Retreating glaciers in the Antarctic and implications for penguins

This time last year Graham and I were lucky enough to have spent about three weeks visiting the Falkland Islands, South Georgia and the Antarctic Peninsula. The scenery is fantastic, and we saw thousands of breeding penguins, lots of seals, whales and sea birds. However, one of the most significant observations and lasting memories is the the rate at which glaciers are retreating due to anthropogenic activity causing global and ocean warming. You hear about these things, but the penny only really drops when you see massive slow moving glaciers that contained ice laid down thousands of years ago now relatively rapidly retreating up glacier valleys and huge ice sheets floating away from the mainland areas. It should be noted that not all glaciers are retreating, but the majority on the Antarctic Peninsula are.

Scheuchl et al. (2016) for example, recorded the ground line for the Pope, Smith and Kohler glaciers in west Antarctica in 1992, 1996, 2011 and 2014-2016 and reported ongoing, rapid retreat with Smith retreating at 2km/yr (40km since 1996), Pope retreating 11km (0.5km/yr) and Kohler retreating 2km since 2011 (~7km since 1996), with the retreat rate consistent with basal slopes (i.e., fast along retrograde beds and slow along prograde beds). Icesheets are also contracting.

So how does this impact on penguins? The majority of penguins live in Antarctica, and are dependent on abundant and predictable food sources. Some penguins are ice-obligates (e.g. Emperor Penguins (Aptenodytes forsteri) and Adelie Penguins (Pygoscelis adeliae)) and reduction of sea-ice and glaciers will result in a general polar shift for these two species, whereas, the ice-intolerant Gentoo (Pygoscelis papua) and Chinstrap Penguins (Pygoscelis antarctica) will and have expanded their range. Polar ice coverage is also affected by the El Nino-oscillation and the Antarctic Oscillation (or Southern Annular Mode; i.e. north-south movement of the westerly wind belt that circles the Antarctic). Incubation periods and chick rearing typically vary from 30-70 days and 20-50 days respectively across all species (Table 1). This is followed by a fledging period were down is eventually lost and juveniles are about to go to sea and fend for themselves. The fledging period is typically 40-70 days, except for the Emperor Penguin (~150 days) and the king penguin (310-350 days). Global warming has the potential to alter the highly predictable patterns of the presence of ice-sheets. Late snow falls that delay egg laying or an early loss of ice can result in the lack of recruitment in entire colonies.

Table 1 from Foracada and Trathan (2009)

Penguins have long lifespans with slow evolutionary processes, so adaptations to changing ice patterns are more likely to come from changes in dispersal rather than adaption (Forcada and Trathan 2009). Species that are ice-obligates are therefore more likely to be affected by the ice contraction as it will destroy the ice at breeding colony sites, and these sites may subsequently be colonised the more ice-intolerant species. We saw this at Petermann Island. Eight years ago, the area was used almost exclusively used by Adelie Penguins, but during our visit there were a few Adelie Penguins and mostly Gentoo Penguins.

With a continued contraction in the ice in the Antarctic, it is likely the number of Emperor and Adelie Penguins will continue to decrease, but the number of Gentoo and Chinstrap Penguins will increase and increase their geographic range and breeding sites. This article from the Guardian further details significant declines in breeding events for Adelie Penguins.

References

Forcada, J., and P. N. Trathan. 2009. Penguin responses to climate change in the Southern Ocean. Global Change Biology 15:1618-1630.

Scheuchl, B., J. Mouginot, E. Rignot, M. Morlighem, and A. Khazendar. 2016. Grounding line retreat of Pope, Smith, and Kohler Glaciers, West Antarctica, measured with Sentinel-1a radar interferometry data. Geophysical Research Letters 43:8572-8579.