Dissolved organic sulfur in the ocean: Biogeochemistry of a petagram inventory

Abstract

Although sulfur is an essential element for marine primary production and critical for climate processes, little is known about the oceanic pool of nonvolatile dissolved organic sulfur (DOS). We present a basin-scale distribution of solid-phase extractable DOS in the East Atlantic Ocean and the Atlantic sector of the Southern Ocean. Although molar DOS versus dissolved organic nitrogen (DON) ratios of 0.11 ± 0.024 in Atlantic surface water resembled phytoplankton stoichiometry (sulfur/nitrogen~0.08), increasing dissolved organic carbon (DOC) versus DOS ratios and decreasing methionine-S yield demonstrated selective DOS removal and active involvement in marine biogeochemical cycles. Based on stoichiometric estimates, the minimum global inventory of marine DOS is 6.7 petagrams of sulfur, exceeding all other marine organic sulfur reservoirs by an order of magnitude.

Experimental Evidence for Abiotic Sulfurization of Marine Dissolved Organic Matter

“…However, this first attempt illustrates that benthic DOS flux is potentially one order of magnitude larger than the riverine organic sulfur input to the ocean (8 Tg S a −1 , Ksionzek et al, 2016) and may be able to balance the estimated global net removal of refractory DOS (1.1 Tg S a −1 , Ksionzek et al, 2016). Based on our estimate, we suggest that sulfurization in sulfidic environments is possibly an important source mechanism of refractory DOS to the oceans.…”

“…From those values the extraction efficiencies were calculated. DOS concentrations of the SPE-extracts were measured on an Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES, iCAP 6000, Thermo Fisher Scientific GmbH, Bremen, Germany) and bulk DOS concentrations were estimated based on the extraction efficiency for DOC as done previously (Pohlabeln and Dittmar, 2015;Gomez-Saez et al, 2016;Ksionzek et al, 2016).…”

“…Many compounds within the DOM mixture contain sulfur (dissolved organic sulfur, DOS), and in sum they make up the largest reservoir of organic sulfur in the ocean (global inventory of >6.7 Pg S, Ksionzek et al, 2016). Despite the relevance of DOS in global biogeochemical cycles, knowledge on its sources and turnover, and its molecular composition is scarce (Lechtenfeld et al, 2011).…”

“…Marine primary production is considered a major source of organic sulfur, explaining elevated DOS concentrations in surface waters (Ksionzek et al, 2016). A part of the marine organic sulfur is rapidly cycled and thus labile (Ksionzek et al, 2016), and may contribute little to refractory DOS in the oceans' interior . The source of the large refractory DOS pool which is evenly distributed in the water column is unknown (Levine, 2016).…”

“…Despite the relevance of DOS in global biogeochemical cycles, knowledge on its sources and turnover, and its molecular composition is scarce (Lechtenfeld et al, 2011). Marine primary production is considered a major source of organic sulfur, explaining elevated DOS concentrations in surface waters (Ksionzek et al, 2016). A part of the marine organic sulfur is rapidly cycled and thus labile (Ksionzek et al, 2016), and may contribute little to refractory DOS in the oceans' interior .…”