Seasonal change in ocean acidification state in Kongsfjorden: implications for calcifying organisms

Chair: Yuri Artioli

Melissa Chierici(1), Agneta Fransson(2), Haakon Hop(2), Helen Findlay(3), Svein Kristiansen(4), Vladmir Pavlov(2), Anette Wold(2)
1 Institute of Marine Research and FRAM-High North Centre of Climate and the Environment, Tromsø, 9294 Norway

2 Norwegian Polar Institute, Fram Centre, Tromsø 9296, Norway
3 Plymouth Marine Laboratory, Southampton, UK
4 UiT- The Arctic University of Norway, Tromsø, Norway

Background
Kongsfjorden is a fjord in West Spitsbergen and has no pronounced sill which makes it influenced by warm and saline Atlantic water inflow. The two retreating glaciers add freshwater to the water which also affects the ocean acidification state such as the calcium carbonate (CaCO3) saturation. By investigating the seasonal change in ocean acidification state and biogeochemical properties from winter-to-summer in two years we investigate the strength and effect of freshwater and photosynthesis on the carbonate system.

Methods
Water samples from April (winter) and July (summer) in 2013 and 2014 were collected in the water column from the glacier front to the outer shelf. The samples were analysed either directly onboard the RV Lance or were preserved for post-cruise analysis in laboratory. Samples were determined for total dissolved inorganic carbon (CT or DIC), total alkalinity (AT) and nutrient concentrations, and we calculated the full carbonate system including pH, CaCO3 saturation, fCO2 using chemical speciation models. Published data on the effect on calcifiers such as Limacina helicina at different CaCO3 saturation levels were compared with the observed saturation states in Kongsfjorden.

Findings
We found large differences between the winter and summer data entailing higher salinity and fugacity/partial pressure of CO2 (fCO2/pCO2) in winter and lower pH, compared to the summer values.

Conclusions
In winter, calcium carbonate (CaCO3) saturation (Ω) was approximately 1.6, reaching values for first signs of shell dissolution of aragonite-forming organisms such as pteropods (W<1.4). Biological CO2 consumption mitigated partly the decrease in Ω due to freshening, similar to what we found in other fjords.