“Young Get Older, but Old Get Younger”: Counterintuitive Ocean Waters
Warming surface waters and increased stratification result in uneven loss of dissolved oxygen across the Pacific basin that shifts water mass age.
A recent study published in AGU Advances reveals an unexpected twist in ocean circulation patterns due to climate change. According to the research led by scientists at the University of California, Santa Barbara, warming ocean temperatures will cause higher-oxygen regions in the subtropical North Pacific to lose dissolved oxygen, while lower-oxygen areas in the Tropical Pacific will gain oxygen.
This counterintuitive result, dubbed "young gets older, but old gets younger," is the result of a slowdown in vertical ocean currents caused by a combination of factors. Pacific basin warming and heat forcing from the remote Southern Ocean are jointly responsible for the changes.
As the Pacific basin warms, the upper layer of the ocean becomes more compressed, reducing the ventilation along the North Pacific ventilated thermocline. At the same time, warming in the mid-latitude Southern Ocean is remotely reducing the upwelling of old, low-oxygen water in both the Tropical and North Pacific regions. Together, these changes set up a situation where younger waters become older, while older waters become younger.
The study's authors, including researchers from the University of California, Santa Barbara and other institutions, used a climate model to project future ocean circulation and dissolved oxygen changes in the Pacific basin. The results show a clear pattern of deoxygenation in the subtropical North Pacific and oxygenation in the Tropical Pacific, with significant implications for marine ecosystems and fisheries.
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