/10.1016/j.epsl.2019.02.001
Show in context A homogeneity similar to that of δ138Ba signatures is also observed in the dissolved δ30Si and δ114Cd distribution in the deep Pacific, where both isotope values are indistinguishable from those of the deep Southern Ocean (de Souza et al., 2014; Janssen et al., 2017; Xie et al., 2019).
View in article
Yu, Y., Siebert, C., Fietzke, J., Goepfert, T., Hathorne, E., Cao, Z., Frank, M. (2020) The impact of MC-ICP-MS plasma conditions on the accuracy and precision of stable isotope measurements evaluated for barium isotopes. Chemical Geology 549, 119697. https://doi.org/10.1016/j.chemgeo.2020.119697
Show in context Seawater samples for dissolved [Ba] and δ138Ba were measured at GEOMAR, Kiel, applying methods detailed in Yu et al. (2020) and the Supplementary Information
View in article
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Supplementary Information
The Supplementary Information includes:
Download Table S-1 (xlsx)
Download the Supplementary Information (PDF)
Figures
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
Horner, T.J., Kinsley, C.W., Nielsen, S.G. (2015) Barium-isotopic fractionation in seawater mediated by barite cycling and oceanic circulation. Earth and Planetary Science Letters 430, 511–522. https://doi.org/10.1016/j.epsl.2015.07.027
; Bates et al., 2017Bates, S.L., Hendry, K.R., Pryer, H.V., Kinsley, C.W., Pyle, K.M., Woodward, E.M.S., Horner, T.J. (2017) Barium isotopes reveal role of ocean circulation on barium cycling in the Atlantic. Geochimica et Cosmochimica Acta 204, 286–299. https://doi.org/10.1016/j.gca.2017.01.043
; Hsieh and Henderson, 2017Hsieh, Y.-T., Henderson, G.M. (2017) Barium stable isotopes in the global ocean: Tracer of Ba inputs and utilization. Earth and Planetary Science Letters 473, 269–278. https://doi.org/10.1016/j.epsl.2017.06.024
; Bridgestock et al., 2018Bridgestock, L., Hsieh, Y.-T., Porcelli, D., Homoky, W.B., Bryan, A., Henderson, G.M. (2018) Controls on the barium isotope compositions of marine sediments. Earth and Planetary Science Letters 481, 101–110. https://doi.org/10.1016/j.epsl.2017.10.019
; Geyman et al., 2019Geyman, B.M., Ptacek, J.L., LaVigne, M., Horner, T.J. (2019) Barium in deep-sea bamboo corals: Phase associations, barium stable isotopes, & prospects for paleoceanography. Earth and Planetary Science Letters 525, 115751. https://doi.org/10.1016/j.epsl.2019.115751
; Whitmore et al., 2022Whitmore, L.M., Shiller, A.M., Horner, T.J., Xiang, Y., Auro, M.E., Bauch, D., Dehairs, F., Lam, P.J., Li, J., Maldonado, M.T., Mears, C., Newton, R., Pasqualini, A., Planquette, H., Rember, R., Thomas, H. (2022) Strong Margin Influence on the Arctic Ocean Barium Cycle Revealed by Pan‐Arctic Synthesis. Journal of Geophysical Research: Oceans 127, e2021JC017417. https://doi.org/10.1029/2021JC017417
). Produced using Ocean Data View (Schlitzer, 2022Schlitzer, R. (2022) Ocean Data View. http://odv.awi.de
).
Figure 2 Depth profiles of dissolved δ138Ba in the Weddell Sea (green), the Labrador Sea (orange), the Fram Strait (pink), and the low and mid-latitude Atlantic Ocean (black, Bates et al., 2017
Bates, S.L., Hendry, K.R., Pryer, H.V., Kinsley, C.W., Pyle, K.M., Woodward, E.M.S., Horner, T.J. (2017) Barium isotopes reveal role of ocean circulation on barium cycling in the Atlantic. Geochimica et Cosmochimica Acta 204, 286–299. https://doi.org/10.1016/j.gca.2017.01.043
). Dissolved [Ba] data are from the GEOTRACES intermediate data product 2017 (Schlitzer et al., 2018Schlitzer, R., Anderson, R.F., Dodas, E.M., Lohan, M., Geibert, W., et al. (2018) The GEOTRACES Intermediate Data Product 2017. Chemical Geology 493, 210–223. https://doi.org/10.1016/j.chemgeo.2018.05.040
) and this study. SAMW, Subantarctic Mode Water; AAIW, Antarctic Intermediate Water; CDW, Circumpolar Deep Water; AABW, Antarctic Bottom Water; NADW, North Atlantic Deep Water; LSW, Labrador Sea Water; NEADW, Northeast Atlantic Deep Water; NWABW, Northwest Atlantic Bottom Water; NOW, Northern Overflow Water. Produced using Ocean Data View (Schlitzer, 2022Schlitzer, R. (2022) Ocean Data View. http://odv.awi.de
).
Figure 3 Depth profiles of dissolved δ138Ba in the Pacific Ocean (blue). The depth profile of δ138Ba in the mid-latitude North Pacific (SAFe station, black) is from Geyman et al. (2019)
Geyman, B.M., Ptacek, J.L., LaVigne, M., Horner, T.J. (2019) Barium in deep-sea bamboo corals: Phase associations, barium stable isotopes, & prospects for paleoceanography. Earth and Planetary Science Letters 525, 115751. https://doi.org/10.1016/j.epsl.2019.115751
. Dissolved [Ba] data are from the GEOTRACES intermediate data product 2017 (Schlitzer et al., 2018Schlitzer, R., Anderson, R.F., Dodas, E.M., Lohan, M., Geibert, W., et al. (2018) The GEOTRACES Intermediate Data Product 2017. Chemical Geology 493, 210–223. https://doi.org/10.1016/j.chemgeo.2018.05.040
) and this study. UCDW, Upper Circumpolar Deep Water; LCDW, Lower Circumpolar Deep Water; NPIW, North Pacific Intermediate Water; NPDW, North Pacific Deep Water; PSIW, Pacific Subpolar Intermediate Water. Produced using Ocean Data View (Schlitzer, 2022Schlitzer, R. (2022) Ocean Data View. http://odv.awi.de
).
Figure 4 Deep ocean mixing line (black dashed line; data from this study) of δ138Ba against 1/[Ba] and results of a regeneration model assuming a pre-formed [Ba] of 35 nmol kg−1 and a δ138Ba value of 0.62 ‰ (grey dashed line). Literature dissolved δ138Ba and [Ba] data (black) are from Horner et al. (2015)
Horner, T.J., Kinsley, C.W., Nielsen, S.G. (2015) Barium-isotopic fractionation in seawater mediated by barite cycling and oceanic circulation. Earth and Planetary Science Letters 430, 511–522. https://doi.org/10.1016/j.epsl.2015.07.027
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. The potential impacts of hydrothermal Ba input in the Atlantic and progressive Ba accumulation in the deep Pacific are denoted by bold light grey arrows.