Woods Hole Oceanographic Institution

Dr Phoebe J Lam

»Inverse methods for particle dynamics
»The speciation of marine particulate iron
»The dynamic biological pump
»The continental margin is a key source of iron
»High Biomass Low Export regimes in the Southern Ocean
»Wintertime phytoplankton bloom in the Subarctic Pacific supported by continental margin iron
»Differential effects of iron additions on organic and inorganic carbon production by phytoplankton


Phoebe J. Lam, Scott C. Doney, and James K. B. Bishop


The dynamic ocean biological pump: Insights from a global compilation of particulate organic carbon, CaCO3, and opal concentration profiles from the mesopelagic

, Global Biogeochemical Cycles, 25(3): GB3009, doi:10.1029/2010GB003868, published 22 July 2011

We have compiled a global data set of 62 open ocean profiles of particulate organic carbon (POC), CaCO3, and opal concentrations collected by large volume in situ filtration in the upper 1000 m over the last 30 years. We define concentrationbased metrics for the strength (POC concentration at depth) and efficiency (attenuation of POC with depth in the mesopelagic) of the biological pump. We show that the strength and efficiency of the biological pump are dynamic and are characterized by a regime of constant and high transfer efficiency at low to moderate surface POC and a bloom regime where the height of the bloom is characterized by a weak deep biological pump and low transfer efficiency. The variability in POC attenuation length scale manifests in a clear decoupling between the strength of the shallow biological pump (e.g., POC at the export depth) and the strength of the deep biological pump (POC at 500 m).

We suggest that the paradigm of diatomdriven export production is driven by a too restrictive perspective on upper mesopelagic dynamics. Indeed, our full mesopelagic analysis suggests that large, blooming diatoms have low transfer efficiency and thus may not export substantially to depth; rather, our analysis suggests that ecosystems characterized by smaller cells and moderately high %CaCO3 have a high mesopelagic transfer efficiency and can have higher POC concentrations in the deep mesopelagic even with relatively low surface or nearsurface POC. This has negative implications for the carbon sequestration prospects of deliberate iron fertilization.

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