HR: 1400h
AN: OS23F-05    [Abstracts]
TI: Effects of Climate Change on Production of Siliceous Phytoplankton Over the Twentieth Century as Recorded in Sediments of the Santa Bárbara Basin off Southern California
AU: * Martinez Lopez, A
EM: amartin@ipn.mx
AF: Centro Interdisciplinario de Ciencias Marinas (CICIMAR-IPN), Av. Instituto Politécnico Nacional s.n., La Paz, BCS 23096, Mexico
AU: Baumgartner, T R
EM: tbaumgar@cicese.mx
AF: División de Oceanología, CICESE, Km 107 Carretera Tijuana-Ensenada, Ensenada, BCN 22860, Mexico
AU: Lange, C
EM: clange@udec.cl
AF: Departamento de Oceanografía y Centro FONDAP-COPAS, Casilla 160-C, Universidad de Concepción, Concepción, Chile
AB: The relationship between production of siliceous phytoplankton and interannual through multidecadal climate variability is examined by analysis of a high-resolution paleo-record of diatoms and silicoflagellates for the period 1909-1991. The record is reconstructed from the annually layered sediments (varves) preserved in the hypoxic Santa Barbara Basin providing an annual history of production and settling to the sediments of an important fraction of the new production in the coastal environment. Location of the depositional site makes it sensitive to change in ocean climate governing large scale dynamics of the California Current ecosystem. Variables used for comparison to indices of large-scale climate change are: 1) total flux rate to the sediments of both diatom tests and silicoflagellates; 2) change in species richness; 3) the absolute and relative flux of specific functional groups (indicating conditions of upwelling and turbulence vs. stability in the water column); and 4) absolute and relative flux of a species assemblage identified as having warm water affinities. Although the combination of these variables indicates a response to interannual variability associated with ENSO, a more striking feature is the persistence over decadal and interdecadal periods exemplified by the steep decline and reduced values in the overall rate of flux after 1976 (indicating a response to the basin-scale climate shift in 1976-77). The most prominent feature, however, is a major shift in the nature of total flux, and particularly a drastic change in the relative abundances of two different species assemblages, from one that dominated through the first 30 years of the series to another that dominated through the final 40 years of the record. Although the exact nature and timing of this major transition cannot be ascertained because of a break in the record from 1944 through 1948, the change is clearly marked by the replacement of a group of small diatom species (indicative of coastal upwelling and turbulent conditions characteristic of spring and early summer) by a dissimilar assemblage of larger, more robust species (indicating warmer, more stable and oceanic conditions during late summer and fall). This transition between assemblages occurred between the late 1930s and the early 1950s and marks the change between two different states in ocean climate that appears to reflect a local response to warming along the eastern boundary of the Pacific that is a feature of the global greenhouse effect. The shift in character of the siliceous phytoplankton deposition occurred at a similar time as the change in composition of the planktonic foraminifera in the sediments at the same location, interpreted as a response to global warming by Field et al. (Science, 311: 63-66, 2006).
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
DE: 1630 Impacts of global change (1225)
DE: 3305 Climate change and variability (1616, 1635, 3309, 4215, 4513)
DE: 4516 Eastern boundary currents
DE: 4944 Micropaleontology (0459, 3030)
SC: Ocean Sciences [OS]
MN: 2007 Joint Assembly