Abstract

Hydrothermal vents modify and displace subsurface dissolved organic matter (DOM) into the ocean. Once in the ocean, this DOM is transported together with elements, particles, dissolved gases, and biomass along with the neutrally buoyant plume layer. Considering the number and extent of actively venting hydrothermal sites in the oceans, their contribution to the oceanic DOM pool may be substantial. Here, we investigate the dynamics of DOM in relation to hydrothermal venting and related processes at the as-yet unexplored Aurora hydrothermal vent field within the ultraslow spreading Gakkel Ridge in the Arctic Ocean at 82.9° N. We examined the vertical distribution of DOM composition from sea ice to deep waters at six hydrocast stations distal to the active vent and its neutrally buoyant plume layer. In comparison to background seawater, we found that the DOM in waters directly affected by the hydrothermal plume was composed of lower numbers of molecular formulas and 5–10 % less abundant compositions associated with the molecular categories related to lipid and protein-like compounds. Samples that were not directly affected by the plume, on the other hand, were chemically more diverse and had a higher percentage of chemical formulas associated with the carbohydrate-like category. We suggest, therefore, that hydrothermal processes at Aurora may influence the DOM distribution in the bathypelagic ocean by spreading more thermally and/or chemically induced compositions, while DOM compositions in epipelagic and mesopelagic layers are mainly governed by the microbial carbon pump dynamics, and sea ice surface water interactions.

Highlights

  • Dissolved organic matter (DOM) in the vicinity of high temperature hydrothermal vents shows discrepancies in concentration compared to ocean background concentrations, mainly due to thermal decomposition of dissolved organic matter (DOM) during hydrothermal circulation (Hawkes et al, 2015; Lang et al, 2006)

  • We categorize the water column in three water layers as epipelagic (0-200 m), mesopelagic (200-1000 m) and bathypelagic (1000-4000 m) considering the depth and the four water masses that are defined by the density layers of σt ≤27.7 for Polar Surface Waters 215 (PSW), 27.727.97 and σ0.5 ≤30.444 for Arctic Intermediate Waters (AIW) and σ0.5 >30.444 for Deep Waters (DW) (Marnela et al, 2008; Rudels et al, 2005)

  • We show that DOM compositions in the plume layer samples had lower numbers of molecular formulae, molecular diversity, average abundance, and percentage of formulas assigned to the LPD molecular class

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Summary

Introduction

Dissolved organic matter (DOM) in the vicinity of high temperature hydrothermal vents shows discrepancies in concentration compared to ocean background concentrations, mainly due to thermal decomposition of DOM during hydrothermal circulation (Hawkes et al, 2015; Lang et al, 2006). As well as models, show that rising, neutrally buoyant plumes can disperse horizontally at isopycnal surfaces for tens to even thousands of kilometres (Baker et al, 1995; Lupton and Craig, 1981; Rudnicki and Elderfield, 1993; Speer and Rona, 1989; Tao et al, 2013) Thereby, they form environmental gradients ( called ecotones) conducting particles, nutrients, organic matter, trace elements and biomass (Levin et al, 2016; Ramirez-Llodra et al, 2010).

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