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interpreted to indicate the start of the influx of mate-
rial eroded from the watershed. This interpretation was
bolstered by the appearance of anisotropy of anhys-
teric remanence (AAR) fabric at this time, indicating
the initiation of the major infl ow stream into the
lake. These changes probably refl ect a major change
in the hydrologic regime in the area. The clear-cutting
of the watershed at
c.
100-200 years BP was also
detected magnetically by large increases in the mag-
netic mineral concentration of magnetite, probably
indicating the erosion of topsoil into the lake.
Kodama
et al
. (1997b) also looked at magnetic prop-
erties of recent lake sediments from several glacial
lakes in the Pocono Mountains of northeastern Penn-
sylvania, including Lake Lacawac and Lake Giles. They
observed an abrupt increase in ARM intensity in the
top 10 cm of the sediment column that started at
c.
1900 AD. SEM observation of magnetic extracts from
the sediments indicates that framboidal magnetite
microspherules are the culprit, and an indicator of the
initiation of signifi cant amounts of fossil fuel combus-
tion in the northeastern United States for electrical
power generation.
Oldfi eld (1990) had made similar observations in Big
Moose Lake in the Adirondak Mountains of New York.
The presence of antiferromagnetic minerals in the top
10 cm of one lake, also seen in soil samples from the
lake's watershed, indicated erosion of the catchment
due to European settlement in the area. Finally, time
series analysis of magnetic mineral concentration vari-
ations identifi ed a 50 year period in magnetic intensity
variation similar to the same frequency of variation in
historic rainfall data from the northeastern US over
the past 150-250 years (Fig. 8.4). The implication is
that magnetic mineral concentration variations could
be used as a proxy for rainfall variations in a lake's
watershed.
The last of our examples of how magnetic mineral
parameters can aid paleoenvironmental studies of lake
sediments comes from Hurleg Lake in China (Zhao
et al.
2010 ). Zhao
et al
. used a multi-proxy record col-
lected from the lake sediments to look at millennial-
scale changes in lake level on the Tibetan Plateau to
monitor fl uctuations in the strength of the monsoon.
Spikes in magnetic mineral concentration detected by
ARM, SIRM, and χ and low ARM/SIRM ratios suggest
more coarse-grained magnetic minerals entering the
lake due to lower lake levels. This interpretation was
made in concert with other paleoclimatic indicators,
i.e. percentage carbonate and Mg/Ca ratios, and shows
A
. White Lake
B
. North Atlantic
WL 03-1
Wet
WL 03-2
Cold
Events
0
(LIA)
Dry
Wet
Dry
Warm
Cold
0
1000
1
*
2000
*
3000
2
4000
*
3
5000
4
6000
*
7000
*
0204060
0
20 40 60
0510 15 20
IRM
IRM
Hematite-Stained
10
-5
Am
2
/kg)
10
-5
Am
2
/kg)
(
×
(
×
Grains (%)
Fig. 8.2
Comparison of IRM peaks in White Lake sediment
compared to cold events recorded in the North Atlantic by
Bond
et al
. (2001). Figure from Li
et al
. (2007) . Asterisks are
the locations of
14
C samples used for dating the White Lake
sediments. The IRM peaks are caused by oxidation of lake
sediments during low stands of the lake water level. Y-X Li, Z
Yu and KP Kodama, Sensitive moisture response to
Holocene millenial-scale climate variations in the Mid-
Atlantic region, USA,
The Holocene
, 17, 1, 3-8, 2007, Sage
Publishing. (See Colour Plate 14)
(Fig. 8.2). The high-intensity layers were interpreted to
be due to oxidation of the magnetic minerals in the lake
during the exposure of lake sediments at times of low
lake level. The increase in magnetic intensity due to
oxidation was supported by observing sediment oxida-
tion in the laboratory with sediment collected from
deeper parts of the lake. The periods of low lake level
observed magnetically coincided with cold periods in
the North Atlantic based on North Atlantic sediment
records of paleoclimate.
Cioppa & Kodama ' s (2003a) study of the Holocene
sediments of Lake Waynewood in the Pocono Moun-
tains of northeast Pennsylvania used the abrupt change
in environmental magnetic parameters (ARM, SIRM,
χ and their ratios, as well as the
S
- ratio) at 2900 years
BP to indicate a signifi cant change in watershed
dynamics (Fig. 8.3). The change in parameters was
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