Research

Coastal Studies     Geoarchaeology    Paleoclimates    Vegetation Dynamics
Spruce distribution for 21,000 calendar years ago.

Spruce distribution for 21,000 cal yr B.P.
Click to enlarge. (8KB)

At Brown, Quaternary environmental research focuses primarily on the last 21,000 years — the time since the last glacial maximum or the last "Ice Age."  The world then was 6oC colder than it is today and in regions near the large ice sheets, temperatures were 10-15oC lower than today. The Laurendtide ice sheet covered Canada and extended south across New England and the upper Midwest as the advancing ice gouged out the Great Lakes and bulldozed up sediments to form Long Island, Martha’s Vineyard, and Nantucket.  Later this ice sheet would retreat enough that its continued bulldozing formed Cape Cod and the Charlestown Moraine, whose outwash now forms the great beaches of southern Rhode Island.

The ice sheet’s shaping of the New England landscape makes this late-Quaternary time a natural one for study.  After ice retreat, the vegetation of southern New England changed from tundra to spruce, pine, and then oak forests as climates warmed. Lakes and bogs formed, and their sediments are the repositories for the pollen and other data about this period.  With sea level rise, salt marshes developed along the coast, and these contain a history of sea level rise and hurricane overwash. The regional changes in New England are part of global changes including global warming from 16,000 to 6000 years ago. Continental maps of the changing vegetation, hydrology and climates during this warming provides a good test for climate models now being used to predict future climate change.

Tom Webb has been directing research about Quaternary Environments ever since coming to Brown in 1972. His students have generally had two focuses, one in the field and the other in data analysis and synthesis. For the former, students have conducted field work from Africa to Alaska but most have worked in the Northeast. These field studies have often been associated with archaeological sites and contributed to the Down to Geoarchaeology bookmark Geoarchaeology   theme noted below. Recently interests in sea level history and hurricane strikes have led to a new research theme in Down to Coastal Studies bookmark Coastal Studies. The bulk of the research in Quaternary Environments at Brown has focused on data analysis and synthesis and been concerned with the study of  Down to Palaeoclimates bookmark Paleoclimates and Down to Vegetation Dynamics bookmark Vegetation Dynamics. This research is aimed at showing the "big picture" and testing the results of global climate and vegetation models. The maps of the pollen data with vegetation and climatic estimate provide a context for interpreting the individual field studies. Recent results include a set of animations for eastern North America showing the migration of plant taxa in response to the climate changes of the last 21,000 years.

Coastal Studies  Given current trends of increased human development in the coastal zone and predictions of accelerated sea-level rise due to CO2-induced warming of the global climate system, recent and geologic records of past sea levels and  intense storm activity are needed to understand the range of variability of these phenomena. We use stratigraphic studies of salt marshes to reconstruct the history of storm-induced sedimentation and sea level changes in the last 5,000 years.

Geoarchaeology  Pollen and lake-level data provide key information about the past vegetation and environments in which native Americans lived. Brown researchers have coordinated with several archaeologists in reconstructing the recent and late Quaternary changes in vegetation, local habitats, lake levels, and climate in southern New England.

Paleoclimates With a focus on the climate dynamics since the last glacial maximum 21,000 years ago, Brown University researchers have mapped and modeled the changes in vegetation and hydrological data in 5000-year, 3000-year, and 1000-year intervals.  They have interpreted these data in terms of changing temperature and moisture conditions and used these data for checking climate simulations from global climate models.  Brown researchers have also collected new pollen and lake-level data in New England and North America to test and clarify existing climate patterns.

Vegetation Dynamics  The vegetation responded to the many large climate changes during the last 21,000 years.  Time series of maps illustrate and animate these vegetation changes in terms of plant migrations and the formation of new biomes.   Regional, continental, and global maps of the changing abundance and location of plant taxa and biomes provide data for testing global biome models.