When uranium hits the news, it’s usually as the bad guy: an element
that can fuel bombs and emit dangerous radiation over millennia. But
oceanographers like Candace Major and Jerry McManus
are putting the slow decay rate of this rare but widespread element to
a good use: understanding ocean circulation, especially how the
ocean-climate system worked in the past. Major described some of her
work at a press conference Wednesday morning and in a scientific session that afternoon.
issue is the way that water flows through the Atlantic Ocean, bringing
heat from the tropics north to warm the climate over Europe. As uranium
in that water decays, it forms two different products that settle onto
the sea bottom. By analyzing differences in the buildup of the two
products, ocean scientists can gauge how much water was flowing through
the ocean currents at particular times in the past.
the end of the last ice age (about 23,000 years ago) stronger Atlantic
currents have corresponded with warmer temperatures, a study found last year.
Major and her colleagues did more work to see if the ocean-climate
system worked the same way 30,000 to 60,000 years ago, during the
last ice age.
It’s a valid question considering how different the
oceans must have been when glaciers covered much of the Earth. Sea
levels were 120 m (almost 400 feet) lower, meaning ocean currents might
have flowed differently and exerted a much different effect on the
Major analyzed uranium decay products in Atlantic
sediments and matched them against estimates of temperature for the
period she studied. Her results showed that during warm periods in the
last ice age, Atlantic currents were carrying about as much water as
they do today. Cooler climate periods were accompanied by weaker
currents. The results are a further suggestion that watching ocean
circulation -- particularly in the North Atlantic -- is a prudent way
to keep tabs on Earth’s climate.
Rising Sea-Level Caused Sudden Flood?
Could the Black Sea have been the site of Noah’s flood many centuries ago? The idea has been intriguing but the evidence scanty ever since William Ryan, of Lamont-Doherty Earth Observatory, and colleagues proposed the idea in 1997. On Wednesday, Liviu Giosan spoke about new evidence he had collected with Ryan and Mark Siddall of the University of Bern, Switzerland.
Today, the Black Sea flows into the Mediterranean through a narrow strait called the Bosporus. Ryan suggested that about 9,200 years ago, as ice sheets retreated across northern Europe, that strait was actually a dam that kept out salty Mediterranean waters. As glaciers melted worldwide, sea level rose until water on the Mediterranean side of the dam was up to 70 m (230 feet) higher than in the Black Sea. When the dam broke, it would have unleashed a deluge that, if not precisely Biblical in proportion, would have lasted at least 30 years and flooded early human settlements around the Black Sea shore.
To look for evidence, Giosan, Ryan, and their colleagues boarded their own ark (actually a research vessel) and used bathymetric and seismic instruments to make detailed maps of the seafloor around the Bosporus. They uncovered a pattern of erosion and sedimentation that had the unmistakable shape of a river delta: a broad main channel fanning out into a network of branches. Between the channels were rows of low, muddy rises in the sea bottom that resembled the way sediments collect when a river floods its banks.
Earlier investigations of Ryan’s theory looked for evidence of ancient settlements submerged along an old shoreline. But Giosan, a geologist who specializes in river deltas, said he thought it made more sense to look for clues at the scene of the flood.