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Research about Monterey Bay

Source-linked reports with geographic coverage including Monterey Bay.

At least 37 records · Page 2Linked to original sources
USGS2002

Physiography of the Monterey Bay National Marine Sanctuary and implications about continental margin development

Combined EM-300 multibeam bathymetric data and satellite photography reveal the physiography of the continental margin between 35°50′ and 37°03′N and from the shoreline west of 122°40′ and 122°37′W, which includes Monterey Bay, in a previously unprecedented detail. Patterns in these images clearly reveal the processes that are actively influencing the current geomorphology of the Monterey Bay region, including the Monterey Bay National Marine Sanctuary (MBNMS). Our data indicates that seafloor physiography within the MBNMS results from plate margin tectonic deformation, including uplift and erosion along structural lineaments, and from fluid flow. Mass wasting is the dominant process active within the Ascension–Monterey and Sur–Partington submarine canyon systems and along the lower slopes. Meanders, slump dams, and constricted channels within the submarine canyons, especially within Monterey Canyon, slow and interrupt down-canyon sediment transport. We have identified for the first time thin sediment flows, rotational slumps, rills, depressions that may be associated with pipes, and other fluid-induced features we call ‘scallops’ off the Ascension slope, and suggest that fluid flow has sculptured the seafloor morphologies here. These unusual seafloor morphologies are similar to morphologies found in terrestrial areas modified by ground-water flow.

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USGS2002

Long-term cliff retreat and erosion hotspots along the central shores of the Monterey Bay National Marine Sanctuary

Quantification of cliff retreat rates for the southern half of Santa Cruz County, CA, USA, located within the Monterey Bay National Marine Sanctuary, using the softcopy/geographic information system (GIS) methodology results in average cliff retreat rates of 7–15 cm/yr between 1953 and 1994. The coastal dunes at the southern end of Santa Cruz County migrate seaward and landward through time and display net accretion between 1953 and 1994, which is partially due to development. In addition, three critically eroding segments of coastline with high average erosion rates ranging from 20 to 63 cm/yr are identified as erosion ‘hotspots’. These locations include: Opal Cliffs, Depot Hill and Manresa. Although cliff retreat is episodic, spatially variable at the scale of meters, and the factors affecting cliff retreat vary along the Santa Cruz County coastline, there is a compensation between factors affecting retreat such that over the long-term the coastline maintains a relatively smooth configuration. The softcopy/GIS methodology significantly reduces errors inherent in the calculation of retreat rates in high-relief areas (e.g. erosion rates generated in this study are generally correct to within 10 cm) by removing errors due to relief displacement. Although the resulting root mean squared error for erosion rates is relatively small, simple projections of past erosion rates are inadequate to provide predictions of future cliff position. Improved predictions can be made for individual coastal segments by using a mean erosion rate and the standard deviation as guides to future cliff behavior in combination with an understanding of processes acting along the coastal segments in question. This methodology can be applied on any high-relief coast where retreat rates can be measured.

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USGS2000

Geology and coastal hazards in the northern Monterey Bay, California: Field trip guidebook, November 4, 2000

The purpose of this field trip is to explore the relationships between local geology, coastal hazards, and human influences in the northern Monterey Bay, which is a tectonically active high wave energy coastal environment. Seacliffs, shore platforms, pocket beaches and a headland/embayment morphology characterize this rocky coastline. Many studies of the onshore and offshore geology and geophysics, the local wave climate, and the effects of large storm events and earthquakes on the coastline have been conducted in this region (see Related Reading section). This field trip summarizes many of the findings of these research investigations, and also considers the relationship between the rates and styles of seacliff erosion and the variations in the local geology. The field trip stops allow the participant to examine seacliff sites of different geological lithologies, geographic orientations, and varying protection from wave attack, and consider how these variables affect not only the rate or magnitude of seacliff retreat but also the styles of retreat. In general the two primary forcing factors in the retreat of seacliffs are marine and terrestrial processes. At the various field trip stops, the relative importance of these processes in shaping the coastline at that particular location will be explored. Where beaches have developed, whether naturally or by emplacement of man-made structures, field trip stops are designed to look at the occurrence of the beaches (why they exist where they do) and to understand the response of the beaches to large storm events. Finally, this trip focuses on the various coastline protection structures that have been built in the area, and their effectiveness in protecting development on the beaches or at the tops of the seacliffs. The first stop of the trip is the Long Marine Lab facility where the seacliffs are composed of the most resistant geological unit in the area, the Miocene Santa Cruz Mudstone. This stop also includes discussion of some of the interesting geological features associated with this part of the Bay, including the arches at Natural Bridges State Beach. The field trip stops are progressively east and south, moving into the inner Monterey Bay, as well as into the less resistant lithologies of the late Miocene to Pliocene Purisima Formation, and finally the Pleistocene Aromas Sand. The route will follow the coast wherever possible so participants can get a full perspective of the northern Monterey Bay coastline, even where stops have not been planned.

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USGS1994

Breeding patterns and reproductive success of California sea otters

Following commercial exploitation in the eighteenth and nineteenth centuries, sea otter ( Enhydra lutris ) populations in Alaska, British Columbia, and Washington recovered at 17-20% a year, yet the California population increased at only 5% a year. This slow rate of increase is perplexing, given that unoccupied and apparently favorable habitats occur throughout the sea otter's California range, and higher growth rates occurred among northern sea otter populations. Better knowledge of the demography of the California population is important in understanding these disparate population growth rates. We studied the reproductive biology and behavior of 53 tagged female sea otters from 1985 to 1991 in Monterey Bay, California. During the study, 136 pups were born to these females. Observations of each female enabled us to determine exact or estimated pup birth dates, which we used to calculate lengths of gestation, pup dependency, and reproductive cycle. Seasonal trends in pupping, in the proportion of adult females with pups, and in pup separations from their mothers were relatively uniform throughout the year. The average interval between separation from pup and subsequent birth was 198 days, the interbirth interval was 407 days, and estimated birth rate was 0.90/year for all adult females. For females that pupped annually (did not lose undetected newborns), the average interbirth interval was 342 days, given an estimated birth rate of 1.07/year. Length of the reproductive cycle increased with increasing length of prior pup dependency. However, the interval between separation from pup and subsequent birth was delayed among females that prematurely lost their pups. The average length of dependency for pups that survived to weaning was 166 days, but ranged from 120 to 280 days. The maximum preweaning survival rate was 0.60-0.65, less than values measured or inferred for some Alaskan populations. Most pups that did not survive to weaning were lost within a month of birth. The probability of successfully weaning pups and the length of dependency increased ( P = 0.077) with mothers' ages, thus indicating that reproductive success may increase among females with greater mothering experience. The high preweaning pup mortality we observed probably accounts for much of the relatively slow growth rate of the California sea otter population.

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USGS1994

Molluscan evidence for a late Pleistocene sea-level lowstand from Monterey Bay, central California

One hundred and twenty-three molluscan taxa are reported from four samples collected from a sea level lowstand deposit located between 100 m and 300 m below sea level in Monterey Bay, central California. Ecological interpretations of these mollusks suggest temperatures essentially equivalent to those from Puget Sound, Washington, to southern British Columbia; much cooler water than exists in Monterey Bay today; and water depths of about 10 to 50 m. Chlamys rubida from these deposits yield a 14C age determination of about 17,000 yr B. P. This age is generally equivalent to a worldwide sea level lowstand between 20,000 and 15,000 yr B. P. of at least 100 m below modern sea level. The cooler and shallow-water aspect of the lowstand molluscan fauna is in full accord with the late Pleistocene paleogeography of Monterey Bay.

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USGS1980

Modern sedimentary facies of the open Pacific coast and Pleistocene analogs from Montery Bay, California

Depositional processes and sedimentary structures of wave-dominated Pacific coastal environments vary systematically with water depth. The depth-limited open-coast facies identifiable by their sedimentary structures are the inner shelf, barred or nonbarred nearshore, beach, and coastal dune facies. These facies are most commonly preserved in shallowing-upward progradational sequences. The vertical sequence of sedimentary structures preserved in marine terrace deposits in the northern Monterey Bay region is very similar to that predicted on the basis of the modern facies. Few marine sediments deposited during the marine transgression that accompanied rising sea level were preserved. Most of the the marine and eolian sediments form a progradational sequence deposited mainly during intervals of falling sea level. In contrast, the sediments that form the adjacent fluvial terraces were deposited mainly during periods of rising sea level and became entrenched during the subsequent lowering of sea level. In combination, these fluvial, marine, and eolian deposits provide a record of a complete eustatic cycle. The recognition of the role of changing sea level in controlling patterns of coastal sedimentation and landform development during the Quaternary allows the development of a generalized model for Quaternary sedimentation along a wave-dominated coastline. The application of this model has aided in the interpretation of older Pleistocene sediments in the region (e.g. the Aromas Sand). It also has resulted in the recognition of at least eleven glacio-eustatic cycles preserved in the stratigraphic record of the Monterey Bay area during the Quaternary.

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USGS1973

Petrography and structural relations of granitic basement rocks in the Monterey Bay area, California

In the past, the granitic basement of the Coast Ranges has been thought to be dominantly quartz diorite and low in K-feldspar. However, a study of outcrops around Monterey Bay, basement well samples, and dredge samples from Monterey Bay shows that the granitic basement averages about 15 to 20 percent K-feldspar. Therefore, as a sedimentary provenance, the basement around Monterey Bay could have contributed abundant K-feldspar to the Cenozoic sedimentary deposits of the region; that is, in the Monterey Bay area the local basement is an adequate source for the abundant K-feldspar in the sedimentary units. The distribution of basement rocks and mapped faults, coupled with gravity-geophysical data, suggests that the area between the San Andreas and Sur-Nacimiento fault zones (the Salinian block) near Monterey Bay is broken into several discrete structural blocks. Some of these blocks juxtapose not only different basement rocks, but also different contour patterns on the buried basement surface. These features suggest large strike-slip movements along some faults within the Salinian block in the Monterey Bay area.

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USGS1970

Coastal currents and mass transport of surface sediments over the shelf regions of Monterey Bay, California

In Monterey Bay, the highest concentrations of medium and fine sands occur nearshore between ten and thirty fathoms. Silt and clay accumulate in greater depths. Contours of median diameter roughly parallel the isobaths. Fine-grained materials are supplied to the bay region from erosion of cliffs which partly surround Monterey Bay, from sediment laden river discharge, and from continual reworking of widespread Pleistocene and Recent sea floor sediments. These sediments in turn are picked up by coastal currents and distributed over the shelf regions by present day current regimes. Studies of bottom currents over the shelf regions and in Monterey Canyon have revealed patterns which vary with seasonal changes. Current patterns during August and September exhibit remarkable symmetry about the axis of Monterey Submarine Canyon. Central Shelf currents north and south of Monterey Canyon flowed northwest at an average rate of 0.2 knots and south at 0.3 knots respectively. On the North Shelf between January and March currents flowed east to southeast at 0.3–0.5 knots with mirror image patterns above the South Shelf during the same period. Irregular current flow in the canyon indicates a complex current structure with frequent shifts in counterclockwise and clockwise direction over very short periods of time. Bottom topography of the canyon complex often causes localization of canyon currents. One particular observation at a depth of 51 fathoms indicated up-canyon flow at a rate of 0.2 knots. Most of the observed currents are related to seasonal variations, upwelling, ocean swell patterns, and to changes in the California and Davidson currents. Changes in current regimes are reflected in the patterns of sediment distribution and transport. Sediment transport is chiefly parallel to the isobaths, particularly on the North and South Shelf regions. Complex dispersal patterns are observed near Monterey Canyon and Moss Landing Harbor jetties. Longshore currents move sediments southward except near Monterey Canyon which acts as a physiographic barrier and the extreme southern end of the bay where currents are non persistent. Some sediments are also transported offshore by rip currents and other agencies and deposited in deeper, quieter waters. Supply of sediments to the canyon head results in over-filling and steepening with subsequent mass movement of sediments seaward followed by deposition in channels and on the broad deep sea fan.

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