Geoscience Reference
In-Depth Information
the coastal ocean during the little ice age
Because the climate in the West is strongly inl uenced by the temperature
of the eastern Pacii c Ocean, paleoceanographers—those who study past
ocean conditions—have examined sediment cores from the coastal ocean
for evidence of correlations with climate on land. One such researcher, John
Barron of the U.S. Geological Survey, used the fossils of diatoms in the Santa
Barbara Basin to reconstruct long records of ocean surface water conditions.
Barron and his colleagues have shown that, whereas coastal surface water
was generally cooler during the Medieval Climate Anomaly than today, the
Little Ice Age coastal surface waters tended to be warmer, and more variable,
than coastal waters during the Medieval period. Warm waters in the eastern
Pacii c are associated with El Niño, and, as we will discuss in the next chap-
ter, a growing body of evidence, including coral records from the tropical
Pacii c Ocean, suggests that El Niño events were stronger and more frequent
during the Little Ice Age, leading to wetter and more variable conditions in
the West.
h e droughts that punctuated this generally wetter period were also
shown to be tied to coastal ocean conditions. Larry Benson and his research
team compared the dry periods from Mono Lake in the eastern Sierra with
sea surface temperature records from coastal California, and they were
intrigued to i nd a close correlation between the droughts and the periods
when coastal waters were relatively cool. As we discussed in chapter 4, one of
the oceanic cycles that inl uences climate in the West is the Pacii c Decadal
Oscillation (PDO). h is is an oscillation of water temperature in the North
Pacii c Ocean, with cooler surface water temperatures associated with the
negative phase of the oscillation and warmer surface temperatures associated
with the positive phase. Benson and his colleagues found that the drought
periods in the Sierra that led to the lowering of the Mono Lake surface level
occurred when the PDO was in a negative (cool) phase.
h e evidence of past megal oods is a cause of concern for California. Even
as we enter a period that is predicted to be warmer and drier, catastrophic
l ooding will continue to threaten the region. As more precipitation falls as
rain instead of snow, l ooding during the winter is predicted to inundate the
region even more frequently. h e deadly climate patterns that have occurred
repeatedly in the past are likely to recur in the future.
