HR: 09:00h
AN: OS11C-05 INVITED     [Abstracts]
TI: Physical and biogeochemical controls on the air-sea disequilibrium of trace gases
AU: * Ito, T
EM: ito@ocean.mit.edu
AF: Program in Atmospheres Oceans and Climate, Massachusetts Institute of Technology, 54-1511 77 Massachusetts Avenue, Cambridge, MA 02139 United States
AU: Follows, M
EM: mick@ocean.mit.edu
AF: Program in Atmospheres Oceans and Climate, Massachusetts Institute of Technology, 54-1511 77 Massachusetts Avenue, Cambridge, MA 02139 United States
AB: The degree of saturation of trace gases in surface waters drives the flux across the sea surface, and influences interior tracer distributions. We develop a conceptual framework for understanding the mechanisms controlling the disequilibrium of trace gases in the surface ocean, and illustrate it using a global ocean biogeochemistry model. Air-sea heat flux, physical transport and biological sources drive surface concentrations away from equilibrium, and the degree of saturation depends on the relative timescale of these processes with respect to the timescale of air-sea gas exchange. Numerical simulations allow us to separate and quantify the relative importance of these processes. For example, in the region of deep water formation, the intense heat loss drives both surface O$_2$ and CO$_2$ toward undersaturation. However, deep convection and associated entrainment of deep waters bring old, O$_2$-depleted and CO$_2$-enriched waters to the surface, driving surface waters toward undersaturation of O$_2$ and supersaturation of CO$_2$. Furthermore, sea ice cover increases the timescale of air-sea gas exchange, and effectively increases the magnitude of surface disequilibrium. Although air-sea equilibration of oxygen is relatively rapid, "preformed" O$_2$ in deep waters is significantly undersaturated due to the reinforcing effects of these processes. This leads to a significant, systematic bias in estimates of respiration based on Apparent Oxygen Utilization (AOU).
DE: 4820 Gases
DE: 4842 Modeling
DE: 4255 Numerical modeling
DE: 4532 General circulation
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting