Dmitry Beletsky

Mean Circulation in the Great Lakes

Abstract In this paper new maps are presented of mean circulation in the Great Lakes, employing long-term current observations from about 100 Great Lakes moorings during the 1960s to 1980s. Knowledge of the mean circulation in the Great Lakes is important for ecological and management issues because it provides an indication of transport pathways of nutrients and contaminants on longer time scales. Based on the availability of data, summer circulation patterns in all of the Great Lakes, winter circulation patterns in all of the Great Lakes except Lake Superior, and annual circulation patterns in Lakes Erie, Michigan, and Ontario were derived. Winter currents are generally stronger than summer currents, and, therefore, annual circulation closely resembles winter circulation. Circulation patterns tend to be cyclonic (counterclockwise) in the larger lakes (Lake Huron, Lake Michigan, and Lake Superior) with increased cyclonic circulation in winter. In the smaller lakes (Lake Erie and Lake Ontario), winter circulation is characterized by a two-gyre circulation pattern. Summer circulation in the smaller lakes is different; predominantly cyclonic in Lake Ontario and anticyclonic in Lake Erie.

Modeling circulation and thermal structure in Lake Michigan: Annual cycle and interannual variability

A three-dimensional primitive equation numerical model was applied to Lake Michigan for the periods 1982–1983 and 1994–1995 to study seasonal and interannual variability of lake-wide circulation and thermal structure in the lake. The model was able to reproduce all of the basic features of the thermal structure in Lake Michigan: spring thermal bar, full stratification, deepening of the thermocline during the fall cooling, and finally, an overturn in the late fall. Large-scale circulation patterns tend to be cyclonic (counterclockwise), with cyclonic circulation within each subbasin. The largest currents and maximum cyclonic vorticity occur in the fall and winter when temperature gradients are low but wind stresses are strongest. The smallest currents and minimum cyclonic vorticity occur in spring and summer when temperature gradients are strong but wind stresses are weakest. All these facts are in agreement with observations. The main shortcoming of the model was that it tended to predict a more diffuse thermocline than was indicated by observations and explained only up to half of the variance observed in horizontal currents at timescales shorter than a day.

A model of sediment resuspension and transport dynamics in southern Lake Michigan

A quasi-three-dimensional suspended sediment transport model was developed and generalized to include combined wave-current effects to study bottom sediment resuspension and transport in southern Lake Michigan. The results from a three-dimensional circulation model and a wind wave model were used as input to the sediment transport model. Two effects of nonlinear wave-current interactions were considered in the sediment transport model: the changes in turbulence intensity due to waves and the enhancement of induced bottom shear stresses. Empirical formulations of sediment entrainment and resuspension processes were established and parameterized by laboratory data and field studies in the lake. In this preliminary application of the model to Lake Michigan, only a single grain size is used to characterize the sedimentary material, and the bottom of the lake is treated as an unlimited sediment source. The model results were compared with measured suspended sediment concentrations at two stations and several municipal water intake turbidity measurements in southern Lake Michigan during November–December 1994. The model was able to reproduce the general patterns of high-turbidity events in the lake. A model simulation for the entire 1994–1995 two-year period gave a reasonable description of sediment erosion/deposition in the lake, and the modeled settling mass fluxes were consistent with sediment trap data. The mechanisms of sediment resuspension and transport in southern Lake Michigan are discussed. To improve the model, sediment classifications, spatial bottom sediment distribution, sediment source function, and tributary sediment discharge should be considered.

Biophysical Model of Larval Yellow Perch Advection and Settlement in Lake Michigan

ABSTRACT Potential for large-scale physical transport processes to affect recruitment of Lake Michigan yellow perch (Perca flavescens) was studied by examining the variation in larval distribution, growth rate, and settlement during June–August 1998–2003 using a 3D particle transport model linked with an individual-based bioenergetics growth model. In all years, virtual larvae were released nearshore in southwestern Lake Michigan, a known and important spawning region for yellow perch. For any given year, the same circulation pattern and water temperature either promoted or reduced yellow perch settlement depending on the consumption rates and settlement size chosen in the growth model. Increased consumption increased the number of settled larvae and expanded the total area where larvae settled, whereas increased settlement size reduced the number of settled larvae and reduced the overall settlement area. Interannual variability in circulation patterns and water temperature also resulted in contrasting larval settlement rates, settlement locations, and size of settlement areas between years. Model predictions were most consistent with field observations of age-0 yellow perch from Illinois and Michigan waters when settlement was assumed to occur at 50 mm. Moreover, our model suggests that larvae originating from southwestern Lake Michigan can recruit anywhere within the southern basin and even in the northern basin. Future model improvement will require information on the relative contribution of various sectors to the larval pool, their distribution with reference to the hydrodynamic landscape, the feeding and growth of yellow perch during their pelagic phase, and the size at transition to demersal stage.

Lake Erie hypoxia prompts Canada‐U.S. study

Because of its size and geometry, the central basin of Lake Erie, one of North Americas Great Lakes, is subject to periods in the late summer when dissolved oxygen concentrations are low (hypoxia). An apparent increase in the occurrence of these eutrophic conditions and ‘dead zones’ in recent years has led to increased public concern. The International Field Years for Lake Erie (IFYLE) project of the Great Lakes Environmental Research Laboratory (GLERL, a U.S. National Oceanic and Atmospheric Administration (NOAA) laboratory), was established in 2005 in response to this increase. This project is investigating the causes and consequences of hypoxia in the lake. As part of the effort, scientists from the United States and Canada conducted an extensive field study in 2005 to gather more information on the duration and extent of the hypoxic zone and its effects on the biota in the lake. This article gives a brief history and description of the problem and presents initial results from the field study.

A hydrodynamic approach to modeling phosphorus distribution in Lake Erie.

ABSTRACT The purpose of this paper is to show how a high-resolution numerical circulation model of Lake Erie can be used to gain insight into the spatial and temporal variability of phosphorus (and by inference, other components of the lower food web) in the lake. The computer model simulates the detailed spatial and temporal distribution of total phosphorus in Lake Erie during 1994 based on tributary and atmospheric loading, hydrodynamic transport, and basin-dependent net apparent settling. Phosphorus loads to the lake in 1994 were relatively low, about 30% lower than the average loads for the past 30 years. Results of the model simulations are presented in terms of maps of 1) annually averaged phosphorus concentration, 2) temporal variability of phosphorus concentration, and 3) relative contribution of annual phosphorus load from specific tributaries. Model results illustrate that significant nearshore to offshore gradients occur in the vicinity of tributary mouths and their along-shore plumes. For instance, the annually averaged phosphorus concentration can vary by a factor of 10 from one end of the lake to the other. Phosphorus levels at some points in the lake can change by a factor of 10 in a matter of hours. Variance in phosphorus levels is up to 100 times higher near major tributary mouths than it is in offshore waters. The model is also used to estimate the spatial distribution of phosphorus variability and to produce maps of the relative contribution of individual tributaries to the annual average concentration at each point in the lake.

Numerical Simulation of Internal Kelvin Waves and Coastal Upwelling Fronts

Two three-dimensional primitive equation numerical ocean models are applied to the problem of internal Kelvin waves and coastal upwelling in the Great Lakes. One is the Princeton Ocean Model (POM) with a terrain-following (sigma) vertical coordinate, and the other is the Dietrich/Center for Air Sea Technology (DIECAST) model with constant z-level coordinates. The sigma coordinate system is particularly convenient for simulating coastal upwelling, while the z-level system might be better for representing abrupt topographic changes. The models are first tested with a stratified idealized circular lake 100 km in diameter and 100 m deep. Two bottom topographies are considered: a flat bottom and a parabolic depth profile. Three rectilinear horizontal grids are used: 5, 2.5, and 1.25 km. The POM was used with 13 vertical levels, while the DIECAST model was tested with both 13 and 29 vertical levels. The models are driven with an impulsive wind stress imitating the passage of a weather system. In the case of the flat-bottom basin, the dynamical response to light wind forcing is a small amplitude internal Kelvin wave. For both models, the speed of the Kelvin wave in the model is somewhat less than the inviscid analytic solution wave speed. In the case of strong wind forcing, the thermocline breaks the surface (full upwelling) and a strong surface thermal front appears. After the wind ceases, the edges of this thermal front propagate cyclonically around the lake, quite similar to an internal Kelvin wave. In the case of parabolic bathymetry, Kelvin wave and thermal front propagation is modified by interaction with a topographic wave and a geostrophic circulation. In both models, higher horizontal resolution gives higher wave and frontal speeds. Horizontal resolution is much more critical in the full upwelling case than in the Kelvin wave case. Vertical resolution is not as critical. The models are also applied to Lake Michigan to determine the response to strong northerly winds causing upwelling along the eastern shore. The results are more complex than for the circular basin, but clearly show the characteristics of cyclonically propagating thermal fronts. The resulting northward warm front propagation along the eastern shore compares favorably with observations of temperature fluctuations at municipal water intakes after a storm, although the model frontal speed was less than the observed speed.

Modeling wind‐driven circulation during the March 1998 sediment resuspension event in Lake Michigan

[1] A three-dimensional primitive equation numerical ocean model was applied to Lake Michigan to simulate hydrodynamic conditions during the March 1998 sediment resuspension event in southern Lake Michigan caused by a storm with winds up to 20 m/s. The hydrodynamic model is driven with surface winds derived from observed meteorological conditions at 18 land stations and a meteorological buoy and also with surface winds calculated using a mesoscale meteorological model. Current observations from 11 subsurface moorings showed that the model driven with observed winds was able to qualitatively simulate wind-driven currents but underestimated current speeds during the most significant wind event. In addition, a pronounced offshore flow in the area of observations was also underestimated. Hydrodynamic model results using the meteorological model winds as the forcing function showed significant improvement over model results which were based on observed winds proving the importance of mesoscale winds for current modeling in large lakes.

A Simple 1-Dimensional, Climate Based Dissolved Oxygen Model for the Central Basin of Lake Erie

ABSTRACT A linked 1-dimensional thermal-dissolved oxygen model was developed and applied in the central basin of Lake Erie. The model was used to quantify the relative contribution of meteorological forcings versus the decomposition of hypolimnetic organic carbon on dissolved oxygen. The model computes daily vertical profiles of temperature, mixing, and dissolved oxygen for the period 1987–2005. Model calibration resulted in good agreement with observations of the thermal structure and oxygen concentrations throughout the period of study. The only calibration parameter, water column oxygen demand (WCOD), varied significantly across years. No significant relationships were found between these rates and the thermal properties; however, there was a significant correlation with soluble reactive phosphorus loading. These results indicate that climate variability alone, expressed as changes in thermal structure, does not account for the interannual variation in hypoxia. Rather, variation in the production of organic matter is a dominant driver, and this appears to have been responsive to changes in phosphorus loads.

Modeling summer circulation and thermal structure of Lake Erie

] Athree-dimensionalprimitiveequationnumericalmodelwasappliedtoLakeErieona2kmgridtostudyitssummercirculation andthermalstructure.Modelresultswerecomparedtolong-termobservationsofcurrentsandtemperaturemadein2005at severallocations,mostlyinitscentralbasin.IntheshallowandmostlyunstratifiedwesternbasincirculationisdrivenbyDetroitRiverinflow(modifiedtosomeextentbywind)andisfromwesttoeast. Inthecentralbasin(which isofintermediate depthandhasarelativelyflatbottom),themodeledcirculationisanticyclonic (clockwise),drivenbyanticyclonicvorticityinthesurfacewind,andthethermocline isbowl-shaped,inlinewithobservations.Inthedeeppartoftheeastern basin,the thermoclineisdome-shapedandcirculationiscyclonic (counter-clockwise),duetodensitygradients(aconfigurationtypicalforotherlargedeeplakes),whileshallower areasareoccupiedbyanticyclonic circulationdrivenbyanticyclonic windvorticity.Inthe centralbasin,modeledtemperatureandcirculationpatternsare quitesensitivetothespecificationofthe windfield.Anticyclonicwindvorticityleadstothinningofthehypolimnion inthecentralbasinandearlierdestratificationinthefall.