A sea-level rise curve from Guilford, Connecticut, USA

Abstract

High-resolution stratigraphic studies based on sediment chemistry, lithology, macroflora, and benthic foraminiferal assemblages in three peat cores from coastal salt marshes at Guilford, Connecticut, show that coastal marshes are ephemeral environments. Marsh-wide environmental variations were common, and century-long episodes of relative submergence alternated with emergence. Despite about 2 m of relative sea-level rise (RSLR) in Connecticut over the last 1500 years, the marshes have expanded both landwards and seawards, and marsh accretion has been outpaced only marginally by RSLR. We used radiocarbon dating and the level of anthropogenic markers (metal pollution, as dated with 210Pb) in the cores for age control. For most of the last 1000 years the rate of RSLR was between 1.3 and 1.8 mm/yr, but over the last 300–400 years it increased to 2.9–3.3 mm/yr, and has been faster than the accretion rate, especially in the middle marsh. The net-submergence rate or “submergence index” (ratio of the rate of RSLR and marsh-accretion rate) averaged about 1.15 over the last 1000 years, and increased to about 1.5 over the last 200 years. The rate of RSLR was very sluggish during the early part of the Little Ice Age, but we found a slightly higher rate during the Little Climate Optimum; this excursion is close to the noise level, however. The most significant observation is that RSLR increased strongly around A.D. 1650. The onset of this acceleration falls in the middle to end of the Little Ice Age, and thus preceded the period of modern global warming that started late last century and that has been tentatively correlated with anthropogenic emissions of greenhouse gases.