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Spectroscopic detection of a ubiquitous dissolved pigment degradation product in subsurface waters of the global ocean

Authors
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Copernicus Publications
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  • Earth Science

Abstract

Biogeosciences, 9, 2585–2596, 2012 www.biogeosciences.net/9/2585/2012/ doi:10.5194/bg-9-2585-2012 © Author(s) 2012. CC Attribution 3.0 License. Biogeosciences Spectroscopic detection of a ubiquitous dissolved pigment degradation product in subsurface waters of the global ocean R. Ro¨ttgers1 and B. P. Koch2,3 1Helmholtz-Zentrum Geesthacht, Center for Materials and Coastal Research, Institute for Coastal Research, Max Planck Str. 1, 21502 Geesthacht, Germany 2Alfred Wegener Institute for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany 3University of Applied Sciences, An der Karlstadt 8, 27568 Bremerhaven, Germany Correspondence to: R. Ro¨ttgers ([email protected]) Received: 12 October 2011 – Published in Biogeosciences Discuss.: 31 October 2011 Revised: 4 June 2012 – Accepted: 4 June 2012 – Published: 13 July 2012 Abstract. Measurements of light absorption by chro- mophoric dissolved organic matter (CDOM) from subsurface waters of the tropical Atlantic and Pacific Oceans showed a distinct absorption shoulder at 410–415 nm. This indicates an underlying absorption of a pigment whose occurrence is partly correlated with the apparent oxygen utilization (AOU) but also found in the deep chlorophyll maximum. A similar absorption maximum at ∼ 415 nm was also found in the particulate fraction of samples taken below the surface mixing layer and is usually attributed to absorption by respiratory pigments of heterotrophic unicellular organisms. In our study, fluorescence measurements of pre-concentrated dissolved organic matter (DOM) samples from 200–6000 m confirmed a previous study suggesting that the absorption at ∼ 415 nm was related to fluorescence at 650 nm in the oxygen minimum zone. The absorption characteris- tics of this fluorophore was examined by fluorescence emission/excitation analysis and showed a clear excitation maximum at 415 nm that could be linked to the absorption shoulder in the CDOM spectra. The spectral characteristics of the substance found in

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