Zoogeography of Holocene Ostracoda off western North America and paleoclimatic implications

Holocene shelf samples (255) from off the west coasts of the United States and Baja California, Mexioo, yielded 341 species of ostracodes. The distributions of biogeographically diagnostic specie.s are established. Sp,ecies pre,sent within each 15-minute segment of latitude constitute samples which are compared on the basis of their faunal composition. Cluster analysis of 110 samples containing 192 ostracode species from the continental shelf between 21 o 43' N. and 48 o 24' N. permits recognition of four faunal provinces which are similar to modern molluscan provinces of the eastern Pacific. The existence of subprovinces is also evident from this analysis. Faunal distributions and faunal provinces are principally controlled by marine climate, especially water temperature. 8e.asonal climatic changes and the influence of the California Current, in conjunction with intense seasonal upwelling, are responsible for the configuration of marine isotherms off these coasts. The faunal discontinuity at the Oregonian-Californian provincial boundary (3530' N.) is characterized by range terminations of many northward ranging thermophiles, and nine important southern genera do not occur north of this boundary; many southward ranging cryophiles terminate their ranges at the Galifornian-Surian boundary (2815'N.).