Lakes watered the now-parched southwestern United States between 14,000 and 20,000 years ago while Canada was cloaked in ice. An international team of oceanographers and climatologists found evidence that these lakes may have been fed by a storm system pushing up from the tropics.
“Large ice caps profoundly altered where storms went during glacial periods,” said study leader Mitch Lyle, oceanographer at Texas A&M, in a press release. “Before this study, it was assumed that Pacific winter storms that now track into Washington and Canada were pushed south into central and southern California. However, by comparing timing between wet intervals on the coast, where these storms would first strike, with growth of the inland lakes, we found that they didn’t match.”
Indeed, summer’s sopping-wet southern storms
seemed to be the source of the ancient lakes. Lyle’s group found a
mixture of pollen that would be expected in the summer time. To the
west, pollen were trapped in marine sediments along the California
coast during summer.
“We think that the extra precipitation may have come in summer, enhancing the now weak summer monsoon in the desert southwest. But we need more information about what season the storms arrived to strengthen this speculation,” Lyle said.
Understanding the weather patterns of the ancient past may help climatologists understand the changing patterns of the modern atmosphere.
“We need to understand better the processes that directed the storms thousands of years ago, and to predict better what changes might occur in the future,” said Lyle.
Bear grass in mid-summer above Lower Grinnell Lake, Glacier National Park. (Kerrick James/Corbis)
Pleistocene lakes and rivers of the Mojave Desert about 15,000 years ago (Philip Stoffer, Wikimedia Commons