Deep Scattering Layers of the Northern Gulf of Mexico Observed With a Shipboard 38-kHz Acoustic Doppler Current Profiler

Midwater sound-scattering layers containing aggregations of zooplankton and micronekton prey form in response to a trade-off between predator avoidance at depth and optimal foraging near the surface. Although the volume backscatter strength of zooplankton aggregations have been extensively studied in the past, fewer studies have specifically examined other descriptive characteristics of these layers such as depth of layers, timing of migrations, and the presence of secondary scattering layers below the main scattering layer. In the present study, patterns of deep scattering layers (DSLs) were characterized using relative acoustic backscatter from a ship-mounted 38-kHz phased-array, acoustic Doppler current profiler (ADCP) in the northern Gulf of Mexico in summers 2002 and 2003. Temporal patterns of scattering layers were analyzed with respect to the timing of the daytime and nighttime diel vertical migrations, and spatial patterns of scattering layers were analyzed with respect to their proximity to mesoscale circulation features associated with upwelling, downwelling, and water depth. The most prominent main scattering layer was consistently found at daytime depth of 450 to 550 m below the surface except during an unusual shoaling event in which a significant shallowing of the layer was observed at 200 to 300 m below the surface. This event coincided with the crossing of a strong frontal boundary between high salinity, blue water and low salinity, green water from the Mississippi River plume. Less prominent secondary scattering layers found deeper than the main scattering layer showed regional variability and appear to be more frequently associated with shallower shelf depths than in the deepwater basin. Variability among deep scattering layers in this region may have important implications for the behavior and interactions of higher trophic levels dependent on these prey layers

38-kHz ADCP investigation of deep scattering layers in sperm whale habitat in the northern Gulf of Mexico

A hull-mounted 38-kHz phased-array acoustic Doppler current profiler (ADCP) was used to acoustically survey the continental margin of the northern Gulf of Mexico (GOM) during 6 cruises in 2002-2003. This is the first backscatter survey with a 38-kHz ADCP in the Gulf of Mexico. ADCPs have been used as a proxy to measure the volume backscatter return from plankton in the water column, however previous studies were restricted to the upper 200 to 300 meters due to the relatively high frequency of operation (150-300 kHz) of the transducers. In addition to measuring deep water current velocities, the 38-kHz phased-array ADCP can measure Relative Acoustic Backscatter Intensity (RABI) as deep as 1000 meters. The daytime depth of the main deep scattering layer at 400 to 500 meters was resolved, and locally high backscatter intensity can be seen down to 800 meters. The objectives were to determine how to analyze RABI from the instrument to resolve scattering layers, and then to seek secondary deep scattering layers of potential prey species below the main deep scattering layer, from 600 to 800 meters in the feeding range for Gulf of Mexico sperm whales. Based on RABI from the 38-kHz ADCP, secondary DSLs in sperm whale diving range were more commonly recorded over the continental shelf than in the deep basin region of the Gulf of Mexico. The daytime depths of migrating plankton showed variation depending on physical circulation features (cyclone, anticyclone, proximity to Mississippi river, and Loop Current) present. Vertical migrations compared between concurrently running 38 and 153-kHz ADCPs showed an overlap of acoustic scatterers recorded by the two instruments, however the 153-kHz instrument has much finer vertical resolution. Vertical migration rates were calculated and simultaneous net tow samples from one of the cruises was used to compare abundance estimates by the two methods

Bio-physical interactions of small pelagic fish schools and zooplankton prey in the California Current System over multiple scales

Small pelagic fish represent a critical trophic link between plankton and large predators in marine upwelling ecosystems such as the California Current System. Populations of these fish are highly variable over time and are characterized by extreme fluctuations in abundance, which have significant ecosystem impacts. The causes driving this instability are not well understood, but several climactic and ecological factors have been hypothesized. This research investigated the linkages between habitat, plankton prey resources, and the abundance and behavior of small pelagic fish at various temporal and spatial scales (i.e., daily, weekly patterns of wind-driven upwelling, and seasonal) to understand how changes in physical and prey habitats influence trophic interactions. This research utilized a combination of stationary and shipboard acoustics, net sampling, and physical oceanography sampling approaches. A comparison of diel schooling behavior and zooplankton availability off Oregon and Monterey Bay, California revealed that changes in fish aggregation behaviors were caused by different timings of zooplankton availability in each region attributable to the extent of zooplankton diel vertical migrations. An analysis of the spatial relationships of acoustic scatterers across ocean fronts caused by wind-driven coastal upwelling indicated that upwelling may lead to a spatial mismatch between small plankton prey and schooling fish that select habitat based on their preference of warmer temperatures. The temporal patterns of zooplankton and pelagic fish abundance near the Columbia River plume were identified, finding that the seasonal appearance of small pelagic fish occurred very abruptly. The timing of fish arrival was poorly correlated with zooplankton abundance but was strongly linked with temperature, salinity, and river flow. Zooplankton abundance was highly variable with very large spikes occurring with the passage of tidally-driven river fronts. This research on the ecological and environmental factors between habitat, plankton, and small pelagic fish has revealed that both the physical habitat and prey fields play an important role in determining these interactions. Variability in the trophic interaction between small pelagic fish and zooplankton over varying scales has important ecosystem consequences, including the potential availability of these prey resources to larger predators, as well as impacts for management

The Necessary Limits of Religious Influence on Public Policy

In this thesis, I argue that Christian fundamentalism is a threat to the traditions of religious liberty and the separation of church and state in US liberal democracy. I support this claim by exploring the writings of men who were instrumental in the foundation of the US, concluding that they stressed several concepts, including support for religious liberty and the separation of church and state. Thereafter, I explore how the blueprint laid out by the founders has been followed by looking at the debate around church/state separation in terms of modern day arguments. I then discuss the position of Christian fundamentalism, what it is reacting to and what it is proposing. Lastly, I discuss the ramifications of the Christian fundamentalist agenda and propose a course of action that preserves religious liberty and church/state separation and alleviates anxiety about religious trivialization

Mapping Stratification : the industry-occupationspace reveals the network structure ofinequality

Social stratification is determined not only by income, education, race, and gender, but also by an individuals job characteristics and their position in the industrial structure. Utilizing a dataset of 76.6 million Brazilian workers and methods from network science, we map the Brazilian Industry-Occupation Space (BIOS). The BIOS measures the extent to which 600 occupations co-appear in 585 industries, resulting in a complex network that shows how industrial-occupational communities provide important information on the network segmentation of society. Gender, race, education, and income are concentrated unevenly across the core-periphery structure of the BIOS. Moreover, we identify 28 industrial occupational communities from the BIOS network structure and report their contribution to total income inequality in Brazil. Finally, we quantify the relative poverty within these communities. In sum, the BIOS reveals how the coupling of industries and occupations contributes to mapping social stratification

Mapping Stratification : the industry-occupationspace reveals the network structure ofinequality

Social stratification is determined not only by income, education, race, and gender, but also by an individuals job characteristics and their position in the industrial structure. Utilizing a dataset of 76.6 million Brazilian workers and methods from network science, we map the Brazilian Industry-Occupation Space (BIOS). The BIOS measures the extent to which 600 occupations co-appear in 585 industries, resulting in a complex network that shows how industrial-occupational communities provide important information on the network segmentation of society. Gender, race, education, and income are concentrated unevenly across the core-periphery structure of the BIOS. Moreover, we identify 28 industrial occupational communities from the BIOS network structure and report their contribution to total income inequality in Brazil. Finally, we quantify the relative poverty within these communities. In sum, the BIOS reveals how the coupling of industries and occupations contributes to mapping social stratification