Chair: Libby Jewett

Melissa Chierici ^(1)*, Agneta Fransson ⁽²⁾, Ingunn Skjelvan ⁽³⁾ , Kai Sørensen ⁽⁴⁾, Andrew King ⁽⁴⁾, Marit Norli ⁽³⁾, Helene Lødemel ⁽¹⁾

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 UniResearch, Bergen, Norway

Background
Increased attention and need for advice on ocean acidification and its consequences for the marine ecosystem motivated the Norwegian government to fund OA monitoring projects. Since 2011, two major research projects with multi-institutional participants were established to investigate the carbonate system and ocean acidification state in Norwegian(Norwegian Environment Agency) and Arctic waters (OA Flagship in the FRAM centre). The Fram Strait is the main gateway for exchange of Arctic and Atlantic waters entering the Arctic Ocean and studies here may give an integrated signal of the climate stressors affecting the Ocean acidification state in the Arctic Ocean. One of the aim of the repeated surveys in the Norwegian Sea is to investigate the trends in pH, which has been observed to decrease at a faster rate than modelled mainly due to the influence of anthropogenic CO₂. Another aim is to investigate the carbonate system state and variability in some of the major Cold Water Coral reef areas, which has been little investigated.

Methods
We use a combination of sampling platforms such as water column measurements (mainly in winter) along repeated transects and underway surface water carbonate system measurements for seasonal studies.
Water samples are collected and analysed either directly onboard or preserved for post-cruise analysis in laboratory. Samples are determined for total dissolved inorganic carbon (CT), total alkalinity (AT), pH and in surface waters underway fugacity of carbon dioxide (fCO2) combined with surface water sampling for analysis of either CT, AT or pH.

Findings
The variability is large, which are partly due to mixing of different water masses. Along the Norwegian coast, total carbon (CT) and total alkalinity (AT) are influenced by the fresh and cold coastal current, and the carbon values are low. A similar effect is seen at the marginal ice zone in the northern Barents Sea. Biological activity is also an important driver for the observed changes in the carbonate system and the effects of this are seen at some locations. Low pH values due to increased CO₂-content are seen at some locations, e.g. in the southern Norwegian Sea. In 2014, aragonite saturation averaged over all depths and stations is 1.6 in Skagerrak (in February), 1.7 and 1.7 in southern and northern Norwegian Sea, respectively, 1.9 the in Barents Sea Opening, and 1.8 in the North Eastern Barents Sea (in September). Low aragonite saturation is seen in the bottom water, and in the Barents Sea and Skagerrak this value is around 1.4. Deeper than about 1900 m in the Norwegian Sea the water is undersaturated with respect to aragonite, while supersaturation is seen at a few locations during winter in the Skagerrak surface water.

Conclusions
This is five years of monitoring of the OA state and we start to reveal trends, but they cannot be confirmed and the drivers are not yet fully understood. Further monitoring of the carbonate system is required to assess trends in and drivers of ocean acidification. Annual sampling of the water column in winter time is not satisfactory to address and extract the biological and physical processes behind the natural variability. Data is used in models to improve future projections of OA state. Seasonal and frequent sampling in surface waters results in understanding of CO₂ uptake and main drivers for seasonal change.