Premium
Global Contrasts Between Oceanic Cycling of Cadmium and Phosphate
Author(s) -
Roshan Saeed,
DeVries Tim
Publication year - 2021
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/2021gb006952
Subject(s) - biogeochemical cycle , thermocline , cycling , cadmium , oceanography , nutrient cycle , geotraces , nutrient , latitude , geochemical cycle , environmental science , surface water , deep sea , biogeochemistry , ocean current , geology , environmental chemistry , phosphate , seawater , chemistry , ecology , biology , archaeology , organic chemistry , geodesy , environmental engineering , history
Cadmium (Cd) is a trace metal whose distribution in the ocean bears a remarkable resemblance to the nutrient phosphate (PO 4 3− ). This resemblance has led to the use of Cd as a proxy for ocean nutrient cycling in paleoceanographic applications, but the processes governing the cycling of Cd in the modern ocean remain unclear. In this study, we use previously published Cd observations and an Artificial Neural Network to produce a dissolved Cd climatology that reproduces the observed subtle deviations between the Cd andPO 4 3 −distributions. We use the Cd andPO 4 3 −climatologies, along with an ocean circulation inverse model, to diagnose the biogeochemical sources and sinks of dissolved Cd andPO 4 3 −. Our calculations reveal that dissolved Cd, likePO 4 3 −, is removed in the surface ocean and has a source in the subsurface, consistent with the simultaneous incorporation of Cd andPO 4 3 −into sinking organic particles. However, there are also contrasts between the cycling of dissolved Cd andPO 4 3 − . In particular, theCd:PO 4 3 −surface export ratio varies 8‐fold across latitudes, reaching highest values in the iron‐limited sub‐Antarctic Southern Ocean. This depletes Cd relative toPO 4 3 −in the low‐latitude thermocline while adding excess Cd to deep waters by the regeneration of Cd‐enriched particles. Also, Cd tends to regenerate slightly deeper thanPO 4 3 −in the subsurface ocean, and theCd:PO 4 3 −regeneration ratio reaches a maximum at 700–1,500 m. These contrasts are responsible for a slight concavity in theCd ‐ PO 4 3 −relationship and should be considered when interpreting paleoceanographic Cd records.