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Re: Climate and Biogeography of Maastrichtian North America



The Gulf Stream as we know it wasn't established during the K. So, I'd
shy away from using it and/or its effects in the Mesozoic.

Off the top of my head… The thing to remember about the K ocean is
that unlike today, where large gyres dominate circulation, the K ocean
(and Paleogene) was filled with mesoscale eddies. Due to the lack of
constant Weasterlies (due to seasonal reversals of high lat pressure
systems, unlike today), there would have been no subtropical and polar
fronts in the ocean, no well-developed ocean pycnocline, and no
tropical subtropical gyres dominating ocean... only those mesoscale
eddies (for example, it's thought that a counter-clockwise eddy
existed off the west and east coasts of NA).  In fact, these eddies
probably were far from stable… The only steady ocean currents would
have been the equatorial systems which were forced by constant
Easterly winds.  At mid and high lats, however, the ocean would have
been filled with shallow eddies that were variable in both intensity
and position and would have been the means for transporting equatorial
heat northward.  The larger, more deeply penetrating eddies would have
been steered by bathymetry.  Furthermore, dramatically different ocean
water densities from those of today would have had a huge impact on
ocean circulations... K climate simulations indicate that for various
reasons, half of the entire ocean surface and deep water would have
had nearly the same density... Therefore, storm and wind-generated
eddies were the main pumps that moved water up and down the column
(unlike today's system driven by huge basin-crossing conveyors). This
eddy-ocean would have therefore lacked the highly-developed structure
we see in today’s stratified ocean... so the vertical circulation
would have been more local and chaotic. This happens to be a good
explanation for why there were periodic widespread anoxic events in
the K ocean. The present ocean structure is kept the way it is because
of constant wind systems, which in turn depend on the high degree of
stability in atmospheric pressure systems located in the polar
regions… which are forced by permanent icecaps... all of which the K
lacked…

So anyway… There was no Gulf Stream.  The Gulf Stream came into being
only after North and South America were connected via the Isthmus of
Panama... a mere 5 mya.  Prior to that time, North and South America
were not connected... a gap called the Central American Seaway allowed
warm tropical waters to flow between the Atlantic and Pacific Oceans.
The formation of the Isthmus of Panama partitioned the Atlantic and
Pacific Oceans, fundamentally changing global ocean circulation, and
in consequence global climate/weather...  The Pacific and Atlantic
salinities, which were once nearly the same, greatly diverged, with
the Pacific becoming relatively fresher, salinity steadily increased
in the Atlantic (Trade Winds also came about at roughly this time),
and over time the new northward-diverted current called the Gulf
Stream intensified, transporting a more warm, salty water mass high
into northern latitudes, where it was cooled by Arctic winds until it
became dense enough to sink to the ocean floor... giving birth to the
Ocean Conveyor, which in turn intensified the Gulf Stream in a
feedback loop that pulled even more water northward.

Kris


On Tue, Dec 20, 2011 at 2:55 PM, Renato Santos <dracontes@gmail.com> wrote:
> Dan,
>
> It really depends on the ocean currents,
> http://en.wikipedia.org/wiki/File:Corrientes-oceanicas.gif , and
> prevailing winds, http://en.wikipedia.org/wiki/Atmospheric_circulation
> : if there was a Gulf Current established by then I would expect a
> similar climate pattern, albeit accommodating for the interior sea
> way, with a tropical southeastern coast drying progressively
> northwards and inland.
>
> --
> Renato Santos
> http://dracontes.deviantart.com