ABSTRACT: A central topic of modern biological oceanography is the flux of biogenic carbon (BC) towards large metazoans (i.e. renewable resources) and into deep waters (i.e. carbon sequestration, which may mitigate climate change). Two relevant characteristics of marine pelagic food webs are the turnover time of BC (t) and the size ratio of consumers to their food particles (x). Based on an extensive review of the literature, the present paper develops empirical equations to quantify the minimum turnover time (t_min) of BC incorporated in marine pelagic organisms and the residence time (t_s) of BC above depth z_s (e.g. 1000 m), below which BC cannot rapidly return to the surface waters or the atmosphere. Both t_min and t_s are used in conjunction with x to assess the food-web regulation of BC fluxes. The paper shows that t_min, t_s, and x provide objective criteria for defining functional groups of organisms that are well suited for studying food-web mediated C flux. As the size of organisms feeding on smaller prey increases, there is a proportional lengthening of t_min (incorporation of BC in the body mass of larger organisms) and proportional shortening of t_s (aggregation in faster sinking faecal pellets). The resulting increased flux towards the pools of long-lived organic C (10^-2< t< 10² yr) and sequestered BC (t > 10² yr) are significant for renewable resources and climate change, respectively.

KEY WORDS: Carbon flux · Ocean · Food web · Allometry · Turnover time · Residence time

Published in MEPS Vol. 164 (1998) on April 9
Print ISSN: 0171-8630; Online ISSN: 1616-1599. Copyright © Inter-Research, Oldendorf/Luhe, 1998