Oxygen consumption in the Eastern Mediterranean

Abstract

Rates of oxygen consumption are determined by fitting simulated oxygen concentrations to observations from a medium-resolution survey of the Eastern Mediterranean in 1987 (METEOR cruise M5/6). The simulations are obtained with 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 previous work. The consumption rate is obtained as R(z)=22 (z/100) −2 +0.31 μmol/(kg yr) for z <1000 m , and R =0.53 μmol/(kg yr) for z ⩾1000 m . For the waters below about 700 m depth, the uncertainty in R is approximately ±35%. Significant error contributions arise from the oxygen concentration of the waters newly supplied to the deep waters, and from possible deviations from a steady state in circulation and in oxygen cycling. The upper ocean rates are rather more uncertain, but they are compatible with rates from the literature. The deduced deep-water oxygen 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 5.1×10 5 m 3/s (±20%), of which 2.8×10 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 intermediate waters requires 150 years (±30%).