Undocumented water column sink for cadmium in open ocean oxygen-deficient zones.
Cadmium (Cd) is a micronutrient and a tracer of biological productivity and circulation in the ocean. The correlation between dissolved Cd and the major algal nutrients in seawater has led to the use of Cd preserved in microfossils to constrain past ocean nutrient distributions. However, linking Cd to marine biological processes requires constraints on marine sources and sinks of Cd. Here, we show a decoupling between Cd and major nutrients within oxygen-deficient zones (ODZs) in both the Northeast Pacific and North Atlantic Oceans, which we attribute to Cd sulfide (CdS) precipitation in euxinic microenvironments around sinking biological particles. We find that dissolved Cd correlates well with dissolved phosphate in oxygenated waters, but is depleted compared with phosphate in ODZs. Additionally, suspended particles from the North Atlantic show high Cd content and light Cd stable isotope ratios within the ODZ, indicative of CdS precipitation. Globally, we calculate that CdS precipitation in ODZs is an important, and to our knowledge a previously undocumented marine sink of Cd. Our results suggest that water column oxygen depletion has a substantial impact on Cd biogeochemical cycling, impacting the global relationship between Cd and major nutrients and suggesting that Cd may be a previously unidentified tracer for water column oxygen deficiency on geological timescales. Similar depletions of copper and zinc in the Northeast Pacific indicate that sulfide precipitation in ODZs may also have an influence on the global distribution of other trace metals.
School of Earth and Ocean Sciences, University of Victoria, Victoria, BC, Canada V8W 2Y2;
David J
DJ
Janssen
Department of Earth and Ocean Sciences, University of South Carolina, Columbia, SC 29208; and.
Tim M
TM
Conway
Department of Earth and Ocean Sciences, University of South Carolina, Columbia, SC 29208; and.
Seth G
SG
John
Fisheries and Oceans Canada, Victoria, BC, Canada V8W 3V6.
James R
JR
Christian
School of Earth and Ocean Sciences, University of Victoria, Victoria, BC, Canada V8W 2Y2;
Dennis I
DI
Kramer
School of Earth and Ocean Sciences, University of Victoria, Victoria, BC, Canada V8W 2Y2;
Tom F
TF
Pedersen
School of Earth and Ocean Sciences, University of Victoria, Victoria, BC, Canada V8W 2Y2; jcullen@uvic.ca.
Jay T
JT
Cullen
D002104:Cadmium / Q000378:metabolism*; D008386:Marine Biology; D009791:Oceanography; D009792:Oceans and Seas; D010100:Oxygen / Q000378:metabolism*; D010710:Phosphates / Q000378:metabolism; D012623:Seawater / Q000737:chemistry*; D058009:Stramenopiles / Q000254:growth & development* / Q000378:metabolism*; D014131:Trace Elements / Q000378:metabolism
D010710:Phosphates; D014131:Trace Elements; D002104:Cadmium; D010100:Oxygen
GEOTRACES; biogeochemistry; marine chemistry; paleoceanography; trace elements