Respiration in the mesopelagic and bathypelagic zones of the oceans

Abstract

Outline In this chapter the mechanisms of transport and remineralization of organic matter in the dark water-column and sediments of the oceans are reviewed. We compare the different approaches to estimate respiration rates, and discuss the discrepancies obtained by the different methodologies. Finally, a respiratory carbon budget is produced for the dark ocean, which includes vertical and lateral fluxes of organic matter. In spite of the uncertainties inherent in the different approaches to estimate carbon fluxes and oxygen consumption in the dark ocean, estimates vary only by a factor of 1.5. 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 −1 . Carbon mass balances in the dark ocean suggest that the dark ocean receives 1.5–1.6 Pmol C a −1 , 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 <1%. Mesopelagic (150–1000 m) respiration accounts for ∼70% of dark ocean respiration, with average integrated rates of 3–4 mol C m −2 a −1 , 6–8 times greater than in the bathypelagic zone (∼0.5 mol C m −2 a −1 ). The results presented here renders respiration in the dark ocean a major component of the carbon flux in the biosphere, and should promote research in the dark ocean, with the aim of better constraining the role of the biological pump in the removal and storage of atmospheric carbon dioxide.