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impacts along the west coast
h e Younger Dryas as well as other major global climate changes inl uenced
conditions along the Pacii c Coast. Evidence for these impacts is found in
sediment cores from the eastern Pacii c Ocean, including those accumulating
in the Santa Barbara Basin of the Southern California coast. As described
in the preceding chapter, sediments are laid down there, year at er year, leav-
ing behind distinct layers. During warm interglacial periods, the deepwater
entering the basin bottom is very old and depleted in oxygen, so that bottom-
dwelling marine animals cannot survive to mix and churn the sediments.
h e basin sediments form in undisturbed seasonal layers, with light-colored
layers resulting from the siliceous diatoms raining down the water column
during the spring and summer, and darker layers resulting from the silts and
clays transported with runof from the land during the winter. But was this
also the case during the ice ages and the Younger Dryas event?
h is was one of the questions that James Kennett, a founding father of the
i eld of paleoceanography—the study of ocean and climate conditions of the
past—set out to answer. Kennett was the co-chief scientist for the Ocean
Drilling Program's coring ef orts in the Santa Barbara Basin in the early 1990s.
h ere, he and his team retrieved the longest cores from the eastern Pacii c to
date, spanning the past 160,000 years. h ese cores reveal that, during the
last ice age, Santa Barbara Basin sediments lacked their unique annual layers.
In a collaborative ef ort between Kennett and one of this topic's authors,
B. Lynn Ingram, we discovered that, during the last ice age, ocean circulation
appeared to have been altered, with the l ow of younger, more oxygenated
waters to the eastern Pacii c Ocean and into the basin. h ese more oxygen-
ated waters would have supported bottom-dwelling organisms—worms,
clams, and so on—that churn through the bottom sediments as they dig
burrows and search for food, destroying the i ne laminations. Kennett had
observed that the dark brown and i nely layered sediments typical of the
late Pleistocene and Holocene sequences in the Santa Barbara Basin were
abruptly replaced by a three-foot-thick layer of light-colored, homogeneous
sediment during the Younger Dryas, a period when younger, more oxygen-
ated waters entered the basin.
Kennett separated out the fossil shells of tiny, single-celled protists called
foraminifera (or “forams”) from the sediments to extract from their chemical
composition information about the water conditions in which these organ-
isms grew. From these shells, Kennett has been able to reconstruct the temper-
