Publication Date:
2022-05-25
Description:
Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here by permission of Elsevier for personal use, not for redistribution. The definitive version was published in Earth and Planetary Science Letters, 430 (2015): 511-522, doi:10.1016/j.epsl.2015.07.027.
Description:
The marine biogeochemical cycle of Ba is thought to be controlled by particulate BaSO4 (barite) precipitation associated
with the microbial oxidation of organic carbon and its subsequent dissolution in the BaSO4-undersaturated
water column. Despite many of these processes being largely unique to Ba cycling, concentrations of Ba and Si in
seawater exhibit a strong linear correlation. The reasons for this correlation are ambiguous, as are the depth ranges
corresponding to the most active BaSO4 cycling and the intermediate sources of Ba to particulate BaSO4. Stable
isotopic analyses of dissolved Ba in seawater should help address these issues, as Ba-isotopic compositions are
predicted to be sensitive to the physical and biogeochemical process that cycle Ba. We report a new methodology
for the determination of dissolved Ba-isotopic compositions in seawater and results from a 4, 500 m depth profile
in the South Atlantic at 39.99 S, 0.92 E that exhibit oceanographically-consistent variation with depth. These data
reveal that water masses obtain their [Ba] and Ba-isotopic signatures when at or near the surface, which relates to
the cycling of marine BaSO4. The shallow origin of these signatures requires that the substantial Ba-isotopic variations
in the bathypelagic zone were inherited from when those deep waters were last ventilated. Indeed, the water
column below 600 m is well explained by conservative mixing of water masses with distinct [Ba] and Ba-isotopic
compositions. This leads us to conclude that large scale oceanic circulation is important for sustaining the similar
oceanographic distributions of Ba and Si in the South Atlantic, and possibly elsewhere. These data demonstrate
that the processes of organic carbon oxidation, BaSO4 cycling, and Ba-isotopic fractionation in seawater are closely
coupled, such that Ba-isotopic analyses harbor great potential as a tracer of the carbon cycle in the modern and
paleo-oceans.
Description:
T.J.H. acknowledges support from Makoto
A. Saito (Gordon and Betty Moore Foundation; Project # 3782) and the Postdoctoral Scholar Program at the Woods
Hole Oceanographic Institution, with funding provided by the Doherty Foundation. Development of Ba-isotopic
protocols at NIRVANA was made possible with funding from The Andrew W. Mellon Foundation Endowed Fund
for Innovative Research (T.J.H. and S.G.N.).
Keywords:
Barium
;
Isotopic fractionation
;
Barite
;
Seawater
;
Biogeochemistry
Repository Name:
Woods Hole Open Access Server
Type:
Preprint
Format:
application/pdf
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