What is striking about that plot (to me at least), is the extreme variability of the series, in this blog post I hazard a guess as to one of the reasons for this.
I've plotted September volume for Laptev, in terms of Gice. Gice is the sub grid thickness distribution within the PIOMAS model, the legend for the different colours in the following graph follow the order in the columns of the graph, those thicknesses are the centre points of bands of thickness used within each grid cell of the PIOMAS model. I usually present plots using 'grid box effective thickness, which is the thickness weighted integral of the volumes at those thickness points. Here I am showing what the PIOMAS models as thickness, calculated across the whole region of the Laptev Sea.
So in past years ice as thick as 16.24 metres is modelled by PIOMAS as having a significant presence, even in late summer.
But back to the issue at hand, why is that plot of PIOMAS thickness, and the plot of extent above, show such variation? The first thing to look at is initial ice state. So I produced the same plot for Laptev Sea ice volume in June and April.
By June the pattern of high volume leading to high September volume appears stronger, but still has occasional years' breaking the pattern. So at this point I will turn attention to the atmosphere.
I have taken a series of September high years and low years. The high years are taken as those years with volume in September exceeding 600 cubic km, the low are more arbitrarily taken as years that are lows given the surrounding few years. In each case those years selected are visible in the list of years on the following plots. Not very scientific, but this is just a blog. Using this set of high volume and low volume years I have plotted average anomaly from the 1981 to 2010 sea level pressure.
High Volume Years.
What this might mean is that the high volume years could be caused in large part by summer weather in which ice is blown towards Siberia (spreading ice towards the coast and keeping extent up) and the winds across the Laptev Sea are cold winds from over the ice pack which reduce volume loss. In contrast, in the low years winds blow from the Siberian coast poleward (compacting ice away from the coast and lowering extent), and the winds across the Laptev Sea are warm summer winds from Siberia which increase volume loss.