It was bitingly cold, as we charted a course through Antarctic Sound and into the northern reaches of the Weddell Sea. In the hushed light, driven forward by the snow littered wind, our bearing was towards the colossal stretching face of iceberg A68A. At sea, size is often hard to comprehend, but not in this instance, as the towering 50m wall of ice filled the entire horizon. The snow blink on the top seemed like an eery beacon, giving all else a strange, grey quality. It’s height belied the vastly greater depths to which it plummeted; eighty percent of a bergs mass being below the water. The striations are often very clear in large tabular bergs, visible layers of firn snow near the top, giving way to dense layers of compacted ice further down, a visual timeline stretching back thousands of years.
In 2017, this berg had famously cleaved from the Larson C ice shelf, which is fastened to the inner eastern side of the Antarctic peninsula. Until relatively recently, this large shelf had two smaller siblings; Larsens A and B - filling the bays further up the peninsula. The Larsen A shelf was the smallest and most northerly and as such, collapsed and disappeared in 1996. The B shelf, followed suit and broke into bergs in 2001, leaving C alone.
Now, the rate at which ice is being lost from Antarctica is accelerating, showing a significant threefold increase since 2012, as described by the Ice Sheet Mass Balance Intercomparison (IMBIE) Project. The project is conducted by an international cohort of eighty scientists, working to assess ice loss from satellite data. They report that 219 billion tonnes of ice are now being lost per year from Antarctica, contributing to a 7.6mm sea level rise since 1992. This antarctic season has seen a series of unprecedented loses; including to the Pine Island Glacier, (on the west of the antarctic continent) which calved a slew of bergs, equating to 120 square miles of ice, one of which was large enough to be named B49. This pattern of loss will leave many ice shelves in negative equity, loosing more ice than they gain until they become unstable and inevitably collapse.
As our climate warms, more energy in our weather systems lead to increased frequency and ferocity of storms. These storms act to work up the seas that lap ice shelves and tidewater glaciers from below, increasing incidences of calvings. Of course, sea ice melt doesn’t contribute to sea level rise. However, these mighty shelves are the gatekeepers, that fasten onto land and hold the ice and snow that it bears, locked in place.
In polar regions, temperature rise will also lead to snow being replaced by rain, which is increasingly what we are now experiencing in Antarctica, with temperature records repeatedly being broken this Austral summer. A new all-time high was recorded this February on Seymore Island by Brazilian Scientists; 20.75ºC. The first time antarctic temperatures have been recorded above 20ºC. As I sit, enjoying a window of unseasonal British sunshine during national lockdown, my mind is drawn to the week of worrying rain that we experienced a month and a half ago in Marguerite Bay. Marguerite Bay sits at below 68º South, at the base of the Antarctic Peninsula. Conversations with my more senior colleagues, very quickly painted a picture of the truly unprecedented nature of this weather. Many who had been working in Antarctica for over two decades, reported never having experienced such persistent rain this far south.
These factors spell an uncertain future for more than just ice sheets. Adelie, gentoo and chinstrap penguin chicks, all born during the austral summer, are highly vulnerable to rain. Waterlogged, downy feathers freeze, stripping these chicks of all insulation and warmth, in some cases leading to dramatic colony collapses. Similarly, the iconic bird of the south, the emperor penguin, nest in colonies on ice sheets - the only bird that has managed to do away with land from its life history altogether. So the fate of the emperor is also intrinsically linked to the fate of the ice, along with a plethora of other, less charismatic, but as equally important species.
At the bottom of the earth, hidden away beyond the drake passage, is a world that can seem relatively unconnected to our mostly northern hemisphere-based lives. But this hidden world is not invulnerable to the changes that we are enacting, thousands of miles away. And the response of this distant, seventh continent to our changes, are to be palpable.
A68A’s huge mass meant that our passage south into the Weddell Sea was blocked. So after cruising along its side (where we met a small pod of type B1 killer whales, to much general excitement) we headed back West. As we left, it occurred to me that the water that had been trapped inside this berg for tens of thousands of years, would now return to the oceans. When, I wondered, would conditions be right once again to allow the Larsen C shelf to accrue the volume of ice that it had lost? And how much water is in a berg of that size anyway? The answer, is 1 trillion metric tonnes (when I met it at 137km by 42km); which is equivalent to the volume of water that continuously gushes from the giant mouth of the Amazon river for 23 straight days. Or 166,000,000 olympic swimming pools.
