Proc. Natl Acad. Sci. USA http://doi.org/n94 (2013)

Credit: © AILSA BURN-MURDOCH / ALAMY

A shift in atmospheric circulation 2,800 years ago curtailed the supply of the nutrient phosphorus to the Florida Everglades, sediment analyses suggest. The loss of this nutrient — combined with a shift to less humid conditions — dramatically altered the composition of vegetation in this region.

Paul Glaser of the University of Minnesota, Minneapolis, and colleagues assessed mineral composition and pollen content in a sediment core taken from the Northeast Shark River Slough, in the southern reaches of the Everglades. There were four distinct phases in the 4,500 year-long record. The first two phases record a rise in water levels and the development of extensive wetlands. The start of the third phase 2,800 years ago, however, saw a shift to vegetation associated with lower water levels and an abrupt drop in nutrient content, particularly phosphorus. Sediments from this period show a lower accumulation of Saharan dust particles as well, suggesting that dust was previously a key source of phosphorus. Water levels continued to decline throughout the final phase.

The team suggests the loss of this dust subsidy — linked to a southward shift of the storm track roughly 3,000 years ago — may have initiated a series of feedbacks that created the pattern of ridges, sloughs and tree islands that define the modern-day Everglades.