An international team has successfully drilled through 580 metres of ice, obtained the longest sediment core ever retrieved from the remote Siple Coast, and gathered crucial information in their mission to understand the West Antarctic Ice Sheet’s past response to climate warming.
A deep-field research camp close to the ‘grounding zone’ of the West Antarctic Ice Sheet, where the vast ice mass begins to float as the Ross Ice Shelf, has been the site of a multitude of groundbreaking scientific achievements this Antarctic summer.
A team of 27, comprising scientists, drillers, and crew set up camp at the KIS-3 drilling site 860 km from Scott Base, living and working in tents on ice from late November through to January, as part of the SWAIS2C (Sensitivity of the West Antarctic Ice Sheet to 2°C) project, with logistical support from Antarctica New Zealand and the United States Antarctic Program (USAP).
Their mission was hugely ambitious - to obtain a geological record contained in sediment layers hidden under the ice shelf, at depths of up to 200 metres below the ocean floor. To retrieve a sediment core this deep into an Antarctic seafloor requires a custom-designed drilling system (known as the AIDD – Antarctic Intermediate Depth Drill) and has never been attempted so far from a base and so close to the centre of the West Antarctic Ice Sheet.
“We’re at the frontier, drilling through an ice shelf into the seafloor, to acquire sediment samples that no one has previously been able to obtain. It’s cutting-edge science and incredibly challenging work,” says Dr Richard Levy, SWAIS2C co-chief scientist, from GNS Science Te Pū Ao and Te Herenga Waka—Victoria University of Wellington.
The coveted core is expected to reach back hundreds of thousands of years, potentially even millions of years. Such a record would include the last interglacial period 125,000 years ago, when Earth was around 1.5°C warmer than pre-industrial temperatures – similar to the temperatures we are approaching this year due to climate change.
“The West Antarctic Ice Sheet is currently losing mass at an unprecedented rate. It is one of the most vulnerable components in the Earth system to increasing warming. But we fundamentally do not know when and how fast it will disintegrate and raise global sea level by several metres,” says Dr Tina van de Flierdt, SWAIS2C co-chief scientist, from Imperial College London.
“The sequence of rocks in the sediment should tell us how the West Antarctic Ice Sheet behaved when it was a bit warmer than today – if we find marine algae it’s likely the ice sheet retreated. This information will allow us to build a much better picture of how Antarctic ice will respond to future warming, which parts will melt first, and which parts will remain,” says Dr Levy.
A hot water drill was used to melt through nearly 580 m of ice, breaking through the base of the ice shelf into the 55 m-thick ocean cavity lying between the ice and the ancient layers of mud and rock below.
The drillers got underway with the ‘big’ rig – the AIDD – lowering heavy equipment, drill string, and glass reinforced epoxy ‘sea-riser’ tubing through the new hole in the ice, all the while applying hot water to avoid it freezing back over. However, due to technical challenges operations were halted, and the decision was made to retrieve the equipment and end deep-drilling operations for the season.
Levy says having tested the equipment in the field, the team now know the modifications – a relatively simple fix – that are needed to improve the chance for success when they return next season.
“This year we got tantalisingly close. With the knowledge we’ve gained from the samples collected and the technological experiments conducted we have an excellent chance next year to recover the long sediment cores to provide the climate insights we’re chasing.”
With the AIDD parked, the team innovated using other coring methods – including the physically demanding hammer coring technique, in which a rope is pulled to hammer attached weights up and down and drive a steel tube into the seafloor to collect sediment. With all hands on-deck, they were able to recover a 1.92 m core – a record for the Siple Coast – as well as 9 shorter cores.
“These samples offer a huge increase in the amount of material we have to help us understand the present-day environment beneath the ice shelf, and the history those sediments represent. They also give us insight into the types of rock we will need to drill through to get those deeper records we’re seeking,” says Levy.
The samples will also be studied for their microbiological content to reveal more about the microorganisms living in the unique cold and dark environment.
The ocean cavity itself holds important information, and oceanographic data was gathered with a device (CTD) to measure salinity, temperature and density in the ocean. A long-term mooring with a range of oceanographic instruments was also deployed to collect data about the ocean currents and properties at the grounding zone for years to come. Such observations are far and few between in the Ross Sea and will allow the scientists to understand if and when warming ocean water around Antarctica will eventually cause the water that flows below the ice shelf to warm and increase melting at the grounding zone.
Preparations are already underway for the next season when SWAIS2C will return to the site armed with the new knowledge and experience gained.
“We are thrilled with what we’ve achieved, it’s a massive step forward towards our ultimate goal to recover the sediment we need to answer the big questions that are crucial for humanity as we adapt and plan for sea-level rise,” says van de Flierdt.