Wind-driven coastal ocean upwelling supplies nutrients to the euphotic zone near the coast. Nutrients fuel the growth of phytoplankton, the base of a very productive coastal marine ecosystem [Pauly D, Christensen V (1995) Nature 374:255-257]. Because nutrient supply and phytoplankton biomass in shelf waters are highly sensitive to variation in upwelling-driven circulation, shifts in the timing and strength of upwelling may alter basic nutrient and carbon fluxes through marine food webs. We show how a 1-month delay in the 2005 spring transition to upwelling-favorable wind stress in the northern California Current Large Marine Ecosystem resulted in numerous anomalies: warm water, low nutrient levels, low primary productivity, and an unprecedented low recruitment of rocky intertidal organisms. The delay was associated with 20-to 40-day wind oscillations accompanying a southward shift of the jet stream. Early in the upwelling season (May-July) off Oregon, the cumulative upwelling-favorable wind stress was the lowest in 20 years, nearshore surface waters averaged 2°C warmer than normal, surf-zone chlorophyll-a and nutrients were 50% and 30% less than normal, respectively, and densities of recruits of mussels and barnacles were reduced by 83% and 66%, respectively. Delayed early-season upwelling and stronger late-season upwelling are consistent with predictions of the influence of global warming on coastal upwelling regions.climate variability ͉ coastal marine ecosystems ͉ coastal ocean upwelling ͉ marine ecology E quatorward winds along the eastern boundaries of the world's oceans drive offshore surface Ekman transport and the upwelling of cold, nutrient-rich water into the euphotic zone near the coast. These nutrient pulses stimulate high phytoplankton production, which, in turn, supports a rich coastal marine ecosystem and productive fisheries (1). Examples of such dynamics include the California Current, the Humboldt Current, the Benguela Current, and the Canary Current (2).The strength and extent of the seasonal cycle in upwellingfavorable winds varies along the U.S. west coast. In the northern California Current Large Marine Ecosystem (CCLME), there is a strong seasonal cycle with upwelling-favorable winds, the appearance of cold, saline, nutrient-rich water near the coast, and equatorward currents over the shelf occurring after a spring transition (3). Alongshore winds in the northern CCLME are more variable than those farther south because they are more frequently influenced by eastward-traveling Gulf of Alaska low-pressure systems. The intermittent cessation of upwelling-favorable winds is called relaxation and plays an important role in coastal circulation and the recruitment of marine organisms † † . The timing of the spring transition and the total amount of upwelling-favorable winds during the spring-summer upwelling season have a considerable impact on coastal ecosystem responses. Farther south in the CCLME, winds are more persistently upwelling-favorable and the transition to a more productive spring-su...

The temperature in the coastal ocean off the northeastern U.S. during the first half of 2012 was anomalously warm, and this resulted in major impacts on the marine ecosystem and commercial fisheries. Understanding the spatiotemporal characteristics of the warming and its underlying dynamical processes is important for improving ecosystem management. Here, we show that the warming in the first half of 2012 was systematic from the Gulf of Maine to Cape Hatteras. Moreover, the warm anomalies extended through the water column, and the local temperature change of shelf water in the Middle Atlantic Bight was largely balanced by the atmospheric heat flux. The anomalous atmospheric jet stream position induced smaller heat loss from the ocean and caused a much slower cooling rate in late autumn and early winter of 2011–2012. Strong jet stream intraseasonal oscillations in the first half of 2012 systematically increased the warm anomalies over the continental shelf. Despite the importance of advection in prior northeastern U.S. continental shelf interannual temperature anomalies, our analyses show that much of the 2012 warming event was attributed to local warming from the atmosphere.

An analysis of the structure and transport of the Gulf Stream is undertaken using direct current meter observations from a 13-mooring array deployed near 68øW from June 1988 to August 1990. The analysis is based on a "stream-coordinate" approach, in which velocities are rotated into a local, downstream coordinate frame and averaged according to their relative cross-stream location within the current. The picture so obtained represents the average synoptic structure of the Gulf Stream, rather than the Eulerian-averaged structure in which the current is weakened and broadened by lateral meandering of the current and adjacent recirculations. Many familiar features of the Gulf Stream are reproduced in the analysis, including an asymmetric velocity profile with larger shear on the cyclonic (shoreward) side of the current, an offshore displacement of the velocity core with depth, and a subsurface velocity maximum on the offshore side of the current. Westward recirculations are also seen on both sides of the Gulf Stream. Maximum downstream speeds at the axis of the Gulf Stream reach approximately 2.0 m/s at the surface and 0.7 m/s at 1000 m, roughly twice the corresponding Eulerian-averaged values. The analysis also reveals a deep extension of the Gulf Stream at 3500 rn depth with a width of 130 km and average speeds of 3-4 cm/s. The transport of the Gulf Stream in the stream-coordinate frame is 113 ---8 Sv, approximately 30% larger than the Eulerian-averaged transport of 88 Sv. On the basis of these results and other recent studies the downstream transport increase of the Gulf Stream and the inflow structure to the Gulf Stream are reconsidered. It is concluded that approximately 30 Sv, or over half of the transport increase between Cape Hatteras and 68øW, is fed by inflow from the northern side of the Gulf Stream and that this inflow is concentrated near Cape Hatteras and 68øW, where the Gulf Stream flows steeply across isobaths converging from the north. [Worthington, 1976; Halkin and Rossby, 1985; Hogg, 1983]. Knauss [1969] showed that in the first 1000 km downstream of Cape Hatteras the Gulf Stream transport increases from 65 Sv (1 Sv = 10 6 m3/s) to approximately 150 Sv (at 65øW), an average rate of increase of 8 Sv per 100 km. This large transport, of order 150 Sv, is apparently maintained at least as far as 55øW [Hendry, 1982; Hogg, 1992]. Despite this large increase in transport, hydrographic sections show that the Gulf Stream has a very similar baroclinic structure over this domain, in terms of its horizontal and vertical scales and total density contrast across the current. The evolution of the Gulf Stream downstream of 55øW is not well understood at this time, but near the Grand Banks, there appears to be a distinct change in the character of the Gulf Stream, from a single meandering front to multiple, branching fronts feeding into the Azores and North Atlantic Currents [Krauss, 1986]. The region east of 55øW is also thought to be where most of the detrainment from the Gulf Stream to the bordering recirculati...

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Simultaneously measured Eulerian currents and spatially extensive subsurface temperatures have provided a time series of eight synoptic, three‐dimensional views of the Gulf Stream frontal zone along the Carolina continental margin. Two large‐amplitude meanders were observed to progress through the study area between Charleston and Cape Hatteras during February 1979. Each meander had a vertically coherent, skewed wave‐like subsurface structure. The Eulerian velocity and temperature signatures produced by the meanders at the 250‐m level over the 390‐m isobath reflect this skewness. At a particular instrument, the in‐phase increases in temperature and downstream velocity associated with an approaching meander crest occurred during a longer time interval than did the more rapid decreases in these quantities following the crest's passage. Typically, the downstream velocity component at this level fluctuated from about −20 cm s−1 to near 100 cm s−1, while the cross‐stream component varied approximately ±25 cm s−1 about a near‐zero mean. For a particular meander, the maximum in the offshore velocity component led the downstream maximum in time in a manner typical of progressive wave motions; however, the lead time was always less than one quarter of a meander period implying that u and υ were not in quadrature, as would have been the case for stable waves. The two meanders were observed downstream of the area off Charleston where a seaward deflection of the stream is often found. Subsurface temperature data from February 10, 1979, show that on that date the degree of deflection was greatest near the surface, and that almost no deflection existed within the deeper reaches of the water column. According to later data, the deflection decreased as the meanders progressed alongshore away from the area, suggesting that the vertical structure of the deflection observed on the tenth may have been associated with the late stages of a meander passage. Filaments of warm Gulf Stream water extended southwestward ‘behind’ the crests of the two meanders. The filaments were relatively shallow features, extending from the surface to a depth of a few tens of meters. They were oriented essentially parallel to the bottom contours over the outer shelf and upper slope, and were separated from the main body of the Gulf Stream by cool water. The presence of the cool water between the stream and the filaments at the surface was due to upwelling of water from deep within or below the main stream. Peaks in the time series of vorticity components indicate that maximum cyclonic relative vorticity occurred behind the meander crests, in the leading portion of the trough near where a warm filament joined a meander crest. The meanders may have been initiated upstream of our study area, and then ‘amplified’ by the deflection process off Charleston. Energy flux calculations for the region off Onslow Bay indicate that meander kinetic energy was being converted to mean energy there. It seems likely that the deflection produces meander growth within the 100...

Some of the highlights of an experiment designed to study coastal atmospheric phenomena along the California coast (Coastal Waves 1996 experiment) are described. This study was designed to address several problems, including the cross-shore variability and turbulent structure of the marine boundary layer, the influence of the coast on the development of the marine layer and clouds, the ageostrophy of the flow, the dynamics of trapped events, the parameterization of surface fluxes, and the supercriticality of the marine layer.Based in Monterey, California, the National Center for Atmospheric Research (NCAR) C-130 Hercules and the University of North Carolina Piper Seneca obtained a comprehensive set of measurements on the structure of the marine layer. The study focused on the effects of prominent topographic features on the wind. Downstream of capes and points, narrow bands of high winds are frequently encountered. The NCAR-designed Scanning Aerosol Backscatter Lidar (SABL) provided a unique opportunity to connect changes in the depth of the boundary layer with specific features in the dynamics of the flow field.An integral part of the experiment was the use of numerical models as forecast and diagnostic tools. The Naval Research Laboratory's Coupled Ocean Atmosphere Model System (COAMPS) provided high-resolution forecasts of the wind field in the vicinity of capes and points, which aided the deployment of the aircraft. Subsequently, this model and the MIUU (University of Uppsala) numerical model were used to support the analysis of the field data.These are some of the most comprehensive measurements of the topographically forced marine layer that have been collected. SABL proved to be an exceptionally useful tool to resolve the small-scale structure of the boundary layer and, combined with in situ turbulence measurements, provides new insight into the structure of the marine atmosphere. Measurements were made sufficiently far offshore to distinguish between the coastal and open ocean effects. COAMPS proved to be an excellent forecast tool and both it and the MIUU model are integral parts of the ongoing analysis. The results highlight the large spatial variability that occurs directly in response to topographic effects. Routine measurements are insufficient to resolve this variability. Numerical weather prediction model boundary conditions cannot properly define the forecast system and often underestimate the wind speed and surface wave conditions in the nearshore region.