CS08 Biogeochemical Cycles
Date: Monday, June 10, 2002
Time: 4:45:00 PM
Location: Saanich
 
LegendreL, Villefranche Oceanography Laboratory, Villefranche-sur-Mer, France, legendre@obs-vlfr.fr
Rivkin, R, B, Ocean Sciences Centre, Memorial Univ of Newfoundland, St. John's, Canada, rrivkin@mun.ca
Rassoulzadegan, F, , Villefranche Oceanography Laboratory, Villefranche-sur-Mer, France, rassoul@obs-vlfr.fr
 
NON-STOICHIOMETRY OF ORGANIC MATTER EXPORT FROM THE EUPHOTIC ZONE: EFFECTS ON MESOPELAGIC CARBON CYCLING
image
Most of the organic matter that is exported (E) from the euphotic zone is remineralized to CO2 in the underlying mesopelagic layer (MPL) or twilight zone (i.e. mesopelagic respiration, Rmpl). A large fraction of this remineralized CO2 is ventilated back to the surface layer on decadal time scales, where it equilibrates with the atmosphere. Only the carbon that is remineralized or buried below the permanent pycnocline is isolated from the atmosphere long enough to be of significance to the global climate (i.e. sequestration, S = E - Rmpl). The usual model of organic export assumes that E = new production, based on the assumption that the long-term ratio of carbon to the limiting element in the exported material [(C:L)E)] is the same as in long-term phytoplankton net production (i.e. the Redfield ratio when L is N, P or Si). In oceans, however, (C:L)E for both dissolved and particulate organic matter in the MPL is higher than the Redfield ratio. The elemental composition of the organic input to the MPL has a deep influence on its in situ remineralisation, and thus on S.