Tropical Oceans Were Overheated During Prehistoric
Greenhouse Effect
Netherlands Organization For Scientific Research
Tropical Oceans Were Overheated During Prehistoric Greenhouse Effect
Biogeochemists from the Royal Netherlands Institute for Sea Research
have shown that prehistoric tropical oceans were no less than five to
eight degrees warmer than they are now. Their findings have been published
in the December issue of the renowned American journal Geology.
During the mid-Cretaceous period, some 90 to 120 million years ago, the
seawater around the equator had a temperature of 30 to 37 degrees Celsius,
which is five to eight degrees higher than the temperature now. This was
revealed in research that used a new method to determine the temperatures
of oceans in the distant past.
The finding concurs with recently developed climate models, which indicate
that higher carbon dioxide concentrations in the greenhouse climate of
90 to 120 million years ago resulted in warmer tropical oceans. The biogeochemists'
findings reveal how seawater temperatures changed when large quantities
of greenhouse gases entered the atmosphere.
Scientists had suspected that seawater temperatures were significantly
higher then, but no method had been available to precisely determine these.
The new method is based on the chemical structure of membrane lipids
in archaea, which are also referred to as archeabacteria. These organisms
live in the surface waters of oceans. The composition of the membrane
lipids was found to depend on the seawater temperature. At higher temperatures,
the organisms produce greater quantities of lipid molecules containing
rings.
The researchers examined fossil remains taken from the floors of the
Atlantic and Pacific Oceans. The remains were located in deposits from
the mid-Cretaceous period, which is known for its very high concentrations
of greenhouse gases.
Earlier research by the biogeochemists had demonstrated that the membrane
lipids of archaea remained conserved in sediments. In a paper published
in Science two years ago, scientists described the discovery of fossil
remains containing membrane lipids 112 million years old. Since then the
researchers have found remains as old as 140 million years.
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