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.

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).

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.