Top Layers of the Pacific Ocean Were Mixed Over the Last Ice Age, According to New Fossil Coral Data

The Tasman Sea, which separates Australia from New Zealand, is a crucial but hitherto ignored part of the world's ocean conveyor belt.

According to recent research, this marginal sea in the South Pacific was crucial to the movement of water masses between the major ocean basins during the last ice age.

An international team of researchers led by geoscientist Dr. Torben Struve from the University of Oldenburg published their findings in the journal Nature Communications.

These results will aid in the improvement of climate models as well as our knowledge of ocean circulation and carbon storage in the sea.

Overturning circulation of the pacific

(Photo : Kitera Dent/Unsplash)

The stony coral Desmophyllum dianthus was investigated in 62 fossilized specimens for the study.

These were gathered at a depth of between 1,400 and 1,700 meters by the remotely controlled underwater vehicle JASON during a research excursion south of Tasmania.

These creatures lived between 10,000 and 70,000 years ago, between the height and conclusion of the last glacial epoch, according to dating analyses.

Struve, a researcher in the Marine Isotope Geochemistry department at the University of Oldenburg's Institute for Chemistry and Biology of the Marine Environment, stated that corals thrive in regions with strong currents and turbulence that prevent the accumulation of silt.

The ratio of distinct isotopes of the trace element neodymium, some of which are created by radioactive decay, and are referred to as radiogenic isotopes, was the specific focus of the researchers' investigation.

The comparatively high concentration of radiogenic neodymium in the coral samples suggested, according to the research, that water from the Pacific Ocean flowed through the depths of the Tasman Sea during the height of the last ice age.

Investigations also revealed that, in comparison to other water masses in the same depth range, this Pacific water had just recently come into touch with the sea surface, or that it had been relatively "new."

The data, according to the team's paper, supports a scenario in which the upper Pacific Ocean was more mixed than it is today during the last ice age, while at the same time the deepest layers were more isolated from the atmosphere, which helped to store carbon dioxide over a long period of time and create the colder glacial climate.

The new research suggested that the last glacial period's circulation patterns would have like this: in the North Pacific, surface water sunk to a depth of roughly 2,000 meters before spreading far southward.

This water might have entered the Indian Ocean, where it would have joined the global "conveyor belt," after flowing through Tasmania, an Australian island.

Also Read: Sea Ice and Circulation: North Pacific Sea Ice Plays Significant Role, New Research Says

The Deep Water that Leaves the Atlantic Is Replaced By What?

A warm-water route and two cold-water channels are the three major ways that water may replenish NADW and return to the North Atlantic.

The migration of surface and thermocline water from the Pacific to the Indian Ocean via the Indonesian Seas is the start of the "warm-water pathway".

Both cooler return flows involve the aforementioned Antarctic Intermediate Water (AAIW).

Through the Drake Passage between Antarctica and South America, AAIW reaches the southern South Atlantic, with some of its water flowing into the Atlantic and some into the Indian Ocean.

The other branch of AAIW meets the warm-water flow and continues westward towards Africa where it reaches the Indian Ocean from south of Tasmania, before reaching southern Africa.

AAIW from the Drake Passage, flowing over Tasman AAIW, combines with surrounding water as it travels to the North Atlantic and adds to the "warm-water path".

High northern latitudes receive a substantial amount of heat from these return flows.

The deep Atlantic's southerly water flow and its shallower return flow together make up a significant portion of the so-called global Meridional Overturning Circulation (MOC).