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Stronger inversion of circulation in the Pacific during the last ice age – Did it emerge because of that?

news7g07/12/2022

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Stronger inversion of circulation in the Pacific during the last ice age - Did it emerge because of that?

Data from fossil corals indicate changes in the circulation of ocean currents – an important finding for climate models

A peer-reviewed publication

UNIVERSITY OF OLDENBURG

Located between Australia and New Zealand, the Tasman Sea is an important but hitherto neglected component of the global ocean conveyor belt. Now a new study has discovered evidence that this marginal sea in the South Pacific also played an important role in the exchange of water mass between large ocean basins during the last ice age. . These findings will help improve climate models and advance our understanding of ocean circulation and marine carbon storage, said an international team of researchers led by geologist Dr. from the University of Oldenburg led the journal report Essential communication.

For their study, the researchers examined 62 fossil specimens of the stony coral Desmophyllum dianthus. They were collected by the JASON underwater remotely operated vehicle during a research expedition south of Tasmania at depths between 1,400 and 1,700 meters. According to dating analysis, these animals lived about 10,000 to 70,000 years ago, a period that includes the peak and end of the last ice age. Struve, who conducts research in the Marine Isotope Geology group at the Institute of Marine Environmental Chemistry and Biology at the University of Oldenburg, explains: “Corals grow in areas with strong currents and inhibitory disturbances. deposition of sediments.

Since the skeletons of these sedentary animals record the chemical fingerprints of the surrounding seawater, sophisticated analyzes can reveal the chemical composition of the oceans at respective water depths over time. coral life. This in turn provides clues about the volume of water flowing through the Tasman Sea at the time. “These cold-water corals are a particularly good repository for studying the chemical composition of past deep ocean currents,” explains Struve.

Young water flows through the depths of the Tasman Sea

In their study, the researchers focused specifically on the ratio of different variations of the trace element neodymium, some of which are produced by radioactive decay and are commonly referred to as radioisotopes. radiation. The analysis showed water from the Pacific Ocean flowing through the depths of the Tasman Sea around the peak of the ice age – indicated by the relatively high levels of radioactive neodymium in the coral samples. Surveys also show that this body of water from the Pacific Ocean has been in contact with the sea surface relatively recently compared with other bodies of water in the same depth range, or in other words, it is relatively “young” “. As the team writes in their paper, the data support a scenario in which the upper Pacific Ocean was more mixed during the last glacial period than it is today – while the deepest layers were also affected. more isolated from the atmosphere, which contributes to the long-term storage of carbon dioxide and a cooler glacial climate.

According to new research, circulation patterns during the last ice age would look like this: in the North Pacific, surface water sank to a depth of about 2,000 meters and then spread southward. After flowing around the southern pole of the Australian island of Tasmania, the water may have flowed into the Indian Ocean, where it joined the global “conveyor” of ocean currents and underpinned it. This conveyor plays an important role in the distribution of heat between different oceanic basins: the warm North Atlantic currents, for example, are responsible for the relatively mild climate of Northwest Europe. Europe. From the North Atlantic, the circulation extends through the Antarctic and Indian Ocean Currents to the northern Pacific Ocean – and then back again. In today’s system, the water in the North Pacific Ocean is the oldest, which means that the last contact with the surface occurred a long time ago.

The historical view allocates the return flow of this conveyor belt to the Indian Ocean primarily to a relatively shallow strait north of Australia. However, recent studies show that the flow of Pacific waters through the Tasman Sea is also significantly involved in water mass exchange between ocean basins – albeit at shallower depths than about the last glacial period. It is possible that up to half of the water flowing north in the global conveyor belt in the Atlantic today originates in the southern region of Australia. “Our study contributes to a better understanding of the dynamics of this global ocean circulation system under changing climates,” said Struve. There is now evidence that there is a strong link between changes in the Tasman deep currents and changes in circulation in the Pacific Ocean during the last ice age.