Cretaceous Arctic and Alaskan Temperatures

From: Stan Friesen [swf@ElSegundoCA.ATTGIS.COM]

From: Lightwaves@aol.com
> I have to ask, where was Alaska at the time? I mean in the continental
> positioning scheme during the Cretaceous. Was it farther south, north, east,
> or west of the present position?

It was not much different - it has rotated a little, and moved a little west since then. The particular location where the dinosaurs were found, the North Slope, was actually slightly further north (if I remember correctly).

> Also, the surrounding ocean temps played a
> role, didn't it? Global weather patterns surely were very different.

Absolutely. The Late Cretaceous had a "hothouse" climate. That is global temperatures were notably higher than now. (But if the greenhouse warming continues we may get to see what it was like first hand).

The best estimate is that the North slope climate was cool temperate, maritime. That is on the cool side, but with very little freezing, even in winter.

> Were
> there not many more shallow seas, globally?

Not by the Late Maastrichtian - most of the inland seas had receded by then.

From: Elisabeth Brouwers [brouwers@gdsvr1.cr.usgs.gov]

Thanks to Stan Friesen, someone is reading the papers!!!

The North Slope was at least at 70 degrees north (the present latitude), and some paleomag measurements from sedimentary rocks in the foothills of the Brooks Range indicate that paleolatitude could have been as much as 85 degrees north.

The deltaic setting was right next to the Beaufort Sea, which probably did play an ameliorating role in climate. That is probably why the climate was mild temperate and not colder--after all, because of the high latitude, the winters had to be dark, and probably dusk for part of the fall and spring. There has been some oxygen isotope paleotemperature work, but it is not consistent and has not been published. One study showed a tropical ocean, which is not consistent with the marine fossils, and one recently by Mike Arthur showed a more temperate temperature range.

The seaway that extended from the Arctic to the Gulf of Mexico had indeed receded to a small remnant in the Western Interior U.S. by late Cretaceous. By the end of the Cretaceous the Arctic Ocean was isolated because the seaway receded and a connection with the Atlantic was closed--the Pacific connection did not reopen until about 3 million years [ago], during the Pliocene. The Atlantic seaway looks like it was open around the Paleocene or Eocene.

The first evidence of ice in the Arctic is in the Pliocene--Alaskan fossils indicate about 2.4 my for the first real frigid marine animals in the fossil record.

From: Thomas_R_HOLTZ@umail.umd.edu (th81)

>Out of curiosity, anybody know when the ice cap(s) first formed?

There have been several different periods of ice cap formation. The current northern ice cap was probably not permanent year-round until about 2 million years ago. During the Pliocene, for example, the Arctic Ocean was almost certainly ice free during the summer.

Antarctica is more ambiguous, though. Some evidence points to a similar age (c. 2 Ma) for permanent ice formation, other to 8 or more million years ago.

Given the ameliorating effects of oceanic highstands (say THAT 3 times fast), the Cretaceous may have been ice free year round (except for mountain tops, etc.).

From: "Bonnie Blackwell, x 3332" [bonn@qcvaxa.acc.qc.edu]

evidence suggests that the antarctic cap formed about early-mid eocene maybe as old as 45 Ma, but more likely about 35 Ma. the greenland cap is much later, probably about 5-10 Ma.

From: Dinogeorge@aol.com

In a message dated 95-10-13 11:40:35 EDT, Thomas_R_HOLTZ@umail.umd.edu (th81) writes:

>The shallow seas were probably the major factor in keeping more stable, less
>variable continental temps. during the later Mesozoic. The middle
>Cretaceous is one of the greatest oceanic highstands in the last 500 million
>years, and even the Late Cretaceous was fairly flooded.

So it puzzles me why the Bering Strait is said to have opened and closed so often to let all those dinosaurs cross over from Asia to North America and vice versa, if the sea level was so high. I think the Bering land bridge was mostly unavailable during the Late Cretaceous because of the high sea level, which means the Mongolian and North American dinos of that time were not as closely related as we might think. Same families, yes; same genera, very doubtful, even in the case of Saurolophus osborni and Saurolophus angustirostris. Do you know of any references documenting geological evidence that the Bering land bridge was open (i.e., above sea level) during the Mesozoic after the Campanian?

From: Thomas_R_HOLTZ@umail.umd.edu (th81)

Of course, the configuration of NE Siberia and Alaska during the Late Cretaceous is yet to be resolved. Alaska, and possibly Siberia, include a LOT of accreted terrain, so it is uncertain what the land looked like back then. Also, given the various orogenies going on in that region, even today, there is no sure way (save some intensive, yet-to-be done geologic and paleontologic field work) to establish when and where the Asia-American connection of the Late Cretaceous was extant.