5
(less ice growth) and also to more ocean heat being available to reduce ice growth
or increase melt (Alexeev et al. 2017; Polyakov et al. 2017).
The snow cover insulates the ice from a cold atmosphere. However, if the ice gets
so thin that the weight of the snow can press the surface of the ice below sea level,
i.e. negative freeboard, seawater can flood the bottom of the snow pack. This slush
can then freeze, to what we call snow-ice. Only recently such conditions have been
documented in the Arctic (Granskog et al. 2017; Merkouriadi et al. 2017), likely as
a consequence of the thinning sea ice, while it is less certain whether (snow) precipitation has increased or not. This changed thermodynamic growth mechanisms
of Arctic sea ice, can partly compensate for less ice growth due to a warming Arctic.
Snow-ice growth at the surface of the ice can be more rapid than typical ice growth
at the bottom, because the heat sink (cold atmosphere) is much closer. Given that the
ice gets thinner, it is likely that this phenomenon will become more widespread in
the Arctic (Merkouriadi et al. 2017). However, the snow to ice thickness relationship is rendered complex in the new seasonal Arctic icescape, because only the ice
that has survived summer melt will collect the whole seasonal snow precipitation.
Most of the snow falls in the autumn, while later formation of new ice will result in
less snow accumulation on first-year sea ice (Webster et al. 2014).
The thick snow cover on sea ice in the Atlantic sector of the Arctic (Rösel et al.
2018), contradicts the assumption that snow depth on sea ice has decreased as
observed in the western Arctic (Webster et al. 2014). There are likely a number of
reasons for this. Surprisingly, there are very few observations in the Atlantic sector,
and values typically assumed are based on a snow-on-sea-ice climatology that has
rather few observations in this region (Warren et al. 1999). Secondly, this region
experiences frequent low pressure systems (cyclones or storms) entering the Arctic,
carrying warm air masses and moisture with them, even in midwinter (Graham et al.
2017). There are some indications that these winter storms are also becoming more
frequent (Rinke et al. 2017). This, and the thinning of the ice, appears to have shifted
the ice pack to something what is typical for the Antarctic sea ice zone, where surface flooding is widespread.
Recent observations also indicate that the thinner ice pack is more dynamic and
vulnerable to atmospheric forcing (Itkin et al. 2017). Especially the frequent (winter) storms in the Atlantic sector (Rinke et al. 2017) bring along such forces that can
precondition the ice pack later in the season. The ice pack will thus be more mobile,
and is also likely more susceptible to subsequent storms. However the full impacts
of these changes are not well known. Further these processes act on rather small
scales in the ice pack itself, such as breaking up of the ice floes and formation of
open water (leads) that occur on scales from meters to a kilometer, at subgrid scales
in climate models. It is imperative that these processes are realistically represented
in models. Given that the ice pack is weaker than before, which could be due to a
thinner ice pack, its response to external wind forcing may be more pronounced
than earlier when the ice pack was composed of thicker older ice. Indications for
this have been recently observed north of Greenland (Barber et al. 2018), where the
ice pack is typically very static.
Emerging Traits of Sea Ice in the Atlantic Sector of the Arctic
(less ice growth) and also to more ocean heat being available to reduce ice growth
or increase melt (Alexeev et al. 2017; Polyakov et al. 2017).
The snow cover insulates the ice from a cold atmosphere. However, if the ice gets
so thin that the weight of the snow can press the surface of the ice below sea level,
i.e. negative freeboard, seawater can flood the bottom of the snow pack. This slush
can then freeze, to what we call snow-ice. Only recently such conditions have been
documented in the Arctic (Granskog et al. 2017; Merkouriadi et al. 2017), likely as
a consequence of the thinning sea ice, while it is less certain whether (snow) precipitation has increased or not. This changed thermodynamic growth mechanisms
of Arctic sea ice, can partly compensate for less ice growth due to a warming Arctic.
Snow-ice growth at the surface of the ice can be more rapid than typical ice growth
at the bottom, because the heat sink (cold atmosphere) is much closer. Given that the
ice gets thinner, it is likely that this phenomenon will become more widespread in
the Arctic (Merkouriadi et al. 2017). However, the snow to ice thickness relationship is rendered complex in the new seasonal Arctic icescape, because only the ice
that has survived summer melt will collect the whole seasonal snow precipitation.
Most of the snow falls in the autumn, while later formation of new ice will result in
less snow accumulation on first-year sea ice (Webster et al. 2014).
The thick snow cover on sea ice in the Atlantic sector of the Arctic (Rösel et al.
2018), contradicts the assumption that snow depth on sea ice has decreased as
observed in the western Arctic (Webster et al. 2014). There are likely a number of
reasons for this. Surprisingly, there are very few observations in the Atlantic sector,
and values typically assumed are based on a snow-on-sea-ice climatology that has
rather few observations in this region (Warren et al. 1999). Secondly, this region
experiences frequent low pressure systems (cyclones or storms) entering the Arctic,
carrying warm air masses and moisture with them, even in midwinter (Graham et al.
2017). There are some indications that these winter storms are also becoming more
frequent (Rinke et al. 2017). This, and the thinning of the ice, appears to have shifted
the ice pack to something what is typical for the Antarctic sea ice zone, where surface flooding is widespread.
Recent observations also indicate that the thinner ice pack is more dynamic and
vulnerable to atmospheric forcing (Itkin et al. 2017). Especially the frequent (winter) storms in the Atlantic sector (Rinke et al. 2017) bring along such forces that can
precondition the ice pack later in the season. The ice pack will thus be more mobile,
and is also likely more susceptible to subsequent storms. However the full impacts
of these changes are not well known. Further these processes act on rather small
scales in the ice pack itself, such as breaking up of the ice floes and formation of
open water (leads) that occur on scales from meters to a kilometer, at subgrid scales
in climate models. It is imperative that these processes are realistically represented
in models. Given that the ice pack is weaker than before, which could be due to a
thinner ice pack, its response to external wind forcing may be more pronounced
than earlier when the ice pack was composed of thicker older ice. Indications for
this have been recently observed north of Greenland (Barber et al. 2018), where the
ice pack is typically very static.
Emerging Traits of Sea Ice in the Atlantic Sector of the Arctic