Title : NSF 93-58 NSF FACILITY USING FOSSIL MOLLUSCS TO DATE "CLIMATIC
Type : Press Release
NSF Org: OD / LPA
Date : August 3, 1993
File : pr9358
Cheryl Dybas August 3, 1992
(202) 357-9498 NSF PR 93-58
NSF FACILITY USING FOSSIL MOLLUSCS
TO DATE "CLIMATIC OPTIMUM"
WITH ACCELERATOR MASS SPECTROMETRY Most of Greenland, the world's largest
island, is covered by a 3,000 meter-thick ice cap; only 16 percent of this
arctic island -- its coastal perimeter -- is exposed. In summer, countless
lakes and melt water rivers drain into glacier-scoured fjords. Hardly a place
one would expect to find evidence of the warm period of Earth's history known
as the Climatic Optimum. However, during the past two summers, director
Glenn Jones of the National Ocean Sciences Accelerator Mass Spectrometry (AMS)
facility in Woods Hole, Massachusetts, has done just that: by combing the
weather-beaten coast and fjords of this region to locate and collect fossil
molluscs from a time warmer than today. The AMS facility is used to date
seawater, marine sediments and other material containing carbon, and is
funded by the National Science Foundation (NSF)'s division of ocean sciences.
Many tales are told of Viking exploration during Greenland's "Medieval Warm
Period." Eric the Red, a rebellious warrior, made his famous voyage of
discovery to southwestern Greenland after being forced to leave Iceland in
981 CE. Archaeological remains of two earlier Inuit cultures are preserved
in the Sisimiut district where the AMS fieldwork was carried out.
Jones' fieldwork involved recovering fossil shells of seven thermophilous, or
"warm-loving," molluscs that extended their range northward during the
Climatic Optimum, 4,000 to 8,000 years ago - a time considerably warmer than
today. Beginning about 8,500 years ago, these mollusc populations formed in
isolated pockets along the coast of southwest Greenland and in the shelter of
smaller fjords. By 4,000 years ago, when colder conditions returned, the
molluscs had died out. They have remained extinct into the present. Although
evidence associated with the Climatic Optimum is relatively common in high
latitudes, records of the rate at which these events occurred are not.
Although thermophilous molluscs were identified from collections made by
Danish geologists as early as the 1890's, the recent technological innovation
of AMS radiocarbon dating has allowed the most detailed study yet of these
The logistics of the Greenland fieldwork involved covering rugged terrain by
foot and portaging necessary gear -- and frequently a 12-foot inflatable
"boat." "We learned to sleep without darkness, to be comfortable in headnets,
to cook and dry clothes with a Primus stove, and reluctantly, to forego a
shower or fresh food for weeks on end," says Kathryn Elder, a research
assistant at the AMS facility.
A team of scientists excavated three mollusc species (Panopaea norvegica,
Arctica islandica, and Zirphaea crispata), and shells of two other mollusc
species. By correlating the dates of first and last appearance of each
species with its known temperature tolerance, researchers can produce a time
history of the evolution of marine temperatures during a period warmer than
today. This record can in turn be used to better understand the response of
high latitudes to projected "greenhouse warming."
The mollusc Zirphaea crispata currently lives in regions with water
temperatures greater than 9o C. Using AMS radiocarbon dates of Z. crispata
from southwest Greenland, scientists can ascertain that as early as 5,500
years ago the water at that locality was near 9o C. Panopaea norvegica can
tolerate colder conditions, around 3 1/2o C, and was the first of these
species to inhabit southwestern Greenland about 8,500 years ago. This data
implies as much as a 6o C increase in water temperature in approximately 3,000
years. This 6o C difference compares in magnitude to the difference observed
today in summer ocean temperatures between Woods Hole, Massachusetts, and
AMS researchers hope to establish whether Z. crispata was the first and P.
norvegica the last of the thermophilous molluscs to die out from Greenland
waters at the close of the Climatic Optimum. Says Elder, "This dataset might
provide modelers with a tool for comparing computer-predicted rates of
greenhouse warming with
actual rates of past change in an attempt to answer questions like how
quickly we might re-enter a human-induced `Climatic Optimum,' and what the
biological response to that change might be." AMS radiocarbon dating of
molluscs from southwest Greenland may supply one more piece to the global
climate change puzzle.
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