Arctic Sea Ice Extent, Area, and Volume

[bluewave]

Extent very close to last year at this time.

 

[Typhoon Tip]

Climate Reanalyzer "looks" like the curve is about to do a cliff dive during these 4-weeks heading into the climo nadir. That's one data source - no claim as to its accuracy or how well it jives with what others use. 

If the former is clad, it will be interesting to see if that dive happens and the curve catches up enough to be in the top 5 lowest.   

The AO index is supposed to be modestly negative, which is somewhat of a warm signal up there. 

[GaWx]

 The Arctic sea ice area has fallen back to near the 2013-24 mean:

 

 Perhaps this is partially related to the temps at 80+N finally rising to NN recently:

[bluewave]

This season is more conformation that the a long term regime shift occurred back in 2007. Thickness dramatically fell as the older sea ice melted.

A June and July pattern like this season with deep low pressure north of Alaska before 2005-2007 would have resulted in a September minimum in the 6 to 8 million sq km range.

But since the thickness was so low where the big Pacific side melt recently occurred, the area couldn’t hold the extent gains like it would have back in the colder climate era with thick multiyear ice more resistant to higher pressure and warmer recent conditions.

 

https://www.nature.com/articles/s41586-022-05686-x

Regime shift in Arctic Ocean sea ice thickness

Manifestations of climate change are often shown as gradual changes in physical or biogeochemical properties¹. Components of the climate system, however, can show stepwise shifts from one regime to another, as a nonlinear response of the system to a changing forcing². Here we show that the Arctic sea ice regime shifted in 2007 from thicker and deformed to thinner and more uniform ice cover. Continuous sea ice monitoring in the Fram Strait over the last three decades revealed the shift. After the shift, the fraction of thick and deformed ice dropped by half and has not recovered to date. The timing of the shift was preceded by a two-step reduction in residence time of sea ice in the Arctic Basin, initiated first in 2005 and followed by 2007. We demonstrate that a simple model describing the stochastic process of dynamic sea ice thickening explains the observed ice thickness changes as a result of the reduced residence time. Our study highlights the long-lasting impact of climate change on the Arctic sea ice through reduced residence time and its connection to the coupled ocean–sea ice processes in the adjacent marginal seas and shelves of the Arctic Ocean

 

The relationship between sea ice residence time in the Arctic Ocean and ice thickness distribution highlights the importance of coupled ocean–sea ice processes in the Alaskan and Siberian sectors of the Arctic (areas A and B in Fig. 3b). Several interrelated factors have become more prominent in the late twentieth century and have contributed to preconditioning the ocean–sea ice system before the stepwise changes in the ice formation areas: Arctic-wide rise of surface air temperature³⁵, thinning of sea ice³⁶, decrease of sea ice albedo³⁷ concurrent with a reduction of multi-year sea ice³⁸, increase of ocean heat flux through the Bering Strait³⁹ and increase of the upper ocean heat content⁴⁰. September sea ice concentration in the Siberian sector dropped below 40% in 2005 and the dramatic Arctic summer sea ice extent minimum occurred in 2007 (ref. ⁴¹). This series of events initiated intensive and widespread ice–albedo feedback in the Alaskan and Siberian sectors in the summer^42,43, which resulted in a perennial increase of ocean heat content in areas of ice formation (Extended Data Fig. 1). After 2007, suppression of winter ice growth due to the accumulated ocean heat became conspicuous⁴⁴ and the resultant thinner ice pack became more vulnerable to summer melt in the following year. Prolongation of the summer melt season promoted further ice–albedo feedback⁴⁵ and has increased oceanic heat absorption in the summer⁷. Thus, summer ice extent and thickness in areas of ice formation has not recovered to the state before 2007 (Fig. 4c). In addition, continuing weakening of the cold halocline in the Siberian sector also influenced the upper ocean heat content⁴⁶ and possibly slowed down ice growth offshore of the Laptev Sea in recent years¹⁷.

Our analysis demonstrates the long-lasting impact of climate change on Arctic sea ice through reduced residence time, suggesting an irreversible response of Arctic sea ice thickness connected to an increase of ocean heat content in areas of ice formation. The large reduction of summer ice extent in the Alaskan and Siberian sectors in 2005 and 2007 triggered intensive ice–albedo feedback^42,45 and initiated the perennial increase of ocean heat content in these areas⁴⁴. This resulted in the stepwise reduction of residence time of sea ice in the Siberian sector of the Arctic, and hence a nonlinear response of the system. Before the shift, sea ice formed in and offshore of the Siberian shelves overwintered (spent about 15 months) in this area before entering the TPD (Extended Data Fig. 2), during which the ice thickened and increased its deformed fraction. After the shift, ice stayed in this area only about 6 months on average (Extended Data Fig. 2), resulting in recruitment of newly formed younger ice into the TPD and more sea ice formation during TPD transit to the Fram Strait²⁶. The younger ice is thin, weakly linked and features ridges with more shallow keels; hence, it is more prone to wind forcing pushing the ice towards the Atlantic sector of the Arctic^28,47. This process accelerated the TPD from 2007 onwards (Fig. 4d), while enhanced wind forcing after 2007 may also have contributed to the acceleration of the TPD (Extended Data Fig. 7). Because of the shorter residence time, the part of the ice that has thermodynamically grown is thinner¹⁷ (reduction of modal thickness in Fig. 1b) and the relative amount of the deformed fraction of ice has decreased (Figs. 1band 2).

Impacts of this regime shift in Arctic sea ice on the pan-Arctic environment are extensive and require further investigation. Thinner and less deformed sea ice causes reduced momentum exchange between ice and ocean, contributing to reduced mixing in the upper ocean underneath areas that are fully covered with ice. This may affect entrainment of heat and nutrients from subsurface to surface ocean with a potential consequence on the biogeochemical cycles involving higher trophic levels. By contrast, however, sea ice retreat in marginal ice zones and continuing weakening of the cold halocline in the Atlantic sector allows for more turbulent mixing and winter convection in the upper ocean⁴⁶. These counteracting effects can influence the regional contrasts of the ocean environment between fully ice-covered areas and marginal ice zones in the Arctic. In addition, habitat conditions of younger, level sea ice are different from those in older multi-year ice and might affect the sympagic (ice-associated) communities and their diversity^48,49. Ridged sea ice supports higher biomass⁴⁸ and represents safe havens for organisms to hide from predators⁵⁰. The amount of ridges and deformed ice has also consequences for human activity. Thinner, more level ice is less challenging for ship navigation than in thicker, deformed ice and, along with less ice/shorter ice seasons in general, may allow for an increase in Arctic maritime traffic. Finally, interdisciplinary studies in the Atlantic sector of the Arctic and downstream of the Fram Strait outflow are needed to shed light on the consequences of the described sea ice regime shift and its impacts on physical and biogeochemical processes.

 

 

 

 

Zack Labe

 

 @zacklabe.com

· 3d

It's time! Join me in tracking this year's #Arctic sea ice minimum! A new record is unlikely again this year. Sea ice melt substantially slows every September as solar energy decreases and temperatures drop in the far north. Follow along with the data at zacklabe.com/arctic-sea-i...

 

ALT