Antarctic ocean circulation slowing ahead of schedule

New research indicates that the circulation of waters to the deepest parts of the ocean surrounding Antarctica, driven by climate change, is occurring earlier than expected. The accelerated melting of Antarctic ice and rising temperatures, primarily caused by greenhouse gas emissions, are predicted to have a significant impact on the global network of ocean currents, which transport nutrients, oxygen, and carbon. This not only poses a threat to marine life but also jeopardizes the ocean’s crucial role in absorbing carbon dioxide and heat.

Previously, a computer model-based study suggested that the “overturning circulation” of deep ocean waters would slow by 40 percent by 2050 if emissions continued to rise. However, the new research, based on observational data, reveals that this process has already slowed by 30 percent between the 1990s and 2010s.

Lead author Kathryn Gunn from the Australian Science agency CSIRO and Britain’s Southampton University expressed concerns about the implications of these findings. Antarctica’s deep ocean plays a vital role as a key “pump” for the global network of ocean currents. As the ocean circulation slows down, more carbon dioxide and heat are retained in the atmosphere, creating a feedback loop that amplifies global warming.

While the occurrence of these changes is not surprising, the accelerated timeline is unexpected. The remote nature of the region, along with limited data and various challenges for scientific research, such as securing funding and facing extreme conditions at sea, has made it difficult to fully understand the transformations taking place. To overcome these limitations, the researchers utilized observational data collected by hundreds of scientists over several decades and supplemented it with computer modeling techniques.

Carbon storage

Oceans play a crucial role in regulating the climate by absorbing a substantial amount of the carbon dioxide and heat generated by human activities since the mid-1800s. However, due to global warming, sea surface temperatures have risen to unprecedented levels, and melting ice sheets are releasing large quantities of freshwater into the ocean.

These changes are disrupting the vital life support function that the ocean provides to marine life. A recent study published in the journal Nature Climate Change has revealed a decrease in the amount of oxygen reaching the deep ocean. Deep-sea creatures are adapted to low oxygen conditions but still require oxygen to survive. The loss of oxygen may force these organisms to seek refuge in different regions or alter their behavior, leading to impacts on biodiversity and food webs.

Moreover, the changes in ocean circulation patterns are expected to reduce the ocean’s capacity to absorb carbon, while also bringing to the surface carbon that has been stored in the deep ocean for hundreds of thousands of years.

Ariaan Purich from Australia’s Monash University, who was not involved in the study, highlighted the significance of the research. It provides observational evidence supporting the idea that the melting Antarctic ice sheet and shelves will affect the global ocean overturning circulation, which will have important implications for the absorption of heat and carbon by the ocean.

Overall, these findings underscore the far-reaching consequences of climate change on the oceans, impacting marine life, carbon absorption, and the delicate balance of Earth’s climate system.

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