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4 cores were collected at the following stations: Station
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Latitude Longitude 3 41 50.1171
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69 58.2639 4 41 50.1490 69 58.3307 2 41 50.0174
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69 58.1467 6 41 49.8340 69 57.8076 A total of 63
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sediment samples were collected at 30-cm intervals from the four
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|
cores. Cores were collected in aluminum casing (irrigation pipe)
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and split, described, photographed, sampled, and discarded in the
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field. Porewater was extracted from cores for salinity measurement
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by refractometer in the lab. Samples were also processed for
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grainsize and two radiocarbon analyses. Data including core
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description table and core images were included in an open-file
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|
report along with electrical resistivity data from the area
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collected in 2004 and 2006 and groundwater data from 2005. Results,
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primarily from one core, were presented at the NEGSA meeting in
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|
Durham, NH in March 2007. Abstract: HOLOCENE SEDIMENTATION IN A
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KETTLE POND BREACHED BY RISING SEA LEVEL ON CAPE COD BRATTON, John
|
|
F., Coastal and Marine Geology Program, U.S. Geological Survey, 384
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|
Woods Hole Rd, Woods Hole, MA 02543-1598, jbratton@usgs.gov A
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|
sediment coring study was performed in a former kettle pond located
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|
at Cape Cod National Seashore that is connected to a larger estuary
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|
via a narrow channel. The longest core (607 cm) collected near the
|
|
center of the pond (water depth approximately 9 m) recovered glacial
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|
sand and gravel directly overlain by 115 cm of fine-grained
|
|
lacustrine sediments, and 257 cm of estuarine sediments. Given the
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|
shallow depth of the connecting channel, the thickness of the
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|
estuarine deposits relative to the lacustrine deposits (> twice as
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|
thick) was unexpected, as the pond would have only been breached
|
|
within the last 2,000 years based on published sea-level curves for
|
|
the region. The fresh kettle pond, however, would have likely
|
|
existed for about 15,000 yrs prior to the marine invasion. This
|
|
pattern suggests that either, 1) estuarine sedimentation rates are
|
|
much higher than lacustrine sedimentation rates in breached kettle
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|
ponds, or 2) the breaching took place earlier than would be expected
|
|
by modern sill elevations relative to sea level. Other drowned
|
|
kettle depressions that are completely filled with fine-grained
|
|
estuarine and marine sediments are known from Cape Cod, consistent
|
|
with the first scenario. Land use changes could also have increased
|
|
sedimentation rates within the last few centuries. The second
|
|
scenario, however, could only be distinguished from the first by
|
|
development of core chronologies using radiocarbon dating, and would
|
|
not rule out the possibility of multiple episodes of breaching. More
|
|
detailed studies of sediments in other breached or drowned kettle
|
|
depressions will be necessary to determine how common this pattern
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|
of sedimentation might be in other formerly glaciated coastal
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|
settings. Similar kettle depressions may preserve other sediment
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|
transitions from lacustrine to estuarine that could complement
|
|
sea-level reconstructions based on salt marsh peats, as well as
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|
serving as archives of major coastal storms. The nature of the fill
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|
in such depressions also has important implications for coastal
|
|
construction and dredging, as well as for investigations of coastal
|
|
hydrogeology and submarine groundwater discharge.
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