Setting the Ice Sheet Record Straight

30 May 2006 - Interviews, Logistics, Ice & Snow

Dr Carlota Escutia

Dr Carlota Escutia has worked in the United States, and recently in her native Spain at the CSIC-Granada University, on understanding better the factors causing formation of the Antarctic ice sheets " around 34 million years ago " and what has since influenced its growth or contraction. Her important new research project, to obtain further evidence from the Antarctic under the Integrated Ocean Drilling Program (IODP), will likely take place in 2008-09.

Dr Escutia gave a well-received presentation to the March BEPOLES workshop. SciencePoles took the opportunity to talk to her in Brussels " about what has actually happened over the last 34 million years and what might happen in future.

SciencePoles: How can we really know what happened in Antarctica in the distant past?

Dr Escutia: To date what we know about the Antarctic ice sheets comes mainly from "distal" records. These are usually proxy indicators of global temperatures " non-polar ocean sediment samples that allow us to estimate temperature by looking at levels of particular elements' isotopes in different geological eras. It is possible in this way, and by cross-checking with proxy sea level indicators, to get a good general idea about large-scale trends in global temperature and how that relates to ice volume building up or falling away at the poles.

What we cannot get by these means is a detailed picture of ice sheet extent in Antarctica. For that we need to take samples from its continental shelf and in the Southern Ocean.

You've described discrepancies in the various records of Antarctic ice sheet behaviour. How will your work assist in clearing up such discrepancies?

On the few occasions it has previously been possible to drill in the Antarctic, our knowledge has greatly increased. Discrepancies appear between what low latititude results have suggested and what the evidence on the spot tells us. Low latitude isotope records suggest that from the middle Miocene (around 14 million to 17 million years ago) until now the Antarctic ice sheets have been permanently in place. But when we look at the actual Antarctic records we discover that during this extended glaciation there were a number of significant regional warming events going on which have led to the icesheets' growing or contracting significantly. Some of these have lasted many hundreds of thousands of years " including at around 10.7-9.0 million, 3.6 million and 1.1 million years ago.

There are also places where the sea level and isotopic records appear to disagree. In this case it's necessary to go to Antarctica to get the real story. Drilling in the continental shelf has enabled us to recover strata which have been deposited directly by ice, demonstrating exactly when the ice sheets extended that far and when they receded. Having said that, erosion of the shelf means that the Antarctic record, while very precise, contains gaps. So you get "snapshots" of what is happening at precise periods.

Why is it so important to know about what happened to the Antarctic ice sheet millions of years ago?

The current forecasts for greenhouse gas levels by 2100 range from a doubling of pre-industrial levels to dramatically higher levels. These levels correspond to temperatures on average 1.4 degrees centigrade higher than today up to more than 5 degrees higher.

Let's consider the more "conservative" case. Average global temperatures of around two degrees centigrade higher than today were last seen 10-15 million years ago. We don't know whether the Antarctic ice sheet of that time was a very dynamic "come and go" ice sheet or whether it was a permanent icesheet. By the way, we had a unipolar world then: the Greenland ice sheet only formed around 2-3 million years ago.

What's really important for us to know is how the Antarctic ice sheets operated under "warm scenarios" and how did it react to changes. Did it react slowly and melt over thousands of years? Did it perhaps react slowly up to a point, and then melt away very quickly?

If the Antarctic continental ice sheets were to melt then you'd be looking at a vast increase in sea level: if all the world's icesheets were to melt then we would face a 60-70 metre sea level rise. The Greenland ice sheet, which is most under threat, represents 7 of those metres, which is scary enough! But the East Antarctic ice sheet, regarded as the most solid and stable, represents most of it.

We're trying to find out about all this because at the pessimistic end of the IPCC forecasts we're looking at the disappearance of the Antarctic ice sheets as a real possibility. The last time the world was 5 degrees warmer was over 35 million years ago " before the formation of the Antarctic ice sheets. This is referred to as a "greenhouse world".

So just how long do these ice sheets take to melt? Thinking to date has been that they take thousands of years to disappear.

We really don't know. We're trying to find out how these massive geological formations transition from one state to another (glacial to interglacial). Some think the major ice sheets are very slow to build and fast to collapse. Others think that they are slow to build and slow to collapse. But it's not very clear. This is what needs more work.

Why hasn't there been more drilling in the Antarctic previously?

It's easier to collect sediment samples from low latitude locations. Sampling expeditions have to be linked to ship itineraries which are being organised for a range of reasons. There are many such itineraries which proceed in the Pacific or in the Atlantic but it has not been easy to arrange trips to Antarctica, as the last leg of the journey is very costly. In the past ten years there've been only three deep drilling expeditions on the continental margin. Two of these have been by the Ocean Drilling Program, or ODP, and the other one was by another program, Cape Roberts (co-funded by New Zealand and the United States).

The ODP and its successor program, the Integrated Ocean Drilling Program (IODP), funded by the U.S. National Science Foundation and 22 international partners (JOIDES), conducts basic research into the history of ocean basins and the earth's crust beneath " using the ship JOIDES Resolution.

When will the new drilling programme take place?

It's currently scheduled for the Austral summer of 2008-09 as one of the contributions to the forthcoming International Polar Year being made by the Scientific Committee on Antartic Research's (SCAR's) Antarctic Climate Evolution (ACE) program. It's to be in the Wilkes Land area, opposite the continental margins of Australia and will be funded under IODP-. No other Antarctic IODP drilling programs are being considered for the near future, but there will also be drilling in the Ross Sea, I believe starting in 2007, by ANDRILL the successor to the Cape Roberts program.

By: Richard de Ferranti