Both respiration and photosynthesis determine the scaling of plankton metabolism in the oligotrophic ocean

Abstract

Despite its importance to ocean–climate interactions, the metabolic state of the oligotrophic ocean has remained controversial for >15 years. Positions in the debate are that it is either hetero- or autotrophic, which suggests either substantial unaccounted for organic matter inputs, or that all available photosynthesis (P) estimations (including 14C) are biased. Here we show the existence of systematic differences in the metabolic state of the North (heterotrophic) and South (autotrophic) Atlantic oligotrophic gyres, resulting from differences in both P and respiration (R). The oligotrophic ocean is neither auto- nor heterotrophic, but functionally diverse. Our results show that the scaling of plankton metabolism by generalized P:R relationships that has sustained the debate is biased, and indicate that the variability of R, and not only of P, needs to be considered in regional estimations of the ocean's metabolic state.

Ecosystem metabolism in salt marsh tidal creeks and ponds : applying triple oxygen isotopes and other gas tracers to novel environments

“…Good agreement exists between production rates based on in situ biogeochemical tracers (this study) and incubation based methods [Marañón et al 2003, Tilstone et al 2009, Serret et al 2015 across the South and Equatorial Atlantic surface ocean.…”

“…Other methods used to calculate primary production in this region include one study in the Amazon River Plume also using the O2/Ar and triple oxygen isotope tracers as well as dissolved inorganic carbon drawdown and multiple years of coverage across the basin in May and October as part of the Atlantic Meridional Transect Program [Robinson et al 2006[Robinson et al , 2009, using radiocarbon uptake [Marañón et al 2003, Tilstone et al 2009] and oxygen light-dark bottle incubations [Serret et al 2015]. All rates are converted to oxygen fluxes using the conversions described in section 2.2.2.…”

Surface ocean carbon dioxide during the Atlantic Meridional Transect (1995–2013); evidence of ocean acidification

“…This difference between the two gyres is also reflected in AMT NCP data which show that the south Atlantic gyre is more frequently autotrophic while the northern gyre is in trophic balance or heterotrophic . While the in vitro work of Serret et al (2015) gives an instantaneous measure of NCP, DfCO 2 may give an integrated measure of NCP over longer time scales similar to geochemical measures of NCP. The inference of trophic status from DfCO 2 may be somewhat speculative, but is nevertheless consistent with previous work.…”

“…Nevertheless, this does not explain the different ocean acidification rates in these biomes. The reasons for this are unclear in the absence of seasonally-resolved data, but add to the growing body of evidence which suggests that the two subtropical gyre biomes are biogeochemically distinct despite their many similarities (Baker and Jickells, submitted for publication; Goetze et al, submitted for publication; Moore et al, 2009Moore et al, , 2013Serret et al, 2015).…”

Dynamics of phytoplankton and heterotrophic bacterioplankton in the western tropical South Pacific Ocean along a gradient of diversity and activity of diazotrophs

“…The metabolic state of oligotrophic oceans is still controversial Ducklow and 445 Donney, 2013;Williams et al, 2013;Serret et al, 2015, Letscher et al, 2017, and a consensus emerges that in vitro estimates, (involving O 2 derived rates or labelling with 18 O 2 13 C, or 14 C isotopes) tend to show net heterotrophy in oligotrophic environments. However, those estimates suffer from many biases related to bottle effects, type of flasks used (selecting light wavelengths), condition of incubations and handling artefacts, as well as a lack of high frequency measurements.…”