Longshore Variations Research Articles

Observations of pCO2 in the coastal upwelling off Chile: Spatial and temporal extrapolation using satellite data

Atmospheric and oceanic partial pressures of carbon dioxide and fluorescence were measured underway off the coast of northern Chile in January 1997. Seawater samples were taken for the analysis of nutrient and chlorophyll concentrations at 31 stations. The objectives were to improve the understanding of the biologically induced responses of upwelling processes off the coast of Chile and to assess the air‐sea exchange of CO2 during the austral summer. The cruise sampled within a grid from 22°40S to 24°S extending offshore to 71°52′W during 10–16 January 1997 (survey 1) and 22–27 January 1997 (survey 2). Survey 1 measurements showed relatively uniform hydrographic and chemical properties, except south of the Mejillones peninsula, where colder and fresher water was observed. During the second survey, concurrent satellite imagery showed colder water in a narrow coastal band. The relatively cold and fresh water recorded there suggested that upwelled water originated mainly from subantarctic water rather than from the nutrient‐rich equatorial subsurface water. Onshore‐offshore variability dominated over longshore variability. The offshore subtropical water was characterized by a temperature of 23°C, a salinity of 34.9, and relatively uniform pCO2 around 400 μatm that was mainly temperature driven. Although strong CO2 drawdowns (pCO2 as low as 200 μatm) were located close to the coast following the upwelling events, overall, the region was a source of CO2 to the atmosphere. A pCO2 algorithm was constructed using the cruise data of sea surface temperature (SST) and salinity (S). Synthetic salinity was calculated from S‐SST relationships determined for survey 2 and used with advanced very high resolution radiometer SST to calculate pCO2 over the cruise area, weekly, from January to March. European Centre for Medium‐Range Weather Forecasts wind speeds were used to calculate the CO2 flux in the upwelling off Chile (22°S–29°S, 68°W–73°W). The region was a source of CO2 flux of 1.6 mmol m−2 d−1 from 1 January to 25 March 1997.

Standing edge waves on a pocket beach

Field measurements of edge waves obtained on a narrow pocket beach are described. The beach (named Usgo) is located on the north coast of Spain immediately to the west of the city of Santander and is exposed to the Atlantic Ocean. The edge wave field on this beach is analyzed utilizing data from a longshore array of current meters located in about 3 m of water depth. Frequency spectra of longshore velocities display several significant peaks, suggesting that the edge wave field on this pocket beach consists of several dominant modes. This is in contrast to observations on open coastal beaches [e.g., Oltman‐Shay and Guza, 1987], which show the existence of a broad‐banded edge wave field. We isolate four frequency peaks and examine the longshore variation of the motions at these frequencies and find convincing evidence of a nodal structure. Utilizing the measured bathymetry, we compute the cross‐shore profiles and theoretical wavelengths of edge waves at the dominant frequencies using a numerical solution of the shallow water equations by Howd et al. [1992]. We find that edge waves at these frequencies are theoretically confined between the headlands since their amplitudes decay to insignificant levels within a cross‐shore distance that is less than the offshore extent of the headlands. In addition, assuming perfect sidewall reflections, the theoretical nodal locations closely correspond to those inferred from the measurements. We conclude that discrete standing edge waves resulting from resonances related to the longshore width of the beach are present on Usgo Beach.

Steep beach morphology changes due to energetic wave forcing

The three-dimensional variability of the sub-aerial beach is examined for Waimea Bay, Hawaii, a steep-slope pocket beach subject to energetic winter swell events. The beach is mapped using 32 Real-Time Kinematic Global Positioning System (RTK-GPS) surveys collected from March 1996 to July 1997. The survey method provides 4 m horizontal spacing and 2–3 cm vertical accuracy. The primary morphology change is the episodic removal and re-establishment of a foreshore dune during the winter swell season. The average sand volume flux between surveys reaches −8 and 4 m 2/day during peak erosion and accretion periods. The sand volume of the sub-aerial beach is found to be highly correlated (0.96) with the position of the shoreline. Longshore variations in morphology include beach cusps with typical peak to trough amplitudes of 0.5–1.5 m and longshore wavelengths of 30–70 m. The relationships between the energetic swell forcing and the volume and flux of sand on the sub-aerial beach are examined. The highest correlation (−0.88) is found between the total sand volume and the wave energy flux after the latter is filtered following Wright et al. [Wright, L.D., Short, A.D., Green, M.O., 1985. Short-term changes in the morphodynamic states of beaches and surf zones: an empirical predictive model. Mar. Geol. 62, 339–364]. The filter is effective at capturing slow accretion phases following energetic erosion events.

Longshore patterns of distribution of macroinfauna on a Uruguayan sandy beach:an analysis at different spatial scales and of their potential causes

Spatial distribution of macrofaunaalong the longshore axis was studied on an exposed (Uruguayan) sandybeach in order to assess (1) its dependence on beach topography,and (2) the validity to extrapolate local distribution patterns to largerspatial scales (i.e. km). The distribution of the isopods Excirolanaarmata and Excirolana braziliensis, the sand crab Emeritabrasiliensis and several species of insects was analyzed at 3spatial scales. A grid sampling was used at small scale(intersample distance: 4 m; extension sampled: 30 to 40 m), atransect design at meso scale (intersample distance 4 to 20 m;extension sampled: 100 to 120 m), and random sampling at largescale (intersample distance: 100 m; extension sampled: 3000 m).Spatial distribution at small and meso scales were describedusing autocorrelation functions, and tested for effects oftopography at meso and large scales using ANOVA and pairedt-tests. We found that at small and meso scales the distribution ofE. armata and E. brasiliensis was patchy and affected by cusptopography. At large scales, the effect of cusp topography wasrestricted to E. armata. E. armata and E. brasiliensis showedlarge-scale aggregations, and E. braziliensis and insects showedlarge-scale patchiness associated with longshore variability insediment water content and dune characteristics. We conclude thatcusp topography affects longshore distribution patterns, and that itis not valid to extrapolate local longshore distribution to largerscales for every species. We suggest that different processesaffecting spatial distribution must be operating at different scales.At small scales, patterns of distribution may be affected by swashtransport of food and/or organisms, involving factors such as beachtopography, swash and animal movements. At larger scales, inaddition to larval and food supply, sediment transport by the windwould play an important role. Spatial patterns of sand transport bythe wind may be affected by longshore changes in vegetationcover on the dune field. We further suggest that there may be a linkbetween the beach and the dune habitats operating at large spatialscales.

Effects of Freshwater Discharge in Sandy Beach Populations: The Mole Crab Emerita brasiliensis in Uruguay

Sandy beaches are ecosystems which are heavily affected by human activities. An example of this is freshwater discharges, which are known to change salinity, temperature and nutrient regimes and degrade nearshore environments. However, the effects of this kind of disturbance on sandy beach fauna have been little studied. This paper reports the spatial effects of a man-made freshwater canal discharge on the population structure, abundance and reproductive characteristics of the sandy beach mole crab Emerita brasiliensis. Along the 22km of sandy beach sampled, the mole crab showed a marked longshore variability in population structure and abundance. Abundance of different population components (juveniles, males, females and ovigerous females) significantly decreased towards the canal. Population structure by sex and size, individual weight, fecundity and female maturity patterns at size also displayed a non-linear response to the distance from the freshwater discharge. Only the size structure of males did not follow this pattern. For males, spatial heterogeneity enhanced the detection of density-dependence at less disturbed sites. The authors conclude that artificial freshwater discharges could significantly influence the distribution, abundance and life-history traits of the biota of sandy beaches, and that further study of these ecosystems should include human activities as important factors affecting spatial and temporal trends. The need to consider different spatial and temporal scales in order to detect the effect of anthropogenically-driven impacts in sandy beach populations is stressed.

Morphosedimentary evolution of a delta-sourced, drift-aligned sand barrier–lagoon complex, western Bight of Benin

The coast of eastern Ghana and Togo is bounded by a major Holocene sand barrier complex hinged on the Volta Delta to the west and subject to high rates of longshore sand drift (1–1.5×10 6 m 3/yr). In spite of its proximity to this major deltaic sediment source, this barrier system shows marked longshore variations in progradation following the middle Holocene eustatic stillstand. It is a `hybrid' system in terms of internal facies composition and plan-view morphology, in that it has evolved from an essentially regressive to a stationary (synonymous with cessation of progradation) system. Both transgressive and barrier-inlet facies have also developed through time and space. These temporal and spatial changes in patterns of development reflect variations in longshore sand transport and deposition over the last 5000 years. Such variations have been controlled by sediment supply from the Volta, by antecedent topography, by lagoonal and river drainage, by sediment cell development and maturation, and in the very recent past, by anthropogenic perturbation. Barrier progradation in the western Bight of Benin diminished considerably or ceased probably as early as 3400 yr B.P. as a single major equilibrium `drift aligned' bight cell matured, permitting transport of Volta sand toward the rest of the eastern bight in Benin and Nigeria. The eastward longshore supply from the Volta has involved both direct inputs of upland-derived sand by the Volta river channel and reworking of nearshore deltaic deposits. A recent reduction in direct fluvial supply, exacerbated by the Akosombo Dam, completed in 1961, has induced a wave of erosion of the downdrift delta-mouth barrier and shoreface deposits to fulfil the strong drift requirements. In Togo, construction of a deepwater port in 1967 has also affected the barrier system. Both of these changes have had considerable impacts on longshore sediment dynamics. The most significant impact has been segmentation of the former unique sediment cell characterising the 400-km-long Bight of Benin coast, resulting in differential longshore erosion, progradation or equilibrium. These changes have also induced new patterns of barrier behaviour that include transgressive and regressive dynamics at various locations alongshore.

Coastal retention and longshore displacement of meroplankton near capes in eastern boundary currents: examples from the California Current

Nearshore larval retention mechanisms influence the dispersal and recruitment patterns for a wide variety of meroplanktonic species in eastern boundary regions. Areas of coastal larval retention associated with capes in eastern boundary currents provide important spatial structure to coastal populations of fish and invertebrates through their influence on longshore settlement variability. Some patterns observed in the northern California Current for three meroplanktonic species groups (crabs, sea urchins and rockfish) relative to two such apparent retention features are synthesized. It is found that spatial variability in settlement of crabs is predictable at the scale of headlands. Apparent timing of upwelling intermittency and variability on weekly time-scales, as indicated by temperature change, is critical to interannual settlement variability. The average magnitude of upwelling, measured by an upwelling index, is by comparison a poor predictor of interannual settlement variability. Distribution of planktonic larvae relative to a nearshore retention feature is dependent on taxon. These nearshore retention features may act as reservoirs for some taxa or as conduits to the coast for others, likely depending on larval behaviour, timing and cross-shelf location of release relative to upwelling features. The longshore variability in recruitment created by the above patterns can result in differences in subpopulation productivity. For example, strength of a cohort of sea urchins varies longshore in accordance with proximity to retention features.

Population dynamics and management implications of larval dispersal

Strong advective fields in coastal shelf ecosystems, particularly in eastern boundary currents, lead to significant longshore dispersal of the larval phase of meroplanktonic benthic invertebrates. Field observations of larvae and settlement in the California Current by recent workers are an example of the increasing research on the biological/physical mechanisms underlying larval transport. In particular, these studies identify physical/biological interactions that control the spatial distribution of larvae settling successfully. The current study demonstrates how the results of such studies contribute to (1) better understanding of population dynamics, and (2) better population management, using the cyclic covariability in the Dungeness crab Cancer magister population as an example of the former and management of the red sea urchin Strongylocentrotus franciscanus population as an example of the latter. Earlier modelling studies have shown that dispersal influences the stability and synchrony of variability in metapopulations such as the Dungeness crab, and that the spatial scale of covariability is roughly the scale of dispersal. The mechanism identified by recent research implies that the spatial scale of dispersal should be the distance between promontories in the California Current, roughly 100–200 km. Analysis of covariability between time-series of recruitment at different locations along the coast confirm that this is the spatial scale of longshore variability in the Dungeness crab. The spatial pattern in red sea urchin settlement caused by the identified mechanism provides: (1) the basis for spatially explicit management, and (2) an explanation for the observed spatial variability in the degree of overfishing. Research on larval dispersal is also providing the information necessary to design spatially explicit management strategies involving either permanent or temporary fishery closures. Both population dynamics and management require further research to describe the origins of larvae and the early larval phase, in addition to the transport just before settlement.

Effects of human activities on long-term trends in sandy beach populations:the wedge clam Donax hanleyanus in Uruguay

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 123:73-82 (1995) - doi:10.3354/meps123073 Effects of human activities on long-term trends in sandy beach populations: the wedge clam Donax hanleyanus in Uruguay Defeo O, de Alava A A long-term analysis of the structure of a bivalve population consisting of the wedge clam Donax hanleyanus is described for an exposed temperate sandy beach of Uruguay. The potential effects of human harvesting on the sympatric bivalve Mesodesma mactroides (yellow clam) and of salinity were analyzed through time and space (longshore variation). Inter- and intra-annual fluctuations of the different population components (recruits, juveniles and adults) were detected. D. hanleyanus showed uneven periods of abundance, with the occurrence of peaks of different magnitude that appeared related to fluctuations in the fishing effort targeting on the yellow clam. D. hanleyanus showed a marked longshore variability in population structure and abundance along the 22 km of sandy beach sampled. Spatial variations in salinity and also in the amount of fishing effort exerted on M. mactroides seem to be key factors in explaining this variation. This study suggests that further research on sandy beach populations should include human activities as important factors affecting long-term trends. Donax . Bivalves . Sandy beach . Long-term . Human impact . Uruguay Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 123. Publication date: July 20, 1995 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1995 Inter-Research.

Steady, frictionally modified wind and current forced shelf circulation: application to Vancouver Island

This paper examines the steady barotropic frictionally controlled circulation over a linear shelf which has an abrupt change in width. The model allows the net longshore transport to be specified and includes forcing due to: (1) flow through a gap in the coastline located along the discontinuity; and (2) longshore wind stress. Rapid longshore variations in the flow occur in the neighbourhood of the shelf width discontinuity and therefore both the cross-shelf and long-shore components of bottom friction must be retained. These give rise to a vorticity equation of elliptic character, in contrast to the parabolic “arrested topographic wave equation”. A “shadow zone” is produced on the wide shelf, adjacent to the shelf width discontinuity, in response to a uniform longshore wind stress. Within the shadow zone the fluid is almost stagnant. As friction increases, greater cross-isobath flow occurs, which reduces the area of the shadow zone. A combination of flow through the strait and longshore wind stress can generate complicated flow patterns in which eddies are ubiquitous. A combination of prescribed non-zero net poleward longshore transport and a uniform longshore wind stress generate a nearshore flow which is equatorward-poleward when the wind is directed equatorward-poleward. Further, the axis of the poleward longshore current migrates towards the shelf edge in response to an equatorward longshore wind stress of increasing magnitude. Seasonal variations in the nearshore flow off Vancouver Island, described by Hickey [(1979) Progress in Oceanography, 8, 191–279] and Freeland et al. [(1984) Atmosphere-Ocean, 28, 288–302] can be qualitatively reproduced by this simple method.

Holocene Coral Reef Terraces and Coseismic Uplift of Huon Peninsula, Papua New Guinea

As many as six levels of emerged Holocene coral terraces occur along 40 km of coastline on the Huon Peninsula, Papua New Guinea, recording uplift history since culmination of the postglacial transgression. The Holocene reef crest, ca. 6000 yr B.P., is tilted down to the northwest, parallel to the coast and concordant with the deformation of the last interglacial coral reef terrace, and descends from 23 to 12 m in the study area. The pattern and rate of deformation have been uniform in the late Quaternary because average uplift rates have remained the same since the last interglaciation. The Holocene terraces described here are erosional features with regressive encrusting corals, developed upon the Holocene transgressive reef. The multiple levels represent episodic, probably coseismic uplift, which has occurred repeatedly in the last ca. 6000 yr. Significant longshore variation in the age of the lowest terrace, from 1700 to 2500 yr B.P., suggests independent coseismic uplift on different sectors of the coast. This is supported by age-height relationships of the higher Holocene terraces. Nonlinear uplift during the Holocene, with recurrence intervals increasing toward the present, is clearly recorded by the regressive terraces in each subregion. Some of the Holocene regressive terraces grade laterally into fluvial terraces capped with debris-flow deposits, probably reflecting seismically triggered mass movement.

Irregular Wave Setup and Run‐up on Beaches

The one-dimensional equations of mass, momentum, and energy are derived from the two-dimensional continuity and Reynolds equations in order to elucidate the approximations involved in these one-dimensional equations, which have been used previously to predict normally incident wave motions on coastal structures and beaches. The numerical model based on these equations is compared qualitatively with the wave setup and swash statistics on a moderately steep beach with a nearshore bar. The numerical model is shown to predict the irregular wave transformation and swash oscillation on the barred beach, at least qualitatively. The computed setup and swash heights are found to follow the lower bound of the scattered data points partly because of the neglect of the longshore variability on the natural beach and low-frequency components in the specified incident wave train. A more quantitative comparison is also made with the spectrum of the shoreline oscillation measured on a 1:20 plane beach, for which the corresponding wave spectrum was given. The numerical model is shown to predict the dominant low-frequency components of the measured spectrum fairly well.

Patterns of nearshore sediment transport along the Nile Delta, Egypt

The nearshore sediment-transport system along the Nile Delta has been determined from the response of beaches to the construction of engineering structures, from the forms of geomorphological shoreline features, from large-scale changes in shoreline orientations due to erosion and accretion, and from longshore variations in beach-sand mineralogy and grain sizes. The analyses reveal local patterns of erosion and accretion that have resulted from the interruption of the longshore sediment transport by jetties and groins as well as the major erosion of the promontories adjacent to the mouths of the Rosetta and Damietta branches of the Nile River, brought about by the cutoff of the supply of river sand by construction of the High Aswan Dam. Major zones of shoreline accretion are positioned to the east of the eroding promontories, demonstrating that there are strong longshore gradients in the quantities of the eastward sand transport. The variation east of the Rosetta Branch has been quantitatively evaluated from the patterns of erosion and accretion, based on sediment-continuity considerations. A similar delta-wide comparison is made between the patterns of longshore sediment movements found in this study and those calculated by others from wave-refraction diagrams. Based on the various lines of evidence for beach erosion, longshore sediment transport and shoreline accretion, four nearly self-contained cells have been identified in the littoral zone of the Nile Delta: Abu Quir Bay, the eastern flanks of the Rosetta and Damietta Promontories, and the Burullus central-delta region.

The spatial and temporal variability of sand bar morphology

The spatial and temporal variability of nearshore sand bar morphology is quantified using a unique data set spanning 2 years. The data consist of daily time exposure images of incident wave breaking on an open coast sandy beach which may be used to infer bar morphology (Lippmann and Holman, 1989). The morphology in each image is classified into an eight state morphologic scheme in which bars are uniquely defined by four independent criteria. The most frequently observed morphologies are the longshore‐periodic (rhythmic) bars, observed in 68% of the data. Linear bars occur under highest wave conditions and are unstable (mean residence time ≈ 2 days). Shore‐attached rhythmic bars are the most stable (mean residence time ≈ 11 days) and generally form 5–16 days following peak wave events. Non‐rhythmic, three‐dimensional bars are very transient (mean residence time ≈ 3 days). Eighty‐seven percent of transitions to lower bar types (defined in text) occurred one state at a time, supporting our selection of the ordering of states, and suggesting the suitability of a sequential morphology model. Transitions to higher states occurred under rising wave energy and were evenly spread among the possible higher states, with more substantial changes in morphology resulting from larger wave increases. This suggests that up‐state, erosional transitions (based on offshore bar migration) are better described by an equilibrium model where response is better correlated with incident wave energy than with preceding morphological state. Time exposure images were also digitized to yield quantitative estimates of bar crest location as a function of longshore distance. Principal component analysis was used to decompose bar position into two‐dimensional (linear) and three‐dimensional (longshore variable) components. Cross‐shore (linear) bar position ranges ±50 m about the 2‐year mean (27 m standard deviation) and dominates bar variability (74.6%). Three‐dimensional bar structure accounts for ∼14% of the variance (12 m standard deviation). Changes in incident wave height precede cross‐shore bar migration by less than 1 day. Changes in longshore variability are inversely correlated to changing wave conditions, with bar morphology becoming linear rapidly during storms (on time scales of less than 1 day). Evolution to significantly three‐dimensional structure typically occurs over 5–7 days following peak wave events.

Migration of swash zone, step and microtopographic features during tidal cycles on an estuarine beach, Delaware Bay, New Jersey, U.S.A.

A time-series analysis of changes in surface elevation on the foreshore of an estuarine beach was conducted to compare movement of topographic features in the swash and breaker zones with results derived from study of ocean beaches. Wave heights on the upper foreshore during the field study averaged 0.15 m, with an average period of 2.4 s. The average height of the beach step was 21 mm. Smaller elevation changes, up to 12 mm in height, occurred at 10–15 min periods. There were more small elevation changes, greater longshore variations in these changes, and greater variation in the form of the beach step during the rising tide than during the falling tide. The variation in the small elevation changes and the beach step are attributed to greater short-term fluctuations in beach saturation during rising tides, causing greater variability in the velocity of swash and backwash.

Storm wave induced mortality of giant kelp, Macrocystis pyrifera, in Southern California

The storm-related mortality rates of adult Macrocystis pyrifera in a Southern California giant kelp forest were determined over several winter storm seasons and compared with the hydrodynamic attributes of the most energetic storms. The data include stormy and relatively benign years and an exceptional storm which resulted in almost total destruction of a major Macrocystis forest. High orbital velocities (associated with large, high frequency waves), the presence of breaking waves, and entanglement by drifters were found to increase mortality through stipe breakage or holdfast failure. Longshore variability in wave intensity was found to affect kelp mortality rates. The data suggest that wave breaking may be an important factor in determining the inner boundary of the kelp bed.

THREE DIMENSIONAL FLOW PROFILES ON LITTORAL BEACHES

The problem of combined cross-shore and longshore currents generated by waves in and around a surf zone is considered in its full three-dimensional formulation. The equations for the two current components are decoupled and it is found that for a cylindrical coast with no longshore variations the longshore current variation with depth and distance from the shoreline satisfies a Poisson equation. This equation is solved by a perturbation method and it is shown that the longshore velocities are always larger than the velocities found by classical theory. In the simple uncoupled case, the full 3-D current profile is constructed by combining the results with cross - shore velocities determined in previous publications. Also, the total velocities are larger than velocities found from simple depth averaged models.

Coastal Erosion and Engineering Structures: The Oregon Experience

Seawalls and riprap revetments are used on the Oregon coast to protect properties threatened during erosion of seacliffs and sand spits. The erosion processes involve the combined effects of swash from storm waves and embayments cut through the berm by rip currents. Most shore protection structures on the Oregon coast have not been designed by engineers, and therefore commonly do not follow sound design practices. They often are grossly overbuilt and do not take into consideration the processes of erosion and beach morphology. Particularly difficult is the protection of high cliffs where the structures can defend only the toe of the slope. Questions have been raised as to whether the structures might contribute to erosion of the beach and adjacent unprotected properties. Although such adverse impacts have been demonstrated in our laboratory wave-basin experiments, the role of rip currents in Oregon-coast erosion produces significant longshore variability in property losses and tends to mask impacts by structures. We are presently monitoring beach-topography changes adjacent to seven structures, including both seawalls and riprap, with the objective of determining whether the structures do cause erosion.

Tides on continental shelves with longshore topographic variations

In this note, present theory on the effect of continental shelves on tides is extended to include longshore variations in bottom topography. Existing formulae for the cross-shelf variation in tidal elevation and currents are corrected to include the effect of a widening or narrowing shelf. Given the coastal tide, it is shown that the offshore behaviour of tidal height and currents is strongly dependent on whether the shelf widens or narrows in the direction of increasing coastal tidal amplitude. In the absence of longshore gradients in coastal amplitude and phase, the effect of longshore bathymetric gradients is to increase the amplitude of the longshore component of tidal current. It is also shown that semidiurnal tides may be affected differently from diurnal tides, particularly in relation to coastal amplification.

Spatial and temporal variability of phytoplankton pigment off northern California during Coastal Ocean Dynamics Experiment 1

The distribution of phytoplankton pigment during the 1981 Coastal Ocean Dynamics Experiment (CODE) was examined using coastal zone color scanner (CZCS) imagery. Twenty‐five CZCS images were of sufficient quality to be used for further analysis. The distribution of the data was dependent on the patterns of wind forcing, with the data set biased toward regions and periods of strong equatorward winds. The weighted mean pigment image and the coefficient of variation image showed three clearly defined regions: a coastal region approximately 100 km wide, an offshore region of low pigment and low variability, and two filaments that extended several hundred kilometers offshore. Coastline topography and longshore variations in wind forcing are important in the coastal region. The offshore filaments appear to be related to the patterns of wind stress curl and perhaps explain the large‐scale patterns of Zooplankton biomass in the California Current. Analysis of the temporal variability delineated three nearshore areas: a northern region off Cape Mendocino a central region near the CODE Central line, and a southern area off San Francisco. The width of the coastal zone seemed to vary with a 5‐ to 6‐day cycle. During two equatorward wind events, the patterns of temporal variability were consistent with the patterns of wind forcing revealed by empirical orthogonal function decomposition.