SEDIMENT RECORDS OF THE 1938 GREAT NEW ENGLAND HURRICANE AT BLOCK ISLAND (RI)

Block Island (RI) is a beautiful island (~ 7 by 3 miles) located 12 miles from the Connecticut - Rhode Island shoreline, east of Long Island Sound (LIS). It consists of a northern and southern hilly region made up of morainal material, connected by two low, sandy spits covered with dunes, enclosing Great Salt Pond. The western tombolo (towards Block Island Sound) is breached so that ocean waters can enter the Pond. The Great New England Hurricane of 1938 caused major destruction on Block Island through its strong winds and a storm -surge 3.5 - 4.5 feet high. We found evidence for the severe environmental effects of the hurricane in cores from Great Salt Pond, from salt marshes along the shores of Great Salt Pond, and from Sachem Pond on the northern tip of the Island. Cores from Great Salt Pond typically contain fine sands and silts with estuarine, low diversity, inner neritic benthic foraminiferal assemblages dominated by species of Ammonia, Elphidium and Haynesina. A core in western Great Salt Pond, however, contains a coarse sand layer (~20 cm thick) dated to about 1940 through the core’s mercury pollution profile. This coarse gray layer contains marine snails, bryozoans, serpulid worms and specimens of the foraminifer Poroeponides lateralis, biota characteristic for the shelf to the South of Block Island. Extensive coring in the salt marshes along Great Salt Pond and dating of the cores by Hg-pollution profiles showed that the modern marshes became only established around 1940, on a base of coarse sand, with no evidence for the presence of older marsh peats. In a core from Sachem Pond, bulk organic carbon isotope values typically are around -21 per mille and nitrogen isotope values 4.5 to 5.0 per mille, but sediment deposited around 1940 shows an increase in carbon isotope values to about -16 per mille, with a decrease in N-isotope values to 2.5 per mille, reflecting increased input of organic matter from C4 salt-marsh grasses. Later hurricanes (e.g., 1954, 1960) may have left similar isotope signals in the Sachem Pond sediment record. Our core data thus show that the storm surge caused by the 1938 hurricane deposited a large amount of coarse sand derived from the shelf of the Atlantic Ocean into Great Salt Pond, destroyed the coastal salt marshes around the Great Salt Pond, and deposited abundant marsh plant debris in nearby ponds.