Presenter: Jonathan Lauderdale (Massachusetts Institute of Technology)

Description:
Primary production in the Southern Ocean, along with about half of the  global ocean surface, is limited by the availability of the micronutrient  iron. Ferric iron is rapidly scavenged or precipitated in seawater, but  standing stocks of dissolved iron are maintained by association with  organic chelating ligands which, in turn, are produced by the activity of  microbes themselves.  This coupling between biology and trace metal biogeochemistry has not  previously been considered in models used to examine the climatic  importance of "High Nutrient Low Chlorophyll" regions, like the Southern  Ocean, in the global carbon cycle, or in estimating the impact of a  changing ocean circulation on atmospheric carbon dioxide levels. Using a suite of idealized box model and coarse resolution global ocean  biogeochemistry model simulations that incorporate the feedback between  microbial activity, ligand production, and iron concentration allows us to reassess the climatic effects of changing Southern Ocean physical drivers  and biogeochemical forcing on atmospheric pCO₂. We will show that the  "ligand-iron-microbe" coupling is critical in determining the magnitude and the sign of atmospheric pCO₂ anomalies to perturbations in the Southern  Ocean residual circulation and ocean iron input. We hypothesize that these ligand-iron cycle feedbacks may have shaped the  ocean's response to past climate changes, such as inception of Northern  Hemisphere glaciation or the Glacial-Interglacial cycles, and may play a  role under future changes in climate.