Patterns and drivers of dimethylsulfide concentration in the northeast subarctic Pacific across multiple spatial and temporal scales

Abstract

Abstract. The northeast subarctic Pacific (NESAP) is a globally important source of the climate-active gas dimethylsulfide (DMS), yet the processes driving DMS variability across this region are poorly understood. Here we examine the spatial distribution of DMS at various spatial scales in contrasting oceanographic regimes of the NESAP. We present new high-spatial-resolution measurements of DMS across hydrographic frontal zones along the British Columbia continental shelf, together with key environmental variables and biological rate measurements. We combine these new data with existing observations to produce a revised summertime DMS climatology for the NESAP, yielding a broader context for our sub-mesoscale process studies. Our results demonstrate sharp DMS concentration gradients across hydrographic frontal zones and suggest the presence of two distinct DMS cycling regimes in the NESAP, corresponding to microphytoplankton-dominated waters along the continental shelf and nanoplankton-dominated waters in the cross-shelf transitional zone. DMS concentrations across the continental shelf transition (range < 1–10 nM, mean 3.9 nM) exhibited positive correlations to salinity (r=0.80), sea surface height anomaly (SSHA; r=0.51), and the relative abundance of prymnesiophyte and dinoflagellates (r=0.89). In contrast, DMS concentrations in nearshore coastal transects (range < 1–24 nM, mean 6.1 nM) showed a negative correlation with salinity (r=-0.69; r=-0.78) and SSHA (r=-0.81; r=-0.75) and a positive correlation to relative diatom abundance (r=0.88; r=0.86). These results highlight the importance of bloom-driven DMS production in continental shelf waters of this region and the role of prymnesiophytes and dinoflagellates in DMS cycling further offshore. In all areas, the rate of DMS consumption appeared to be an important control on observed concentration gradients, with higher DMS consumption rate constants associated with lower DMS concentrations. We compiled a data set of all available summertime DMS observations for the NESAP (including previously unpublished results) to examine the performance of several existing algorithms for predicting regional DMS concentrations. None of these existing algorithms was able to accurately reproduce observed DMS distributions across the NESAP, although performance was improved by the use of regionally tuned coefficients. Based on our compiled observations, we derived an average summertime distribution map for DMS concentrations and sea–air fluxes across the NESAP, estimating a mean regional flux of 0.30 Tg of DMS-derived sulfur to the atmosphere during the summer season.

Dimethylated sulfur compounds in the Peruvian upwelling system

“…5a), which is in agreement with the finding of a previous study in the equatorial Pacific Ocean (Bates and Quinn, 1997). A comparison with DMS data from other EBUS and the Arabian Sea illustrates that DMS concentrations off Peru (up to 44 nmol L -1 ) are higher than those measured off northwest Africa (Mauritania and Morocco) (Belviso et al, 2003;Franklin et al, 2009;Zindler et al, 2012), Benguela (Andreae et al, 1994), California (Herr et al, 2019) and the west Arabian Sea (Oman) (Hatton et al, 1999).…”

Potential roles of dimethysulfoxide in regional sulfur cycling and phytoplankton physiological ecology in the NE Subarctic Pacific

“…O1–O2), based on satellite observations of elevated calcite concentrations (~ 2 mmol PIC/m 3 ), and HPLC‐based diagnostic pigment analysis suggesting that prymnesiophytes accounted for more than 25% of total Chl a in this region. More information on the hydrography and phytoplankton assemblage composition across our survey region is presented in Herr et al (2019).…”

“…We conducted field sampling on two oceanographic cruises in the Subarctic NE Pacific, a region of elevated DMS concentrations (Herr et al 2019). To date, only three studies have measured DMSO concentrations in this region (Bates et al 1994;Asher et al 2015Asher et al , 2017b, and one study has provided preliminary observations of DMSO reduction rates (Asher et al 2017b).…”

Improved Prediction of Dimethyl Sulfide (DMS) Distributions in the NE Subarctic Pacific using Machine Learning Algorithms

“…To date, these studies have focused on a number of variables, including ratio of chlorophyll a (Chl-a) to mixed layer depth (MLD) (Simó and Dachs, 2002), sea surface temperature (SST) and nitrate (SSN) (Watanabe et al, 2007), solar radiation dose (SRD) (Vallina and Simó, 2007), photosynthetically active radiation (PAR) and modelled DMSP concentrations (Galí et al, 2018). Some of these models have demonstrated reasonably good performance at global scales, but their predictive power is generally diminished at regional scales (Herr et al, 2019), failing to accurately resolve important smaller-scale features (Belviso et al, 2003;Nemcek et al, 2008;Royer et al, 2015;Tortell, 2005b).…”

“…These new datasets potentially enable new insights into small-scale and regional patterns in oceanic DMS distributions, as well as the characterization of oceanic DMS 'hot-spots'. One such global DMS hotspot is the northeast subarctic Pacific (NESAP) (Asher et al, 2017;Herr et al, 2019;Lana et al, 2011), a region encompassing both highly productive coastal upwelling regimes, and off-shore, iron-limited waters (Martin and Fitzwater, 1988). Several factors have been proposed to account for the elevated DMS production in the NESAP, including increased productivity from entrainment and upwelling along coastal fronts (Asher et al, 2017), and the stimulation of DMS production in response to oxidative stress in low iron waters (Sunda et al, 2002;Herr et al, 2020).…”