66 Million Years of Data Suggests, Global Heating Means Faster Ocean Currents

The University of Sydney's Professor Dietmar Müller and Dr Adriana Dutkiewicz have gone even further back to fill in the gaps. Dutkiewicz and Müller show in Geology that massive deep-sea currents have increased throughout warm epochs, meaning that we should anticipate this to happen again. "To date, the ocean has absorbed a quarter of human CO2 and over 90% of the related extra heat," says Dutkiewicz.

However, we know nothing about the long-term consequences. "The satellite data typically used to feed ocean models only covers a few decades," Dutkiewicz noted, "resulting in a lack of understanding of longer-term ocean variability." Dutkiewicz and Müller analyzed the accumulation of plankton seashells at 293 sites on continental shelves and in the deep ocean over the last 66 million years. They were particularly interested in hiatuses, which occur when strong currents sweep away material that would otherwise collect.

Due to the dispersed character of the sites, simultaneous hiatuses at numerous locations imply a speeding up of the deep currents rather than more local factors. Some of the findings may be related to well-known events, such as the enlargement of the Drake Passage and the space between Tasmania and Antarctica, which allowed the Antarctic Circumpolar Current to form a little more than 30 million years ago. The most immediately relevant discovery is that deep ocean hiatuses have decreased over the last 13 million years as the Earth has entered a long-term cooling phase.

This indicates that abyssal currents have slowed over time. Nonetheless, Dutkiewicz and Müller were able to detect spikes indicating faster current movement during this phase, which coincided with known warm times. Because the majority of sites are included in this time period, and only a few drill holes date back to the start of the study, the more recent data is also more credible. According to the article, greater currents during warm periods are generated by stronger winds blowing over surface waters at this time, as well as less ocean stratification.

"Independent studies using satellite data indicate that large-scale ocean circulation and ocean eddies have become more powerful over the last two to three decades of global warming," Müller said. As ocean circulation improves, climate scientists will be able to update their forecasts of how rising global temperatures would affect local climates.

Study on deep-sea currents and climate change done by Professor Dietmar Müller and Dr. Adriana Dutkiewicz at the University of Sydney. A crucial but little understood feature of climate change, the researchers sought to determine if increasing surface temperatures might impact the movement of deep-sea currents. To determine how deep-sea currents have altered over millions of years, dating back to the time of the dinosaurs, researchers looked at the geological record. They found that enormous deep-sea currents increased throughout hotter epochs. This conclusion shows that if surface temperatures continue to rise owing to human-induced climate change, we should expect a corresponding increase in deep-sea currents.

The absence of long-term data on deep-sea currents was noted by the researchers. Since just a few decades' worth of satellite data is included in current ocean models, they are insufficient to comprehend longer-term ocean variability. Müller and Dutkiewicz examined the accumulation of plankton seashells at several places during the last 66 million years in order to get around this constraint. Hiatuses, which are times when powerful currents sweep away material that might otherwise gather, were the subject of their particular attention.

The researchers conclude that as our understanding of ocean circulation improves, climate scientists will be able to refine their predictions of how rising global temperatures will impact local climates. This research contributes to addressing the fundamental question of how deep-sea flows are affected by climate change and provides valuable insights into the long-term consequences of increasing greenhouse gas levels and rising temperatures.