Climate change in the Arctic has been twice as fast as the global average (Blunden and Arndt 2012), causing general declines to the sea ice thickness, extent and concentration. It is important, though, to consider the volume of the sea ice, because this depends on both ice thickness and extent, hence suitably reflects changes to the exchange of fresh water between sea ice and the ocean. This is highlighted by the simulations of coupled global climate models, such as the Pan-Arctic Ice Ocean Modeling and Assimiation System (PIOMAS). The simulations display a 3.4% decline in Arctic sea ice volume per decade (Fig.1) (PIOMAS, Zhang and Rothrock,2003), whilst the decline in sea ice extent is predicted at 2.4% per decade (Gregory et al., 2002).
However, a continuous record of Arctic sea ice volume cannot currently be observed. One method for estimating sea ice volume changes uses satellite observations of sea ice thickness and concentration, and sea ice volume can then be extrapolated from this. Satellite altimetry is used to measure sea ice thickness. The satellite’s laser or radar pulse measures the height difference between the ocean surface and the ice surface - the freeboard. Measurements of thickness are possible with the approximation that the freeboard is 1/9th of the sea ice thickness (Vihma, 2014). The weight of snow cover, invisible to the radar altimeters, is one contribution of uncertainty in this measurement (Schweiger et al., 2011). The CryoSat-2 radar altimeter, which launched in 2010, has provided new thickness and volume estimates of Arctic Ocean sea ice (Laxon et al., 2013), with coverage up to 89°N. The observations show the ice volume inside the Arctic Basin decreased between the period of previous satellite ICESat (2003–2008) and the CryoSat-2 period (2010–present), by a total of 4291km3 in the autumn months and by 1479km3 in the winter months (Vaughan et al., 2013).
The PIOMAS simulations supports this, showing decline of sea ice volume over all seasons (Zhang and Rothrock, 2003) since the satellite record began in 1979 (Fig.1). September 2016 sea ice volume (4500km3) was 60% below the 1979-2015 mean and the third lowest for September on record, behind 2012 and 2011. The largest decline has come at the end of the summer melt season (Serreze et al. 2007) and the change in September minimum sea ice extent is becoming steeper with time (Cosimo et al. 2008). The period with sea ice cover has become shorter over large areas (Stammerjohn et al. 2012) and Overland et al. (2011) estimates an ice-free Artic Ocean will occur around year 2050. Holland et al. (2008) suggests that the summer ice volume is also increasing in variability, due the increasingly thinner ice being more vulnerable to melting out during the summer under favourable atmospheric conditions.
However, a continuous record of Arctic sea ice volume cannot currently be observed. One method for estimating sea ice volume changes uses satellite observations of sea ice thickness and concentration, and sea ice volume can then be extrapolated from this. Satellite altimetry is used to measure sea ice thickness. The satellite’s laser or radar pulse measures the height difference between the ocean surface and the ice surface - the freeboard. Measurements of thickness are possible with the approximation that the freeboard is 1/9th of the sea ice thickness (Vihma, 2014). The weight of snow cover, invisible to the radar altimeters, is one contribution of uncertainty in this measurement (Schweiger et al., 2011). The CryoSat-2 radar altimeter, which launched in 2010, has provided new thickness and volume estimates of Arctic Ocean sea ice (Laxon et al., 2013), with coverage up to 89°N. The observations show the ice volume inside the Arctic Basin decreased between the period of previous satellite ICESat (2003–2008) and the CryoSat-2 period (2010–present), by a total of 4291km3 in the autumn months and by 1479km3 in the winter months (Vaughan et al., 2013).
The PIOMAS simulations supports this, showing decline of sea ice volume over all seasons (Zhang and Rothrock, 2003) since the satellite record began in 1979 (Fig.1). September 2016 sea ice volume (4500km3) was 60% below the 1979-2015 mean and the third lowest for September on record, behind 2012 and 2011. The largest decline has come at the end of the summer melt season (Serreze et al. 2007) and the change in September minimum sea ice extent is becoming steeper with time (Cosimo et al. 2008). The period with sea ice cover has become shorter over large areas (Stammerjohn et al. 2012) and Overland et al. (2011) estimates an ice-free Artic Ocean will occur around year 2050. Holland et al. (2008) suggests that the summer ice volume is also increasing in variability, due the increasingly thinner ice being more vulnerable to melting out during the summer under favourable atmospheric conditions.
Figure 1. Monthly sea ice volume anomaly from PIOMAS. The 1979-present trend is shown in blue. Shaded areas shows two standard deviations from the trend.
From: http://psc.apl.washington.edu/research/projects/arctic-sea-ice-volume-anomaly/
References
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Zhang, J.L. and D.A. Rothrock, “Modeling global sea ice with a thickness and enthalpy distribution model in generalized curvilinear coordinates“, Mon. Weather Rev., 131, 845-861, 2003
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