Oceanic distribution and sources of bromoform and dibromomethane in the Mauritanian upwel­ling.

Quack, Birgit, Peeken, Ilka, Petrick, Gert and Nachtigall, Kerstin (2007) Oceanic distribution and sources of bromoform and dibromomethane in the Mauritanian upwel­ling. Open Access Journal of Geophysical Research: Oceans, 112 . C10006. DOI 10.1029/2006JC003803.

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Abstract

The tropical oceans are a source of reactive bromine to the atmosphere in the form of short-lived brominated methanes as bromoform (CHBr3) and dibromomethane (CH2Br2). Elevated atmospheric concentrations above the tropical oceans are related to oceanic supersaturations of the compounds and especially to upwelling regimes. Although the sources of these brominated gases in the open ocean are not well understood, they have been habitually linked to phytoplankton, especially diatom abundance. Thus according to common assumptions, high concentrations of the brominated trace gases were expected to occur in the biologically active and diatom-rich Mauritanian upwelling. However, contrary to expectations, only low levels were encountered in the upwelling waters, 10.7 (range 5.2–23.8) pmol L−1 CHBr3 and 4.7 (range 3.1–7.0) pmol L−1 CH2Br2, values more typical of open ocean concentrations. The aqueous CHBr3 concentrations were not correlated to high chlorophyll a values or diatom abundances. However, significant correlations existed with low concentrations of marker pigments for diatoms, cyanobacteria, and degradation, suggesting miscellaneous small biological sources of the compound in the upwelling. Air-sea exchange could additionally account for an oceanic source in fresh upwelled waters, while advection of different water masses also influenced the distribution. CHBr3 concentrations were maximized in warm and nitrogen-depleted surface waters, while CH2Br2 was maximized in colder and nitrogen-enriched deeper waters, suggesting that both compounds, at least in part, have different sources and fates.

Document Type: Article
Keywords: Oceanography; reactive bromine sources, upwelling, bromoform, biogeosciences; POS320; POSEIDON
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-CH Chemical Oceanography
OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-BI Biological Oceanography
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1029/2006JC003803
ISSN: 2169-9275
Projects: Future Ocean
Expeditions/Models/Experiments:
Date Deposited: 29 Apr 2009 10:33
Last Modified: 19 Apr 2018 11:03
URI: http://oceanrep.geomar.de/id/eprint/4777

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