HR: 0800h
AN: PP41B-0543    [Abstracts]
TI: Seasonal and annual variation in planktonic foraminiferal fluxes including warm period related El Niño in the northwestern North Pacific
AU: * Kuroyanagi, A
EM: a-kuroyanagi@ori.u-tokyo.ac.jp
AF: Graduate School of Frontier Sciences and Ocean Research Institute, The University of Tokyo, 1-15-1 Minamidai, Nakano-ku, Tokyo, 164-8639, Japan
AU: Kawahata, H
AF: Graduate School of Frontier Sciences and Ocean Research Institute, The University of Tokyo, 1-15-1 Minamidai, Nakano-ku, Tokyo, 164-8639, Japan
AU: Nishi, H
EM: hnishi@mail.sci.hokudai.ac.jp
AF: Department of Natural History Sciences, Faculty of Science, Hokkaido University, Kita-10, Nishi-8, Kita-Ku, Sapporo, 060-0810, Japan
AU: Honda, M C
EM: hondam@jamstec.go.jp
AF: Mutsu Institute for Oceanography, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima, Yokosuka, 237-0061, Japan
AB: Planktonic foraminifera provide a record of the upper ocean environment through their species assemblage and individual tests. To investigate the relationship between foraminifera and oceanographic conditions and the impact of El Niño on foraminifera, we analyzed foraminiferal fluxes and relative abundances by using sediment trap samples collected biweekly at three sites in the northwestern North Pacific: Site 40N (39 °60'N, 165 °00'E), Site KNOT (43 °58'N, 155 °03'E), and Site 50N (50 °01'N, 165 °02'E) from 1998- 2001, a period that included an El Niño effect. Based on foraminiferal production and assemblage composition, we divided the sampling duration into several periods during which certain characteristic oceanographic properties were observed. These sampling periods were classified into five types (I-V) based upon four factors: 1) the predominant foraminiferal group, 2) total foraminiferal fluxes (TFFs), 3) organic matter (OM) fluxes, and 4) hydrographic conditions, which included sea surface temperature (SST) and thermal structure. Our results suggest that seasonal changes in foraminifera were closely related to water mass properties in addition to SST. If species compositions were the same, then water mass properties were the most important factors affecting the seasonal variation of foraminiferal abundance in the northwestern North Pacific. Although one of the major controlling factors for foraminiferal fluxes is food availability, the controlling factors for each type (types I-V) are different because of specific oceanographic situations, such as phytoplankton blooms, which result in an excess food supply for foraminifera. At Site KNOT in 1998, SST was remarkably high because of El Niño, and high surface temperatures and weak winds would have lowered nutrient supply and intensified water column stratification, resulting in the relatively low fluxes of total foraminifera, N. pachyderma, and G. bulloides, and the high fluxes of N. dutertrei that were observed. The response of foraminifera to El Niño at Site KNOT in 1998 was similar to the response of foraminifera off the coast of Chile during a weak El Niño event in 1991-1992. The impact of El Niño on foraminifera was variable, depending on the strength of the El Niño event and the location, even though some cases showed common patterns of foraminiferal response. At Site KNOT, El Niño conditions affected foraminiferal abundance not only because of higher sea surface temperature, but also through the formation of a stratified water column.
DE: 4922 El Nino (4522)
DE: 4944 Micropaleontology (0459, 3030)
DE: 4950 Paleoecology
DE: 9355 Pacific Ocean
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting