Concentrations and cycling of DMS, DMSP, and DMSO in coastal and offshore waters of the Subarctic Pacific during summer, 2010‐2011

Abstract

Concentrations of dimethylsulfide (DMS), measured in the Subarctic Pacific during summer 2010 and 2011, ranged from ∼1 to 40 nM, while dissolved dimethylsulfoxide (DMSO) concentrations (range 13‐23 nM) exceeded those of dissolved dimethyl sulfoniopropionate (DMSP) (range 1.3–8.8 nM). Particulate DMSP dominated the reduced sulfur pool, reaching maximum concentrations of 100 nM. Coastal and off shore waters exhibited similar overall DMS concentration ranges, but sea‐air DMS fluxes were lower in the oceanic waters due to lower wind speeds. Surface DMS concentrations showed statistically significant correlations with various hydrographic variables including the upwelling intensity (r2 = 0.52, p < 0.001) and the Chlorophyll a/mixed layer depth ratio (r2 = 0.52, p < 0.001), but these relationships provided little predictive power at small scales. Stable isotope tracer experiments indicated that the DMSP cleavage pathway always exceeded the DMSO reduction pathway as a DMS source, leading to at least 85% more DMS production in each experiment. Gross DMS production rates were positively correlated with the upwelling intensity, while net rates of DMS production were significantly correlated to surface water DMS concentrations. This latter result suggests that our measurements captured dominant processes driving surface DMS accumulation across a coastal‐oceanic gradient.

Sea-surface dimethylsulfide (DMS) concentration from satellite data at global and regional scales

“…While in situ DMS is accurately estimated by DMS SAT in February and June, the variable DMS peak occurring around August is strongly underestimated. Previous studies emphasized the role of iron limitation at OSP, which configures phytoplankton communities dominated by high DMSP taxa (Asher et al, 2017;Levasseur et al, 2006;Royer et al, 2010;Steiner et al, 2012). Interestingly, DMSPt SAT peaks in August at OSP, in phase with the in situ DMS peak and in good accordance with the few available DMSPt measurements (Fig.…”

“…4.2 we speculate about potential causes behind high DMS / DMSPt ratios in late summer and early fall. This exercise shows our limited capacity to account for relevant biogeochemical pro- (Asher et al, 2017;Levasseur et al, 2006;Royer et al, 2010). BATS data are comprised of the monthly 2005-2008 time series (Levine et al, 2016) and cruise data from the vicinity of BATS station in July 2004 (Bailey et al, 2008;Gabric et al, 2008).…”

“…In these regions, sharp productivity gradients and dynamic ecosystem processes complicate the task of sampling DMS through all appropriate scales (Nemcek et al, 2008), suggesting the need to apply finer-scale or dynamic regionalization (Devred et al, 2007) prior to interpolation. Emerging biogeochemical relationships, like that between net community production and DMS observed by Kameyama et al (2013) in the northeast Pacific, might assist DMS interpolation and determination, but require validation across contrasting regions and relevant scales (Asher et al, 2017). In low-latitude oligotrophic areas where DMS shows reduced spatial variability , the method used to construct interpolation-based climatologies (Kettle et al, 1999;Lana et al, 2011) seems appropriate regarding spatial resolution.…”

“…9c), even though the DMSPt SAT sub-algorithm does not explicitly resolve phytoplankton taxonomy . Therefore, high DMS yields, possibly co-occurring with low DMS removal rate constants (Asher et al, 2017), are required to explain DMS / DMSPt ratios observed at OSP. High DMS yields probably result from a combination of processes, including algal and bacterial DMSP metabolism Royer et al, 2010) and microzooplankton grazing (Steiner et al, 2012).…”

Dimethylsulfoniopropionate (DMSP) and dimethyl sulfide (DMS) cycling across contrasting biological hotspots of the New Zealand subtropical front

“…Oceanic frontal and convergence zones are regions of intense mesoscale turbulence displaying enhanced levels of chlorophyll a (Chl a) (Belkin et al, 2009) detectable from space (Weeks and Shillington, 1996). The heightened biological activity in these regions (Llido et al, 2005) is thought to lead to intensified carbon drawdown on seasonal timescales (Metzl et al, 1999) as well as high concentrations of DMS (Asher et al, 2017;Holligan et al, 1987;Matrai et al, 1996;Nemcek et al, 2008;Tortell, 2005;Tortell and Long, 2009). These productive regions sometimes form unique biogeographic habitats of their own such as the subtropical convergence province proposed by Longhurst (2007).…”