Radiolarian responses to recent and neogene California El Niño and anti-El Niño events

Abstract

Plankton tows from 1983 and 1964 California El Niños suggest that high standing crops of both warm and cold radiolarian faunas are characteristic of these conditions over the southern California continental borderland. High standing crops of both warm and cold radiolarians are suggested to occur during California El Niños because the California Current diminishes in intesity allowing warm faunas to invade from the west (central-gyre waters) and south (gyre and eastern tropical Pacific waters); and, a strongly developed California Countercurrent aids in creating a geostrophic dome that allows cold faunas to invade from the north. These same radiolarian faunas characteristic of California El Niños are found in the Holocene varved sediments of the Santa Barbara Basin and can be correlated to the known California El Niño events of 1957–1958 and 1964. El Niño like events determined via the same radiolarian criteria are found at 6 and 8 Ma in Monterey laminated (presumably varved) sedimentary rocks. It is suggested that warm and cold periods in Monterey may be related to the frequency and magnitude of El Niño like events. It is also suggested that during Neogene warm periods (such as at 8 and 10 Ma) the paleo-California Current was narrower, closer to the coast, and did not extend as far south as during anti-El Niño periods (such as at 5 Ma).