Guy A. Meadows

Verification and Application of a Bio-optical Algorithm for Lake Michigan Using SeaWiFS: a 7-year Inter-annual Analysis

ABSTRACT In this paper we utilize 7 years of SeaWiFS satellite data to obtain seasonal and inter-annual time histories of the major water color-producing agents (CPAs), phytoplankton chlorophyll (chl), dissolved organic carbon (doc), and suspended minerals (sm) for Lake Michigan. We first present validation of the Great Lakes specific algorithm followed by correlations of the CPAs with coincident environmental observations. Special attention is paid to the satellite observations of the extensive episodic event of sediment resuspension and calcium carbonate precipitation out of the water. We then compare the obtained time history of the CPAs spatial and temporal distributions throughout the lake to environmental observations such as air and water temperature, wind speed and direction, significant wave height, atmospheric precipitation, river runoff, and cloud and lake ice cover. Variability of the onset, duration, and spatial extent of both episodic events and seasonal phenomena are documented from the SeaWiFS time series data, and high correlations with relevant environmental driving factors are established. The relationships between the CPAs retrieved from satellite data and environmental observations are then used to speculate on the future of Lake Michigan under a set of climate change scenarios.

The Relationship between Great Lakes Water Levels, Wave Energies, and Shoreline Damage

The latter half of the twentieth century can be characterized as a period of rising water levels on the Great Lakes, with record high levels in 1974 and 1986. Concurrent with these periods of high water level are reported periods of high shoreline damage and property loss. Water levels of the Great Lakes are determined by precipitation, evaporation, river outflow, and groundwater inflow, while wave energy is primarily a function of wind speed, duration, and fetch. A comparison between a recently completed long-term (1956–87) wave climate hindcast and historical lake levels for the Great Lakes shows a strong correlation between periods of high wave energy and high lake levels. Statistical comparison of these two time series indicates an approximately constant correlation from +24 months to −6 months, around a zero lag/lead. The causational link between increasing lake levels and more intense wind-generated waves appears to be related to significant changes in the climatology of Great Lakes basin cyclones....

Evidence for early hunters beneath the Great Lakes

Scholars have hypothesized that the poorly understood and rarely encountered archaeological sites from the terminal Paleoindian and Archaic periods associated with the Lake Stanley low water stage (10,000–7,500 BP) are lost beneath the modern Great Lakes. Acoustic and video survey on the Alpena-Amberley ridge, a feature that would have been a dry land corridor crossing the Lake Huron basin during this time period, reveals the presence of a series of stone features that match, in form and location, structures used for caribou hunting in both prehistoric and ethnographic times. These results present evidence for early hunters on the Alpena-Amberley corridor, and raise the possibility that intact settlements and ancient landscapes are preserved beneath Lake Huron.

Cumulative Habitat Impacts of Nearshore Engineering

Abstract A multi-disciplinary, multi-institutional research team evaluated a broad range of physical and biological characteristics at six Great Lakes nearshore sites in order to develop and test a conceptual modeling framework to assess linkages between bluff erosion, sediment supply, coastal processes, and biological utilization of nearshore and coastal habitats. The sites were chosen to represent a broad range of hydrogeomorphic conditions, with the objective of assessing the response of these nearshore systems to anthropogenic modifications and coastal change. As a result of this 2-year field effort, new methods and integrated approaches were developed to characterize, map, and assess the dynamic nature of the nearshore zone (area generally less than 10 m water depth). Thus, these data provide an initial quantitative assessment of nearshore change. In addition, our data indicate that shoreline modifications have led to cumulative impacts that have irreversibly modified Great Lakes nearshore coastal habitats and the processes that create and maintain them. Of special note is our observation that altered nearshore substrate dynamics resulting from shoreline modifications may enhance the colonization success of lithophilic aquatic invasive species in nearshore areas of the Great Lakes. Continued development of the shoreline may exacerbate changes in Great Lakes nearshore food-web structures and ecosystem services. Further study and monitoring of these phenomena are needed, and our work suggests that a holistic, multidisciplinary approach is necessary to develop effective management strategies to address these and other issues affecting nearshore areas of the Great Lakes.

Groundwater Plume Mapping in a Submerged Sinkhole in Lake Huron

A multidisciplinary exploratory project team from the Institute for Exploration, the Great Lakes Environmental Research Laboratory, Grand Valley State University, and the University of Michigan located and explored a submerged sinkhole in Lake Huron during September 2003. A CTD system and an ultra-short baseline (USBL) acoustic navigational tracking system integrated with an open frame remotely operated vehicle (ROV) provided high-resolution depth, temperature, and conductivity maps of the sinkhole and plume. Samples were also peristaltically pumped to the surface from a depth of 92 meters within and outside of the sinkhole plume. A 1-2 m thick cloudy layer with a strong hydrogen sulfide odor characterized the water mass close to the plume. Relative to ambient lake water, water samples collected within this layer were characterized by slightly higher (4-7.5 oC) temperatures, very high levels of chloride and conductivity (10-fold) as well as extremely high concentrations of organic matter (up to 400 mg C/L), sulfate, and phosphorus. Our observations demonstrated the occurrence of unique biogeochemical conditions at this submerged sinkhole environment. I N T R O D U C T I O N he Laurentian Great Lakes were formed about 10,000-12,000 years before present (ybp), and presently contain approximately 19% of the Earth’s surface liquid freshwater (Beeton, 1984). The Lake Huron Basin is mostly covered with a layer of glacial till, sand, silt and clay. Underlying these sediments are aquifers formed within Paleozoic (Silurian-Devonian) bedrock. These bedrock aquifers were laid down when the shallow seas still spread widely over the continental areas approximately 350430 million ybp. The Silurian-Devonian aquifer consists of carbonate, shale, and sandstone matrix with some evaporite beds, and has fresh and saline water, which can contain varying amounts of sulfates, chlorides and iron. Dissolution of the Silurian-Devonian evaporites has produced the major karst features (Olcott, 1992) such as the sinkholes discovered during the 2001 acoustic survey expedition (Coleman, 2002) conducted by the Thunder Bay National Marine Sanctuary and the Institute for Exploration. The sinkhole vents, producing a visible cloudy layer above the lake bottom (Figure 1), were a serendipitous discovery made during a 2002 remotely operated vehicle (ROV) survey of the sinkholes. Recharge areas of freshwater replenishment for the Silurian-Devonian aquifers have been documented on land in the Lake Huron basin; these areas are typically sinkholes (Figure 2). In this report, we discuss the mapping of the Isolated Sinkhole located approximately 10 miles from shore at a depth of 93 m in the north central region of the Thunder Bay National Marine Sanctuary during September 2003.

The Flying Fish Persistent Ocean Surveillance Platform

*† ‡ § ** †† , The Flying Fish platform is an ocean, environmental monitoring buoy that repositions as an Unmanned Aerial System (UAS), maintaining a pre-set watch circle. To operate in the open ocean, the platform must be robust to moderate sea state conditions and must function unattended thus fully-autonomously. Our concept was conceived as an alternate solution to surface boat designs, avoiding the hydrodynamic drag of ocean waves and currents while in flight. Over the first project year, we developed and repeatedly demonstrated our prototype vehicle’s ability to autonomously “hop” across a GPS-defined “watch circle”, providing initial validation of the unified UAS-buoy (air/sea vehicle) persistent ocean monitoring concept. This paper will describe the vehicle design and performance characterization through simulation and flight-testing and provide insight to the Phase II vehicle which will operate for long periods with a balanced energy budget.

BathyBoat: An Autonomous Surface Vessel for Stand-alone Survey and Underwater Vehicle Network Supervision

Exploration of remote environments can now be conducted in relative safety using unmanned vehicles. This article describes the joint University of Michigan and Michigan Tech Research Institute project to design and build a new autonomous surface vessel (ASV) for use in research, education, and resource management as well as in the commercial sector. The article highlights relevant real world testing and recent missions involving the BathyBoat ASV on Alaskas North Slope, the harbors of Illinois, and various riverine environments in Michigan.

Hydrography and Circulation of Ice-marginal Lakes at Bering Glacier, Alaska, U.S.A

ABSTRACT An extensive suite of physical oceanographic, remotely sensed, and water quality measurements, collected from 2001 through 2004 in two ice-marginal lakes at Bering Glacier, Alaska—Berg Lake and Vitus Lake—show that each has a unique circulation controlled by their specific physical forcing within the glacial system. Conductivity profiles from Berg Lake, perched 135 m a.s.l., show no salt in the lake, but the temperature profiles indicate an apparently unstable situation, the 4°C density maximum is located at 10 m depth, not at the bottom of the lake (90 m depth). Subglacial discharge from the Steller Glacier into the bottom of the lake must inject a suspended sediment load sufficient to marginally stabilize the water column throughout the lake. In Vitus Lake, terminus positions derived from satellite imagery show that the glacier terminus rapidly retreated from 1995 to the present resulting in a substantial expansion of the volume of Vitus Lake. Conductivity and temperature profiles from the tidally influenced Vitus Lake show a complex four-layer system with diluted (~50%) seawater in the bottom of the lake. This lake has a complex vertical structure that is the result of convection generated by ice melting in salt water, stratification within the lake, and freshwater entering the lake from beneath the glacier and surface runoff. Four consecutive years, from 2001 to 2004, of these observations in Vitus Lake show little change in the deep temperature and salinity conditions, indicating limited deep water renewal. The combination of the lake level measurements with discharge measurements, through a tidal cycle, by an acoustic Doppler Current Profiler (ADCP) deployed in the Seal River, which drains the entire Bering system, showed a strong tidal influence but no seawater entry into Vitus Lake. The ADCP measurements combined with lake level measurements established a relationship between lake level and discharge, which when integrated over a tidal cycle, gives a tidally averaged discharge ranging from 1310 to 1510 m3 s−1.

A model of the thermal bar circulation in a long basin

A thermal bar is defined here as a zone of descending water at or near the fresh water temperature of maximum density. In the present study, we model physical properties such as velocity, temperature, turbulent fluxes, time of onset, and migration speed of the thermal bar in an idealized basin. Unlike models using prescribed eddy viscosity and diffusivity coefficients, our model uses a second-order turbulence closure scheme to model mixing due to turbulence. The only inputs in the calculation are the surface wind, the surface heat flux, and the initial state of the fluid. Numerical simulations of the resulting circulation are presented for flow in a long rotating basin under prescribed surface heat and wind conditions. The results show the influence of the relative magnitudes of mechanical and thermal forcing on the circulation. A comparison with field observations shows reasonable agreement between computed and measured bar migration speeds. The time necessary for the formation of the bar is computed, and is found to depend on the surface forcing.

Radar backscatter from mechanically generated transient breaking waves. II. Azimuthal and grazing angle dependence

For Pt. I see ibid. vol. 26, pp. 181-200 (2001). This paper describes the results of experimental investigations into the microwave backscatter from mechanically generated transient breaking waves. The investigations were carried out in a 110 m/spl times/7.6 m/spl times/4 m deep model basin, utilizing chirped wave packets spanning 0.75-1.75 Hz. Backscatter measurements were taken by a K-band continuous wave radar (24.125 GHz) at 40/spl deg/ angle of incidence, and at azimuth angles of 0/spl deg/, 45/spl deg/, 90/spl deg/, 135/spl deg/ and 180/spl deg/ relative to the direction of wave propagation. Grazing measurements were conducted using an X-band (10.525 GHz) FMCW radar at 85/spl deg/ angle of incidence, and azimuth angles of 0/spl deg/ and 180/spl deg/. Results show that the maximum radar backscatter was obtained in the upwave direction prior to wave breaking and was caused by the specular or near specular presentation of the wave to the radar. After breaking, the backscatter transitioned from a specular or near-specular dominated scattering, primarily seen in the upwave direction, to a small scale roughness dominated scattering, observed at all azimuths. Physical optics solutions were found to correctly predict the backscatter for the specular or near-specular dominated scattering and the small perturbation method was found to accurately model the VV polarization post-break radar backscatter.