Particulate Cadmium Accumulation in the Mesopelagic Ocean.

Area of Science:

• Marine chemistry
• Biogeochemical cycles
• Oceanography

Background:

• Dissolved cadmium (dCd) and phosphate (PO4) observations indicate dCd loss to particulate matter in tropical oxyclines.
• The mechanisms driving this dCd loss remain unclear.

Purpose of the Study:

• Examine the phenomenon of dCd loss to particulate phases from a particulate cadmium (pCd) perspective.
• Investigate the processes of regeneration and subsurface accumulation of pCd and particulate phosphorus (pP).

Main Methods:

• Compiled existing observations of pCd and pP.
• Presented new data from the US GEOTRACES GP15 Pacific Meridional Transect.
• Utilized a simple algorithm to model station depth profiles of pCd and pP.

Main Results:

• Regeneration processes showed decoupling of pCd and pP due to variable partitioning between labile and non-labile particulate pools.
• Evidence for subsurface pCd accumulation was found at 31 stations, most consistently in the mesopelagic tropical Pacific.
• Subsurface pCd accumulation was not strongly correlated with dissolved oxygen or particulate sulfide but occurred where dissolved cadmium (dCd) was high relative to dissolved zinc (dZn).

Conclusions:

• The observed decoupling suggests complex regeneration pathways for Cd and P.
• Subsurface pCd accumulation may be linked to enhanced biological uptake of dCd in response to the subsurface micronutrient balance.
• Further research is needed to fully understand the biogeochemical cycling of cadmium in the ocean.