Respiration in the mesopelagic and bathypelagic zones of the oceans

This chapter reviews the mechanisms of transport and remineralization of organic matter in the dark water-columns and sediments of the oceans. Different approaches to estimating respiration rates are compared, and the discrepancies obtained by different methodologies are discussed. Finally, a respiratory carbon budget is produced for dark ocean areas, which includes vertical and lateral fluxes of organic matter. Overall, direct measurements of respiration, as well as indirect approaches, converge to suggest a total dark ocean respiration of 1.5-1.7 Pmol C/a. Carbon mass balances in the dark ocean suggest that the dark ocean receives 1.5-1.6 Pmol C/a, similar to the estimated respiration, of which >70% is in the form of sinking particles. Almost all the organic matter (~92%) is remineralized in the water column, the burial in sediments accounts for less than 1%. Mesopelagic (150-1000 m) respiration accounts for ~70% of dark ocean respiration, with average integrated rates of 3-4 mol C/m2-a, 6-8 times greater than in the bathypelagic zone. The results show that respiration in dark ocean is a major component of the carbon flux in the biosphere.