Mysterious Meltwater Pulse 1A


by Andre
Tags: meltwater, mysterious, pulse
Andre
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Mar10-06, 12:46 PM
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In another thread I murmured something about asymmetric climate problems at the end of the last ice age. Here, I’ll show three studies that form a big conflict together around a sudden sea level rise that is known as “Melt Water Pulse 1A”. Curiously enough one person, Prof Clark of the Oregon Uni, (co)authored all three of these papers. So I wonder if he wonders about those problems. Let’s start with the most recent one.

Clark et al (2004), Rapid Rise of Sea Level 19,000 Years Ago and Its Global Implications. Science 21 May 2004: 1141-1144

In which it is shown that clear geologic evidence exists that the great melting at the end of the ice ages started 19,000 years ago, which is a bit odd since the ice cores of Antarctica did not start to show any warming before 17,300 years ago, whilst the Greenland Ice cores waited until some 14,600 years ago. So Clark et al contend:

The initiation of warming at 19,000 years B.P. at Atlantic and Antarctic sites (Fig. 3, D to F) records this expected ocean response to the 19-ky MWP. In particular, we note that warming occurred at Antarctic sites before any substantial rise in atmospheric CO2 (23) and despite a gradual decrease in austral summer insolation.
We have two remarkable things here that the warming began some 2000 years before the CO2 rose, which is held responsible for a large role in that warming and second, that it was Antarctica that warmed and hence started to melt. Let’s keep that in mind when we look at a second study about that Meltwater Pulse 1A.

Weaver A.J. et al (2003) Meltwater Pulse 1A from Antarctica as a Trigger of the Bølling-Allerød Warm Interval 14 March 2003 Vol 299 Science pp1710 - 1713

Meltwater pulse 1A (mwp-1A) was a prominent feature of the last deglaciation, which led to a sea-level rise of about 20 meters in less than 500 years. Concurrent with mwp-1A was the onset of the Bølling-Allerød 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…
That’s pretty clear. If you scan the article you’ll see that Clark is amongst the authors and it’s also mentioned again that the warming in the south started as early as 19000 years ago. BTW this is not the only study that gives Meltwater Pulse 1A an Antarctic origin.

Also keep in mind that the current ice sheet of Greenland, central in the public interest, is good for a sea level rise of 7 meters. Apparently, Meltwater Pulse 1A was equivalent to the melting of almost three Greenland ice sheets within 500 years.

But now the third study:

Clark P.U. and Mix A.C (2002) Ice sheets and sea level of the Last Glacial Maximum, Quaternary Science Reviews 21 (2002) 1–7

We are interested in table 1 about the contribution of the several Ice sheets to the sea level rise. For Antarctica we see a series of 24,5 meters from the oldest studies to 14,0 meters in the more recent studies. Given the fact that there is hardly any tectonic post glacial rebound at Antarctica, that only land ice counts and that there is no room whatsoever to have 2-3 additional Greenland Ice sheets anywhere on the Antarctic continental shelf, 14 meters does seem to be quite a bit already. Now as the melting apparently started 19,000 years ago and lasted several thousand years as the end of the Ice age is marked at 11,600 years ago, you’d expect only millimetres per year from Antarctica but no, it was 20 meters in 500 years, meltwater pulse 1A.

But how can you write all those papers and not even mention that problem?
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georgemarvin2001
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Mar14-06, 03:07 PM
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GMP 1A happened suddenly; it was an anomaly, and it wasn't the only unusual event that happened at that time; the coral around Hawaii drowned, after having survived 400,000 years of previous glacial onsets and retreats, and the entire flood plain of the Mississippi river in Wisconsin lost about 50 feet of silt, indicating a huge flood instead of a gradual melting; 500 years is an etremely, massively conservative estimate. I remember reading that ninety percent of large land animals went extinct at the end of this last Ice Age, most of which had survived several previous ones. GMP-1A could have quite conceivably been a sudden event with an unknown cause totally unrelated to normal glaciation patterns.
Mk
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Mar16-06, 01:26 AM
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GMP 1A happened suddenly; it was an anomaly
How suddenly?

Andre
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Mar20-06, 03:13 AM
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Mysterious Meltwater Pulse 1A


Quote Quote by georgemarvin2001
... GMP-1A could have quite conceivably been a sudden event with an unknown cause totally unrelated to normal glaciation patterns.
Sorry George, speculation and personal theories are not welcome here. and I'm utterly surprised that this thread has not been closed for such a clear infringement of the rules, considering that this thread got closed without any clarification. It's only crime may have been that it linked to several other people and threads that had their own ideas.

Needless to say that I have no more business here under such a regime.

This is a much better place for discussions about Meltwater pulses, Bolling Allerod and Younger Dryas, etc, etc with the freedom of proposing an odd hypothesis every now and then -following the Popperian scientific methods, like another -non ice sheet melting- cause for MWP1A

All the best.
georgemarvin2001
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Mar20-06, 03:14 PM
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ANDRE: There was no need to be insulting just because you didn't like the answer. I was neither speculating nor giving personal theories or conjecture about mwp-1a. The rapid onset of mwp-1a is pretty well documented in a variety of sources, from studies of animal and plant life worldwide to the results of data collected from numerous studies of several ice core samples collected over the last 3 decades. All of the data was collected from very well-respected sources. Just because it may not fit your own personal theories doesn't make it any less true.

Measurements of oxygen isotopes from the GISP2 ice core suggest the end of the Younger Dryas took place over just 40 - 50 years in three discrete steps, each lasting five years. Other proxy data, such as dust concentration, and snow accumulation, suggest an even more rapid transition, requiring a ~7 °C warming in just a few years.

For one group of American scientists on the ice in Greenland, the "moment of truth” struck on a single day in midsummer 1992 as they analyzed a cylinder of ice, recently emerged from the drill hole, that came from the last years of the Younger Dryas. They saw an obvious change in the ice, visible within three snow layers, that is, scarcely three years. The team analyzing the ice was first excited, then sobered — their view of how climate could change had shifted irrevocably. The European team reported seeing a similar step within at most five years. "The general circulation [of the atmosphere] in the Northern Hemisphere must have shifted dramatically," Dansgaard’s group eventually concluded. Oceanographers soon confirmed that the abrupt changes seen in Greenland ice cores were not confined to Greenland alone. Later work on seabed cores from the California coast to the Arabian Sea, and on chemical changes recorded in cave stalagmites from Switzerland to China, confirmed that the oscillations found in the Greenland ice had been felt throughout the Northern Hemisphere. References: Dansgaard et al. (1989); increasingly abrupt changes were seen on further study, Johnsen et al. (1992); Grootes et al. (1993); jumps of Greenland snow accumulation "possibly in one to three years" were reported by Alley et al. (1993), see also Mayewski (1993); five-year steps: Taylor et al. (1997); changes in dust had been noted, indicating at least continental scope for the change, and a Younger Dryas temperature step in less than a decade was found to be hemisphere-wide since methane gas changed as well: Severinghaus et al. (1998). Good histories are Alley (2000) and Cox, (2005), ch. 8

There was a massive flood of the river, in which water levels rose 165 feet and flooded Wisconsin, at about 14,300 years ago. Of special interest to this discussion is the fact that the waters were so rapid that they caused severe erosion across the entire flood plain; the initial flood washed away silt to a depth of 50 feet. Reference: Geological Society of America: Abstract from research paper #184-13 by James Knox, professor of Geography, Univ. of Wisconsin-Madison

A 1961 study mentioned in passing that at one location in Wisconsin, the transition from glacial-period pines to oak trees had only taken about 100 years. Reference: West, R.G. (1961). "Late- and Postglacial Vegetational History in Wisconsin, Particularly Changes Associated with the Valders Readvance." American J. Science 259: 766-83.

Emiliani published in 1975 of some deep-sea cores from the Gulf of Mexico. Thanks to unusually clear and distinct layers of silt, he found evidence of a remarkable event around 11,600 years ago: a rise of sea level at a rate of meters per decade. *Reference: *Emiliani, Cesare, et al. (1975). "Paleoclimatological Analysis of Late Quaternary Cores Form the Northeastern Gulf of Mexico." Science 189: 1083-88.

Dansgaard's group cut out 67,000 samples, and in each sample analyzed the ratios of oxygen isotopes. The temperature record showed what they called "violent" changes — which corresponded closely to the jumps at Camp Century. Moreover, the most prominent of the changes in their record corresponded to the Younger Dryas oscillation seen in pollen shifts all over Europe. It showed up in the ice as a swift warming interrupted by "a dramatic cooling of rather short duration, perhaps only a few hundred years. Reference: Dansgaard, W., et al. (1982). "A New Greenland Deep Ice Core." Science 218: 1273-77.

As ice drillers improved their techniques, making ever better measurements along their layered cores, they found a variety of large steps not only in temperature but also in the CO2 concentration. This was a great surprise to everyone. Since the gas circulates through the atmosphere in a matter of months, the steps seemed to reflect world-wide changes. Reference 1: Oeschger, Hans, et al. (1984). "Late Glacial Climate History from Ice Cores." In Climate Processes and Climate Sensitivity. (Geophysical Monograph 29, Maurice Ewing Vol. 5), edited by James E. Hansen and Taro Takahashi, pp. 299-306. Washington, DC: American Geophysical Union.


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