Geologic Studies in Alaska by the U.S. Geological Survey, 1992

LATE HOLOCENE LONGITUDINAL AND
PARABOLIC DUNES IN NORTHERN ALASKA:
PRELIMINARY INTERPRETATIONS OF AGE
AND PALEOCLIMATIC SIGNIFICANCE
ABSTRACT
Climatic changes during the late Holocene have
caused repeated stabilization and reactivation of parabolic
and longitudinal dunes and sand sheets over a major por-
tion of the landscape on the western Arctic Coastal Plain.
The dunes are currently stabilized, and their density varies
throughout the region from a few dunes to over 275 dunes
for a 100-square-kilometer area. Dune length ranges from
320 to 2,500 m and most dunes are about 15 to 40 m wide.
Field observations suggest that most dunes are I to 3 m
thick. Modem blowouts indicate a bimodal wind regime
of ENE-WSW, with the majority of the blowouts produced
by easterly winds. Most stabilized parabolic and longitu-
dinal dunes are parallel to this trend, and the parabolic
dunes indicate westerly sand transport. This suggests that
these late Holocene dunes formed in a wind regime similar
to the present one. Twelve radiocarbon ages on peat and
humic sand (paleosols) from nine locations suggest that
three episodes of dune stabilization separated four periods
of late Holocene sand movement and dune building. The
episodes of stabilization are dated at about 4.3 to 3.9, 2.7
to 2.0, and 1.1 to 0.7 ka. Each of the four dune building
episodes (I) before 4.3, (2) 3.9 to 2.7, (3) 2.0 to 1.1, and
(4) 0.7 ka to near the present, broadly correlates with one
or more Neoglacial expansions of cirque glaciers in the
Brooks Range. Reactivation of small longitudinal and
parabolic dunes on the western Arctic Coastal Plain appar-
ently occurred as a result of cooler and drier surface condi-
tions than those that exist today.
INTRODUCTION
Late Holocene stabilized longitudinal and parabolic
dunes and thin sand sheets occur over a major portion of
the landscape on the western Arctic Coastal Plain between
the Colville and Meade Rivers (fig. 1). The dunes were
first described by Black (1951), but he presented little in-
formation about their age or paleoclimatic significance.
By John P. Galloway and L. David Carter
More recent investigations indicated that these small dunes
and sand sheets overlie an older sand sheet that in turn
covers large stabilized dunes of a Pleistocene sand sea
(Carter, 1981). Also, it is now known that the dunes de-
scribed by Black have formed during the late Holocene,
following a middle Holocene period of landscape stability
and the formation of organic soils (Carter, 1992, and in
press).
A parabolic dune forms when a disruption of stabi-
lizing vegetation exposes underlying sand to erosion. The
dune accumulates downwind from the local sand source
and does not migrate (Pye and Tsoar, 1990). The wide-
spread occurrence of the parabolic dunes and associated
longitudinal dunes on the western Arctic Coastal Plain in-
dicates that the disruption of vegetation was regional.
Such a regional decrease in ground cover indicates drier
surface conditions, which were almost certainly caused by
climatic change. This paper describes the geomorphic set-
ting of the dunes, provides preliminary information on the
age of dune formation, and presents a discussion of the
possible significance of the dunes for regional interpreta-
tions of late Holocene climatic change.
DESCRIPTION OF THE DUNES
Stabilized longitudinal and parabolic dunes occur
across much of the western Arctic Coastal Plain except for
river floodplains and terraces. Measurements from aerial
photographs in areas subjectively judged as regionally rep-
resentative show that the density of dunes varies through-
out the study area from a few dunes per 100 km2 to a
maximum of over 275 dunes for a 100-km2 area 12 krn
south-southwest of Teshekpuk Lake. Just west of the
Ikpikpuk River, there is an average of 135 dunes per 100
km2, and from there eastward to the Meade River, dune
density decreases to 10 to 40 per 100 km2.
The dunes vary in length locally and regionally.
Dune length in the 100-km2 areas chosen as regionally
representative increases from the range 320 to 960 m