Summary of Abstract Submission

Abstract Submission No. IO50-06-0007PresentationPoster

THE SOUTHERN BORDER OF THE UPPER OMZ IN THE CENTRAL ARABIAN SEA

Prof. Karl BANSE*1, James R. Postel1

1 School of Oceanogr., Univ. of Washington, USA

ABSTRACT :

At depth in the oceanic water column, dissolved O2 is maintained by the balance between the supply, principally by horizontal advection and mixing versus the demand by degradable organic matter, largely from organisms and settling particles. Three-D models of, say, 0.1o resolution, place O2-rich and O2-poor regions correctly but are not definite about the gradients in the transition zones. For the mid-1980s -1990s between 150 and at least 500 m depth, we infer that the location of the southern border zone was determined by hydrography rather than a shifted balance between supply and consumption of O2. Steep horizontal declines from >10-20 to < 1 mol L-1 O2 were associated with a change in water masses on a section along 65E occupied seven times in one year (U.S. JGOFS program). During December 1994 and 1995 the transitions occurred between 11 and 12N versus 10 and 11N, respectively (see Figures). The T-S relations changed to the south of the principal horizontal O2 gradients, as similarly at the other five visits to the section by R/V T. G. Thompson. Likewise, during December 1986 along 64E, the very sharp border zone (decline from 30-50 to 4-7 mol L-1 in = 50 km) occurred near 13N, accompanied by a water mass change (RRS Charles Darwin, cruise 19).