HR: 15:10h
AN: OS23F-07    [Abstracts]
TI: Decreasing trends in the dissolved oxygen content of North Atlantic thermocline waters: Possible causes and implications for the ocean carbon cycle
AU: * Gruber, N
EM: ngruber@igpp.ucla.edu
AF: University of California, Los Angeles, IGPP, 5853 Slichter Hall, Los Angeles, CA 90095 United States
AU: Bullister, J L
EM: John.L.Bullister@noaa.gov
AF: NOAA/PMEL, Ocean Climate Research Division, 7600 Sand Point Way NE, Seattle, WA 98115 United States
AU: Johnson, G C
EM: Gregory.C.Johnson@noaa.gov
AF: NOAA/PMEL, Ocean Climate Research Division, 7600 Sand Point Way NE, Seattle, WA 98115 United States
AU: Swift, J H
EM: jswift@ucsd.edu
AF: Scripps Institution of Oceanography, Physical Oceanography Research Division, UCSD, 9500 Gilman Drive, La Jolla, CA 92093 United States
AU: Joyce, T M
EM: tjoyce@whoi.edu
AF: Woods Hole Oceanographic Institution, Dept. of Physical Oceanography, Clark 349, Woods Hole, MA 02543 United States
AU: Macdonald, A
EM: amacdonald@whoi.edu
AF: Woods Hole Oceanographic Institution, Dept. of Physical Oceanography, Clark 349, Woods Hole, MA 02543 United States
AU: Toole, J
EM: jtoole@whoi.edu
AF: Woods Hole Oceanographic Institution, Dept. of Physical Oceanography, Clark 349, Woods Hole, MA 02543 United States
AU: Smethie, W A
EM: bsmeth@ldeo.columbia.edu
AF: Lamont Doherty Earh Observatory, Columbia University, Palisades, NY 10964 United States
AU: Zhang, J
EM: Jia-Zhong.Zhang@noaa.gov
AF: NOAA/AOML, Ocean Chemistry Division, Rickenbacker Causeway, Miami, FL 33149 United States
AU: Wanninkhof, R
EM: Rik.Wanninkhof@noaa.gov
AF: NOAA/AOML, Ocean Chemistry Division, Rickenbacker Causeway, Miami, FL 33149 United States
AB: Investigations of thermocline waters in the Pacific and Southern Ocean have revealed substantial recent decreases in their dissolved oxygen content. Simulations with ocean biogeochemistry models suggest that some of these decreases are consistent with expected trends arising from the impact of global climate change on ocean biogeochemistry. These models simulated similar changes in the North Atlantic. We investigate this model prediction by using results from three CO$_2$/CLIVAR repeat hydrography cruises in the North Atlantic (A16N, A20, A22) that permit us to investigate changes in thermocline oxygen concentrations between the early to mid 1990-ties and 2004 in the entire North Atlantic basin. Preliminary analyses in the eastern basin show a strong decrease of the oxygen concentration and corresponding increase in the apparent oxygen utilization (AOU) in the lower thermocline north of about 35$^{\circ}$N (sigma-theta about 27.0 to 27.5), with changes of up to 40 $\mu$mol kg$^{-1}$ within 10 years. The affected regions are not associated with a particular water mass, but extend from just below recently ventilated waters towards the interior ocean oxgyen minimum. We propose that the primary reason for this synchronous increase in AOU across a wide density range is a recent change in ocean circulation that has decreased the ventilation of all isopycnals outcropping in the northern North Atlantic with densities between about sigma-theta 27.0 and 27.5. Adopting an oxygen utilization rate of about 5 to 10 $\mu$mol kg$^{-1}$ yr$^{-1}$, we estimate an increase in the apparent ventilation age of several years, amounting in some case to a near doubling of this age. We suspect that a large-scale change in North Atlantic climate, perhaps associated with the decadal trend in the North Atlantic Oscillation, must have been at the root of these changes in thermocline oxygen. We will present results from an extended study that includes changes in the western basin and discuss the impact of these findings on our understanding of ocean biogeochemistry and the carbon cycle in greater detail during the presentation.
UR: http://ushydro.ucsd.edu/
DE: 4805 Biogeochemical cycles (1615)
DE: 4806 Carbon cycling
DE: 4283 Water masses
DE: 1615 Biogeochemical processes (4805)
DE: 1635 Oceans (4203)
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting