Adaptation Actions for a Changing Arctic: Perspectives from the Barents Area

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Chapter 4 · Physical and socio-economic environment

and polar bears among others, and in the Barents Sea forms an important element of the marine ecosystem.Water temperature and salinity (basic seawater properties) affect the functioning of ecosystems, directly or indirectly through secondary effects such as density stratification and light transmission. Ocean waters are in constant motion, due to winds and tides. This motion drives constant renewal of the water at any given location. Any change in currents or tidal features may in turn affect water properties and nutrient transport, with potential for impacts on the marine ecosystem. The Barents Sea supports various industrial sectors, including those important for local communities as well as those important for the wider Barents area (such as international shipping routes connecting Europe andAsia, see Danilov et al., 2014). Changes in oceanic and ice conditions in the Barents Sea are likely to have socio-economic consequences, locally and in distant regions. Projections for the future include continued warming and declining sea ice. Less sea ice leads to greater heat release to the atmosphere and reduced vertical stability, as well as a shift in the large-scale atmospheric circulation pattern over Europe in winter (Christensen et al., 2015). Models suggest further reductions in sea ice in the Barents and Kara seas may bring colder winter temperatures in Europe. Recent model simulations suggest that the North Atlantic Oscillation (NAO; the dominant mode of near-surface pressure variability over the NorthAtlantic and neighboring landmasses) is highly sensitive to the location of sea ice loss, and that its northern center of action shifts westward or eastward depending on whether the sea ice loss occurs in theAtlantic or Pacific sectors of theArctic (Pedersen et al., 2016). 4.3.2 Past trends and future projections The Barents Sea is one of the Arctic regions with the greatest sea ice variations (Deser et al., 2000; Francis and Hunter, 2007). About 50% of the Barents Sea is ice-covered in winter, but most of it is open sea during summer.Daily to annual sea ice variations are mainly caused by variations in wind strength and direction (Kimura andWakatsuchi, 2001; Kwok et al., 2005; Koenigk et al., 2009).Anomalously northerly winds transport more and thicker ice from the central Arctic into the Barents Sea and further south, mainly through the section between Svalbard and Franz Josef Land. In contrast, southerly winds prevent ice transport southward while simultaneously moving warmer air and water masses from theAtlantic into the Barents Sea, preventing sea ice formation (Sandø et al., 2014b; Sato et al., 2014).The Arctic sea ice cover is influenced by the northward ocean heat transport in the Norwegian Sea (e.g. Sandø et al., 2010; Smedsrud et al., 2010),and the ocean heat transport through FramStrait and the Barents SeaOpening plays an important role in sea ice variability in the Barents Sea over annual time scales (Schlichtholz, 2011; Årthun et al.,2012; Nakanowatari et al.,2014; Ivanov et al.,2016) and longer (Koenigk et al., 2009; Alekseev et al., 2015). The observed sea ice decline in the Barents Sea has occurred at the same time as an observed increase inAtlantic heat transport due to both strengthening and warming of the inflow (Årthun et al., 2012). During winter, the ice margin has shifted towards the north and east (Årthun and Schrum, 2010). Autumn sea ice variations and reductions in the Barents Sea have been linked to the NorthAtlantic Circulation in the following winter, and to

(including the city of Murmansk) at 0.4 kt in 2012. The most important sources were diesel trucks and machinery in the mining industry, followed by on-road transport. There are also other atmospheric pollutants such as mercury, but they are not necessarily connected to climate change other than through an indirect connection with coal burning (AMAP, 2011).

4.3 Changes in the ocean and sea ice

4.3.1 Importance of the Barents Sea The Barents Sea constitutes about 10% of the Arctic Ocean by area and has a mean depth of only 230 m. Despite this limited volume it influences a much larger region. It is favorably located for exchanges of heat between the ocean and atmosphere because it occupies a key position in one of the main gateways to the Arctic Ocean. The Barents Sea dominates the Arctic heat budget and has the strongest ocean-air heat exchanges in the Arctic (Häkakinen and Cavalieri, 1989). It is an important production area for dense water (Ivanov et al., 2004), which leaves the Barents Sea through relatively deep channels and sinks into the Arctic Ocean, thus contributing to the global thermohaline circulation. The sea ice cover is seasonal over the major part of the Barents Sea; in summer the area is ice free except for the very northern margin, whereas in winter, the marginal ice zone (the transition zone between open water and consolidated ice cover) is located north of the polar front (Smedsrud et al., 2013). The state of the upper ocean is crucially important for weather and climate in the surrounding area. The ocean and atmosphere are continuously interacting, through the exchange of momentum, moisture and heat (Bintanja and Selten, 2014). Surface waves are the most visible effect of this interaction in the ocean. The properties of the upper mixed layer are a less visible but no less important an outcome since they determine themarine biota.Changes in sea water temperature are reflected in air temperature (for example, the warming effect of the ocean elevates mean winter temperature on Spitsbergen by about 10°C relative to the zonal average at the same latitude), cloudiness and precipitation. In the Arctic, the ocean-atmosphere interaction is strongly mediated by sea ice,where sea ice properties (concentration and thickness) determine the strength of energy fluxes. In winter, the upward heat flux from the open ocean is about two orders of magnitude higher than through the pack ice (Smith et al., 1990).The area of open water determines fetch length and wave height. Sea ice also influences the underlying water column. In spring and summer, sea ice controls the amount of solar radiation absorbed, thus limiting warming in ice-covered areas, and ice melt contributes to the freshwater balance. Occasional opening of polynyas (compact ice-free zones in consolidated ice cover) in winter may trigger instant convective mixing of the water column to substantial depths (or cascading of dense water from the shelf) leading to ventilation of deep layers and upwelling of nutrients to surface waters (Marshall and Schott, 1999; Ivanov et al., 2004). Sea ice also provides a habitat for various Arctic species, including plankton, seals,

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