August 4, 2003
Studies show weaker coastal upwelling 6,000 years
ago
By Tim Stephens
The California Current is a major influence on the climate of western
North America and on the productivity of both terrestrial and marine
ecosystems along the West Coast. But 6,000 years ago, the California
Current wasn't quite what it is today, according to a team of researchers
at UCSC.
The high biological productivity of California's coastal waters
is a direct result of the spring and summer upwelling season,
which brings deep, cold, nutrient-rich waters to the ocean surface,
supporting a diverse and complex ecosystem.
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New findings suggest that coastal upwelling in the California Current
was significantly weaker 6,000 years ago than it is today as a result
of differences in Earth's orbit around the Sun. This hypothesis is based
on a combination of results from computer modeling of the California
regional climate and analysis of geologic records.
Noah Diffenbaugh, a graduate student in Earth sciences, presented the
new results at a meeting of the International Union for Quaternary Research
(INQUA) in Reno, Nevada, July 24 through 30.
The past 11,000 years is known as the Holocene, or "Age of Humans,"
when people became the dominant shapers of regional and global environments.
Archaeological records indicate that the mid-Holocene (8,000 to 3,000
years ago) was a particularly important period of global climatic and
cultural transition, with important innovations in agricultural, architectural,
and ceremonial complexity occurring throughout the world.
Geological records suggest that these increases in cultural complexity
coincided with regional climatic change, and evidence for such changes
has been seen in archaeological and geological records from the Pacific
Coast in the California Current region. It has not been clear, however,
exactly how climate and culture interacted in the California Current
region during that time.
The high biological productivity of California's coastal waters is
a direct result of the spring and summer upwelling season, which brings
deep, cold, nutrient-rich waters to the ocean surface, supporting a
diverse and complex ecosystem. While ancient peoples would likely have
been affected by changes in the California Current through time, the
geologic record of mid-Holocene California Current upwelling is ambiguous,
with some studies indicating increased mid-Holocene upwelling and others
reduced.
In order to better understand the nature of coastal upwelling in the
California Current at that time, the UCSC researchers employed a high-resolution
regional climate model. The regional climate model was developed by
a team led by Diffenbaugh's adviser, professor of Earth sciences Lisa
Sloan. The model showed that 6,000 years ago, the California Current
was affected by differences in the amount of solar energy reaching the
Earth due to predictable changes in Earth's orbit.
At the INQUA Congress, Diffenbaugh presented results from the climate
model in conjunction with geologic data from the California Current
analyzed by a group of researchers headed by John Barron of the U.S.
Geological Survey in Menlo Park, California.
The combined results indicate that, relative to the present, the mid-Holocene
California Current upwelling season was longer and less vigorous than
today, with reduced seasonal contrast. Such a change in California Current
activity would have impacted marine ecosystems and perhaps also affected
ancient human communities relying on those marine resources.
The comparison of geologic data and climate model results presented
by the UCSC-USGS team helps to explain the evolution of California Current
activity during the Holocene. It may also provide insight into the environmental
factors that shaped anthropological change in the region during the
culturally important mid-Holocene.
The primary results presented at the INQUA Congress were published
recently in Paleoceanography, a peer-reviewed journal published
by the American Geophysical Union.
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