Reply on RC3

Abstract

<strong class="journal-contentHeaderColor">Abstract.</strong> Dimethyl sulfide (<span class="inline-formula">DMS</span>) plays an important role in the atmosphere by influencing the formation of aerosols and cloud condensation nuclei. In contrast, the role of methanethiol (<span class="inline-formula">MeSH</span>) for the budget and flux of reduced sulfur remains poorly understood. In the present study, we quantified <span class="inline-formula">DMS</span> and <span class="inline-formula">MeSH</span> together with the trace gases carbon monoxide (<span class="inline-formula">CO</span>), isoprene, acetone, acetaldehyde and acetonitrile in North Atlantic and Arctic Ocean surface waters, covering a transect from 57.2 to 80.9<span class="inline-formula">^∘</span> N in high spatial resolution in May–June 2015. Whereas isoprene, acetone, acetaldehyde and acetonitrile concentrations decreased northwards, <span class="inline-formula">CO</span>, <span class="inline-formula">DMS</span> and <span class="inline-formula">MeSH</span> retained substantial concentrations at high latitudes, indicating specific sources in polar waters. <span class="inline-formula">DMS</span> was the only compound with a higher average concentration in polar (31.2 <span class="inline-formula">±</span> 9.3 <span class="inline-formula">nM</span>) than in Atlantic waters (13.5 <span class="inline-formula">±</span> 2 <span class="inline-formula">nM</span>), presumably due to <span class="inline-formula">DMS</span> originating from sea ice. At eight sea-ice stations north of 80<span class="inline-formula">^∘</span> N, in the diatom-dominated marginal ice zone, <span class="inline-formula">DMS</span> and chlorophyll <span class="inline-formula"><i>a</i></span> markedly correlated (<span class="inline-formula"><i>R</i>²</span> <span class="inline-formula">=</span> 0.93) between 0–50 <span class="inline-formula">m</span> depth. In contrast to previous studies, <span class="inline-formula">MeSH</span> and <span class="inline-formula">DMS</span> did not co-vary, indicating decoupled processes of production and conversion. The contribution of <span class="inline-formula">MeSH</span> to the sulfur budget (represented by <span class="inline-formula">DMS</span> <span class="inline-formula">+</span> <span class="inline-formula">MeSH</span>) was on average 20 % (and up to 50 %) higher than previously observed in the Atlantic and Pacific oceans, suggesting <span class="inline-formula">MeSH</span> as an important source of sulfur possibly emitted to the atmosphere. The potential importance of <span class="inline-formula">MeSH</span> was underlined by several correlations with bacterial taxa, including typical phytoplankton associates from the <i>Rhodobacteraceae</i> and <i>Flavobacteriaceae</i> families. Furthermore, the correlation of isoprene and chlorophyll <span class="inline-formula"><i>a</i></span> with <i>Alcanivorax</i> indicated a specific relationship with isoprene-producing phytoplankton. Overall, the demonstrated latitudinal and vertical patterns contribute to understanding how concentrations of central marine trace gases are linked with chemical and biological dynamics across oceanic waters.