The dramatic changes in the Arctic environment over the past couple of decades, caused by rising surface temperatures, loss of sea ice and diminishing habitat for its wild life have forced policy makers to find science-based answers to the problem. The surface air temperatures over the Arctic have been rising twice as fast as the global average (Fig. 1). The Arctic amplification- as it has been termed- is resulting in a perceptible shift of this region to a new environment which is warmer, wetter and more variable than ever before (www.amap.no/swipa).
The Second assessment report of the Arctic Monitoring and Assessment Programme’s Snow, Water, Ice and Permafrost in the Arctic (SWIPA) provides findings related to the observed changes in the Arctic during 2010 to early 2017 (SWIPA, 2017). Some of the significant observations of this assessment are:
- Arctic Ocean could be largely free of sea ice in summer as early as the 2030s,
- Recent data on additional melting processes affecting the Polar Regions seem to suggest that the low-end projections of global sea-level rise made by the Intergovernmental Panel on Climate Change (IPCC) are underestimated,
- Changes in the Arctic may be affecting weather in mid-latitudes, even influencing the Southeast Asian monsoon,
The extent and thickness of Arctic sea ice has been declining over the past few decades with an annual-mean aerial reduction of ~20 per cent since 1980 (Fig. 2). Despite the prominent year-to-year variabilities, this long-term decline appears to be largely, but not wholly, due to greenhouse gas forcing (IPCC, 2007). The Observatory for atmospheric research and monitoring located on the Zeppelin Mountain at Ny-Ålesund, in an untouched Arctic environment, has recorded an increase in the concentration of atmospheric CO2 from 355 ppm in 1988 to 400 ppm in 2015 (aces.su.se). Black carbon and tropospheric ozone have also been suggested to have contributed ~0.5–1.4o C and ~0.2–0.4o C, respectively, to Arctic warming since 1890.
Superimposed on the long-term trend of declining sea ice and warming surface temperatures over the Arctic is the natural decadal-scale forcings by atmospheric and ocean circulation. Model simulations of sea-ice variability by Ding et al (2017) indicate that trends in summertime atmospheric circulation could have contributed to as much as 60 per cent to the observed sea-ice extent decline since 1979 (usually interpreted on the basis of September readings). The studies also show that about 30–50 per cent of the overall decline in September sea ice since 1979 is attributable to the internal variabilities in the circulation trend as against long-term anthropogenic forcing.
Another important natural forcing mechanism responsible for a warming Arctic is related to decadal oceanic variability (Rajan and Singh, 2017). For instance, based on model simulations, Day et al. (2012) attribute 0.5–3.1 per cent per decade of the decadal decline in the September sea ice extent for 1979–2010 to such natural variability such as Atlantic Multi-decadal Oscillation (AMO) with expression in north Atlantic Sea Surface Temperatures (SST) which in turn is driven by the Atlantic Meridional Overturning Circulation (AMOC). Multi-decadal variations of the North Atlantic Oscillation (NAO) have also been demonstrated to induce variations in the AMOC and poleward ocean heat transport, contributing to the rapid loss of Arctic sea ice, Northern Hemisphere extra-tropical temperature variations and changing Atlantic tropical storm activity (Delworth et al. 2016).
As can be seen, while model simulations suggest an important role for natural atmospheric and oceanic climate variabilities in driving Arctic temperatures and sea ice trends, their relative roles especially vis-a-vis long-term anthropogenic forcing are largely uncertain—knowledge which is critical to projections of future climate. This would call for more and better observational and instrumental data and proxy-reconstructions. It is in this context that the location of the Svalbard group of islands in the middle of one of the important oceanic gateways to the Arctic becomes significant. Positioned right where the Arctic front separates the polar and extra-tropical air masses, and adjacent to Fram Strait, the major arterial route for seawater and heat to and from the polar area, Svalbard, which constitutes only about 0.4 per cent of the Arctic region, can be considered in many ways, as a natural laboratory for observing and understanding the effects of short-term climatic variabilities.
These islands are characterised by diverse habitats in the ecosystems over relatively small spatial scales which are exposed to various dynamic driving forces. The fjord systems especially on the western coast of the Spitsbergen island of Svalbard, which remain largely ‘Arctic’ the year-round (e.g. Horsund fjord) or are ‘Arctic-Atlantic’ over an annual cycle (e.g. Kongsfjord), and lakes which respond to alteration by both natural change and human disturbance provide ideal locales to study the responses of the Arctic aquatic ecosystems to seasonal to inter-annual variabilities (Rajan and Krishnan, 2016; David and Krishnan, 2017; Prominska et al. 2017). Some of the more dramatic visible effects of a warming Svalbard, a decline in sea ice thickness and extent, changes in the precipitation pattern and the occurrence of rain-on-snow and winter thaw/refreezing events over the past two decades are manifested in the following (see Descamps et al. 2017, for a detailed review):
- Data for the period 1999-2010 shows that reindeer are shrinking in both size and numbers, in response to the decreasing amount of winter food available (Hansen et al. 2013).
- Decrease in the population growth of Svalbard Rock Ptarmigans during the period 1997-2010, and decreasing numbers of Ringed seals in the period 2002-12 (Hamilton et al. 2016).
- Northward migration of species such as Atlantic cod, mackerel etc from Atlantic (Renaud et al. 2012)
- Decrease in the population of polar bears by around 15 per cent in both average weight and in the number of cubs during 2009-12 (Aras, 2013).
Since our understanding of the Arctic is mostly based on data when the Arctic had a thick sea ice cover, a paradigm shift in thinking and developing a strategy to predict the future of the Arctic sea ice, its effects on the climate, ocean and ecosystems, is called for. Knowledge of the state of the system operating today under the changed scenario is essential. To fill this knowledge gap, the Norwegian Polar Institute initiated a project in 2015—Norwegian Young Sea Ice Cruise (N-ICE 2015)—aimed at understanding “….how the rapid shift to a younger and thinner sea ice regime in the Arctic affects energy fluxes, sea ice dynamics and the ice-associated ecosystem, as well as local and global climate. The multidisciplinary observational study on drifting Arctic sea ice from winter to summer in early 2015 had components of climate, ecology, oceanography, sea ice, biology, chemistry, acidification, atmosphere, biodiversity, eco-toxicology, marine ecosystems, remote sensing, etc as core subjects. The preliminary results of this multinational cruise have been made freely available to the research community to appreciate the actual situation in the Arctic, and ultimately improve our capacity to model the future” (npolar.no).
The highlights of the preliminary findings of N-ICE 2015 (Fig 3) as published on the NPI website are:
- The ice pack had already accumulated nearly 0.5 m of snow in January. This is much more than we expected based on climatology.
- The thick snow cover slowed sea ice growth. Ice formed mainly in leads (fractures in sea ice). The thick heavy snow also contributed positively to the ice mass balance through snow-ice formation.
- Many storms took place, especially in winter. These brought with them warm and moist air, even in the middle of the polar night, also slowing ice growth.
- The storms also affected ocean mixing. Heat, nutrients, and CO2 were mixed throughout the upper water column during storms. We saw the ocean heat flux increased twofold during storms.
- The thinner sea ice was more easily broken up and we saw more ridging and lead formation than previously.
- Leads caused by storms allowed enough light to reach the water, sufficient to initiate and maintain an algae bloom under thick snow-covered ice that otherwise would have kept the algae community in the dark and unable to grow.
- The heavy snow load resulted in seawater infiltration at the snow–ice interface. This provided a habitat that supported ample algae growth, resembling conditions in the Antarctic sea ice zone.
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Inputs from : Dr S Rajan, Co-ordinator, International Indian Ocean Expedition-2, INCOIS, Hyderabad.