Toxic algal events are an annual burden on aquaculture and coastal ecosystems of California. The threat of domoic acid (DA) toxicity to human and wildlife health is the dominant harmful algal bloom ...(HAB) concern for the region, leading to a strong focus on prediction and mitigation of these blooms and their toxic effects. This paper describes the initial development of the California Harmful Algae Risk Mapping (C-HARM) system that predicts the spatial likelihood of blooms and dangerous levels of DA using a unique blend of numerical models, ecological forecast models of the target group, Pseudo-nitzschia, and satellite ocean color imagery. Data interpolating empirical orthogonal functions (DINEOF) are applied to ocean color imagery to fill in missing data and then used in a multivariate mode with other modeled variables to forecast biogeochemical parameters. Daily predictions (nowcast and forecast maps) are run routinely at the Central and Northern California Ocean Observing System (CeNCOOS) and posted on its public website. Skill assessment of model output for the nowcast data is restricted to nearshore pixels that overlap with routine pier monitoring of HABs in California from 2014 to 2015. Model lead times are best correlated with DA measured with solid phase adsorption toxin tracking (SPATT) and marine mammal strandings from DA toxicosis, suggesting long-term benefits of the HAB predictions to decision-making. Over the next three years, the C-HARM application system will be incorporated into the NOAA operational HAB forecasting system and HAB Bulletin.
Abstract
Four current-meter moorings and 12 pressure sensor–equipped inverted echo sounders (PIES) were deployed during summer 2011 in the South China Sea. The goal of the experiment was to obtain ...synoptic observations of the large-amplitude nonlinear internal waves from the near field to the far field as they propagated west-northwest across the sea. The program was unique because it was the first to observe the latitudinal variability of the wave crests in addition to the transformations along a single east–west transect. The waves were strongest down the center of the PIES array along roughly 20°45′N and were weaker off axis in both directions. Both a-waves and b-waves arrived earlier in the south than the north, but with different lag times indicating different propagation directions and therefore different sources. The waves were classified by their arrival patterns and source locations and not by their amplitude or packet structure. The Stanford Unstructured Nonhydrostatic Terrain-Following Adaptive Navier–Stokes Simulator (SUNTANS) model, calibrated against the array, showed that the a-waves developed out of the internal tide spawned in the southern portion of the Luzon Strait and the b-waves originated in the north. The northern tides were refracted and suffered large dissipative losses over the shallow portion of the western ridge, whereas the southern tides propagated west-northwest unimpeded, which resulted in a-waves that were larger and appeared sooner than the b-waves. The results were consistent with previous observations that can now be understood in light of the full three-dimensional structure of the internal waves and tides in the northeastern South China Sea.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A moored array of current, temperature, conductivity, and pressure sensors was deployed across the Chinese continental shelf and slope in support of the Asian Seas International Acoustics Experiment. ...The goal of the observations was to quantify the water column variability in order to understand the along and across-shore low-frequency acoustic propagation in shallow water. The moorings were deployed from April 21-May 19, 2001 and sampled at 1-5 min intervals to capture the full range of temporal variability without aliasing the internal wave field. The dominant oceanographic signal by far was in fact the highly nonlinear internal waves (or solitons) which were generated near the Batan Islands in the Luzon Strait and propagated 485 km across deep water to the observation region. Dubbed trans-basin waves, to distinguish them from other, smaller nonlinear waves generated locally near the shelf break, these waves had amplitudes ranging from 29 to greater than 140 m and were among the largest such waves ever observed in the world's oceans. The waves arrived at the most offshore mooring in two clusters lasting 7-8 days each separated by five days when no waves were observed. Within each cluster, two types of waves arrived which have been named type-a and type-b. The type-a waves had greater amplitude than the type-b waves and arrived with remarkable regularity at the same time each day, 24 h apart. The type-b waves were weaker than the type-a waves, arrived an hour later each day, and generally consisted of a single soliton growing out of the center of the wave packet. Comparison with modeled barotropic tides from the generation region revealed that: 1) The two clusters were generated around the time of the spring tides in the Luzon strait; and 2) The type-a waves were generated on the strong side of the diurnal inequality while the type-b waves were generated on the weaker beat. The position of the Kuroshio intrusion into the Luzon Strait may modulate the strength of the waves being produced. As the waves shoaled, the huge lead solitons first split into two solitons then merged together into a broad region of thermocline depression at depths less than 120 m. Elevation waves sprang up behind them as they continued to propagate onshore. The elevation waves also grew out of regions where the locally-generated internal tide forced the main thermocline down near the bottom. The "critical point" /spl alpha/ where the upper and lower layers were equal was a good indicator of when the depression or elevation waves would form, however this was not a static point, but rather varied in both space and time according to the presence or absence of the internal tides and the incoming trans-basin waves themselves.
Four oceanographic moorings were deployed across the South China Sea
continental slope near 21.85∘ N, 117.71∘ E, from 30 May
to 18 July 2014 for the purpose of observing high-frequency ...nonlinear
internal waves (NLIWs) as they shoaled across a rough, gently sloping
bottom. Individual waves required just 2 h to traverse the array and
could thus easily be tracked from mooring to mooring. In general, the
amplitude of the incoming NLIWs tracked the fortnightly tidal envelope in
the Luzon Strait; they lagged by 48.5 h and were smaller than the waves
previously observed to the southwest near the Dongsha Plateau. Two types of waves,
a waves and b waves, were observed, with the b waves always leading the
a waves by 6–8 h. Most of the NLIWs were remotely generated, but a few
of the b waves formed locally via convergence and breaking at the leading
edge of the upslope-propagating internal tide. Waves incident upon the
moored array with amplitude less than 50 m and energy less than 100 MJ m−1 propagated adiabatically upslope with little change of form. Larger
waves formed packets via wave dispersion. For the larger waves, the kinetic
energy flux decreased sharply upslope between 342 and 266 m, while the
potential energy flux increased slightly, causing an increasing ratio of
potential-to-kinetic energy as the waves shoaled. None of the waves met the
criteria for convective breaking. The results are in rough agreement with
recent theory and numerical simulations of shoaling waves.
The interplay between the Point Año Nuevo upwelling center, an offshore anticyclonic mesoscale eddy, and the waters of the Monterey Bay was studied during a series of up‐ and downwelling favorable ...wind events during August 2000. The upwelling events were characterized by the appearance of cold, salty water at Point Año Nuevo at the north end of the bay that subsequently spread southward across the mouth of the bay as the winds continued. During the downwelling/relaxation events, the surface current and temperature response was dominated by the onshore translation of the offshore eddy and by local surface heating in the bay itself. The circulation within the bay was cyclonic during both wind regimes but slightly more barotropic under poleward forcing. The ICON model, a nested, data assimilating, sigma coordinate model, was used to simulate the upwelling and relaxation events and calculate the subsurface current and density fields. The model reproduced the dominant current and temperature patterns outside the bay, including the southward flowing upwelling filament, the movement of the offshore eddy, the poleward flow off Point Sur, and the circulation within the bay. The model salinity fields at the surface and 100 m levels show that during upwelling, the bay was filled with higher‐salinity water stemming from the Point Año Nuevo upwelling center to the north. During downwelling, the source water for both the surface and 100 m levels was the colder, fresher California Current water offshore, which had advected southward well past Point Piños during the previous upwelling event.
► A combination of aircraft, autonomous vehicles, and moorings was used to study the coastal circulation near Point Año Nuevo, CA. ► The observed currents were due to local forcing by the wind stress ...and remote forcing by offshore eddies and alongshore pressure gradients. ► Compared to the observations, three numerical models performed better during the high wind, upwelling favorable conditions than during the wind relaxations.
A comprehensive data set from the ocean and atmosphere was obtained just north of the Monterey Bay as part of the Monterey Bay 2006 (MB06) field experiment. The wind stress, heat fluxes, and sea surface temperature were sampled by the Naval Postgraduate School's TWIN OTTER research aircraft.
In situ data were collected using ships, moorings, gliders and AUVs. Four data-assimilating numerical models were additionally run, including the Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS
®) model for the atmosphere and the Harvard Ocean Prediction System (HOPS), the Regional Ocean Modeling System (ROMS), and the Navy Coastal Ocean Model (NCOM) for the ocean.
The scientific focus of the Adaptive Sampling and Prediction Experiment (ASAP) was on the upwelling/relaxation cycle and the resulting three-dimensional coastal circulation near a coastal promontory, in this case Point Año Nuevo, CA. The emphasis of this study is on the circulation over the continental shelf as estimated from the wind forcing, two ADCP moorings, and model outputs. The wind stress during August 2006 consisted of 3–10 day upwelling favorable events separated by brief 1–3 day relaxations. During the first two weeks there was some correlation between local winds and currents and the three models’ capability to reproduce the events. During the last two weeks, largely equatorward surface wind stress forced the sea surface and barotropic poleward flow occurred over the shelf, reducing model skill at predicting the circulation. The poleward flow was apparently remotely forced by mesoscale eddies and alongshore pressure gradients, which were not well simulated by the models. The small, high-resolution model domains were highly reliant on correct open boundary conditions to drive these larger-scale poleward flows. Multiply-nested models were no more effective than well-initialized local models in this respect.
Abstract
Bursts of upwelling-favorable winds lasting 4–20 days occur year-round south of Cape Blanco, a major headland on the Oregon coast. The ocean’s response to these events was studied using ...moored current, temperature, and salinity data; satellite SST data; and a few across-shelf sections near the mooring site. The mooring was located at 42°26.49′N, 124°34.47′W, 6 n mi off Gold Beach, Oregon, from May 2000 to October 2003. After the spring transition but before upwelling jet separation, equatorward wind stress produced a steady upwelling response much the same as a long, straight coast. Currents and winds had similar spectral characteristics with a peak near 15 days. After jet separation, upwelling-favorable winds forced a much more variable current consisting of a series of thin equatorward jets that evolved and moved offshore across the mooring, with shorter time scales than the wind stress forcing. During autumn, the equatorward wind stress weakened slightly and a transition period occurred, with the flow often poleward along the bottom. During winter, the water column was unstratified during poleward winds and currents with little variation in SST across the shelf. Winter upwelling restratified the water column from the bottom up by drawing cold, salty water onshore along the bottom, with little or no change in SST. This scenario was modulated by strong intraseasonal and interannual variability in the ocean and atmosphere. A wavelet transform analysis of alongshore wind stress and the first empirical orthogonal mode of the alongshore currents revealed strong energy peaks in the 30–70-day band. These signals were particularly clear in the ocean and were not coherent with the local wind stress, suggesting they were due to Kelvin waves of equatorial origin. The shift toward longer (40–45–60 days) periods from 2000 to 2003 was consistent with decreasing (warming) northern oscillation index, suggesting that the period as well as the energy of the intraseasonal waves may be important in transmitting heat poleward during warm years.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The biological carbon pump has been estimated to export ~5–15 Gt C yr−1 into the deep ocean, and forms the principal deep-sea food resource. Irregular, intense pulses of particulate organic carbon ...(POC) have been found to make up about one-third of the overall POC fluxes at a long-term deep-sea research station influenced by coastal upwelling of the California Current, Station M (34°50′N, 123° W, 4000 m depth). However, the drivers of these pulses have been challenging to quantify. It has long been recognized that ocean currents can result in particles being advected while sinking to the point of collection by a sediment trap. Thus, a sediment trap time series can incorporate material from a dynamic catchment area, a concept sometimes referred to as a statistical funnel. This concept raises many questions including: what are the day-to-day conditions at the source locations of the sinking POC? And, how might such ‘ocean weather’ and related ecosystem factors influence the intense variation seen at the seafloor? Here we analyzed three-dimensional ocean currents from a Regional Ocean Modeling System (ROMS) model from 2011 to 2017 to trace the potential source locations of particles sinking at 1000, 100, and 50 m d−1 from an export depth of 100 m. We then used regionally tailored satellite data products to estimate export flux of POC from these locations. For the 100 m d−1 speed, the particles had origins of up to ~300 km horizontal distance from the sediment trap location, moored at Station M at 3400 m depth., and nearly 1000 km for the 50 m d−1 speed. Particle tracking indicated that, there was considerable inter-annual variation in source locations. Particle source locations tended to originate from the east in the summer months, with higher export and POC fluxes. Occasionally these locations were in the vicinity of highly productive ocean features nearer to the coast. We found significant correlations between export flux of organic carbon from the estimated source locations at 100 m depth to trap-estimated POC fluxes at 3400 m depth. These results set the stage for further investigation into sinking speed distributions, conditions at the source locations, and comparisons with mechanistic biogeochemical models and between particle tracking model frameworks.
•Sinking particulates sequester ocean carbon and provide food for deep-sea life. Such dynamics remain challenging to quantify.•This work highlights that particle sinking speeds can have important implications for the horizontal distances travelled.•Particles with slower sinking speeds may originate from hundreds of km or more away from sediment trap sampling systems.•Estimating the source location can aid in understanding carbon sequestration and deep-sea food supply dynamics.
Two field programs, both parts of the Asian Seas International Acoustics Experiment (ASIAEX), were carried out in the central East China Sea (28/spl deg/ to 30/spl deg/N, 126/spl deg/ 30' to 128/spl ...deg/E) during April 2000 and June 2001. The goal of these programs was to study the interactions between the shelf edge environment and acoustic propagation at a wide range of frequencies and spatial scales. The low-frequency across-slope propagation was studied using a synthesis of data collected during both years including conductivity-temperature-depth (CTD) and mooring data from 2000, and XBT, thermistor chain, and wide-band source data from 2001. The water column variability during both years was dominated by the Kuroshio Current flowing from southwest to northeast over the continental slope. The barotropic tide was a mixed diurnal/semidiurnal tide with moderate amplitude compared to other parts of the Yellow and East China Sea. A large amplitude semidiurnal internal tide was also a prominent feature of the data during both years. Bursts of high-frequency internal waves were often observed, but these took the form of internal solitons only once, when a rapid off-shelf excursion of the Kuroshio coincided with the ebbing tide. Two case studies in the acoustic transmission loss (TL) over the continental shelf and slope were performed. First, anchor station data obtained during 2000 were used to study how a Kuroshio warm filament on the shelf induced variance in the transmission loss (TL) along the seafloor in the NW quadrant of the study region. The corresponding modeled single-frequency TL structure explained the significant fine-scale variability in time primarily by the changes in the multipath/multimode interference pattern. The interference was quite sensitive to small changes in the phase differences between individual paths/modes induced by the evolution of the warm filament. Second, the across-slope sound speed sections from 2001 were used to explain the observed phenomenon of abrupt signal attenuation as the transmission range lengthened seaward across the continental shelf and slope. This abrupt signal degradation was caused by the Kuroshio frontal gradients that produced an increasingly downward-refracting sound-speed field seaward from the shelf break. This abrupt signal dropout was explained using normal mode theory and was predictable and source depth dependent. For a source located above the turning depth of the highest-order shelf-trapped mode, none of the propagating modes on the shelf were excited, causing total signal extinction on the shelf.
PDF
