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Frosty Times for Dinosaurs: Major Fall in Temperature 137 Million Years Ago



I thought this might be of interest to some.

Journal Reference:

1.G. D. Price, E. V. Nunn. Valanginian isotope variation in
glendonites and belemnites from Arctic Svalbard: Transient glacial
temperatures during the Cretaceous greenhouse. Geology, 2010; 38 (3):
251 DOI: 10.1130/G30593.1


http://www.sciencedaily.com/releases/2010/09/100914074816.htm

Frosty Times for Dinosaurs: Major Fall in Temperature 137 Million
Years Ago During Cretaceous Greenhouse Period, Evidence Shows


ScienceDaily (Sep. 14, 2010) — A major drop in temperature 137 million
years ago briefly interrupted the warm, equable climate of the
Cretaceous Period. The water temperature in the Arctic Ocean fell from
around 13°C to between 4 and 7°C, possibly causing the poles to freeze
over.

Gregory Price from the University of Plymouth, UK and Elizabeth Nunn
from Johannes Gutenberg University Mainz, Germany investigated rock
samples with fossil belemnites and glendonites from Svalbard in order
to determine the temperature of the Arctic Ocean between 140 and 136
million years ago. Such paleoclimate reconstructions help to improve
predictions for future climate and environmental development and to
gauge the impact of the human race on climate. The temperature of the
oceans plays an important role in the history of the Earth's climate.

Current findings indicate that the global climate during the
Cretaceous Period was warm and equable with high atmospheric CO2
values, although scientists have already speculated that this global
warmth may have been punctuated by colder episodes.

The latest research carried out by Price and Nunn shows that there was
a brief cold episode approximately 137 million years ago.
"Temperatures fell drastically compared with the average water
temperatures of 13°C or even 20°C in the Arctic region during the rest
of the Cretaceous Period," states Nunn. Dinosaurs inhabited the polar
regions during the Cretaceous greenhouse period. While marine reptiles
such as pliosaurs and ichthyosaurs may have migrated with the onset of
the cold snap, it is not clear how dinosaurs would have handled the
colder conditions.

During the course of their work, Nunn and Price investigated rock
outcrops on Svalbard, which provide an ideal sequence of marine
deposits offering paleontologists insights into a time when the area
was still a flat sea. Some rock layers from the Valanginian Stage of
the Lower Cretaceous are rich in belemnites, i.e., fossils reminiscent
of modern squid, and glendonites, calcium carbonate crystal aggregates
of between two and three centimeters in size. Scientists can use these
relics to determine the relationship between two oxygen isotopes and
use these findings to draw conclusions about the water temperature.
"If global temperatures fall, the oxygen isotope O16 is increasingly
incorporated into polar ice and the isotope O18 is consequently
enriched in the seawater relative to O16. Belemnites and glendonites
store this ratio," Nunn explained.

Dr Elizabeth Nunn joined the Department of Applied and Analytical
Palaeontology in the Mainz Institute for Geosciences from the
University of Plymouth two and a half years ago. She is currently
carrying out research to determine whether, and to what extent,
seasonal temperature fluctuations occurred during the Early Cretaceous
interval. Such changes from summer to winter values or vice versa are
probably recorded during the short life span of the belemnites -- they
probably only lived between one and three years -- and could be
identified today using modern analytical methods.