Evidence for Climate Teleconnections Between Greenland and the Sierra Nevada of California During the Holocene, Including the 8200 and 5200 Climate Events - Abrupt Climate Change: Mechanisms, Patterns, and Impacts - page 192

during the Holocene. Alley and Agustsdottir [2005] deter-
mined that extreme cold and drought at 8200 years ago
caused rapid vegetation change in many parts of the world.
Morrill and Jacobsen [2005] reviewed 52 sites worldwide
and concluded that the 8200 ACCE was detected in many
areas of the Northern Hemisphere extratropics and tropics.
They noted, however, that many more records were needed
from the Southern Hemisphere. For example, Tinner and
Lotter [2001] reported the sudden collapse of a depauperate
hazel-dominated (Corylus avellana) woodland in southern
Germany and Switzerland and the woodland ' s replacement
by a more diverse closed-forest type of vegetation 8200 years
ago. Clark et al. [2002] reported a permanent change from
C4- to C3-dominated grasslands on the United States Great
Plains as a result of a severe drought at 8200 years ago.
The term

1.2. In This Chapter

This study seeks to explain the unusually peaked Coburn
Lake macrocharcoal record and its relationship to climate
and fire events in the Sierra Nevada, eastern Canada, and

Greenland. Here I present a high-resolution climate and
disturbance history for the Sierra Nevada based upon com-
parisons between my 8500 year long charcoal record from
Coburn Lake and six published high-resolution paleo-
records: (1) a drought record from Pyramid Lake, Nevada
[Mensing et al., 2004]; (2) a temperature record from Cirque
Peak, California [Scuderi, 1993]; (3) a charcoal record from
eastern Canada [Carcaillet et al., 2001]; and (4) precipita-
tion, (5) temperature, and (6) soot records from Greenland
[National Snow and Ice Data Center (NSIDC) and World
Data Center-A for Paleoclimatology (WDC-A), 1997].
The results of these comparisons provide evidence for
synchronicity between the timing of the following climate
and disturbance events: (1) between the timing of severe fires
and erosion at Coburn Lake and the timing of the beginnings
of severe droughts and high temperatures in the Sierra Ne-
vada, (2) between the timing of severe droughts and high
temperatures in the Sierra Nevada and the timing of increas-
ing precipitation and warming temperatures in Greenland,
and (3) between the timing of severe droughts in the northern
Sierra Nevada and associated

as used here, refers to mega-
droughts lasting decades or centuries. The 8200 year ACCE
initiated hundreds of years of drought worldwide. In the
western United States, this period from 8200 to 6300 years
ago has been referred to variously as the Holocene Altither-
mal, thermal maximum, etc. Barron et al. [2003] reported
that sea surface temperatures along the Northern California
coast were 1°C - 2°C colder at 8200 years ago than at any
other time in the Holocene, resulting in drier conditions
inland in the Sierra Nevada [Moser et al., 2004]. Cold tem-
peratures off the coast of Northern California and dry condi-
tions inland lasted until 3200 years ago [Barron et al., 2003].
This time interval coincided with a period of widespread
aridity in the western interior of North America [Fritz et al.,
2001]. In the northern Sierra Nevada, three severe droughts
in a row occurred from 7300 years ago (near the beginning of
the Mensing et al. [2004] precipitation record) until the
arrival of moister conditions approximately 6300 years ago
[Mensing et al., 2004].

“ severe drought, ”

res at Coburn Lake and the

timing of severe fires in eastern Canada. This study also

provides new evidence that the 8200 and 5200 year ACCEs
affected California and that the magnitude of changes in
temperature and precipitation increased in Greenland at ap-
proximately 3700 and 3100 years ago, respectively.
Basedontheabove findings, I propose the following

hypotheses: (1) that most instances of severe fire and erosion

at Coburn Lake occurred in response to stresses that ACCEs
put on vegetation adapted to cooler and wetter conditions;
(2) that the synchronous beginnings and endings of drought
conditions in the Sierra Nevada and Greenland were caused
by abrupt, large-scale northward and southward shifts in the
locations of the Earth

1.1.2. The 5200 year abrupt climate change event. The
5200 year ACCE represented both the driest climate interval
and one of the three largest reductions in meridional over-
turning circulation (MOC), sometimes inaccurately referred
to as thermohaline circulation, in the North Atlantic during
the Holocene [Oppo et al., 2003]. The other two large reduc-
tions in MOC in the North Atlantic occurred at 8200 and
2800

s major precipitation belts (the Inter-
tropical Convergence Zone (ITCZ), the Subtropical Desert
Zone, and the Polar Front) during ACCEs; and (3) that
increased climate variability increased the number of ACCEs
during the late Holocene. Using the Coburn Lake Charcoal
record and published data, I wish to provide evidence sup-
porting these hypotheses.

'

3000 years ago [Oppo et al., 2003]. The 5200 year
ACCE ended the moister conditions that had begun approx-
imately 6300 years ago, which changed vegetation in loca-
tions as diverse as British Columbia [Spooner et al., 1997],
Minnesota [Smith et al., 2002], eastern Greenland [Cremer et
al., 2001], Sweden [Regnell et al., 1995], and Australia
[McKenzie and Kershaw, 1997]. Clark et al. [2002] noted
that a major vegetation and environmental shift occurred at
5000 years ago in the northern Great Plains.

-

2. STUDY AREA

W) is
located just below and to the west of the crest of the northern
SierraNevadaandisalsoadjacenttotheSierraValley

The Coburn Lake study area (39°32 30 ″ N, 120°27

′ ′