Surface Pigment Concentrations Research Articles

Drone-based hyperspectral remote sensing of cyanobacteria using vertical cumulative pigment concentration in a deep reservoir

The remote sensing of algal pigments is essential for understanding the temporal and spatial distribution of harmful algal blooms (HABs). In particular, the vertical distribution of cyanobacterial pigment (e.g., phycocyanin (PC)) is critical factor in remote sensing because the diel vertical migration of cyanobacteria may affect the spectral signals according to observational time. Although numerous studies have been conducted on the remote sensing of algal bloom using pigments, few studies considered the vertical distribution of the pigments for the remote sensing of cyanobacteria in inland waters. In this regard, the objective of this study was to develop an improved bio-optical remote-sensing method using in-situ remote-sensing reflectance (Rrs) at different water depths and cumulative PC and Chlorophyll-a (Chl-a) concentrations, which was cumulated from the surface to a 5-m water depth. The results showed that the bio-optical algorithm using surface Rrs and surface pigment concentration was more accurate than that using the subsurface Rrs and surface pigments. The bio-optical algorithm using subsurface Rrs showed the highest R-squared (R2) values (0.87–0.94) in each regression with the cumulative PC concentration from surface to each depth. The regressions between drone-based surface reflectance and cumulative PC concentration for each depth indicated a better performance than those between the reflectance and surface PC concentration; the highest R2 value of 0.82 was obtained from a bio-optical algorithm using drone-based reflectance and a 1.0-m cumulative PC concentration, which was the best-performing algorithm. The PC maps developed using the best bio-optical algorithm accurately described the spatial and temporal distributions of the PC concentrations in the reservoir. This study demonstrates that the application of vertical cumulative pigment concentration and subsurface Rrs measurement in bio-optical algorithms can improve their performance in estimating pigments, and that drone-based hyperspectral imagery is an efficient tool for the remote sensing of cyanobacterial pigments over a wide area.

Continuous and High Transport of Particles and Solutes by Benthos in Coastal Eutrophic Sediments of the Pomeranian Bay

We present results on bioirrigation and reworking of sediments by benthic macrofauna in sediments of the Pomeranian Bay (southern Baltic Sea), that were obtained ~22 years ago. The investigation took place at four stations ranging from 9 – 19 m water depth, which we observed between 1993 and 1995 over the course of 30 months. In order to assess exchange of solutes across and particles from the sediment-water interface with the underlying sediments, we used bromide as ex situ tracer for bioirrigation and chlorophyll a equivalents as in situ tracer for particle reworking. Using models to interpret tracer distributions in the sediment, we compare the magnitudes of small scale, diffusion – like, versus relatively large-scale, non-local, transport modes. Our results indicate a spatial differentiation of the bay: the coastal station most heavily impacted by eutrophication close to the Oder River mouth showed medium reworking and intense bioirrigation combined with lower chlorophyll concentrations throughout the sediment. This contrasts with high surface pigment concentrations at the shallow Oder Bank station, indicating benthic primary production and intense particle mixing.Medium local particle reworking at the northwestern station and medium mean solute transport rates characterized the two deeper stations in the northern Bay. The bromide tracer experiments, which exclusively depict animal activity, showed significant biological solute transport to ~10 cm sediment depth within 3 days. Non-biological transport mechanisms in the field (e.g. resuspension, fishing activity) might additionally affect the in situ tracer chlorophyll a - depth distributions. This tracer, too, indicates mixing within the uppermost 10 cm of the sediment within ~2-3 months. In general, experimentally obtained solute transport constants were higher than most values reported previously (surface : 155 yr-1) and particle reworking was at the high end of reported values as well. Thus, benthic fauna is responsible for an intense bioturbation in Pomeranian Bay. Specifically, high bioirrigation rates were associated with high density and biomass of deep burrowing polychaetes. Recently published rates of particle reworking in the area are on the same order of magnitude as ours obtained two decades ago.This finding is consistent with the species composition which generally remained the same

Are Hotspots Always Hotspots? The Relationship between Diversity, Resource and Ecosystem Functions in the Arctic

The diversity-ecosystem function relationship is an important topic in ecology but has not received much attention in Arctic environments, and has rarely been tested for its stability in time. We studied the temporal variability of benthic ecosystem functioning at hotspots (sites with high benthic boundary fluxes) and coldspots (sites with lower fluxes) across two years in the Canadian Arctic. Benthic remineralisation function was measured as fluxes of oxygen, silicic acid, phosphate, nitrate and nitrite at the sediment-water interface. In addition we determined sediment pigment concentration and taxonomic and functional macrobenthic diversity. To separate temporal from spatial variability, we sampled the same nine sites from the Mackenzie Shelf to Baffin Bay during the same season (summer or fall) in 2008 and 2009. We observed that temporal variability of benthic remineralisation function at hotspots is higher than at coldspots and that taxonomic and functional macrobenthic diversity did not change significantly between years. Temporal variability of food availability (i.e., sediment surface pigment concentration) seemed higher at coldspot than at hotspot areas. Sediment chlorophyll a (Chl a) concentration, taxonomic richness, total abundance, water depth and abundance of the largest gallery-burrowing polychaete Lumbrineristetraura together explained 42% of the total variation in fluxes. Food supply proxies (i.e., sediment Chl a and depth) split hot- from coldspot stations and explained variation on the axis of temporal variability, and macrofaunal community parameters explained variation mostly along the axis separating eastern from western sites with hot- or coldspot regimes. We conclude that variability in benthic remineralisation function, food supply and diversity will react to climate change on different time scales, and that their interactive effects may hide the detection of progressive change, particularly at hotspots. Time-series of benthic functions and its related parameters should be conducted at both hot- and coldspots to produce reliable predictive models.

On the relationship between satellite‐estimated bio‐optical and thermal properties in the Gulf of Mexico

Three years of Sea‐viewing Wide Field‐of‐view Sensor (SeaWiFS) ocean color data were combined with three‐dimensional thermal fields generated by the U.S. Navy's Modular Ocean Data Assimilation System (MODAS) in order to examine the interdependencies between bio‐optical fields and their relationship to seasonal and mesoscale changes in upper ocean thermal structure. The combined data set suggests that the oceanic boundary layer within the Gulf of Mexico may be broadly defined by two seasonally occurring bio‐thermal periods. A winter mixing period, characterized by net heat losses to the atmosphere, deepening of the isothermal layer depth, and annual maxima of satellite‐estimated colored detrital matter (CDM) absorption coefficients and surface pigment concentration, was followed by a thermally stratified period characterized by net surface ocean heating, reduced isothermal layer depths, and annual minima in surface bio‐optical fields. Variability in the interdependencies of ocean color products was used to diagnose an attendant shift in the size‐structure of surface phytoplankton communities as well as identify CDM as the constituent responsible for the majority of blue‐light absorption in Gulf of Mexico surface waters. The mesoscale circulation, as resolved by MODAS thermal fields into cold and warm‐core eddies, appears to significantly modulate the seasonal bio‐optical cycle of CDM absorption and surface pigment concentration. An empirical model was developed to describe CDM absorption as a function of upper ocean thermal energy. The model accounted for nearly half the variance in the satellite‐estimate of this bio‐optical variable. Large mismatches between the model and satellite data implied episodes of shelf water export to the deep Gulf of Mexico.

CZCS chlorophyll patterns in the South Atlantic Bight during low vertical stratification conditions

We examine all available high-resolution Coastal Zone Colour Scanner (CZCS) data for the South Atlantic Bight (SAB), and adjacent Gulf Stream, during low vertical stratification months (October–May, from 1978 to 1986) to investigate the seasonal/long-time variations and the dominant spatial scales and patterns of near surface pigment concentrations. Each CZCS image is divided into four regions and 21 areas, as well as into 24 across- and 21 along-shelf transects. A distinct seasonal cycle is observed everywhere, superimposed to a linear time decay that reached almost 50% by the end of the mission. Mean winter SAB pigment concentrations (1.3 mg m −3) are about 50% greater than spring values (0.8 mg m −3), confirming that winter chlorophyll production represents a significant fraction of the total year's production. Mean pigment concentration (and absolute variability) generally decreases seaward, in winter from 2.2 mg m −3 (1.3 mg m −3) over the inner shelf to about 0.3 mg m −3 (0.3 mg m −3) over the Gulf Stream. Local maxima take place in the inner and middle shelves off all capes, in the northern region separated by some 150 km. High relative pigment variability is observed both along and across-shelf in narrow bands (order 10 km) on the middle and outer shelves (except across-shelf off Charleston). Along-shelf dominant scales of pigment variability increase offshore, from some 50 km in the inner and middle shelves, possibly related to squirt type fingers, to some 90 km in the outer shelf, related to meander-streamer patterns, and up to 170 km in the Gulf Stream, associated to the meanders themselves. High pigment concentrations in the inner shelf appear to be overestimated due to high turbidity water, permanently off the capes and on a seasonal basis (fall/winter maxima) within the inner and middle shelves. There are instances of squirts that emanate from all along the coast, although the dominant feature in the northern inner and middle shelves are along-shelf filaments stretching from the capes. Cold air outbreaks are responsible for the frequent vertical redistribution of chlorophyll and nutrients, which may originally be associated to Gulf Stream intrusions, and cause that winter productivity is not nutrient-limited.

Reflectance at 610 nanometers estimates oxymyoglobin content on the surface of ground beef

This research evaluated the utility of direct (K/S 610÷K/S 525) and indirect (100%−% deoxymyoglobin+% metmyoglobin) methods for estimation of oxymyoglobin (OMb) on the surface of ground beef. Direct estimation was highly correlated to visual color scores ( r=−0.93), indirect determination of OMb ( r=0.98), and % metmyoglobin ( r=−0.98). Since indirect OMb was based partially on % deoxymyoglobin, which was poorly correlated to visual color scores, the accuracy of the subtraction method may be limited. Both direct and indirect methods produced similar variability when estimating OMb. All calculations for pigment forms produced outliers, which were adjusted to 0 and 100% to more precisely represent surface pigment concentrations. This work suggests that the K/S 610÷K/S 525 method is accurate and repeatable and can be used to quantify surface OMb concentration and discoloration of ground beef.

The response of phytoplankton production to periodic upwelling and relaxation events at the Iberian shelf break: estimates by the 14C method and by satellite remote sensing

The primary productivity of the NW Iberian margin has been determined by a combination of 14C incorporation experiments on natural phytoplankton assemblages and satellite remote sensing with the ocean colour sensor, SeaWiFS. The approach to the field determination of phytoplankton production was Eulerian, involving measurements on a fixed grid of stations covering the region from 41°30′N to 43°00′N and 09°00′W to 10°30′W. Three different laboratories made primary production measurements over a 3-year period. Each group used variations of the 14C method—in situ incubations and two modelling approaches based on P– E parameter derivation. An intercalibration experiment showed acceptable agreement between the three estimates. Measurements by the three groups on eight cruises have been merged to provide estimates of regional productivity. However, the temporal coverage of the data was too limited to provide robust seasonal estimates since few experiments were done in the autumn and winter months. A second approach to the estimation of primary production utilised surface pigment concentrations derived from satellite remote sensing. Two models were used. Firstly, an empirical relationship was found between depth-integrated primary production and surface chlorophyll concentration, which explained 78% of the variance in the production estimates. The second approach used a semi-analytical model which incorporates irradiance and temperature as well as chlorophyll-derived parameters. Both models have been applied to SeaWiFS-derived, surface chlorophyll concentrations to estimate primary production during 1998, 1999 and 2000 for three regions—the shelf, the slope and the open ocean of the region of study. Using the semi-analytical model, the mean primary production for the 3 years is estimated to be 319 g C m −2 year −1 for the shelf, 280 g C m −2 year −1 for the slope and 217 g C m −2 year −1 for the adjacent open ocean. Interannual variation in production on the shelf ranged from 334 g C m −2 year −1 in 1998 to 301 g C m −2 year −1 in 2000. It is estimated that upwelling increased primary production, relative to that in the open ocean, by ∼50%. Satellite-derived estimates of the ratio of new production to primary production were 0.37, 0.28 and 0.40 for the shelf region during the upwelling seasons of 1998, 1999 and 2000.

Photosynthetic rates derived from satellite‐based chlorophyll concentration

We assembled a dataset of 14C‐based productivity measurements to understand the critical variables required for accurate assessment of daily depth‐integrated phytoplankton carbon fixation (PP(PPeu)u) from measurements of sea surface pigment concentrations (Csat)(Csat). From this dataset, we developed a light‐dependent, depth‐resolved model for carbon fixation (VGPM) that partitions environmental factors affecting primary production into those that influence the relative vertical distribution of primary production (Pz)z) and those that control the optimal assimilation efficiency of the productivity profile (P(PBopt). The VGPM accounted for 79% of the observed variability in Pz and 86% of the variability in PPeu by using measured values of PBopt. Our results indicate that the accuracy of productivity algorithms in estimating PPeu is dependent primarily upon the ability to accurately represent variability in Pbopt. We developed a temperature‐dependent Pbopt model that was used in conjunction with monthly climatological images of Csat sea surface temperature, and cloud‐corrected estimates of surface irradiance to calculate a global annual phytoplankton carbon fixation (PPannu) rate of 43.5 Pg C yr‒1. The geographical distribution of PPannu was distinctly different than results from previous models. Our results illustrate the importance of focusing Pbopt model development on temporal and spatial, rather than the vertical, variability.

Assessment of interannual variation (1979-1986) in pigment concentrations in the tropical Pacific using the CZCS

Abstract Coastal Zone Color Scanner (CZCS) pigment concentrations, sea surface temperature, and sea level from 1979 through to mid-1986 in the tropical Pacific are examined. The relationships among surface pigment concentration, sea surface temperature and sea level during the El Ni~o/Southern Oscillation event of 1982-83 exhibit marked zonal variations. Sea level in the western and central Pacific decreased dramatically during the autumn of 1982 with both north-to-south and west-to-east time lags and corresponding increases in pigment concentrations. There was no apparent relationship between sea surface temperature and pigment in the Warm Pool. In contrast, sea surface temperature increases in the eastern Pacific along the Peruvian coast and the Galapagos Islands coincided with pronounced increases in sea level and decreases in surface pigment concentrations. Across the entire basin, pigment variability was linked to sea level height, and, presumably, thermocline depth with an inverse relationship between sea level and pigment occurring on both sides of the Pacific.

Ship and satellite observations of chlorophyll stocks in interacting cyclone‐anticyclone eddy pairs in the western Gulf of Mexico

When anticyclonic eddies shed by the Loop Current of the Gulf of Mexico reach the western margin of the gulf, they influence the surface circulation over the continental slope and rise. Of particular interest is the generation of cyclone (cold‐core)‐anticyclone (warm‐core) pairs when aging Loop Current eddies interact with the continental margin. In this paper we describe the physical and biological characteristics of these cyclone‐anticyclone pairs. Our objective was to determine how eddy pairs affect the distribution of phytoplankton in the region and how satellite ocean color measurements are applicable to tracing of the eddies. We present shipboard data collected between 1980 and 1982 on the hydrography, chlorophyll stocks, and nutrient concentrations of eddy pairs in the western Gulf of Mexico and compare these data with coastal zone color scanner (CZCS) images collected during the time frame of the cruises. Surface pigment concentrations followed a seasonal cycle, with low concentrations (0.05–0.1 mg m−3) found within cyclones and anticyclones from April through early November and higher concentrations (>0.1 mg m−3) found in the winter. CZCS pigment concentrations were locally high in the flow confluence of cyclone‐anticyclone pairs. The CZCS imagery shows that some cyclone‐anticyclone geometries transport high‐chlorophyll shelf water seaward at least 100–200 km off‐shelf.

Offshore export of shelf production in the Cape Blanc (Mauritania) giant filament as derived from coastal zone color scanner imagery

Particulate organic carbon flux from the shelf to oceanic waters during upwelling between 19°N and 25°N off Mauritania has been analyzed using coastal zone color scanner (CZCS) imagery. Biomass in the giant filament has been estimated using surface pigment concentration registered by CZCS during time series in December 1983, March 1984, and October 1984. Evidence for active phytoplankton growth in offshore waters is presented. Formation of the giant filament seems to be favored by the combination of a number of factors perhaps unique to the Mauritanian shelf. The large‐scale circulation patterns promote offshore advection, and the typically long period of wind forcing can move the upwelling center to the shelf break area, thus causing maximal phytoplankton growth rate to be achieved in oceanic waters. The relatively high pigment concentrations registered by CZCS in oceanic waters suggest that nutrients have not been depleted on the shelf and that in situ growth is occurring in deep waters. We have used a baroclinic, hydrodynamic model to estimate cross‐slope flux of particulate organic carbon at the 200‐m isobath and derive a mean value of about 1 × 105 g C s−1 during each of the CZCS time series.

Varve formation in the Gulf of California: Insights from time series sediment trap sampling and remote sensing

The varved sediments that accumulate in the central Gulf of California (Guaymas and Carmen Basins) provide a record that allows for the resolution of annual to decadal-scale climate variability in this region. Time-series sediment trapping, combined with remotely sensed observations of sea surface temperature (AVHRR) and color (CZCS), have been used to examine the mechanism of varve formation in the central Gulf. SST and surface pigment concentration records for both the mainland and Baja sides of the Gulf display similar seasonal trends. High temperatures and low pigment concentrations occur synchronously on both sides of the central Gulf from June through to October. In association with the 1991/92 El Niño, warm temperatures persist in the central Gulf until December. Low SSTs typically occur from December through May, with high pigment concentrations marking the period from November through April. The summer-early fall (June–October) is a time of high terrigenous and biogenic sediment fluxes. During this time of year, the total flux is dominated by eolian-transported lithogenic material and dark laminae are deposited during this period. During El Niño years, high terrigenous fluxes may extend into winter. Light laminae represent deposition from November through May, during which time biogenic material dominates the total sediment flux. High opal fluxes beginning in November are attributed to seasonal cooling of surface water and upward mixing of nutrients. True upwelling conditions do not develop in the Gulf until late winter-spring. During this time, the total flux is still dominated by opal but the magnitude of the flux is reduced. This may be an artifact of phytoplankton grazing and not lower production rates.

Predictive bio-optical relationships for polar oceans and marginal ice zones

An analysis of more than 500 stations from polar seas was undertaken to evaluate predictive models linking in situ phytoplankton pigment concentrations to measurable optical parameters. The data set consists of profiles of spectral downwelling irradiance [ E d( λ)], upwelling radiance [ L u( λ)], chlorophyll and phaeopigments from 3 cruises to the Antarctic Peninsula (RACER, UVDOZ-88, UVDOZ-89), one cruise to the Barents Sea (PRO MARE) and one cruise to Fram Strait in the Greenland Sea (CEAREX). The pigment specific diffuse attenuation coefficient [K d ∗(λ) m 2 mg −1 chl a + phaeo] for polar regions is significantly smaller, particularly in the blue region of the spectrum, than previous statistical models for temperate oceans predict. Consistent with the observations for K d ∗(λ) , phytoplankton remote sensing pigment retrieval algorithms, based on L u( λ), show significant differentiation from temperate ocean models. The presently recommended water-leaving radiance algorithm for Coastal Zone Color Scanner data processing underestimates surface pigment concentrations by more than a factor of two for the polar observations reported here. The observations are interpreted in the context of variations in pigment specific particulate absorption [a p ∗(λ) m 2 mg −1 chl a + phaeo] which have been described elsewhere. Specifically, the magnitude of a p ∗(λ) in the blue is hypothesized to be smaller for polar regions due to significant pigment packaging effects, and a relatively small amount of detrital absorption compared to phytoplankton absorption. Implications for remote sensing of phytoplankton pigments and pigment-based models of light propagation in the oceans are discussed.

On the seasonal phytoplankton concentration and sea surface temperature cycles of the Gulf of Mexico as determined by satellites

Monthly climatologies of near‐surface phytoplankton pigment concentration and sea surface temperature (SST) were derived for the Gulf of Mexico from multiyear series of coastal zone color scanner (CZCS) (November 1978 to November 1985) and advanced very high resolution radiometer (AVHRR) (January 1983 to December 1987) images. We complement these series with SST from the comprehensive ocean‐atmosphere data set (1946–1987) and Climate Analysis Center (1982–1990), and hydrographic profile data from the NOAA National Oceanographic Data Center (1914–1985). The CZCS ocean color satellite data provide the first climatological time series of phytoplankton concentration for the region. The CZCS images show that seasonal variation in pigment concentration seaward of the shelf is synchronous throughout the gulf, with highest values (>0.18 mg m−3) in December to February and lowest values (∼0.06 mg m−3) in May to July. Variation in SST is also synchronous throughout the gulf, with maxima in July to September and minima in February to March, The amplitude of the SST variation in the western gulf is about twice that observed in the eastern gulf, and SST maxima and minima persist longer in the west. Larger amplitudes in SST variation are also observed toward the margins. While annual cycles of SST and pigment concentrations are out of phase relative to each other, the phases of mixed layer depth change and pigment concentration change are similar. Model simulations suggest that the single most important factor controlling the seasonal cycle in surface pigment concentration is the depth of the mixed layer. The combined use of ocean color and infrared images permits year‐round observation of spatial structure of the surface circulation in the gulf and the pattern of dispersal of the Mississippi River plume. Infrared images are most useful between November and mid‐May, when strong SST gradients occur. During this time, pigment concentrations are high and can be horizontally homogeneous. In contrast, between late May and October, SST fields are uniform, but the Loop Current and large anticyclonic eddies could be traced with the CZCS. Three anticyclonic eddies were observed in 1979, and at least two were observed in 1980. No eddies were observed during summers of subsequent years in the CZCS time series, but this may be a result of the dramatic decrease in the satellite sampling rate. The series of color images showed that small parcels of Mississippi River water were frequently (2–4 times a year) entrained in the cyclonic edge of the Loop Current, stretched along the Current, and carried to the southeast along the western Florida shelf. However, most of the Mississippi River water flowed to the west, following the Louisiana‐Texas coast as far south as the Mexico‐United States border. Here, a persistent cyclone may reside, exporting shelf constituents to deeper regions of the gulf.

Physical and biological processes in the North Atlantic during the first GARP Global Experiment

The seasonal cycle of the phytoplankton biomass in the North Atlantic Ocean (20°S to 70°N) is discussed using monthly mean surface pigment concentration fields from the Nimbus 7 coastal zone color scanner (CZCS) for the period of December 1978 through December 1979. The temporal and spatial distributions of surface pigments are compared with quantities derived from the First GARP Global Experiment (FGGE) wind data set (1000‐mbar streamlines, Ekman upwelling, horizontal Ekman transport and |τ|3/2), Climate Analysis Center (CAC) sea surface temperature (SST) fields, concurrent hydrographic station data, and climatological mixed‐layer depths and heat fluxes. The objective of the analysis is to clarify the role of some physical mechanisms that regulate the supply of nutrients to the euphotic zone at different locations in the basin and at different times of the year. It is observed that during this period, the spring bloom was, in most locations, sustained for 2 to 3 months. At a given latitude the onset of the spring bloom varied by several months and, in some cases, could be referred to as a fall bloom. In other cases there were both spring and fall blooms. Time series at 11 selected sites throughout the basin are used to illustrate, in detail, the relation of phytoplankton biomass to local physical forcing. Finally, separate analyses of the mean pigment concentrations for the shelf and open ocean regions indicate that the phytoplankton of both regimes had spring and fall blooms of equal magnitude, the spring bloom being located at northern latitudes and the fall bloom in the equatorial region. Analysis of the open ocean Ekman upwelling field shows similar peaks approximately 2 months in advance of the surface pigment concentration peaks.

Seasonal and nonseasonal variability of satellite‐derived surface pigment concentration in the California Current

Satellite‐derived pigment concentrations from the west coast time series (WCTS) are averaged into monthly mean fields over the California Current system (CCS) for the period July 1979 to June 1986. Errors caused by the scattering algorithm used in the WCTS are reduced by an empirical correction function, although winter values (November–February) remain unreliable. For the March–October period we look at both the mean seasonal development and the nonseasonal monthly anomalies of pigment concentration. These are compared with fields of alongshore wind stress, mixing power of the wind (u*3) and wind stress curl. Outside of the Southern California Bight there is a strong seasonal cycle with a spring‐summer maximum, a northward progression of high pigment concentrations from California to Oregon and a double maximum off Washington (spring and summer, with a lull in between). Within the Southern California Bight, seasonality is low, with a relative minimum in late summer. Off Baja California the pattern is similar to that off northern California. In regions where previous work has been done, there is general agreement with the seasonal cycles found here. Nonseasonal variability in pigment concentration over the large‐scale CCS (400 km wide) is most closely related statistically to synoptic fields of wind stress curl. Within 100 km of the coast, the strongest relations are between pigment concentration and both u*3 and alongshore wind stress. Correlations with these wind variables account for only 25% of the monthly variance in anomalous satellite‐derived pigment concentrations. This is partly due to the noise in both wind and pigment data sets but also demonstrates the fact that much of the anomalous pigment variability is not a response to anomalous wind forcing on these time scales. Correlations are also low between anomalous pigment concentrations and anomalous sea level heights, which serve as a crude proxy for the strength of the alongshore current over the shelf. The largest nonseasonal anomaly in the data occurred during the 1982–1983 El Niño, which caused a large‐scale decrease in pigment concentration, stronger and longer lasting in the south than in the north.

Variability of surface pigment concentrations in the South Atlantic Bight

A 1‐year time sequence (November 1978 through October 1979) of surface pigment images from the South Atlantic Bight (SAB) was derived from the Nimbus 7 coastal zone color scanner. This data set is augmented with in situ observations of hydrographic parameters, freshwater discharge, sea level, coastal winds, and currents for the purpose of examining the coupling between physical processes and the spatial and temporal variability of the surface pigment fields. The SAB is divided into three regions: the east Florida shelf, the Georgia‐South Carolina shelf and the Carolina Capes. Six‐month “seasonal” mean pigment fields and time series of mean values within subregions were generated. While the seasonal mean isopleths were closely oriented along isobaths, significant differences between seasons in each region were found to exist. These differences are explained by correlating the pigment time series with physical parameters and processes known to be important in the SAB. Specifically, summertime concentrations between Cape Romain and Cape Canaveral were greater than those in winter, but the opposite was true north of Cape Romain. It is suggested that during the abnormally high freshwater discharge in the winter‐spring of 1979, Cape Romain and Cape Fear were the major sites of cross‐shelf transport, while the cross‐shelf exchange during the fall of 1979 occurred just north of Cape Canaveral. Finally, the alongshore band of high pigment concentrations increased in width throughout the year in the vicinity of Charleston, but near Jacksonville it exhibited a minimum width in the summer and a maximum width in the fall of 1979.

Observations of Gulf Stream‐induced and wind‐driven upwelling in the Georgia Bight using ocean color and infrared imagery

Ocean color and infrared imagery from aircraft and satellite sensors are combined with in situ measurements of currents, chlorophyll, temperature, salinity, coastal winds, and sea level to study upwelling events in the Georgia Bight where the Gulf Stream and continental shelf waters strongly interact. These interactions were observed over an 8 day period in April 1980 during which five independent upwellings occurred. The upwellings included a nearshore wind‐driven upwelling enhanced by topographic effects, three Gulf Stream filament‐induced upwellings, and what appears to have been a Gulf Stream meander‐induced event. The chlorophyll distributions as inferred from the imagery are found to be reliable tracers which indicate filamentary circulation and propagation and advective routes by which nearshore water moves offshore. The propagation of two of the filaments and the meander are studied in detail using the imagery and mooring array temperature time series. Both techniques yield nearly identical results for the phase speeds of each event. There is evidence that one of the filaments accelerated as it entered into the Charleston Bump area where the Gulf Stream deflects offshore. The other filament exhibited a steady deceleration as it moved past Cape Canaveral and eventually lost any semblance of wave motion. Also included are data from April 1979 which offer corroborating evidence of filamentary structure and circulation. Intercomparisons of field measurements and the Nimbus 7/coastal zone color scanner estimates of surface pigment concentrations show excellent agreement over the range of 0.1–7.0 mg/m3.

EFFECTS OF COLD STORAGE ENVIRONMENT ON COLOR OF EXPOSED LEAN BEEF SURFACES

ABSTRACTA model system approach utilizing a wind tunnel designed to control temperature, humidity and air velocity was used to evaluate the effects of cold storage conditions on the color of exposed lean beef surfaces. Measurements made on the stored samples included: evaluation of pigment oxidation rate by reflectance spectrophotometry, objective color measurement in standard CIE and Munsell units using a color difference meter, and weight loss. The rate of metmyoglobin (Mb+) formation or browning increased with increasing temperature and air velocity. Low relative humidity, however, did not promote Mb+ formation. The lightness index of beef was highly correlated with water loss and initial pigment concentration. At high humidity and low air velocity, pigment oxidation was accelerated, and this may be attributed to stimulated bacterial growth under these conditions. Relative humidity near 90%, air velocity near 0.5 mps, and near freezing temperature appeared to represent the best environment for beef color maintenance. Consumers';perception of good beef color, as evaluated by a trained panel, showed that lower levels of Mb+ were tolerated when higher surface pigment concentrations were present and surface desiccation occurred. A regression equation showing the relationship between visual color scores and surface pigment concentration, extent of surface desiccation, and Mb+ concentration was developed. From the regression equation for Mb+ formation and desiccation rates as affected by storage conditions, color scores as a function of storage time can be predicted and storage conditions for color maintenance can be optimized.