28
In this chapter, we provided an introductory overview on
the complex interactions of the coupled Arctic system in a
changing climate with specific interest in the ways in which
Arctic Ocean and adjacent seas may respond and modulate
the observed and projected changes over high and midlatitude. Next, we give an overview of the complex interplay
between the dynamics and thermodynamics of the sea ice,
atmosphere and ocean. We start by addressing the sea ice
cycle, variability, and importance in the climate system
(Section “Arctic sea ice”). In Section “Arctic – subarctic
atmosphere” we give background information on the Arctic –
Subarctic atmosphere (Section “Atmospheric circulation:
Why does it matter?”) and present the main atmospheric circulation modes (Section “Major modes of atmospheric circulation in the Arctic”). Then, we finally get to discuss the
changing climate from the ocean perspective (Section
“Ocean”): at first, we describe the main geographical features and the hydrography of the northern seas; subsequently,
we address recent research and discussion of the global relevance of the region in a changing world. Final remarks are
given in Section “Outlook”.
Arctic Sea Ice
Sea Ice Cycle
The sea ice cover has a natural cycle as a consequence of the
periodic changes of incident solar radiation over high latitudes. As the cold season arrives, atmospheric temperatures
rapidly begin to drop. This leads to a positive thermal gradient from ocean to the surrounding air, resulting in a direct
loss of sensible heat from the upper ocean. Dynamical instability in the upper meters of the ocean is generated as a consequence to density changes caused by cooling, and a vertical
mixing is maintained until a significant layer of the upper
water column approaches homogeneous temperature. Once
the ocean freezing temperature of −1.9 °C is achieved, sea
ice structures begin to form, and during this process a salt
solution (brine) is expelled into the ocean further increasing
its density. However, if mixing is deep enough, the surface
waters may not reach freezing temperatures due to mixing
with the warmer waters at intermediate depths and sea ice
formation will not occur.
After initial formation in fall, sea ice continues growing
through winter months and increases in vertical and horizontal extent. It can be characterized by highly complex and
variable macrostructures, such as ridges, melt ponds, leads
and polynyas. By the end of wintertime, the sea ice extent
has reached its maximum. During spring, the solar radiation
gradually increases thereby initiating the melting phase,
which carries on until the next cooling season. If all the sea
ice melts away, the area is characterized by the presence of
fist year ice. However, if sea ice persists until the end of the
warm season a perennial (multiyear) sea ice cover establishes. The fundamental differences between them relate to
the vertical growth and surface roughness.
Overall, freezing and melting are controlled by net surface heat energy flux variations during the year, and environmental conditions, e.g., wind and oceanic currents, play a
role in determining expansion and thickening. Furthermore,
the horizontally confined Arctic Ocean allows for thicker sea
ice growth (in comparison to the Southern Ocean), and winter sea ice thickness ranges on average from 3 to 4 m. For
more details the reader is referred to Thomas and Dieckmann
(2010).
Sea Ice Role in the Climate System
Sea ice is a highly reflective surface, with albedo ranging
from 50% to 70%. Albedo is a measure of a surface’s reflectivity, and may be even higher if a snow cover is present. A
thicker ice pack supports a greater layer of snow and this
system can reflect up to 90% of solar energy. Additionally, it
acts as an insulator between ocean and atmosphere, and,
therefore, restricts heat and momentum fluxes at this interface. If the atmosphere or the ocean warms up (above melting temperatures) sea ice melts and, since the exposed ocean
surface has a much lower albedo than sea ice, the overall
albedo of polar areas decrease. The low reflectance oceanic
surface takes in extra heat, driving major changes in the
regional radiative equilibrium and further sea ice melt. The
described processes is the so-called ice-albedo feedback
mechanism and is accounted as the main reason of nonlinear
changes over polar regions (Winton 2008; Serreze and Barry
2011; Vihma 2014). Changes to ocean density caused by the
sea ice cycle are important processes for the local oceanic
stratification and global oceanic circulation.
A few specific areas of the high latitude oceans are crucial
for the production of dense water masses, which contribute
to the lower limb of the global oceanic overturning circulation. The upper layers of the ocean are densified through
cooling of surface waters and the injection of brine during
sea ice formation resulting in vertical mixing and deep convection (Tomczak and Godfrey 1994). In these regions the
dense water sinks and is replaced by surface water from
other areas and the continuation of this process is one of the
drivers of the Meridional Overturning Circulation; the sinking of these waters is compensated by upwelling at other
sites (Talley et al. 2011). On the other hand, sea ice constitutes a source of relatively fresh water (with an average salinity ranging from 2 to 7 (Thomas and Dieckmann 2010)) and
when it melts it decreases the density of the water directly
underneath, creating a stable surface layer. Changes in the
water density at the deep convection sites may alter mixing
C. Campos and M. Horn
In this chapter, we provided an introductory overview on
the complex interactions of the coupled Arctic system in a
changing climate with specific interest in the ways in which
Arctic Ocean and adjacent seas may respond and modulate
the observed and projected changes over high and midlatitude. Next, we give an overview of the complex interplay
between the dynamics and thermodynamics of the sea ice,
atmosphere and ocean. We start by addressing the sea ice
cycle, variability, and importance in the climate system
(Section “Arctic sea ice”). In Section “Arctic – subarctic
atmosphere” we give background information on the Arctic –
Subarctic atmosphere (Section “Atmospheric circulation:
Why does it matter?”) and present the main atmospheric circulation modes (Section “Major modes of atmospheric circulation in the Arctic”). Then, we finally get to discuss the
changing climate from the ocean perspective (Section
“Ocean”): at first, we describe the main geographical features and the hydrography of the northern seas; subsequently,
we address recent research and discussion of the global relevance of the region in a changing world. Final remarks are
given in Section “Outlook”.
Arctic Sea Ice
Sea Ice Cycle
The sea ice cover has a natural cycle as a consequence of the
periodic changes of incident solar radiation over high latitudes. As the cold season arrives, atmospheric temperatures
rapidly begin to drop. This leads to a positive thermal gradient from ocean to the surrounding air, resulting in a direct
loss of sensible heat from the upper ocean. Dynamical instability in the upper meters of the ocean is generated as a consequence to density changes caused by cooling, and a vertical
mixing is maintained until a significant layer of the upper
water column approaches homogeneous temperature. Once
the ocean freezing temperature of −1.9 °C is achieved, sea
ice structures begin to form, and during this process a salt
solution (brine) is expelled into the ocean further increasing
its density. However, if mixing is deep enough, the surface
waters may not reach freezing temperatures due to mixing
with the warmer waters at intermediate depths and sea ice
formation will not occur.
After initial formation in fall, sea ice continues growing
through winter months and increases in vertical and horizontal extent. It can be characterized by highly complex and
variable macrostructures, such as ridges, melt ponds, leads
and polynyas. By the end of wintertime, the sea ice extent
has reached its maximum. During spring, the solar radiation
gradually increases thereby initiating the melting phase,
which carries on until the next cooling season. If all the sea
ice melts away, the area is characterized by the presence of
fist year ice. However, if sea ice persists until the end of the
warm season a perennial (multiyear) sea ice cover establishes. The fundamental differences between them relate to
the vertical growth and surface roughness.
Overall, freezing and melting are controlled by net surface heat energy flux variations during the year, and environmental conditions, e.g., wind and oceanic currents, play a
role in determining expansion and thickening. Furthermore,
the horizontally confined Arctic Ocean allows for thicker sea
ice growth (in comparison to the Southern Ocean), and winter sea ice thickness ranges on average from 3 to 4 m. For
more details the reader is referred to Thomas and Dieckmann
(2010).
Sea Ice Role in the Climate System
Sea ice is a highly reflective surface, with albedo ranging
from 50% to 70%. Albedo is a measure of a surface’s reflectivity, and may be even higher if a snow cover is present. A
thicker ice pack supports a greater layer of snow and this
system can reflect up to 90% of solar energy. Additionally, it
acts as an insulator between ocean and atmosphere, and,
therefore, restricts heat and momentum fluxes at this interface. If the atmosphere or the ocean warms up (above melting temperatures) sea ice melts and, since the exposed ocean
surface has a much lower albedo than sea ice, the overall
albedo of polar areas decrease. The low reflectance oceanic
surface takes in extra heat, driving major changes in the
regional radiative equilibrium and further sea ice melt. The
described processes is the so-called ice-albedo feedback
mechanism and is accounted as the main reason of nonlinear
changes over polar regions (Winton 2008; Serreze and Barry
2011; Vihma 2014). Changes to ocean density caused by the
sea ice cycle are important processes for the local oceanic
stratification and global oceanic circulation.
A few specific areas of the high latitude oceans are crucial
for the production of dense water masses, which contribute
to the lower limb of the global oceanic overturning circulation. The upper layers of the ocean are densified through
cooling of surface waters and the injection of brine during
sea ice formation resulting in vertical mixing and deep convection (Tomczak and Godfrey 1994). In these regions the
dense water sinks and is replaced by surface water from
other areas and the continuation of this process is one of the
drivers of the Meridional Overturning Circulation; the sinking of these waters is compensated by upwelling at other
sites (Talley et al. 2011). On the other hand, sea ice constitutes a source of relatively fresh water (with an average salinity ranging from 2 to 7 (Thomas and Dieckmann 2010)) and
when it melts it decreases the density of the water directly
underneath, creating a stable surface layer. Changes in the
water density at the deep convection sites may alter mixing
C. Campos and M. Horn