Tidal and residual currents measured by an acoustic doppler current profiler at the west end of Carquinez Strait, San Francisco Bay, California, March to November 1988

1993 ◽  
2005 ◽  
Vol 23 (6) ◽  
pp. 1963-1975 ◽  
Author(s):  
C. Carollo ◽  
I. Astin ◽  
J. Graff

Abstract. An analysis of current profiles carried out on moored Acoustic Doppler Current Profiler data sets recorded during the Variability of Exchanges In the Northern Seas project is presented here for several locations in three sections in the vicinity of the Iceland-Scotland Ridge: (1) north of the Faroes, (2) in the Faroe-Bank Channel and (3) in the Faroe-Shetland Channel. Total currents have been decomposed into three components, namely the mean residual flow, tide and surge. The mean residual flow is found to be dominant. Results for the major tidal constituents (M2, S2, N2, O1 and K1) are shown and discussed. It is found that the predominant tidal harmonic M2 becomes steered through depth to align with the bottom topography. The mean residual flow is found to be generally larger than the surge, particularly in the Faroe-Bank Channel below 500m depth where it is the dominant component. Here tidal rectification, i.e. the topographic rectification of tidal currents originating in nonlinearities that rectify the oscillatory tidal motion, is identified as the process enhancing the large mean residual currents found. From the current structure, two water masses are identified in the channel: the upper slowing moving inflow water and the colder outflow water characterised by a 3–6-day periodicity. In the Faroe-Shetland Channel the flow is characterised by large tidal currents, particularly in shallow waters. Instead, north of the Faroes none of the component was identified as dominant. The results show that the variability of the current components is strongly dependent upon topography and water depth. Keywords. Oceanography: Physical (Currents; General circulation; General or miscellaneous)


1993 ◽  
Vol 67 (6) ◽  
pp. 1058-1063 ◽  
Author(s):  
Peter U. Rodda ◽  
Nina Baghai

Disarticulated elements from three individuals of Mammuthus cf. M. columbi (Falconer) and one individual of Bison cf. B. latifrons (Harlan) were recovered from an excavation in gravelly, sandy clay of the Colma Formation at the southeast base of Telegraph Hill, San Francisco, California. This is the most abundant collection of late Pleistocene terrestrial vertebrates reported from San Francisco, and only the fourth record from excavations in the city proper. The Mammuthus-Bison association indicates a Rancholabrean age, and elements of these two taxa from this site have been radiocarbon dated at 25,380 ± 1,100 years B.P. Geologic setting, lithology, associated diatoms and pollen, and preservation of the bones suggest that these animals were buried rapidly in a boggy environment on the west margin of the broad valley now occupied by San Francisco Bay.


1998 ◽  
Vol 49 (1) ◽  
pp. 102-110 ◽  
Author(s):  
B. Lynn Ingram

The West Berkeley shellmound, the oldest well-dated archaeological site in the San Francisco Bay region, contains shell and charcoal ranging in age from ca. 1200 to 5700 cal yr B.P. Radiocarbon ages of marine shell and charcoal collected from fifteen stratigraphic levels in the West Berkeley shellmound suggest changes in the 14C content of San Francisco Bay surface waters relative to the atmosphere (the oceanic reservoir age) over the past 5000 yr. The reservoir age of San Francisco Bay waters fluctuated between 870 and −170 14C yr over the past 5000 yr, with the lowest values occurring 2900 to 3800 cal yr B.P. and the highest values between 1200 and 2000 cal yr B.P. Changes in the radiocarbon reservoir age may be due to changes in the strength of seasonal wind-driven upwelling off coastal California, where upwelling brings 14C-depleted waters to the surface. The period of lowest ΔR values (at 3500 to 3900 cal yr B.P.) is coincident with relatively low salinity in San Francisco Bay (indicating high freshwater inflow) and wet climate in California based on lake level records. The period of high ΔR values (1200–2000 cal yr B.P.) is coincident with one of the driest periods in California during the late Holocene. These data suggest a link between coastal upwelling and precipitation over central California. The age of the top of West Berkeley mound and several other mounds in the San Francisco Bay region (1100 to 1300 cal yr B.P.) coincides with a prolonged dry period in California and low river inflow to San Francisco Bay. Perhaps the sites were abandoned because of the drought.


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