34
Sea and the Labrador Sea (Bamber et al. 2012). This
increased freshwater flux is mainly attributed to increased
ice discharge from accelerated outlet glaciers in south
Greenland (van den Broeke et al. 2009), which might be triggered by the warming of the waters at the glacier ice-ocean
interface resulting in increased basal melting (e.g., Holland
et al. 2008). Although the freshwater flux is highest in the
South, there are also indications in the Northeast of Greenland
that warm waters get close to the outlet glaciers and may
initiate increasing glacier retreat and associated freshwater
fluxes to the ocean (e.g., 79 North Glacier, Schaffer et al.
2017). Also the ice mass loss of glaciers in the Canadian
Arctic Archipelago has sharply increased in recent years and
almost tripled between 2004 and 2009 (Gardner et al. 2011;
Lenaerts et al. 2013).
Oceanic Transport of Sea Ice and Liquid
Fresh water
About 2500 km
3
year
−1
of liquid fresh water (relative to a
salinity of 34.8) enter the Arctic Ocean through the Bering
Strait, while 3200 km
3
year
−1
and 2800 km
3
year
−1
exit the
Arctic via the Canadian Arctic Archipelago and Fram Strait,
respectively (Serreze et al. 2006; Haine et al. 2015). There
are only small amounts of sea ice transported through the
Bering Strait (140 km
3
year
−1
) and the Canadian Arctic
Archipelago (160 km
3
year
−1
), whereas large amounts of sea
ice are exported through Fram Strait (1900 km
3
year
−1
solid
freshwater transport) (Serreze et al. 2006; Haine et al. 2015).
Observations presented by Woodgate et al. (2012) showed
a slight increase in Bering Strait freshwater flux since 2001
due to increased volume fluxes, which can be explained by
changes in the Pacific-Arctic pressure head and local winds.
Although the liquid freshwater outflow through the Canadian
Arctic Archipelago and the Fram Strait show large interannual variability, there is no significant long-term trend since
the beginning of record (Haine et al. 2015). However, a new
data record of Fram Strait sea ice area export, which was
developed from satellite radar images and surface pressure
observations across Fram Strait by Smedsrud et al. (2017),
reveals a positive trend of about 5.9% per decade from 1979
to 2014. Ionita et al. (2016) related changes in the simulated
Fram Strait sea ice export to atmospheric blocking events
over Greenland, which block the winds over the Strait that
mainly drive the sea ice transport. These Greenland blocking
events are proposed to happen more frequently in recent
years due to climate change (e.g., Hanna et al. 2016).
The freshwater export through the various channels of the
Canadian Arctic Archipelago varies mainly due to volume
flux anomalies governed by variations in the large-scale
atmospheric circulation (Jahn et al. 2010a, b; Peterson et al.
2012) or driven by the sea surface height gradient across the
strait (e.g., McGeehan and Maslowski 2012; Wekerle et al.
2013). Proshutinsky and Johnson (1997) identified two
wind-driven circulation regimes in the Arctic Ocean that
either accumulate fresh water in the western Arctic Ocean
(anticyclonic) or releases it to the North Atlantic (cyclonic).
During anticyclonic circulation regimes, fresh water accumulates in the Beaufort Gyre north of the Canadian Arctic
Archipelago due to a wind-driven spin-up as a response to
anomalously high sea level pressure over the Arctic (low AO/
NAO). During cyclonic regimes (high AO/NAO), the
Beaufort Gyre slows down due to cyclonic winds and
releases the accumulated fresh water (Proshutinsky et al.
2002; Giles et al. 2012). This fresh water mainly exits the
Arctic via the Canadian Arctic Archipelago and partly via the
Fram Strait. A tracer study by Jahn et al. (2010a) showed that
the main sources of the freshwater export through the
Canadian Arctic Archipelago is PW and North American
runoff. Although the Arctic Ocean’s circulation alternated
between the cyclonic and anticyclonic pattern at 5–7 yearintervals in the past, it has remained in an anticyclonic mode
for 17 years since 1997 (Proshutinsky et al. 2015).
Proshutinsky et al. (2015) speculated that freshwater fluxes
from the Greenland Ice Sheet to the North Atlantic interrupted an ocean-atmosphere feedback loop that previously
lead to an automatic decadal alternation between cyclonic
and anti-cyclonic circulation regimes (“auto-oscillatory
system”).
The variability of liquid freshwater export through Fram
Strait is driven by both, variations in the volume flux and
changes in the salinity of the advected waters (e.g., Jahn
et al. 2010b). The salinity of the waters exported through
Fram Strait depends of the source water, which is mainly
Eurasian runoff or PW (Jahn et al. 2010a). During years of
an anticyclonic circulation anomaly (low AO) Eurasian runoff is released from the Eurasian Shelf (Jahn et al. 2010a)
and directed towards Fram Strait by a strong Transpolar Drift
(Morison et al. 2012). During a cyclonic circulation regime
(high AO) the Eurasian runoff is kept by a cyclonic circulation in the Eurasian basin (Morison et al. 2012) and PW that
is released from the Beaufort Gyre flows along the northern
shelf of Greenland and penetrates into Fram Strait (Jahn
et al. 2010a). In agreement with this, Karcher et al. (2012)
found, from iodine-129 observations and modeling, changing contributions of AW and PW in the Fram Strait outflow
to result from changes in the Arctic Ocean circulation as a
response to the large-scale atmospheric circulation.
Heat and Volume Fluxes in the Arctic Ocean
It is by now evident that changes in any of the components
of the Earth system play a role in determining climate
responses over high latitudes and consequent teleconnections. Therefore, it is expected that the interannual variability and recent decline trend of sea ice cover are not
C. Campos and M. Horn
Sea and the Labrador Sea (Bamber et al. 2012). This
increased freshwater flux is mainly attributed to increased
ice discharge from accelerated outlet glaciers in south
Greenland (van den Broeke et al. 2009), which might be triggered by the warming of the waters at the glacier ice-ocean
interface resulting in increased basal melting (e.g., Holland
et al. 2008). Although the freshwater flux is highest in the
South, there are also indications in the Northeast of Greenland
that warm waters get close to the outlet glaciers and may
initiate increasing glacier retreat and associated freshwater
fluxes to the ocean (e.g., 79 North Glacier, Schaffer et al.
2017). Also the ice mass loss of glaciers in the Canadian
Arctic Archipelago has sharply increased in recent years and
almost tripled between 2004 and 2009 (Gardner et al. 2011;
Lenaerts et al. 2013).
Oceanic Transport of Sea Ice and Liquid
Fresh water
About 2500 km
3
year
−1
of liquid fresh water (relative to a
salinity of 34.8) enter the Arctic Ocean through the Bering
Strait, while 3200 km
3
year
−1
and 2800 km
3
year
−1
exit the
Arctic via the Canadian Arctic Archipelago and Fram Strait,
respectively (Serreze et al. 2006; Haine et al. 2015). There
are only small amounts of sea ice transported through the
Bering Strait (140 km
3
year
−1
) and the Canadian Arctic
Archipelago (160 km
3
year
−1
), whereas large amounts of sea
ice are exported through Fram Strait (1900 km
3
year
−1
solid
freshwater transport) (Serreze et al. 2006; Haine et al. 2015).
Observations presented by Woodgate et al. (2012) showed
a slight increase in Bering Strait freshwater flux since 2001
due to increased volume fluxes, which can be explained by
changes in the Pacific-Arctic pressure head and local winds.
Although the liquid freshwater outflow through the Canadian
Arctic Archipelago and the Fram Strait show large interannual variability, there is no significant long-term trend since
the beginning of record (Haine et al. 2015). However, a new
data record of Fram Strait sea ice area export, which was
developed from satellite radar images and surface pressure
observations across Fram Strait by Smedsrud et al. (2017),
reveals a positive trend of about 5.9% per decade from 1979
to 2014. Ionita et al. (2016) related changes in the simulated
Fram Strait sea ice export to atmospheric blocking events
over Greenland, which block the winds over the Strait that
mainly drive the sea ice transport. These Greenland blocking
events are proposed to happen more frequently in recent
years due to climate change (e.g., Hanna et al. 2016).
The freshwater export through the various channels of the
Canadian Arctic Archipelago varies mainly due to volume
flux anomalies governed by variations in the large-scale
atmospheric circulation (Jahn et al. 2010a, b; Peterson et al.
2012) or driven by the sea surface height gradient across the
strait (e.g., McGeehan and Maslowski 2012; Wekerle et al.
2013). Proshutinsky and Johnson (1997) identified two
wind-driven circulation regimes in the Arctic Ocean that
either accumulate fresh water in the western Arctic Ocean
(anticyclonic) or releases it to the North Atlantic (cyclonic).
During anticyclonic circulation regimes, fresh water accumulates in the Beaufort Gyre north of the Canadian Arctic
Archipelago due to a wind-driven spin-up as a response to
anomalously high sea level pressure over the Arctic (low AO/
NAO). During cyclonic regimes (high AO/NAO), the
Beaufort Gyre slows down due to cyclonic winds and
releases the accumulated fresh water (Proshutinsky et al.
2002; Giles et al. 2012). This fresh water mainly exits the
Arctic via the Canadian Arctic Archipelago and partly via the
Fram Strait. A tracer study by Jahn et al. (2010a) showed that
the main sources of the freshwater export through the
Canadian Arctic Archipelago is PW and North American
runoff. Although the Arctic Ocean’s circulation alternated
between the cyclonic and anticyclonic pattern at 5–7 yearintervals in the past, it has remained in an anticyclonic mode
for 17 years since 1997 (Proshutinsky et al. 2015).
Proshutinsky et al. (2015) speculated that freshwater fluxes
from the Greenland Ice Sheet to the North Atlantic interrupted an ocean-atmosphere feedback loop that previously
lead to an automatic decadal alternation between cyclonic
and anti-cyclonic circulation regimes (“auto-oscillatory
system”).
The variability of liquid freshwater export through Fram
Strait is driven by both, variations in the volume flux and
changes in the salinity of the advected waters (e.g., Jahn
et al. 2010b). The salinity of the waters exported through
Fram Strait depends of the source water, which is mainly
Eurasian runoff or PW (Jahn et al. 2010a). During years of
an anticyclonic circulation anomaly (low AO) Eurasian runoff is released from the Eurasian Shelf (Jahn et al. 2010a)
and directed towards Fram Strait by a strong Transpolar Drift
(Morison et al. 2012). During a cyclonic circulation regime
(high AO) the Eurasian runoff is kept by a cyclonic circulation in the Eurasian basin (Morison et al. 2012) and PW that
is released from the Beaufort Gyre flows along the northern
shelf of Greenland and penetrates into Fram Strait (Jahn
et al. 2010a). In agreement with this, Karcher et al. (2012)
found, from iodine-129 observations and modeling, changing contributions of AW and PW in the Fram Strait outflow
to result from changes in the Arctic Ocean circulation as a
response to the large-scale atmospheric circulation.
Heat and Volume Fluxes in the Arctic Ocean
It is by now evident that changes in any of the components
of the Earth system play a role in determining climate
responses over high latitudes and consequent teleconnections. Therefore, it is expected that the interannual variability and recent decline trend of sea ice cover are not
C. Campos and M. Horn