Oxygen consumption in the Eastern Mediterranean

Rates of oxygen consumption are determined by fitting simulated oxygen conc entrations to observations from a medium-resolution survey of the Eastern M editerranean in 1987 (METEOR cruise M5/6). The simulations are obtained wit h a previously described two-dimensional kinematic model of the sea, which is newly calibrated using concurrent hydrographic and tracer data, and with oxygen consumption as a function of depth being parameterized following pr evious work. The consumption rate is obtained as R(z) = 22 (z/100)(-2) + 0. 31 mu mol/(kg yr) for z < 1000 m, and R = 0.53 <mu>mol/(kg yr) for z greate r than or equal to 1000 m. For the waters below about 700 m depth, the unce rtainty in R is approximately +/- 35%. Significant error contributions aris e from the oxygen concentration of the waters newly supplied to the deep wa ters, and from possible deviations from a steady state in circulation and i n oxygen cycling. The upper ocean rates are rather more uncertain, but they are compatible with rates from the literature. The deduced deep-water oxyg en consumption rate is considerably higher than the rates found in previous deep-ocean work. Such rather high rates, which possibly are related to the comparatively high temperatures of the deep waters, have repercussions in various contexts, e.g. in the assessment of environmental conditions in the past that led to the formation of sapropel layers. The updated circulation model yields a deep-water renewal rate for the Eastern Mediterranean only moderately different from a previous value. The rate actually replenishing the deep regime amounts to 5.1 x 10(5) m(3)/s (+/- 20%), of which 2.8 x 10( 5) m(3)/s (+/- 30%) are recirculated deep water. Convective renewal of the deep regime (> 1200 m depth) by the combined addition of surface and interm ediate waters requires 150 years (+/- 30%). (C) 2001 Elsevier Science Ltd. All rights reserved.