NOAA Paleoclimatology slide sets.

Wandering about more in a completely casual, amateurish way, I found a rather interesting citation. It says, in short, that an Antarctic meltwater pulse at the end of the last ice age strengthened North Atlantic Deep Water (NADW) formation, thereby warming the North Atlantic, which caused a pulse of meltwater from the Laurentide and Fennoscandian ice sheets, which then shut down the NADW, thus causing the Younger Dryas. Got that?

The Younger Dryas is an anomalous 1300 year cold snap just after the end of the last ice age. It seems to have begun and ended with astonishing rapidity, and involved a 7 degree C temperature drop globally in as little as 20 years. Essentially, the world emerged from the last ice age briefly, and then snapped back into and out of it.

Oh, the Bolling-Allerod of this entry’s title is the interstadial (that is, warm period) that ended the last ice age.

Here’s the cite (It’s from PubMed, here):

1: Science. 2003 Mar 14;299(5613):1709-13. Related Articles, Links

Comment in:

* Science. 2003 Mar 14;299(5613):1645.

Click here to read
Meltwater pulse 1A from Antarctica as a trigger of the Bolling-Allerod warm interval.

Weaver AJ, Saenko OA, Clark PU, Mitrovica JX.

School of Earth and Ocean Sciences, University of Victoria, Post Office Box 3055, Victoria, British Columbia V8W 3P6, Canada. weaver@uvic.ca

Meltwater pulse 1A (mwp-1A) was a prominent feature of the last deglaciation, which led to a sea-level rise of approximately 20 meters in less than 500 years. Concurrent with mwp-1A was the onset of the Bolling-Allerod interstadial event (14,600 years before the present), which marked the termination of the last glacial period. Previous studies have been unable to reconcile a warm Northern Hemisphere with mwp-1A originating from the Laurentide or Fennoscandian ice sheets. With the use of a climate model of intermediate complexity, we demonstrate that with mwp-1A originating from the Antarctic Ice Sheet, consistent with recent sea-level fingerprinting inferences, the strength of North Atlantic Deep Water (NADW) formation increases, thereby warming the North Atlantic region and providing an explanation for the onset of the Bolling-Allerod warm interval. The established mode of active NADW formation is then able to respond to subsequent freshwater forcing from the Laurentide and Fennoscandian ice sheets, setting the stage for the Younger Dryas cold period.

PMID: 12637739 [PubMed]

Ah, disaster: it’s so much fun. I’ve long had an interest in geology, and that led in turn to related areas, such as glaciology, paleoclimatology, and the like.

Vredefort dome, South Africa
Space shuttle image STS51I-33-56AA

I just watched the movie, The Day After Tomorrow, and following that I was browsing the net, checking out what has been found in the attempt to piece together the transition from the last ice age to this most recent of interregnums, our warm period, the Holocene. And of course one finds on the net plenty of scientific information, but also a plethora of wacky obssession with doomsday scenarios. It’s a curious propensity, this fascination with events approaching from the periphery of human consciousness and memory. Shadows from beneath the bed.

The biggest local cosmic train wreck so far? The Vredefort dome.

Where else would one find descriptions as colorful as this (from the link above):

This ring of hills comprises quartz conglomerates as found in the gold-bearing strata of the Witwatersrand reefs.

Village, Vredefort dome, South Africa

Village stones, Vredefort dome, South Africa

Photos from
Hartebeesthoek Radio Astronomy Observatory

The white quartz pebbles are evident. This was once the bed of a fast flowing water course which
deposited grains of quartz and the pebbles. This area was mined for gold in the 1880’s. However the concentration of gold was much poorer than at Johannesburg, and the diggings were soon abandoned. Old mine adits are still to be seen in the hills. This is the Amazon Reef.

The outermost ring of hills was home to a quite different group of people in the 1500’s to 1700’s. These were SeSotho/SeTswana-speaking farmers. This village at Askoppies was a defensive position on the crest of the hill, but it did not save the village from destruction, by the warriors of Mzilikazi. The view shown above left looks east, back in towards the inner rings of the Vredefort dome.

The stone walls of the village are shown above right. They are made of the fine-grained grey Ventersdorp lavas that comprise this ridge. These rocks are 2700 million years old.

of illustrative climate-change related charts is here (I’ll try to include attributions later, but most are from the excellent American Scientist article cited in the graph caption, below).

My favorite of these? The chart that shows anthropogenic induced change in the atmospheric concentration of C02. The two graphs shown are derived from an ice core from Vostok, Antarctica. The top chart is of deuterium, a proxy for temperature. The bottom is of CO2, parts per million. The time scale at the bottom is in thousands of years before the present.

Vostok Ice Core, Antarctica, 0 to 160,000 years before present
Top chart is deuterium (per mil).
Bottom chart is C02 (parts per million by volume).

Graphic from “Rapid Climate Change,” Kendrick Taylor,
American Scientist, July-August, 1999.

The Holocene is the 10,000 or so year-long warm period that we’re living in now. The cold stretch of 125,000 years prior to the Holocene is the most recent Pleistocene era glaciation, know as the Wisconsin ice age in North America. Just before the Wisconsinin is the Eemian, another brief warm spell like our own; and before that lies an earlier glacial period (but still lying within the 2 million year extent of the Pleistocene). The red spike on the left side, bottom chart is the increase in atmospheric C02 caused by humans in the industrial era, now 150 years old.

I’ve been reading a little more about the Younger Dryas, which was an abrupt state change in climate, probably global in scale, from warm back to cold, lasting for about 1300 years, and ending 11640 years before present. This AGU page describes the event:

The Younger Dryas (YD) was the most significant rapid climate change event that occurred during the last deglaciation of the North Atlantic region. Previous ice core studies have focused on the abrupt termination of this event [ Dansgaard et al., 1989] because this transition marks the end of the last major climate reorganization during the deglaciation. Most recently the YD has been redated–using precision, subannually resolved, multivariate measurements from the GISP2 core–as an event of 1300 +/- 70 years duration that terminated abruptly, as evidenced by an 7C rise in temperature and a twofold increase in accumulation rate, at 11.64 kyr BP [ Alley et al., 1993] (Figure 2). The transition into the Preboreal (PB), the PB/YD transition, and the YD/Holocene transition were all remarkably fast, each occurring over a period of a decade or so [ Alley et al., 1993]. Fluctuations in the electrical conductivity of GISP2 ice on the scale of <5-20 years have been used to reveal rapid changes in the dust content of the atmosphere during the same periods and throughout the last glacial [ Taylor et al., 1993b]. These rapid changes appear to reflect a type of “flickering” between preferred states of the atmosphere [ Taylor et al., 1993b], which provides a new view of climate change. Holocene climates are by comparison stable and warm.