The Antarctic Ocean have been cooling in recent decades, contrary to what climatic models foresee. Increased defrost and rainwater explains 60% of decades’ disadvantage between predicted temperatures and those observed in the ocean around Antarctica
Global climate models predict that the ocean around Antarctica should be warming, but in fact these waters have cooled for most of the last four decades.
In a new study, researchers at Stanford University concluded that the discrepancy between the results of the models and the observed cooling is mainly due to the lack of melting water e to Precipitation underestimation.
During the course, presented in an article published this week in Geophysical Research Lettersscientists have quantified the amount of cooling observed since 1990, due to a freshwater influx which is not taken into account in the most advanced climate models.
The investigators found that freshwater entrances along the coast, from the fusion of the ice layersthey exert a surprisingly strong influence on southern ocean surface temperatures and the climate system in general.
“We found that the trend of cooling of the Antarctic Ocean is, in fact, A response to global warmingwhich accelerates the fusion of ice sheets and local precipitation, ”he said Earle Wilsonprofessor at the Stanford Doerr Sustainability School and senior author of the study at the University.
As the growing temperatures melt the antarctic ice cloak and cause more precipitation, the upper layer of the Antarctic Ocean is becoming less salty and therefore less dense.
This creates a lid that limits the exchange of cold surface waters with the warmer waters below. “The fresher it is the superficial layer, It is more difficult to mix hot water“Explained Wilson.
But This freshness is not fully represented in models more advanced climatic – a failure that scientists have long recognized as an important source of uncertainty in projections of the future climb of sea level.
“The impact of glacial fusion water on oceanic circulation is completely absent from most climate models,” Wilson said.
Reconcile global discrepancies
The discrepancy between the temperatures of the observed and simulated sea surface around Antarctica is part of a greatest challenge for scientists and governments seeking to prepare for climate impacts.
Global climate models usually do not simulate accurately The cooling observed in the last 40 years in the Antarctic Ocean and the Eastern Pacific around the equator, nor the intensity of heating observed in the Western Indian and Pacific Oceans.
There is also a discrepancy between the simulations and the observed frequency of the weather conditions The girldefined by the fact that the East Pacific Ocean is colder than average.
Antarctic ocean heating phenomena in the last eight years has decreased a little the trend of cooling for 40 years.
But if the seafront’s surface temperature trends around the world continue to resemble the standards of recent decadesinstead of moving to the expected standards, this would change expectations of scientists for some short -term impacts of climate change.
“Our results can help reconcile these discrepancies Global, ”said Wilson.
The oceans They absorbed globally more than a quarter of the co2 emitted by human activities and more than 90% of the excess heat withheld in our climate system by greenhouse gases.
“The Antarctic Ocean It is one of the main places where this happens“Explains Zachary Kaufman, a postdoctoral student in sciences in the terrestrial system and corresponding author of the study.
Thus, the Antarctic Ocean has a huge influence on the global climb of sea level, heat absorption by the oceans and the carbon sequestration, and the temperatures of its surface affect climatic patterns and that influence precipitation in places as distant as California.
A surprising discovery
To understand the physical mechanism of the cooling of the Antarctic Ocean-and to allow more reliable projections of its future impacts on the Earth’s climate system-Wilson and Kaufman set out to what extent the sea surface temperatures around Antarctica cooled in response to the presence of colder freshwater.
“We thought naively that it didn’t matter exactly where The freshwater was put, ”admits Wilson.
Investigators were surprised to find that surface temperatures They are much more sensitive to freshwater flows concentrated along the coast than flows that cross the ocean in the form of rain.
“The application of freshwater near the antarctic margin has a greater influence on the formation of marine ice and the seasonal cycle of marine ice extension, which has downstream impacts on the surface temperature of theR, ”says Wilson.
“This was a surprising result that we are looking forward to exploring more in future work,” adds the researcher.
“There has been any debate on whether This melted water is sufficient During the historical period to really import, ”says Kaufman.“ In our study, We show that yes“.
