HR: 0830h
AN: B31D-0338    [PDF]
TI: $^{15}$N/$^{14}$N Variation in CalCOFI Zooplankton: A 51 year history of Marine Nitrogen Dynamics and Climate Variability off Central California
AU: * Rau, G H
EM: rau4@llnl.gov
AF: Institute of Marine Sciences, University of California, Santa Cruz, CA 95064 United States
AU: Ohman, M D
AF: Integrative Oceanography Division, Scripps Institution of Oceanography, La Jolla, CA 92093 United States
AU: Pierrot-Bults, A
AF: Institute for Biodiversity and Ecosystem Dynamics,, Zoological Museum, University of Amsterdam, Amsterdam, 2000 Netherlands
AB: Long-term variability in marine zooplankton $^{15}$N/$^{14}$N was investigated in two species of calanoid copepods ({\it Calanus pacificus} and {\it Eucalanus californicus}) and two chaetognaths ({\it Sagitta bierii} and {\it Sagitta euneritica}) sampled in the spring of selected years from 1951 to 2001 near Monterey Bay, California. No statistically significant trend in $^{15}$N/$^{14}$N was detected for any of the four species, with isotopic ratios in 2001 resembling those in copepods and chaetognaths sampled from the same area five decades earlier. With respect to proposed oceanographic regime shifts in this region, heterogeneity in $^{15}$N/$^{14}$N was detected only for {\it S. bierii} when comparing the periods 1951-1975, 1978-1998, and 1999-2001. In this species the $^{15}$N/$^{14}$N in the most recent, brief period (1999-2001) averaged slightly lower than in the previous period. Three of the four species ({\it C. pacificus, S. bierii}, and {\it S. euneritica}) showed significant increases in $^{15}$N/$^{14}$N during major El Ninos. El Nino-related enrichment in $^{15}$N could arise as a consequence of increased nitrate demand/supply at the base of the food web or advection of $^{15}$N-enriched nitrate from more southerly waters. While a range of physical and climate indices were evaluated, anomalies of $^{15}$N/$^{14}$N from the long-term mean were found to be significantly related only to; i) the Southern Oscillation Index in the case of both chaetognath species, ii) a regional surface water temperature record ({\it S. bierii} only), iii) an index of wind-driven coastal upwelling for the surface-dwelling {\it C. pacificus}, and iv) variability in the Pacific Decadal Oscillation for the somewhat deeper-dwelling {\it E. californicus}.
DE: 0400 Biogeosciences
DE: 4215 Climate and interannual variability (3309)
DE: 4845 Nutrients and nutrient cycling
DE: 4870 Stable isotopes
SC: Biogeosciences [B]
MN: 2003 Fall Meeting