The development and stability of a cool-water carbonate beach system, Maine

Brandes, Allison

From the abstract: "Sand Beach is a cool-water carbonate beach system that lies on the southeastern side of Mount Desert Island, Maine. Adjacent south-facing beaches on Mount Desert Island, Otter Cove and Hunter's Beach, have a similar offshore supply of comminuted shell material but are composed of terrigenous rather than calcium carbonate. Therefore, the existence of Sand Beach raises the question of why there is a high-latitude carbonate beach system in this area. This study uses vibracores, surface samples, ground-penetrating radar and topographic beach profile data to address this problem. Vibracores and ground-penetrating radar suggest that this beach has built up on former glacial deposits. Dune material overlies lagoon and tidal flat material, which lie unconformably on glacial-marine clay and till deposits. The barrier most likely migrated into its present bayhead position during Holocene sea-level rise. In recent history there is a dynamic stability of carbonate input and degradation. Profile data between April and December 1999 show that at Sand Beach large volumes of sand accreted during the summer when there was a westward-moving current within the cove. In late fall and winter months, there was a loss of material at the berm, but a gain towards the vegetation line. The total flux of sand in the beach system was 16,675 m3 while adjacent Otter Cove Beach showed only marginal seasonal change in beach volume. Sand Beach is mostly a combination of reworked glacial material and bioclastic remains of barnacles, echinoderms and molluscs. The overall carbonate concentration decreases from 70% in the nearshore zone to 30% in the backbarrier region. This change in concentration is most likely a result of selective transport processes within this beach system. Downcore the carbonate concentration was mostly constant with the exception of a drop at the water table to 5-15%, possibly due to dissolution. The Sand Beach data suggest that cool-water carbonate beach development is dependent on a high benthic productivity to counterbalance degradation of carbonate and dilution of the carbonate concentration from terrigenous input."