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 194

cellophane and aluminum foil, and then placed in wooden
boxes for transport to the laboratory. All samples were kept
cool in transit and then stored at 4°C in the laboratory.

3.2. Methods in the Laboratory

One set of cores was designated to be the primary set of
cores used for analysis. The other set of cores is referred to
here as the secondary set of cores. Both sets of deep core
sediments were split horizontally, sketched, and photo-
graphed. Sediment layers were then visually classified as to
composition: gyttja ( (fine, organically rich lake sediments),

macro-sized organic detritus, clay, or ash (Figure 2). Deep
core sediments were also subsampled at 1 cm intervals unless,
again, smaller intervals were necessary to locate stratigraphic
boundaries or charcoal visible in core segments.
A radiocarbon-based chronology was developed for Co-
burn Lake based upon 14 C accelerator mass spectrometry

Figure 3. Age-depth diagram for Coburn Lake. Locations of 14 C-
AMS (accelerator mass spectrometry) dates, a thick layer of Maza-
ma ash, bent strata, and where older sediments (above) were thrust
up and over younger lake sediments are highlighted.

(AMS) dating of 24 plant macrofossils taken from the pri-
mary set of deep core sediments (Figure 3). Radiocarbon
dates (Table 1) were converted to calibrated years before
present (cal years B.P., A.D. 1950) using the Cologne Ra-
diocarbon, Calibration, and Paleoclimate Research (CalPal):
Online quickcal2004 version 1.2 (B. Weninger et al., 2004,
available at http://download.calpal.de/calpal-info/). Layers
of organic detritus and clay were not excluded from the
age-depth curve for the following reasons: (1) much of the
core was made up of nongyttja material, (2) relying on dates
in gyttja alone would have produce unrealistic results, and
(3) peaks in charcoal, the focus of this study, were often
associated with nongyttja layers. Calibrated radiocarbon
dates were graphed proportionally between dates without
developing a formal age-depth model because (1) the large
number of 14 C-AMS dates available made such modeling
unnecessary, (2) lake deposition appeared to be strongly

Figure 2. Relationships between stratigraphy layers, charcoal
peaks, sediment bulk density, and magnetic susceptibility at Coburn
Lake. (a) Stratigraphy of sediments. (b) Number of charcoal parti-
cles of >250 m in size per g 3 found within lake sediments. The two

largest charcoal peaks (>1000 charcoal g 3 ) have been truncated to

μ

fit the column size. (c) Bulk density of sediments. (d) Magnetic
susceptibility (MS) of sediments.