Report 2014:
Variability of Melt

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Regional Variability in Sea Ice Melt in a Changing Arctic: 1957 to 2014


     The Ice Mass Balance Buoys (IMB's) provide a means to observe and understand changes in the sea ice mass balance.  This involves measuring ice growth and melt on both the surface and the bottom of the ice. Using results from the IMBs and other complementary data sets, including data collected at manned camps, we compiled sea ice mass balance results made over an entire summer melt season from 41 distinct sites for the period 1957 to 2014 (Perovich and Richter-Menge, 2015). The location of the 41 sites on 15 July is shown in Figure 3a. The sites were divided into three geographical groupings: Beaufort Sea (15 sites), Intermediate (13 sites), and North Pole (13 sites).

     Averaging the results from each of the regions indicates no significant difference in mean snow depth for the Beaufort (24 cm), Intermediate (26 cm), and North Pole (27 cm) regions (Figure 2). In contrast, the results show significant regional and temporal variability in surface and bottom melt. This is not surprising due to the many factors that contribute to ice melt. Surface melt is affected by clouds, incident solar radiation, the start and end dates of the melt season, air temperature, and winds. Bottom melt is related to the heat content of the upper ocean, ice – ocean mixing, solar input to the upper ocean, and the ice concentration.

Figure 1. Map showing the locations on 15 July of the 41 sea ice mass balance sites. Green designates Beaufort sites, blue is Intermediate, and red is North Pole. The star denotes the position of the geographic North Pole and the white portion represents the1981 – 2010 median sea ice extent for July.


Figure 2. Summary statistics of maximum snow depth, total surface melt, and bottom melt plotted for the three regions. The solid square is the mean, the horizontal line the median, the box is plus or minus one standard deviations and the whiskers are the maximum and minimum values of the parameter.


     The full range of ice melt at individual sites is from 6 cm of surface melt (Intermediate) to 210 cm of bottom melt (Beaufort). When taken over the course of the summer these differences in total melt correspond to a huge variability of net surface and bottom fluxes from just a few Wm-2 to nearly 150 Wm-2. The combined average surface and bottom melting of all the sites is roughly comparable, with a mean ice equivalent surface melt of 48 cm and a mean bottom melt of 53 cm. On average, surface melting decreases moving northward from the Beaufort Sea (66 cm), to the Intermediate (42 cm), to the North Pole (34). This result suggests that latitude is a rough proxy for incident solar irradiance and temperature. However, it is apparent that interannual differences in atmospheric forcing that can overwhelm the influence of latitude. There is a profound regional difference in bottom melting. The mean bottom melt in the Beaufort (82 cm) is roughly double that for the Intermediate (36 cm) and North Pole (42 cm) cases and has a much larger standard deviation and range of values.

 

Arctic in Summer with Melt Ponds

Acrtic Sea Ice in Summer

Substantial increases in bottom melting are a major contributor to ice losses in the Beaufort Sea, and are linked to a regional decrease in ice concentration (Perovich et al., 2011; Perovich et al., 2008). In the central Arctic, away from the ice edge, surface and bottom melting demonstrate interannual variability, but show no strong temporal trends from 2000 to 2014. The results at the Intermediate and North Pole sites suggest that under current conditions summer melting is not large enough to completely remove the sea ice cover, consistent with the findings in Perovich et al. (2014).

Refferences:

Perovich, D.K. and J.A. Richter-Menge (2015) Regional variability in sea ice melt in a changing Arctic, Proceedings of the Royal Society, in press.

Perovich, D., J.A. Richter-Menge, C. Polshenski, B. Elder, T. Arbetter and O. Brennick (2014) Sea ice mass balance observations from the North Pole Environmental Observatory, Geophys. Res. Lett., 41, 6, doi: 10.1002/2014GL059356.

Perovich, D.K., J.A. Richter-Menge, K.F. Jones, B. Light, B.C. Elder, C.M. Polashenski, D. LaRoche, T. Markus, and R. Lindsay (2011), Arctic sea-ice melt in 2008 and the role of solar heating, Ann Glaciol., 52, 355-359.

Perovich, D.K., J.A. Richter-Menge, K.F. Jones, and B. Light (2008), Sunlight, water, and ice: Extreme Arctic sea ice melt during the summer of 2007, Geophys. Res. Lett., 35, L11501, doi:10.1029/2008GL034007.