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



Oh now that's funny... (as I've suspected for too long)  It looks like
the Cretaceous (and the Mesozoic in general) may very well have
suffered from something akin to Dansgaard-Oeschger events... Killer.

If anyone has access to this paper, please, send it my way. I'd most
appreciate it.

One of the most important things to be resolved before seeking a cause
is to determine whether or not this cooling was regional or global.
The answer to that makes all the difference.  I'll point to the
Younger Dryas as an example of why this matters; a cold snap that
happened between 12.9 and 11.6 thousand years ago while the earth was
warming up from its last glaciation.  A new study that surfaced in
2010 compiled over 100 high-resolution proxy records from all over the
world to nail down the timing and extent of the Last Glacial Maximum
and the deglacial that took place after, including the short-lived and
annoying Younger Dryas cold snap.  One of the conclusions relevant to
the Cretaceous event is that the Younger Dryas, which was once assumed
to have been a widespread global cooling event, was actually confined
to the northern hemisphere.  In fact, the tropics, showed little
temperature change, if any at all, and the southern hemisphere
actually warmed. This means that the dynamics and cause(s) behind the
Younger Dryas were of a different order than those behind global
climate changes, which generally follow a pattern of the entire world
heading down a warming or cooling trend.

The article on the Cretaceous event is using samples only from
Svalbard.  So it is unknown whether or not the cooling was regional or
global. If we assume regional, as in confined to high latitudes in the
Northern Hemisphere (which right now I'm thinking was the case until
more evidence is presented), then we should consider looking at the
millennial-scale climate changes during the last glaciation, not for
direct comparison, but as generalized models for the hows and the
whys. The many abrupt climate swings that took place during this time
are seen as being driven/kicked off by internal dynamics, such as
changes in ice cover and changes in ocean circulations (not solar and
not directly greenhouse gases).  These temperature changes, therefore,
are ruled by changes in temperature distribution, which are explained
via changes in atmospheric and oceanic heat transport, rather than
changes in overall global temperature. This is not the same as global
climate changes, which are understood as being caused by perturbations
to the global energy balance (this would be your solar and greenhouse
gases).

Furthermore, past millennial-scale climate changes that we can
reconstruct fairly well have been confirmed to function kinda like a
see-saw; the northern hemisphere cools while the southern hemisphere
warms.  Granted, this pattern sometimes is not in perfect sych, but
appears to exist, nevertheless. So, it would be really neato to know
what was happening with temperature in the southern hemisphere at the
time of the Cretaceous cooling. If we get an answer to that question,
then a much better understanding of the ocean circulation during the
Cretaceous could possible be figured out. I say this because data
clearly point to changes in ocean heat transport as the primary reason
behind abrupt climate changes, at least during the past 40,000 yrs of
so in Greenland. This also goes back to my first statement about
understanding whether or not the Cretaceous event was global or
regional.

Although comparing the atmospheric and oceanic dynamics of the last
couple of hundred thousand years to the Mesozoic is like comparing
lemons to oranges, right now, my money is on changes in ocean
circulation as the culprit behind the cooling in the Cretaceous.  If
we base what happened in the Cretaceous after the known atmo-ocean
changes that occurred during the last glaciation, then it was changes
in internal dynamics, such as the re-organizations of ocean
circulation that caused the cooling. (Keep in mind that the cooling
over the land masses was likely larger than that of the ocean since
the ocean is typically less sensitive to temperature change than
landmasses.) What would have kicked that off???  I haven't the
foggiest idea... In fact, we still don't know for sure what caused the
changes in ocean circulation during the abrupt climate changes during
the last ice ages, and that was only a few hundred thousand years ago,
not tens of millions. So, put that into perspective.

At this point, I will go ahead and sound like a crack pot for a
moment... blame it on my profession... as say that I am a fan of the
idea of ice existing at the poles from time to time during the
Mesozoic.  So not only am I very interested to see what Dr Nunn can
find out about seasonal changes, but if ice was there from time to
time, then the Cretaceous cooling event may have been very much like a
Younger Dryas event... Yes, it's time to take my "special" medicine.

Kris

(Nearly everything I said here hinges on gaining a better
understanding of ocean circulation during the Mesozoic. Couple that
with the fact that there are key parts of the ocean cirulation today
that we don't fully understand... parts that play huge roles in
climate. Talk about shooting from the hip with this one... But, that's
ok. One is allowed to shoot from the hip as long as there is good
aim.)

Broecker, W.S., Denton G.H., Edwards L.R., Cheng H., Alley R.B.,
Putnam A.E., 2010. Putting the Younger Dryas cold event into context.
Quaternary Science Reviews , 29, 1078-1081




On Wed, Sep 15, 2010 at 12:41 PM, kelly wicks <kwicks78@gmail.com> wrote:
> 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.
>