Thursday, 16 October 2014

The Fast Transition

The peripheral seas of the Arctic Ocean are now virtually ice free in September, they are seasonal sea ice seas.

Need I say more?

It seems I do...

In comments Oale wanted to see this in terms of area, which is fair enough. I've done two graphs, one for area one for extent, both with a plot as percentage of April area and extent.


Oale said...

yes, what's the maximum 100% level of this?

Chris Reynolds said...

Hi Oale,

I'm confused. The vertical axis is in km^3. What do you mean by 100%?

I now realise I incorrectly put thousand km^3 - doh!

Chris Reynolds said...

Corrected the scale legend.

Oale said...

ah yes, that's not an accurate expression. there might be several levels of 100%. 1.the total area of the peripheral seas 2. the maximum area covered by sea ice in winter on these seas or 3. the sum of the maximum area in each sea during september, which is closest to what I guess I meant...

Chris Reynolds said...


Looking at regional area and extent the peak area in April for each sea is near 100%. However, obviously, the summer sea ice area or extent may be a better indicator as it is what most people are used to from the literature w.r.t. a virtually ice free state.

I'll add a graph of Extent and percentage of April Extent for September average for the same region.

iceman said...

The contrast between the peripheral and central Arctic is quite striking. I suppose it's too simplistic to say that positive feedbacks caused the fast transition in the regions shown here, while negative feedbacks have reasserted dominance of the Central Arctic Basin in the past two years. The latter wouldn't adequately explain the relatively slow volume regrowth during the last freeze season, bracketed by two summers of slow volume loss (relative to recent years).

Chris Reynolds said...

Hi Iceman,

I've previously posted on what caused the volume loss in PIOMAS. See here.

That's based on Lindsay & Zhang 2004, who find that the volume loss was driven by the ice/ocean albedo feedback.

Some explanatory detail is needed: Whilst it may seem strange to point to ice/ocean albedo feedback for a volume loss that has mainly been in the Central Arctic, the ice in the Central Arctic is continually depleted by export out through Fram and into the Beaufort Gyre. So summer losses in the peripheral seas impact by reducing the inflow of older MYI cycled through Beaufort Gyre and returned via the transpolar drift back into the Central Arctic. As indicated in this image.

Because the ice/ocean albedo has caused the loss of volume, as an amplifier to anthropogenic global warming, It should come as no surprise that the peripheral seas have seen the fastest decline towards a virtually ice free state. The Central Arctic still holds a significant amount of MYI (even more this autumn!), and is to a significant degree sheltered from recession of the ice edge by the presence of ice through spring and into June/July in the peripheral seas. So on two counts there is reason to expect the ice/ocean albedo effect to have less of an impact in the Central Arctic. However as spring/summer recession of the ice edge in the peripheral seas becomes earlier that feedback should get a better chance to work on the Central Arctic (as in 2012).

Compared to other recent years, especially 2012 last year's volume increase in autumn was fairly slow because there was more September ice cover than in minimum years like 2007, 2011 or 2012. The same will happen this year. The ice cover insulates heat loss from the ocean slowing ice thickening (as compared to ice growth over open water).