Scientists Find Antarctica’s Deep Ocean Has Warmed Over the Last Two Decades

(SeaPRwire) –   According to a new multi-decade study, heat from the deep ocean is advancing toward Antarctica, offering definitive proof that the Southern Ocean is undergoing changes driven by climate change.

Published today in Communications Earth & Environment, the research cautions that this warming endangers the structural integrity of Antarctic ice sheets. As one of the planet’s most rapidly warming regions, Antarctica is seeing an acceleration in ice loss as the ocean warms, which in turn contributes to higher sea levels. In 2022, the global mean sea level hit a record, measuring four inches higher than in 1993. These results serve as a serious alert that major climate threats are developing in the deep waters around Antarctica.

“We see a strong signal in the observational data from recent decades showing that large water masses, holding substantial anthropogenic and general heat, are intruding upon the Southern Ocean near Antarctica. This is happening at the expense of the natural deep waters and is linked to the shrinking of Antarctica,” stated Ali Mashayek, a professor in the University of Cambridge’s earth sciences department and a co-author of the study.

This marks the first occasion scientists have documented this movement of deep-ocean heat across the Southern Ocean. Previously, a lack of sufficient data prevented the detection of this warming pattern. “Gathering observations in this area is extremely challenging,” explained Joshua Lanham, the study’s lead author. The team utilized data from research sites called transects, which collect measurements such as temperature and nutrient levels approximately every ten years. They enhanced this dataset with publicly accessible information from “Argo floats,” robotic instruments that supply ongoing data for the upper ocean. Using machine learning, they merged the Argo data with the long-term transect records to generate monthly reconstructions spanning the last forty years.

The analysis verifies a long-held suspicion among climate scientists: a warm body of water called “circumpolar deep water” has grown in size and moved closer to the Antarctic continental shelf over the last two decades. The ocean takes in about 90% of the surplus heat from global warming, and the majority of this is held in the Southern Ocean. The warming of waters beneath the ice sheets poses a risk to the stability of Antarctica’s ice shelves, which are crucial for holding back the inland ice sheets and glaciers from sliding into the sea.

“The primary way these ice shelves become unstable is through melting caused by warm water beneath them. This can remove their supporting role, leading to sea level rise. Therefore, the implications of this warm water moving poleward are highly significant,” Lanham said. “The total volume of fresh water locked in these inland glaciers has the potential to elevate sea levels by approximately 58 meters [190 ft.].”

The findings, however, were anticipated. “Broadly speaking, there is substantial, accumulated observational proof that the ice shelves are increasingly at risk,” Mashayek commented. “Our research demonstrates an observable trend indicating that additional heat is reaching Antarctica.”

The global mean sea level has increased by eight to nine inches since 1880, and this rate is speeding up as glaciers and ice sheets melt, pouring fresh water into the oceans. Rising seas from Antarctic ice melt heighten the threat of coastal flooding and can lead to more powerful storms.

The Antarctic ice sheets and the Southern Ocean are also vital for controlling the global climate system—alterations to Antarctica’s ice mass could influence weather phenomena such as El Niño. This study contributes to an expanding collection of recent research that records major transformations in the Earth’s polar oceans.

Separate research released earlier this month indicated that the Atlantic meridional overturning circulation (AMOC), a network of global ocean currents, is nearer to a breakdown than earlier estimates suggested. The system is weakening as Arctic air temperatures climb quickly due to global warming. A failure of this circulation would cause sea levels in the Atlantic to rise, displace the tropical rainfall belt essential for food production for millions, and bring exceptionally cold winters and summer droughts to parts of Europe.

The AMOC depends on the cold, dense water present in the Arctic and Antarctic. These cold waters descend into the deep ocean, fueling a global “conveyor belt” of deep-sea currents. As waters in both polar regions warm, this circulation is thrown off balance because warm, fresh water from melted land ice is less dense and does not sink as readily as cold, salty water.

“There’s a well-known saying that what happens in the Southern Ocean doesn’t stay in the Southern Ocean,” Mashayek cautioned. “The same applies to the Arctic. Both regions have massive global consequences that can manifest quite rapidly on timescales relevant to humanity.”