35
only controlled by atmospheric heating and cooling, but
also largely by heat flux from the underlying ocean. The
oceans are the largest thermal reservoir of the Earth’s climate system (Fig. 7). According to recent estimates,
around 90% of the warming of the Earth’s system over the
last century has been stored in the oceans (e.g., Levitus
et al. 2012; Riser et al. 2016). The biggest share of this
amount is kept trapped in the upper ocean, hence being
potentially available for atmosphere warming and sea ice
melt. Thus, small changes in the pathways and amounts of
heat carried and stored by the ocean currents could have a
significant effect on present and future changes in Arctic
coupled ocean-ice-atmosphere system. For an in-depth
review and speculation on this topic see Carmack et al.
(2015).
Shortwave radiation and sensible heat fluxes are the
sources of net heat input in the upper ocean (Itoh et al. 2011).
Most of the heat input to the upper ocean in summer is given
off in autumn and winter as longwave radiation and turbulent
sensible heat fluxes to the atmosphere cool the open water
and the ice/snow surfaces (e.g., Serreze et al. 2009). Still,
important observations indicated that a surplus of heat is preserved in the ocean during winter, potentially hindering the
seasonal growth of sea ice (e.g., Timmermans 2015).
Another source of heat into the Artic system is the relatively warm AW carried through the main gateways connecting the Arctic Ocean with the Atlantic Ocean: the Fram Strait
and Barents Sea. There is also some exchange with the
Pacific Ocean, but, according to up-to-date estimates
reviewed in Beszczynska-Möller et al. (2012), the net volume and heat fluxes flowing from the Pacific Ocean into the
Arctic through the Bering Strait are small, particularly when
compared to those through Barents Sea (0.8 Sv and 10* to
20* TW, against 2.0 Sv and 50** to 70*** TW, respectively
1
). In fact, the inflow of AW to the Barents Sea accounts
for about half of the northward heat transport to the Arctic
Ocean and the Barents Sea combined (Smedsrud et al. 2013).
Notwithstanding, the heat carried by the AW into the Barents
sea is lost to the atmosphere as latent, sensible, and long
wave radiation (Smedsrud et al. 2010).
Atlantic Water
Recent observations report a warming of the North Atlantic
Ocean resulting in trackable changes in the Arctic Ocean.
Since the 1990’s, temperature and salinity have rapidly
increased from the eastern North Atlantic subpolar gyre
branch to the Fram Strait (Holliday et al. 2008). Furthermore,
during the last decade, a net temperature increase of the
incoming AW in the Fram Strait of 1 °C has been reported
(Schauer et al. 2008; Polyakov et al. 2013). Over the period
from 1997 to 2006, an increase of 1 °C was described for AW
entering the Barents Sea (Beszczynska-Möller et al. 2012).
The warming of the AW is accompanied by estimates of
volume transport increase into the Barents Sea, setting the
so-called “Atlantification” of the basin (Årthun et al. 2012;
Oziel et al. 2016; Smedsrud et al. 2013). Oziel et al. (2016)
suggested that the increased inflow of AW into the Barents
Sea would also cause the enhancement of the outflow of the
dense modified AW mode (also called Barents Sea Water)
into the intermediate layers of the Arctic. The reason to this
is that more warm waters could initiate a sea ice melt-freeze
1 Estimation of heat transport is dependent on a chosen reference temperature. For thorough understanding we refer to Schauer and
Beszczynska-Möller (2009). Here:
* referenced to freezing temperature
** referenced to 0 °C
*** heat flux for closed volume budget
Fig. 7 Stored energy in the Earth climate system (modified from IPCC
2014). Discretisation of energy accumulation change in zeta joules (ZJ)
in each component of the climate system relative to 1971 for periods as
given. Ocean: upper ocean heat change (from surface to 700 m) in light
blue; deep ocean (below 700 m, including below 2000 m estimates
starting from 1992) in dark blue. Ice melt: glaciers and ice caps (light
grey), Greenland and Antarctic ice sheet estimates starting from 1992,
and Arctic sea ice estimate from 1979 to 2008. Land: continental warming (orange). Atmosphere: warming estimate starting from 1979 (purple). Uncertainty in the ocean estimate also dominates the total
uncertainty (dot-dashed lines indicate the uncertainty from all five components at 90% confidence intervals)
The Physical System of the Arctic Ocean and Subarctic Seas in a Changing Climate
only controlled by atmospheric heating and cooling, but
also largely by heat flux from the underlying ocean. The
oceans are the largest thermal reservoir of the Earth’s climate system (Fig. 7). According to recent estimates,
around 90% of the warming of the Earth’s system over the
last century has been stored in the oceans (e.g., Levitus
et al. 2012; Riser et al. 2016). The biggest share of this
amount is kept trapped in the upper ocean, hence being
potentially available for atmosphere warming and sea ice
melt. Thus, small changes in the pathways and amounts of
heat carried and stored by the ocean currents could have a
significant effect on present and future changes in Arctic
coupled ocean-ice-atmosphere system. For an in-depth
review and speculation on this topic see Carmack et al.
(2015).
Shortwave radiation and sensible heat fluxes are the
sources of net heat input in the upper ocean (Itoh et al. 2011).
Most of the heat input to the upper ocean in summer is given
off in autumn and winter as longwave radiation and turbulent
sensible heat fluxes to the atmosphere cool the open water
and the ice/snow surfaces (e.g., Serreze et al. 2009). Still,
important observations indicated that a surplus of heat is preserved in the ocean during winter, potentially hindering the
seasonal growth of sea ice (e.g., Timmermans 2015).
Another source of heat into the Artic system is the relatively warm AW carried through the main gateways connecting the Arctic Ocean with the Atlantic Ocean: the Fram Strait
and Barents Sea. There is also some exchange with the
Pacific Ocean, but, according to up-to-date estimates
reviewed in Beszczynska-Möller et al. (2012), the net volume and heat fluxes flowing from the Pacific Ocean into the
Arctic through the Bering Strait are small, particularly when
compared to those through Barents Sea (0.8 Sv and 10* to
20* TW, against 2.0 Sv and 50** to 70*** TW, respectively
1
). In fact, the inflow of AW to the Barents Sea accounts
for about half of the northward heat transport to the Arctic
Ocean and the Barents Sea combined (Smedsrud et al. 2013).
Notwithstanding, the heat carried by the AW into the Barents
sea is lost to the atmosphere as latent, sensible, and long
wave radiation (Smedsrud et al. 2010).
Atlantic Water
Recent observations report a warming of the North Atlantic
Ocean resulting in trackable changes in the Arctic Ocean.
Since the 1990’s, temperature and salinity have rapidly
increased from the eastern North Atlantic subpolar gyre
branch to the Fram Strait (Holliday et al. 2008). Furthermore,
during the last decade, a net temperature increase of the
incoming AW in the Fram Strait of 1 °C has been reported
(Schauer et al. 2008; Polyakov et al. 2013). Over the period
from 1997 to 2006, an increase of 1 °C was described for AW
entering the Barents Sea (Beszczynska-Möller et al. 2012).
The warming of the AW is accompanied by estimates of
volume transport increase into the Barents Sea, setting the
so-called “Atlantification” of the basin (Årthun et al. 2012;
Oziel et al. 2016; Smedsrud et al. 2013). Oziel et al. (2016)
suggested that the increased inflow of AW into the Barents
Sea would also cause the enhancement of the outflow of the
dense modified AW mode (also called Barents Sea Water)
into the intermediate layers of the Arctic. The reason to this
is that more warm waters could initiate a sea ice melt-freeze
1 Estimation of heat transport is dependent on a chosen reference temperature. For thorough understanding we refer to Schauer and
Beszczynska-Möller (2009). Here:
* referenced to freezing temperature
** referenced to 0 °C
*** heat flux for closed volume budget
Fig. 7 Stored energy in the Earth climate system (modified from IPCC
2014). Discretisation of energy accumulation change in zeta joules (ZJ)
in each component of the climate system relative to 1971 for periods as
given. Ocean: upper ocean heat change (from surface to 700 m) in light
blue; deep ocean (below 700 m, including below 2000 m estimates
starting from 1992) in dark blue. Ice melt: glaciers and ice caps (light
grey), Greenland and Antarctic ice sheet estimates starting from 1992,
and Arctic sea ice estimate from 1979 to 2008. Land: continental warming (orange). Atmosphere: warming estimate starting from 1979 (purple). Uncertainty in the ocean estimate also dominates the total
uncertainty (dot-dashed lines indicate the uncertainty from all five components at 90% confidence intervals)
The Physical System of the Arctic Ocean and Subarctic Seas in a Changing Climate