ANDRILL is a USD 30 million multinational sedimentary drilling program to recover a history of paleoenvironmental changes in Antarctica. It will guide our understanding of the speed, size and frequency of past and future glacial and interglacial changes in the Antarctic region, and test global linkages between climate changes in the Northern and Southern hemispheres.

On 16 December 2006, the ANDRILL program drilled to a new record depth of 1,285 metres below the seafloor from a site on the Ross Ice Shelf near Scott Base in Antarctica, making it the most successful Antarctic drilling program to date in terms of depth and rock core recovered.

ANDRILL is one of the largest science projects currently taking place in Antarctica. Why does this research matter?

The first goal of ANDRILL is to get a climate record for the high latitudes. Our previous records from high latitude are fairly scattered and very piecemeal in terms of the time that is represented. Up to now much of the Earth's paleoclimate record comes from deep marine cores from lower latitudes, and from these cores, people have been inferring what has been happening in the Antarctic. What we believe, however, is that we really need to get records "from the horses' mouth". So we are collecting records which we hope we can use for interpreting what the ice sheet has done and how it behaved at critical times, especially during warm transitions such as the one we believe we are heading into; what water temperatures where like at these times; and even whether there was land vegetation around during warmer periods.

When you talk about ice sheets, are you referring to the Ross Ice Shelf (which floats on the sea), or about continental ice sheets such as the ones that currently cover most of East and West Antarctica and which are grounded on bedrock?

It's a combination of the two, because the Ross Ice Shelf wouldn't exist without the continental ice sheet (the ice shelf flows from the ice sheet). Certainly the core we have just extracted enables us to see the presence of the ice sheet, of the ice shelf, and of open water, so that we can map those changes through time. For example, the last time the ice sheet was grounded in the McMurdo region (where we now have a floating ice shelf) was about six or seven thousand years ago.

What key observations have you been able to make from the core you have just recovered?

It is still too early to make a full interpretation, and Tim Naish, my co-chief and I have given our science team a two year window to analyze the core fully, but what the drilling this season (2006-07) was targeting is a younger record that should go back to something in the region of ten million years. In the last ten million years, we know that the Earth has gone through some significant climatic fluctuations. What we want to know is what did the Antarctic ice sheet do during these past warming and cooling episodes? How fast did it react to changes?

Because you are drilling into sedimentary rock, your record will go much further back than those obtained from ice cores extracted from the Antarctic ice sheets (which go back to a maximum of about 900 000 years). Nevertheless, can you tell us whether you are comparing or picking up some of the same climate cycles and fluctuations over these last 900 000 years?

Again, it's a bit too early to say, but these kinds of comparisons are certainly our aim. Right now we are still unsure as to how many glacial fluctuations there have been and whether they are equivalent in time to what has been observed in the EPICA Antarctic ice core which goes back 900 000 years. At the moment it does look like we have corresponding cycles which are shorter than 100 000 years, however we didn't recover the first 20 metres of sediment, and we are still unsure as to what kind of time period that represents.

How come you weren't able to recover those first 20 metres?

With rotary coring, it's always difficult to recover soft sediment, and the upper 20 metres were very soft. However, we did recover the first 1,5 metres - the youngest part of the core - but then there is a gap to about 20 metres. Below that level, however, we've had exceptional core recovery - something like 97% recovery. This is thanks to the technique that ANDRILL drillers have developed.

With the opening up of the Drake Passage and the formation of the Antarctic Circumpolar Current some 30 to 50 million years ago, Antarctica is said to have become cut off climatically from the rest of the Earth. How do you explain fluctuations in Antarctic climate since that time?

The opening up of the Drake Passage and the formation of the Circumpolar Current has been an explanation for the cooling of Antarctica, and it certainly is a factor, but some recent modeling has shown that it is not solely due to that, and that the cooling has also been driven by the amount of carbon dioxide in the atmosphere.

Global fluctuations in CO₂ as recorded in ice cores do have an effect on the Antarctic, independent of its isolation in the ocean circulation system. There is transfer globally of the effect of the amount of CO₂, and that's what is important for us to know. We know that the CO₂ in the atmosphere is increasing and that it has fluctuated naturally in the past, but also that we are now heading to levels well beyond what's known in natural variations over the last few tens of millions of years.

What we are trying to understand is what the link is, and what are the tipping points or thresholds of global temperature that can then be linked to the amount of CO₂ in the atmosphere and that have an important effect on ice sheet condition. Certainly the isolation of the Antarctic in terms of ocean circulation is a factor, but the big thing to realize is that CO₂ and greenhouse gas concentrations in the atmosphere are also significant for driving fluctuations in the volume of ice.

Can you tell us about the future of ANDRILL. What is the program for next year and beyond?

Next year we will set up a drill site on the other side of Ross Island in McMurdo Sound, with the aim of obtaining a sedimentary record that is both overlapping and older in age. We hope to go back to a time, roughly around 17 million years ago, when many believe the Antarctic ice sheet became cold and much like it is today. There are different views on exactly how that happened, so this will hopefully provide us with answers.

Besides both being funded, this year and next year also fit nicely together as a package. Beyond that there are probably as many as six different contenders all at different stages of development, so there will be funding proposals going out very soon to get the next phase off the ground. These are all in the Ross Ice Shelf and McMurdo area and are part of what we view as the McMurdo Sound portfolio of drilling. After that, it we may aim to go to the Weddell Sea or even right the way round Antarctica like the ocean drilling program, but we have no firm projects at this stage.

Photos: Jean de Pomereu
Text: SciencePoles