Respiration patterns in the deep ocean

Abstract

[1] The biological pump affects atmospheric CO 2 levels and fuels most heterotrophic activity in the deep ocean. The efficiency of this pump depends on the rate of carbon fixation, export out of the euphotic zone and the depth of respiration. Here we study the depth dependence of respiration patterns, hence particulate carbon flux, using a compiled data set of sediment oxygen consumption rates. We show that the depth relationship can best be described by a double exponential model. For the upper part of the ocean, our resulting equation is similar to previous fluxdepth relationships but predicted fluxes are significantly larger in deeper waters. This implies a more efficient biological pump. Total oceanic respiration below the shelf break (200 m) is estimated to be 827 Tmol O 2 yr À1.

Respiration in the mesopelagic and bathypelagic zones of the oceans

“…Sediments, however, provide the ultimate sediment trap and integrate carbon fluxes over a considerable period of time. Following these considerations, Andersson and coworkers have used sediment oxygen consumption rates to derive an expression for the depth attenuation of the organic carbon flux in the ocean (Andersson et al 2004 where the flux of carbon is given in mmol O 2 m −2 d −1 and z is water depth in meters. At steady state, the divergence of this organic carbon flux with depth should balance oxygen utilization rate at that depth (Suess 1980).…”

“…Table 10.5 shows the derived respiration rates for the dark water column and sediments. These rates correspond only to particulate organic carbon remineralization, and do not account for the Table 10.5 Global estimates of respiration in the dark water column and sediments (Pmol C a −1 ), derived from oxygen consumption measurements in sediments (from Andersson et al 2004 Oxygen units converted to carbon units using a respiratory quotient, RQ = 0.69.…”

“…Nevertheless it is sufficient to support a large number (3.5 × 10 30 ) and high biomass (25 Pmol C) of prokaryotic cells in subsurface oceanic sediments (Whitman et al 1998) that appear to be metabolically active (D'Hondt et al 2002). The global organic carbon burial, recently estimated at 13 Tmol C a −1 (range 11-18 Tmol C a −1 ; Hedges and Keil 1995) represents only a fraction (4-9%) of global sedimentary mineralization (190 Tmol C a −1 , Jørgensen 1983; 220 Tmol C a −1 , Smith and Hollibaugh, 1993;140-260 Tmol C a −1 , Middelburg et al 1997; 210 Tmol C a −1 , Andersson et al 2004). This is often expressed in terms of the burial efficiency: that is, the organic carbon accumulation rate below the diagenetic active surface layer divided by the organic carbon delivery to sediment surface.…”

“…Sediment oxygen consumption rates range over 4 orders of magnitude from more than 200 in coastal sediments to about 0.02 mmol O 2 m −2 d −1 in some deep-sea sediments (Jørgensen 1983;Middelburg et al 1997;Andersson et al 2004). A number of researchers have derived empirical relationships from compiled datasets of sediment oxygen consumption.…”

“…In contrast to the destruction of organic matter, primary synthesis of organic matter is restricted-except for a marginal contribution of chemosynthesis-to the upper 100-200-m skin of the ocean, where sufficient light penetrates to support photosynthesis. The synthesis processes occurring in the photic layer, which encompasses only about 5% of the water column, have been the object of most of the research effort, and the degradation processes occurring in the dark layers of the ocean remain comparatively poorly studied, despite evidence that the rates involved may be substantial (Williams 2000;del Giorgio and Duarte 2002;Arístegui et al 2003;Andersson et al 2004). Yet, the dark ocean is an important site for the mineralization of organic matter, and is the site of long-term organic carbon storage and burial.…”