Fueling Western Mediterranean deep metabolism by Deep Water formation and shelf-slope cascading : Evidence from 1981

Abstract

We focus here on microbial respiration and its potential enhancement by organic-carbon injection via Deep and Intermediate Water formation in the western Mediterranean Sea. Electron transport system (ETS) activities of the nanoplankton and microplankton in the intermediate and deep water from this area show unexpected enhancement. Since ETS is a proxy for respiration these measurements indicate elevated respiration in these waters. In addition, they suggest horizontal transport of organic-carbon rich water-masses. In the western Mediterranean Sea the metabolic rates below 1,500 m were greater than rates at the same depths in the Atlantic. When all the profiles were corrected to the same temperature and normalized by the metabolic rate at 200 m, the Western Mediterranean rates were greater than rates from the same depths in both the Atlantic and equatorial Pacific Oceans. They also exceeded rates predicted from sediment traps. Furthermore they were not consistent with organic matter being supplied via rapidly sinking particulate material. Instead, they may be supported by dissolved organic carbon (DOC) transported to depth by eddies (van Haren et al., 2006), wintertime deepwater convection, or the type of wintertime cold-water cascading recently observed in the canyons on the Catalan-Occitan continental shelf and slope (Canals et al., 2006; Font et al., 2007).