Block Island, RI: a Microcosm for the Study of Anthropogenic and Natural Environmental Change

Long Island Sound on a map of Adriaen Block (~1613) with Block Island circled at the lower right.

What: Block Island (RI) is a beautiful islet (~ 7 by 3 miles) situated 12 miles from the Connecticut-Rhode Island shoreline, east of Long Island Sound (LIS). It is largely built from material emplaced by terminal and recessional moraines during the last two glacial maxima. The moraines contain locally derived, fossiliferous Upper Cretaceous sediments deposited in a coastal plain setting, providing information on the local climate millions of years ago, when the world did not have ice caps (‘Greenhouse World’).

The glacial deposits provide evidence for accumulation, motion and melting of large ice sheets at a location where we now enjoy a moderate, mid-latitude climate. Varved lake deposits formed in periglacial lakes during retreat of the ice sheet offer insights on the rates of glacial rebound. With further retreat of the ice sheet, salt marshes and fresh water bogs developed in which peat accumulated, containing a record of local climate and vegetational history. These sediments also carry a record of anthropogenic metal pollution that arrived at this ‘remote’ location through atmospheric deposition.

Microfossils in the peat offer a record of environmental change, which we can relate to rates of relative sea level rise over the last decades, centuries and millennia. Coastal erosion of the cliffs of the island continues, but so does accumulation of dunes, coastal spits, and peat in other locations.

Block Island thus offers unequalled opportunities for integrative research in earth and environmental sciences: within its modest perimeter we can study rates of recent sea level rise and anthropogenic pollution within the framework of climate and environmental changes over centuries to thousands of years,with even a peek into the past a hundred million years ago.

When: 23 June through 18 July, 2008

Where: Wesleyan University, CT; and Block Island, RI

Who: 6 students and Joop Varekamp, Professor, Earth & Environmental Sciences, Wesleyan University and Ellen Thomas, Senior Research Scientist, Geology & Geophysics, Yale University

Project Description and Goals

The formation and evolution of Long Island Sound is a reflection of the deglaciation history of the N-American continent, followed by more recent human impacts. During the early deglaciation, periglacial lakes formed south of the retreating glaciers. Varved sediments from Glacial Lake Connecticut, the pre-cursor lake of Long Island Sound are found in outcrops on Block Island. This lake drained at a poorly constrained time, and a tundra-like environment was established from which windblown material was deposited as loess on Long Island. A river valley system was carved into the old lake beds, and about 10,000 years ago the ocean invaded the region and Long Island Sound formed relatively quickly (meltwater pulse 1b). Going forwards 9500 years and the colonial period started with landuse changes, and the first dramatic human impacts on the Sound. From 1800 on, human activity and climate change were the main drivers of the environmental deterioration of the Sound, and enhanced rates of sea level rise related to modern global warming cause the drowning of coastal marshes on Block Island. The various marsh, lake and pond sediments on Block Island as well as some of the older rock outcrops provide insight into the paleoenvironmental history of the Sound, be it the ‘geological period’ or the anthropocene. We are studying evidence for processes ranging from long term sea level rise to the modern sea level rise acceleration, the pollution of sediments with anthropogenic Mercury, as well as ecological aspects of the brackish water environments. Our direct goals are to date major geological and paleoenvironmental events with radiocarbon, derive precise rates of sea level rise, and establish rates of Mercury accumulation in an area with no known local sources. Our ecological work is in support of the sea level rise studies as well as fundamental aspects of the ecology of marsh foraminifera in brackish waters.

Student Projects

Modern Block Island with the Great Salt Pond in the middle and various small ponds all over the island.

  • We will conduct a field study of outcrops of glacial, periglacial and postglacial deposits in order to evaluate possibilities to date the timing of deglaciation events, to be combined with our data from Long Island Sound. We will study and sample the varved lakebeds and the overlying marsh deposits and try to constrain their ages with radiocarbon dating. The marsh deposits will be studied to see if they are salt marsh or fresh water marshes using marsh foraminifera.
  • We will conduct a field study of the outcrops of Cretaceous material, and collect fossil material if available. We will sample and analyze for foraminifera, because the coastal plain sediments may contain brackish-marine intervals. If fossil leaves are found, we will compare these with samples from the collection at the Peabody Museum (Yale University) for further evaluation of the climate in Cretaceous times.
  • We will map and core (Dutch Corer; cores 1-2 m length) marsh sequences from bogs and ponds and determine if these were deposited in salt or fresh water marshes though field and laboratory study of metaphyte remains (and their carbon isotope composition), marsh foraminiferal assemblages and bulk chemical composition (e.g., sulfide contents, organic carbon content). These data will provide indirect information on the geological history of Block Island, e. g. on the timing of inundation with sea water. Sequences of freshwater peat overlain by salt water pea will show transgressive contacts to be dated.
  • We will obtain surface samples from mud flats and marshes in order to evaluate the local foraminiferal intertidal zonation. The tidal ranges on Block Island are well known, since there are two local tidal stations (Old Harbour, Great Salt Pond). The tidal ranges are similar to these within some marshes along Long Island Sound (e.g., Thomas and Varekamp, 1991; Nydick et al., 1995), but faunas will probably differ because average salinities are higher this far east.
  • We will use the data on recent foraminiferal assemblages to determine changes in marsh elevation over time, using salt marsh peat cores.
  • We will determine rates of relative sea level rise over the last decades and rates in earlier years through combined radiocarbon dating and paleoenvironmental proxies as developed in the past (Thomas and Varekamp, 1991; Varekamp et al., 1992; Varekamp and Thomas, 1998).
  • We will measure concentrations of mercury in the salt marsh peat cores and fresh water lake and bog cores in order to estimate atmospheric deposition at a location remote from pollution source, and compare these values to our existing estimates for the Long Island Sound region.
  • We will use maps and aerial photographs of Block Island in order to estimate area loss through marine erosion and gain through coastal deposition.

Field Conditions and schedule

  • Students will arrive at Wesleyan for one day of preparation and short lectures on goals, methods and techniques. We will leave that evening (June 23) for Block Island.
  • We will spend the first week (5 days, 4 nights) of the project on Block Island, where we will study the local geology, and evaluate which outcrops are suitable for our work. The outcrops change rapidly with coastal cliff erosion, slumping, and human activities, so older descriptions are no guarantee. We will perform surface sample collection and obtain several cores for field study, and an initial evaluation of marsh environments based on plants and fauna.
  • The second week will be spent at Wesleyan, for initial chemical and micropaleontological studies (4th of July holiday falls in this week, when Block Island is overbooked)
  • The third week (5 days, 4 nights) we will go back to Block Island, in order to collect more core material, as required by the pilot study results in the laboratory studies from the second week.
  • The fourth week we will spend in the laboratory for continued chemical and micropaleontological studies.

Course Preparation

It is recommended to have one or more of the following classes:

  • Geomorphology
  • Sedimentology/Stratigraphy
  • Quaternary geology
  • Glacial Geology
  • Geochemistry
  • Paleoclimatology

Reading List

Glacial/Deglacial History of Block Island and Environments:

  1. Boothroyd, J. C., and Sirkin, L., 2002. Quaternary Geology and Landscape Development of Block Island and Adjacent Regions. In: P. W. Paton, L. L. Gould, P. V., August, and A. O. Frost, eds., The Ecology of Block Island, The Rhode Island Natural History Survey, p. 13-27
  2. Uchupi, E., Driscoll, N., Ballard, R. D., and Bolmer, S. T., 2001. Drainage of late Wisconsin glacial lakes and the morphology and late Quaternary stratigraphy of the New Jersey – southern New England continental shelf and slope. Marine Geology, 172: 117-145.
  3. Varekamp,.J. C., Thomas, E., and Groner, M., 2005. The late Pleistocene – Holocene History of Long island Sound, Seventh Biennual LIS Research Conference Proceedings, 2004, p. 27-32

Mercury in Long Island Sound

  1. Varekamp, J.C., Kreulen, B., Buchholtz ten Brink, M.F, and Mecray, E., 2003, Mercury contamination chronologies from Connecticut wetlands and Long Island Sound sediments. Environmental Geology, 43, 268-282.

Sea Level Rise and Salt Marshes

  1. Varekamp, J. C., Thomas, E., and Van de Plassche, O., 1992. Relative sea-level rise and climate change over  the last 1500 years (Clinton, CT, USA). Terra Nova, 4: 293-304
  2. Varekamp, J. C., and Thomas, E., 1998, Sea Level Rise and Climate Change over the Last 1000 Years, EOS, 79: 69-75