Abstract
Dissociating gas hydrates, submerged permafrost, and gas bearing sediments release methane to the water column from a multitude of seeps in the Arctic Ocean. The seeping methane dissolves and supports the growth of aerobic methane oxidizing bacteria (MOB), but the effect of seepage and seep related biogeochemical processes on water column dissolved organic matter (DOM) dynamics is not well constrained. We compared dissolved methane, nutrients, chlorophyll, and particulate matter concentrations and methane oxidation (MOx) rates from previously characterized seep and non-seep areas at the continental margin of Svalbard and the Barents Sea in May and June 2017. DOM molecular composition was determined by Electrospray Ionization Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS). We found that the chemical diversity of DOM was 3 to 5% higher and constituted more protein- and lipid-like composition near methane seeps when compared to non-seep areas. Distributions of nutrients, chlorophyll, and particulate matter however, were essentially governed by the water column hydrography and primary production. We surmise that the organic intermediates directly derived from seepage or indirectly from seep-related biogeochemical processes, e.g., MOx, modifies the composition of DOM leading to distinct DOM molecular-level signatures in the water column at cold seeps.
Highlights
Dissolved organic matter (DOM) is the operationally defined mixture of organic compounds that passes through a 0.7 μm pore size filter (Repeta, 2015) and constitutes the largest reservoir of organic carbon in the oceans
Cold seeps are being studied intensively due to the possible influence of escaping methane
indirect impacts of seeping fluids are also evident for water column biogeochemical concentrations
Summary
Dissolved organic matter (DOM) is the operationally defined mixture of organic compounds that passes through a 0.7 μm pore size filter (Repeta, 2015) and constitutes the largest reservoir of organic carbon in the oceans. The major part (humic acids, condensed aromatics, black carbon etc.) is considered refractory and remains in the water for years or even millennia (Williams and Druffel, 1987; Amon and Benner, 1994; Lechtenfeld et al, 2014). More biologically reactive DOM in the ocean, considered as bio-labile DOM (amino acids, sugars, proteins etc.), is available to heterotrophic microorganisms and rapidly remineralized by prokaryotes in the upper layers of the water column (Carlson et al, 1994; Carlson et al, 2010; Koch et al, 2014). Bio-labile DOM is produced and transformed by numerous biological processes including extracellular release, excretion, cell lysis, solubilisation and chemosynthetic processes (Carlson and Hansell, 2015)
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