Coastal ocean and shelf-sea biogeochemical cycling of trace elements and isotopes: lessons learned from GEOTRACES

• Continental shelves and shelf seas play a central role in the global carbon cycle. However,their importance with respect to trace element and isotope (TEI) inputs to ocean basinsis less well understood. Here, we present major findings on shelf TEI biogeochemistryfrom the GEOTRACES programme as well as a proof of concept for a new method toestimate shelf TEI fluxes. The case studies focus on advances in our understanding of TEIcycling in the Arctic, transformations within a major river estuary (Amazon), shelf sedimentmicronutrient fluxes and basin-scale estimates of submarine groundwater discharge. Theproposed shelf flux tracer is 228-radium (T1/2 =5.75 yr), which is continuously supplied tothe shelf from coastal aquifers, sediment porewater exchange and rivers. Model-derived shelf228Ra fluxes are combined with TEI/ 228Ra ratios to quantify ocean TEI fluxes from thewestern North Atlantic margin. The results from this new approach agree well with previousestimates for shelf Co, Fe, Mn and Zn inputs and exceed published estimates of atmosphericdeposition by factors of approximately 3–23. Lastly, recommendations are made for additionalGEOTRACES process studies and coastal margin-focused section cruises that will help refinethe model and provide better insight on the mechanisms driving shelf-derived TEI fluxesto the ocean.This article is part of the themed issue ‘Biological and climatic impacts of ocean trace elementchemistry’.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Geokemi (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Geochemistry (hsv//eng)

Nyckelord

GEOTRACES

trace elements

isotopes

coastal-ocean

The changing Earth

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