OS13A-0502 1340h
Daily forecast of Columbia River plume: a tale of two cruises
The Columbia River plume has a very dynamic and complex response to external forcings such as wind, freshwater discharge, and tides. In May and July 2004, the CORIE (http://www.ccalmr.ogi.edu/CORIE/) forecasting technology was used to provide daily predictions of baroclinic plume circulation in support of multi-vessel NOAA Fisheries and NSF RISE cruises. Model simulations were transferred real-time or daily to the vessels, and the results were contrasted against data from the CORIE real-time observation network and the Oregon State University coastal radar network, as well as against selected data from the vessels and (in May) airborne remote sensors. The forecasts proved effective in capturing major characteristics of the plume including its response to shifting winds. Post cruise simulations added quality to the quantitative characterization of the plume.
OS13A-0503 1340h
Moored Observations of Oceanographic Variability in the Columbia River Plume during the Summer of 2004
As part of the RISE (NSF CoOP) program, 3 moorings were placed over the Oregon and Washington shelves in the Columbia River plume from June to September 2004. The moorings were deployed north, south and immediately offshore of the Columbia River mouth at the 72 m isobath. The moored array was designed to sample the plume under various synoptic conditions. The distance between the northern and central moorings was 31 km and that between the central and southern mooring was 14 km. All moorings included anemometers, temperature loggers, acoustic Doppler current profilers (ADCPs) and near-surface salinity, fluorescence, light transmission, and dissolved inorganic nitrogen (DIN) measurements. 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 and DIN was measured 1 m beneath the surface. Temperature data were collected about every 5 m in the upper water column and at reduced resolution from 30-72 m. 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. Moorings are scheduled for recovery in September, and preliminary results from them will be discussed.
OS13A-0504 1340h
Characterizing the Chemical Composition of the Columbia River Plume: the use of Silicic Acid, Nitrate, Manganese and Salinity as Tracers of Sources of Waters Contributing to the Plume.
The RISE program is examining the influence of the Columbia River plume on the coastal waters off Washington and Oregon. It is important to define the macro and micro nutrient chemistry of the plume as it enters these coastal waters. Low salinity waters of the Columbia River are encountered just a short distance inside the mouth of the Columbia River estuary. These low salinity waters (salinities of 1 to 5) are low in nitrate (3 to 10 $\mu$M), high in silicic acid (140 to 160 $\mu$M), high in dissolved manganese and relatively high in dissolved iron. Within a remarkably short distance of exiting the mouth of the estuary into the coastal waters, the plume has attained salinities of roughly 13 to 22. The source of seawater that is entrained together with the river water in this near-field mixing regime to form the Columbia River plume can be defined using silicic acid, nitrate, manganese and salinity as tracers. During June and July of 2004, it appears that the seawater being initially entrained with the plume is subsurface, high salinity (>33), nutrient rich (nitrate 25 $\mu$M and silicic acid 35 $\mu$M) water. This is particularly important for the macronutrient nitrate, as this adds a substantial amount of additional nitrate to the plume. The plume water then advects and mixes further away from the source. The combination of these same tracers is useful in identifying the far-field mixing as well. We will present examples of these processes and tracers using data from the 2004 RISE cruises.
OS13A-0505 1340h
Distribution of Manganese, Silicic Acid, and Salinity Over Large Spatial Scales as Tracers of the Columbia River Plume off Oregon and Washington
The Columbia River provides a large source of silicic acid and trace metals such as manganese to the coastal waters off Oregon and Washington. Here we report the use of manganese, silicic acid, and salinity as tracers for the Columbia River plume. Dissolved manganese and silicic acid were measured on several surface transects off Oregon and Washington during June/July 2004. The concentrations of silicic acid and dissolved manganese in the near-field plume are markedly greater than those of surface oceanic waters (even during upwelling conditions). As the plume travels and mixes the concentrations of these two constituents remain relatively high within the plume providing, together with salinity, excellent tracers over large spatial scales for the Columbia River plume. California current water has low concentrations of both dissolved manganese and silicic acid (roughly 5 nM and 5 $\mu$M, respectively), freshly upwelled water is highly variable (2-20 nM) in dissolved manganese and can be as high as $\sim$35 $\mu$M in silicic acid, while in the near-field plume concentrations of silicic acid can excede 100 $\mu$M and dissolved manganese can be as high as 200 nM. Because the near-field plume is relatively low in nitrate ($\sim$20 $\mu$M) the biological drawdown of silicic acid is minor, and even after mixing, the far-field plume can contain over 30 $\mu$M of silicic acid. Similarly, the biological drawdown of manganese combined with dilution through mixing and scavenging are not sufficient to remove its signal from the plume, and concentrations of $\sim$25 nM manganese can be found in the far reaches of the plume.
OS13A-0506 1340h
Estuary River Plume Connections
Estuarine circulation and mixing determine the boundary values for coastal river plumes, controlling the initial volume flux and density contrast, as well as the initial chemical and biological properties. At the same time, the presence of the river plume changes the oceanic boundary condition for the estuary. Analytical theory and 3D numerical simulation with the ROMS model are used to explore the linkage between these two dynamical systems. Three questions are addressed. First, can strong tidal currents at the mouth of the estuary overcome the constraint of hydraulic control on the exchange flow there (Stommel's "overmixed" solution), and thereby decreasing the minimum density contrast of the river plume? Second, does the presence of the river plume substantially change the oceanic boundary condition for the estuary, leading to a smaller than expected value for the non-gravitational dispersion coefficient near the mouth? Third, where on the shelf does the water flowing into the estuary come from? Is it drawn from along the coast as proposed by Beardsley and Hart (1978, JGR), or do tidal currents bring it in symmetrically from all directions offshore?
http://www.ocean.washington.edu/rise/index.htm
OS13A-0507 1340h
Turbulence and Mixing in the Columbia River Plume
Thin bouyant plumes represent a technical challenge for in-situ observations. In July 2004 a unique set of measurements were taken in which our vertical microstructure profiler, Chameleon, and acoustics (300 kHz ADCP and 120 kHz echosounder) were modified to measure the O(1-5 m) thick plume. The Chameleon profiles included measurements of density, fluorescence, optical backscatter and turbulent energy dissipation. Intense turbulence was observed in plume fronts (with 30 m vertical displacements), at the plume base (with O(1 s$^{-1}$) shear) and in O(20 m) thick bottom boundary layers. Preliminary results from 10 days of observations will be presented and discussed.
OS13A-0508 1340h
Near-Field Frontal Observations From a High-Volume River Plume
We present observations of very strong convergence, vertical velocities, mixing and bottom boundary layer impacts associated with the leading edge front of the tidally-pulsed Columbia River plume. During four successive greater-ebb spring tides in May 2001, with typical summertime upwelling-favorable winds and riverflow (4900 m$^{3}$ s$^{-1}$), shipboard and helicopter-derived front tracking maps show front propagation patterns similar to those generally seen in Synthetic Aperture Radar (SAR) observations. Shipboard observations during the latter part of ebb tide (5 to 8 h past high water) are consistent with an inertial force balance and a rotary, bore-like vertical circulation. Downwelling velocities are 5-35 cm s$^{-1}$, extending down to the bed below the frontline, reaching our deepest measurements of 70 m. Based on comparisons between oceanic and plume T-S diagrams, the mixing layer extends down to an average depth of 18 m in the region from 50-400 m behind the frontline. We estimate mean mixing parameters over this distance and depth using instability length-scales in $\sim$200 CTD density profiles (a "Thorpe scale" analysis). The mean dissipation, eddy diffusivity, and Thorpe overturn scale are 2 x 10$^{-4}$ W kg$^{-1}$, 6 x 10$^{-2}$ m$^{2}$ s$^{-1}$ and 0.79 m respectively, and decrease with distance behind the front. These observations corroborate the conclusion, from prior laboratory studies and observations of low-volume river plumes, that the leading-edge front plays a dominant role in the flux of buoyancy and other constituents between ocean and plume.
http://www.ldeo.columbia.edu/~orton/
OS13A-0509 1340h
Frontal circulation and sediment distribution in the Columbia River plume during the 2004 RISE cruise
The National Science Foundation-funded RISE (River-Influenced Shelf Ecosystems) project seeks to understand how the Columbia River plume affects the productivity of the Washington and Oregon shelves by redistributing and mixing nutrients in coastal waters. Based on observations from the first RISE cruise, we present a description of the frontal circulation and sediment distribution in the Columbia River plume. River-borne sediments may play an important role in mediating productivity in this system by transporting nutrients and regulating light availability in the water column. During the first RISE cruise on July 8-28, 2004, we sampled the upper water column of the plume area intensively with a Triaxus tow-fish aboard the R/V Pt Sur. The Triaxis was outfitted with three CTDs, a fluorometer, a transmissometer, a nitrate sensor, a Laser In-Situ Scattering Transmissometer (LISST-25), an upward looking acoustic Doppler current profiler (1200 kHz), and a laser-optical plankton counter (LOPC). We obtained additional information on the sediment class distribution in the plume with a LISST-100 mounted to a CTD array and deployed separately from the Triaxis. Preliminary results suggest that strong fronts are generated on the windward side of the plume and that fronts on the northern side of the plume are typically stronger than those on the south. These fronts create strongly convergent flow near the surface and penetrate well below the buoyant surface layer. In shallow areas the front-induced flow appears to re-suspend nutrient-rich bottom sediments.
OS13A-0510 1340h
Influence of Non-Uniform Cross-Sectional Area on the Salinity Intrusion
Observations in estuaries as diverse as the Delaware and San Francisco Bays indicate that the salinity intrusion is buffered against changes in runoff. One suggested explanation is the feedback between circulation and stratification. Another, which we explore in this paper, is the influence of non-uniform bathymetry. We develop a model with a linearly varying cross-sectional area and a dispersive salt-budget for the region between the freshwater end and a specified isohaline, which we define as the location of the salinity intrusion. We find that predicted variability in the salinity intrusion is much closer to observations than for uniform channel models. This approach is applied to observations from the Chesapeake Bay, the Delaware Bay and River, and the Connecticut River, which shows anomalously strong variation in the salinity intrusion.
OS13A-0511 1340h
Columbia River Plume Salinity: the effect of maintenance dredging in the mouth of the Columbia River
The Columbia River Plume provides a transitional habitat for juvenile salmonids moving from the river into the ocean, so there is public concern about possible changes in plume salinity associated with dredging at the mouth of the Columbia River, and other human activities on that salinity (e.g., flow divergence). The Army Corps of Engineers (ACE) conducts regular maintenance dredging in the mouth of the Columbia River, to aid the safe passage of ships through the "graveyard of the Pacific". The present study was undertaken to determine the impact of the channel dredging upon the initial formation of the Columbia plume and therefore on plume salinity. Constrictions in the mouth of the Columbia River act as hydraulic controls, determing the location and nature of plume liftoff, where the fresh water lifts off the bottom to form the plume. Prior studies indicated that the lateral constriction dominated the dynamics, and that plume formation was relatively unaffected by the sill a few kilometers seaward of the constriction. The ACE requested a more detailed study of the effect of dredging at this sill. We present a model study in three parts. First, a two-layer Eulerian model is used to describe the currents in the Columbia entrance channel, in the absence of any friction between the layers. The shape of the salt/ fresh interface is calculated at the location of plume liftoff, and different forcing and depth scenarios are compared. Then, a bulk Richardson number criterion is used to estimate the amount of mixing between the layers. The salinity and thickness of the nascent plume at peak ebb are extracted at the location of a depth constriction, and used to initialize a Lagrangian model. Finally, the Lagrangian model traces water parcels out over the continental shelf. Because the width control landward of the area of dredging provides the dominant influence on plume formation, dredging was found to have only modest impacts on plume conditions.
OS13A-0512 1340h
Decadal-Scale Changes in Shelf Internal Tides in the Columbia River Plume Area
Columbia River plume waters are rich in silicate and iron, but relatively depleted in nitrate. Mixing of nitrate-rich upwelled water with the plume appears, therefore, to be important to plume primary production. Part of this mixing is accomplished by strong, irregular plume internal tides, and changes in these internal tides could impact productivity. A view of decadal scale changes in the internal tides in the plume area can be obtained through analysis of coastal tidal elevation records, 1925 to date. Coastal tide-gauge signals are difficult to interpret, however, because observed changes may be caused by altered river flow and estuarine morphology, as well as by changes in shelf internal tides. Use of tidal records to diagnose changes in internal tides in the plume area requires, therefore, separation of changes in estuarine tidal dissipation from those in the tidal boundary conditions at the estuary mouth. This can be carried out through analyses of changes in multiple constituents at multiple sites. Observations indicate that there has been about a 0.7 mm/yr increase in M2 amplitude at Astoria, OR since 1925. The diurnal tide has increased at a proportional rate. Since linear diurnal internal tides cannot occur at this latitude, there has clearly been a reduction in bed friction, an idea supported by a simultaneous decrease in the M4/M2 ratio. Changes in estuarine bed friction have been quantified from changes in the spatial distribution of M2 and S2, i.e., from changes in neap-spring variations. Even after removal of the effects of reduced estuarine bed friction, there remains an increase in estuarine M2 amplitude that implies a shift in shelf internal tides. A key issue, whether this shift in internal tides results from a trend in amplitude (perhaps implying a change in vertical mixing) or a phase change (leaving mixing largely unchanged), remains open. The situation in Astoria, where long-term changes in coastal tides are the result of both alteration of the estuary and changes in shelf processes, may be contrasted with that in San Francisco, where M2 has increased since 1900 without any increase in K1; the latter changes may be dominantly due to changes in shelf processes.
http://www.ebs.ogi.edu/~jaylab/
OS13A-0513 1340h
Surface Drifter Behavior off of the Columbia River - July 2004
Surface GPS-drifters were released offshore of the Columbia River in July 2004 as part of the first RISE (River Influences on Shelf Ecosystems) cruise. The deployments were made in order to track surface currents and Columbia River plume water near the river mouth and over the shelf. Nineteen deployments ranging from 1 to 45 days in length were completed over 10 different days. Along-track measurements of temperature were recorded by each drifter. Roughly half of the drifters deployed also measured conductivity. Drifter behavior proved to be highly dependent on both wind stress and tidal phase. Drifters deployed in the river mouth near the time of maximum ebb were exported $\sim$27 km offshore to the head of Astoria Canyon in only six hours. One drifter was also deployed off the river mouth during a period of strong downwelling-favorable winds. This drifter circulated anti-cyclonically and moved onshore in a retentive feature north of the mouth. Drifters released off the river mouth near the start of ebb were initially transported southwestward. These drifters then circulated shoreward in a cyclonic eddy-like feature south of the river mouth as the winds changed to favor downwelling. Half of the deployments ended with drifters washing ashore. Overall, the drifter tracks illustrate an enhanced dispersion of plume waters over the Oregon and Washington shelves by both the winds and tidal outflow.
http://www.ocean.washington.edu/rise/index.htm
OS13A-0514 1340h
Dispersal Scaling from the World's Rivers
Although rivers provide important biogeochemical inputs to oceans, there are currently no descriptive or predictive relationships of the spatial scales of these river influences. Our combined satellite, laboratory, field and modeling results show that the coastal dispersal areas of small, mountainous rivers exhibit remarkable self-similar scaling relationships over many orders of magnitude. River plume areas scale with source drainage area to a power significantly less than one (average = 0.65), and this power relationship decreases significantly with distance offshore of the river mouth. Observations of plumes from large rivers reveal that this scaling continues over six orders of magnitude of river drainage basin areas. This suggests that the cumulative area of coastal influence for many of the smallest rivers of the world is greater than that of single rivers of equal watershed size, implying that the cumulative biogeochemical effects of many very small rivers would extend over larger areas of coastal waters than would the effects of one large river. We suggest that future investigations of fluvial inputs to the world's ocean focus on the timing and processes of dispersal from small, mountainous rivers to evaluate the applicability of our results to these important coastal settings.
OS13A-0515 1340h
Combined Use of a Coral Reef Instrumented Platform (CRIMP) to Characterize Temporally the Biogeochemical Response of Kaneohe Bay, Hawaii to Storm Runoff Input
Pulsed inputs to coastal waters in Hawaii from storm runoff rapidly affect water quality, especially in semi enclosed coastal embayments. Traditionally the response of coastal waters to such inputs was evaluated through synoptic (low frequency) sampling that only provides snapshots of the evolution of these highly dynamic environments. In contrast, continuous in-situ measurements can potentially yield data that reflect the short-term biogeochemical response that cannot be captured through manual sampling. Data acquired by instrumented platforms facilitate the characterization of impacts of storm runoff on coastal waters and can be used to evaluate the overall ecosystem response over extended periods of time. We have deployed successfully a multi-instrument Coral Reef Instrumented Monitoring Platform (CRIMP) under conditions ranging from calm to windy dry periods through extreme rain events. Our CRIMP measures physical and biogeochemical parameters (temperature, salinity, pH, dissolved oxygen, turbidity, and chl-a, nutrients, and suspended particle distributions). Use of CRIMP in conjunction with synoptic water sampling has enabled spatial characterization of the response of Kaneohe Bay to storm inputs, the elucidation of relationships between physical, biological, and chemical processes in the bay, and the evolution of the community structure during phytoplankton blooms. In this presentation we discuss high rainfall episodes in the winter 2003-2004 that resulted in large runoff events and increased nutrient loading to coastal waters. DIN:DIP ratios in Kaneohe Bay normally range from 2 to 4, suggesting a nitrogen-limitation that has been confirmed by nutrient-enrichment experiments. Elevated DIN:DIP (25) in storm runoff changes significantly the proportion of dissolved nutrients available for biological uptake. Increases in Chl-a in the bay shortly after storms and changes in the plankton community structure reflect an evolving biological response stimulated by the inputs of excess nutrients. Extremely low phosphate levels combined with the very high DIN:DIP values in Bay waters immediately after storms imply that phosphorus becomes the ultimate limiting-nutrient. Therefore, stream runoff shifts the "normal" N-limitation to a P-limitation as the Bay is flooded with high N:P river and groundwater discharge. This shift has consequences for the management of fluvial nutrient inputs to Kaneohe Bay. A rise and persistence of elevated NH3 concentrations (10-15 M) in the water column for several months after a rain event may also sustain longer-term bay productivity. Enhancements in primary productivity during storms also lead to drawdown of dissolved CO2 changing bay waters from a net source of CO2 to near or below atmospheric levels.
OS13A-0516 1340h
Nature of Decadal-scale Sediment Accumulation in the Mississippi River Deltaic Region
Rivers deliver approximately 15 x 10$^{9}$ tons of sediment to coastal margins each year. This sediment delivery to coastal systems plays a key role in the global carbon and nutrient cycles as deltas and continental shelves are considered to be the main repositories of organic matter in marine sediments. The Mississippi River, delivering more than 50% of the total dissolved and suspended materials from the conterminous U.S., is the dominant stimulus for coastal processes in the northern Gulf of Mexico. Draining approximately 47% of the conterminous U.S., the Mississippi delivers approximately 2 X 10$^{8}$ tons of suspended matter to the northern Gulf shelf each year. Although many researchers have evaluated sediment accumulation in different areas on the shelf near the Mississippi River Delta, this study examines data from more than 90 cores collected throughout the last decade covering majority of the shelf ($<$150 m water depth) adjacent to the Mississippi River Delta. This provides a unique and invaluable dataset of the spatial and modern temporal variations of the sediment accumulation in this dynamic coastal environment. Four types of $^{210}$Pb profiles were observed from these short cores (15-45 cm) collected on the shelf. Proximal to Southwest Pass in 30-100 m of water, two types of non-steady state profiles were observed. These profiles either showed (1) rapid accumulation or (2) an event layer with a change in sedimentation rate. Sedimentation rates in this area are typically $>$2.5 cm yr$^{-1}$ ($>$1.6 g cm$^{-2}$ y$^{-1}$). Two Kasten cores ($\sim$200 cm in length) collected near Southwest Pass also indicate rapid deposition ($>$4 cm y$^{-1}$) on a longer timescale than that captured in the box cores. Near shore ($<$20 m), profiles are dominated by (3) mixing, probably reworked by waves and currents, with the exception of an area just south of Barataria Bay that have steady state profiles. The remainder of the shelf (distal of Southwest Pass) is dominated by (4) steady state accumulation beneath a $\sim$10 cm mixed layer. Sedimentation rates for the distal shelf are typically $<$0.7 cm yr$^{-1}$ ($<$0.4 g cm$^{-2}$ y$^{-1}$). A preliminary sediment budget indicates that more than 50% of the sediment delivered by the river annually are either deposited prior to exiting Southwest Pass or is transported out of the study area, presumably off the shelf.
OS13A-0517 1340h
Control of Estuarine Stratification by Lateral Dynamics
In estuarine systems, scaling arguments suggest that as stratification increases and rotation becomes increasingly important, lateral momentum terms become as large or larger than their axial counterparts. Two data sets collected in the York River estuary under contrasting river flow conditions support these scaling arguments. In fact, during a month long experiment conducted under stratified conditions, the lateral density gradient was, on average, over four times larger than the longitudinal density gradient. Such strong lateral density gradients drive lateral flows that play a significant role in controlling the vertical density stratification. Including the lateral terms in a simple potential energy model enabled relatively accurate prediction of the time varying vertical density stratification at two locations in the estuary cross-section. The lateral change of tidal phase across the estuary favored stronger lateral density gradients during the flood tide. As a result, stronger lateral circulation during flood tides increased stratification more than on ebb, often offsetting the asymmetry expected due to longitudinal tidal straining.
OS13A-0518 1340h
Downwelling dynamics of the western Adriatic Coastal Current
The western Adriatic coastal current (WACC) flows for hundreds of kilometers along the east coast of Italy at speeds of 20 to 100 cm/s. It is fed by the buoyancy input from the Po River and other rivers of the northern Adriatic Sea, with typical freshwater discharge rates of 2000 m**3/s. The Bora winds provide the dominant forcing agent of the WACC during the winter months, resulting in peak southeastward flows reaching 100 cm/s. The energy input of the Bora is principally in the northern Adriatic, and the coastal current response is due mainly to the set up of the pressure field, although there is sometimes an accompanying local component of down-coast winds that further augments the coastal current. Downwelling conditions occur during Bora, with or without local wind-forcing, because the bottom Ekman transport occurs in either case. Downwelling results in destratification of the coastal current, due to both vertical mixing and straining of the cross-shore density gradient. The relative contributions of mixing and straining depends on the value of the Kelvin number K=Lf/(g_Oh)**1/2, where L is the width of the coastal current, f is the Coriolis parameter, g_O is reduced gravity, and h is the plume thickness. For a narrow coastal current (K$<$1), straining occurs more rapidly than vertical mixing. This is the case in the WACC during Bora events, with strain-induced destratification occurring in less than 24 hours. The straining process limits vertical mixing of the coastal current with the ambient Adriatic water, because once the isopycnals become vertical, no more mixing can occur. This limitation of mixing may explain the persistence of the density anomaly of the coastal current in the presence of high stresses. The straining process also has important implications for sediment transport: destratification allows sediment to be distributed throughout the water column during Bora events, resulting in enhanced down-coast fluxes. The influence of the downwelling dynamics on cross-shore sediment transport is still under examination.
OS13A-0519 1340h
Statistical Analysis of Surface Current of the Coast of NJ/NY
We use High Frequency radars to measure ocean current off the coast of NJ and NY. Two direction finding radar systems made by CODAR Ocean Sensor are deployed at Sandy Hook, NJ and Breezy Point, Long Island, NY. Data collection began April 2004 in coordination with LaTTE's 2004 pilot study. Our coverage area extends 15 nautical miles offshore with a 1 mile resolution. We perform statistical analysis on this dataset using Complex Empirical Orthogonal Function (EOF) to identify significant features in surface current. We explore the connection between dynamical forcing mechanisms such as wind and river discharge, and the dominant EOF modes. We pay particular attention to the effect of Hudson River discharge on mode characteristics.
OS13A-0520 1340h
The time varying structure of a river plume: Observations with an autonomous glider.
During the 2004 LaTTE (Lagrangian Transport and Transformation Experiment) pilot study we deployed a Slocum Autonomous glider on a 10-day mission to run repeated transects across the Hudson River Plume in the vicinity of Sandy Hook. The glider completed 13 cross-plume surveys during the mission with horizontal resolution of approximately 100 meters. Wind forcing was highly variable and fluctuated between upwelling and downwelling conditions at 1-2 day intervals. Tidal forcing decreased markedly from spring to neap tide conditions and river discharge averaged approximately 500 m3/s during the survey. The plume responded rapidly to the variable wind forcing. During upwelling conditions the plume thinned and extended over 30 km from shore, while during downwelling winds the plume thickened and was compressed at the shore. However, during both upwellling and downwelling conditions the plume remained detached from the bottom. The cross-sectional area of the plume also tended to vary with the wind forcing. However, a significant increase in the plume's area during the last half of the mission does not appear to be related to either wind forcing or river discharge. Instead, we suggest that the plumes structure could be impacted by spring neap variability which is known to control stratification and freshwater fluxes out of the Hudson River Estuary. This presentation will relate the structure of the plume to wind forcing, river flow and the spring/neap cycle.
OS13A-0521 1340h
Processes Controlling Air-Sea Exchange of CO$_{2}$ in a Subtropical Pacific Estuary
In contrast to the open ocean, shallow-water coastal ocean air-sea CO$_{2}$ exchange has been given relatively little attention. Available data suggest that continental shelves may act as sinks for atmospheric CO$_{2}$ while estuaries, coral reefs, and upwelling regions, in general may act as sources. However, all data do not comply with these general trends and the data available are geographically relatively scarce and short in duration. Consequently, at the time, it is not possible to unequivocally conclude whether the global shallow-water ocean acts as a source or a sink of atmospheric CO$_{2}$. The present study represents the first evaluation of air-sea CO$_{2}$ exchange for a subtropical high island of the Pacific. Kaneohe Bay, located on the eastern side of Oahu, Hawaii, is a complex estuarine system with a large barrier coral reef, numerous patch reefs, and several riverine inputs. Since Sep 2003 surface water has been collected bimonthly throughout the bay for total alkalinity (TA) and dissolved inorganic carbon (DIC) analysis. The partial pressure of carbon dioxide (P$_{CO2}$) is calculated using TA, DIC, and constants from Mehrbach et al. (1973), refit by Dickson and Millero (1987). For all data collected before Dec 2003, P$_{CO2}$s were above the atmospheric level (375 uatm) for all sites throughout the bay (400 to 1300 uatm). The highest values occurred at sites within Kaneohe Stream. The lowest values, still above atmospheric concentration, occurred at sites outside the barrier reef, indicating that high surface water P$_{CO2}$s extend beyond the boundaries of the bay. Two large storms occurred at the end of Nov 2003 and the end of Feb 2004 that dramatically reduced P$_{CO2}$s to at or below the atmospheric partial pressure throughout the entire bay. This appears to be the result of increased river runoff adding excess nutrients to the bay that enhanced photosynthesis throughout the bay thereby drawing down surface water CO$_{2}$. Despite the significant effects of the storms, average P$_{CO2}$s for Sep 2003 through March 2004 are above the atmospheric level and indicate that Kaneohe Bay probably behaves as a net source of CO$_{2}$ throughout the year because of calcification and perhaps heterotrophy.
OS13A-0522 1340h
Knowing Where You Are: Using coastal observatories to design and interpret plankton surveys in the New York Bight Apex
As part of LaTTE, the New York Bight Apex benefited from considerable integrated ocean observing system infrastructure. To apply this IOOS capability to a fisheries problem, a joint Rutgers-NOAA Fisheries pilot project was launched in June 2004 to conduct periodic hydroacoustic/ichthyoplankton surveys throughout the summer and into the autumn. These surveys were aimed at sampling important features (the Hudson River Plume, the Cold Pool, and shelf water) as they changed through time; identifying important water mass-community associations; and moving toward methods of Essential Fish Habitat determination for pelagic habitats. Here we present preliminary findings from the field effort, and outline our use of IOOS capability in fisheries research.
http://marine.rutgers.edu/~quinlan/ECOS/
OS13A-0523 1340h
The Across Shelf and Hudson River Estuary: a Synoptic Glimpse of Hydrographic, Biogeochemical, and Biological Processes
In July 2004, oceanographic data were measured from the shelf edge to fresh water in the Hudson River estuary onboard the research vessel Tioga by researchers from the Woods Hole Oceanographic Institution, the Lamont-Doherty Earth Observatory at Columbia University, the University of New Hampshire, and the University of Rhode Island. Multi-disciplinary observations including parts of the life cycle and carbon cycle were performed. Data included surface temperature, salinity, fluorescence, turbidity, dissolved oxygen, nitrogen, the partial pressure of carbon dioxide, dissolved inorganic carbon, dissolved organic carbon, colored dissolved organic matter, phytoplankton, zooplankton, and a focus on zebra mussel larvae. The very large gradients observed from shelf waters to fresh water provided a wide range of environmental conditions governing the carbonate system and the life cycle of phytoplankton and larvae. This unique suite of measurements provides insight into the transport, distribution, and dynamics of the physiology of the Hudson River plume. The relationship between hydrographic conditions, biogeochemistry, and biology will be discussed.