A separating coastal upwelling jet at Cape Blanco, Oregon and its connection to the California Current System

The effectiveness of dissolved cadmium (Cd) as a tracer of coastal upwelling is demonstrated by comparing its water column distribution to that of traditional upwelling indicators, in particular phosphate (P) and salinity, as well as equatorward wind forcing at the Oregon coast. Cd and P concentrations in samples collected on board ship on 17-27 August 1995 between 3 and 100 km from the coast offshore of Cape Blanco, Oregon, ranged between 0.2 and 0.9 nmol kg Ϫ1 and Ͻ0.1 and 2.5 mol kg Ϫ1 , respectively. Both tracers behaved conservatively during onshore transport at depth; linear Cd-salinity and P-salinity relations in offshore source waters were preserved in bottom waters over the shelf. Following upwelling to the surface, however, Cd and P distributions diverged, with Cd remaining essentially constant while P was taken up by phytoplankton, predominantly diatoms. The Cd content of nearshore water collected from the beach inshore of the cruise area was very similar to that of upwelling source waters sampled from the ship, suggesting efficient exchange of waters between the shelf bottom layer and the very nearshore region, including the surfzone. A simple box model, in which onshore Ekman transport occurs through a well-mixed bottom layer extending from the edge of the continental shelf to the very nearshore region, illustrates a close link between upwelling-favorable wind forcing and very nearshore Cd concentrations. The close agreement between Cd time series generated by the model and surfzone Cd sampled every 2-4 weeks during [1994][1995][1996] suggests that the effectiveness of Cd as a tracer of wind-driven coastal upwelling off the Oregon coast is due in large part to conveyor-like circulation and the remarkably efficient mixing of newly upwelled water into the very nearshore region.Eastern boundary currents such as the California Current system are among the most productive waters in the world ocean (Ryther and Dunstan 1969;Chavez and Toggweiler 1995). While a complex set of factors regulate productivity in the California Current (Abbott and Barksdale 1991;Chavez et al. 1991;Mann 1993), the supply of nutrient-rich water by coastal upwelling undoubtedly plays an important role. Coastal upwelling is particularly intense at midlatitudes along the northwestern U.S. coast during spring and summer because the gradient between warm air temperatures (low atmospheric pressure) over the central valley of California and comparatively cool temperatures (high atmospheric pressure) over the coastal ocean drives strong equatorward upwelling-favorable winds (Huyer 1983;Beardsley et al. 1987; Bakun and Nelson 1991). By using the trace element cadmium as a tracer of nearshore circulation, the present study provides a new perspective on the relation between AcknowledgmentsWe thank Jack Barth and Bob Smith for allowing us to participate in their August 1995 RV Wecoma cruise; Pat Wheeler for the use of deck incubators; Stefan Petranek for cruise preparation and diatom counting; Lloyd Burkle for assistance in diatom ide...

show abstract

“…Physical observations and carbon and nutrient data collected during this cruise were previously reported by Barth et al (2000) Fig. 1.…”

Section: Methodsmentioning

confidence: 70%

Nearshore circulation during upwelling inferred from the distribution of dissolved cadmium off the Oregon coast

Takesue

Geen

2002

Limnology & Oceanography

View full text Add to dashboard Cite

show abstract

“…We did not view this as an acute problem owing to the time and space coherence scales in the northern CCS. As indicated by Barth et al (2000), the offshore (depth >~ 100 m) meanders in the region last for weeks to months. Inshore (depth < ~100 m), currents throughout the water column and surface temperature and salinity change with the wind forcing on 2-10 day time scales.…”

Section: Methodsmentioning

confidence: 96%

“…Using time varying lags and an optimized-thermal-mass-correction, the 24-Hz temperature and conductivity data were corrected and used to calculate 24-Hz salinity, and then averaged to yield 1-Hz values (Barth et al, 2000). The final 1-Hz data files contain unfiltered GPS latitude and longitude; pressure; temperature; salinity; density anomaly (sigma t) computed using the 1980 equation of state; chlorophyll concentration (mg m -3 ); date and time-of-day.…”

Section: Hydrographic and Bioacoustic Datamentioning

confidence: 99%

Physical and biological variables affecting seabird distributions during the upwelling season of the northern California Current

Ainley

Spear

Tynan

et al. 2005

Deep Sea Research Part II: Topical Studies in Oceanography

View full text Add to dashboard Cite

As a part of the GLOBEC-Northeast Pacific project, we investigated variation in the abundance of marine birds in the context of biological and physical habitat conditions in the northern portion of the California Current System (CCS) during cruises during the upwelling season 2000. Continuous surveys of seabirds were conducted simultaneously in June (onset of upwelling) and August (mature phase of upwelling) with ocean properties quantified using a towed, undulating vehicle and a multi-frequency bioacoustic instrument (38-420 kHz). Twelve species of seabirds contributed 99% of the total community density and biomass. Species composition and densities were similar to those recorded elsewhere in the CCS during earlier studies of the upwelling season. At a scale of 2-4 km, physical and biological oceanographic variables explained an average of 25% of the variation in the distributions and abundance of the 12 species. The most important explanatory variables (among 14 initially included in each multiple regression model) were distance to upwelling-derived frontal features (center and edge of coastal jet, and an abrupt, inshore temperature gradient), sea-surface salinity, acoustic backscatter representing various sizes of prey (smaller seabird species were associated with smaller prey and the reverse for larger seabird species), and chlorophyll concentration. We discuss the importance of these variables in the context of what factors may be that seabirds use to find food. The high seabird density in the Heceta Bank and Cape Blanco areas indicate them to be refuges contrasting the low seabird densities currently found in most other parts of the CCS, following decline during the recent warm regime of the Pacific Decadal Oscillation.

show abstract

“…For this reason reference levels < 100 m have proven useful in shelf regions (e.g. Barth et al, 2000Castelao and Barth, 2005). While we are able to identify upwelling structures in the shallow shelf waters, absolute estimates of geostrophic velocities are not possible using this technique.…”

Section: The Upwelling Frontmentioning

confidence: 99%

Transport and retention in an upwelling region: The role of across-shelf structure

Roughan

Garfield

Largier

et al. 2006

Deep Sea Research Part II: Topical Studies in Oceanography

View full text Add to dashboard Cite

The paradox of upwelling is the relationship between strong wind forcing, nutrient enrichment and shelf productivity. Here we investigate how across-shelf structure in velocity and hydrography plays a role in the retention (inshore) and export (offshore) of particles such as nutrients, plankton and larvae.We examine the spatial structure of the coastal currents during wind-driven upwelling and relaxation on the northern Californian Shelf. The field work was conducted as part of the Wind Events and Shelf Transport (WEST) project, a 5-year NSF/CoOP-funded study of the role of wind-driven transport in shelf productivity off Bodega Bay (northern California) from 2000 − 2003. We combine shipboard velocity profiles (ADCP) and water properties from hydrographic surveys during the upwelling season to examine the mean across-shelf structure of the hydrography and velocity fields during three contrasting upwelling seasons, and throughout the upwelling-relaxation cycle. We also present results from two winter seasons which serve as contrast to the upwelling seasons.During all three upwelling seasons clear spatial structure is evident in velocity and hydrography across the shelf, exemplified by current reversals inshore and the presence of a persistent upwelling jet at the shelf break. This jet feature changes in structure and distance from the coast under different wind forcing regimes. The jet also changes from the north of our region where it is a single narrow jet, adjacent to the coast and to the south of our region where it broadens and at times two jets become evident. We present observations of the California Under Current which was observed at the outer edge of our domain during all three upwelling seasons. The observed across-shelf structure could aid both in the retention of plankton inshore during periods of upwelling followed by relaxation and in the export of plankton offshore in the upwelling jet.

show abstract

A separating coastal upwelling jet at Cape Blanco, Oregon and its connection to the California Current System

Cited by 211 publications

References 46 publications

Nearshore circulation during upwelling inferred from the distribution of dissolved cadmium off the Oregon coast

Nearshore circulation during upwelling inferred from the distribution of dissolved cadmium off the Oregon coast

Physical and biological variables affecting seabird distributions during the upwelling season of the northern California Current

Transport and retention in an upwelling region: The role of across-shelf structure

Contact Info

Product

Resources

About