Coastal upwelling along the western Americas: Past, present, and future
A. van Geen
Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964
Phone: (914) 365 8644, Fax: (914) 365 8154, e-mail: avangeen@ldeo.columbia.edu
Background
This page provides access to preliminary results from a coordinated
program of surfzone water collection and analysis along the western coasts
of Chile, Mexico, and the United States. Sampling started at the end of
1996 and is currently supported by the Inter-American Institute for Global
Change Research (IAI), the US National Science Foundation, and the Climate
Center of the Lamont-Doherty Earth Observatory. The short-term objective
of the program is to provide an integrated picture of large-scale
variations in the intensity of coastal upwelling in response to variations
in alongshore winds over the Peru/Humboldt and California Current systems.
The sampling strategy is based on the observations of van Geen et al.
(1992) and van Geen and Husby (1996) near San Francisco Bay, California,
showing that concentration of upwelling-sensitive tracers such as nutrients
and the trace metal cadmium in surfzone water is determined mainly by
large-scale wind-forcing rather than local processes. The long-term
objective is to use this information to reconstruct past changes in wind
patterns, and therefore climate, along the western Americas by inferring
the past composition of nearshore waters from the composition of carbonate
shells formed by foraminifera and mollusks. Shells formed by these
organisms over the past 9000 years of the Holocene can be recovered from
estuarine sediments and archeological middens. Either orbital changes in
insolation or changes in the intensity of the El Niņo/Southern Oscillation
could have significantly affected the intensity of coastal upwelling along
the western Americas during the Holocene. A simple consideration of
interhemispheric differences in the effect of these two agents of climate
change suggests that it should be possible to distinguish their relative
importance from paleo-upwelling reconstructions at a few carefully selected
sites in both hemispheres. This information will, in turn, provide a
useful test of general circulation models designed to predict the impact of
future climate change along the western Americas.
Current participants
The longest available time series of surfzone salinity, nutrients,
and cadmium started in 1991 at Pillar Point, California. This site is
presently sampled periodically by Darcy Gordon from Stanford University.
Samples are processed in the laboratory of Samuel Luoma at the US
Geological Survey in Menlo Park, California. Two sampling sites on the
open coast were added in 1994 at Trinidad Head, California, and Seven
Devils Beach, Oregon. These samples are currently collected and processed
by John Hill from Humboldt State University in Arcata, California, and by
Chris Cziesla from the Oregon Institute of Marine Biology in Charleston,
Oregon. Surface water has also been collected inside the mouths of San
Francisco Bay, Humboldt Bay, and Coos Bay to determine how faithfully the
composition of estuaries tracks the composition of nearshore water on the
open coast. Renee Takesue, Michelle Large, Shad Baiz, Laura Verhegge, and
Isaac Kaplan have also collected and processed surfzone samples from the US
sites in the past. In late 1996, five students from Chile and Mexico
started collected surfzone water at 10 new sites. Students participating
in this program include Claudia Figueroa (advised by Marco Salamanca) from
Universidad de Concepcion, Chile, Manuel Varas (Juan Carlos Castilla) from
Pontificia Universidad Catolica de Chile, Santiago, Nury Guzman (Ruben
Escribano/Luc Ortlieb) from Universidad de Antofagasta, Chile, Ernesto
Vasquez (Lucio Godinez) from Centro Interdisciplinario de Ciencias Marinas,
La Paz, Mexico, and Eduardo Ortiz (Jose Carriquiry) from Universidad
Autonoma de Baja California, Ensenada, Mexico. Each of the Latin American
students is funded by IAI to spend 4 months doing research at
Lamont-Doherty which includes analysis of the samples that were collected.
The first student, Manuel Varas, arrived in New York in January 1998.
The available data
Samples are collected periodically for salinity, nutrients
phosphate, silicate, and nitrate, and Cd at each site. Cd is important for
this project for two reasons. (1) Dissolved Cd is enriched in subsurface
water offshore, just like the nutrient phosphate, but is taken up less
rapidly by coastal phytoplankton. Cd measured in the surfzone is therefore
a sensitive and nearly conservative indicator of coastal upwelling. (2) Cd
incorporated in biogenic carbonate reflects the composition of ambient
water during the life of the organism and can therefore be used to
reconstruct past upwelling.
Available results can be viewed with a software written by Benno
Blumenthal from the Lamont-Doherty Earth Observatory. Click here to view
sampling locations. Note that the data viewer allows you to zoom in on the
different locations. Click here for a complete list of sampling locations
and their latitude and longitude. Click here to view all the available
data on a color scale for a specific tracer. You can also get
a line plot of a time series for a selected tracer at a specific
location (see table). The data viewer also allows you to overlay
line plots for several stations. You can also obtain tables of the data
for specific sites (see table).
Note that you can access many other ocean and climate data sets
using the same viewer through the Lamont-Doherty Earth Observatory web page
by clicking here.
Future developments
This web page will be updated periodically to provide the latest
surfzone data in a convenient format to participants and other interested
parties. A preliminary interpretation will be added in the near future.
Current funding for surfzone sampling will run out at the end of 1998. I
am actively looking for ways to extend surfzone sampling at all sites for
at least another year in order to document the effect of the La Niņa,
predicted to follow the present El Niņo (Webster and Palmer, 1997), on
nearshore water chemistry.
Comments and suggestions regarding the surfzone sampling program or
future paleo-upwelling reconstructions can be sent to
avangeen@ldeo.columbia.edu.
References
van Geen, A., S. N. Luoma, C. C. Fuller, R. Anima, H. E. Clifton, S.
Trumbore, Evidence from Cd/Ca ratios in foraminifera for greater upwelling
off California 4,000 years ago, Nature, 358, 54-56, 1992.
van Geen, A. and D. M. Husby, Cadmium in the California Current system:
Tracer of past and present upwelling, J. Geophys. Res., 101, 3489-3507,
1996.
Webster, P. J., and T. N. Palmer, The past and the future of El Niņo,
Nature, 390, 562-564, 1997.
