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Thinning sea ice has rapidly accelerated Arctic ocean currents and mixing speeding up the normal processes of export of sea ice from the Arctic to the North Atlantic and the import of warm, salty Atlantic ocean water into the Arctic.

Warm salty water enters the Arctic from the eastern north Atlantic (at 100m depth) moving towards Siberia then flowing parallel to the Siberian continental shelf towards Alaska.
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By FishOutofWater

Warm, salty Atlantic ocean water normally enters the Arctic to replace water that flows out of the Arctic through the Fram Strait along the east coast of Greenland. However, that normal process has greatly accelerated this fall allowing Atlantic Ocean water to penetrate much further into the Arctic Ocean than normal.

Salinity anomalies show the strongly enhanced transport of Atlantic water into the Arctic along the Siberian continental shelf and Arctic Ocean water into the Atlantic along the east coasts of Greenland and Canada.
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By FishOutofWater

Open water in formerly ice covered ocean is changing the Arctic weather in the fall. The open water acted on by winds, speeding up currents. Moreover the heating caused by the open water is generating stronger southerly winds off of Siberia in the fall are speeding up the rate of flow of Atlantic water towards Alaska.

Two papers just published reveal 2 additional processes that are speeding up currents and mixing in the Arctic. Both of these processes are accelerating the loss of summer sea ice, strongly affecting Arctic ecosystems. First, the loss of summer sea ice is allowing larger waves to form in the Arctic Ocean. These waves are increasing mixing of fresh surface waters that originate from rivers flowing into the Arctic with saltier water of Atlantic or Pacific origin.


Figure 2(a) Daily (gray) and 30-day running-mean (black) NCEP wind speed at the SBI3 mooring site. Red arrows indicate storms, defined as periods when daily wind speed exceeds 10 m s−1. (b) Magnitude of the inertial currents at SBI3 as a function of depth and time, in m s−1. Black contours indicate vertical shear >10−2 s−1. (c) Time series of the east component of the SBI3 inertial current at 10-m depth. (d) Time-series of inertial shear magnitude, calculated between 10 and 30 m and smoothed over 3 days, from ADCP data from SBI3 (black) and SBI4 (gray). Mean shear from the 1994 SIMI ice camp [Halle and Pinkel, 2003] is indicated by thin red bars. Thick black bars at the top of Figures 2b, 2c, and 2d indicate the presence of sea ice as derived from the ADCP data. White arrows are discussed in the text.

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By FishOutofWater

The authors note that there is still a large amount of uncertainty in understanding the dynamics of the circulation of the Arctic Ocean. Given that caveat, they suggest that it is probable that strongly increased mixing will change the transport of water across the Arctic ocean affecting northern hemisphere ocean currents and climate. Geophysical Research Letters (firewalled)

It is still unclear what dynamics force the pan-Arctic circulation of Atlantic Water. Zhang and Steele [2007] found that, by changing mixing parameterizations in their coupled ice-ocean model from mid-latitude values to the weak values assumed for the Arctic Ocean, they could reverse the direction of Atlantic Water flow in the western Arctic (weaker mixing resulted in more cyclonic circulation). Moreover, there is increasing evidence that the double diffusive structures that are so ubiquitous to the Arctic [Carmack et al., 1997] may be an integral part of mid-depth exchange between the Arctic Ocean boundary currents and the interior [McLaughlin et al., 2009]. The velocity of these structures is 2 orders of magnitude less than the IWs (ed. note - Internal Wave) we observe, and thus any significant wind-generated IW activity is likely to become a dominant mixing mechanism in the Arctic. It seems probable that a dramatic increase in mixing could fundamentally change pan-Arctic water transport and water mass transformations. This in turn would influence the Arctic's climate connections with the world ocean.
...
We are perhaps about to experience a one-off experiment, the wind-driven spin-up of the Arctic Ocean.

The second paperJGR Oceans (firewalled) shows that ocean currents and sea ice transport rapidly sped up from 1979 to 2004, but that neither weather nor climate change were the direct causes. The authors observe that currents increased strongly in the fall in areas where the ocean had partial sea ice cover. This is a possible example of an unanticipated feedback loop indirectly caused by global warming.

The speed of sea ice motion greatly increased increased from 1979 to 2004.
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By FishOutofWater

The authors propose that the ice velocity increased in response to ice thinning and the increase in open ocean area. Wind velocities were similar in the periods 1979-1986 and 1997-2004, but the speed of ice movement was much faster. Changes in winds and weather cannot explain the faster moving ice.

In this study, we examined the seasonal and interannual to decadal variability of the downwelling in the interior Beaufort Sea. The downwelling reaches its seasonal maximum in the fall and minimum in the summer. The seasonal variability is forced by the appearance of a high SLP center from the fall to spring. The wind stress and ice velocity are both anticyclonic from fall to spring. They force an offshore Ekman transport (ed. link explains Ekman transport) away from the Alaskan and Canadian coasts. The transport converges in the Beaufort Sea, and results in a downwelling in all seasons. The downwelling in the Beaufort Sea varied significantly on the interannual to decadal time scales. The variation, however, was not correlated significantly with the Arctic Oscillation index. We performed three additional experiments and were able to identify that the change of sea ice velocity was mainly responsible for the variability of the downwelling. It was interesting to note that the ice velocity accelerated in the 28 year period. The acceleration was not driven solely by the wind stress. The geostrophic wind condition was actually similar between 1979–1986 and 1997–2004. But the ice velocity was much greater in the latter period. We hypothesize that the change of ice dynamics (thinner and less areal coverage) was responsible for the change of ice velocity.

The weather patterns that have been causing the cold spell in the eastern United states and western Europe are enhancing the flow of warm salty water originating in the Gulf stream towards Greenland and Norway. The Gulf Stream is north of  normal.

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By FishOutofWater

Weather, ocean currents and climate are changing in the north Atlantic and Arctic oceans as the speed of global warming accelerates. Positive feedbacks caused by thinning sea ice, open ocean water, warming water and atmospheric warming are rapidly removing sea ice from the Arctic.

Originally posted to FishOutofWater on Wed Dec 30, 2009 at 08:01 PM PST.

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