PIOMAS ice volume anomaly q

Q: I've got a question that you may be able to answer with your sea ice hat on.

Why is it that the minimum volume anomaly of ice appears in mid summer and not in September when the minimum volume happens? See piomas.
(From Alastair)

A: I'm hard-pressed to tell what season the anomaly extremes are occurring from this graph, but can say that your reading isn't surprising to me.  At the seasonal minimum of ice volume, you're at the minimum -- so it is relatively difficult to get even lower.  Late winter, towards the maximum doesn't have that problem -- since it's maximum, there's lots of room to go lower.  But the Arctic is cold in winter, so it's going to pile up a lot of additional mass (from the prior minimum) pretty consistently.  The place/time that there's the most room for decreasing the ice volume is a time of year when the ice volume hasn't already declined a lot, but it is melting rapidly -- early- to mid- summer.

As you also see from the figure, the main trend is the year-round decline.  For your question, we're looking at the timing of largest excursions below the line. 

The converse question, for largest excursions above the trend, is that I'd expect those in late fall - early winter, during the freeze-up season.  Then, there isn't much volume, and it's freezing fast.  A couple weeks earlier start to freeze-up makes a comparatively large difference.