Tuesday, April 2, 2013

Antarctic Octopus Living Testament To Global Warming

Tell me, O Octopus, I begs
Is those things arms, or is they legs?
I marvel at thee, Octopus;
If I were thou, I'd call me Us.
-Ogden Nash

The octopus, formerly known as both a delicacy food item and for being thrown onto the ice at hockey games, now has a new recognition: a living testament to the effects of global warming.

Genetic information from an Antarctic octopus species adds to a growing body of evidence of at least a partial collapse of the West Antarctic Ice Sheet (WAIS) during a previous interglacial period (like during the Eemian interglacial some 125,000 years ago).

Members of Turquet’s octopuses (pictured) tend to live in one place and only move to escape predators. This led to the understanding that specimens from areas on either side of Antarctica would be genetically different. What scientists found after examining specimens from each side of the WAIS was that both populations were genetically nearly identical.

Dr Phill Watts, from the University’s Institute of Integrative Biology, explains: “We expected to find a marked difference between Turquet’s octopuses living in different regions of the ocean, particularly between areas that are currently separated by approximately 10,000 km of sea. These creatures don’t like to travel and so breeding between the populations in the Ross and Weddell Seas [now separated by those 10,000 km of ocean] would have been highly unusual."

To check, scientists examined data on octopuses from other parts of Antarctica, not separated by this particular ice sheet. What they found was that the depth of the ocean and its currents limited the movement of the octopus in certain areas, as would have been expected for those living on either side of the West Antarctic Ice sheet. This added further evidence that at some point in recent history the WAIS might have collapsed.

Dr Louise Allcock, from the National University of Ireland, Galway, added: “A previous study has shown evidence that the Ross and Weddell Seas could have been connected. We wanted to investigate whether there was any genetic information that could tell us what the past environment could have been like, and this octopus species, with its large populations around the region and limited movements, was an ideal species to use.

“The fact that we found more similarities than we did differences supports the theory that the WAIS could have collapsed in the past. It also provides further evidence that scientists should continue to raise awareness about the impact of climate change on Antarctica today.”

So what is the supporting evidence from other studies?

Yin et al 2011 show that warming ocean currents can undercut polar ice sheets. The results from Hellmer et al 2012 include that these warming currents could increase ice mass losses from 80 gigatons per year to over 1,600 gigatons per year, just in the area of the Filchner-Ronne Ice Shelf alone. Further, a newly discovered basin underlying the WAIS at the head of the Filchner-Ronne Ice Shelf (Ross et al 2012), serves to highlight the inherent weakness represented by this weak underbelly of the WAIS.

The evidence on the Amundsen Sea side of the WAIS tells a similar tale. Marcott et al 2011 examined evidence from previous episodes of ice sheet deglaciation and found that warming oceanic currents can penetrate ice sheets and shelves, helping to trigger rapid deglaciation events. Jacobs et al 2012 show that warming ocean currents are already undercutting the ice sheets and shelves in the area, allowing water as warm as 4°C to reach the grounding lines of the ice. Additionally, the ice shelves in the area are losing their grips on their anchor points and are tearing themselves apart in the process (MacGregor et al 2012).

Looking at further evidence from previous interglacials, work by Grant et al 2012 found a rapid coupling between ice volume and polar temperatures over the past 150,000 years, including that the timing of ice volume fluctuations agrees well with that of variations in Antarctic climate and that the amplitudes of ice volume fluctuations closely match Antarctic climate changes.

Researching an earlier interglacial (MIS 11 from about 400,000 years ago), Raymo and Mitrovica 2012 found that the West Antarctic Ice Sheet collapsed during that protracted warm period. Evidence from the NEEM Community Members study (2013) shows that during the Eemian interglacial, the Greenland Ice sheet could not have contributed much more than 1 meter of the 6-8 meters of sea level rise known to have occurred at that time.

That leaves the WAIS as the likeliest source for the remaining 4-6 meters of sea level rise known to have occurred during the Eemian interglacial. It is this collapse of the WAIS that paved the way for an opportunistic octopus species to thrive, via adaptation to a changing climate. Like the changing climate that we face today.

Credit an obscure species of octopus for the inspiration for this post.

Image courtesy of the University of Liverpool

Reference Sources:

A map of Antarctica

Antarctic Octopus Study Shows West Antarctic Ice Sheet May Have Collapsed 125,000 Years Ago – Strugnell et al 2012

Warming Ocean Layers Will Undermine Polar Ice Sheets, Climate Models Show – Yin et al 2011

New Weak Point Discovered in the Antarctic Ice Sheet – Hellmer et al 2012

Potential Instability in West Antarctic Ice Sheet from Newly Discovered Basin Size of New Jersey – Ross et al 2012

Ancient Glacial Melting Shows That Small Amount of Subsurface Warming Can Trigger Rapid Collapse of Ice Shelves - Marcott et al 2011

Ocean Currents Speed Melting of Antarctic Ice: A Major Glacier Is Undermined from Below - Jacobs et al 2012

West Antarctic Ice Shelves Tearing Apart at the Seams - MacGregor et al 2012

Rapid coupling between ice volume and polar temperature over the past 150,000years - Grant et al 2012

Collapse of polar ice sheets during the stage 11 interglacial - Raymo and Mitrovica 2012

Eemian interglacial reconstructed from a Greenland folded ice core - NEEM Community Members (2013)

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