Sediment cores collected along a transect in Crooked Pond, southeastern Massachusetts,
provide evidence of water-level changes between 15,000 cal yr B.P. and present.
The extent of fine-grained, detrital, organic accumulation in the basin, inferred
from sediment and pollen stratigraphies, varied over time and indicates low
water levels between 11,200 and 8000 cal yr B.P. and from ca. 5300 to 3200 cal
yr B.P. This history is consistent with the paleohydrology records from nearby
Makepeace Cedar Swamp and other sites from New England and eastern Canada and
with temporal patterns of regional changes in effective soil moisture inferred
from pollen data. The similarities among these records indicate that (1) regional
conditions were drier than today when white pine (Pinus strobus) grew
abundantly in southern New England (11,200 to 9500 cal yr B.P.); (2) higher
moisture levels existed between 8000 and 5500 cal yr B.P., possibly caused by
increased meridonal circulation as the influence of the Laurentide ice sheet
waned; and (3) drier conditions possibly contributed to the regional decline
in hemlock (Tsuga) abundances at 5300 cal yr B.P. Although sea-level
rise may have been an influence, moist climatic conditions during the late Holocene
were the primary reason for a dramatic rise in water-table elevations.
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Figure 1. The upper map shows the present bathymetry of Crooked Pond, with the locations of cores and probing transects. The profile of the basin shown in Figure 2 is based on probing data from the northern (upper) transect. The lower map shows the Plymouth-Carver Aquifer (dark grey) and the sites mentioned in the text, which are used to provide a regional pollen stratigraphic framework. |
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Figure 2. A profile of the southwestern basin of Crooked Pond from northwest to southeast showing A) the percent organic content of surface-samples, and B) core locations, sediment stratigraphies, and pollen stratigraphic correlations. The dashed lines connect the positions of the second peak in spruce pollen abundance (S2), the peak in heath pollen abundance (HE), the point at which oak pollen first rises above 30% abundance (O), the hemlock decline (HD), the late-Holocene hemlock rise (HR), and the ragweed rise (RR). The core stratigraphies are generalized to show three types of sediment: detrital organic sediments, inorganic clay and sands. |
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Figure 3. Age model for core D, showing the dating error and depth range for each date. Solid circles represent calibrated radiocarbon dates, open boxes indicate the relative position of calibrated radiocarbon dates from core K, and gray points represent the calibrated ages of several regional pollen stratigraphic events, based on the ages calculated for other nearby sites. Table 2 lists the specific date information. |
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Figure 4. Percent organic matter and percent hemlock pollen in cores D and G. Both cores show a substantial reduction of organic content and hemlock pollen percentages at ca. 1 to 1.5 m depth. |
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Figure 5. Percentage pollen diagram from core D. A sum of all trees, shrubs, and herbs was used to calculate the percentages. |
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Figure 6. Selected pollen types from cores D, K, I, C, and B, with lines of correlation (as in Fig. 2). Bars to the left represent the sediment stratigraphies, with dark gray for detrital organic mud and light gray for sand. Circles mark the position of calibrated radiocarbon dates (cal yr B.P.) The inset shows the position of sand layers (shaded) in cores I, J, and H relative to the total pine (thin line) and white pine (Pinus subgenus strobus-type; heavy line) stratigraphies. Light gray curves in the upper cores K and I stratigraphies also represent percent white pine. Pollen taxa are abbreviated in diagrams for cores K, I, C, and B, but the order of presentation is the same as for core D. |
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Figure 7. Water table elevations at Crooked Pond through time. The plot illustrates the estimated elevation of the water surface, based on stratigraphic and sedimentary evidence summarized in Table 3. Boxes indicate the constraint on water-level elevations, as well as dating error. |
