Newell Garfield

Bifurcated flow from an upwelling center: a cold water source for Monterey Bay

Abstract AVHRR and CTD data from the Monterey Bay region during spring-summer 1989 show two basic hydrographic states, upwelling and relaxation. These occur in response to local wind forcing and are modified by interaction with a California Current meander. Upwelling at Pt An˜o Nuevo, north of Monterey Bay, is identified as the source of cold, salty near-surface water frequently seen in the Bay. No evidence is found in any available data to support the commonly held belief that the Monterey Submarine Canyon is responsible for the introduction of upwelled water to the Bays euphotic zone. During wind relaxations, upwelling ceases and a persistent California Current meander translates shoreward. Data support the idea that upwelling centers are associated with coastal headlands. The flow of upwelled water from these centers is bifurcated, with one tongue trending offshore and one equatorward. We propose a conceptual model to explain this pattern of flow and its impact on the California Current.

Evidence of a turbidity current in Monterey Submarine Canyon associated with the 1989 Loma Prieta earthquake

Abstract Evidence of a turbidity current sweeping through the Monterey Submarine Canyon following the October 1989 Loma Prieta earthquake was documented by the movement of bottom-deployed acoustic transponders used to navigate free-falling oceanographic instrumentation. Measuring sites located along the Canyon at distances of 55, 130 and 190 km from the Canyon head off Moss Landing, CA, all showed evidence of tectonically induced sediment transport. At the site 55 km from the Canyon head, one transponder, located in the axis of the Canyon, was carried 1.9 km down the axis and was deposited among a field of rocks. The other three transponders had been deployed on the sides of the canyon and showed evidence of sediment slumping toward the Canyon axis. Circumstantial evidence from the site 130 km down the canyon suggests that sediment deposition occurred outside the channel axis. Sediment slumping or erosional cutting moved one transponder deeper at the site 190 km from the canyon head.

Ocean currents across the entrance to the Gulf of California

Observations of transport and currents in April, May, and December 1992 and January 1993 were made across the entrance to the Gulf of California with an acoustically tracked dropsonde. Flow was into the gulf along Sinaloa and out of the gulf along Baja California. The transports were 5–10 Sv and the currents were deep, with 10 cm s−1 flow extending to depths greater than 1000 m. The currents were intensified in the upper 300 m. Geostrophic flows compared well with observed currents when smoothed to 2–3 times the Rossby radius. Salinity in the upper 300 m was higher on the Baja California side of the gulf, indicating modification of Subtropical Subsurface waters within the Gulf as well as the presence of surface and near-surface gulf waters. The salinity minimum associated with California Current waters at 50 m had narrow cores that can be resolved only with closely spaced conductivity-temperature-depth casts. Mass and heat fluxes for the upper 300 m were estimated as 280 t s−1 and −0.1×1012 W in May and 170 t s−1 and 2.0×1012 W in December.

Lagrangian measurement of subsurface poleward flow between 38°N and 43°N along the West Coast of the United States during summer, 1993

Subsurface Lagrangian measurements at about 140 m showed that the path of the California Undercurrent lay next to the continental slope between San Francisco (37.8°N) and St. George Reef (41.8°N) during mid-summer 1993. The mean speed along this 500 km path was 8 cms−1. The flow at this depth was not disturbed by upwelling centers at Point Reyes or Cape Mendocino. Results also demonstrate the ability to acoustically track floats located well above the sound channel axis along the California coast.

An empirical model of the tidal currents in the Gulf of the Farallones

Abstract Candela et al. (1990, 1992) showed that tides in an open ocean region can be resolved using velocity data from a ship-mounted ADCP. We use their method to build a spatially varying model of the tidal currents in the Gulf of the Farallones, an area of complicated bathymetry where the tidal velocities in some parts of the region are weak compared to the mean currents. We describe the tidal fields for the M 2 , S 2 , K 1 , and O 1 constituents and show that this method is sensitive to the model parameters and the quantity of input data. In areas with complex bathymetry and tidal structures, a large amount of spatial data is needed to resolve the tides. A method of estimating the associated errors inherent in the model is described.