RECONSTRUCTING A LATE HOLOCENE HURRICANE RECORD WITHIN A SHALLOW WATER ESTUARY, WAQUOIT BAY, MASSACHUSETTS

The vulnerability of the United States’ densely populated east coast to extreme storm events has recently been demonstrated by Hurricane Sandy. The brevity of the instrumental record and lack of detailed historical accounts is a limiting factor in our understanding of the relationship between climate change and the frequency and intensity of extreme storm events. As climate changes we can expect the nature of future storms to likewise be altered. An understanding of this relationship will allow us to better prepare for these storms thus mitigating the extent and cost of damage. The objective of this study was to apply paleotempestological methods to reconstruct a late Holocene storm record within Waquoit Bay, Massachusetts. Positioned along the southern shore of Cape Cod, Waquoit Bay is particularly sensitive to tropical cyclone induced storm-surge.

Three sediment cores (6.0 m, 8.4 m, and 8.2 m) were collected in 3 m of water using a vibracore coring system. Grain sizes were measured along core to identify coarse grain anomalies that serve as a proxy for past storm events. A historical age model (1620-2011 AD) was developed based on Pb pollution chronomarkers derived from X-Ray Florescence bulk Pb data, equating to a sedimentation rate of 8 mm/yr (R² = 0.99). In addition, a long-term (3000 to 275 years before present) sedimentation rate of 1.4 mm/yr (R² = 0.89) was calculated based on twenty four continuous flow atomic mass spectrometry ¹⁴C ages of marine bivalves.

There were eleven coarse grain anomalies identified during the historical interval that coincide with documented hurricane events. During the prehistoric period (pre-1620 AD), there were 32, 34, and 25 coarse grain anomalies identified within the three separate cores, which compared to modern analogues we infer to be storm induced. The frequency of events during the 3000 year record averaged one event per century with significantly higher frequencies occurring during the post-1700 AD interval (5 events per century) and between 2500 and 3000 years before present (3 events per century). Similar periods of increased hurricane activity during the historic and prehistoric intervals were identified in the region and are comparable to western Atlantic records.