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M. Noble

Publications and source records attributed to M. Noble.

11 recordsLinked to original sources
USGS2012

The structure of subtidal currents within and around Lydonia Canyon: Evidence for enhanced cross-shelf fluctuations over the mouth of the canyon

Between October 1980 and April 1981, currents were measured within Lydonia Canyon and on the adjacent shelf and slope. The amplitude of the subtidal currents over the shelf and slope ranged between 10 and 30 cm s −1 , but within the canyon, they were typically smaller than 5 cm s −1 . The subtidal currents had well-defined spatial structures over the shelf and the slope and in the middle and outer portions of the canyon. The along-isobath flow over the shelf and slope was unaltered by the canyon. Currents within the canyon and just above it were driven up and down the canyon by the cross-shelf pressure gradient in geostrophic equilibrium with the along-shelf flow. The measurements suggest that the Coriolis force on the cross-canyon flow, turbulent Reynolds stresses, and acceleration of the along-canyon flow balanced the imposed pressure gradient for flow near the rim of Lydonia Canyon. The Coriolis force was not important in the deeper portions of the canyon, where baroclinic adjustments of the density field began to be an important factor in the momentum balance. A simple model indicates that the magnitude of the horizontal turbulent viscosity coefficient for subtidal flow in this narrow canyon is 10 6 to 10 7 cm 2 s −1 . The mixing indicated by the large amplitude of the viscosity coefficient was probably caused by the strong tidal currents present within Lydonia Canyon. On the shelf, along-isobath currents were locally driven by the large-scale component of the wind field; along-shelf currents were equally correlated with local winds and with winds from sites 700 km northeast of Lydonia Canyon. Wind stress was not correlated with currents over the slope in water deeper than 450 m or with currents within the canyon.

Journal of Geophysical Research - Oceans↗
USGS2010

Variations in the fine-scale composition of a central Pacific ferromanganese crust: Paleoceanographic implications

A 47- to 60-mm-thick Fe-Mn crust from Horizon Guyot (water depth 1800–1780 m), central Pacific, was used to evaluate the potential of crusts as recorders of Neogene paleoceanographic and paleoclimatic conditions. The chemical composition was determined by microprobe for 16 elements from a polished thin section. Three analyses were made per millimeter and averaged to give the composition of each millimeter. The age of the crust was determined by measuring the strontium isotope composition of the crust and comparing it with the Tertiary seawater curve. The crust represents 18.5 m.y. of growth of Fe and Mn oxyhydroxides. The crust is composed of alternating botryoidal and laminated layers. The botryoidal layers formed during the same time intervals that widespread Neogene deep-sea hiatuses were forming in bottom sediments. The botryoidal layers represent growth during times of intensified deepwater flow, whereas the laminated intervals represent more quiescent conditions. The correspondence between the botryoidal layers and the Neogene hiatuses is so strong that we were able to choose a variable growth rate model over a constant growth rate model for the crust. Chemical changes in the crust take two forms. The first is represented by broad changes in the composition defined chiefly by fourth-order polynomial fits to the chemical profiles of each element with depth in the crust. The second is high-frequency changes in composition. The broader changes occurred primarily at about 15, 11.5, 7.4, 6.4, 5.2, and 4.6 Ma, which may correlate with major changes in paleoceanographic circulation and development of ice caps at the poles. The periods of the high-frequency changes may reflect climatic changes that resulted from orbital forcing. These high-frequency changes may correspond to the high-order eccentricity periods of 3.47, 2.04, and 1.31 m.y.

Paleoceanography and Paleoclimatology↗
USGS2010

Event-driven sediment flux in Hueneme and Mugu submarine canyons, southern California

Vertical sediment fluxes and their dominant controlling processes in Hueneme and Mugu submarine canyons off south-central California were assessed using data from sediment traps and current meters on two moorings that were deployed for 6 months during the winter of 2007. The maxima of total particulate flux, which reached as high as 300+ g/m 2 /day in Hueneme Canyon, were recorded during winter storm events when high waves and river floods often coincided. During these winter storms, wave-induced resuspension of shelf sediment was a major source for the elevated sediment fluxes. Canyon rim morphology, rather than physical proximity to an adjacent river mouth, appeared to control the magnitude of sediment fluxes in these two submarine canyon systems. Episodic turbidity currents and internal bores enhanced sediment fluxes, particularly in the lower sediment traps positioned 30 m above the canyon floor. Lower excess 210 Pb activities measured in the sediment samples collected during periods of peak total particulate flux further substantiate that reworked shelf-, rather than newly introduced river-borne, sediments supply most of the material entering these canyons during storms.

Marine Geology↗
USGS2002

Suspended sediment transport on the continental shelf near Davenport, California

Suspended sediment transport on the shelves off Santa Cruz and Davenport, California is studied using field measurements and bottom boundary layer modeling. Strong transport events mostly occur during storms in winter; the volume of winter sediment transport is at least one order of magnitude greater than that of summer/spring transport. Rock outcrops on the inner shelf (< 40 m of water) indicates an erosional environment, but an elongated mid-shelf mud deposit evidently suggests a depositional environment on the mid-shelf. The seafloor geology appears to correlate to the poleward and offshore sediment transport pattern. This study also suggests that suspended sediment moves out of Monterey Bay, roughly along the isobaths of the northern bay. This fine material, originally from river sources, and the material from the coastal cliff erosion that is subsequently introduced to the transport system through cross-shelf sediment transport, are believed to be the sources of the mid-shelf mud deposit. ?? 2002 Elsevier Science B.V. All rights reserved.

Marine Geology↗
USGS2002

Distribution and transport of suspended particulate matter in Monterey Canyon, California

From August 1993 to August 1994, six moorings that measure current, temperature, salinity, and water clarity were deployed along the axis of Monterey Canyon to study the circulation and transport of water and suspended particulate matter through the canyon system. The moorings occupied three sites that are morphologically different: a narrow transverse section (axis width 900 m) at 1450 m water depth, a wide transverse section at 2837 m, and a third site in the fan valley axis farther offshore at 3223 m that recorded for 3 yr. In addition, CTD/transmissometer casts were conducted within and near the Monterey Canyon during four cruises. Our data show a mainly biogenic, surface turbid layer, a limited intermediate nepheloid layer, and a bottom nepheloid layer. There is a consistent presence of a turbid layer within the canyon at a water depth of about 1500 m. Tidal flow dominates at all sites, but currents above the canyon rim and within the canyon appear to belong to two distinct dynamic systems. Bottom intensification of currents plays an important role in raising the near-bottom shear stress high enough that bottom sediments are often, if not always, resuspended. Mean flow pattern suggests a convergence zone between the narrow and wide site: the near-bed (100 m above bottom where the lowest current meter was located) mean transport is down-canyon at the 1450-m site, while the near-bottom transport at the 2837-m site is up-canyon, at a smaller magnitude. Transport at the 3223-m site is dominantly NNW, cross-canyon, with periods of up-canyon flow over 3 yr. A very high-turbidity event was recorded 100 m above the canyon bottom at the narrow site. The event started very abruptly and lasted more than a week. This event was not detected at either of the deeper sites. A canyon head flushing event is likely the cause. ?? 2002 Elsevier Science B.V. All rights reserved.

Marine Geology↗
USGS2002

Towards a sediment budget for the Santa Cruz shelf

A conceptual model is presented for the northern Monterey Bay continental shelf in which coarse sediment moves southward along the coast in the littoral zone while fine sediment moves to the north by advection and diffusion along the midshelf. Data from measurements and estimates of various sediment sources and sinks show that the midshelf mudbelt is the dominant sink for fine-grained sediment introduced into Monterey Bay. The principal sources of the fine sediment are the three rivers that enter Monterey Bay: the San Lorenzo, Pajaro and Salinas rivers. Accumulation rates in the midshelf mudbelt are high relative to documented yields of rivers and cliff erosion, and also are high relative to other documented mud accumulations of the west coast continental shelves. ?? 2002 Elsevier Science B.V. All rights reserved.

Marine Geology↗
USGS1989

Internal tidal currents over the summit of cross seamount

Spectral analysis of 46 days of record from a current meter deployed above the summit of Cross Seamount (approximately 300 km west of the Hawaiian Islands) indicates that the strongest current fluctuations were driven by the semidiurnal tide. The tides accounted for 28% of the variance in the current spectrum, were mainly baroclinic in character, and were propagated towards the west-northwest. The amplitude of the S2 current flowing parallel to the major axis of the current ellipse ranged between 4 and 9 cm-1 s. The S2 current was 1.5 times larger than the M2 current. This ratio is 4 times larger than is expected for this region of the Pacific and is not a general characteristics of flows over seamounts. Instantaneous current speeds over the seamount often exceeded 20 cm s-1 and were probably responsible for the small ripples observed on the sediment-covered regions of the summit. ?? 1990.

Deep Sea Research Part A, Oceanographic Research P↗
USGS1988

Internal tides and sediment movement on Horizon Guyot, Mid-Pacific Mountains

Internal tidal currents are the likely cause of erosional features such as current ripples, sand waves, and truncated bedding horizons on the sediment cap of Horizon Guyot. Current meter data obtained over a 9 month period in 1983-1984 at about 213 m above the guyot show that the tidal currents are anomalously strong for mid-oceanic depths, probably the result of topographically induced generation of internal tidal waves. An analysis of the initiation of motion of the foraminiferal sand by the internal tidal currents indicates that these currents, particularly during the months of March-May, are likely to transport the surficial sediment and generate the observed bedforms. ?? 1988 Springer-Verlag New York Inc.

Geo-Marine Letters↗