This study presents sea surface concentrations of marine dimethylsulfide (DMS) measured across the Labrador Sea and the Canadian Arctic Archipelago during summer of 2017 (July-August). Using a novel automated instrument (ACT-MIMS) more than 2500 DMS observations were collected at high frequency alongside ancillary measurements of salinity, temperature, fluorescence (chlorophyll a proxy), solar radiation, ice concentration and the algal precursor of DMS, dimethylsulfoniopropionate. DMS concentrations ranged from ca. 1 to 32 nmol L-1 (average of 6 nmol L-1) in 2017 over an area covering a wide range of contrasting marine environments from coastal to open ocean, ice-free waters, as well as under-ice waters. Surface water DMS hotspots were measured in association with thermohaline oceanographic features in high productivity coastal waters, as well as with the presence of ponded first-year ice (FYI). Nighttime increases and daytime decreases of DMS concentrations were also observed in productive areas of the Labrador Sea and Davis Strait continental shelf. The association of DMS concentrations with diurnal solar radiation variation suggests the involvement of photobiological processes. Overall, our results strengthen the view that aqueous DMS cycling in the Arctic is intimately linked with sea ice dynamics and physiological responses to light. As such, future changes in the seasonality of the Arctic cryosphere will likely play an important role in shaping DMS emissions, although the sign and magnitude of the change remain highly uncertain.

The database consists of hourly atmospheric DMS concentrations, daily SO2 and total sulfate concentrations and three-day concentrations of size segregated aerosol sulfate. Samples were taken on the top of the navigation bridge of the CCGS Amundsen as it cruised along Baffin Bay and the Northwest Passage. Hourly samples of DMS was obtained using a customized DMS sampler. Samples were analyzed using a gas chromatograph fitted with a sulfur chemiluminesence detector (GC-SCD) to obtain atmospheric DMS concentrations. SO2 and total aerosol samples were obtained daily using a high volume sampler fitted with a quartz microfiber filter and K2CO3 treated cellulouse filter. Size segragated aerosol samples were obtained using a highvolume sampler fitted with slotted quartz filters on a 5 stage cascade impactor run for three days each sample. Concentrations of SO2, sulfate and MSA as well as other ions from the filter papers were obtained using ion chromatography. Delta34S values of SO2 and sulfate were obtained using a continuous flow isotope ratio mass spectrometer. Delta34S is reported based on the Vienna Canyon Diablo Troillite (V-CDT) international standard.

We are seeking answers to two key questions regarding the influence of marine processes on Arctic climate: 1) How will the increased flow of Pacific waters through the Canadian Archipelago affect the dynamics of climate-active gases in the ocean, and 2) How will these gases be affected by a reduction of sea-ice cover, and increased areas of open water? These questions have been addressed by our multidisciplinary team during two expeditions on the Canadian research ice-breaker Amundsen as part of the International Polar Year. The expeditions took place during the fall of 2007 and 2008. Eleven (2007) and ten (2008) Arctic SOLAS scientists from 7 Canadian institutions participated to these expeditions which allowed a unique and extensive longitudinal survey of these trace gases and aerosols in the High Canadian Arctic, from Baffin Bay to the Beaufort Sea. The missions enabled us to collect new oceanographic and atmospheric data on the distribution and cycling of DMS, N2O, and VOCs across the Canadian Archipelago and to relate these measurements to the distribution and chemical characteristics of aerosol particles. Activities of this program where coordinated with those of the IPY programs CFL, the Canadian program ArcticNet, and the international programs OASIS and SOLAS.

The database consists of hourly atmospheric DMS concentration, daily SO2 and total sulfate concentrations and three-day concentrations of size segregated aerosol sulfate. Samples were taken on the top of the navigation bridge of the CCGS Amundsen as it cruised along Baffin Bay and Lancaster Sound. Hourly samples of dimethyl sulfide was obtained using a customized DMS sampler. Samples were analyzed using a gas chromatograph fitted with a sulfur chemiluminesence detector (GC-SCD) to obtain atmospheric DMS concentrations. SO2 and total aerosol samples were obtained daily using a high volume sampler fitted with a quartz microfiber filter and K2CO3 treated cellulouse filter. Size segragated aerosol samples were obtained using a highvolume sampler fitted with slotted quartz filters on a 5 stage cascade impactor run for three days each sample. Concentrations of SO2, sulfate and MSA as well as other ions from the filter papers were obtained using ion chromatography. Delta34S values of SO2 and sulfate were obtained using a continuous flow isotope ratio mass spectrometer. Delta34S is reported based on the Vienna Canyon Diablo Troillite (V-CDT) international standard.

DMSP and DMS water concentrations were determine at fixed depths and at selected stations (ArcticNet stations) along a transect beginning in the North Water Polynya, going through the Lancaster Sound and the Northwest Passage, and terminating in the Beaufort Sea. During transit time, near surface DMS measurements were conducted every 2 hours from the pumping system of the CCGS Amundsen. In all cases, DMSP and DMS measurements were done following the methods of Kiene and Slezak 2006 (Limnol. Oceanogr.: Methods 4: 80-95). At selected stations, DMSP and DMS microbial cycling was determined during onboard incubations following the 35S-DMSP protocol (Merzouk et al. 2006, Deep Sea Res. 53:2370-2383).

An incubation experiment was conducted on board of the Canadian research icebreaker CCGS Amundsen between 6 and 15 August 2015. The water was collected near the nitracline at 38 m depth in Baffin Bay using 12-L Niskin-type bottles deployed on a CTD rosette system. A natural Arctic plankton community in a pre-bloom stage (initial high nutrient-low Chl a concentrations) was exposed over 9 days to reduced pH conditions under two contrasting light regimes. The two light regimes were designed to simulate the mean irradiance in an ice-free 5-m thick surface mixed layer (HL, marginal ice bloom conditions) and the mean irradiance at 5 m depth under a melting ponded ice pack (LL, under-ice bloom/ subsurface chlorophyll maximum conditions). The pH gradient comprised 6 levels covering the range of pH expected between the present and the year 2300. During the incubation, a phytoplankton bloom developed in every incubation bag and diatoms dominated the biomass (Chaetoceros spp.). Temporal variations of pH, dissolved inorganic carbon, total alkalinity, chlorophyll a, macronutrients, DMS(P), flow cytometry (nano- and pico-phytoplankton, bacteria, virus), taxonomy, salinity and incubator's temperature are available.

The Arctic Ocean in summer is thought to be a nexus of biogenic dimethylsulfide (DMS) production associated, in part, with diversified niches within or bordering dynamic sea-ice where DMS-rich microbial communities may thrive. However, critical uncertainties remain regarding the strength of sources, sinks and efflux of marine DMS in the Arctic. Quantifying contemporary oceanic reservoirs of DMS is pivotal for the prediction and interpretation of future reservoirs of this climate-active compound. While a global DMS database of ca. 50,000 points exists, only 2.5% of these inputs originate from Arctic oceans highlighting the relevance of continued sampling efforts particularly in the context of rapid and conspicuous climate alterations in this part of the Global Ocean. A joint NETCARE-ArcticNet campaign aboard the CCGS Amundsen during July and August 2016 served as the launching platform for the deployment of a high frequency autonomous underway DMS sampling instrument (MIMS – Membrane Inlet Mass Spectrometer). Providing real-time data, the MIMS allowed the detection of surface reservoirs of oceanic DMS at greater spatial and temporal scales than traditional single-sample gas chromatography analysis, in conjunction with measurements of temperature, salinity and fluorescence (water line TSG sensor)