Open Water In Areas Around North Pole
22
June, 2013
In
some areas around the North Pole, thickness of the sea ice has
declined to virtually zero, i.e. open water.
What
could have caused this open water? Let's go through some of the
background.
North Hemisphere snow cover has been low for some time. Snow cover in May 2013 was the lowest on record for Eurasia. There now is very little snow left, as shown on the image right, adapted from the National Ice Center.
North Hemisphere snow cover has been low for some time. Snow cover in May 2013 was the lowest on record for Eurasia. There now is very little snow left, as shown on the image right, adapted from the National Ice Center.
Low snow cover is causing more sunlight to be absorbed, rather than reflected back into space. As can be expected, there now are high surface temperatures in many areas, as illustrated by the NOAA image below. Anomalies can be very high in specific cases. Zyryanka, Siberia, recently recorded a high of 37.4 C, against normal high temperatures of 20 C to 21 C for this time of year. Heat wave conditions were also recorded in Alaska recently (satellite image of Alaska below).
|
NASA
image June
17, 2013, credit: NASA/Jeff Schmaltz, LANCE MODIS Rapid Response
Team, NASA GSFC - from caption by Adam Voiland: "Talkeetna,
a town about 100 miles north of Anchorage, saw temperatures reach
96°F (36°C) on June 17. Other towns in southern Alaska set
all-time record highs, including Cordova, Valez, and Seward. The
high temperatures also helped fuel wildfires and hastened the
breakup of sea ice in the Chukchi Sea." |
Accordingly,
a large amount of relatively warm water from rivers has flowed into
the Arctic Ocean, in addition to warm water from the Atlantic and
Pacific Oceans.
Sea
surface temperatures have been anomalously high in many places around
the edges of the sea ice, as also shown on the NOAA
image below.
Nonetheless,
as the above images also make clear, sea surface temperatures closer
to the North Pole have until now remained at or below zero degrees
Celsius, with sea ice cover appearing to remain in place. The webcam
below from the North
Pole Environmental Observatory shows
that there still is a lot of ice, at least in some parts around the
North Pole.
Webcam
#2 of the North
Pole Environmental Observatory monitoring
UPMC's Atmospheric Buoy, June 21, 2013
|
So,
what could have caused the sea ice to experience such a dramatic
thickness decline in some areas close to the North Pole?
Firstly, as discussed in earlier posts, there has been strong cyclonic activity over the Arctic Ocean (see also Arctic Sea Ice blog post). This has made the sea ice more prone and vulnerable to the rapid decline that is now taking place in many areas.
Furthermore, Arctic sea ice thickness is very low, as illustrated by the image below.
Firstly, as discussed in earlier posts, there has been strong cyclonic activity over the Arctic Ocean (see also Arctic Sea Ice blog post). This has made the sea ice more prone and vulnerable to the rapid decline that is now taking place in many areas.
Furthermore, Arctic sea ice thickness is very low, as illustrated by the image below.
|
Finally,
there has been a lot of sunshine at the North Pole. At this time
of year, insolation in the Arctic is at its highest. Solstice (June
20 or June 21, 2013, depending on time zone) is the day when the
Arctic receives the most hours of sunlight, as Earth reaches its
maximum axial
tilt toward
the sun of
23° 26'. In fact, insolation during the months June and July is
higher in the Arctic than anywhere else on Earth, as shown on the
image below.
Monthly
insolation for selected latitudes - adapted from Pidwirny,
M. (2006),
in "Earth-Sun Relationships and Insolation",
Fundamentals
of Physical Geography, 2nd Edition.
|
In
conclusion, the current rapid sea ice thickness decline close to the
North Pole is mostly due to a combination of earlier cyclonic
activity and lots of sunlight, while the sea ice was already very
thin to start with. The cyclone broke up the sea ice at the center of
the Arctic Ocean, which is turn made it more prone to melting
rapidly. The cyclone did more though, as Veli
Albert Kallio,
contributor to the Arctic-news blog explains:
"The ocean surface freezes if the temperature falls below -2.5C. The reason for the negative melting point is the presence of 4-5% of sea salt. Only in the polar regions the sea surface cools sufficiently for the sea ice to form during winters.
The sea ice cover is currently thinning near the North Pole between 80-90 degrees north. This part of the ocean is very deep. It receives the heat of the Gulf Stream from the south: as the warm water vapourises, its salt content to water increases. This densifies the Gulf Stream which then falls onto the sea floor where it dissipates its heat to the overlying water column. The deep basin of the Arctic Ocean is now getting sufficiently warmed for the thin sea ice cover to thin on top of it. The transportation of heat to the icy surface is combined with the winds that push cold surface water down while rising heat to surface."
Indeed,
vertical mixing of the water column was enhanced due to cyclonic
activity, and this occurred especially in the parts of the Arctic
Ocean that also are the deepest, as illustrated by the animation
below.
Legend
right: Ice thickness in m from Naval
Research Laboratory
Legend bottom: Sea depth (blue) and land height (brown/green) in m from NIBCAO Arctic map at NOAA |
The
compilation of images below shows how the decline of sea ice has
taken place in a matter of weeks.
|
This
spells bad news for the future. It confirms earlier analyses (see
links below) that the sea ice will disappear altogether within
years. It shows that the sea ice is capable of breaking up abruptly,
not only at the outer edges, but also at the center of the Arctic
Ocean. As the Arctic sea ice keeps declining in thickness, it does
indeed look set to break up and disappear abruptly across most of the
Arctic Ocean within a few years. Models that are based on sea ice
merely shrinking slowly from the outer edges inward should reconsider
their projections accordingly.
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