Ocean-ice Interaction in the Ross Sea during Past Warm Periods

The two polar ice sheets in Greenland and Antarctica contain enough ice to raise global sea levels by ~65 metre. In total, 58 metre of sea level equivalent ice is tied up in Antarctica, of which ~4m is located in West Antarctic areas that are particularly vulnerable to environmental change. These are areas where the ice rests on a bed several hundred meters below sea level, meaning the ice is in direct contact with the warming ocean. In such a set up the ice sheet is not just melting from the top down by means of higher atmospheric temperatures and surface melting, but also from the bottom up, via contact with warmer ocean water.

Recent estimates on how fast West Antarctica may lose most of its ocean terminating ice range from a few hundred to a few thousand years into the future. The lower end of this range is just a few generations away, and is something that becomes increasingly likely under unabated carbon dioxide emissions, increased atmospheric carbon dioxide concentrations and resulting global warming.

We can make detailed observations on how the ice sheet reacts to ongoing environmental change. But what we can't observe with our own eyes is what will happen to the ice when global temperature are 1, 2, 4 or even 8 degrees warmer than today.

As Earth Scientists we love our detective stories. Figuring out the response of the Antarctic ice sheets to warmer climates is something we can do by using the mud deposited at the bottom of the ocean. Just like an old-fashioned tape recorder, this mud preserves an environmental signal from times in the past, where earth's climate was warmer and atmospheric carbon dioxide levels were higher than today.

It is such records that we want to recover when we set sail on Expedition 374 of the International Ocean Discovery Program in January 2018 to March 2018. My role on the expedition will be to look at the chemical fingerprint in the mud. Every rock that gets crushed by the overlying ice sheet and transported from the continent to the ocean has a typical fingerprint, just like every human being has a very specific DNA. We can use this fingerprint to decipher where the material was located on the continent, which in turn can tell us about the location of the ice margin that scrapes off the mud. You can imagine that back in times of greater warmth that location was not the same as it is today.

Another part of the climate system that changes with changing environmental conditions is how the oceans circulate and transport heat and carbon around the globe. We are all used to thinking about the Gulf Stream that brings warm waters to the shores of Northern Europe. Down south, next to the giant Antarctic continent, another process comes into play: Freezing of surface waters and interaction of warmer water with cold floating ice shelves creates very salty, cold and dense water, which sinks to the bottom of the ocean. Such waters are called Antarctic Bottom Waters and fill up 30-40% of our global oceans. Will this be the same in a warming world? Or will the retreat of the Antarctic ice sheets also have a major impact on global ocean circulation? Another question we can tackle as Earth Science detectives by looking at the chemical fingerprint of mud.

IODP Expedition 374 is going to be a great opportunity to collect unique material and advance our basic understanding of polar ice sheets and ocean circulation in a warmer world -a world which may just look like the one we are headed towards.

Monitoring ice sheets and sea level change has risen to the top of the agenda, not only for research institutions, but also for government and policy agencies. The last fifteen years have seen a dramatic increase in observational data, and associated scientific understanding. In the negotiations around the 2015 Paris Agreement, potential sea level rise from future warming and ice melting played a central role in deciding to aim for 'global temperature rise this century well below 2 degrees Celsius above pre-industrial levels and pursue efforts to limit the temperature increase even further to 1.5 degrees Celsius.'

Palaeoclimate research is our only window to investigated ice sheet behaviour under warmer conditions before experiencing them ourselves. Hence society as a hole will benefit from research advancing our understanding on mechanisms of ice destabilisation, tresholds of ice sheet collapse, and associated timescales. The UNFCC commissioned a Special Report on the Impacts of 1.5 degree warming from the IPCC, to be released in early October 2018. Continued basic research needs to inform the questions raised in this report, as any future assessment can only be as accurate as our modern and past observational data are.

Besides policy makers, schools and universities are targeted with outreach activities from aboard the JOIDES resolution. I will help deliver live broadcasts and blogs. Upon return to shore I will give talks at universities, museums and festivals to convey the importance of warming-related ice melting and subsequent sea level rise to the general public and the next generation of scientists. I will also involve a number of graduate and undergraduate students in my post-cruise research.