Currents in Monterey Submarine Canyon


Book Description

Time series were obtained from two current meters near bottom on one mooring in Monterey Submarine Canyon. These records were analyzed to determine the general character of the currents, the volume transport at different levels above the canyon floor, the power spectral estimates of the upcanyon and cross-caynon directional components, and the coherence between directional components. Current speed variations appeared as a series of peaks occurring every 5 to 6 hr with maxima of 17 to 21 cm/sec. Current directions oscillated with a discernible period of about 12 hr. Currents 30 m above the bottom were aligned nearly along the canyon axis; currents 60 m above the bottom were nearly perpendicular to the canyon axis. The spectral analysis indicated tides as a major driving force of the deep currents, but also indicated the presence of other forcing functions, possibly internal waves, with shorter periods. The coherence between instruments was low, suggesting the possible presence of a near-bottom boundary layer, or that significant signal deterioration was caused by noise.




Apparent Surface Currents Over the Monterey Submarine Canyon Measured by the Method of Towed Electrodes


Book Description

Five data cruises were taken on board R/V ACANIA to study the effect on the Geomagnetic Electrokinetograph (GEK) of various environmental factors, including wings, tides, and internal waves, over the Monterey Submarine Canyon. An in situ current meter was used successfully on one occasion to obtain data to establish a k-factor for the GEK in the Submarine Canyon, and to directly measure the particle velocities of internal waves. The observed surface currents measured with the GEK all exhibited little or no correlation with winds and tides. The flows were all generally southerly; their averages agreed with previous measurements made with the GEK. This direction of flow was opposite to the generalizations of Scott and possibly agreed with those of Pirie, depending upon the placement of one of his eddies. The k-factor for the GEK could not be determined because currents measured directly in the thermocline were found to be not correlated with the GEK measurements. However, the average current speeds were in reasonable agreement with currents measured at other times in Monterey Bay, leading to the conclusion that k cannot be much greater than the assumed value of 1.0. (Author).




Bottom Current Measurements in the Head of Monterey Submarine Canyon


Book Description

Bottom current measurements were taken in the head of Monterey Submarine Canyon in a water depth of 130 meters (72 fathoms) utilizing an Ekman current meter placed 480 centimeters (15.7 feet) above the bottom. Currents were observed to follow the canyon axes, and flow was seaward (down-canyon) on the rising tide and coastward (up-canyon) on the falling tide. Current speed was sometimes fairly steady and other times variable. It ranged between 0 and 41 centimeters per second (0 to 0.8 knot) and had a median speed of 10 cm/sec (0.2 knot). The six hours centered around low tide generally had considerably stronger currents than the similar period of time centered around high tide. (Author).







Characterization of Tidal Currents in Monterey Bay from Remote and In-situ Measurements


Book Description

A first order description of tidal heights and currents in Monterey Bay is provided. Analysis of sea level records indicate that a mixed, predominantly semidiurnal tide nearly co-oscillates within the bay. Analysis of month-long moored ADCP records obtained in the winter and summer of 1992 reveals that tidal-band currents account for approximately 50 percent of the total current variance in the upper ocean (20-200 m). A relatively strong (7 cm/s) fortnightly tide (MSf) is present in both seasons. Considerable rotation of the semidiurnal ellipse orientations occurs with depth during both seasons. A month- long record of surface current measurements obtained with CODAR, an HF radar system, during September 1992 reveals that the Monterey Submarine Canyon clearly influences the strength and direction of semidiurnal (M2) tidal currents. Good agreement exists between the strength and orientation of ADCP- and CODAR-derived tidal ellipses, with the exception of the constituent K1. Large, spatially uniform K1 surface currents (20-30 cm/s) appear to be the result of diurnal sea breeze forcing.







Observations and Modeling of Currents Within the Monterey Bay During May 1988


Book Description

April and May of 1988 along the central California coast were characterized as a period of strong coastal upwelling produced by moderate to strong northwesterly winds present throughout the period. A product of this upwelling event was the manifestation of southward geostrophic currents which extended to a distance of approximately 50 km from the coast. From 08 to 11 May 1988, hydrographic surveying was conducted within the Monterey Bay. Internal waves, with amplitudes of up to 30 m were present throughout the period and effectively masked the mean signal, implying that averaging is essential to avoid aliasing. The current -- temperature -- depth (CTD) data were averaged to estimate the mean field during this time frame. Acoustic Doppler Current Profiler (ADCP) data, were also averaged. The mean flow field and dynamic topography implied anticyclonic surface flow with cyclonic flow at 200 m depth. ADCP derived mean flows compared favorably with geostrophic mean flow rate in all areas except one, the deep outflow region along the northern wall of the Canyon. Application of ocean models of boundary layer flow of the geostrophic mean field yielded flows similar to those described above. Wind stress experiments indicated that strong wind field may influence surface circulation in the Bay. Interactions between the coastal upwelling geostrophic jet and the Monterey Submarine Canyon is believed to have been a major mechanism responsible for the mean flow.




Ecosystem Observations


Book Description




The Desert


Book Description

From endless sand dunes and prickly cacti to shimmering mirages and green oases, deserts evoke contradictory images in us. They are lands of desolation, but also of romance, of blistering Mojave heat and biting Gobi cold. Covering a quarter of the earth’s land mass and providing a home to half a billion people, they are both a physical reality and landscapes of the mind. The idea of the desert has long captured Western imagination, put on display in films and literature, but these portrayals often fail to capture the true scope and diversity of the people living there. Bridging the scientific and cultural gaps between perception and reality, The Desert celebrates our fascination with these arid lands and their inhabitants, as well as their importance both throughout history and in the world today. Covering an immense geographical range, Michael Welland wanders from the Sahara to the Atacama, depicting the often bizarre adaptations of plants and animals to these hostile environments. He also looks at these seemingly infertile landscapes in the context of their place in history—as the birthplaces not only of critical evolutionary adaptations, civilizations, and social progress, but also of ideologies. Telling the stories of the diverse peoples who call the desert home, he describes how people have survived there, their contributions to agricultural development, and their emphasis on water and its scarcity. He also delves into the allure of deserts and how they have been used in literature and film and their influence on fashion, art, and architecture. As Welland reveals, deserts may be difficult to define, but they play an active role in the evolution of our global climate and society at large, and their future is of the utmost importance. Entertaining, informative, and surprising, The Desert is an intriguing new look at these seemingly harsh and inhospitable landscapes.