POLLEN STRATIGRAPHY AND PALEOECOLOGIC INTERPRETATION OF THE 160-K.Y. RECORD FROM SANTA BARBARA BASIN, HOLE 893A

Linda E. Heusser

ABSTRACT

Pollen data (159 samples taken at approximately less than or equal to 1000 yr intervals) provide the first continuous, chronologically controlled record of southern California terrestrial environments over the past 160 k.y., a record that is directly correlated with changes in the marine environment inferred from organic and inorganic components of the same sediment samples. In the well-laminated sediments deposited during the last interglacial interval, pollen assemblages are characterized by Quercus and other taxa similar to those of present arid coastal biomes (e.g., oak woodland, chaparral, coastal sage scrub, and salt marsh). Pollen assemblages in the massive glacial sediments, dominated by conifers (referable to the Taxodiaceae, Cupressaceae, Taxaceae, and Pinaceae families) imply altitudinal and latitudinal expansion of montane conifer woodland and forest associations (e.g., juniper woodlands and yellow pine forests of the Transverse Ranges). Variable representation of oak woodland and coniferous forests characterizes interstadials and stadials.

During the last glacial maximum on the south coast of California, mean annual temperature and effective precipitation estimates inferred from pollen data in Santa Barbara Basin are ~5C and ~1000 mm, respectively. Interglacial temperatures and evapotranspiration were comparable to or possibly higher than at present. High-frequency variability in the pollen/vegetation assemblages from Ocean Drilling Program Hole 893A implies frequent and rapid change between these two climatic endmembers throughout the last 160 k.y. For example, following an abrupt warming at ~14 k.y., a brief mesic, cooling event precedes the development of Holocene interglacial conditions.

Systematic variations in the pollen assemblages deposited in Santa Barbara Basin are similar in amplitude and duration to changes reconstructed from oxygen isotopes in the same sediment samples. The apparent synchroneity of the terrestrial (pollen/vegetation of south coastal California) and marine (oxygen isotope) proxy climate signals from Hole 893A concurs with previous results from the North and South Pacific which showed similar rapid responses of terrestrial ecosystems to global climate change during the last glacial cycle.

Date of initial receipt: 18 August 1994
Date of acceptance: 13 February 1995


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