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

LATE HOLOCENE LONGITUDINAL AND PARABOLIC DUNES IN NORTHERN ALASKA 9
Ages in radiocarbon years (table 1) were converted to calen-
dar yr B.P. (table 2) using the calibration curve of Stuiver and
Reimer (1986). From one to several calibrated ages are pos-
sible for each radiocarbon age, because the measured radiocar-
bon activity of the sample may intersect the calibration curve
in one or more places. Values shown in parentheses in table 2
are the calibration curve intersections, and the limiting values
shown without parentheses represent intersections of the ra-
diocarbon analytical error with the calibration curve and its
analytical error.
PALEOCLIMATIC SIGNIFICANCE
Eolian sand on the Arctic Coastal Plain is highly
susceptible to wind erosion if the stabilizing tundra vegeta-
tion is absent or disturbed by natural or anthropogenic pro-
cesses. Over the past 20,000 years, climatic change has
caused repeated stabilization of the dunes and sand sheets
(Carter and others, 1984; Carter, in press). Stabilization of
the eolian surfaces occurred when climatic conditions were
relatively moist and allowed the growth of stabilizing veg-
etation, whereas reactivation of eolian activity occurred
when surface conditions were relatively dry. Alternating
periods of eolian sand transport and soil formation thus
record changes in surface-moisture conditions, and dating
these periods provides information that can be integrated
with other proxy climatic information to produce a more
complete record of climatic change.
The time of late Holocene dune reactivation follow-
ing middle Holocene development of organic soils is not
precisely known. Two radiocarbon ages for the uppermost
parts of the middle Holocene paleosols are calibrated to
5.9 and 5.1 ka ( Carter, in press). The thin, discontinuous
paleosols associated with the late Holocene eolian sand in-
dicate that during most of the late Holocene, dry surface
METERS
8 -
conditions promoted eolian sand transport and dune forma-
tion. The calibrated radiocarbon ages reported here for
these paleosols (fig. 9) suggest that these generally dry
surface conditions were interrupted by at least three rela-
tively moist intervals of soil formation and relative land-
scape stability.
The maximum limiting age for the parabolic dune at
site 3 suggests a possible period of soil formation at about
4 ka (table 2). This possibility is strengthened by a cali-
brated age of 4,264 yr B.P. (table 2) determined for a bur-
ied organic horizon beneath a stabilized dune near the
Ikpikpuk River (fig. 1, site A) described by Rickert and
Tedrow (1 967).
At least two longitudinal dunes formed after the de-
velopment of paleosols that have calibrated basal dates of
about 2.7 to 2.4 ka (fig. 9). Paleosols in eolian sand at
four other localities (sites 6 through 9, figs. 1 and 2 and
tables 1 and 2) are about the same age as the paleosols
beneath the two longitudinal dunes, which suggests the
possibility that the period 2.7 to 2 ka may have been a
time of regional soil formation and dune stabilization on
the Arctic Coastal Plain. At site 3, however, no evidence
for soil development during the period 2.7 to 2 ka is
present. It is possible that the soil was removed by ero-
sion, or that soil development was patchy during this inter-
val. Renewed eolian transport evidently occurred after
about 2 ka.
A third episode of soil formation and stabilization is
suggested by paleosols at several sites. The age of the
paleosol near the top of the parabolic dune (site 3, fig. 1)
is similar to ages for the youngest paleosol in eolian sand
at two other localities (sites 4 and 5, figs. 1 and 2 and
tables 1 and 2). The calibrated ages range from about 1.15
to 0.72 ka (fig. 9), which is roughly contemporaneous with
the Medieval Warm Period in temperate northern latitudes
(Williams and Wigley, 1983). Graybill and Shiyatov
6 - Parabolic dune
I
/-
li Tundm mat (I-10.890)
/ , -
5,745+115 yr B P. ~ ~ d e d
\
Unccmfam~ty , - - -
\,
- (I-10,899) m h sand
, --_ -
,
- -
/
/
~one ofm~m-m~ - - . wth_tunnd &rub:
- ----------------
Eolian nand
Figure 8. Diagrammatic cross section showing location of dated paleosols, site 3 (fig. 7).
.
\
-= . \
10,200-t 15OyrBP
(I-10,716)
\