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.

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Data from the Coastal Transition Zone (CTZ) experiment axe used to describe the velocity fields and water properties associated with cold filaments in the California Current. Combined with previous field surveys and satellite imagery, these show seasonal vaxiability with maximum dynamic height ranges and velocities in summer and minimum values in late winter and early spring. North of Point Arena (between 39øN and 42øN) in spring-summer the flow field on the outer edge of the cold water has the chaxacter of a meandering jet, carrying fresh, nutrient-poor water from farther north on its offshore side and cold, salty, nutrient-rich water on its inshore side. At Point Arena in midsummer, the jet often flows offshore and continues south without meandering back onshore as strongly as it does faxther north. The flow field south of Point Arena in summer takes on more of the chaxacter of a field of mesoscale eddies, although the meandering jet from the north continues to be identifiable. The conceptual model for the May-July period between 36 øN and 42øN is thus of a surface jet that meanders through and interacts with a field of eddies; the eddies are more dominant south of 39øN, where the jet broadens and where multiple jets and filaments axe often present. At the surface, the jet often separates biological communities and may appeax as a barrier to cross-jet transport, especially north of Point Arena early in the season (March-May). However, phytoplankton pigment and nutrients are carried on the inshore flank of the jet, and pigment maxima axe sometimes found in the core of the jet. The biological effect of the jet is to define a convoluted, 100 to 400-km-wide region next to the coast, within which much of the richer water is contained, and also to carry some of that richer water offshore in meanders along the outer edge of that region.

Seasonal cycles of coastal wind stress, adjusted sea level (ASL), shelf currents, and water temperatures off the west coast of North America (35øN to 48øN) are estimated by fitting annual and semiannual harmonics to data from 1981-1983. Longer records (9-34 years) of monthly ASL indicate that these two harmonics adequately represent the long-term monthly average seasonal cycle and that the current measurement period is long enough to estimate the seasonal cycles. We characterize the differences between fall/winter and spring/summer as follows: For fall/winter, monthly mean winds north of 35øN are northward for 3-6 months (longer in the north than in the south); south of 35øN, the mean winds are near zero or weakly southward; monthly mean alongshore currents are northward over midshelf and shelf break at all locations sampled at depths of 35 m and deeper and are associated with high coastal sea levels and relatively warm water temperatures. For spring/summer, monthly mean wind stresses are southward at all latitudes for 3-6 months (longer in the south than in the north), sea levels are low, and water temperatures are relatively cool; monthly mean currents at 35 m depth over the shelf are southward for 1-6 months (longer at the shelf break than over midshelf and longer in the north than in the south), while the deeper currents are less southward or northward. The magnitudes of the seasonal cycles of all variables are maximum between approximately 38øN and 43øN, generally decreasing slightly to the north and greatly to the south. At each location the seasonal cycle of the alongshore current from 35 m depth at midshelf leads the sea level slightly and both lead the wind stress and temperatures by 1-2 months. The seasonal cycles of all variables show a south-to-north progression (south leads north by 1-2 months). At 48øN, annual mean currents at 50 m depth over the shelf break oppose the annual mean wind (northward wind and southward current). Similarly, at 35øN, annual mean currents at 35 m depth over both midshelf and shelf break are opposed to the annual mean wind (southward wind and northward current). From 35øN to 43øN, both summer and winter regimes are dominated by strongly fluctuating currents. 1507 1508 STRUB ET AL.: SEASONAL CYCLES OVER THE WESTERN U.S. CONTINENTAL SHELF

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 <20%. For nutrients, site and bench explained most of the variance, but neither was consistently more important. The data tentatively suggest that nutrient levels are weakly related to the between-site ecological differences. In addition to the between-site differences, Chl a changed seasonally, with maximum levels in summer. For nutrients, temporal changes were more complex, with highest levels tending to occur in late summer and autumn. No nutrient, howcvcr, was scarce enough at either site to limit phytoplankton growth, with the possible exception of nitrate in June. These results were consistent with the hypothesis that nearshore phytoplankton standing stock, a bottom-up factor, could underlie differences in rocky intertidal community structure.

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.

Abstract. Over 30 years of hydrographic data from the northern Chile (18øS-24øS) upwelling region are used to calculate the surface and subsurface seasonal climatology extending 400 km offshore. The data are interpolated to a grid with sufficient spatial resolution to preserve crossshelf gradients and then presented as means within four seasons: austral winter (JulySeptember), spring (October-December), summer (January-March), and fall (April-June). Climatological monthly wind forcing, surface temperature, and sea level from three coastal stations indicate equatorward (upwelling favorable) winds throughout the year, weakest in the north. Seasonal maximum alongshore wind stress is in late spring and summer (DecemberMarch). Major water masses of the region are identified in climatological T-S plots and their sources and implied circulation discussed. Surface fields and vertical transects of temperature and salinity confirm that upwelling occurs year-round, strongest in summer and weakest in winter, bringing relatively fresh water to the surface nearshore. Surface geostrophic flow nearshore is equatorward throughout the year. During summer, an anticyclonic circulation feature in the north which extends to at least 200 rn depth is evident in geopotential anomaly and in both temperature and geopotential variance fields. Subsurface fields indicate generally poleward flow throughout the year, strongest in an undercurrent near the coast. This undercurrent is strongest in summer and most persistent and organized in the south (south of 21øS). A subsurface oxygen minimum, centered at ~250 m, is strongest at lower latitudes.Low-salinity subsurface water intrudes into the study area near 100 m, predominantly in offshore regions, strongest during summer and fall and in the southernmost portion of the region. The climatological fields are compared to features off Baja within the somewhat analogous California Current and to measurements from higher latitudes within the Chile-Peru Current system.

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