Three-dimensional Ocean Research Articles

Modeling Turbulent Subglacial Meltwater Plumes: Implications for Fjord-Scale Buoyancy-Driven Circulation

AbstractFjord-scale circulation forced by rising turbulent plumes of subglacial meltwater has been identified as one possible mechanism of oceanic heat transfer to marine-terminating outlet glaciers. This study uses buoyant plume theory and a nonhydrostatic, three-dimensional ocean–ice model of a typical outlet glacier fjord in west Greenland to investigate the sensitivity of meltwater plume dynamics and fjord-scale circulation to subglacial discharge rates, ambient stratification, turbulent diffusivity, and subglacial conduit geometry. The terminal level of a rising plume depends on the cumulative turbulent entrainment and ambient stratification. Plumes with large vertical velocities penetrate to the free surface near the ice face; however, midcolumn stratification maxima create a barrier that can trap plumes at depth as they flow downstream. Subglacial discharge is varied from 1–750 m3 s−1; large discharges result in plumes with positive temperature and salinity anomalies in the upper water column. For these flows, turbulent entrainment along the ice face acts as a mechanism to vertically transport heat and salt. These results suggest that plumes intruding into stratified outlet glacier fjords do not always retain the cold, fresh signature of meltwater but may appear as warm, salty anomalies. Fjord-scale circulation is sensitive to subglacial conduit geometry; multiple point source and line plumes result in stronger return flows of warm water toward the glacier. Classic plume theory provides a useful estimate of the plume’s outflow depth; however, more complex models are needed to resolve the fjord-scale circulation and melt rates at the ice face.

Numerical modeling of cohesive sediment transport in a tidal bay with current velocity assimilation

Tidal currents play an important role in sediment dynamics in coastal and estuarine regions. The goal of this study is to investigate the effects of current velocity assimilation (CVA) on sediment transport modeling in tide-dominated waters. A hydrodynamic and sediment transport model for Deep Bay, Hong Kong, was established based on a three-dimensional primitive equation Finite Volume Coastal Ocean Model. An additional numerical simulation was conducted with in situ current velocity measurements sequentially assimilated into the model using a three-dimensional optimal interpolation scheme. The performance of CVA shows improvements in the root-mean-square errors and average cosine correlations of simulated current velocity by at least 9.1 % and 10.3 %, respectively. Moreover, the root-mean-square error of the simulated sediment concentration from the model with CVA was decreased by at least 7 %. A reasonable enhancement in the vertical and spatial distributions of sediment concentrations was demonstrated from the simulation results from the model with CVA. It was found that the bottom shear stress changed significantly when the simulated velocities were corrected with CVA. The results suggest that CVA has the potential to improve sediment transport prediction because tidal currents dominate sediment dynamics in the studied areas.

Reconstructions of surface ocean conditions from the northeast Atlantic and Nordic seas during the last millennium

We undertake the first comprehensive effort to integrate North Atlantic marine climate records for the last millennium, highlighting some key components common within this system at a range of temporal and spatial scales. In such an approach, careful consideration needs to be given to the complexities inherent to the marine system. Composites therefore need to be hydrographically constrained and sensitive to both surface water mass variability and three-dimensional ocean dynamics. This study focuses on the northeast (NE) North Atlantic Ocean, particularly sites influenced by the North Atlantic Current. A composite plus regression approach is used to create an inter-regional NE North Atlantic reconstruction of sea surface temperature (SST) for the last 1000 years. We highlight the loss of spatial information associated with large-scale composite reconstructions of the marine environment. Regional reconstructions of SSTs off the Norwegian and Icelandic margins are presented, along with a larger-scale reconstruction spanning the NE North Atlantic. The latter indicates that the ‘Medieval Climate Anomaly’ warming was most pronounced before ad 1200, with a long-term cooling trend apparent after ad 1250. This trend persisted until the early 20th century, while in recent decades temperatures have been similar to those inferred for the ‘Medieval Climate Anomaly’. The reconstructions are consistent with other independent records of sea-surface and surface air temperatures from the region, indicating that they are adequately capturing the climate dynamics of the last millennium. Consequently, this method could potentially be used to develop large-scale reconstructions of SSTs for other hydrographically constrained regions.

A modeling study on saltwater intrusion to western four watercourses in the Pearl River estuary

Saltwater intrusion has been serious in the Pearl River estuary in recent years. For better understanding and analysis of the saltwater movement to the estuary, the three-dimensional Finite-Volume Coastal Ocean Model (FVCOM) is made to simulate the salinity intrusion to the four western watercourses in the Pearl River estuary under three semilunar conditions. With the measured and simulated Root Mean Square Error (RMSE) and the mean absolute percentage error of water level and salinity at multiple sites, the results show that the numerical water levels, salinity and flow velocities are in agreement with the measured data. It is acceptable and feasible to apply the FVCOM to simulate the salt water intrusion in the western four watercourses of the Pearl River. With the numerical data, the time and spatial movement patterns of saltwater intrusion along the Modao watercourse are analyzed. The salinity contour reaches its peak generally during 3∼5 days before the spring tide. The salinity stratification is more obvious in the period of ebb tide than that in the rising tide whether in the spring or neap tides. Salt fluxes reflect changes of salt into the estuary, and the change rules are close to the rules of salinity intrusion.

Toward a physically plausible upper bound of sea-level rise projections

Anthropogenic sea-level rise (SLR) causes considerable risks. Designing a sound SLR risk-management strategy requires careful consideration of decision-relevant uncertainties such as the reasonable upper bound of future SLR. The recent Intergovernmental Panel on Climate Change’s (IPCC) Fourth Assessment reported a likely upper SLR bound in the year 2100 near 0.6 m (meter). More recent studies considering semi-empirical modeling approaches and kinematic constraints on glacial melting suggest a reasonable 2100 SLR upper bound of approximately 2 m. These recent studies have broken important new ground, but they largely neglect uncertainties surrounding thermal expansion (thermosteric SLR) and/or observational constraints on ocean heat uptake. Here we quantify the effects of key parametric uncertainties and observational constraints on thermosteric SLR projections using an Earth system model with a dynamic three-dimensional ocean, which provides a mechanistic representation of deep ocean processes and heat uptake. Considering these effects nearly doubles the contribution of thermosteric SLR compared to previous estimates and increases the reasonable upper bound of 2100 SLR projections by 0.25 m. As an illustrative example of the effect of overconfidence, we show how neglecting thermosteric uncertainty in projections of the SLR upper bound can considerably bias risk analysis and hence the design of adaptation strategies. For conditions close to the Port of Los Angeles, the 0.25 m increase in the reasonable upper bound can result in a flooding-risk increase by roughly three orders of magnitude. Results provide evidence that relatively minor underestimation of the upper bound of projected SLR can lead to major downward biases of future flooding risks.

Modelling of Physical Processes and Assessment of Climate Change Impacts in Great Bear Lake

Polar lakes are highly sensitive to changes in the climate. As a contribution to the International Polar Year (IPY), the impact of climate warming on the thermal characteristics of Great Bear Lake is studied. During the summer of 2008, time series observations of meteorological, hydrological and physical limnological parameters in the lake were obtained to characterize the thermal regime. These observations and the forecasted forcing from a regional version of the Canadian operational Global Environmental Multiscale (GEM) model are used to simulate the ice-free hydrodynamics in Great Bear Lake using the high-resolution, three-dimensional hydrodynamic Princeton Ocean Model (POM). The model results of surface and sub-surface temperatures are first compared with satellite and in-lake measurements. The model simulates weak stratification and predicts mean cyclonic circulation reasonably well. The impact of climate warming caused by greenhouse gases is studied using Canadian Regional Climate Model (CRCM) scenarios for the base climate (1970–2000) and future warmer climate (2041–70). This scenario predicts an increase in surface temperature of over 2°C in the northeast corner, whereas in the rest of the lake the increases vary from 0.5° to 1°C. The results show that brief thermal stratification is possible in the deeper waters. The increase in water temperature caused by climate warming in the lake appears largely because of the positive increase in net longwave radiation and sensible heat flux, which result from changes in the temperature gradient between the air and the lake and slightly reduced wind speeds in the climate warming projections. RÉSUMÉ [Traduit par la rédaction] Les lacs des régions polaires sont extrêmement sensibles aux changements dans le climat. Notre contribution dans le cadre de l'Année polaire internationale (IPY) consiste à étudier les répercussions du réchauffement climatique sur les caractéristiques thermiques du Grand lac de l'Ours. Pendant l’été 2008, nous avons effectué des observations de séries chronologiques par rapport aux paramètres météorologiques, hydrologiques et limnologiques physiques dans le lac afin de caractériser le régime thermique. Ces observations conjuguées au forçage radiatif prévu établi à partir de la version régionale du modèle global environnemental multiéchelle canadien (GEM), utilisé pour produire les prévisions météorologiques opérationnelles, nous permettent de simuler l'hydrodynamique sans glace dans le Grand lac de l'Ours au moyen d'un modèle hydrodynamique tridimensionnel à haute définition, le modèle océanique de Princeton (POM). Nous comparons d'abord les températures subsurfaces et de surface obtenues au moyen du modèle, aux mesures satellitaires et du lac. Le modèle présente la simulation d'une stratification faible et il prédit raisonnablement bien la circulation cyclonique moyenne. Nous étudions les répercussions du réchauffement climatique causé par les gaz à effet de serre en nous servant des scénarios du MRCC pour le climat de référence (1970–2000) et le climat plus doux à l'avenir (2041–2070). Ce scénario prévoit une hausse de la température de surface, supérieure à 2°C dans la partie nord-est. En revanche, l'augmentation de la température dans le reste du lac varie de 0,5° à 1°C. Les résultats démontrent qu'une brève stratification thermique est possible en eau profonde. L'augmentation de la température de l'eau attribuable au réchauffement climatique dans le lac semble essentiellement due à l'augmentation du rayonnement de grandes longueurs d'onde et du flux de chaleur sensible nets, qui s'explique par les changements survenus dans le gradient de température entre l'air et le lac et par la légère diminution de la vélocité des vents dans les prévisions relatives au réchauffement climatique.

Realistic Rendering of Three-Dimensional Ocean Waves Based on Fractal

Realistic Rendering of Three-Dimensional Ocean Waves Based on Fractal

Three-Dimensional Ocean Wave Simulation Based on Directional Spectrum

Simulating real virtual ocean environment is necessary for the research of interaction simulation of underwater gravity aided inertial navigation system. One of the key techniques of realizing virtual ocean environment is modeling and simulating three-dimensional ocean waves. Numerical simulation of three-dimensional ocean waves in the case of different wind speeds is realized using MATLAB based on directional spectrum composed of Pierson-Moscowitz frequency spectrum and directional spreading function. Experiments show that the simulation speed is fast and the simulation results are vivid if suitable simulation frequency band, interval of wave frequency and interval of direction angle are selected. The simulation can provide some technological supports for interaction simulation of gravity aided navigation system for underwater vehicles.

Development and application of a marine ecosystem dynamic model

A nutrient-phytoplankton-zooplankton-detritus (NPZD) type of marine ecosystem model was developed in this study, and was further coupled to a three-dimensional primitive-equation ocean circulation model with a river discharge model and a solar radiation model to reproduce the dynamics of the low nutrition level in the Bohai Sea (BS). The simulation results were validated by observations and it was shown that the seasonal variation in the phytoplankton biomass could be characterized by the double-peak structure, corresponding to the spring and summer blooms, respectively. It was also found that both nitrogen and phosphate declined to the lowest level after the onset of the summer bloom, since the large amounts of nutrients were exhausted by phytoplankton for photosynthesis, and the concentrations of nutrients could resume in winter after a series of the biogeochemical-physical processes. By calculating the nitrogen/phosphorus (N/P) ratio, it is easy to see that the phytoplankton dynamics is nitrogen-limited as a whole in BS, though the phosphorus limitation may occur in the Yellow River (YR) Estuary where the input of riverine nitrogen is much more than that of phosphate.

Pathways of PFOA to the Arctic: variabilities and contributions of oceanic currents and atmospheric transport and chemistry sources

Abstract. Perfluorooctanoic acid (PFOA) and other perfluorinated compounds are industrial chemicals in use for decades which resist degradation in the environment and seem to accumulate in polar regions. Transport of PFOA was modeled using a spatially resolved global multicompartment model including fully coupled three-dimensional ocean and atmosphere general circulation models, and two-dimensional top soil, vegetation surfaces, and sea ice compartments. In addition to primary emissions, the formation of PFOA in the atmosphere from degradation of 8:2 fluorotelomer alcohol was included as a PFOA source. Oceanic transport, delivered 14.8±5.0 (8–23) t a−1 to the Arctic, strongly influenced by changes in water transport, which determined its interannual variability. This pathway constituted the dominant source of PFOA to the Arctic. Formation of PFOA in the atmosphere led to episodic transport events (timescale of days) into the Arctic with small spatial extent. Deposition in the polar region was found to be dominated by wet deposition over land, and shows maxima in boreal winter. The total atmospheric deposition of PFOA in the Arctic in the 1990s was ≈1 t a−1, much higher than previously estimated, and is dominated by primary emissions rather than secondary formation.

Numerical simulation of seawater intrusion from estuary into river using a coupled modeling system

One of the most important causes of the freshwater shortage in estuarine area is the increasing seawater intrusion into the river. To simulate seawater intrusion properly, two important factors should be considered. One is the bidirectional and time-dependent coupling effects between river discharges and tidal forces. The other is the three-dimensional and stratified structure of dynamic processes involved. However, these two factors have rarely been investigated simultaneously, or they were often simplified in previous researches, especially for the estuary connected with an upstream river network through multiple outlets such as the Pearl River Estuary (PRE). In order to consider these two factors, a numerical modeling system, which couples a one-dimensional river network model with a three-dimensional unstructured-grid Finite-Volume Coastal Ocean Model (FVCOM), has been developed and successfully applied to the simulation of seawater intrusion into rivers emptying into the PRE. By treating the river network with a one-dimensional model, computational efficiency has been improved. With coupling 1D and 3D models, the specification of upstream boundary conditions becomes more convenient. Simulated results are compared with field measured data. Good agreement indicates that the modeling system may correctly capture the physical processes of seawater intrusion into rivers.

The Role of Oceanic Heat Transport and Wind Stress Forcing in Abrupt Millennial-Scale Climate Transitions

Abstract The last glacial period was punctuated by rapid climate shifts, known as Dansgaard–Oeschger events, with strong imprint in the North Atlantic sector suggesting that they were linked with the Atlantic meridional overturning circulation. Here an idealized single-hemisphere three-dimensional ocean–atmosphere–sea ice coupled model is used to explore the possible origin of the instability driving these abrupt events and to provide a plausible explanation for the relative stability of the Holocene. Focusing on the physics of noise-free millennial oscillations under steady external (solar) forcing, it was shown that cold climates become unstable, that is, exhibit abrupt millennial-scale transitions, for significantly lower freshwater fluxes than warm climates, in agreement with previous studies making use of zonally averaged coupled models. This fundamental difference is a direct consequence of the weaker stratification of the glacial ocean, mainly caused by upper-ocean cooling. Using a two-hemisphere configuration of a coupled climate model of intermediate complexity, it is shown that this result is robust to the added presence of a bottom water mass of southern origin. The analysis reveals that under particular conditions, a pronounced interdecadal variability develops during warm interstadials. While the nature of the instability driving the millennial oscillations is identical to that found in ocean models under mixed boundary conditions, these interstadial–interdecadal oscillations share the same characteristics as those previously found in ocean models forced by fixed surface fluxes. The wind stress forcing is shown to profoundly affect both the properties and bifurcation structure of thermohaline millennial oscillations across a wide range of variation of freshwater forcing. In particular, it is shown that the wind stress forcing favors the maintenance of thermally direct meridional overturning circulations during the cold stadial phases of Dansgaard–Oeschger cycles.

Nonlinear Crest Height Distribution in Three-Dimensional Ocean Waves

The interest and studies on nonlinear waves are increased recently for their importance in the interaction with floating and fixed bodies. It is also well-known that nonlinearities influence wave crest and wave trough distributions, both deviating from the Rayleigh law. In this paper, a theoretical crest distribution is obtained, taking into account the extension of Boccotti’s quasideterminism theory (1982, “On Ocean Waves With High Crests,” Meccanica, 17, pp. 16–19), up to the second order for the case of three-dimensional waves in finite water depth. To this purpose, the Fedele and Arena (2005, “Weakly Nonlinear Statistics of High Random Waves,” Phys. Fluids, 17(026601), pp. 1–10) distribution is generalized to three-dimensional waves on an arbitrary water depth. The comparison with Forristall’s second order model (2000, “Wave Crest Distributions: Observations and Second-Order Theory,” J. Phys. Oceanogr., 30(8), pp. 1931–1943) shows the theoretical confirmation of his conclusion: The crest distribution in deep water for long-crested and short-crested waves are very close to each other; in shallow water the crest heights in three-dimensional waves are greater than values given by the long-crested model.

Ensemble perturbation smoother for optimizing tidal boundary conditions by assimilation of High-Frequency radar surface currents – application to the German Bight

Abstract. High-Frequency (HF) radars measure the ocean surface currents at various spatial and temporal scales. These include tidal currents, wind-driven circulation, density-driven circulation and Stokes drift. Sequential assimilation methods updating the model state have been proven successful to correct the density-driven currents by assimilation of observations such as sea surface height, sea surface temperature and in-situ profiles. However, the situation is different for tides in coastal models since these are not generated within the domain, but are rather propagated inside the domain through the boundary conditions. For improving the modeled tidal variability it is therefore not sufficient to update the model state via data assimilation without updating the boundary conditions. The optimization of boundary conditions to match observations inside the domain is traditionally achieved through variational assimilation methods. In this work we present an ensemble smoother to improve the tidal boundary values so that the model represents more closely the observed currents. To create an ensemble of dynamically realistic boundary conditions, a cost function is formulated which is directly related to the probability of each boundary condition perturbation. This cost function ensures that the boundary condition perturbations are spatially smooth and that the structure of the perturbations satisfies approximately the harmonic linearized shallow water equations. Based on those perturbations an ensemble simulation is carried out using the full three-dimensional General Estuarine Ocean Model (GETM). Optimized boundary values are obtained by assimilating all observations using the covariances of the ensemble simulation.

Pliocene three-dimensional global ocean temperature reconstruction

Abstract. The thermal structure of the mid-Piacenzian ocean is obtained by combining the Pliocene Research, Interpretation and Synoptic Mapping Project (PRISM3) multiproxy sea-surface temperature (SST) reconstruction with bottom water temperature estimates from 27 locations produced using Mg/Ca paleothermometry based upon the ostracod genus Krithe. Deep water temperature estimates are skewed toward the Atlantic Basin (63% of the locations) and represent depths from 1000 m to 4500 m. This reconstruction, meant to serve as a validation data set as well as an initialization for coupled numerical climate models, assumes a Pliocene water mass framework similar to that which exists today, with several important modifications. The area of formation of present day North Atlantic Deep Water (NADW) was expanded and extended further north toward the Arctic Ocean during the mid-Piacenzian relative to today. This, combined with a deeper Greenland-Scotland Ridge, allowed a greater volume of warmer NADW to enter the Atlantic Ocean. In the Southern Ocean, the Polar Front Zone was expanded relative to present day, but shifted closer to the Antarctic continent. This, combined with at least seasonal reduction in sea ice extent, resulted in decreased Antarctic Bottom Water (AABW) production (relative to present day) as well as possible changes in the depth of intermediate waters. The reconstructed mid-Piacenzian three-dimensional ocean was warmer overall than today, and the hypothesized aerial extent of water masses appears to fit the limited stable isotopic data available for this time period.

Mechanisms of interdecadal climate variability and the role of ocean–atmosphere coupling

Climate variability and mid-latitude mechanisms of ocean–atmosphere interactions are investigated with coupled and uncoupled integrations of a three-dimensional ocean–atmosphere–land–ice climate model of intermediate complexity. We focus on the decadal and interdecadal variability of the system and give a statistical and dynamical description of its oceanic and atmospheric signatures. In our coupled control integration, an oceanic oscillation of a period of around 20 years is found to be associated with variability of the meridional overturning circulation and is manifested by surface anomalies of temperature and salinity. On such timescales the oceanic oscillation is able to imprint itself on the atmosphere, which then covaries with the ocean at the oscillation period. The essentially slaved atmospheric pattern helps maintain the oceanic oscillation by providing large-scale anomalous heat fluxes, so catalyzing the oscillation. That is to say, because the atmosphere covaries with the ocean the damping felt by the ocean is less than what would be felt with a fixed atmosphere, so broadening the parameter regime over which such variability occurs. In addition to the presence of an atmosphere, the period and amplitude of the oscillation are found to be influenced both by the oceanic vertical diffusivity κ v , by geometrical factors, and by the presence of stochastic heat fluxes. In general, oscillations occur most readily for large values of κ v , when the mean state of the ocean is characterized by a strong meridional overturning circulation. If κ v is sufficiently strong, the ocean will oscillate even in the absence of a dynamical atmosphere. However, for more realistic values of κ v , the presence of an interacting atmosphere is required for significant oscillations. If the ocean is forced by imposed stochastic heat fluxes, instead of a fully interacting atmosphere, then decadal-scale oscillations can be produced suggestive of a damped oscillator. However, the parameter range over which oscillations occur is smaller than when the ocean is coupled to full atmosphere. More generically, the ability of comprehensive coupled ocean–atmosphere models to produce multi-decadal variability, realistic or otherwise, will depend on the oceanic mean state, and so on the diapycnal diffusivity of the modelled ocean, as well as on the ability of the atmosphere to reduce the damping felt by the ocean and so on the atmosphere’s ability to respond to persistent sea-surface temperature anomalies.

Physical and biological responses to Hurricane Katrina (2005) in a 1/25° nested Gulf of Mexico HYCOM

Recent studies indicated sea surface temperature (SST) cooling of 6–7 °C and a phytoplankton bloom of 3 mg chlorophyll-a m − 3 during the passage of Hurricane Katrina (23–30 August 2005) in a region from 23.5° to 25.5°N and 85° to 83°W in the Gulf of Mexico (GoM). Employing a 20-layer, 1/25° horizontal resolution nested GoM HYbrid Coordinate Ocean Model (HYCOM), the evolving three-dimensional ocean response to Hurricane Katrina in the GoM was examined. During the passage of Hurricane Katrina, analysis of model surface and subsurface dynamics in this region revealed strong upwelling/downwelling of 1.5–2 × 10 − 4 m s − 1 , wind-driven currents dominating the surface circulation, and near-inertial oscillations following Hurricane Katrina. Associated with the storm, the 26 °C isotherm was raised by 28 m, generating SST cooling of 3–4 °C and salinity freshening of 0.1–0.2 in less than 24 h. Comparison of model-simulated SSTs with in situ buoy data and satellite observations revealed that model SSTs were cooler by 1–2 °C and had a greater spatial extent of cooling. Analysis of heat budget terms in the mixed layer (20 m) indicated that surface heat flux accounted for pre-storm temperature changes, and wind-driven mixing (− 3375 W m − 2 ) dominated net upper-ocean cooling (− 2464 W m − 2 ) during Hurricane Katrina. At 50 m depth, temperature changes were largely due to vertical advection associated with upwelling and downwelling processes. A temperature–nitrate relationship was derived to illustrate the potential contribution that nitrate influx had upon the satellite-observed phytoplankton bloom associated with Hurricane Katrina. Comparison of calculated nitrate agreed reasonably well with in situ nitrate profiles in the interest region. Nitrate concentrations of 3.7 μM were entrained from 30 m depth during hurricane passage. An approximate nitrate to chlorophyll-a ratio provided a chlorophyll-a value of 3 mg m − 3 , which was consistent with that derived from satellite. Thus, the elevated chlorophyll-a concentration following the passage of Katrina was greatly influenced by nitrate entrainment into the surface layer through vertical mixing and Ekman divergence.

Numerical Simulation of Bay of Bengal Circulation Features from Ocean General Circulation Model

The Bay of Bengal circulation features have been analyzed using a three-dimensional Ocean General Circulation Model (OGCM). The northward propagation of eastern boundary coastal Kelvin wave and its movement throughout the entire Bay is evident from the study. The trapping of Kelvin waves in the central Bay for many months causes warming of the central basin, which acts as a potential breeding ground of cyclones. The seasonal variations of circulation, temperature, and salinity have been reproduced by the model. These variations compare favorably with observations. The existence of a salt finger towards north and its eastward movement are two important results of the study. The cyclonic gyres in the Bay of Bengal during different months agree reasonably well with the SeaWiFS chlorophyll observations and indicate the upwelling zones over the basin. The presence of a subsurface Bay-of-Bengal dipole in summer monsoon months is another important result of the study.

Contributions of Long-Term Research and Time-Series Observations to Marine Ecology and Biogeochemistry

Time-series observations form a critical element of oceanography. New interdisciplinary efforts launched in the past two decades complement the few earlier, longer-running time series to build a better, though still poorly resolved, picture of lower-frequency ocean variability, the climate processes that drive variability, and the implications for food web dynamics, carbon storage, and climate feedbacks. Time series also enlarge our understanding of ecological processes and are integral for improving models of physical-biogeochemical-ecological ocean dynamics. The major time-series observatories go well beyond simple monitoring of core ocean properties, although that important activity forms the critical center of all time-series efforts. Modern ocean time series have major process and experimental components, entrain ancillary programs, and have integrated modeling programs for deriving a better understanding of the observations and the changing, three-dimensional ocean in which the observatories are embedded.

A Hydrodynamic Model of the Circulation within the South Arm of the Great Salt Lake

The effects of surface heat flux and wind forcing on the temporal and spatial variations in flow patterns within the south arm of the Great Salt Lake are investigated numerically using the three-dimensional Estuary, Lake and Coastal Ocean Model (ELCOM) code. Results indicate that wind forcing over an isothermal lake results in nearly steady near-surface flow patterns directed to the right of the wind direction. Forcing through surface heat flux without wind stresses results in the formation of multiple, unsteady gyres. The sense of rotation of these gyres is generally cyclonic during the summer months. These cyclonic gyres are not observed when forcing due to both wind and surface heat fluxes are enforced simultaneously, even with the inclusion of atmospheric instability effects.