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

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

from the shelf to the deep ocean (Shapiro et al., 2003). Dense water formation on the shallow banks of the Barents Sea and western shelf of Novaya Zemlya Archipelago is well- documented (Midttun, 1985; Ivanov et al., 2004).As long as ice forms on the shallow shelves in winter, dense water formation will continue and may even increase (Bitz et al., 2006; Ivanov and Watanabe, 2013; Moat et al., 2014). One of the reasons for this is effective salinization of cold shallow water near the marginal ice zone, as described by Ivanov and Shapiro (2005). Later, however, together with declining sea ice formation in winter, bottom water formation in the Barents Sea is expected to slow, both in terms of open ocean convection and cascading (e.g.Årthun and Schrum, 2010). Recent (2008) measurements confirm that the density of Atlantic-origin water in the Barents Sea and bottomwater in St Anna Trough (through which dense water enters Nansen Basin) have remained higher than those measured in the 1990s (Lien and Trofimov, 2013), potentially indicating greater dense water formation in the ice-depleted conditions of the 2000s. The existence of large-scale open water area in winter caused by increased influx of Atlantic-origin water,might also impact on the atmosphere both locally and remotely. For the hypothetical case of a totally ice-free Arctic Ocean in winter, simple calculations by Newson (1973) suggest that weakening of the meridional temperature gradient would lead to a weakening of westerly winds, atmospheric blocking and general cooling in the mid-latitudes.The veracity of this foresight was recently confirmed by more sophisticated model studies (Petoukhov and Semenov, 2010; Hopsch et al., 2012;Yang and Christensen, 2012; Liptak and Strong, 2014; Mori et al., 2014). 4.3.4 Sea level and surface waves Sea level is the combined result of many factors and local sea level will be affected differently depending on location.These factors include melting ice over land (but not melting sea ice), thermal expansion as water warms,prevailing winds,distribution of land and ice masses, and the shape of the ocean basin. Land rebound following the disappearance of the Fennoscandian ice sheet is

in the central and northern parts of the Barents Sea.These results support the idea of oceanic heat transport having a critical role in sea-ice decay in this region. The decreasing trend in average sea-ice thickness for the 50-year period 2010–2070 (Figure 4.13) is less than observed from 1980 to 2008. This may be due to natural variability, which is typically stronger on a decadal scale than a multi-decadal scale. 4.3.3 Water temperature and salinity A continued northward shift in the ice edge in the Barents Sea will affect thermohaline properties in the upper mixed layer. Prolonged exposure of the open sea surface to the atmosphere will lead to a substantial increase in the uptake of short-wave solar radiation and consequent warming of surface waters (Sandø et al., 2010). Together with reduced surface salinity, as indicated by the downscaled NorESM results the warming strengthens density stratification over most of the Barents Sea (Figure 4.14).The excess freshwater input at the surface is due to increased high latitude precipitation, as projected in almost all CMIP5 models (Collins et al., 2013). The significance of the large-scale inflow of warm and saline Atlantic-origin water in shaping thermohaline conditions in the Barents Sea is well-established (Smedsrud et al.,2013; Sandø et al., 2014b). Under conditions of gradually shrinking ice cover, the effect of Atlantic-originwater inflow is expected to strengthen and extend further east, since cooling and freshening of theAtlantic- originwater en routewill slow,as therewill be less ice tomelt.Signs to support this idea have recently been reported (Årthun et al., 2012; Dmitrenko et al.,2015).Warmer and saltierAtlantic-origin water further to the north-east in the ice-free Barents Sea will provide more heat for release to the atmosphere in winter, and the associated heat loss will increase water density and favor the development of deeper convection.This phenomenon results in the formation of a well-ventilated water column and enhances nutrient transport to the surface waters. In shallow waters, convection may extend to the seabed, providing the prerequisite conditions for cascading (down- slope gravity-driven current), which transports dense water

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Figure 4.14 Change in salinity (left) and stratification (right) in the upper 50 m in March based on downscaled NorESM data. Present (2010-2019) and future (2060-2069) using the RCP4.5 scenario.