Poor melt weather in the summers 2013 and 2014 has led to an increase in ice survival over the summer and a sea ice volume pulse has entered the Arctic Ocean sea ice system, bucking the trend of years of decline. Looking at things on a regional basis this pulse can clearly be seen in the Central Arctic. Note that the Central Arctic (black) is on a much larger scale than the other regions.
This volume pulse persists into January 2016 but is slightly down on January 2015. How did this happen?
Using volume data for the entire PIOMAS model domain I have worked out the difference for each month from January 2014 to January 2016 from the volume 12 months earlier. The result is shown below (blue trace). The red bars (right hand scale) are for the difference from the August 2015 difference from 12 months earlier.
The 12 month difference in volume (blue) crashed in August 2015 going strongly negative and remaining fairly level afterwards. The cause of this was discussed last year. That post uses extent, but here is an annotated graph of Sector Extent from that post, sectors are given here.
The above plot is for anomalies, difference from the long term seasonal cycle, so as it goes negative losses are greater than average. Losses are seen to be far greater than average during the period of an Arctic Dipole last July, after which the rate of loss relaxes but continues to be a state of greater losses than average. It was this Arctic Dipole and the following losses due to preconditioning during the Arctic Dipole event that led to a loss of volume that then persisted through the following autumn and winter.
The overall volume loss between January 2015 and January 2016 was 1.26k km^3, to what degree can this be attributed to the exceptionally warm weather last month? That weather was discussed in the previous post. The blue line in the above plot suggests that a lot of the decline in volume over the last 12 months has persisted since then relatively unchanged.
As discussed previously the low extent is seen in the Atlantic Sector, this is also seen in the Atlantic Sector as a 37% contribution to the drop between January 2015 and January 2016. However there has also been a drop in the Arctic Ocean Basin of 67% of the total.
So what of breaking down the situation in the Arctic Ocean Basin? The following graphic shows the relative roles in establishing the 67% of the total drop in volume since last January.
Kara borders Barents (which is part of the Atlantic Sector), and appears to suffer from the same wind-driven warm influx that has hammered the Atlantic Sector this January. However despite the overall warmth north of 70degN this January Chukchi, the East Siberian Sea and Laptev all along the Siberian coast show increased volume compared with last January.
Of course when I say warm I mean relatively speaking, it is still well below zero over the vast majority of the pack.
Now I will change the baseline from last January to January 2013, the January following the record volume and extent minimum of 2012.
Now the Arctic Ocean Basin is seen to account for almost all of the volume increase since January 2013 and the record lows following 2012.This pattern has, if anything intensified this January.
And narrowing in to the Arctic Ocean Basin's regions most of the Arctic Ocean Basin's volume increase is seen to be within the Central Arctic.
In January 2015 the volume increase in the Central Arctic was 70% of the total increase over January 2013, by this year the Central Arctic accounts for all of the volume increase.
|Jan 2015 - 2013
|Jan 2016 - 2013
However the overall volume difference from Jan 2015 to 2013 has decreased by half when comparing this January to 2013.
Having still not found the time to rejig my code to do difference plots. Here is a blink comparison between January 2013 and January 2016 PIOMAS grid box effective thickness.
Ice is generally thicker but the region north of Greenland and the Canadian Arctic Archipelago is seen to have much thicker ice which holds a substantial amount of the increased volume.
Qualitative confirmation is seen in ASCAT, which shows older ice as whiter than the grey of first year sea ice. The images shown are for 21 February.
There is clearly still more older ice in the Arctic Ocean than was left following the crash of 2016.
Back in 2014 I noted that April volume seemed to have hit a floor, a floor dictated by the preponderance of first year ice. I developed the idea and posted recapping my work last May.
This year in April volume will be well above 19.3k km^3 for the second year, it will be at least another year before we see the floor implied by an average thickness of 2m re-emerge.