Papers by Andrew Fischer
Oceanography, 2005
Abstract Dense accumulations of certain phytoplankton make the ocean appear reddish. Some of thes... more Abstract Dense accumulations of certain phytoplankton make the ocean appear reddish. Some of these" red tides" poison marine life and negatively impact coastal fisheries and human health. Complex variability in coastal waters coupled with rudimentary ...
There is concern that thermal discharge from coastal power stations impact coastal ocean ecosyste... more There is concern that thermal discharge from coastal power stations impact coastal ocean ecosystems. The introduction of heated water from these sources, for example, can influence the aquatic environment by decreasing oxygen solubility and affecting metabolic activity of marine organisms. Here we describe and compare the general flow structure, dynamics and temperature differences between a thermal discharge from an anthropogenic point source (the Moss Landing Power Plant) and the natural heat flux between two natural bodies of water, an estuary (the Elkhorn Slough) and the open ocean. The data used in this analysis were collected on different occasions for two indivdual and separate studies. Data colletion of temperature, as well as other physical, chemical and biological parameters in both studies involved a variety of in situ and remote sensing techniques, from stationary temperature loggers on buoys, underway mapping systems, an autonomous underwater vehicle, and remotely sensed data collected by visible and infrared airborne sensors. The results show that tidal inertia produces a surface advected plume exiting the Elkhorn Slough through the Moss Landing Harbor channel that extends approximately one kilometer in a southwesterly direction. The plume is approximately 500 m wide and extends 5-10 m in depth. By contrast, the Moss Landing Power Plant outfall discharge extends vertically through the water column directly over the discharge site, and at the surface a plume disperses shoreward and south of the discharge site. Temperature measurements from each of the plumes show high levels of variability due to tidal mixing. The difference in average daily temperature between the Elkhorn Slough plume and nearshore waters was usually ~1°C , but overall temperatures differences ranged from 1.3°C cooler to 2.3°C warmer. Temperature variability measured at the Moss Landing Power plant outfall discharge site, ranged from 3.7°C cooler to 6.4°C warmer than ambient ocean conditions and the overall average temperature during the sampling period was ~0.5°C warmer than the surrounding nearshore waters. Temperatures cooler than surrounding bay waters at the outfall discharge site occurred only 15% of the time during the sampling period, compared to 20% of the time for the Elkhorn Slough plume. Overall, prelimiary results show that the thermal contribution to the coastal ocean from the Elkhorn Slough maybe greater than that from the outfall discharge. Future research directions are recommended to further understand the interaction of these plumes with each other, as well as their contribution to the coastal waters of Monterey Bay and the Monterey Bay National Marine Sanctuary.
Journal of Marine Research, 2006
Analysis of in situ temperature records collected on six coral reefs in the Caribbean, Bahamas, a... more Analysis of in situ temperature records collected on six coral reefs in the Caribbean, Bahamas, and Florida Keys reveal significant variability across a range of temporal and spatial scales from minutes to seasons, across depths, and among sites. Subsurface variability occurring at daily and faster frequencies is prevalent across the region, likely driven by combinations of diurnal heating and cooling,
Marine Environmental Research, 2014
The transformation of estuaries by human activities continues to alter the biogeochemical balance... more The transformation of estuaries by human activities continues to alter the biogeochemical balance of the coastal ocean. The disruption of this balance can negatively impact the provision of goods and services, including fisheries, commerce and transportation, recreation and esthetic enjoyment. Here we examine a link, between the Elkhorn Slough and the coastal ocean in Monterey Bay, California (USA) using a novel application of fatty acid and pigment analysis. Fatty acid analysis of filtered water samples showed biologically distinct water types between the Elkhorn Slough plume and the receiving waters of the coastal ocean. A remarkable feature of the biological content of the plume entering the coastal ocean was the abundance of bacteria-specific fatty acids, which correlated well with concentrations of colored dissolved organic matter (CDOM). Pigment analysis showed that plume waters contained higher concentrations of diatoms and cryptophytes, while the coastal ocean waters showed higher relative concentrations of dinoflagellates. Bacteria and cryptophytes can provide a source of labile, energy-rich organic matter that may be locally important as a source of food for pelagic and benthic communities. Surface and depth surveys of the plume show that the biogeochemical constituents of the slough waters are injected into the coastal waters and become entrained in the northward flowing, nearshore current of Monterey Bay. Transport of these materials to the northern portion of the bay can fuel a bloom incubator, which exists in this region. This study shows that fatty acid markers can reveal the biogeochemical interactions between estuaries and the coastal ocean and highlights how man-made changes have the potential to influence coastal ecological change.
Continental Shelf Research, 2009
It has recently been shown that inner shelf waters of NE Monterey Bay, California function as an ... more It has recently been shown that inner shelf waters of NE Monterey Bay, California function as an ''extreme bloom incubator'', frequently developing dense ''red tide'' blooms that can rapidly spread. Located within the California Current upwelling system, this open bay is strongly influenced by oceanographic dynamics resulting from cycles of upwelling favorable winds and their relaxation and/or reversal. Different wind forcing causes influx of different water types that originate outside the bay: cold nutrient-rich waters during upwelling and warm nutrient-poor waters during relaxation. In this study, we examine how the bay's bloom incubation area can interact with highly variable circulation to cause red tide spreading, dispersal and retention. This examination of processes is supported by satellite, airborne and in situ observations of a major dinoflagellate bloom during August and September of 2004. Remote sensing of high spatial, temporal and spectral resolution shows that the bloom originated in the NE bay, where it was highly concentrated in a narrow band along a thermal front. Upwelling circulation rapidly spread part of the bloom, mixing cool waters of an upwelling filament with warm bloom source waters as they spread. Vertical migration of the dinoflagellate populations was mapped by autonomous underwater vehicle surveys through the spreading bloom. Following bloom expansion, a two-day wind reversal forced intrusion of warm offshore waters that dispersed much of the bloom. Upwelling winds then resumed, and the bloom was further dispersed by an influx of cold water. Throughout these oceanographic responses to changing winds, an intense bloom persisted in sheltered waters of the NE bay, where extreme blooms are most frequent and intense. Microscopic examination of surface phytoplankton samples from the central bay showed that spreading of the bloom from the NE bay and mixing with regional water masses resulted in significantly increased abundance of dinoflagellates and decreased abundance of diatoms. Similar dinoflagellate bloom incubation sites are indicated in other areas of the California Current system and other coastal upwelling systems. Through frequent bloom development and along-coast transports, relatively small incubation sites may significantly influence larger regions of the coastal marine ecosystems in which they reside.
Geophysical Research Letters, 2008
1] Marine ecosystems are greatly influenced by the structure and dynamics of fronts. In coastal u... more 1] Marine ecosystems are greatly influenced by the structure and dynamics of fronts. In coastal upwelling systems, frontogenesis occurs frequently by upwelling and transport of cold water and warming in sheltered "upwelling shadow" retention sites. Monterey Bay, in the California Current upwelling system, hosts a dynamic upwelling shadow environment. Using a decade of satellite synthetic aperture radar (SAR) observations with ancillary remote sensing and in situ data, we describe recurrent surface slicks that develop along the seaward periphery of the Monterey Bay upwelling shadow, and we examine their relationships with fronts. Slick median dimensions, 17.5 km long and 0.8 km wide, describe their elongated structure. Although the typical pattern is a single slick, multiple slicks may concurrently develop in association with different types of fronts. Repeated volume surveys through a front, underlying a slick, revealed lateral mixing and interleaving of regional water types. Velocity fields from coastal HF radar show that slicks may coincide with a variety of surface circulation patterns, that they may extend contiguously across regions having very different surface velocity, and that they may be separated from the shear front of upwelling filaments by 5-10 km. Slicks occur in all seasons and may coincide with both upwelling and downwelling wind forcing. Surfactant accumulation in small-scale convergence zones is indicated as the primary mechanism of slick formation, not ocean current shear or small-scale air-sea coupling. The results of this study emphasize the role of upwelling system fronts in creating small-scale structure and dynamics that influence plankton ecology.
Conference Presentations by Andrew Fischer
Landsat 8 imagery is of interest to water managers due to its regular schedule, open data access ... more Landsat 8 imagery is of interest to water managers due to its regular schedule, open data access and a spatial resolution of 30m which makes it suitable for monitoring smaller water bodies. But can it be effective in the detection of cyanobacteria blooms? In blooms dominated by cyanobacteria, chlorophyll-a (chl-a) is an effective surrogate for algal biomass [1]. Recent literature evaluating more than a dozen Landsat 8 chl-a retrieval algorithms based on both individual spectral bands and band ratios [4], difference indices and spectral shape functions [2] and a new linear combination index model [3] have been unable to yield a relationship with observed chl-a better than R 2 =0.67. We propose using a partial least squares (PLS) regression based model with band ratio inputs to improve detection of chl-a and in turn cyanobacteria dominated blooms using Landsat 8. The model explains 83% variance in observed chl-a with a predicted RMSE of 4.93 mg m-3.
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Papers by Andrew Fischer
Conference Presentations by Andrew Fischer