We have compared the radio emission from a sample of parsec-scale AGN jets as measured by the VLBA at 15 GHz, with their associated gamma-ray properties that are reported in the Fermi LAT 3-month bright source list. We find in our radio-selected sample that the gamma-ray photon flux correlates well with the quasi-simultaneously measured compact radio flux density. The LAT-detected jets in our radio-selected complete sample generally have higher compact radio flux densities, and their parsec-scale cores are brighter (i.e., have higher brightness temperature) than the jets in the LAT non-detected objects. This suggests that the jets of bright gamma-ray AGN have preferentially higher Doppler-boosting factors. In addition, AGN jets tend to be found in a more active radio state within several months from LAT-detection of their strong gamma-ray emission. This result becomes more pronounced for confirmed gamma-ray flaring sources. We identify the parsec-scale radio core as a likely location for both the gamma-ray and radio flares, which appear within typical timescales of up to a few months of each other.

We have compared the radio emission from a sample of parsec-scale AGN jets as measured by the VLBA at 15 GHz, with their associated gamma-ray properties that are reported in the Fermi LAT 3-month bright source list. We find in our radio selected sample that the gamma-ray photon flux correlates well with the quasi-simultaneously measured compact radio flux density. The LAT-detected jets in our radio-selected complete sample generally have higher compact radio flux densities, and their parsec-scale cores are brighter (i.e., have higher brightness temperature) than the jets in the non-LAT detected objects. This suggests that the jets of bright gamma-ray AGN have preferentially higher Doppler-boosting factors. In addition, jets of the LAT-detected AGN tend to be in a more active radio state, when quasi-simultaneous data are used. This result becomes more pronounced for confirmed gamma-ray flaring sources. We identify the parsec-scale radio core as a likely location for both the gamma-ray and radio flares, which appear within typical timescales of up to a few months of each other.

Distribution of the toxin microcystin was studied in Saginaw Bay, Lake Huron during two summer (August) cruises in 2003–2004. Intracellular microcystin concentrations averaged 1.1 μ g l− 1 (range 0.01–3.5 μ g l− 1), and extracellular concentrations averaged only 0.09 μ g l− 1 (range 0.01–0.18 μ g l− 1). Highest microcystin concentrations were found in the nearshore regions of the bay, which were shallow and had high total phosphorus concentrations. Microcystin concentrations were strongly correlated with Microcystis aeruginosa abundance (r = 0.8). M. aeruginosa abundance was strongly correlated with total phosphorus, and growth rates were negatively correlated with C:P ratio. Particulate nutrient ratios suggested that Saginaw Bay algae were severely phosphorus deficient. Microcystin cell quotas for M. aeruginosa averaged 140 fg cell− 1, and were not correlated with any environmental factor or growth rates. In Saginaw Bay, phosphorus availability primarily influences microcystin concentrations through direct control of M. aeruginosa abundance and growth rates, and not through direct control of cellular microcystin synthesis.

As part of the Episodic Events Great Lakes Experiment, we sampled total suspended matter (TSM), light climate, nutrients, and plankton along cross‐margin transects in southern Lake Michigan during February, March, and April 1998–2000 to capture conditions before, during, and after the occurrence of storm‐driven recurrent coastal sediment plumes to define the anatomy of the resuspension events and get insights into their interactions with nutrients and plankton. Variability in timing and strength of winter storms among years led to different timing, intensity, and extent of plumes among years. TSM concentrations in the core of plumes varied between 15 and 30 mg L−1, and photic depth was reduced to ∼1 to 2 m, thus potentially seriously limiting phytoplankton growth in plume areas. Total P concentration was highly correlated with TSM and river influence. Chlorophyll concentrations were lower in plume regions than in adjacent areas, in contrast to the relatively constant chlorophyll concentration across the plume predicted by a coupled hydrodynamic and nutrient‐phytoplankton‐zooplankton model. Contrary to expectation, protozoan microzooplankton (MZ) biomass was not more abundant in the plume than adjacent waters, but was highest in nearshore areas receiving river inflow. Storms affected horizontal distribution of zooplankton. Because of the lower concentrations of phytoplankton in the plume, the plume over the short term had a negative impact on zooplankton during this food‐limiting season. Our results combined with those of other EEGLE studies lead us to conclude that storms and storm‐driven plumes had a negative effect on the planktonic food web.

The benthic amphipod Diporeia spp. is the dominant benthic macroinvertebrate in the offshore region (>30m) ofthe Laurentian Great Lakes and, as a detritivore, plays a critical role in the offshore food web. Diporeia feed on organic material that settles from the water colurnn and, in turu, are fed upon by many fish species. This organism, therefore, serves as an important trophic link between lower and upper trophic levels (GARDNER et al. 1990). Diporeia are currently declining in all the Great Lakes except Lake Superior (DERMOTT & KEREc 1997, NALEPA et al. 1998, LOZANO et al. 2001, DERMOTI 2001). While declines have been coincidental with the introduction and spread of the zebra mussel (Dreissena polymorpha) and the quagga mussel (Dreissena bugensis), exact mechanisms for the negative response have not been clearly defined (NALEPA et al. 2004).

(2006). Lake Champlain Lagrangian experiment. SIL Proceedings, 1922-2010: Vol. 29, No. 3, pp. 1683-1687.

Moored observations of winds, currents, and temperature made off the southeastern Lake Michigan shore during 1998 to 2000 winter‐spring periods are studied to describe the mean winter circulation and episodic circulation during northerly storms in Lake Michigan. Late winter‐spring sediment plumes in southeastern Lake Michigan were attributed to these episodic circulation features. The winter‐spring currents in southeastern Lake Michigan are quite depth independent, and the mean currents flow predominantly alongshore and toward the north. The observed currents show the signature of a forced two‐gyre circulation in the southeastern basin. The interannual variability of mean and fluctuating currents is mainly due to the variability of prevailing wind‐forcing. The intermittent episodic circulation influenced by northerly storms causes significant asymmetry to the mean circulation. During northerly storm episodes, the mean current speeds increased significantly, and the currents within 10 km of shore followed the surface wind stress, while farther offshore the circulation was oppositely directed. During these episodes it is also observed that the combination of directly wind‐forced currents and northward propagating vorticity wave generates significant offshore transport in this region.

Lake whitefish (Coregonus clupeaformis) support the largest commercial fishery in Lake Michigan, yet relatively little is known of the thermal ecology of free-ranging lake whitefish. In 2000 six commercial trap nets were instrumented with self-recording temperature data loggers to examine the relationship between lake whitefish harvest, water temperature statistics, and fishing effort. Several variables including surface water temperature (SWT), bottom water temperature (BWT), difference between SWT and BWT, and fishing effort were used in both a backward and forward stepwise regression model against fishing harvest. Both the backward and forward results generated similar R2 statistics of 0.62 and 0.58 respectively, with the backward model suggesting BWT, variance of BWT, and the difference between SWT and BWT as the best regression model. The forward regression results suggested that SWT alone was the best model. Subsequent ANOVA tests support selecting the simpler model for describing the lake whitefish dependence on temperature, which was:y=21,000e−0.366Twhere y is dressed lake whitefish harvest (kg) and T is SWT (°C). This model worked well for surface water temperatures between approximately 10 and 20°C. The success in describing the fish harvest with surface water temperatures is most likely the consequence of warm surface water intrusions into the hypolimnion from coastal downwellings being the dominant factor controlling lake whitefish distribution.

In the Great Lakes, as well as in the coastal oceans, the gradients of many biogeochemically important materials (BIMs) are considerably higher in the offshore direcrion than in the alongshore direction (BRINKet al. 1992). In the presence of these large gradients, cross-isobath circulation is a primary mechanism for the exchange of material berween nearshore and offshore waters. In the coastal regions of the Great Lakes it has been observed that the mean alongshore transport is much larger than the cross-shore transport. However, both the alongshore and cross-shore currem components exhibit strong episodic behavior due to wind forcing. In order £0 understand the cross-shore transport of BIMs, and to quantify the physical processes that are responsible for the nearshore-offshore mass exchange, a multidisciplinary research program, EEGLE (Episodic Events Great Lakes Experiment) was recently initiated by NOAA (National Oceanic and Atmospheric Administration) and NSF (National Science Foundation) in Lake Michigan. Circulation in the lakes is driven by wind, bur the effects of earth's rotation, basin £Opography, and vertical densiry structure are also important. During the unstratified season, the higher wind speeds and the absence of the thermocline allow the effecrs of wind action to penetrate deeper into the water column (BOYCEet al. 1989). In shallow water, the entire water mass moves in the direction of the wind, while return flow occurs in the deeper pans of the lake. This forms rwo coumer-rotating closed gyres (SAYLORet al. 1980), a cyclonic gyre to the right of the wind and an amicyclonic gyre £0 the left. These rotary motions or voniciry waves have been suggested as a main mechanism for nearshore-offshore transpon in the Great Lakes. SCHWABet al. (2000) observed the presence of this rwo-gyre circulation pattern in their numerical experimems during a wind evem in March 1998. MCCORMICKet al. (2000) reported time series of currems at a few stations in southern Lake Michigan during this event.

In the c();lsral regions of large lakes oceans, the horizontal gradients of dis~()lved chernic.lls suspended lluteriais are otten br greater in the otEhore than in the alongshore direction. Therefore, the mechanisms driving cross-isobath circulation playa critical role in maintaining the water quality in coastal regIOns. In the Laurentian Crelt Lakes the absence of any tidal currems their smaller hasin geometry, relative to oceanic condi tions, leaves a ~~locity neld. that is dominated by wind [()fcing. rIme vanabdlty III the surface wind stress in both magnitude and direction resuits in a relatively weak background circulation pattern (BELETSKY et al. 1999). Under conditions like these there is a greater potential impact f()r storms to be a major mechanism for the of Ish ore Hux of coastal materials. As parr of a National Science Foundationand NOAA-sponsored srudy, an extensive array of fixed current meter moorings ;lI1d satellite-reporting drifting buoys were used in the coastal region of southeastern Lake Michigan, as part of an eff()[( to determine the statistics associated with offshore longsh~)re tr;~nsp(~rt. The observational program began 111 the fall or 1997 ended in early summer 2000. With recent improvements in Lagrangian positioning technology, with GPS sophisticated microprocessor-equipped drifters, they have become even more useful tools for studying coastal circulation. PAL et al. (I998) SANDFRS()N (I987) used drifters to help describe the mixing circulation c.haracteristi~s of Lakes Ontario Erie, respectively. In thIS report, findings are described from a Lagrangian experiment in April 1999 on the coastal waters of Lake Michigan.

Sea‐viewing Wide Field‐of‐View Sensor (SeaWiFS) images from June 1998 show a surprising early summer phytoplankton bloom in southern Lake Michigan that accounted for approximately 25% of the lake's annual gross offshore algal primary production. By combining the satellite imagery with in situ measurements of water temperature and wind velocity we show that the bloom was triggered by a brief wind event that was sufficient to cause substantial vertical mixing even though the lake was already stratified. We conclude that episodic events can have significant effects on the biological state of large lakes and should be included in biogeochemical process models.

Intermittent satellite images collected over in the last few years have revealed episodic late winter‐spring plumes coinciding with northerly storms in southern Lake Michigan. A major inter‐disciplinary observational program was initiated to study the importance of these episodic events on nearshore‐offshore transport and the subsequent ecological consequences. In this paper, high density observations of winds and currents made during the winter of 2000 are analyzed to study the variability of the coastal circulation and the physical mechanisms resulting in the alongshore and cross‐shore transport in the lake. The measurements of currents show the signature of forced two‐gyre circulation in the southern basin. During northerly storm episodes the combination of directly wind forced currents and northward propagating vorticity wave generate significant offshore transport in this region.

(2002). Temporal and spatial variability of the resuspension coastal plume in southern Lake Michigan inferred from ADCP backscatter. SIL Proceedings, 1922-2010: Vol. 28, No. 2, pp. 513-518.

During the spring isothermal mixing period (April-May) in 1993-1995, photosynthesis-irradiance and growth-irradiance experiments were conducted in Lakes Erie, Huron, Michigan, and Ontario to assess light limitation. Additionally, nutrient enrichment experiments were conducted in Lake Ontario. Results from the photosynthesis-irradiance experiments suggested that phytoplankton communities in all the lakes can be either light limited or light saturated, as the threshold parameter (Ik) was similar to mean water column irradiances (mean Iwc, ratio = 1.0). Growth-irradiance experiments also suggested the potential for light saturation; mean daily irradiance exceeded the threshold growth irradiance (Ik,g) in 95% of cases. Growth rates became light saturated at lower irradiances than photosynthetic rates. Evidence for a nutrient-light interaction in controlling in situ growth rates was also found in the nutrient enrichment experiments at incubation irradiances [Formula: see text] mean Iwc. Our results suggest that an interaction between nutrients and light is often controlling phytoplankton growth during spring mixing in the Great Lakes. The role of these nutrient-light interactions has increased in the past decade due to increased light availability in the lower lakes caused by phosphorus load reductions and the filtering activities of nonindigenous mussels.

Data from acoustic Doppler current profilers deployed in the nearshore region of southeastern Lake Michigan provide evidence of sediment resuspension episodes and cross-shelf flux of materials during strong winter storms. Significant increases (+20 dB) in echo intensity and current velocities correlate well with satellite imagery of a sediment-laden plume transporting material in a cyclonic flow around the lake basin's perimeter. A decrease in echo intensity to near-background levels following resuspension events suggests that the larger particles settle out, leaving the very fine material that remains visible in satellite imagery for many days. Although there were no concurrent total suspended material measurements during the event, the ADCP results suggest that resuspension events and plume movements can be detected

The structure of the planktonic food-web was studied during the spring (April/May) and summer (August) periods in 1993 to 1995 at twelve stations located in the offshore region of all five Great Lakes. All components of the planktonic food-web were collected from the same water sample (with the exception of crustaceans), counted microscopically, converted to carbon units, and averaged over the euphotic zone. Due to phosphorus load reductions and the impact of non-indigenous mussels in the lower lakes, physical/chemical characteristics of the lower lakes are becoming similar to those in the upper lakes. Spring total phosphorus and euphotic zone depth were relatively similar among all the stations (except western Lake Erie), ranging from 3 to 7 μg/L and 21 to 26 m, respectively. During the summer, total phosphorus concentrations were more variable, but ranged between 4 to10 μg/L at all stations except western Lake Erie. Planktonic biomass was correlated with total phosphorus concentration. Within a season, the structure of the planktonic food-web was remarkably similar among all stations across all the lakes. Of the seventeen food-web structure parameters examined, only two exhibited significant differences among stations during the spring isothermal period; only four parameters exhibited significant differences among stations during the summer. Small plankton were very abundant in all the lakes. Picoplankton (0.2 to 2.0 μm) biomass was approximately equal to the combined biomass of nanno-and microplankton (2 to 200 μm). For microorganisms (all organisms except crustaceans) autotrophic: heterotrophic ratios averaged 1.3 (spring=1.1, summer=1.5). The heterotrophic microorganism community was comprised of bacteria (mean=65%), protozoans (mean=32%), and rotifers (3%). Even though zebra mussel veligers were found in all the lakes except Lake Superior, their contribution to microorganism biomass never exceeded 1%. Due to seasonal variation in crustacean abundance, the mean contribution of major functional groups varied by season; producers (autotrophs), decomposers (bacteria), micrograzers (protozoans and rotifers), and mesograzers (crustaceans) constituted 40%, 30%, 11%, and 19% of total planktonic carbon, respectively, during the spring, and 32%, 15%, 9%, and 43%, respectively, during the summer. The overall similarity in the structure of the planktonic food-web across all stations in the Great Lakes was attributed to the strong influence of abiotic factors.

Cell‐specific growth and cell‐specific production estimates of phytoplankton have been calculated in the past by a simple exponential model (constant uptake‐division) that describes the time rate of change of carbon, C*, and assumes both continuous division and continuous carbon uptake. We propose three new models (variable uptake‐division, variable uptake‐constant division, and diurnal) for making more accurate estimates of the algal growth rate, µ. The variable uptake‐division model is the most complex and requires species‐specific information on the division pattern. The diurnal model can provide accurate µ estimates while requiring only two measurements of C* and no other parameters, but it requires 48‐h incubation times. The variable uptake‐constant division model can also provide accurate µ estimates and can be applied to data with <24‐h incubation times. The variable uptake‐division and variable uptake‐constant division models require additional work compared to the constant uptake‐division model, but the effort is warranted because they also provide a direct approach for quantifying the dependence of µ on the photoperiod and thus enable greater confidence in applying µ to ecological studies, in which the light climate may differ from that of the experiment.