OS35I-01
Moored Observations of Oceanographic Variability in the Columbia River Plume and Over the Oregon Shelf During the Summer of 2005
As part of the RISE (NSF CoOP) program, 3 moorings were deployed from May to October 2005 in areas influenced by the Columbia River plume. The mooring sites were off Cape Meares, OR, off the mouth of the Columbia River, and off Grays Harbor, WA. The moorings off Cape Meares, OR and the Columbia River mouth were successfully recovered. At the Grays Harbor, WA mooring, subsurface instruments were lost due to mooring failure on recovery. The moored instruments were concentrated near the surface in order to sample the plume, which can be trapped very closely (5 m or less) to the surface. Salinity, fluorescence, and light transmission were measured 1, 5, and 20 m beneath the surface. Temperature data was collected about every 5 m throughout the upper water column. Each mooring included 2 ADCPs, a downward looking 300 kHz unit in the surface buoy, and an upward looking 1200 kHz ADCP moored 15 m beneath the surface. The two southern moorings also included buoy measurements of wind velocity, photosynthetically-available radiation PAR and downward longwave radiation. The onset of upwelling in the spring and summer of 2005, has been reported to be unusually late with consequences for phytoplankton, zooplankton, and higher trophic levels. Preliminary results from our moored data indicate low levels of near-surface fluorescence from May 22 (when the moorings were deployed) until about June 25. After this point, fluorescence levels increased dramatically at the northern and southern moorings. Fluorescence also increased at this time at the Columbia River mooring, but the increase was more gradual. These data will be discussed in light of simultaneous wind, velocity, temperature, and salinity observations. 2005 events will also be compared to similar 2004 observations.
OS35I-02
Plume Within a Plume: A Conceptual Model of the Strongly Tidal Columbia River Plume
The Columbia River plume is typical of large-scale, high discharge, mid-latitude plumes. In the absence of strong upwelling winds, freshwater from the river is expected to execute a rightward turn and form an anticyclonic bulge before moving north along the Washington coast. In addition to the above dynamics, however, the river outflow is subject to strong tidal forcing, which significantly modifies the structure of the plume in the region near the mouth. Observations based on velocity and salinity data acquired during the June 2005 RISE (River Influences on Shelf Ecosystems) cruise indicate that the plume consists of two distinct water masses; a new plume and a residual plume. The new plume is formed by water that has been on the shelf for less than a day, is relatively fresh and is characterized by rapid and energetic mixing. In addition, it is observed to turn anticyclonically and has a linear velocity structure similar to that observed in laboratory plume studies. The residual plume is a layer of intermediate salinity fluid that surrounds the new plume. It is relatively homogeneous and characterized by much less intense mixing. The new plume is initially separated from the residual plume by a strong offshore front. Previous studies have shown that the front emits a series of solitons as the ebb relaxes. This is expected to be an important mechanism for communication between the two plumes, whereby freshwater is transported and mixed into the residual water mass. Corresponding measurements indicate that the two plumes are also marked by significant differences in chemical properties.
OS35I-03
Tidally-Forced Turbulence in the Near-Field Columbia River Plume
A pulsating river plume forms from the tidally-forced flow at the mouth of the Columbia River. During an eight day period in August, 2005, 250 repeat transects were made along and across the axis of the plume where turbulence, density and acoustics were measured. These rapid transects capture the M2 tidal modulation of turbulence, velocity and salinity in the momentum-dominated near-field region and are used to explore the advective and turbulent transports of mass, salt and momentum.
OS35I-04
Iron Speciation in the Columbia River Plume Over a Tidal Cycle: Implications for the Importance of Iron-Binding Ligands in a High-Iron Plume
Vertical profiles of dissolved iron and associated chemical speciation were conducted near the mouth of the Columbia River estuary during a flood and ebb tide in July 2004. To characterize both the shallow plume and subsurface waters, all vertical profiles comprised 4 depths within the upper 20 m. Speciation analyses were performed using a competitive ligand exchange- adsorptive cathodic stripping voltammetry (CLE-ACSV) method incorporating salicylaldoxime as the added ligand. A single strong L1 ligand class was identified in the low-salinity, high-iron plume waters. Speciation analyses of subsurface waters were consistent with analyses at a station outside the plume influence, identifying 2 ligand classes: a strong L1 and a weak L2 ligand class. Log conditional stability constants for these ligand classes ranged from 12.7 to 11. Dissolved iron saturated ligands in the plume waters during the ebb tide, while a slight excess of these ligands was observed during the flood tide. This suggests that the Columbia River is not serving as a large source for these ligands; the concentration of which seems to limit the potential dissolved iron concentrations in the plume waters. Thus, the concentrations of these strong iron-binding ligands appear to play an important role in solubilizing particulate iron within the Columbia River plume.
OS35I-05
Benthic Sources of Iron to the Columbia River Plume
The Columbia River provides a source of iron to the coastal waters off Oregon and Washington. However, the supply of iron is highly variable depending on both the river flow and the tidal state. In addition to the river source and of equal importance, is the benthic supply of iron from sediments outside the river mouth which can be entrained into the Columbia River plume. Iron (II) and iron (III) concentrations were determined inside and outside the estuary over three tidal cycles. Iron (II) concentrations revealed the importance of a benthic supply of iron to the Columbia River plume both from sediments within the estuary and just outside the estuary. As the tide changes from ebb to flood bottom sediments within the estuary were resuspeneded and an increased particle load was observed throughout the water column. Iron concentrations increased from 4 to 12 nM in surface waters with iron (II) contributing to 70% of total dissolved iron during this high particle load. Outside the estuary marked differences were observed between the neap and spring tides. During the neap tide total dissolved iron concentrations in surface waters ranged from 1 to 6 nM with highest concentrations observed at depth (8-17 nM) as the tide changed from ebb to flood. Surface total dissolved iron concentrations during the spring tide ranged from 6 to 23 nM and while at depth concentrations up to 750 nM were observed. Iron (II) accounted for 60-80% of the total dissolved iron during the spring tide and only 10-20% during the less energetic neap tides. Surface iron concentrations within the plume were higher than observed within the Columbia River itself thus indicating an additional source of iron. Reducing sediments, entrained to surface waters, provided the additional source of iron observed during the spring tide. Surface transects across the mouth of the estuary also showed increased iron (II) concentrations and total dissolved iron during the spring tide, as compared to the neap tide, indicating that this iron can be transported offshore in the plume. This additional benthic source of iron along with the supply of macronutrients from the river and/or upwelling provides ideal conditions for phytoplankton growth.
OS35I-06
Riverine Input of Macronutrients, Iron, and Organic Matter to the Coastal Ocean off Oregon, USA, During the Winter
Little is known about wintertime biogeochemical cycles or ecosystem function in eastern boundary current systems. Three cross-shelf transects were conducted off northern Oregon in early February 2003, within a few days of one another and coincident with a flood event, but under different wind and current conditions. During downwelling favorable winds, low salinity ($\sim$ 25 psu) river-influenced water was located in a ca. 5 km wide band near the coast. Associated with the low salinity water were significantly elevated macronutrient, dissolvable iron (dFe), and total organic carbon (TOC) concentrations. As winds relaxed and switched to upwelling favorable conditions, the low salinity water spread out at the surface extending to the shelf break and carried with it elevated levels of nutrients and organic carbon. Riverine input of nitrate and silicate increased those pools in the upper 10 m of the coastal ocean by 20-50% and 80-190%, respectively. Riverine dFe flux to the coastal ocean was also high, and given that downwelling conditions during winter tend to minimize cross-shelf transport, dFe supplied by the rivers may remain over the shelf and then become available to spring and summer phytoplankton. Finally, in comparison to the Pacific Northwest's largest river, the Columbia, the smaller coastal rivers can increase the supply of terrestrial TOC to the coastal ocean by 15-20%. These results show that small coastal rivers, key features during the wintertime but rarely studied in eastern boundary current systems, can significantly alter coastal biogeochemical cycles and influence ecosystem structure.
OS35I-07
Characterizing the Optical Signature of the Columbia River Plume
The unique optical signature of a river plume can distinguish it from surrounding coastal waters. The quality and quantity of light attenuation by sediment particles and chromophoric dissolved organic matter (CDOM) is variable by river system, annual precipitation, and season. CDOM absorbs light strongly in the high UV and visible range (300-450 nm). Some river systems in the U.S., e.g. the Mississippi and Hudson River plumes, have well characterized optical signatures; however no comparable data exist for the Columbia River system. The Columbia River drains three-quarters of the northwestern U.S and delivers nutrients, dissolved organic matter, and particles to the Washington and Oregon shelf and beyond. The plume is a dynamic feature with its northward or southward direction of flow strongly influenced by wind stress and the Coriolis effect. Presently, physical models can predict the direction of flow of the Columbia River Plume; our goals are two-fold. We wish to truth these models by using a signature that is specific to the Columbia River and to assess the short-term variability in plume optical parameters that may reflect fine-scale processes such as entrainment or biological transformations. With these goals in mind, we measured the optical signature (as CDOM light absorption) of the Columbia River Plume on the CoOP-River Influences on Shelf Ecosystems cruises in July 2004, June 2005, and August 2005. Using data from the three cruises spanning different months, years, and upwelling conditions, we show that light absorption by CDOM is well correlated with salinity in the Columbia River Plume, and therefore represents a reasonably robust tracer for the plume. CDOM light absorption will be useful in conjunction with satellite data to more accurately define the extent of the plume influence, furthering our understanding of its role in the coastal ecosystem.
OS35I-08
Why is the Columbia River Plume More Productive Than its Surroundings?
Spatial maps of fluorescence, photosynthetic yield, and primary productivity indicate that the Columbia River is more productive than the surroundings, both near-field and far-field. The Columbia River is an important source of silicic acid and minerals to the northeast Pacific, with nitrate as the proximal limiting nutrient for phytoplankton growth. Although nitrate concentrations can be high near the river mouth, levels in the far-field (aged) plume were low (< 1 $\mu$M) in August 2005. Yet, the Columbia River plume showed enhanced productivity compared to the surroundings. In an effort to explain the River Effect, we considered two possibilities: (1) the plume carries additional nitrogen as nitrate and/or reduced species (ammonium or dissolved organic nitrogen); or, (2) the enhancement of primary production arises from plume characteristics unrelated to nitrogen. Our plume survey showed that nitrate concentrations near the river mouth were high both within the plume and in the near-shore surroundings, but that ammonium levels were higher within the near-field plume (but not the aged plume). We conducted experiments to test whether the addition of filtered plume water would yield a positive effect on phytoplankton growth within the aged plume or in non-plume waters. In all cases, chl a, primary production, and nutrient drawdown were enhanced by the addition of nitrate, with no statistical difference between nitrate amended treatments with or without a supplement of filtered plume water. The maximum biomass increase in the control containers was largest in waters collected from the river mouth (48 mg m-3) compared to a 2-day old plume (3 mg m-3) or to waters collected off the coast of Washington (17 mg m-3) or Oregon (10 mg m-3). The addition of nitrate to near-field plume waters did not significantly increase the maximum biomass attained, but it sustained higher chlorophyll concentrations for a longer period of time relative to controls. We conclude that in waters of the near-field plume, nitrogen supply is sufficient to fuel high growth of phytoplankton; however, in waters downstream, some other factor(s) such as differential grazing rates or higher rates of nitrogen regeneration must play an important role in enhancing primary production.
OS35I-09
Modeling nutrient cycling and primary production dynamics in and out of the Columbia River Plume
A coupled circulation-and-ecosystem model, developed as part of the RISE (River Influences on Shelf Ecosystems) program, is used to compare the dynamics of primary production and nitrogen cycling in the Columbia River plume with those in the adjacent coastal waters. The circulation model is an implementation of ROMS (Regional Ocean Modeling System); the domain spans 100 km along the Washington-Oregon coast, and reaches from the Columbia estuary past the shelf break. A constant riverflow and southward wind stress were imposed on seasonal temperature and salinity climatology to produce a steady, southward-tending, "summer" plume, as well as coastal upwelling north and south of it. The ecosystem model adds a budget for nitrate, ammonium, phytoplankton, zooplankton, and detritus to each grid cell. The phytoplankton compartment is divided into two stocks, one of which is given a constant river source and the other of which is seeded throughout the ocean domain at a low level (0.001 $\mu$mol N $m^{-3}$), to allow us to identify the source of the phytoplankton biomass found in the modeled plume. Ecosystem model predictions are validated using observations from summer 2004 and 2005 at stations both in and out of the plume and at the estuary mouth: these data include phytoplankton standing stock, nutrient distributions, nutrient uptake rates, and grazing rates from dilution experiments. In the model, as frequently seen in observations, surface chlorophyll concentration is higher in the Columbia plume than in adjacent surface waters, although phytoplankton specific growth rates are comparable and cannot explain this difference. Furthermore, 50-80% of the phytoplankton biomass found in the modeled plume is oceanic, not riverine, in origin, and, as also suggested by field observation, most of this oceanic fraction is entrained into the plume within a few tidal cycles and a few km of the river mouth.
OS35I-10
Tidal Effects on Recycled Nitrogen Supply to the Columbia River Mouth
The Columbia River is an important source of nutrients and minerals to the coastal waters off Oregon and Washington. Relative to other large rivers such as the Mississippi, the Columbia River delivers comparatively little nitrate. During periods of strong upwelling, enhanced nutrient delivery from below the mixed layer supports high phytoplankton growth and standing stocks. During periods of relaxed upwelling, however, large diatoms persist and algal standing stocks remain high, despite low ambient nitrate concentrations. We investigated the potential strength of regeneration within the river system by measuring ammonium and urea concentrations within the estuary inside of the river mouth, and at the river mouth, over a tidal cycle. Our results show that waters flowing from the estuary during ebb flow are higher in ammonium and urea, but lower in chlorophyll, compared to waters flowing toward the estuary on the flood tide. Conversely, during flood tides chlorophyll concentrations were high and ammonium and urea concentrations were low, presumably due to uptake by phytoplankton. Superimposed on this pattern is a diurnal cycle, with ammonium and urea concentrations reaching a minimum during the day coincident with maximum daily rates of photosynthesis. Approximately 1.5 times more regenerated nitrogen was measured in waters collected during ebb tides compared to flood tides. The influence of tidal dynamics on fluxes of regenerated nitrogen into and out of the estuary may be direct and/or indirect; the enhanced supply of recycled nitrogen products at ebb flow may arise from stronger recycling rates within the estuary (direct) accompanied by a low degree of utilization due to significant advective losses of phytoplankton (indirect) induced by tidal flushing. Thus, patterns of recycled nitrogen are influenced not only by the flood-ebb cycle, but also by algal growth dynamics and the magnitude of advective losses from the estuary. Our results suggest that the Columbia River estuary may act as a hotspot of nutrient recycling that allows near-shore phytoplankton to satisfy nutritional requirements by utilizing nutrients regenerated within the estuary when upwelling strength is weak. Such processes may be important in explaining anomalously high production rates during periods when apparent nitrogen (as nitrate) concentrations are low.
http://www.ocean.washington.edu/rise/index.htm
OS35I-11
Vertical Migration of the Mixotrophic Ciliate {\it Myrionecta rubra} in the Columbia River Mouth: a FlowCAM Study
The phototrophic ciliate {\it Myrionecta rubra} ({\it Mesodinium rubrum}) is common in estuarine waters around the world, capable of forming dense blooms and achieving high rates of primary productivity. Swimming speeds of {\it M. rubra} can be quite high for a protist, allowing it to vertically migrate in order to utilize nutrients or avoid tidal flushing. Vertical distribution of {\it M. rubra} was followed over 18 hours of the tidal cycle on both spring and neap tides at the Columbia River mouth and in a 12 hour time series just inside the Columbia River estuary. Hourly samples were taken from three to five depths and analyzed with a FlowCAM, an instrument which can image and count live plankton samples in real time. Vertical migration of {\it M. rubra} is evident in the FlowCAM data and appears to be timed to the tidal cycle. Cells concentrate near or at the surface on flood tide and disperse into deeper waters on the ebb tide. The FlowCAM is well suited to this type of study in which one distinctive organism dominates the planktonic assemblage. It also makes it possible to sample with the frequency needed to resolve the temporal and spatial distributions of a vertically migrating organism in a dynamic system.
OS35I-12
Cross-shelf Variability in Hydrography, Zooplankton and Juvenile Chinook Salmon Diets in Relation to the Columbia River Plume
The Columbia River plume is a dynamic coastal feature influenced by variable river flow, wind forcing, and tidal forcing. Enhanced production and accumulation of prey within the plume may increase availability of food during salmon early ocean survival. Physical and biological sampling was conducted along a cross-shelf transect through the plume during May 1999. Based on multivariate analyses (PCA and Cluster Analyses) on 11 variables, the stations at 15, 20, and 25 nautical miles (nm) from shore were distinct from those inshore (4-10 nm) and offshore (30-50 nm) as were considered the core of the plume. Five variables (temperature at 3 m, salinity at 3 and 10 m, silicate and nitrate) accounted for 96% of this difference. Subsurface plankton tows (meter net) revealed differences in plankton composition at stations 10-20 nm. Surface neuston tows showed a distinction between inshore <20 nm) and offshore stations. Overall plankton biomass was substantially higher at the outer stations. Stomach contents of juvenile chinook salmon collected in and out the plume were compared with meter net zooplankton and neuston samples from the same stations Substantial inshore-offshore variability in diet composition and overall stomach fullness was observed, with a breakpoint occurring beyond 20 nm. Comparisons of matched similarity matrices showed that the stomach composition was more similar to the neuston (Spearman rho = 0.572) than to the meter net composition (rho= 0.331). Fishes, decapod larvae, and hyperiid amphipods occurred in greater proportion and copepods and euphausiids in lesser proportions in the stomachs compared to the plankton.
OS35I-13
Plankton Dynamics of the Lower Columbia River Estuary
The Columbia River is one of North America's most ecologically and economically important rivers, yet little is known about the phytoplankton and zooplankton dynamics in its lower reaches. In January 2005 we initiated a multi-year field study to investigate several aspects of the plankton dynamics in the lower Columbia River estuary, with particular emphasis on non-indigenous species and freshwater flow effects. Our sampling design consisted of three basic types of surveys: i) monthly sampling at 5 locations ranging from 180 km upstream to the mouth of the estuary, ii) four broad-scale surveys near the mouth of the lower estuary (two each in June and August, corresponding to high and low river flow periods, respectively), and iii) sampling every 3 hours over a full tidal cycle in August, 2005. We sampled hydrography, chlorophyll, nanoplankton, microplankton, and mesozooplankton at each station. The dominant microplankton groups observed were diatoms ({\it Asterionella formosa}, {\it Fragillaria crotonensis}, {\it Synedra} spp., {\it Aulacoseira grannulata}), dinoflagellates ({\it Gonyaulax} sp., {\it Protoperidium} sp.) and aloricate ciliates ({\it Myrionecta rubra}., {\it Strombidium} spp.). Dominant mesozooplankton taxa included the copepods {\it Eurytemora affinis}, {\it Coullana canadensis}, and {\it Acartia tonsa}. Two species of non-native copepods were also observed: {\it Pseudodiaptomus forbesi} and {\it Sinocalanus doerri}. Preliminary results indicate a strong seasonal cycle, with spring blooms of diatoms and copepods, followed by compositional shifts in summer toward flagellates, ciliates and other copepods. With respect to freshwater flow, both biomass and abundance of microplankton were higher in June (high flow) than in August (low flow). The tidal cycle sampling showed large variation in abundance and composition of plankton with tidal stage, especially in diatoms, ciliates and copepods. These results and their implications will be discussed in the context of up-stream conditions during the CoOP RISE field experiments that occurred in June and August 2005 on the continental shelf off the mouth of the Columbia River.
OS35I-14
Hydrographic and Chlorophyll Fluorescence Patterns of the Columbia River Estuary
Spring and neap tide hydrographic conditions in the Columbia River estuary (CRE) are compared for vernal and autumnal periods in 2004 and 2005. Data were collected by ship-borne CTD and ADCP instruments, with casts made along a 30 km transect along the south channel of the CRE. Vertical stratification of the water column was strongly modulated over the spring-neap tidal period. During spring tides, a classic salt wedge developed, while during neap tides, the water column was intensely stratified with salinity gradients in the halocline exceeding 5 psu/m. Salinity intrusion was enhanced during neap periods, and exceeded the most upriver station of the 30 km transect line. Patterns of chlorophyll distribution estimated from fluorometry varied over both synodic and seasonal time frames. During the spring phytoplankton bloom, large concentrations of chlorophyll (maximum > 40 mg/m3) were transported seaward in river water. These freshwater phytoplankters were apparently destroyed by lysis in the CRE during the intense mixing of spring-tide conditions, and appeared to contribute to turbidity maxima. In contrast, during highly stratified neap-tide conditions, phytoplankton were transported to the coastal ocean in undiluted surface flows. Seawater intrusion during the spring season was relatively devoid of chlorophyll. In contrast, during autumn upwelled ocean water (> 31 psu) was advected to the lower estuary. This water was often enhanced in chlorophyll relative to river concentrations, and was likely derived from upwelling dynamics in the coastal ocean. Additionally, conditions in the lower estuary in autumn promoted the development of dense accumulations of the photosynthetic ciliate Mesodinium rubum, which exhibited distinct vertical and horizontal aggregations. These hydrographic conditions have ramifications to migrating juvenile salmon.
OS35I-15
Analyzing Dynamic Characteristics of Internal Solitons Generated by the Columbia River Plume Front with SAR Images
Internal solitons generated at the Columbia River plume front during ebb tides were revealed in Synthetic Aperture Radar (SAR) images. Scale analyses indicate that these internal waves belong to the finite-depth category. A theoretical model for the finite-depth category was developed relating radar backscatter cross-section to dynamic parameters of internal solitons. Using the theoretical model and in-situ density data collected by the River Influences on Shelf Ecosystem (RISE) project cruise in July 2004, we obtained the half width, amplitude, phase speed, and wave energy per crest length of the internal solitons at four sections. For the leading soliton in one typical section, the half width, amplitude, phase speed and energy are derived as 109.8 m, 5.7 m, 0.56 m/s and 5.9\times10$^{4}$ J/m, respectively. As a result of the internal soliton, the Richardson number dramatically decreased from the background value, which increased the possibility of the turbulent mixing. An analytic model was developed for the internal soliton-induced horizontal mass exchange in the upper layer between the plume water and the coastal water. The horizontal transport per crest length in the upper layer reached 673.6 m3/m for the leading soliton in the typical section.
OS35I-16
Aircraft Observations of Sea Surface Salinity and Columbia River Plume Response to Along-shelf Winds
The NRL Salinity Temperature and Roughness Remote Scanner (STARRS) was flown over the Columbia River plume and adjacent shelf waters during Spring, 2004 to study plume evolution under prevailing wind and tidal conditions. STARRS is an advanced airborne radiometer system consisting of microwave L and C-band, and infrared radiometers for measuring salinity, roughness and sea surface temperature, respectively. Using STARRS, nine sea surface salinity remote sensing surveys were conducted off the Oregon coast at intervals of 1-2 days during 17-28th May, 2004. Coincident hydrographic and meteorological data were obtained, as part of the experiment, from ships and from CORIE environmental observation and forecasting system oceanographic moorings (http://www.ccalmr.ogi.edu/CORIE/). NOAA data buoys provided additional wind and temperature data, while an HF coastal radar system operated by Kosro et al., OSU, yielded daily surface current maps. During the 12-day survey period, the CORIE numerical hydrodynamic model provided near real-time forecasts of plume location, to aid flight planning, and STARRS data were analyzed and returned after each flight to CORIE headquarters, for comparison with recent model predictions. The combined data set represents a unique time series of spatial maps that combine remotely sensed, in situ, and modelled sea surface salinity fields. The STARRS sea surface salinity maps were used to track the plume response to fluctuating along-shelf winds, as they switched through a complete cycle of upwelling and downwelling favorable conditions. The results show the plume responded rapidly to daily changes in wind forcing, occasionally shedding eddies as it switched between up and down-coast orientations; in partial agreement with model predictions. The data were used to classify the observed Columbia River plume as surface-advected, and its predominantly bulging appearance suggested prevailing super-critical and weakly-diffusive dynamics.
OS35I-17
Quality-controlled Numerical Investigation of a Large-river Estuary and Plume: a Tale of two Models
Retrospective and predictive simulations of 3D estuarine and plume circulation are integral to CORIE, a multi-purpose cross-scale coastal-margin observatory for the Columbia River. In 2004 and 2005, daily forecasts of circulation were generated near real-time in support of oceanographic and fisheries cruises [1]. These cruises were conducted in the context of extensive surveys involving airborne remote sensing, HF coastal radar, satellite imagery, and fixed-station observations. Data from those surveys are being used for an assessment of retrospective CORIE simulations of the estuary and plume. The overall quality of the simulations is characterized, and the pros and cons of the two models used, ELCIRC [2, 3] and SELFE [4], are discussed. Based on semi-implicit Eulerian-Lagrangian methods, the two models differ primarily in the basic numerical algorithms (finite difference vs. finite element), and the vertical grids used (Z-coordinates vs. hybrid SZ-coordinates). While the two models have been applied to other cross-scale estuarine/plume/shelf systems, this constitutes their most stringent benchmark and their most revealing inter-comparison. Both models capture well key aspects of estuarine and plume variability, in response to changes in river discharge, coastal wind, and large-scale ocean currents. Where differences exist relative to plume observations, both models tend to under-predict salinity. SELFE provides a consistently superior representation of the estuary - from water levels to salinity intrusion - and an often-superior representation of plume size and dynamics. Inter-model differences are attributed in large part to the higher-order numerics and the flexibility of the SZ-coordinates. [1] A. M. Baptista, Y. Zhang, P. J. Turner, C. Seaton, E. VanMatre, B. Hickey, W. Peterson, and E. Casillas, "Estuary and plume forecasts in support of oceanographic cruises: generation, in-vessel delivery and quality control," presented at AGU Fall Meeting, San Francisco, 2005. [2] A. M. Baptista, Y. L. Zhang, A. Chawla, M. Zulauf, C. Seaton, E. P. Myers, III, J. Kindle, M. Wilkin, M. Burla, and P. J. Turner, "A cross-scale model for 3D baroclinic circulation in estuary-plume-shelf systems: II. Application to the Columbia River," Continental Shelf Research, vol. 25, pp. 935-972, 2005. [3] Y. L. Zhang, A. M. Baptista, and E. P. Myers, "A cross-scale model for 3D baroclinic circulation in estuary-plume-shelf systems: I. Formulation and skill assessment," Continental Shelf Research, vol. 24, pp. 2187-2214, 2004. [4] Y. L. Zhang and A. M. Baptista, "A Semi-Implicit S-Z Finite Element Model for Cross-Scale Ocean Circulation," International Journal for Numerical Methods in Fluids, Submitted.
http://www.ccalmr.ogi.edu/CORIE