36
loop assuring a constant mixing and sinking of denser water.
On the contrary, Rudels et al. (2013) state that under a regime
of stronger inflow of the warm AW, no cooling to freezing
temperature would occur. In this case, no brine-induced convection would occur, thus modulating the production of less
dense Barents Sea Water. In either case, changes in the cooling and mixing of AW in the Barents Sea could impact the
ventilation of the intermediate layer inside the Arctic, since
50–80% of the water occupying this layer is influenced by
water mass originated on the Barents Sea basin (Schauer
et al. 2002).
It has been hypothesized that the inflow of warm AW into
the Arctic Ocean has a considerable influence on the decline
and variability of sea ice extent and thickness (Årthun et al.
2012; Smedsrud et al. 2013; Carmack et al. 2015; Long and
Perrie 2015). Roughly 20% of the total trend in sea ice volume loss since 2004 is related to observed episodes of AW
warming (Ivanov et al. 2012).
In their study “Is weaker sea ice changing the Atlantic
Water circulation?”, Itkin et al. (2014) try to understand and
predict the effects of recent loss of sea ice on the overall
intermediate circulation. It is presented that a thinner sea ice
cover offers less hindrance to momentum transfer to the
ocean, thus allowing a spin up of the Arctic circulation. The
strengthening of the surface anticyclonic circulation results
in the accumulation of water in the interior of the Beaufort
Gyre, as a consequence of the enhanced Ekman convergence
(Deser et al. 2014; Itkin et al. 2014; Long and Perrie 2015).
Later, the stored water adds up to an increased outflow into
the Atlantic Ocean, and is compensated by the increased
inflow through the Barents Sea.
The Atlantification of the Arctic Ocean has been recently
shown to extend even further into the Arctic Ocean as sea
ice-ocean-atmosphere interactions change; at the same time
the usual vertical stability of the Arctic Ocean is decreasing
as the warm waters reach further upward and more heat is
made available for inducing further melting of sea ice
(Polyakov et al. 2017).
Outlook
Along with pronounced atmospheric warming, the summer
Arctic sea ice has been projected to disappear by the second
half of the twenty-first century (Overland and Wang 2013).
How this will affect the atmosphere-sea ice-ocean interactions and influence the weather and variability in and beyond
the Arctic boundaries has been more and more under discussion (Jung et al. 2014; Suo et al. 2017).
Model simulations predict that the hydrological cycle will
further intensify and thereby increase the Arctic freshwater
content, as well as the liquid freshwater export (e.g., Arzel
et al. 2008; Holland et al. 2007). At the same time, the sea ice
volume will further shrink, which possibly results in a
decreasing sea ice export as projected by Arzel et al. (2008).
Accelerating melt of the Greenland Ice Sheet and Arctic
glaciers due to increasing air temperature provides even
more freshwater to the North Atlantic with its deep water
formation sites (Yang et al. 2016) and contributes to the projected increase in sea level rise (Rahmstorf 2007). Predictions
on the impact of the increasing freshwater input to the North
Atlantic are very diverse and range from almost no impact to
a complete shutdown of the Atlantic Meridional Overturning
Circulation (AMOC). Böning et al. (2016) argue from their
model simulation that the accumulation of Greenland Ice
Sheet melt water has not been large enough yet to have a
significant impact on the AMOC. Though, they found that an
accumulated freshwater runoff of about 20,000 km
3
, that
could be reached by 2040 considering the current observed
trend in runoff, would slowdown the AMOC by more than
5 Sv. Liu et al. (2017) even projected a complete collapse of
the AMOC 300 years after an abrupt doubling of the atmospheric CO 2 concentration from the 1990 level. However,
Behrens et al. (2013) showed how sensitive model simulations are to small variations in precipitation and the choice of
sea surface salinity restoring to climatological values. From
these small variations they found in their model simulation a
variation of an accelerated AMOC of ~22 Sv to a nearlycollapsed state of ~6 Sv. Swingedouw et al. (2009) showed
with their model experiment that the AMOC response to the
freshwater input is not linear and depends on the mean state
of the climate.
Changes in ocean characteristics and sea ice cover can
have significant influence on the biogeochemical feedbacks
and marine ecosystem (Bates and Mathis 2009; Johannessen
and Miles 2011). The reduction of the sea ice cover allows
for more light to reach and warm the ocean surface, promoting an increase in primary production (Slagstad et al. 2015).
This, in turn, is intrinsically related to an expected increase
CO 2 uptake by the ocean (Bates and Mathis 2009). Still,
some controversy exists with indications that the ocean may
soon enough saturate, and loses its CO 2 uptake capacity (Cai
et al. 2010).
Indeed, fundamental questions on the pathways and time
scales in which the ocean drives and responds to changes in
the coupled system still remain unresolved, hence still
demanding much effort in order to better understand the role
of the northern seas in the context of a changing climate.
Appendix
This article is related to the YOUMARES 8 conference
session no. 9: “The Physics of the Arctic and Subarctic
Oceans in a Changing Climate”. The original Call for
Abstracts and the abstracts of the presentations within this
C. Campos and M. Horn
loop assuring a constant mixing and sinking of denser water.
On the contrary, Rudels et al. (2013) state that under a regime
of stronger inflow of the warm AW, no cooling to freezing
temperature would occur. In this case, no brine-induced convection would occur, thus modulating the production of less
dense Barents Sea Water. In either case, changes in the cooling and mixing of AW in the Barents Sea could impact the
ventilation of the intermediate layer inside the Arctic, since
50–80% of the water occupying this layer is influenced by
water mass originated on the Barents Sea basin (Schauer
et al. 2002).
It has been hypothesized that the inflow of warm AW into
the Arctic Ocean has a considerable influence on the decline
and variability of sea ice extent and thickness (Årthun et al.
2012; Smedsrud et al. 2013; Carmack et al. 2015; Long and
Perrie 2015). Roughly 20% of the total trend in sea ice volume loss since 2004 is related to observed episodes of AW
warming (Ivanov et al. 2012).
In their study “Is weaker sea ice changing the Atlantic
Water circulation?”, Itkin et al. (2014) try to understand and
predict the effects of recent loss of sea ice on the overall
intermediate circulation. It is presented that a thinner sea ice
cover offers less hindrance to momentum transfer to the
ocean, thus allowing a spin up of the Arctic circulation. The
strengthening of the surface anticyclonic circulation results
in the accumulation of water in the interior of the Beaufort
Gyre, as a consequence of the enhanced Ekman convergence
(Deser et al. 2014; Itkin et al. 2014; Long and Perrie 2015).
Later, the stored water adds up to an increased outflow into
the Atlantic Ocean, and is compensated by the increased
inflow through the Barents Sea.
The Atlantification of the Arctic Ocean has been recently
shown to extend even further into the Arctic Ocean as sea
ice-ocean-atmosphere interactions change; at the same time
the usual vertical stability of the Arctic Ocean is decreasing
as the warm waters reach further upward and more heat is
made available for inducing further melting of sea ice
(Polyakov et al. 2017).
Outlook
Along with pronounced atmospheric warming, the summer
Arctic sea ice has been projected to disappear by the second
half of the twenty-first century (Overland and Wang 2013).
How this will affect the atmosphere-sea ice-ocean interactions and influence the weather and variability in and beyond
the Arctic boundaries has been more and more under discussion (Jung et al. 2014; Suo et al. 2017).
Model simulations predict that the hydrological cycle will
further intensify and thereby increase the Arctic freshwater
content, as well as the liquid freshwater export (e.g., Arzel
et al. 2008; Holland et al. 2007). At the same time, the sea ice
volume will further shrink, which possibly results in a
decreasing sea ice export as projected by Arzel et al. (2008).
Accelerating melt of the Greenland Ice Sheet and Arctic
glaciers due to increasing air temperature provides even
more freshwater to the North Atlantic with its deep water
formation sites (Yang et al. 2016) and contributes to the projected increase in sea level rise (Rahmstorf 2007). Predictions
on the impact of the increasing freshwater input to the North
Atlantic are very diverse and range from almost no impact to
a complete shutdown of the Atlantic Meridional Overturning
Circulation (AMOC). Böning et al. (2016) argue from their
model simulation that the accumulation of Greenland Ice
Sheet melt water has not been large enough yet to have a
significant impact on the AMOC. Though, they found that an
accumulated freshwater runoff of about 20,000 km
3
, that
could be reached by 2040 considering the current observed
trend in runoff, would slowdown the AMOC by more than
5 Sv. Liu et al. (2017) even projected a complete collapse of
the AMOC 300 years after an abrupt doubling of the atmospheric CO 2 concentration from the 1990 level. However,
Behrens et al. (2013) showed how sensitive model simulations are to small variations in precipitation and the choice of
sea surface salinity restoring to climatological values. From
these small variations they found in their model simulation a
variation of an accelerated AMOC of ~22 Sv to a nearlycollapsed state of ~6 Sv. Swingedouw et al. (2009) showed
with their model experiment that the AMOC response to the
freshwater input is not linear and depends on the mean state
of the climate.
Changes in ocean characteristics and sea ice cover can
have significant influence on the biogeochemical feedbacks
and marine ecosystem (Bates and Mathis 2009; Johannessen
and Miles 2011). The reduction of the sea ice cover allows
for more light to reach and warm the ocean surface, promoting an increase in primary production (Slagstad et al. 2015).
This, in turn, is intrinsically related to an expected increase
CO 2 uptake by the ocean (Bates and Mathis 2009). Still,
some controversy exists with indications that the ocean may
soon enough saturate, and loses its CO 2 uptake capacity (Cai
et al. 2010).
Indeed, fundamental questions on the pathways and time
scales in which the ocean drives and responds to changes in
the coupled system still remain unresolved, hence still
demanding much effort in order to better understand the role
of the northern seas in the context of a changing climate.
Appendix
This article is related to the YOUMARES 8 conference
session no. 9: “The Physics of the Arctic and Subarctic
Oceans in a Changing Climate”. The original Call for
Abstracts and the abstracts of the presentations within this
C. Campos and M. Horn