– There is almost no sea ice in Antarctica – in the middle of winter
Not since measurements began have so little new ice formed as happened this year. How do researchers explain rapid changes?
Robbie Mallett did not expect that the heat in Antarctica would be such a problem for him. The sea ice researcher has just spent the winter, which runs from March to October, in Antarctica, at the British research station Rothera. There he wanted to examine sea ice off the coast using laser scanners and other instruments. But this year it was so warm and the sea ice was often so thin “that it melted back in bad weather or was carried away by the wind,” Mallett said in an email.
Such conditions make working on the ice life-threatening. An instrument drifted with a broken ice floe, but fortunately researchers were able to recover it with a small boat before it sank. Often, Mallett could only get out on the ice with skis and a survival suit – if at all. Most often, the researcher went to an inland glacier to make measurements.
Very little ice in Antarctica, and in the middle of winter: Mallett’s observation is only a snapshot of West Antarctica, but the image has been confirmed from space. As NASA announced in mid-September, at the peak of ice formation at the end of the Antarctic winter, only 17 million square kilometers were covered by ice in the Southern Ocean, a new negative record since satellite measurements began.
This means that the previous decrease since 1986 was about one million square kilometers, which is equivalent to the area of Germany, France and the Benelux countries combined. An area the size of Argentina is missing from the average value. “Sea ice growth appears to be low across almost the entire continent, not just in one region,” NASA sea ice researcher Walt Meyer emphasizes in a statement.
This is not good news for Antarctic ecosystems. Antarctic krill find shelter and food under sea ice, and the growth of phytoplankton, the basis of many food chains, also depends on the growth of ice. Penguins need sea ice to breed and seals to settle on. Like the plume, sea ice also protects many Antarctic glaciers from sliding into the sea. This slows sea level rise.
Science has not yet agreed on the causes.
Quote from AWI sea ice portal
Antarctica appears to be resisting climate change for a long time. While sea ice on the other side of the world in the Arctic has been shrinking steadily since 1979, it has continued to grow in the Antarctic for decades, surprising climate researchers. A new record was set in 2014, when ice covered more than 20 million square kilometers.
But within a few years, as much sea ice as the Arctic has melted in three decades. This year it stands out again. In February, at the end of the Antarctic summer, only two million square kilometers of sea surface were covered by ice, the lowest level since satellite measurements began. Since then, the ice has regenerated much less than usual, which is not a good sign for the melting period that has now begun.
How can we explain the reversal of this trend within a few years? “Science has not yet agreed on the causes here,” says the Alfred Wegener Institute for Polar and Marine Research’s Sea Ice Portal. While atmospheric conditions in the Arctic, such as air temperatures, are crucial for ice development, the influence of the ocean in the Antarctic is at least as significant.
“Many factors are playing a role in the current slow growth process and thus the decline in Antarctic sea ice extent, not just warmer air or warmer water masses, but also currents, winds or air humidity and cloud cover.” It is still unclear how these factors changed in detail.
But there are some assumptions. In the journal Communications Earth & Environment, Australian climate researchers Edward Doddridge and Ariane Burich recently put forward the hypothesis that Antarctica has transformed into a new state. They divide the evolution since the beginning of satellite measurements into three phases: a “neutral period” from the late 1970s to 2007 followed by a phase containing a relatively large amount of sea ice. From around 2016, Antarctica will be in a new state, characterized by very little sea ice.
But what is strange is that these changes do not appear to be linked to climate phenomena such as El Niño, the Antarctic Oscillation, or the Pacific Decadal Oscillation, which usually affect sea ice. Burish and Doddridge suggest instead that the warming of the ocean around Antarctica was crucial. The fact that the Southern Ocean continues to warm is “primarily due to increased greenhouse gases,” that is, human-caused climate change.
So solve the puzzle? It’s not that easy. For example, the role of meltwater in ice is unclear. Paradoxically, melting ice could stabilize sea ice again. This is because fresh melted water collects on the sea surface, where it replaces salt water. Because fresh water freezes at slightly higher temperatures than salt water, a cold layer can form on the ocean surface, promoting sea ice growth. To what extent this is currently happening is unclear.
Overall, it raises the question of how reliable it is to estimate developments in Antarctica using current methods. Climate researchers were already having difficulty dealing with the long-term growth of sea ice. As a study in Geophysical Research Letters showed, even the latest generation of climate models fail because of this.
Explore underwater cavities
According to Earth system researcher Eric Rignot of the University of California, Irvine, this discrepancy is primarily due to “the limited observational data that goes into the models.” Antarctica is very large; Satellites, for example, cannot record everything that happens under the ice or on the sea floor. “In general, large parts of the Antarctic continental shelf have never been mapped,” Rignot wrote in a commentary in which he called for a “broad, comprehensive, and sustained initiative” to better understand ice-ocean processes. For example, autonomous underwater drones are needed to explore subglacial cavities that may be penetrated by warmer waters.
This particularly affects Antarctica’s inland glaciers, which often extend out to sea and merge into the sea ice there. In order to cover larger areas, new measurement campaigns with aircraft or suborbital flights are needed as well as more satellite missions. Obviously this will cost a lot of money. Reno estimates the cost of all these measures at between several hundred million and billions of US dollars.
The polar night in Antarctica has ended and the sun is shining, writes Robbie Mallett from Rothera Research Station. The sea ice in the Gulf is now melting from the top, side and bottom. “There’s not much left. What remains will soon disappear.”