Phase IIIa-CCS: Latitudinal variation of upwelling, retention, nutrient supply and freshwater effects in the California Current System

US-GLOBEC NEP AbstractThis proposal requests funding to: a) synthesize the moored current meter, shore-based HF radar, ship-based hydrographic, and remotely sensed data from the GLOBEC Northeast Pacific (NEP) Long-Term Observation Program (LTOP) and related programs into a coherent, best description of the mesoscale variability along the Pacific Northwest coast from 42 to 48N; and b) relate this physical variability to primary production, zooplankton distributions, and salmon year-class strength in the region. The long-term moorings will allow quantification of the relevant time scales from internal waves to the inter-annual; the satellite images of sea surface temperature and chlorophyll will show the spatial scales; and the HF surface fields will allow timeand space-varying statistics of the mesoscale currents and quasi-Lagrangian pathways to be assessed. The primary scientific objective will be to characterize the alongshelf variability in the upwelling, the nutrients it supplies to the photic zone for utilization by marine organisms, and the retention times of plankton. This variability is affected by the alongshore distribution of the wind stress and fresh water input, by the changes in the bottom topography and coastline orientation, and by pre-conditioning established by inter-annual variability and climate change

SEASOAR observations during a COARE surveys cruise, W9211B, 12 December 1992 to 16 January 1993

An international Coupled Ocean-Atmosphere Response Experiment (COARE) was conducted in the warm-pool region of the western equatorial Pacific Ocean over a four-month period from November 1992 through February 1993 (Webster and Lukas, 1992). Most of the oceanographic and meteorological observations were concentrated in the Intensive Flux Array (IFA) centered at 1'45'S, 156000'E. As part of this experiment, the R/V Wecoma conducted three survey cruises; each cruise included measurements of the temperature, salinity and velocity distribution in the upper 300 m of the ocean, and continuous meteorological measurements of wind, air temperature, humidity, etc. Most of these measurements were along a butterfly pattern that was sampled repeatedly during the three COARE Surveys cruises, W9211A and W9211B, and W9211 C

Estimates of sea surface height and near-surface alongshore coastal currents from combinations of altimeters and tide gauges

Present methods used to retrieve altimeter data do not provide reliable estimates of sea surface height (SSH) in the nearshore region, resulting in a measurement gap of 25–50 km next to the coast. In the present work, gridded SSH fields produced by Archiving, Validation, and Interpretation of Satellite Oceanographic data (AVISO) in the offshore region are combined with coastal tide gauge time series of SSH to improve estimation in that gap along the west coast of the United States in the northern California Current System between 40° and 45°N and 123.8° and 126°W. To assess the increase in skill provided by this procedure, the geostrophic alongshore currents, calculated from the new SSH fields in the gap region, are compared to three in situ, nearshore current measurements, resulting in correlation coefficients of 0.73–0.83 and standard deviations of the differences of 11.6–12.6 cm/s, substantially improved from the AVISO-only results. When the Ekman current components are estimated and added to the geostrophic currents, comparisons to the 10 m deep acoustic Doppler current profiler velocities are only slightly improved. The Ekman components make a more significant contribution when compared to HF radar surface current measurements, providing correlations of 0.94 and standard deviations of the differences of 6.4–9.5 cm/s. These results represent a dramatic improvement in the quality of the SSH fields and estimated alongshore currents when additional, realistic SSH data from the coastal region are added. Here we use coastal tide gauges to provide the additional SSH data but also discuss more general approaches for altimeter SSH retrievals in coastal regions where tide gauge data are not available

Spatial and Temporal Variability of the M2 Internal Tide Generation and Propagation on the Oregon Shelf

A 1-km-horizontal-resolution model based on the Regional Ocean Modeling System is implemented along the Oregon coast to study average characteristics and intermittency of the M₂ internal tide during summer upwelling. Wind-driven and tidally driven flows are simulated in combination, using realistic bathymetry, atmospheric forcing, and boundary conditions. The study period is April through August 2002, when mooring velocities are available for comparison. Modeled subtidal and tidal variability on the shelf are in good quantitative agreement with moored velocity time series observations. Depth-integrated baroclinic tidal energy flux (EF), its divergence, and topographic energy conversion (TEC) from the barotropic to baroclinic tide are computed from high-pass-filtered, harmonically analyzed model results in a series of 16-day time windows. Model results reveal several “hot spots” of intensive TEC on the slope. At these locations, TEC is well balanced by EF divergence. Changes in background stratification and currents associated with wind-driven upwelling and downwelling do not appreciably affect TEC hot spot locations but may affect intensity of internal tide generation at those locations. Relatively little internal tide is generated on the shelf. Areas of supercritical slope near the shelf break partially reflect baroclinic tidal energy to deeper water, contributing to spatial variability in seasonally averaged on-shelf EF. Despite significant temporal and spatial variability in the internal tide, the alongshore-integrated flux of internal tide energy onto the Oregon shelf, where it is dissipated, does not vary much with time. Approximately 65% of the M₂ baroclinic tidal energy generated on the slope is dissipated there, and the rest is radiated toward the shelf and interior ocean in roughly equal proportions. An experiment with smoother bathymetry reveals that slope-integrated TEC is more sensitive to bathymetric roughness than on-shelf EF.KEYWORDS: Continental shelf/slope, Tides, Internal waves, Hindcasts, North Pacific Ocean, Regional model

Atmospheric forcing of the Oregon coastal ocean during the 2001 upwelling season

Copyrighted by American Geophysical Union. Meteorological conditions during an intensive oceanographic observational program in May through August 2001 along the central Oregon coast are described and related to larger-scale and longer-term conditions. Southward wind stresses of 0.05-0.1 N m⁻² occurred roughly 75% of the time, with a sustained period of dominantly southward stress from mid-June through July. Wind variations were correlated with variations in the large-scale Aleutian Low and North Pacific High pressure centers; correlations with the continental Thermal Low were small. Intraseasonal oscillations in alongshore wind stress (periods near 20 days) correlated with the north-south position of the jet stream. These stress oscillations drove 20 day oscillations in upper ocean temperature, with a lag of roughly 5 days for maximum correlation and amplitudes near 4°C. The sum of sensible and latent air-sea heat fluxes was generally into the atmosphere through June, then weakly into the ocean thereafter, with fluctuations on synoptic timescales. Semidiurnal fluctuations in surface air temperature were observed at two northern moorings, apparently forced indirectly by nonlinear internal ocean tides. The diurnal cycle of wind stress was similar for both southward and northward wind conditions, with the diurnal alongshore fluctuation southward in the evening and northward in the morning. During southward winds the marine atmospheric boundary layer (MABL) was typically defined clearly by a strong temperature inversion, and a shallow stable internal boundary layer often formed within the MABL over cool upwelled waters, with surface air temperature roughly 1°C lower inshore than offshore. During northward winds, essentially no low-level temperature stratification was observed

SEASOAR and CTD observations during a COARE surveys cruise, W9211A, 8 November to 8 December 1992

An international Coupled Ocean-Atmosphere Response Experiment (COARE) was conducted in the warm-pool region of the western equatorial Pacific Ocean over a four-month period from November 1992 through February 1993 (Webster and Lukas, 1992). Most of the oceanographic and meteorological observations were concentrated in the Intensive Flux Array (IFA) centered at 1°45'S, 156°00'E. As part of this experiment, three survey cruises were conducted on the R/V Wecoma; each cruise included measurements of the temperature, salinity and velocity distribution in the upper 300 m of the ocean, and continuous meteorological measurements of wind, air temperature, humidity, etc. Most of these measurements were along a butterfly pattern that was sampled repeatedly during the three COARE Surveys cruises, W9211A and W9211B, and W9211C. Our primary objective was to measure zonal and meridional gradients across the center of the IFA. We originally intended to sample along a larger pattern (with diagonals of 200 km) at the beginning and end of each cruise, and to sample a smaller pattern (diagonals of 100 km) as continuously as possible through the main portion of each cruise. Early in W9211A, we found that the smaller pattern was not large enough to span the actual positions of the profiling current meter array, and that frequent deviations from our initial choice of longitude would be necessary to avoid moorings and quasistationary ships. We therefore abandoned our plan of two separate sampling patterns, and instead chose one Standard Butterfly Pattern with a meridional section along 156°06'W and a zonal section along 1°50'S, connected in the southwestern and northeastern quadrants. Along this track, we measured the upper-ocean temperature and salinity by means of a towed undulating Seasoar vehicle (Figure 1) equipped with a SeaBird CTD system, while underway at 7-8 knots. CTD casts were made at the beginning and end of each tow, primarily to check calibration of the Seasoar sensors; additional CTD casts were occasionally made along portions of the standard sections while Seasoar was disabled. Water velocity along the ship's track was measured by means of the ship-borne acoustic Doppler current profiler. This report summarizes the Seasoar and CTD observations from Wecoma's first COARE Surveys cruise, W9211A. It also provides a cruise narrative, and a brief description of the data processing procedures

SeaSoar CTD observations from the central Oregon shelf, cruise W9907C : 13-31 July 1999 : a component of the Prediction of Wind-Driven Coastal Circulation Project

The primary objectives of R/V Wecoma cruise W9907C were to: 1) collect threedimensional fields of temperature, salinity, and light absorption and attenuation using the towed, undulating vehicle SeaSoar; 2) collect 3-D fields of velocity using shipboard ADCP; 3) to make turbulence profiles along a single cross-shelf transect; and 4) locate, recover, and either redeploy or replace a NOPP mooring which had been damaged by a fishing trawler earlier in the season

Physical versus biological spring transition: 2005

In 2005, the onset of spring conditions in the physics of the coastal ocean (lowered sea level, spin-up of vertically-sheared equatorward coastal jet) came about 50 days later than average off Newport Oregon, on May 24. There was a further delay of 50 days before the subsurface upwelled water penetrated into the anomalously stratified surface layer, becoming most available for biological activity. The warm anomaly in sea surface temperature which provided the surface cap was observed at mid-shelf locations from Washington to central California, but it ended sooner south of Oregon. Biological impacts of these delays to several trophic levels have been reported

River Influences on Shelf Ecosystems: Introduction and Synthesis

River Influences on Shelf Ecosystems (RISE) is the first comprehensive interdisciplinary study of the rates and dynamics governing the mixing of river and coastal waters in an eastern boundary current system, as well as the effects of the resultant plume on phytoplankton standing stocks, growth and grazing rates, and community structure. The RISE Special Volume presents results deduced from four field studies and two different numerical model applications, including an ecosystem model, on the buoyant plume originating from the Columbia River. This introductory paper provides background information on variability during RISE field efforts as well as a synthesis of results, with particular attention to the questions and hypotheses that motivated this research. RISE studies have shown that the maximum mixing of Columbia River and ocean water occurs primarily near plume liftoff inside the estuary and in the near field of the plume. Most plume nitrate originates from upwelled shelf water, and plume phytoplankton species are typically the same as those found in the adjacent coastal ocean. River-supplied nitrate can help maintain the ecosystem during periods of delayed upwelling. The plume inhibits iron limitation, but nitrate limitation is observed in aging plumes. The plume also has significant effects on rates of primary productivity and growth (higher in new plume water) and microzooplankton grazing (lower in the plume near field and north of the river mouth); macrozooplankton concentration (enhanced at plume fronts); offshelf chlorophyll export; as well as the development of a chlorophyll ?shadow zone? off northern Oregon