Through the use of high resolution sampling and
analysis of marine sediments, detailed climatic
histories of the current and last interglacial (the
Holocene and Marine Isotope Stage 5, respectively)
have been constructed for the Santa Barbara Basin,
offshore southern California. The data sets presented
herein are among the most highly resolved marine
records available for these two warm intervals, and they
document that large climate changes have occurred on
decadal time scales in the recent geologic past. The
data also demonstrate that during the middle Holocene
when climate was warmer than today, El Nino warm
events were much more frequent and intense than they
have been over the past century. When compared to
pollen and benthic foraminiferal data from the last
interglacial, the biogenic silica records and stable
oxygen isotopes from two species of planktonic
foraminifera suggest warming of the surface ocean
and the adjacent continent several thousand years
before melting of the ice sheets. This lag is possibly
the result of the difference in response time between
the surface marine and terrestrial reservoirs and the
cryosphere. The silica and isotope data also indicate
dramatic differences between the evolution of the two
most recent interglacial periods. Using six years of
modern sediment trap data from the Santa Barbara
Basin as a basis for interpreting the past, it appears
that the seasonal changes in hydrography and
productivity seen in the modern basin have been a
feature of the climate record throughout the Holocene.
On the other hand, a seasonal cycle similar to today’s
was not apparent in the basin until several thousand
years after the beginning of the last interglacial.
According to models of solar insolation, maximum
Northern Hemisphere summer sunlight peaked near
the beginning of the Holocene but well after the
beginning of the last interglacial. Perhaps the differing
patterns of solar radiation during these two warm
intervals is one of the drivers of the differences
observed in the paleoclimatic data.

friddell@geol.sc.edu