THE stoRies MarsHEs TELL

Scientists at NASA and Columbia University have unraveled important pieces of the climate puzzle in the marshes of the lower Hudson Valley near New York City. Through analysis of sediment layers from tidal marshes in an estuary, Dee Peterson and Dorothy M. Peteet have discovered valuable proxy data in preserved pollen from various plants and seeds. Working with a team of scientists from Columbia University, they have uncovered physical evidence permanently recorded in these sediments of two past significant climatic events:

the Medieval Warm Period, a 500-year-long drought that spanned from 800 to 1300, and the Little Ice Age, the cold period dating from 1400 to 1850.

Through analysis of the pollen proxy in the Piermont Marsh sediments, they confirmed that the dominant vegetation during the Medieval Warm Period consisted of pine and hickory trees. There was also plentiful evidence of charcoal. This is significant because it is indicative of wildfires, another sign of drought. During periods of prolonged drought, vegetation dries out, leaving it vulnerable to lightning strikes. As more dried vegetation accumulates, fire danger increases, so that when lightning strikes it can cause extensive wildfires, leaving deposits of charcoal and ash that become buried in the sediments as a permanent record.

Also present in the sediment record dating earlier than pollen from the pine and hickory was evidence of oak, an indicator of a wetter climate before the Medieval Warm Period. Scientists see this paleorecord as an example of a natural fluctuation in climate rather than a human-caused change, such as those occurring today with global warming. Other evidence to support the occurrence of the Medieval Warm Period includes signs of erosion and an increase in salty marsh plant species in the bay (the drier an area, the more likely salt-resistant species will exist). Scientists view this as important information in relation to global warming today. If continued warming were to trigger drought conditions again in the area, salinity could cause serious problems with water quality and threaten the well-being of nearby populations through contamination of fresh drinking water.

Scientists were also able to discern the Little Ice Age through a change in dominant vegetation species to those that favored cooler and wetter climates. In this case, they found an abundance of spruce and hemlock, forest species that thrive in cooler, wetter climates.

The results of this study further support the use of proxy data to reconstruct the Earth's past climate in order to learn how changes affect the environment and the life that depends on it. The goal is to learn the lessons the data teach, apply them to the conditions that exist on Earth today in light of global warming, and make educated, wise decisions about the future.

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