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Satellite and atmospheric model fields are used to describe the wind forcing, surface ocean circulation, temperature and chlorophyll-a pigment concentrations along the coast of southern Chile in the transition region between 38° and 46°S. Located inshore of the bifurcation of the eastward South Pacific Current into the equatorward Humboldt and the poleward Cape Horn Currents, the region also includes the Chiloe Inner Sea and the northern extent of the complex system of fjords, islands and canals that stretch south from near 42°S. The high resolution satellite data reveal that equatorward currents next to the coast extend as far south as 48°-51°S in spring-summer. They also display detailed distributions of forcing from wind stress and wind stress curl near the coast and within the Inner Sea. Between 38°-46°S, both winds and surface currents during 1993-2016 change directions seasonally from equatorward during summer upwelling to poleward during winter downwelling, with cooler SST and greater surface chlorophyll-a concentrations next to the coast during upwelling, opposite conditions during downwelling. Over interannual time scales during 1993-2016, there is a strong correlation between equatorial El Nino events and sea level and a moderate correlation with alongshore currents. Looking more closely at the 2014-2016 period, we find a marginal El Nino during 2014 and a strong El Nino during 2015 that connect the region to the tropics through the oceanic pathway, with some atmospheric connections through the phenomenon of atmospheric blocking (as noted by others). The period also includes a Harmful Algal Bloom of the dinoflagellate Alexandrium catenella during early-2016 that occurred during a sequence of physical conditions (winds, currents and temperatures) that would favor such a bloom. The most anomalous physical condition during this specific bloom is an extreme case of atmospheric blocking that creates a long period of calm in austral autumn after strong upwelling in austral summer. The blocking is related to the 2015-2016 El Nino and an unusual coincident positive phase of the Southern Annular Mode.

The importance of local versus distant forcing is studied for the wind-driven intra-seasonal (30–120 day) sea level anomaly (SLA) variations along the west coast of India. Significant correlations of altimeter-derived SLA on the west coast are found with the mid-basin SLA east of Sri Lanka and SLA as far as Sumatra and the equator, with increased lags, connecting with the remote forcing from the equator in the form of reflected Rossby waves. The highest correlations between SLA on the west coast and winds are found with the winds at the southern tip of India. Coherence calculations help to identify the importance of a narrow band (40–60 day) for the interactions of winds with the intra-seasonal SLA variations. A multivariate regression model, along with the coherences within this narrower band, suggest the lags of SLA on the west coast with winds to range from 0 to 2 days with the local forcing to 11–13 days with the forcing along south east coast of India. Hovmöller diagrams illustrate the propagation of signals by estimating phase speed for Rossby waves (57 cm/s) across the Indian Ocean from Sumatra and Coastal Trapped Waves (CTWs) along the west coast of India (178 cm/s). Propagation from the south-east coast of India is not as robust as Rossby waves from Sumatra.

A warm anomaly in the upper ocean, colloquially named "the Blob," appeared in the Gulf of Alaska during the calm winter of 2013-2014, spread across the northern North Pacific (NP) Ocean, and shifted eastward and onto the Oregon shelf. At least 14 species of copepods occurred which had never been observed in shelf/slope waters off Oregon, some of which are known to have NP Gyre affinities, indicating that the source waters of the coastal "Blob" were likely of both offshore (from the west) and subtropical/tropical origin. The anomalously warm conditions were reduced during strong upwelling in spring 2015 but returned when upwelling weakened in July 2015 and transitioned to downwelling in fall 2015. The extended period of warm conditions resulted in prolonged effects on the ecosystem off central Oregon, lasting at least through 2016. Impacts to the lower trophic levels were unprecedented and include a novel plankton community composition resulting from increased copepod, diatom, and dinoflagellate species richness and increased abundance of dinoflagellates. Additionally, the multiyear warm anomalies were associated with reduced biomass of copepods and euphausiids, high abundance of larvaceans and doliolids (indictors of oligotrophic ocean conditions), and a toxic diatom bloom (Pseudo-nitzschia) throughout the California Current in 2015, thereby changing the composition of the food web that is relied upon by many commercially and ecologically important species.

The influence of climate variability on the Northeast Pacific (NEP) ocean is mainly linked to the impact of El Nino Southern Oscillation (ENSO), the Pacific Decadal Oscillation (PDO), and North Pacific Gyre Oscillation (NPGO) on the modulation of coastal circulation, coastal upwelling, and ecosystem response. The impact of climate variability on the interannual variability of freshwater river plumes has been largely unstudied. Here, 14.5 years of ocean color satellite imagery were used to study the interannual variability of turbid freshwater plumes off the Oregon coast (with particular emphasis on the influence of the ENSO, PDO, and NPGO). EOF analysis reveals two dominant modes associated with (i) the winter plumes of coastal rivers merged along the entire Oregon shelf (EOF1) in the downstream (northward) direction as coastal-attached buoyancy-driven plumes, and (ii) the offshore Columbia River plume occupying most of the coastal ocean off Oregon (EOF2) as result of its southward and offshore transport during spring-summer upwelling. Large plumes are found to correspond mainly with certain aspects of ENSO cycles, but more extended time series are needed to better evaluate the influence of PDO and NPGO because of their dominant decadal scale of variability. Anomalously large coastal plumes (EOF1) lagged the canonical El Nino primarily during fall and La Nina during winter. The largest offshore Columbia River plume events occurred after persistent La Nina conditions (e.g. 2008, 2011, 2014).

Altimeter sea surface height (SSH) fields are analyzed to define and discuss the seasonal circulation over the wide continental shelf in the SW Atlantic Ocean (27°–43°S) during 2001–2012. Seasonal variability is low south of the Rio de la Plata (RdlP), where winds and currents remain equatorward for most of the year. Winds and currents in the central and northern parts of our domain are also equatorward during autumn and winter but reverse to become poleward during spring and summer. Transports of shelf water to the deep ocean are strongest during summer offshore and to the southeast of the RdlP. Details of the flow are discussed using mean monthly seasonal cycles of winds, heights, and currents, along with analyses of Empirical Orthogonal Functions. Principle Estimator Patterns bring out the patterns of wind forcing and ocean response. The largest part of the seasonal variability in SSH signals is due to changes in the wind forcing (described above) and changes in the strong boundary currents that flow along the eastern boundary of the shelf. The rest of the variability contains a smaller component due to heating and expansion of the water column, concentrated in the southern part of the region next to the coast. Our results compare well to previous studies using in situ data and to results from realistic numerical models of the regional circulation., Key Points: Altimeters can resolve the seasonal circulation over the SW Atlantic coastal shelfSeasonal changes are primarily wind‐driven north of the Rio de la PlataOur results agree with previous studies using models and field surveys

This chapter describes both the improvements in coastal altimetry on the technical side and the ensuing applications, that is, first improvements in retracking and improvements in corrections. Passaro et al. have reviewed the different approaches taken in literature for the processing of coastal pulse-limited waveforms that do not conform to the Brown model. SAR altimetry is intrinsically promising for coastal applications by virtue of the higher signal-to-noise ratio and along-track resolution. The accurate retrieval of sea surface height from satellite altimetry with centimeter-level accuracy requires the knowledge of all terms involved in the altimeter measurement system with similar or better accuracy. Those are satellite height above a reference ellipsoid from precise orbit determination; altimeter range from dedicated retracking, including all instrument effects; and all range and geophysical corrections. The corrections with particular issues in the coastal regions are mainly the wet tropospheric correction, the sea state bias, and to somewhat lesser extent the dry tropospheric correction.

A warm anomaly in the upper ocean, colloquially named “the Blob,” appeared in the Gulf of Alaska during the calm winter of 2013–2014, spread across the northern North Pacific (NP) Ocean, and shifted eastward and onto the Oregon shelf. At least 14 species of copepods occurred which had never been observed in shelf/slope waters off Oregon, some of which are known to have NP Gyre affinities, indicating that the source waters of the coastal “Blob” were likely of both offshore (from the west) and subtropical/tropical origin. The anomalously warm conditions were reduced during strong upwelling in spring 2015 but returned when upwelling weakened in July 2015 and transitioned to downwelling in fall 2015. The extended period of warm conditions resulted in prolonged effects on the ecosystem off central Oregon, lasting at least through 2016. Impacts to the lower trophic levels were unprecedented and include a novel plankton community composition resulting from increased copepod, diatom, and dinoflagellate species richness and increased abundance of dinoflagellates. Additionally, the multiyear warm anomalies were associated with reduced biomass of copepods and euphausiids, high abundance of larvaceans and doliolids (indictors of oligotrophic ocean conditions), and a toxic diatom bloom (Pseudo-nitzschia) throughout the California Current in 2015, thereby changing the composition of the food web that is relied upon by many commercially and ecologically important species.

Author(s): Di Lorenzo, E; Combes, V; Keister, JE; Strub, PT; Thomas, AC; Franks, PJS; Ohman, MD; Furtado, JC; Bracco, A; Bograd, SJ; Peterson, WT; Schwing, FB; Chiba, S; Taguchi, B; Hormazabal, S; Parada, C | Abstract: The goal of the Pacific Ocean Boundary Ecosystem and Climate Study (POBEX) was to diagnose the large-scale climate controls on regional transport dynamics and lower trophic marine ecosystem variability in Pacific Ocean boundary systems. An international team of collaborators shared observational and eddyresolving modeling data sets collected in the Northeast Pacific, including the Gulf of Alaska (GOA) and the California Current System (CCS), the Humboldt or Peru-Chile Current System (PCCS), and the Kuroshio-Oyashio Extension (KOE) region. POBEX investigators found that a dominant fraction of decadal variability in basin and regional-scale salinity, nutrients, chlorophyll, and zooplankton taxa is explained by a newly discovered pattern of ocean-climate variability dubbed the North Pacific Gyre Oscillation (NPGO) and the Pacific Decadal Oscillation (PDO). NPGO dynamics are driven by atmospheric variability in the North Pacific and capture the decadal expression of Central Pacific El Ninos in the extratropics, much as the PDO captures the low-frequency expression of eastern Pacific El Ninos. By combining hindcasts of eddy-resolving ocean models over the period 1950-2008 with model passive tracers and long-term observations (e.g., CalCOFI, Line-P, Newport Hydrographic Line, Odate Collection), POBEX showed that the PDO and the NPGO combine to control low-frequency upwelling and alongshore transport dynamics in the North Pacific sector, while the eastern Pacific El Nino dominates in the South Pacific. Although different climate modes have different regional expressions, changes in vertical transport (e.g., upwelling) were found to explain the dominant nutrient and phytoplankton variability in the CCS, GOA, and PCCS, while changes in alongshore transport forced much of the observed long-term change in zooplankton species composition in the KOE as well as in the northern and southern CCS. In contrast, cross-shelf transport dynamics were linked to mesoscale eddy activity, driven by regional-scale dynamics that are largely decoupled from variations associated with the large-scale climate modes. Preliminary findings suggest that mesoscale eddies play a key role in offshore transport of zooplankton and impact the life cycles of higher trophic levels (e.g., fish) in the CCS, PCCS, and GOA. Looking forward, POBEX results may guide the development of new modeling and observational strategies to establish mechanistic links among climate forcing, mesoscale circulation, and marine population dynamics. © 2013 by The Oceanography Society. All rights reserved.

Concurrent satellite-measured chlorophyll (CHL), sea surface temperature (SST), sea level anomaly (SLA) and model-derived wind vectors from the 13+ year SeaWiFS period September 1997–December 2010 quantify time and space patterns of phytoplankton variability and its links to physical forcing in the Pacific Ocean. The CHL fields are a metric of biological variability, SST represents vertical mixing and motion, often an indicator of nutrient availability in the upper ocean, SLA is a proxy for pycnocline depths and surface currents while vector winds represent surface forcing by the atmosphere and vertical motions driven by Ekman pumping. Dominant modes of variability are determined using empirical orthogonal functions (EOFs) applied to a nested set of domains for comparison: over the whole basin, over the equatorial corridor, over individual hemispheres at extra-tropical latitudes (>20°) and over eastern boundary current (EBC) upwelling regions. Strong symmetry exists between hemispheres and the EBC regions, both in seasonal and non-seasonal variability. Seasonal variability is strongest at mid latitudes but non-seasonal variability, our primary focus, is strongest along the equatorial corridor. Non-seasonal basin-scale variability is highly correlated with equatorial signals and the strongest signal across all regions in the study period is associated with the 1997–1999 ENSO cycle. Results quantify the magnitude and geographic pattern with which dominant basin-scale signals are expressed in extra-tropical regions and the EBC upwelling areas, stronger in the Humboldt Current than in the California Current. In both EBC regions, wind forcing has weaker connections to non-seasonal CHL variability than SST and SLA, especially at mid and lower latitudes. Satellite-derived dominant physical and biological patterns over the basin and each sub-region are compared to indices that track aspects of climate variability in the Pacific (the MEI, PDO and NPGO). We map and compare the local CHL footprint associated with each index and those of local wind stress curl, showing the dominance in most areas of the MEI and its similarity to the PDO. Principal estimator patterns quantify the linkage between dominant modes of forcing variability (wind, SLA and SST) and CHL response, comparing local interactions within EBC regions with those imposed by equatorial signals and mapping equatorial forcing on extra-tropical CHL variability.

The Newport Hydrographic (NH) Line along 44.65°N off central Oregon was sampled seasonally during two epochs: 1961–1971 through the TENOC program and 1997–2003 through the GLOBEC Northeast Pacific Long Term Observations Program (LTOP); some observations are available for 2004 and 2005. During TENOC, the line extended 305 km offshore to 128°W, with stations 18 km apart over the continental shelf and 36 km offshore. During LTOP, the line was shorter (to 126°W) with closer station spacing over the continental shelf (9 km apart) and slope (18 km apart). LTOP cruises included biochemical sampling and underway current measurements. During both TENOC and LTOP, the seasonal cycle is very strong (accounting for >50% of the variance in surface layer properties), with rapid transitions in spring and fall. The summer regime is subject to coastal upwelling driven by southward winds, equatorward surface currents, and advection of low-salinity waters from the Columbia River. The winter regime off Newport is subject to coastal downwelling and poleward surface currents driven by northeastward winds. Comparison between TENOC and LTOP summer regimes shows the near-surface layer (0–100 m) at most locations is significantly warmer and fresher during LTOP than TENOC, and steric heights over the continental margin are significantly higher. Comparison of LTOP and TENOC winters shows that average differences at most locations were not statistically significant, but that the variance of steric height and shelf-break temperatures was significantly higher during LTOP than TENOC. Interannual variability of climate indices is also stronger during LTOP, which included a rare Subarctic invasion in 2002 as well as the strong 1997–1998 El Nino. During both TENOC and LTOP, interannual variability of steric height is closely related to the El Nino/La Nina cycle. Nutrient concentrations and nitrate-to-phosphate ratios of upwelling-source waters vary inversely with halocline temperature. Both reflect alongshore advection by coastal currents: southward currents bring cool, nitrate-rich waters in summer (especially during the Subarctic invasion), and northward currents bring relatively warm, nitrate-poor waters to the NH line in winter (especially during El Nino). Seasonal and interannual variations in the nutrient level of upwelling-source water are reflected in time series of vertically-integrated chlorophyll over the LTOP survey region (about 150 km by 300 km). Seasonal variations in chlorophyll and currents are congruent with seasonal variations in copepod biomass and diversity. We were not successful in establishing a clear connection between chlorophyll levels and interannual variations in copepod biomass or diversity, nor in explaining the large decrease in the survival rate of coho salmon between TENOC (6%) and LTOP (3%).

The first two years of SeaWiFS (Sea viewing Wide Field of view Sensor) data (1997-1999) are used to document the variability of large-scale surface chlorophyll patterns within the coastal region along the full latitudinal extent of each of the four major global eastern boundary currents; the California, Humboldt, Benguela and Canary Currents. Seasonal chlorophyll patterns are compared to coincident seasonal cycles of Ekman transport cal- culated from satellite scatterometer data. In all four regions, maximum chlo- rophyll concentrations are generally temporally and latitudinally coincident with the seasonal maximum in upwelling (offshore Ekman transport) over most of their latitudinal range, but exceptions are documented. Interannual differences are evident in each region, most notably in the two Pacific regions where the 1997-1998 chlorophyll seasonality was affected by El Nino conditions. Significant differences between previously published chlorophyll seasonality deduced from the relatively sparse coverage of the Coastal Zone Color Scanner (CZCS) and the more complete coverage of SeaWiFS in both Southern Hemisphere regions are evident.

The seasonal variability of sea surface height (SSH) and currents are defined by analysis of altimeter data in the NE Pacific Ocean over the region from Central America to the Alaska Gyre. The results help to clarify questions about the timing of seasonal maxima in the boundary currents. As explained below, the long-term temporal mean of the SSH values must be removed at each spatial point to remove the temporally invariant (and large) signal caused by the marine geoid. We refer to the resulting SSH values, which contain all of the temporal variations, as the ‘residual’ SSH. Our main findings are: 1. The maximum surface velocities around the boundaries of the cyclonic Alaska Gyre (the Alaska Current and the Alaska Stream) occur in winter, at the same time that the equatorward California Current is weakest or reversed (forming the poleward Davidson Current); the maximum surface velocities in the California Current occur in summer. These seasonal maxima are coincident with the large-scale atmospheric wind forcing over each region. 2. Most of the seasonal variability occurs as strong residuals in alongshore surface currents around the boundaries of the NE Pacific basin, directly connecting the boundaries of the subpolar gyre, the subtropical gyre and the Equatorial Current System. 3. Seasonal variability in the surface velocities of the eastward North Pacific Current (West Wind Drift) is weak in comparison to seasonal changes in the surface currents along the boundaries. 4. There is an initial appearance next to the coast and offshore migration of seasonal highs and lows in SSH, alongshore velocity and eddy kinetic energy (EKE) in the Alaska Gyre, similar to the previously-described seasonal offshore migration in the California Current. 5. The seasonal development of high SSH and poleward current residuals next to the coast appear first off Central America and mainland Mexico in May–June, prior to their appearance in the southern part of the California Current in July–August and their eventual spread around the entire basin in November–December. Similarly, low SSH and equatorward transport residuals appear first off Central America and Mexico in January–February before spreading farther north in spring and summer. 6. The maximum values of EKE occur when each of the boundary currents are maximum.

A high-resolution model is used to characterize the dominant patterns of sea surface salinity (SSS) variability generated by the freshwater discharges of the Rio de la Plata (RdlP) and the Patos/Mirim Lagoon in the southwestern Atlantic region. We identify three dominant modes of SSS variability. The first two, which have been discussed in previous studies, represent the seasonal variations of the freshwater plumes over the continental shelf. The third mode of SSS variability, which has not been discussed hitherto, represents the salinity exchanges between the shelf and the deep ocean. A diagnostic study using floats and passive tracers identifies the pathways taken by the freshwater plumes. During the austral winter (JJA) the plumes leave the shelf region north of the BMC. During the austral summer (DJF), the plumes are entrained more directly into the BMC. A sensitivity study indicates that the high frequency component of the wind stress forcing controls the vertical structure of the plumes while the low-frequency component of the wind stress forcing and the inter- annual variations of the RdlP discharge controls the horizontal structure of the plumes. Dynamical analysis reveals that the cross-shelf flow has a dominant barotropic structure and, therefore, the SSS anomalies detected by Aquarius represent net mass exchanges between the shelf and the deep ocean. The net cross-shelf volume flux is 1.21 Sv. This outflow is largely compensated by an inflow from the Patagonian shelf. Fil: Matano, Ricardo. Oregon State University. College of Earth, Ocean and Atmospheric Sciences; Estados Unidos Fil: Combes, Vincent. Oregon State University. College of Earth, Ocean and Atmospheric Sciences; Estados Unidos Fil: Piola, Alberto Ricardo. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografia Naval; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; Argentina Fil: Guerrero, Raul Alfredo. Instituto Nacional de Investigaciones y Desarrollo Pesquero; Argentina Fil: Palma, Elbio Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto Argentino de Oceanografía (i); Argentina. Universidad Nacional del Sur. Departamento de Física; Argentina Fil: Strub, P. Ted. Oregon State University. College of Earth, Ocean and Atmospheric Sciences; Estados Unidos Fil: James, Corinne. Oregon State University. College of Earth, Ocean and Atmospheric Sciences; Estados Unidos Fil: Fenco, Harold. Instituto Nacional de Investigaciones y Desarrollo Pesquero; Argentina Fil: Chao, Yi. Remote Sensing Solutions; Estados Unidos Fil: Saraceno, Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; Argentina

We present a modeling study of the upwelling ocean circulation off central Chile (34°–40°S). Using a primitive equation model, we make a numerical simulation of the ocean circulation for summer of 1993, a year characterized by moderate but persistent equatorward winds. The results indicate the formation of an eastern boundary current system that shows classical Ekman and geostrophic dynamics. A strong equatorward coastal jet develops during intense upwelling activity, induced by the prevailing equatorward winds. The spatial and temporal variability of the upwelling-favorable winds strongly controls the variability in the oceanic circulation. Upwelling activity in the coastal areas occurs during periods of growth, peak, and decay. The circulation in the region is divided into two distinct dynamical areas that extend north and south of a prominent cape (Punta Lavapie), located in the center of the model domain. During the peak upwelling stage, the equatorward jet separates from the coast at Punta Lavapie and remains separated in the northern region. This detachment is followed by the formation of cyclonic eddies and decreased upwelling during periods of wind relaxation. The northern area is affected by advection processes and weaker local winds. In contrast, the equatorward flows in the southern region are persistently attached to the coastline and are more coherent with the stronger local winds.

Five years (1979–83) of satellite ocean color data from the coastal zone color scanner (CZCS) data are used to calculate cross-shelf transects of phytoplankton pigment concentrations in the California Current and quantify their seasonal and interannual variability. Alongshore means over six regions, Washington–northern Oregon (48.4–42.8°N), Cape Blanco to Cape Mendocino (42.8–40.4°N), northern California (40.4–37.8°N), central California (37.8–34.5°N), northern Baja (32.5–29.4°N) and southern Baja (27.9–22.9°N) are used to contrast latitudinal differences. The general seasonal cycle shows minimum cross-shelf pigment extensions in March (2.0 mg m−3 isoline within 80 km of shore), expansion of pigment concentrations offshore in April and May often to the annual maximum (2.0 mg m−3 isoline up to 200 km offshore), a mid-summer (July–August) reduction in cross-shelf extension followed by a late summer (September) expansion and a fall collapse back towards the coast by late October. Amplitude of this seasonal pattern is minimum along the northern Baja coast and strongest off central California. Strong interannual variability is evident in both the timing and strength of these seasonal features. The most latitudinally consistent pattern of interannual variability is of negative anomalies and reduced concentrations during the 1983 El Nino. Time series of cross-shelf pigment distribution are compared quantitatively with concurrent alongshore wind stress and wind mixing (U*3) from each region. Maximum correlations occur when pigment lags wind forcing by 1 or 2 ten-day periods. Strongest correlations are in the region from Cape Blanco to Cape Mendocino. Correlations are weaker both in the Pacific Northwest and off Baja. Correlations which excluded the anomalous conditions of 1983 are stronger in the three regions from Cape Blanco south to Point Conception suggesting that connections to wind forcing are stronger during non-El Nino years in these regions. Lastly, preliminary comparisons of the CZCS seasonal cycles are made to those evident in the first 19 months of SeaWiFS chlorophyll data which include the strong 1997–98 El Nino.

A primitive equation ocean model is used to generate trajectories of simulated clusters of drifters in the California Current (CC) region. These trajectories allow us to evaluate a least squares (LS) method of estimating vorticity and vertical velocity along a cluster's path. Two clusters provide examples of successful and less successful estimates of vorticity and vertical velocity. Our analysis quantifies the dependence of estimate quality on several parameters that can be used as error predictors in the LS estimate of vorticity: cluster separation, number of drifters in a cluster, and cluster shape. A combination of cluster separation and ellipticity shows the most promise as an indicator of quality for the vorticity estimate.

The present research was funded by NSF grants OCE-93-03094 (to Roger Lukas), OCE 93-01368 (to David M. Karl), OCE 96-01850 (to David Karl, Roger Lukas and Pierre Flament) and NASA grant NAGW-4596 (to Mark R. Abbott).

Satellite surface height and temperature fields are used to examine the seasonal surface circulation in the California Current System. In spring and summer, an equatorward jet develops next to the coast, with an initial latitudinal structure that responds to the latitudinal distribution of equatorward alongshore winds. This jet moves offshore from spring to fall and develops meanders and closed eddies that contribute eddy kinetic energy and water mass properties to the nearby deep ocean. Higher EKE appears first in spring near the coast and moves offshore with the seasonal jet. Along altimeter tracks parallel to the coastline 200 and 400 km offshore, the greatest EKE is found in summer and fall, respectively, with wavelengths of approximately 300 km. These are the wavelengths of the largest meanders and the distance between the largest eddies visible in altimeter “snapshots” of the jet. At 600–800 km offshore, the wavelengths are generally smaller (100–150 km), similar to eddy sizes reported by others for the quiescent northeast Pacific. Some energy with longer wavelengths arrives at the track 600 km offshore in winter and 800 km offshore in spring, which we interpret as the most offshore extension of the EKE generated by the jet and eddy system closer to the coast in the previous spring and summer. A sequence of snapshots from October 1992 to October 1993 shows details of the evolution of the jet and eddy system over one complete annual cycle.

Insight into the dependence of benthic communities on biological and physical processes in nearshore pelagic environments, long considered a “black box,” has eluded ecologists. In rocky intertidal communities at Oregon coastal sites 80 km apart, differences in abundance of sessile invertebrates, herbivores, carnivores, and macrophytes in the low zone were not readily explained by local scale differences in hydrodynamic or physical conditions (wave forces, surge flow, or air temperature during low tide). Field experiments employing predator and herbivore manipulations and prey transplants suggested top-down (predation, grazing) processes varied positively with bottom-up processes (growth of filter-feeders, prey recruitment), but the basis for these differences was unknown. Shore-based sampling revealed that between-site differences were associated with nearshore oceanographic conditions, including phytoplankton concentration and productivity, particulates, and water temperature during upwelling. Further, samples taken at 19 sites along 380 km of coastline suggested that the differences documented between two sites reflect broader scale gradients of phytoplankton concentration. Among several alternative explanations, a coastal hydrodynamics hypothesis, reflecting mesoscale (tens to hundreds of kilometers) variation in the interaction between offshore currents and winds and continental shelf bathymetry, was inferred to be the primary underlying cause. Satellite imagery and offshore chlorophyll- a samples are consistent with the postulated mechanism. Our results suggest that benthic community dynamics can be coupled to pelagic ecosystems by both trophic and transport linkages.

In this paper, we evaluate the temporal and horizontal resolution of geostrophic surface velocities calculated from TOPEX satellite altimeter heights. Moored velocities (from vector-averaging current meters and an acoustic Doppler current profiler) at depths below the Ekman layer are used to estimate the temporal evolution and accuracy of altimeter geostrophic surface velocities at a point. Surface temperature gradients from satellite fields are used to determine the altimeter's horizontal resolution of features in the velocity field. The results indicate that the altimeter resolves horizontal scales of 50–80 km in the along-track direction. The rms differences between the altimeter and current meters are 7–8 cm s−1, much of which comes from small-scale variability in the oceanic currents. We estimate the error in the altimeter velocities to have an rms magnitude of 3–5 cm s−1 or less. Uncertainties in the eddy momentum fluxes at crossovers are more difficult to evaluate and may be affected by aliasing of fluctuations with frequencies higher than the altimeter's Nyquist frequency of 0.05 cycles d−1, as indicated by spectra from subsampled current meter data. The eddy statistics that are in best agreement are the velocity variances, eddy kinetic energy and the major axis of the variance ellipses. Spatial averaging of the current meter velocities produces greater agreement with all altimeter statistics and increases our confidence that the altimeter's momentum fluxes and the orientation of its variance ellipses (the statistics differing the most with single moorings) represent well the statistics of spatially averaged currents (scales of 50–100 km) in the ocean. Besides evaluating altimeter performance, the study reveals several properties of the circulation in the California Current System: (1) velocity components are not isotropic but are polarized, strongly so at some locations, (2) there are instances of strong and persistent small-scale variability in the velocity, and (3) the energetic region of the California Current is isolated and surrounded by a region of lower energy starting 500–700 km offshore. This suggests that the source of the high eddy energy within 500 km of the coast is the seasonal jet that develops each spring and moves offshore to the central region of the California Current, rather than a deep-ocean eddy field approaching the coast from farther offshore.

On Oregon coastal rocky shores, filter-feeders were relatively abundant and macrophytes were relatively scarce at Strawberry Hill, whereas opposite abundance patterns occurred at Boiler Bay. To determine whether nearshore oceanographic differences were associated with these patterns, we made shore-based measurements of nutrient and Chl a concentrations. We used a three-level nested design to identify ecologically appropriate sampling scales: “site” (10s of km), “bench” nested within site (100s of m), and “location” nested within bench (10s of m). Nutrients varied inconsistently but Chl a was consistently higher at Strawberry Hill. For Chl a, site explained -70% of the variance, whereas bench and location cxplaincd

In this chapter, we review the physical processes that create the mean and variable circulation features along the eastern margins of the ocean basins. Rather than describing the individual systems, we describe the processes and their variability between the systems, dividing the discussion into the low-, mid- and high-latitude regions. We start with the low latitudes, since their signals often move poleward along the coastal wave guides into the midlatitudes, which are the well-known eastern boundary upwelling systems. Our treatment of the higher latitudes is limited to examples from the better-studied NE Pacific Basin (The Alaska Current).

An inversion method is presented that determines mesoscale sea surface currents using satellite altimeter data. The method directly uses geostrophic cross-track velocity components, expands the unknown velocity components with spline functions, and includes weighted constraints for divergence and kinetic energy. The success of this method is measured by the misfit between input and output velocities and depends on the weights of the constraints, the irregular space-time data distribution of the altimeter data, and the nonstationary character of mesoscale oceanic features. Negative effects of the irregular spatial distribution of the altimeter data are overcome by partitioning the larger regions of interest into smaller subareas to make independent inversions. The relatively weak effects of subtrack temporal separations in the presence of slowing evolving fields are addressed by temporal interpolations, which provide the more important benefit of filling in missing data. The procedure is evaluated...

Satellite data from the Geosat altimeter and the Advanced Very High Resolution Radiometer (AVHRR) are used to show the large-scale structure of the surface circulation of the California Current System in summer. These data show the connection between an equatorward jet and temperature front off Oregon that lies within 100 km of the coast, similar to that first observed in the 1960's and 1970's, and a jet that meanders along the convoluted offshore edge of a temperature front off California, as repeatedly observed in the 1980's.

Data from Geosat and TOPEX altimeters are used to infer the structure of the Peru-Chile Countercurrent, a jet that flows from at least as far north as 10 deg S (historical data suggest 7 deg S) to 35 deg - 40 deg S, maintaining its position between approximately 100-300 km offshore. Although the annual mean current cannot be determined from altimeter observations, the nearly antisymmetric patterns in spring and fall, combined with historical observations, suggest that the countercurrent is poleward at most times and is maximum in spring and minimum in fall. Previous studies have linked the offshore countercurrent at 7 deg S to the Equatorial Undercurrent west of the Galapagos Islands, suggesting that the countercurrent is part of a continuous flow that extends from the western equatorial Pacific to the region off Chile between 35 deg - 40 deg S.

[1] Using satellite sea surface height (SSH) and chlorophyll (CHL), the year 2000 is analyzed to characterize the effects of mesoscale circulation patterns on phytoplankton spatial variability in the California Current (CC) off Baja California. Satellite data are combined with and compared to in situ field measurements (chlorophyll-a and hydrographic variables) along vertical alongshore sections located ∼130 km offshore between ∼24.5° −33°N. Monthly average maps of SSH and surface geostrophic velocities depict the characteristics of mesoscale meanders and eddies, which correspond well with the subsurface hydrographic and velocity fields. Satellite-derived pigment (CHL) represent in situ fields in the upper 0–20 m (overall r = 0.53; p < 0.05), but their representation of peak values in Deep Chlorophyll Maxima (DCM) at ∼50 m depth are inaccurate. DCM are traced in all three seasons (January–July), descending from near the surface (north of 31°N) to 50 m over a large extent of the transect to the south, approximately following the 24.7–25.1 isopycnals as they and the isotherms deepen to the south. In January, phytoplankton chlorophyll concentrations in the DCM are relatively uniform, originating during upwelling events that occur farther north, then following the equatorward flow of the CC. During April and July, the discrete maxima in the DCM occur at the centers of cyclonic meanders and the chlorophyll concentrations inside these maxima are enhanced as a result of local coastal upwelling off Baja California. Phytoplankton blooms created by coastal upwelling spread offshore and subduct along the 24.7–25.1 isopycnals, creating the DCM along the inner part of the meandering jet.

[1] We used wavelet analyses of sea surface height (SSH) from >13 years of satellite altimeter data to characterize the variability in mesoscale circulation in the northern California Current (35°N–49°N) and explore the mechanisms of variability. We defined “mesoscale” circulation as features, such as eddies and filaments, which have 50- to 300-km length scales and 4- to 18-week temporal scales. Fluctuations in SSH caused by such features were reflected in wavelet analyses as power (energy). Spatial and interannual variation in mesoscale energy was high. Energy was highest at ∼38°N, decreasing to the north and south. Between ∼43°N and 48°N, energy was low. Zonally, mesoscale energy was highest between ∼125°W and 129°W at latitudes south of 44°N; very little power occurred in the deep ocean west of 130°W. Energy peaked during summer/fall in most years. The primary climate signals were suppressed energy during La Nina and cold years and increased energy during El Nino events. Energy was not strongly linked to upwelling winds, but did correspond to climate indices, indicating that basin-scale processes play a role in controlling mesoscale circulation. We hypothesize that climate affects mesoscale energy through changes in both potential and kinetic energy in the form of density gradients and coastal upwelling winds. The relationship between mesoscale circulation and climate was complex: no single climate, transport, or upwelling index explained the variability. These results are relevant to ecosystem dynamics and the global carbon cycle because mesoscale circulation features deliver nutrient-rich water and coastal organisms from productive upwelling areas to the deep sea.

[1] Satellite-derived data provide the temporal means and seasonal and nonseasonal variability of four physical and biological parameters off Oregon and Washington (41°-48.5°N). Eight years of data (1998-2005) are available for surface chlorophyll concentrations, sea surface temperature (SST), and sea surface height, while six years of data (2000-2005) are available for surface wind stress. Strong cross-shelf and alongshore variability is apparent in the temporal mean and seasonal climatology of all four variables. Two latitudinal regions are identified and separated at 44°-46°N, where the coastal ocean experiences a change in the direction of the mean alongshore wind stress, is influenced by topographic features, and has differing exposure to the Columbia River Plume. All these factors may play a part in defining the distinct regimes in the northern and southern regions. Nonseasonal signals account for ∼60-75% of the dynamical variables. An empirical orthogonal function analysis shows stronger intra-annual variability for alongshore wind, coastal SST, and surface chlorophyll, with stronger interannual variability for surface height. Interannual variability can be caused by distant forcing from equatorial and basin-scale changes in circulation, or by more localized changes in regional winds, all of which can be found in the time series. Correlations are mostly as expected for upwelling systems on intra-annual timescales. Correlations of the interannual timescales are complicated by residual quasi-annual signals created by changes in the timing and strength of the seasonal cycles. Examination of the interannual time series, however, provides a convincing picture of the covariability of chlorophyll, surface temperature, and surface height, with some evidence of regional wind forcing.

The maximum cross correlation (MCC) method of Leese et al. (1971) for estimating sea surface velocities from sequences of satellite images is evaluated by comparing the MCC fields obtained from sequences of AVHRR and CZCS with in situ data and velocity fields calculated with a high-resolution quasi-geostrophic model. The rms differences and vector correlations between the velocity field produced by the MCC method and the model's field are presented. It is shown that much of the difference between the MCC fields and either the in situ data or the model velocity fields can be accounted for by considering physical and biological processes not included in the MCC method. The conditions under which the method is likely to be most successful are discussed.

Los procesos fisicos y biologicos y las actividades humanas determinan los ecosistemas marinos. El manejo futuro de estos valiosos ecosistemas requiere de una aproximacion integrativa que considere las complejas interacciones entre individuos, los procesos oceanograficos que se desarrollan a gran escala espacial y temporal, y la interaccion de los efectos antropogenicos con el medio ambiente. Las costas templadas del oeste de Norteamerica y Sudamerica representan una oportunidad unica para efectuar comparaciones ya que muchos procesos oceanograficos, particularmente la surgencia costera, ocurren en ambas costas. Adicionalmente, numerosos ecosistemas marinos en ambas areas presentan sorprendentes paralelos. La presente revision ofrece una vision general de los procesos oceanograficos dominantes en ambas costas y ofrece ejemplos de ecosistemas y los efectos que la oceanografia, las actividades humanas y las interacciones entre individuos tienen sobre las comunidades marinas

[1] Five years (1997–2002) of northern California Current SeaWiFS ocean color data place cold, low salinity hydrographic anomalies observed in summer 2002 into a larger spatial/temporal context and present their biological ramifications. Monthly mean chlorophyll concentrations were >1.0 mg m−3 larger than the previous 3 year average over the entire shelf from British Columbia (BC) to northern California (CA) in 2001–2002, spatially most extensive over the BC and Washington (WA) shelves but strongest (>2.0 mg m−3) on the southern Oregon shelf. Positive anomalies develop in August 2001 off BC and October 2001 off WA. By October 2002, shelf anomalies are reduced. Offshore, spatially extensive anomalies develop off CA (36°–42°N) in fall 2002, disappearing by December. Concurrent altimeter data show over 1000km of equatorward displacement. The positive chlorophyll anomalies, their spatial patterns and displacement are consistent with advection of subarctic, nutrient-enriched water into the California Current.

[1] Surface transports into the California Current are calculated from TOPEX/POSEIDON altimeter surface height slopes during the 9.5 year period from October 1992–May 2002. These quantify the anomalous onshore and southward displacements of the water column during the 2000–2002 period, which had been hypothesized by others based on anomalous water properties observed in mid-2002 off Oregon. Anomalous eastward transport into the boundary between 52°–54°N occurred first (mid-2000 to mid-2001) followed by eastward transport into the boundary between 50°–52°N in 2001. Equatorward transports during 2001 and 2002 resulted in approximately 800 km of anomalous southward displacements during the 1.5 years prior to the anomalous observations off Oregon. This sequence suggests that both onshore and southward displacement anomalies off British Columbia and the Pacific Northwest contributed to the subarctic characteristics of the water observed off Oregon.

[1] In this article we analyze the momentum and vorticity balances of a numerical simulation of the upwelling circulation off central Chile (34� –40� S) and its response to interannual local wind changes. Our analysis indicates that the path of the upwelling jet is strongly controlled by the bottom topography. This topographic steering causes the jet to separate from the coast at the Punta Lavapie cape (� 37� S). Although the zeroth-order momentum balance is dominated by the geostrophic terms, the circulation is also affected by nonlinear processes, which lead to the formation of large meanders and the shedding of cyclonic eddies north of Punta Lavapie during periods of wind relaxation. The relative contributions of the zeroth-order vorticity balance and the advective terms are also strongly controlled by changes in the coastline geometry and the bottom topography. Vorticity is created along the current axes and transported toward the coast and the Peru-Chile Trench, where it dissipates. South of Punta Lavapie the across-shelf transports are weaker with equatorward flows that are more stable than in the north. Additional numerical simulations

[1] The evolution of oceanographic conditions in the upwelling region off northern Chile (18°–24°S) between 1996 and 1998 (including the 1997–1998 El Nino) is presented using hydrographic measurements acquired on quarterly cruises of the Chilean Fisheries Institute, with sea surface temperature (SST), sea level, and wind speeds from Arica (18.5°S), Iquique (20.5°S), and Antofagasta (23.5°S) and a time series of vertical temperature profiles off Iquique. Spatial patterns of sea surface temperature and salinity from May 1996 to March 1997 followed a normal seasonal progression, though conditions were anomalously cool and fresh. Starting in March 1997, positive anomalies in sea level and sea surface temperature propagated along the South American coast to 37°S. Maximum sea level anomalies occurred in two peaks in May–July 1997 and October 1997 to February 1998, separated by a relaxation period. Maximum anomalies (2°C and 0.1 practical salinity units (psu)) extended to 400 m in December 1997 within 50 km of the coast. March 1998 presented the largest surface anomalies (>4°C and 0.6 psu). Strong poleward flow (20–35 cm s−1) occurred to 400 m or deeper during both sea level maxima and weaker (10 cm s−1) equatorward flow followed each peak. By May 1998, SST had returned to the climatological mean, and flow was equatorward next to the coast. However, offshore salinity remained anomalously high owing to a tongue of subtropical water extending southeast along the Peruvian coast. Conditions off northern Chile returned to normal between August and December 1998. The timing of the anomalies suggests a connection to equatorial waves. The progression of the 1997–1998 El Nino was very similar to that of 1982–1983, though with different timing with respect to seasons.

We present the evolution of oceanographic conditions off the western coast of South America between 1996 and 1999, including the cold periods of 1996 and 1998??9 and the 1997??8 El Nino, using satellite observations of sea level, winds, sea surface temperature (SST), and chlorophyll concentration. Following a period of cold SST and low sea levels in 1996, both were anomalously high between March 1997 and May 1998.

Two methods of estimating surface velocity vectors from AVHRR data are applied to the same set of images and the results are compared with in situ and altimeter measurements. The first technique utilizes an automated feature-tracking algorithm and the second uses an inversion of the heat equation. The two methods were comparable in their degree of agreement with the in situ data, giving velocity magnitudes that were 30 to 50 percent less than drifter and acoustic Doppler current profiler velocities measured at 15 to 20 m depth, with rms directional differences of about 60 degrees.