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Bird, B.W.,Abbott, M.B.,Finney, B.P.,Kutchko, B. 2008 A 2000 year varve-based climate record from the central Brooks Range,
Alaska. Journal of Paleolimnology
| Data Coverage |
North: 68.0869 * South: 68.0869 |
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West: -150.465 * East: -150.465 |
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Altitude: 1275 m |
Start Year: 9 cal yr BP * End Year: 2005 cal yr BP
Data: Please Cite Data Contributors!
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Summary: Varved minerogenic sediments from glacial-fed Blue Lake, northern
Alaska, are used to investigate late Holocene climate variability.
Varve-thickness measurements track summer temperature recorded at
Atigun Pass, located 41 km east at a similar elevation (r 2 = 0.31,
P = 0.08). Results indicate that climate in the Brooks Range from
10 to 730 AD (varve year) was warm with precipitation inferred to
be higher than during the twentieth century. The varve-temperature
relationship for this period was likely compromised and not used
in our temperature reconstruction because the glacier was greatly
reduced, or absent, exposing sub-glacial sediments to erosion from
enhanced precipitation. Varve-inferred summer temperatures and
precipitation decreased after 730 AD, averaging 0.4°C above the
last millennial average (LMA = 4.2°C) from 730 to 850 AD, and
0.1°C above the LMA from 850 to 980 AD. Cooling culminated between
980 and 1030 AD with temperatures 0.7°C below the LMA. Varve-
inferred summer temperatures increased between 1030 and 1620 AD
to the LMA, though the period between 1260 and 1350 AD was 0.2°C
below the LMA. Although there is no equivalent to the European
Medieval Warm Period in the Blue Lake record, two warm intervals
occurred from 1350 to 1450 AD and 1500 to 1620 AD (0.4 and 0.3°C
above the LMA, respectively). During the Little Ice Age (LIA;
1620 to 1880 AD), inferred summer temperature averaged 0.2°C below
the LMA. After 1880 AD, inferred summer temperature increased to
0.8°C above the LMA, glaciers retreated, but aridity persisted
based on a number of regional paleoclimate records. Despite warming
and glacial retreat, varve thicknesses have not achieved pre-730 AD
levels. This reflects limited sediment availability and transport
due to a less extensive retreat compared to the first millennium,
and continued relative aridity. Overall, the Blue Lake record is
similar to varve records from the eastern Canadian Arctic that
document a cool LIA and twentieth century warming. However, the
occurrence and timing of events, such as the LIA and Medieval Warm
Period, varies considerably among records, suggesting heterogeneous
climatic patterns across the North American Arctic.
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