Jules Verne sent his fictional submarine, the Nautilus, to the South Pole through an ocean hidden under a thick layer of ice. Written 40 years before any explorer had reached the pole, its story was, however, only half-fiction.
In fact, there are hidden oceanic cavities around Antarctica, and our last investigation Explore how the ocean circulates beneath the continent’s ice shelves – large floating expanses of land ice that rise and fall with the tides.
These ice shelves reinforce the continent’s huge land ice sheet and play an important role in assessing future sea level rise. Our work sheds new light on how ocean currents contribute to melting in Antarctica, which is one of the biggest uncertainties in climate model predictions.
Read more: Climate scientists explore the ocean hidden beneath Antarctica’s largest ice shelf
An unexplored ocean
The Ross Ice Shelf is the largest floating ice slab on Earth, at 480,000 square kilometers. The hidden ocean cavity stretches 700 km south of the Antarctic coast and remains largely unexplored.
We know that ice shelves melt primarily from below, washed away by a warming ocean. But we have very little data available on how water mixes under ice. This is often overlooked in climate models, but our new measures will help correct this.
The only other expedition to the ocean cavity below the Ross Central Ice Shelf dates back to the 1970s and returned with intriguing results. Despite the limited technology of the time, it showed that the ocean cavity was not a static bathtub. Instead, she found thin layers of bodies of water, with subtly different temperatures and salinities between the layers.
Other ocean studies have been conducted. from the edges or of above. They have provided information on how the system works, but to really understand it, we needed to take measurements directly from the ocean under hundreds of meters of ice.
In 2017, we used a hot water jet, modeled on a British Antarctic Survey design, to drill 350 meters of ice to the ocean below. We were able to keep the well liquid enough to perform detailed ocean measurements, as well as leave instruments behind to continue monitoring ocean currents and temperature. These data still arrive by satellite.
We discovered that the hidden ocean acts as a massive estuary with relatively warm (2 ℃) seawater that enters the sea floor to circulate near the surface in a combination of meltwater and subglacial freshwater squeezed from the ice sheet and the hidden rocky foundations of Antarctica.
Hundreds of meters of ice isolate the ocean cavity from raging winds and freezing Antarctic air temperatures. But nothing stops the tides. Our data suggests that the tides push the layered ocean back and forth in past ripples at the bottom of the ice and mix parts of the ocean cavity.
Read more: How solar heat drives rapid fusion of parts of Antarctica’s largest ice shelf
This type of discovery is the ultimate challenge for climate science. How do we represent processes that work at daily scales in models that make projections over the centuries? Our data shows that daily changes can add up, so finding a solution is important.
For example, data collected outside the ocean cavity and computer models suggest that any parcel of water spends one to six years passing through the cavity. Our new data indicates that the lower end of the range is more likely and that we shouldn’t think in terms of a great circuit anyway.
The Ross is not the ice shelf in increased danger from warming oceans. But its sheer size and its relationship with the neighboring Ross Sea means it is a vital cog in the planetary ocean system.
Read more: Melted ice in Greenland and Antarctica is predicted to bring more extreme weather
The importance of these ice shelves for sea level rise in the coming centuries is very evident. Studies show that if global warming exceeds 2 ℃, major Antarctic ice shelves would collapse and release ice flowing from the continent’s ice sheet, raising sea level to 3 meters by 2,300.
What is less understood, but is also potentially a massive agent for change, is the impact of meltwater on the world. thermohaline circulation, an ocean transport circuit that sees the ocean cycle from the abyss off the coast of Antarctica to tropical surface waters every 1,000 years or so.
Antarctic ice shelves are like a pit stop on this circuit and so what happens in Antarctica? resonates globally. The fastest melting ice shelves will change the stratification of the ocean, with implications for global ocean circulation, and one result of this appears to be greater climatic variability.
This article was originally published in The Conversation.
