COASTAL MASSACHUSETTS POND DEVELOPMENT - EDAPHIC, CLIMATIC, AND SEA-LEVEL IMPACTS SINCE DEGLACIATION

Kettle ponds in the Cape Cod National Seashore in southeastern Massach usetts differ in their evolution due to depth of the original ice bloc k, the clay content of outwash in their drainage basins, and their sit ing in relation to geomorphic changes caused by sea-level rise, barrie r beach formation, and saltmarsh development. Stratigraphic records of microfossil, carbon isotope, and sediment changes also document late- glacial and Holocene climatic changes. The ponds are separated into 3 groups, each of which follow different development scenarios. Group I ponds date from the late-glacial. They formed in clay-rich outwash, ha ve perched aquifers and continuous lake sediment deposition. The earli est pollen and macrofossil assemblages in Group I pond sediments sugge st tundra and spruce-willow parklands before 12 000 yr B.P., boreal fo rest between 12 000 and 10 500 yr B.P., bog/heath initiation and expan sion during the Younger Dryas between 11 000 and 10 000 yr B.P., north ern conifer forest between 10 500 and 9500 yr B.P., and establishment of the Cape oak and pitch pine barrens vegetation after 9500 yr B.P. S edimentation rate changes suggest lowered freshwater levels between 90 00 and 5000 yr B.P. caused by decreased precipitation on the Atlantic Coastal Plain. Lake sediment deposition began in the middle Holocene i n Group II ponds which formed in clay-poor outwash. These ponds date f rom about 6000-5000 yr B.P. In these ponds sediment deposition began a s sea level rose and the freshwater lens intersected the dry basins. T he basal radiocarbon dates of these ponds and stable carbon isotope an alyses of the pond sediments suggest a sea-level curve for Cape Cod Ba y. Holocene topographic changes in upland and the landscape surroundin g the ponds is reconstructed for this coastal area. Group III ponds in the late Holocene landscape of the Provincelands dunes originated as interdunal bogs about 1000 yr B.P. and became ponds more recently as w ater-levels increased. Feat formation in the Provincelands reflects cl imatic changes evident on both sides of the Atlantic region.