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Monterey Bay Studies


Monterey Bay Studies

 

Monterey Bay National Marine Sanctuary Project, 1999

Pollen Study Shows Changes in Vegetation and Climate from the Last Glacial Maximum to the Present in the Monterey Bay Area: Near Disappearance of the Redwoods

by Mary McGann

Abstract

Pollen and spores were analyzed from a sediment core obtained at a depth of 3400 m on the Monterey Submarine Fan. Of the 33 pollen and spore types recognized, the four most abundant are pine, redwood, oak and Compositae, the latter including plants such as thistles, dandelions, sunflowers and ragweed. The relative abundance of these four pollen types was used to define five pollen zones. The oldest zone [Carbon-14 dated at 19,350-16,800 years before present (B.P.)] is characterized by very abundant pine and rare fir pollen, reflecting the vegetational response to the cold climatic conditions during the Last Glacial Maximum. Note that the redwoods, so commonly associated with the Monterey Bay area, were very rare in the region at this time. Overlying this "glacial" vegetation zone is one representing a transitional climatic regime (16,800-12,410 years B.P.), characterized by appreciable amounts of pollen from river-dwelling alders and a form of green algae (Pediastrum) restricted to living in freshwater ponds and shallow lakes. Taken together, their presence is indicative of an improvement in climatic conditions and may reflect an increase in nutrient-rich coastal runoff. The upper three zones (12,410 years B.P. to the present) are characterized by decreasing pine pollen and increasing frequencies of redwood, oak and Compositae. They reflect the Monterey Bay region's vegetational response to the warming climatic conditions after the retreat of the glaciers in the Sierras and elsewhere in the United States.

This abstract (WPG# M98-0386) is from Monterey Bay National Marine Sanctuary Symposium, Sanctuary Currents '98, Human Influences on the Coastal Ocean, Poster Session, 1998.


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