Researchers link ice-age climate-change records to ocean salinity

Oct 04, 2006
Researchers link ice-age climate-change records to ocean salinity
A planktonic foraminifera lives in the subtropical waters of the Atlantic Ocean. Credit: Howard Spero, UC-Davis/NSF

Sudden decreases in temperature over Greenland and tropical rainfall patterns during the last Ice Age have been linked for the first time to rapid changes in the salinity of the north Atlantic Ocean, according to research published Oct. 5, 2006, in the journal Nature. The results provide further evidence that ocean circulation and chemistry respond to changes in climate.

Using chemical traces in fossil shells of microscopic planktonic life forms, called formanifera, in deep-sea sediment cores, scientists reconstructed a 45,000- to 60,000-year-old record of ocean temperature and salinity. They compared their results to the record of abrupt climate change recorded in ice cores from Greenland. They found the Atlantic got saltier during cold periods, and fresher during warm intervals.

"The freshening likely reflects shifts in rainfall patterns, mostly in the tropics," Howard Spero of the University of California at Davis said. "Suddenly, we're looking at a record that links moisture balance in the tropics to climate change. And the most striking thing is that a measurable transition is happening over decades."

Spero, who is currently on leave at the National Science Foundation's Marine Geology and Geophysics Program, worked with lead author Matthew Schmidt of the Georgia Institute of Technology and Maryline Vautravers of Cambridge University in the United Kingdom to conduct the research.

During the Ice Age, much of North America and Europe was covered by a sheet of ice. But the ice records the scientists reconstructed show repeated patterns of sudden warming, called Dansgaard-Oeschger Cycles, when temperatures in Greenland rose by 5 to 10 degrees Celsius over a few decades.

Close to the tropics, warm, moist air forms a zone of heavy tropical rainfall, called the Intertropical Convergence Zone, which dilutes the salty ocean with fresh water. Today, the tropical rainfall zone reaches into the northern Caribbean, but during the colder periods of the Ice Age it was pushed much further south, towards Brazil. That kept fresh water out of the northern Atlantic, so it became more salty, Spero said.

The circulation, or gyre, in the North Atlantic moves warm, salty water north, keeping Europe relatively temperate. The deep ocean circulation is very sensitive to the saltiness of north Atlantic surface waters, Spero said. Warming climate, higher rainfall and fresher conditions can alter the circulation. During glacial times, reduced circulation caused climate to cool.

The new results show that as the climate cooled in Greenland, salinity rapidly increased in the North Atlantic subtropical gyre. The build-up of salt during these cold intervals when the conveyor circulation was reduced would have primed the system to quickly restart on transitions into warm intervals, Schmidt said. However, the actual trigger that caused Atlantic circulation to restart during the Ice Age is still unknown, he said.

Once warming began, melting ice sheets would have contributed fresh water to the Atlantic, but this would have been partly buffered by the elevated saltiness of the Atlantic.

Source: National Science Foundation

Explore further: Tree rings denote century-old weather patterns

Related Stories

Ice sheet collapse triggered ancient sea level peak

Jun 10, 2015

An international team of scientists has found a dramatic ice sheet collapse at the end of the ice age before last caused widespread climate changes and led to a peak in the sea level well above its present ...

The Arctic: Interglacial period with a break

May 28, 2015

Scientists at the Goethe University Frankfurt and at the Senckenberg Biodiversity and Climate Research Centre working together with their Canadian counterparts, have reconstructed the climatic development ...

Uncovering diversity in an invisible ocean world

May 27, 2015

Plankton are vital to life on Earth—they absorb carbon dioxide, generate nearly half of the oxygen we breathe, break down waste, and are a cornerstone of the marine food chain. Now, new research indicates ...

Recommended for you

ESA image: Northwest Sardinia

Jul 03, 2015

This image over part of the Italian island of Sardinia comes from the very first acquisition by the Sentinel-2A satellite.

Experiments open window on landscape formation

Jul 02, 2015

University of Oregon geologists have seen ridges and valleys form in real time and—even though the work was a fast-forwarded operation done in a laboratory setting—they now have an idea of how climate ...

NASA image: Canadian wildfires continue

Jul 02, 2015

Canada is reeling from an early fire season this year as dozens of fires ravage at least three provinces of the country. All of the following reports are as of July 2, 2015.

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.