Spatial and diurnal dynamics of dissolved organic matter (DOM) fluorescence and H₂O₂ and the photochemical oxygen demand of surface water DOM across the subtropical Atlantic Ocean

Author(s)

Ingrid Obernosterer, Piet Ruardij, Gerhard J. Herndl

Abstract

Diurnal dynamics of dissolved organic matter (DOM) fluorescence and hydrogen peroxide (H₂O₂) concentrations were followed in the upper 100 m of the water column at five stations across the subtropical Atlantic Ocean in July and August 1996. The 10% levels of surface solar radiation for the ultraviolet (UV) B range (at 305- and 320-nm wavelengths) were at 16 and 23 m in depth and for the UVA range (at 340- and 380-nm wavelengths) were at 35 and 63 m in depth, respectively. The DOM fluorescence decreased over the course of the day, whereas H₂O₂ concentrations increased, especially in the diurnally stratified surface water layers extending to 10-50-m depth. In situ H₂O₂ net production varied between 5.5 nmol L^-1 h^-1 at 5-m depth and 1 nmol L^-1 h^-1 at 40-m depth, resulting in an H₂O₂ net production of ∼38 μmol m^-2 d^-1 in the upper 50 m of the water column. Photochemical oxygen (O₂) demand of water collected at 10-m depth in the early morning and exposed to surface solar radiation varied between 0.9 and 2.8 μmol O₂ L^-1 d^-1 and was found to be consistently higher (by a 1.3-8.3-fold measure) than bacterial respiration (measured in 0.8 μm-filtered seawater in the dark). UVB radiation was responsible for 0-30% of the photochemical O₂ demand. A simple one-dimensional physical model was combined with a photochemical/ biological model in order to describe the photochemical production of H₂O₂ at different depth layers over the course of the day and to determine the contribution of physical versus biological processes in terms of the loss of H₂O₂ from the surface layers in the late afternoon. The model reflects well the observed diurnal H₂O₂ dynamics. It further provides evidence that mainly biological breakdown determines the loss of H₂O₂ in the upper 50 m of the water column during the day; however, in the late afternoon, vertical mixing is important in transporting H₂O₂ from the uppermost 5-m layer to the 10-20-m layers.

Organisation(s)

Functional and Evolutionary Ecology

External organisation(s)

Royal Netherlands Institute for Sea Research

Journal

Limnology and Oceanography

Volume

46

Pages

632-643

No. of pages

12

ISSN

0024-3590

DOI

https://doi.org/10.4319/lo.2001.46.3.0632

Publication date

01-2001

Peer reviewed

Yes

Austrian Fields of Science 2012

106022 Microbiology

ASJC Scopus subject areas

Oceanography, Aquatic Science

Portal url

https://ucrisportal.univie.ac.at/en/publications/spatial-and-diurnal-dynamics-of-dissolved-organic-matter-dom-fluorescence-and-h2o2-and-the-photochemical-oxygen-demand-of-surface-water-dom-across-the-subtropical-atlantic-ocean(42ee5f1e-bebf-4070-821b-697cef39a43e).html