Salt delivery from the Indian Ocean helped end the ice ages

Jessica Wiseman
Thursday 12 January 2023

Scientists from the Universities of St Andrews and Cardiff, along with international colleagues, have discovered the source of warm super salty water that rushed up the Atlantic 15,000 years ago, ushering in the end of the last ice age.

The study, which was published in Nature, comes as ocean temperatures are reaching record highs and waters in the Atlantic and Southern Oceans become fresher due to ice sheet melt, which could further impact ocean circulation and global climate.

The team measured the chemical fingerprints locked in microscopic fossil shells to reconstruct the temperature and salinity of the seawater in which the shells grew. By taking samples of these fossils going down a 40-metre-long core of deep-sea-mud, they were able to fathom the history of ocean temperature and salinity during each ice age cycle of the last 1.5 million years.

The results show that during the peak of each ice age, waters in the Indian Ocean became super charged with salt. The scientists show that this was driven by a restriction of the fresh-water currents that usually enter the Indian Ocean from the Pacific, allowing the Indian Ocean to become saltier, like a giant salt pan.

The salty waters remained trapped in the Indian Ocean until the end of the last ice age, when a shift in winds and currents allowed them to burst into the Atlantic. This in turn helped re-establish the Atlantic current system that warms the UK and Northwest Europe from its weakened glacial state.

Warm salty currents continue to flow through the Atlantic today yet are starting to weaken due to input of freshwater from melting ice sheets, which could trigger a series of knock-on climatic impacts.

Dr James Rae, from the School of Earth and Environmental Sciences said: “Our work shows how different parts of the climate system are surprisingly inter-connected. Changes in circulation and salinity in one part of the ocean can have huge impacts on the other side of the planet, so we need to stop global warming to prevent further disruption to these critical circulation systems.”

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