Hobart

Seminar Abstract

Wednesday 4 March 2009, 11.00am (Tas time)
CSIRO Auditorium, Hobart

Frank Dehairs
Earth System Sciences Research Group
Vrije Universiteit Brussel

Respiration of organic carbon in the mesopelagic ocean: What is there to learn from the barite proxy and is there a control by Fe?

The oceanic biological pump drives sequestration of carbon dioxide in the deep sea via sinking particles. Rapid biological consumption and remineralization of carbon in the “twilight zone” (depths between the euphotic zone and 1000 meters) reduce the efficiency of sequestration. Assessing this sequestration efficiency is important and requires access to adequate tools for assessing deep ocean respiration. Different approaches based on rate measurements and distributions of tracers are presently being used. These are all indirect approaches and the O_2 or O.C. respiration rates deduced are subject to a series of assumptions, conversion factors which, however, may vary widely. An overview will be given of these currently applied approaches to measure respiration in the deep ocean, highlighting their shortcomings.

Next, the usefulness of authigenic barite (BaSO_4 ) as a proxy for productivity and degradation of plankton detritus will be discussed as well as its link to oxygen consumption in the mesopelagic Southern Ocean water column. The significance of mesopelagic remineralisation (as reflected by suspended barite) relative to export production appears tuned by the impact of iron availability on trophic interactions. Overall it appears that Fe sufficiency favors enhanced respiration in surface waters, relatively little remineralisation at mesopelagic depths, and efficient export to the bathypelagic. In contrast, low Fe conditions lead to relatively less grazing pressure, carbon export via relatively low density aggregate particles, which are prone to easier breakdown and consumption at mesopelagic depths. This scenario rests primarily on observations gathered from natural and artificial Fe experiments, but appears to be corroborated by observations from the SAZ and ACC south of Tasmania.

Seminar Recording

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Location:
CSIRO = Marine Laboratories Auditorium, Castray Esplanade, Hobart

For further information, or to schedule a seminar, contact:
To schedule a seminar, contact:
Clothilde Langlais, (Oceanographic seminars) CSIRO Marine and Atmospheric Research (03) 6232 5399
Natalie Kelly, (Biology/Modelling seminars) CSIRO Marine and Atmospheric Research 0438 452 483
Jillian Enraght-Moony, (seminar administrator) CSIRO Marine and Atmospheric Research (03) 6232 5320
Communications Manager, Antarctic Climate and Ecosystems CRC (03) 6226 2265
Margaret Hazelwood, Institute of Antarctic and Southern Ocean Studies (IASOS) University of Tasmania (03) 6226 2971

Last updated 8/12/09