Summit County Citizens Voice

Warm, salty water from the south could balance impacts of melting polar ice cap

Agulhas Current system and its "leakage" into the Atlantic Ocean, affecting climate. Credit: Erik van Sebille, RSMAS.

By Summit Voice

SUMMIT COUNTY — Leakage from an ocean current running along the east coast of Africa could ameliorate some anticipated global warming impacts in the northern hemisphere, according to University of Miami researchers, who recently published a study in the journal nature suggesting that the Agulhas Current could be a significant player in global climate variability.

The Agulhas Current transports warm and salty waters from the tropical Indian Ocean to the southern tip of Africa. There most of the water loops around to remain in the Indian Ocean (the Agulhas Retroflection), while some water leaks into the fresher Atlantic Ocean via giant Agulhas rings.

Once in the Atlantic, the salty Agulhas leakage waters eventually flow into the Northern Hemisphere and act to strengthen the Atlantic overturning circulation by enhancing deep-water formation. Recent research points to an increase in Agulhas leakage over the last few decades, caused primarily by human-induced climate change.

That finding is profound because it suggests that increased Agulhas leakage could trigger a strengthening in Atlantic overturning circulation — at a time when warming and accelerated meltwater input in the North Atlantic has been predicted to weaken it.

“This could mean that current IPCC model predictions for the next century are wrong, and there will be no cooling in the North Atlantic to partially offset the effects of global climate change over North America and Europe,” said University of Miami Rosenstiel School of Marine & Atmospheric Science Oceanographer Lisa Beal. “Instead, increasing Agulhas leakage could stabilize the oceanic heat transport carried by the Atlantic overturning circulation.”

There are also paleoceanographic data to suggest that dramatic peaks in Agulhas leakage over the past 500,000 years may have triggered the end of glacial cycles.

These data are further evidence that the Agulhas system and its leakage play an important role in the planet’s climate, according to the study.

“This study shows that local changes in atmospheric and oceanic conditions in the Southern Hemisphere can affect the strength of the ocean circulation in unexpected ways,” said Eric Itsweire, director of the National Science Foundation (NSF)’s physical oceanography program, which funded the research.

“Under a warming climate,” said Itsweire, “the Agulhas Current system near the tip of South Africa could bring more warm salty water from the Indian to the Atlantic Ocean and counteract opposing effects from the Arctic Ocean.”

The study establishes the need for additional research in the region that focuses on Agulhas rings, as well as on the leakage, Beal said.

Climate modeling experiments are critical, she said, and need to be supported by paleoceanographic data and sustained observations to firmly establish the role of the Agulhas system in a warming climate.

“Our goal now is to get more of the scientific community involved in research on the Agulhas system and its global effects,” said Beal. “The emphasis has been too long in the North Atlantic.”

The Agulhas Current Time-Series Experiment, or ACT, was launched in April 2010 to measure the variability of the Agulhas Current using a combination of current meter moorings and satellite data.
Beal, who serves as chief scientist, spent one month aboard the research vessel Knorr in the southwest Indian Ocean deploying oceanographic instruments.

The data gathered in situ, when combined with along-track satellite information, will help increase our understanding of how the Agulhas system is changing in a warming climate, Beal said.

Filed under: climate and weather, Environment, global warming Tagged: | Agulhas Current, Atlantic Ocean, climate change, global warming, Gulf Stream, Indian Ocean, National Science Foundation, Northern Hemisphere, ocean currents, Summit County News