Date: 8/26/00 3:24:53 PM Pacific Daylight Time
From: email@example.com (James Cleland)
P.S. Here's some miscellaneous stuff about Heinrich Events. It takes a little while to plow through the jargon, but it's well worth the effort. Anyone who is interested needs only to type "Heinrich Event" into their search engine:
Late glacial warming prior to Heinrich event 1: The influence of ice rafting and large ice sheets on the timing of initial warming
I. Marianne Lagerklint, Institute for Quaternary Studies, University of Maine, Orono, Maine 04469, USA, and Department of Physical Geography, Stockholm University, S-106 91 Stockholm, Sweden
James D. Wright, Institute for Quaternary Studies and Department of Geological Sciences, University of Maine, Orono, Maine 04469, USA. Present address: Department of Geological Sciences, Rutgers, State University of New Jersey, 610 Taylor Road, Piscataway, New Jersey 08854-8066, USA.
High-resolution faunal, isotopic, and sedimentologic data from North Atlantic core V29-191 show that sea-surface temperatures increased from 17.5 to 17.3 ka, prior to the Heinrich event 1 (H1) ice-rafting event ca. 17-16 ka. These new data support previous studies that showed that warming predated the extensive climatic warming ca. 15.9 ka. This relationship indicates that H1 occurred after warming had begun. Loss of latent heat during iceberg melting created near-glacial sea-surface temperatures during H1 and kept much of the subpolar North Atlantic cold despite increasing Northern Hemisphere insolation. The cold-ocean conditions influenced proximal terrestrial climates and may also have affected remote regions.
Blanchon, Paul and John Shaw (1995). "Reef drowning during the last deglaciation: Evidence for catastrophic sea-level rise and ice-sheet collapse." Geology 23 no. 1: 4-8.
Drowned coral reefs in the Caribbean give evidence for three meter-scale increases in sea level during the past 30,000 years. These increases occur simultaneously with Heinrich events. The ocean is affected by the components involved with Heinrich events in that climate is different, ice sheets are collapsing, ocean circulation patterns change, and very large volumes of sub-ice sheet meltwater enters the ocean. What happens is that a certain species of coral (Acropora) has a very limited depth range for habitation. If sea level goes up a meter, corals near the lower limit of the range drown. By radiometrically-dating the corals and finding out when they drowned, one can tell when sea level rose (and get an idea how fast it rose). By determining that this massive meltwater influx into the ocean was pretty fast, Blanchon and Shaw suggest that this expulsion was itself the cause of the ice sheet collapse. Since mid-latitudes are most affected by the changes in summer insolation, and the northern hemisphere's mid-latitude region was large enough to sustain a huge ice cap, the summer insolation maxima was able to produce a huge volume of meltwater. The release of this water was (theoretically) the cause of ice sheet collapse and ocean circulation changes and sea level changes.
What surprised ice-core researchers is the extreme abruptness of the transitions between cold and warm conditions. But then, no other long, continuous climatic record has been studied with such fine resolution as the new Greenland ice cores, and with most kinds of records, it is not possible. Analyses of dust and electrical conductivity in the cores show this most clearly. Enhanced dustiness is closely associated with colder temperatures. Unlike isotopes, dust does not diffuse through the ice. Above a certain threshold, dust curtails electrical conductivity, so measuring the conductivity is one simple way to see how dusty it was. In the GISP2 ice core, Taylor et al. found that the transitions "between glacial and near-glacial conditions" frequently occurred "in periods of less than a decade, and on occasion as quickly as three years." 26 They compare the atmospheric circulation over central Greenland to "a flickering switch that fluctuates between two states before stabilizing" for centuries or thousands of years at a time.
The Younger Dryas climatic reversal is attributed to abrupt shifts in the thermohaline circulation of the North Atlantic.Slide 4, Slide 5, Slide 34 A conveyor belt of currents, including the Gulf Stream, carry heat and salt from low to high latitudes where the dense, salty surface waters sink and return south at depth; convective sinking maintains the meridional (north-south) heat transport. The Younger Dryas cold snap has been credited to lowering of saltiness of North Atlantic surface waters though diversion of glacial meltwater from the Mississipi into the St. Lawrence River. Hypothetically, this infusion of meltwater into the North Atlantic shut off the conveyor belt, lowered temperatures, and thus, suppressed melting of the continental ice sheets. Melting resumed with an increase in salinity due to gradual accumulation by a weakened Gulf Stream, or concentration by evaporation. The most recent test of this hypothesis used high-precision dating of corals from Papua New Guinea to estimate rates of sea-level rise during the last deglaciation. Indeed, the Younger Dryas coincides with a reduced rate of sea level rise (reduced melting), as predicted by the meltwater model. An important discrepancy, however, is that the cold snap continued several hundred years after the conveyor belt started up again.
Evidence for the Younger Dryas in areas other than Europe has always been controversial, although much anticipated given the global teleconnections in todayís climate. This evidence is critical because it might demonstrate the potential for dramatic shifts in regional climates on time scales from years to decades. In the western U.S., much of the evidence revolves around mountain glacier Figure 5 and lake level Figure 6, Figure 7, Figure 8, Figure 9 fluctuations in large pluvial lakes now occupied by dry playas or saline lakes. During deglaciation, lake levels fluctuated considerably at Lakes Bonneville and Lahontan in the Great Basin, Searles in the Mojave Desert, and San Agustin (where the Very Large Array is located) and Estancia (east of Albuquerque) in New Mexico. Retreat of full-glacial high-lake stands began at ca. 15,000 yr. B.P.; a temporary low was reached between 14,000 and 13,000 yr. B.P.; a minor rise coincides with the Younger Dryas between 13,000 and 11,000 yr. B.P.; and the final desiccation at ca. 11,000 marks the beginning of the Holocene. How long did it take lake levels to rise and fall?
Vance Haynes from the Univ. of Arizona now argues that the penultimate low lake stands in the western U.S. happened during Clovis time between 11,300-10,900 yr. B.P.; that it coincided with a subcontinental-scale drought; and that, in the San Pedro Valley of southern Arizona, it was followed by a rapid rise in the water table and deposition of an algal mat, known among aficionados as "the black mat," which buried mammoth tracks and Clovis artifacts. Similar sequences occur at other Clovis sites, including Blackwater Draw near the type site of Clovis, New Mexico.
In short, global phenomena, such as the beginning and the end of the Younger Dryas, may have been manifested in regional changes that were both dramatic and rapid, reflecting rapid reorganizations in climate. Presently, we have few ways of knowing whether the fluctuations in regional water tables, symptomized by the rise and fall of lake levels, the "Clovis drought," or deposition of the "black mat," occurred over years, decades or centuries. If we accept that climate over Greenland switched from one state to another in one to three years, then we should entertain the likelihood that shifts in regional climates were equally swift. Recently, geologists were able to show that millennial-scale oscillations in glacial lake levels at Lake Estancia (east of Albuquerque) occurred as several strong pulses in precipitation that lasted only a few decades and were separated by a few hundred years.
Kent, you will note that a common thread appears through most of the literature...the potential for very, very rapid change. And this is not coming from wild-eyed millenialists. It is coming from orthodox science.
Pardon me, but I'm on an apocalyptic role today, and I really need to get back to work. Meanwhile, as to how much the government is paying attention to this, I note the following:
"The Role of the Ocean in Rapid Climate Change: Evidence from Ice Cores and Marine Sediments", Testimony given to the U.S. Senate Committee on Commerce, Science and Transportation, Senator Al Gore presiding. May 20, 1992.