CLIMATE CHANGE IN NORTH DAKOTA SINCE THE LAST GLACIATION

REVIEW OF THE PALEONTOLOGICAL RECORD

Allan Ashworth

Department of Geosciences, North Dakota State University, Fargo, ND 58105-5517

INTRODUCTION

The terms global change and global warming have entered our everyday language. We are forced to concede
that our activities have already contributed to the degradation of landscapes and the loss of biodiversity, and
are probably contributing to climate change. With the record setting floods in the Red River and Missouri River
valleys in 1997, Devils Lake at its highest level in historical time, and farmland being lost to coalescing lakes
in the southeastern counties, North Dakotan’s know only too well the effects of climate change. From 1988 to
1992 the State experienced drought conditions but since then North Dakota has been in a wet cycle. North
Dakotan’s are stoical when it comes to weather but even so there is a concern about what the future will bring.
Most of our knowledge of climate change comes from an instrumental record that is only 100 years in length.
This record has been extended by dendroclimatology and by high resolution paleontological and geochemical
studies of lake sediments. What these studies are showing is that 100 years is far to short a time to show the
variability in the climate record.

Figure 1. Location of Quaternary sites in North Dakota. The dotted line marks the western margin of the
              Laurentide ice sheet during the last glaciation. Base map is from the Color Landform Atlas of the United
              States (30).
 

In recent years, our knowledge about climate change in North Dakota, especially since the last glaciation, has
grown considerably. In winter, the frozen surfaces of North Dakota’s lakes provide a perfect platform for coring
lake sediments. The use of casing and the application of stronger and lighter alloys in coring rods now make it
possible to obtain longer and more complete cores than ever before. Accelerator Mass Spectroscopy (AMS) has
revolutionized radiocarbon dating so that now only small amounts of carbon are needed for high quality dates.
This makes it possible to calculate rates of processes with greater accuracy than previously. In this
view of the late Quaternary climate history, ^14C ka refers to 1000's of radiocarbon years before present.

THE LAST GLACIATION

North Dakota comprises both glaciated and non-glaciated terrains. During the last glacial maximum, the northern
and eastern parts of the State were ice covered with flow directed generally southwards following the James and
Red River drainages. The western boundary of the ice sheet across North Dakota was east of the Missouri River (1).
Only the southwestern part of the State was ice-free (Fig. 1). Fossil polygons, remnants of patterned ground, are
widespread (2) indicating cold and possibly arid conditions . The age of the polygons is uncertain and may predate
the last glaciation (3). Are they indicators of a polar desert? What was the vegetation and fauna of the ice-marginal
zone? Sediments from shallow depressions in the unglaciated region are unfossiliferous. There are no pollen records,
but based on a profile from site close to the Rocky Mountains (4) we can speculate that vegetation of the Great Plains
before 15¹⁴C ka was dominated by Artemisia (sage), herbs and Poaceae (grasses). The vegetation was probably
what has been referred to as "mammoth steppe" (5). Certainly, the molars of many mammoths have been found in
gravel deposits in western North Dakota but for the majority of the specimens, stratigraphic context is either unknown
or uncertain. None of the teeth have been dated so it is uncertain whether they are from the last or earlier glaciations.
We do know that the Woolly Mammoth, Mammuthus primigeneus, inhabited the western shore of Lake Agassiz about
11 ka and presumably it was from an ancestral population in the southwest (6). What other large animals roamed
the ice margin? Teeth and bones of bison, including partial skulls of Bison latifrons and Bison antiquus (Bison bison antiquus)
are also found in alluvium, but as with the mammoth teeth, their age is uncertain.

Perhaps, the best insight about the megafauna is from the Hot Springs site in the southern Black Hills, South Dakota.
This site was located about 200 km south of the ice margin in North Dakota, a distance within the migratory range of
several of the large animals. At Hot Springs, mammoths and other large animals were trapped in the sediments of a sink
hole lake about 26 ¹⁴C ka. The most prominent fossils are those of Mammuthus columbi (Columbian mammoth), and
M. primigenius (Woolly Mammoth) (7). The fauna also included the herbivores Camelops hesternus (Yesterday's Camel),
Hemiauchenia macrocephalus (Large Headed Llama), Antilocapra americana (Pronghorn), and cf. Euceratherium collinum
(Shrub Ox). The carnivores and scavangers on these animals were Canis lupus (Gray Wolf), Canis latrans (Coyote),
and the largest of the late Pleistocene predators, Arctodus simus ( Giant Short-Faced Bear).

Lake Agassiz formed on the eastern margin of the State as the ice margin retreated northward. At 11¹⁴C ka M. primigenius
(Woolly Mammoth) inhabited the strandlines. Grasses were probably the main diet of M. primigeneus and a grassland, not
a spruce forest, was probably the preferred habitat. Wind and cold surface waters of the lake may have favored a narrow
zone of open vegetation around the shorelines (6). Further, the mammoths, isolated by their ecology into a narrow zone
between spruce forest to the west and the lake to the east, may have been preyed on by paleo-indian hunters who entered
North Dakota about this time (6). Mammoth became extinct in North America about 11 ¹⁴C ka.

The southern basin of Lake Agassiz was colonized by plants when the waters drained to the Atlantic Ocean during the
Moorhead Phase, between 10.9 to about 10.3 ¹⁴C ka (12). Deposits from a cut bank on the Red River, Fargo, with an age
of 10.3 ¹⁴C ka, contain pollen, macroscopic plant remains, fossil beetles, gastropods and bivalves (13). The fossil assemblages
are dominated by aquatic organisms. Most of the wood preserved at the site is Populus, probably P. tremuloides (aspen), but
there is also a cone of Alnus (alder) and a few, poorly preserved leaves of Picea (spruce). The macroscopic fossils indicate
eutrophic conditions in a shallow, lagoonal environment. The climate was probably similar to that in northern Minnesota at
the present day (13). The pollen assemblage from the Seminary site, about 1 km to the south, at a similar stratigraphic position
and with an age of 9.9 ¹⁴C ka, was dominated by Picea (14). This pollen, however, could have been reworked and redeposited
from older sediments.

Further to the west, two late-glacial and early Holocene fossil assemblages have been examined from the area of the stagnant
moraines of the Missouri Coteau. The sediments of Johns Lake, with an age of 10.8 ¹⁴C ka, contain abundant cones and leaves
of Picea. This site also has a rich fossil beetle fauna, including several species of Scolytidae (bark beetles) associated with
Picea (15). A few of the beetle species are those typically found in prairie habitats, suggesting that the forest was open and
possibly more like the southern margins of the boreal forest today. Based on macrofossils from the Seibold site, Picea persisted
until about 9.3 ¹⁴C ka on the Missouri Coteau (16). In addition to Picea, the Seibold sediments contain exceptionally
well-preserved fossils, including complete leaves of Populus (cottonwood), complete skeletons of fish and frogs, bones of
muskrat, coprolites of beaver, exoskeletons of amphipods, insect larvae, aquatic bugs, and beetles. The beetles, like those
of the Johns Lake site, represent some species associated with spruce forest and others associated with prairie (17).
 
 

Figure 2. Summary pollen diagram for Moon Lake, Barnes County, North Dakota (9). Reprinted from the North
              American Pollen Database using Siteseer.
 

THE HOLOCENE

At 9.9 ¹⁴ C ka, an ice advance in Canada blocked the northeastern drainage outlets of Lake Agassiz and the lake rose for the
final time, flooding the southern part of the basin. Shortly afterwards, the ice retreated and Lake Agassiz drained for the last time.
The lake may have persisted in North Dakota until about 8.2 ¹⁴C ka (12). Further west on the Missouri Coteau, buried ice had
melted out by 9 ¹⁴C ka.

Isolated spruce populations persisted in North Dakota until the early Holocene. At Moon Lake, the spruce forest was replaced at
about 10.3 ¹⁴C ka by a parkland of mixed deciduous forest and prairie. This vegetational change is attributed to an increase in
summer temperatures (9). A climate change to progressively drier summers is thought to have caused the demise of Ulmus (Elm)
and finally Quercus (Oak). By 7 ¹⁴C ka, the vegetation surrounding Moon Lake was a prairie (9). At Rice Lake in northwestern North
Dakota, prairie replaced earlier parkland vegetation by 9.4 ¹⁴C ka (Eric Grimm, pers. comm., 1999 ).

At Moon Lake, there is continuous prairie from about 7 ¹⁴C ka to the present. The pollen of Ambrosia and other weedy species is
more abundant than that of grasses until about 5 ¹⁴C ka. The increased representation of grass pollen during the last 5 ¹⁴C ka is
also recorded in the pollen diagram for Rice Lake. The maximum drought conditions during the mid-Holocene occurred between
7-6 ¹⁴C ka. At Moon Lake, between 6.6 to 6.3 ¹⁴C ka, pollen of Iva annua (Marsh Elder), Ruppia (Ditchgrass) and Picea, all show
small increases. Ruppia is an aquatic and the presence of its pollen is believed to indicate a shallowing of the lake (9). The
modern range of Iva does not extend north of Nebraska and its presence is thought to represent warmer conditions. The spruce
pollen is believed to be reworked from older sediments eroded along the margins of the lake as the water-surface was lowered by
intense evaporation (10). In one of the best dated records in the region, maximum drought conditions at Elk Lake, Itasca Park,
Minnesota, occurred between 6.2 to 6 ¹⁴C ka (18).

Fossil diatom assemblages have been studied from several closed-basin lakes in North Dakota which provide one of the best
indicators of salinity changes (9, 19, 20, 21,22). The general assumption is that significant changes in lake levels are the result
of climatic change. At Moon Lake, the water until 10 ¹⁴C ka was fresh, from 10 to 7.3 ¹⁴C ka it was moderately saline, and from
7.3 to about 2 ¹⁴C ka it was highly saline (9). At Devils Lake, the change from fresh water to highly saline conditions occurred at
about 8 ¹⁴C ka, about two thousand years later than at Moon Lake. The very high salinity at Devils Lake persisted until about
5 ¹⁴C ka, but during this time the lake was flushed periodically with freshwater. From about 5 ¹⁴C ka to about about 2 ¹⁴C ka ,
the lake was moderately saline (20). Variations in the timing of salinity events in prairie lakes varies and has been attributed to
a number of causes, including differences in hydrological sensitivity of lake basins to climatic change, poor chronological controls,
and sensitivity differences between different proxy indicators. Even so, most lakes in North Dakota and the surrounding prairie
region record intense episodes of drought during the mid- Holocene from from 8 to 4 ¹⁴C ka.

During the mid-Holocene, evaporation was so intense that shallower lakes completely dried up (23). At these times, wind erosion
removed older sediments from many shallow lake basins. Basal ages of sediments in those basins date only to about 3 ¹⁴C ka.
At Spiritwood Lake, near Jamestown, North Dakota, divers from Northwest Divers, Moorhead, Minnesota, found bison skulls and
bones scattered across a shelf at about 6m depth. The bones could have been from individuals drowned as they broke through
the ice during an early freeze or a late thaw. The horn core dimensions of a skull, however, are most similar to those of Bison
bison occidentalis, the typical mid-Holocene form. This led me to conclude that the bones were more probably from bison that
died on the margins of the mid-Holocene lake. Large bison skulls, initially reported as Bison crassicornis, but revised to B. bison
occidentalis, were also described from the base of an alluvial fill at 6 m depth on Spring Creek, near Zap, North Dakota.
Beaver-gnawed wood associated with those specimens had an age of 5.4 ¹⁴C ka (24, 25).

Holocene climate was the topic of symposia at the 1998 meetings of the Geological Society of America and the American
Quaternary Association. The causes of mid-Holocene drought have been hotly debated. In the northern Great Plains, regional
drought is generally associated with stronger westerly zonal flow. One hypothesis suggests that stronger circulation was initiated
by Milankovitch - driven insolation changes. A lag of 3 ¹⁴C ka following the insolation maximum at 9 ¹⁴C ka is attributed to a
rapidly disintegrating ice sheet cooling the atmosphere and delaying the effects of heating (26). A second hypothesis, suggests
that the increased strength in the westerlies was associated with increased solar-geomagnetic disturbances (27). Using spectral
analyses, it was determined that cycles of 200, 100 , 50 , 22 and 20 years duration were represented in the varve record of Elk
Lake. During the mid-Holocene it was further determined that there was an inverse relationship between varve thickness and
the 200 year cycle in ¹⁴C production determined from tree rings. During this same period, the Earth’s dipole moment was at its
lowest during the Holocene, suggesting a link between an increase in solar-geomagnetic disturbance and the strength of the circulation.

The late Holocene pollen record for Moon Lake indicates an increase in grasses and a decrease in Ambrosia for the last
4 ¹⁴C ka (9).  There were also several small increases in Ruppia pollen during this time that are believed to be associated
with drawdowns of the water level . The diatom-inferred salinity at Moon Lake remained high until about 2.2 ¹⁴C ka, after which
the frequency of droughts increased (9).

North Dakota does not not have any long-lived trees but Pinus ponderosa and Juniperus scopulorum in the North Dakota badlands
have records that extend back to about AD 1600 (29). Instrumental records for climate change in North Dakota are about 100
years old. Comparison of the tree ring records with the instrumental climate records, indicates that the tree ring record is sensitive
to drought. All the trees have thinner rings during the drought of the 1930's. Individual records show a lot of variation, but there
appears to be a cyclicity to drought, with intense droughts occurring on a frequency of 40 - 60 years. What is particularly striking
in the Moon Lake salinity record is the magnitude of a series of droughts prior to AD 1200: at AD 200-370, AD 700-850 and
AD 1000 -1200 (28). These droughts were all of a greater magnitude than the intense drought of the 1930's. They have been
correlated with intense episodes of drought in western North America, suggesting that their cause lies in changes to atmospheric
circulation over the Pacific Ocean( 28).

CONCLUSIONS

Studies in Quaternary paleontology have contributed significantly to our knowledge of climate change on the northern Great Plains.
Future studies will be directed at filling gaps in the knowledge base and in "fine tuning" methods to improve the quality of interpretation.

The climate along the ice margin during the last glacial is still poorly known. The semi-arid climate of the southwestern part of the
State, and the depth of oxidation, is not conducive to the preservation of organic sediments. Nevertheless, the sediments of shallow
basins should continue to be examined for pollen. Future fossil discoveries will probably continue to be vertebrate remains. Radiocarbon
dating of bone has been unreliable but new techniques promise to change that situation. Also, it may be possible to infer vegetation
from isotopic studies of tooth enamel.

Late-glacial and early Holocene sediments on the Missouri Coteau need to be more completely examined. The Seibold site, with its
incredible preservation, is probably not unique. Ancient DNA could well be preserved in these fossils. Future studies in molecular
genetics could provide a real link between populations of the past and those of today that would enable detailed reconstructions of
dispersal routes of organisms in response to climate change.

Micropaleontological studies of lacustrine sediments during the last 10 years have made a significant contribution to our knowledge
of Holocene climate. Historically, the terms altithermal and hysithermal were used to describe a peak of warmth in the mid-Holocene.
The high resolution records of pollen, diatoms, ostracods and geochemistry that are now being studied indicate that that classical
concept was an oversimplification. The latest records indicate much more complexity. The modal changes which seem to be part
of the Holocene record are especially intriguing, as they imply major reorganizations of the Pacific oceanic-atmospheric circulation

The opportunities for future paleontological research in lacustrine sediments are great. There is a need to find out more about the
relationships between specific organisms and their responses to climate parameters and water chemistry. There is also a need to
resolve the complex relationships between climatic parameters and hydrology in such a way that it can be taken into account in
paleoclimatic interpretation. In a vicious pun, paleontology has been referred to as the "dead science". Nothing could be further
from the truth. Quaternary paleontology, with its links to global change and climate change, is very much alive.

REFERENCES

    1.     Clayton, L. and Moran, S.R. 1981, Quaternary Science Reviews 1, p. 55-82
    2.     Clayton, L., 1980, Geologic Map of North Dakota. United States Geological Survey
    3.     Clayton, L., Moran, S.R., and Bluemle, J.P., 1980, NDGS Report of Investigation 69, p. 1-93
    4.     Whitlock, C. 1993, Ecological Monographs 63, p.173-198.
    5.     Guthrie, R.D. and Guthrie, M.L., 1990, Natural History 7, p.34-41.
    6.     Harington, C.R. and Ashworth, A.C. 1986. Canadian Journal of Earth Sciences 23, p. 909-918.
    7.     Agenbrod, L.D. 1997, Natural History 10, 77-79.
    8.     Kehew, A.E. and Teller, J.T., 1994, Quaternary Science Reviews 13, p.859-877.
    9.     Laird, K.R., Fritz, S.C., Grimm, E.C., Mueller, P.G., 1996, Limnology and Oceanography 41, p. 890-902.
   10.    McAndrews, J.H., Stewart, R.E.,Jr., and Bright, R,C., 1967. North Dakota Geological Survey Miscellaneous Series 30, p.101-113.
   11.    Watts, W.A., and Bright, R.C.., 1968, Geological Society of America Bulletin 79, 855-876.
   12.    Thorleifson, L. H., 1996, Geological Association of Canada Field Trip Guidebook B2, p. 55- 84.
   13.    Yansa, C. H. and Ashworth, A. C.,1998, Geological Society of America Abstracts with Programs, 30, p. A-168.
   14.    McAndrews, J.H.,1967, Life, Land, and Water. University of Manitoba Press, Manitoba, p. 253-269 .
   15.    Ashworth, A.C. and Schwert, D.P., 1992, North Dakota Geological Survey Geological Survey Miscellaneous Series 76, p. 257-265.
   16.    Cvancara, A.M., Clayton L., Bickley, W.B., Jr., Jacob, A.F., Ashworth, A.C., Brophy, J.A., Shay, C.T., Delorme, L.D., and
            Lammers, G.E., 1971, Science 171, p. 172-174.
   17.    Ashworth, A.C. and Brophy, J.A., 1972, Bulletin Geological Society of America 83, p. 2981-2988.
   18.    Bradbury, J.P., Dean, W.E., and Anderson, R.Y., 1993, Geological Society of America Special Paper 276, p. 309-328.
   19.    Fritz, S.C., 1990, Limnology and Oceanography 35, p. 1771-178.
   20.    Fritz, S. C., Juggins, S., and Battarbee, R. W., 1993, Canadian Journal of Fish and Aquatic Science 50, p. 1844-1856.
   21.    Fritz, S. C., Juggins, S., Battarbee, R.W., and Engstrom, D.R., 1991, Nature 352, p. 706-708.
   22.    Fritz, S.C., 1996, Limnology and Oceanography 41, 882-889.
   23.    Barnosky, C.W., Grimm, E.C., and Wright, H.E., Jr., 1987. Annals of the Carnegie Museum 56, 259-273.
   24.    Brophy, J. A., 1965, Proceedings of the North Dakota Academy of Science 19, p. 214-223.
   25.    Wilson, M., 1978, Plains Anthropologist, Memoir 14, 23, p. 9-22.
   26.    Webb, T, III, Ruddiman, W.F., Street-Perrott, F.A., Markgraf, V., Kutzbach, J.E., Bartlein, P.J, Wright, H.E., Jr., and
            Prell, W.L., 1993, Global Climates Since the Last Glacial Maximum, University of Minnesota Press, p. 514-535.
   27.    Dean, W.E., Ahlbrandt, T.S.,Anderson, R.Y., and Bradbury, J.P., 1996, The Holocene 6, p. 145-155.
   28.    Laird, K.R., Fritz, S.C., Maasch, K.A., and Cumming, B.F., 1996, Nature 384, p.552-554.
   29.    Meko Sieg, 1990, International Tree-Ring Data Bank
   30.    Sterner, R. ((http://fermi.jhuapl.edu/states/states.html)
 

Source: