Thursday, June 16, 2022

Deep, frigid Antarctic waters move north

Cold, high-density Antarctic Bottom Water sinks and spreads northward to fill the deepest parts of the Southern, Indian, Pacific, and Atlantic Oceans.
These waters have an important and near-global impact on deep-ocean circulation.
However, their paths north are only partially understood. In a new study researchers investigate the transport pathways of Antarctic Bottom Water from its four principal source areas northward, as it navigates obstacles like mid-ocean ridges, using a numerical simulation of Earth's oceans.
Identifying these pathways helps to predict where changes may be seen in coming decades. 

From Meteorological Tec. Int by Elizabeth Baker

Researchers in a new study, published in the AGU’s Geophysical Research Letters, used a numerical simulation of Earth’s oceans to investigate the movement of Antarctic Bottom Water (AABW), discovering that it moves via two distinct pathways (“conduits”) from its four principal source areas northward.

This study, named How Does Antarctic Bottom Water Cross the Southern Ocean?, also found that the geographical boundaries between the water’s conduits occur near seafloor ridges, and little AABW exchange occurs across them.
Circulation pathways within each conduit blend together AABW formed in two of the four main formation regions and export them to different oceans.
Identification of these pathways elucidates the origin of observed trends in AABW properties and helps to predict where these changes may propagate in the coming decades.

Cooling, ice formation and mixing near Antarctica create dense ocean waters, known as Antarctic Bottom Water, which is derived from dense water that forms in several distinct Antarctic shelf regions. Due to their high density, these waters sink and propagate northward to fill the deepest parts of the Southern, Indian, Pacific and Atlantic Oceans.

Previous modeling studies have reached conflicting conclusions regarding export pathways of AABW across the Southern Ocean and the degree to which AABW originating from distinct source regions are blended during their export.
This study addressed these questions using passive tracer deployments in a 61-year global high-resolution (0.1°) ocean/sea-ice simulation.
Two distinct export “conduits” were identified – Weddell Sea- and Prydz Bay-sourced AABW are blended together and exported mainly to the Atlantic and Indian Oceans, while Ross Sea- and Adelie Land-sourced AABW are exported mainly to the Pacific Ocean.

Northward transportation of each tracer occurs almost exclusively (>90%) within a single conduit. These findings imply that regional changes in AABW production may impact the three-dimensional structure of the global overturning circulation.
Hence AABW export has a significant and near-global impact on deep-ocean circulation and the distribution of physical properties (e.g., salinity, temperature, dissolved oxygen).

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