Showing papers on "Monterey Canyon published in 1999"

A new mesopelagic larvacean, Mesochordaeus erythrocephalus, sp. nov., from Monterey Bay, with a description of its filtering house

Abstract: A new species in the genus Mesochordaeus is described from 25 specimens collected by a remotely operated vehicle at mesopelagic depths in Monterey Bay, California. Mesochordaeus erythrocephalus is a large species (tail length up to 50 mm, trunk length up to 7 mm) characterized by large crescent-shaped spiracles, digitate lips, a bifurcate tail and bright red pigmentation of the digestive system. The filtering 'house' is large, 4-5 times the tail length of the animal, and its structure is most similar to that of another large mesopelagic larvacean, Bathochordaeus. This description confirms the distinctness of this recently erected genus, but raises questions as to its taxonomic affili- ation.

Numerical Simulations and Observations of the Internal Tide in a Submarine Canyon

Abstract: Observations and model simulations of internal waves in and around the Monterey Canyon are described here with particular focus on the internal tide generated through interaction of the basin-scale barotropic tide and local topography. Observations reveal strong internal tides along the axis of the Canyon near the Canyon head. Currents are intensified near the bottom and observed to have both onshore-propagating and standing configurations at different times and stratification conditions. Bottom-mounted ADCP observations from within the Canyon axis in depths around 300 m confirm bottom intensified fluctuations throughout the internal wave band. Furthermore, strongly nonlinear fronts or bores are associated with the tidal-band fluctuations. Numerical simulations forced by semidiurnal sea level fluctuations offshore using both idealized and realistic representations of the local topography are used to investigate internal tide generation and propagation in the coastal zone. Canyons with near-critical bottom slopes play a role in bottom intensification, while the actual complex topography leads to significant horizontal variations in the internal wave characteristics on scales of less than 10 km.

Internal tidal bores in the Monterey Canyon

Abstract: : A thirty-four day record of near-bottom temperature and horizontal velocity spanning the lower third of the water column from within Monterey Canyon was examined. The observed internal tide is highly non-linear with kinetic energy dispersed among numerous overtides near the bottom and more concentrated in the primary semi diurnal constituent (M2) higher in the water column. The bottom currents and temperature vary in strength over the record period, taking on the characteristics of an internal bore at times with large up-canyon accelerations accompanied by rapid temperature drops. The bores are nearly phase locked to the sea level variations and arrive at the measurement site ^8.6 h after high tide in Monterey, CA. They are evident in the velocity records up to at least 35 m above the bottom and may be accompanied by high frequency pulses that extend higher. The variation is not caused by direct forcing from the barotropic tidal range as the strongest bores do not exclusively occur during either the spring or neap phase of the barotropic tide. Speculation on the cause for the temporal variation centers on the changes in mid-water stratification observed.

Igneous and Sedimentary Rocks from Monterey Canyon, California and Implications for Regional Tectonics

Abstract: Samples collected from the northern meander of Monterey Canyon, California, and the adjacent Soquel Canyon include Cretaceous granodiorites and middle Tertiary basaltic andesites and sandstones. Plagioclase separated from the granodiorite basement rocks from Soquel Canyon yielded an age of 79 ± 0.8 Ma and are isotopically similar to Salinia-terrane granitoids exposed on the Monterey Peninsula. The Soquel Canyon granodiorite is crosscut by mafic dikes that are basaltic andesite in composition. Plagioclase separated from one mafic rock has been dated at 23.7 ± 0.5 Ma, consistent with the middle Tertiary pulse of volcanism characteristic of this region. This mafic unit also intrudes an overlying sandstone unit forming a “peperite” texture resulting from contemporaneous volcanism and sedimentation. The peperite constrains the lithic-rich sandstone, which we propose to have been deposited in a sedimentary basin associated with local tectonic extension, to a late Oligocene and (or) early Miocene age. The artifacts of the sedimentary basin are truncated (and deformed) on the south by the Monterey Bay fault zone, and exposed within the northern meander of the Monterey Canyon. These new lithologies require a revision of the Neogene lithostratigraphy of Monterey Bay and may also be useful in linking the local volcanic, tectonic and sedimentary history to the complex tectonic development of central California during the middle Tertiary. We suggest that strike-slip or transtensional movement along the Monterey Bay Fault Zone opened a basin in late Oligocene and (or) early Miocene into which was deposited a coarse, lithic-rich (Vaqueros?) sandstone. The contemporaneous volcanism of basaltic andesite is alkalic in character and may have been a result of mantle upwelling within a slab window or local transtension along the major faults active during this period.

Pathological Seismology: An Investigation of Seismic Signals in the Monterey Bay

Abstract: Well-coupled ocean bottom seismometers (OBSs) developed at MBARI have been successfully deployed in Monterey Canyon, collecting over six weeks of data in 1996 and almost three months of data in 1997. These corehole seismometers have sensor packages that are cemented into boreholes in bedrock using the MBARI ROV Ventana. The many advantages of corehole seismometers (e.g., superior coupling with higher signal/noise ratios and known instrument orientations) provide a wealth of information about local seismicity and geologic events, as well as insight into non-geological sources of seismic energy in the ocean environment (e.g., marine mammal calls and ship noise). We have examined the data from two instruments placed in adjacent boreholes 17 m apart during the summer of 1996. More than a thousand arrivals were recorded from geological events, including local and teleseismic earthquakes, T-phases and possible landslide events. Characteristics of landslide events include: peak frequencies ranging from 1.5 to 5 Hz, impulsive to emergent arrivals and codas, and arrivals after an identified T-phase. Based on the time between the first arrival and the landslide event, we estimate a speed on the order of 0.5 km/s, which is consistent with estimates of submarine landslides.