Abstract. The eastern tropical South Pacific (ETSP) hosts the Peruvian upwelling
system, which represents one of the most productive areas in the world ocean.
High primary production followed by rapid heterotrophic utilization of
organic matter supports the formation of one of the most intense oxygen
minimum zones (OMZs) in the world ocean, where dissolved oxygen
(O2) concentrations reach less than 1 µmol kg−1.
The high productivity leads to an accumulation of dissolved organic matter
(DOM) in the surface layers that may serve as a substrate for heterotrophic
respiration. However, the importance of DOM utilization for O2
respiration in the Peruvian upwelling system in general and for shaping the
upper oxycline in particular remains unclear so far. This study reports the
first estimates of diapycnal fluxes and supply of O2, dissolved
organic carbon (DOC), dissolved organic nitrogen, dissolved hydrolysable
amino acids (DHAA) and dissolved combined carbohydrates (DCCHO) for the ETSP
off Peru. Diapycnal flux and supply estimates were obtained by combining
measured vertical diffusivities and solute concentration gradients. They were
analysed together with the molecular composition of DCCHO and DHAA to infer
the transport of labile DOM into the upper OMZ and the potential role of DOM
utilization for the attenuation of the diapycnal O2 flux that
ventilates the OMZ. The observed diapycnal O2 flux
(50 mmol O2 m−2 d−1 at maximum) was limited to the
upper 80 m of the water column; the O2 supply of ∼1 µmol kg−1 d−1 was comparable to previously published
O2 consumption rates for the North and South Pacific OMZs. The
diapycnal DOM flux (31 mmol C m−2 d−1 at maximum) was limited
to ∼30 m water depth, suggesting that the labile DOM is extensively
consumed within the upper part of the shallow oxycline off Peru. The analyses
of DCCHO and DHAA composition support this finding, suggesting that DOM
undergoes comprehensive remineralization within the upper part of the
oxycline, as the DOM within the core of the OMZ was found to be largely
altered. Estimated by a simple equation for carbon combustion, aerobic
respiration of DCCHO and DHAA, supplied by diapycnal mixing
(0.46 µmol kg−1 d−1 at maximum), could account for up
to 38 % of the diapycnal O2 supply in the upper oxycline, which
suggests that DOM utilization plays a significant role for shaping the upper
oxycline in the ETSP.
Corrigendum to “Radiocarbon signatures and size–age–composition relationships of major organic matter pools within a unique California upwelling system” [Geochim. Cosmochim. Acta 126 (2014) 1–17]