Total Water Column Research Articles

Diel changes in vertical distribution and feeding activity of copepods in ice-covered Resolute Passage, Canadian Arctic, in spring 1992

Abstract To examine the role of copepods in the marine ecosystem under sea ice, diel changes in their vertical distribution and feeding activity were observed in May 1992 in Resolute Passage, Canadian Arctic. Copepods were numerically abundant, making up 98% of the zooplankton assemblage. Pseudocalanus was the dominant copepod, accounting for 92% of the copepods in number. All stages, particularly copepodid stages IV and V of Pseudocalanus, showed upward migration at night, concentrating just below the ice between 2000 and 2300 h and descending into the deeper water around midnight. Gut pigment content of Pseudocalanus just below the ice showed diel changes, with higher values in the day than at night. Gut evacuation rates were independent of the initial gut pigment contents. The ingestion rate of the Pseudocalanus population was high at 2000 h in the top 0–1 m layer under the ice, reaching more than 20 μg pig m−3 h−1. In the layers deeper than 3 m, the ingestion rates of the population was relatively high around 1800–8000 h and 0600 h, with a maximum of nearly 0.5 μg pig.m−3 h−1. These higher ingestion rates did not extend throughout the night in the whole water column. Cumulative daily ingestion rates for the population in the top 0–3 m and the whole water column were calculated to be 0.30 and 2.57 mg pig.m−2 d−1, respectively. Similarly, consumption of the daily ice algal production was estimated to be 4.2% in the upper water column and 36.8% for the total water column. Scanning electron microscopic observations of in situ gut contents revealed that ice algal diatoms were not the nutritive sources for Pseudocalanus. We suggest that naked autotrophs could be an important food source for copepods under the ice in Resolute Passage in the spring.

“TOP–DOWN” TROPHIC INTERACTIONS IN LAKES: EFFECTS OF FISH ON NUTRIENT DYNAMICS

We conducted enclosure experiments over two summers in Tuesday Lake, Michigan, to assess how a gradient of zooplanktivorous fish biomass affected the dynamics of nutrients (nitrogen, N, and phosphorus, P), and their partitioning among ecosystem compartments. In both years, fish (the cyprinid Phoxinus eos) reduced the abundance of large zooplankton species and increased the biomass of phytoplankton as predicted by the top–down control hypothesis. Fish had strong effects on the dynamics and fluxes of N and P. Total P concentrations in the water column declined over time in all enclosures, but fish slowed the rate of decline. Thus total water column P increased with increasing fish biomass. Total N increased less strongly with increasing fish biomass, and thus the total N:P ratio decreased with increasing fish biomass. The concentrations of particulate carbon, nitrogen, and phosphorus in the water column also increased with increased fish biomass. Particulate N:P ratio decreased with increased fish biomass, but effects were weaker compared to effects on total N:P ratios. Nutrient ratios of the zooplankton fraction (particles >63 μm) showed a response that was transient but consistent with observed trends in zooplankton species composition. In particular, when the large cladocerans Daphnia and Holopedium increased upon exclusion of fish, C:P and N:P ratios of the zooplankton fraction showed distinct declines, corresponding to the relatively high body P contents of these taxa. Phosphorus budgets revealed that fish were a net source of P to the water column, because they lost mass during the experiments, even at densities below those in the lake. However, loss of P from fish could not account for the higher total P concentration observed in enclosures with fish compared to fishless enclosures. The absolute amount of P sinking from the water column increased with increasing fish biomass but decreased when expressed as percentage of total P sinking, again suggesting that the presence of fish increases the relative retention of P the water column. The rate of decline in water column total P in the presence of fish was accurately predicted by sedimentation of P from the water column and other fluxes. Our results support the hypothesis that fish can exert major influences on the dynamics, distribution, and ratios of limiting nutrients.

Correcting false thermistor string data

In order to monitor the temperature variability over the total water column in a stratified shallow sea, a thermistor string was suspended from a moored loosely tethered surface buoy. Some of the temperature data manifested strong first tidal harmonic variability and unrealistic thermocline deepening. It is shown that the string lifted under the action of horizontal buoy displacement. Although the data may be corrected by using additional pressure or tilt sensors, a method is given to detect and correct them using current data, some simple arguments for buoy displacement under drag force and cross-spectral information from the first harmonic tidal band. The method proves adequate, as has been verified using temperature data measured at a nearby sub-surface mooring and some CTD information.

Measurement of oxygen production and demand in lake waters

Abstract By use of a modern BOD bottle probe, a digital read‐out meter, and quadruplicate sampling, oxygen concentrations were routinely measured with a precision of ± 0.02 g DO m−3. This level of accuracy permitted measurement of Water Oxygen Demand (WOD), Net Production (NP), and Gross Production (GP) at all depths in the water column of lakes. Sediment Oxygen Demand (SOD) was also measured and found to be small when compared to the total water column oxygen demand in unstratified water but was a significant part of the hypolimnetic oxygen uptake. Measurements of GP were found to correlate closely with primary production values determined independently by means of the 14C technique. Significant GP was also found in the hypolimnion of a mesotrophic lake, indicating that WOD does not always provide a measure of hypolimnetic oxygen uptake; net production does so in this situation. Further, WOD was found to decrease by about 20% per day in incubated samples, revealing that WOD incubations should never excee...

Phytoplankton biomass, P-I relationships and primary production in the Weddell Sea, Antarctica, during the austral autumn

An investigation into the changing phytoplankton biomass and total water column production during autumn sea ice formation in the eastern Weddell Sea, Antarctica showed reduced biomass concentrations and extremely low daily primary production. Mean chlorophyll-a concentration for the entire study period was extremely low, 0.15±0.01 mg.m−3 with a maximum of 0.35 mg.m−3 found along the first transect to the east of the grid. Areas of low biomass were identified as those either associated with heavy grazing or with deep mixing and corresponding low light levels. In most cases phytoplankton in the < 20-μm size classes dominated. Integrated biomass to 100 m ranged from 7.1 to 28.0 mg.m−2 and correlated positively with surface chlorophyll-a concentrations. Mean PBmax (photosynthetic capacity) and αB (initial slope of the photosynthesis-irradiance curve) were 1.25±0.19 mgC. mgChl a−1.h−1 and 0.042+-0.009 mgC.mgChla−1.h−1.(μmol.m−2s−1)−1 respectively. The mean index of photoadaptation,Ik, was 32.2±4.0 μmol.m−2.s−1 and photoinhibition was found in all cases. Primary production was integrated to the critical depth (Zcr) at each production station and ranged from 15.6 to 41.5 mgC.m−2.d−1. It appears that, other than grazing intensity, the relationship between the critical depth and the mixing depth (Zmix) is an important factor as, ultimately, light availability due both to the late season and growing sea ice cover severely limits production during the austral autumn.

Abundance, distribution and population structure of the copepod Calanus finmarchicus in a springtime right whale feeding area in the southwestern Gulf of Maine

Springtime aggregations of the planktivorous right whale ( Eubalaena glacialis) occur in the northern Great South Channel region of the southwestern Gulf of Maine, where they feed upon dense concentrations of the copepod Calanus finmarchicus. This association was studied during the multidisciplinary South Channel Ocean Productivity Experiment (SCOPEX) in 1988 and 1989. The spatial and temporal variability of the abundance, geographic distribution, and population structure of these copepods were analyzed using data from 99 vertically-stratified or horizontally-sequenced MOCNESS plankton tows. Higher water column abundances and higher relative proportion of older copepod lifestages occurred near feeding whales compared to sites without whales, but total water column copepod biomass and Calanus abundance did not always differ between these types of locations. This suggests that the whales seek out aggregations of older copepod lifestages rather than simply the most dense aggregations. Other factors (and perhaps an element of chance) may influence which specific patches, among all patches potentially suitable in terms of copepod abundance and age composition, the whales utilize at a particular time. The times and locations of the highest Calansus water column abundances varied between years, as did the presence of feeding whales, probably because of year-to-year differences in the springtime temperature cycle and current strength. A temporal progression of lifestages occurred within the region in both years during the roughly 3-week duration of each survey, indicative of a growing rather than a diapausing population, at least up to the copepodite 4 (C4) stage. Due in part to a delay in the springtime warming in 1989 compared to 1988, the copepod development cycle, which is largely driven by in situ temperature, was delayed about 1–2 weeks in 1989. Peak abundances of younger Calanus were found in the northwestern part of the region each year, whereas peak abundances of older Calanus were found in the southwestern and northeastern part. This was probably due to the advection of maturing copepods by the regional circulation, especially the near-surface current associated with the movement of the low-salinity surface plume which forms each spring off Cape Cod. The copepod development cycle occurs within a moving frame of reference (i.e. the water itself); thus, peak abundances of the older copepods (those fed on by the whales) occurred later in the spring and further downstream in 1989 (when there were colder springtime temperatures and faster currents) than in 1988 (when the springtime temperatures were warmer and currents slower). Maximum Calanus abundances and biomass and water-colum abundances of older copepodite stages were significantly higher (about double) in 1989 than in 1988, both in the region as a whole and at sites where whales were feeding. Maximum concentrations from the MOCNESS tows were 13,300 m −3 in 1988 and 30,800 m −3 in 1989; however, a thin, visibly-red surface patch of Calanus, sampled in 1989 by a bucket, had a concentration of 331,000 m −3. Copepods were also more aggregated in the vertical (i.e. more highly concentrated at the depth of maximum abundance) in 1989 than in 1988, and samples from whale-feeding areas were more homogeneous in composition (higher proportion of Calanus relative to all zooplankton) in 1989. At smaller spatial and temporal scales, abundances varied by a factor of 1–890 X in samples from horizontal tows spanning about 0.5–1.5 km and by a factor of 1–50 X over 24 h in the same geographic location in whale-feeding areas. Some of this variability was probably due to advection by the semidiurnal tidal currents. Near feeding whales, the copepod spatial distribution was patchy on small scales (with an estimated mean patch “size” of about 500 m), but the patchiness varied in texture interannually. Copepod abundances were much lower in early spring (March 1988) than in later spring (May 1988), with the March population structure dominated by adult females and the May population dominated by copepodite 4 and 5 stages (C4 and C5).

Respiration Rates and Hypoxia on the Louisiana Shelf

The spatial and temporal variation in water-column respiration, estimated from enzymatic respiratory electron-transport-system activity, was measured monthly on a cross-shelf transect on the Louisiana shelf from May through October 1991. In July 1991, water-column respiration was also determined on an alongshore transect, and in situ benthic respiration and photosynthesis rates were determined at jour stations on the cross-shelf transect. Bottom waters were persistently hypoxic (O2<2 mg 1−1) at most stations in July and August and sporadically hypoxic at other times. Water-column respiration rates were in the same range as earlier, less extensive studies and not unusually high for coastal and estuarine waters. They were highest in summer, decreased with distance offshore and depth, and increased with temperature. Their variation with pigment and oxygen concentrations were complex functions of season and depth. Oxygen depletion below the oxycline could occur within days to months, depending on the season and location. In July, benthic respiration rates were also not unusually high in comparison with other shallow sediments, although the ratio of benthic: total (water column+benthic) respiration was high. Combined water-column and benthic respiration could deplete the bottom water oxygen in approximately 1 mo. Because the system rarely goes anoxic (defined as observing sulfide), some mechanism(s) must exist to reaerate bottom waters. Most physical mechanisms are unlikely to provide significant reaeration at this time of year. Measured benthic and conservatively estimated bottom-water photosynthesis could resupply 23% of the oxygen lost daily by respiration. Although this is too limited a dataset from which to draw conclusions about the relative importance of bottom-water and benthic respiration and photosynthesis in determining bottom-water oxygen concentrations, it does suggest that all these processes must be considered.

Physical and biological observations of coastal squirts under nonupwelling conditions

Offshore‐directed plumes of inshore water, marked by a shallow mixed layer, low salinity, and low temperature during winter, were observed south of the Hokitika Canyon on the South Island west coast, New Zealand. Hydrographic and satellite observations are presented which show that plume time scales were of the order of a few days, and across‐shelf length scales were approximately 50 km. The low‐salinity plumes were found to be associated with the southern edge of an offshore‐directed jet that followed the Hokitika Canyon bathymetry. Decay of the plumes was rapid and appears to be associated with mixing of plume water into offshore surface waters. The occurrence of the plumes is nonseasonal, and they do not appear to be associated with upwelling. Observations suggest that strong southward flow around the head of the Hokitika Canyon, perhaps as a consequence of coastal‐trapped wave activity, is a possible mechanism for plume formation. Biologically, the plumes were important because they stabilized the water column and prevented the mixing of phytoplankton below the photic zone. Although the plumes were found to transport productive nearshore waters offshore, the major impact of the plumes was to lower total water column chlorophyll a in outer shelf regions. The relationship between the Hokitika plumes and the filaments and squirts identified off the Californian coast is discussed, and it is concluded that the plume dynamics resemble those of the squirts found inshore of the seasonal filaments off California. The results of this study indicate that squirts not only influence biological variability in shelf waters but are important mechanisms for the across‐shelf exchange of coastal and oceanic waters.

Benthic-pelagic flux rates on mussel beds: tunnel and tidal flume methodology compared

Material flux rates in an intertidal mussel bed were measured synchronously over two tidal cycles in June 1989 with Benthic Ecosystem Tunnels and a double lane flume. The tunnels enclosed the near bottom water, whereas the flume canalized the total water column. One tunnel was set up in a mussel bed and another one in an adjacent sand bottom as a control. The flume enclosed a mussel lane and a sand lane. In the tunnel and in the flume the mussel bed revealed ammonium and phosphate discharge. At the same time, phytoplankton, dominated byPhyaeocystis globosa, was taken up intensively. These flux rates showed the same tendency but they were higher in the flume than in the tunnel. Different tendencies and flux rates for oxygen and particulate organic matter (POC, PN) were found in flume and tunnel. These differences demonstrate the importance of water column processes regarding the material exchange of a mussel bed. Tunnels enclose smaller bodies of water and are therefore expected to detect even small effects of the benthos on the passing water. In flumes, benthic influence may be diluted over the entire water column but conditions are more natural. The use of flumes is restricted to shallow waters while tunnels have the potential to be used at any depth.

Oligotrophication after a nutrient reduction in a shallow sand-pit lake (Créteil Lake, Paris suburbs, France) : a case of rapid restoration

A limnological study was performed out, over 8 years from 1979 to 1986, in a shallow recently created sand-pit lake, Lake Creteil (Paris suburb, France). The lake is mainly supplied by phreatic waters. Typical of shallow waters, thermal stratification which occurred from May to October was intermittently broken by wind, leading to high seasonal fluctuations and allowing a reoxygenation of the total water column. The interannual development of the lake was characterized by a regular increase in transparency (from 1 m in 1979 to 2.7 m in 1985) which was partly due to not only stabilization of the bottom sediment and the banks, but also to a reduction of the biological component. A decrease in chlorophyll a concentrations resulted from nutrient diversion of domestic inputs collected through the rainwater pipe coming into the lake. The rapid restoration of water quality shows that this small artificial lake is very sensitive to human interventions.

Effects of ultraviolet radiation on the primary production of natural phytoplankton assemblages in Lake Michigan

Inhibition of primary production of offshore Lake Michigan phytoplankton assemblages by solar ultraviolet radiation (SUVR) was observed from April to October in 1986 during in situ incubations in special Plexiglas chambers. Inhibition of primary production by SUVR was observed to a depth of 6 m and at intensities which were approximately 1% of the UV-B intensity at the lake surface. Significant inhibition of primary production by SUVR was restricted to the top third of the euphotic zone. The order of relative sensitivities of offshore Lake Michigan phytoplankton assemblages during different seasons to inhibition by SUVR were spring (ED 50 = 17.6 kJ/m 2 UV-B) > fall (ED 50 = 30.5 kJ/m 2 UV-B) > summer (ED 50 = 131.6 kJ/m 2 UV-B). A hazard assessment model predicted a significant reduction (13%) in areal (total water column) primary production for offshore Lake Michigan due to current SUVR intensities. Concern about possible increased reduction of primary production in the North American Great Lakes due to depletion of the stratospheric ozone layer appears to be unwarranted.

The Chrysochromulina polylepis bloom in the Kattegat (Scandinavia) May-June 1988. Distribution, primary production and nutrient dynamics in the late stage of the bloom

Chrysochromulina polylepis Manton & Parke bloomed in the Kattegat and the Skagerrak in May-June 1988 and its distribution, as well as primary production and nitrogen dynamics, were investigated in the Kattegat just prior to the decline of the bloom. The bloom occurred throughout the Kattegat area as a subsurface population associated with the pycnocline. The flagellate was actively photosynthesizmg but light-limited in the pycnocline. The primary production of the Chrysochromulina layer represented 50 to 90 % of the total water column production. The specific growth rate of the flagellate was low with doubling times of 4 to 23 d. Ammonium was the major nitrogen source during this late stage of the bloom, accounting for 50 to 85 % of the daily nitrogen uptake. The hourly uptake of ammonium was equal to or exceeded by the ammonium regeneration rate. A minimum primary production of 800 to 1100 fig C 1-I and a nitrogen demand of 10 to 13 fimol N 1-I were estimated from the oxygen supersaturation. Profiles of salinity, temperature and oxygen indicate that the nitrogen was supplied by an intrusion of nutrient-rich water in the pycnocline layer early in the bloom. Possible models for the bloom developments are discussed.

Seasonal abundances of planktonic ciliates and microflagellates in mesohaline Chesapeake Bay waters

Ciliate, heterotrophic microflagellate (hflag) and autotrophic microflagellate (aflag) abundances are reported for mesohaline Chesapeake Bay waters based on samples gathered from April through October 1985–1987. Total water column averages for ciliate and microflagellate abundances were typical of eutrophic marine systems. Ciliate density ranged from 17·2 cells ml −1 in April to 1·8 cells ml −1 in September; hflag ranged from 3·7 × 10 3 cells ml −1 in June to 1·1 × 10 3 cells ml −1 in October. In spring the majority of ciliate and hflag standing stocks (70% and 64%, respectively) were located in bottom and transition waters; during summer months the majority (approximately 85% of both groups) were in surface and transition waters. During fall, ciliate stock was concentrated (72%) in surface waters and hflag were relatively evenly distributed in the three water column zones. Ciliate and microflagellate numbers were not directly related to chlorphyll α concentration except in the bottom layer, where simultaneous declines accompanied anoxia. Ciliate concentrations correlated with total numbers of microflagellates and hflag abundance, but not aflag density. We discuss the relative importance of predation and food availability in regulating ciliate and hflag concentrations in mesohaline Chesapeake Bay waters.

Wave forces on a pipeline in a trench

Wave forces on a model pipeline have been measured. The pipeline was located in a trench, the configuration of which is similar to that proposed for oil and gas production in the Beaufort Sea. It was found that the drag and inertia coefficients were similar to the results reported in the literature for flat beds, assuming the water depth was that of the total water column including the trench. Flow visualization tests confirmed that the horizontal velocities were about the same as those that would be found on a flat bed with the same total depth. Key words: wave forces, pipelines, trenches.

The geochemistry of beryllium-7 in Chesapeake Bay

The dissolved and particulate activities of 7Be in surface and deep water samples from four stations in the main stem of Chesapeake Bay were determined seven times between April, 1986 and April, 1987. Total water column concentrations ranged from < 0·05 to 3·86 dpm l −1, with an average of 0·50 dpm l −1. Batch adsorption experiments indicated a strong affinity of Be for Chesapeake Bay seston, but 7Be in the Bay was predominantly in the dissolved phase. Particulate 7Be activities reached 150 dpm g −1, but averaged 18 dpm g −1, suggesting that rapid variations in the supply of both 7Be and suspended particulates rarely allowed equilibrium partitioning of 7Be between the dissolved and particulate phases. A 7Be budget for Chesapeake Bay indicated that atmospheric deposition was always the dominant source of 7Be in the Bay. Generally, ≥ 95% of the 7Be delivered to the Bay was retained by it. Most (usually > 80%) of the 7Be in Chesapeake Bay at any time was found in the sediments.

Variability of pigment biomass in the California Current System as determined by satellite imagery: 2. Temporal variability

Characteristics of temporal variability in the California Current system are analyzed using a 30‐month time series of Coastal Zone Color Scanner (CZCS) imagery. About 20–25% of the variance is produced by a periodic annual cycle with peak values in winter. Analysis of ship‐based chlorophyll measurements indicates that the winter peak is only characteristic of the upper portion of the euphotic zone and that total water column chlorophyll peaks during the spring upwelling season. Satellite studies of intra‐annual variability are modulated by strong 5‐ to 6‐day oscillation in the availability of usable imagery, resulting from a combination of satellite orbital dynamics, which produces images of the study area roughly 4 out every 6 days, and an oscillation in cloud cover, which controls the availability of clear imagery. The cloud cover oscillation, which is also present in coastal winds, undoubtedly affects the ocean surface and biases the data obtained by satellites. Analysis of data using a 5‐day time step indicates that the predominant mode of nonseasonal variability is characterized by inphase fluctuations throughout the southern and central California coastal region.

Manganese cycling in coastal regions: Response to eutrophication

An indirect biogeochemical consequence of the eutrophication of shallow coastal marine ecosystems was examined. Changes in manganese distribution in water and bottom sediments, and the flux rates between these two, were followed in a nutrient enrichment experiment using marine mesocosms. Conducted at the Marine Ecosystems Research Laboratory (MERL), Narrangansett, RI, U.S.A., the experiment involved a geometric series of daily nutrient additions (N, P, Si) to six mesocosm tanks (plus three controls) for a 2·3-year period. Changes occurred in sediment-water flux rates of dissolved Mn, in total Mn in the water, and in Mn concentrations of sediment pore waters and solids; the direction and magnitude of change in each of these parameters varied somewhat by treatment. Patterns of changes with increasing levels of nutrient loading were observed, but usually these held only across a limited range of loading or for short periods of time. For example, during the first year the benthic flux of Mn increased from controls to mid-levels of the eutrophication gradient. Moreover, the specific nature of the alteration in Mn cycling varied substantially among treatments, relating to the biological, as well as geochemical conditions, specific to any given tank. For example, a change in the benthic community involving the presence of the benthic shrimp Crangon correlated, qualitatively, with a lowered total water column Mn over the latter months of the experiment, and created a pattern seemingly independent of loading level. Seasonal patterns in Mn concentrations and fluxes, normally evident as correlations with temperature, were occasionally altered; disruption of sediment-water interactions of Mn, which shape the water column concentration of Mn during warm seasons, was significant. Related to this, a general model of benthic Mn flux, as influenced by primary production and eutrophication, as well as the past history of the sediments, was suggested by the data. The rates of dissolved Mn release from sediments, measured in a time series of short-term incubations with an in situ chamber, did not reflect well the longer-term observed changes in sediment in ventory of Mn across the gradient. Progressively larger loss of sediment Mn inventory with increased nutrient loading was suggested; loss generally led to elevated Mn in the water, a change itself determined in each situation by imbalances between the processes of Mn particle deposition and remobilization of Mn 2+ from the sediments. Thus, while the details of Mn cycling varied at different levels of eutrophication and were influenced by the composition and activity of the biological community, the major general consequence of nutrient enrichment was the potential for increased export of Mn from more enriched systems to their offshore receiving waters. Our budget calculations suggested that loss of Mn previously stored within bottom sediments could increase Mn export rates by about 33 to 100% within the first few years of enhanced nutrient loading of a shallow coastal area like Narragansett Bay.

Water Column Sampling as a Rapid and Efficient Method of Determining Effluent Quality and the Performance of Waste Stabilization Ponds

Diurnal series of samples of the effluent and the total in-pond water column of facultative and maturation ponds were analysed for COD, suspended solids, faecal coliforms, chlorophyll and ammonia with a view to finding the most efficient way of obtaining reliable mean daily effluent quality data. The results show that individual samples representative of the entire depth of the pond water column taken at any time of day provided reasonably accurate mean daily effluent values for all the parameters measured when compared with the mean values for effluent quality calculated from a series of grab effluent samples collected throughout the day. The same could not be said for the individual grab effluent samples since they varied considerably. The reasons for these differences are discussed as are the benefits of pond water column sampling for monitoring a number of series of ponds at different locations.

Phytoplankton dynamics in the central Great Barrier Reef—II. Primary production

Water column primary production was measured 43 times over a 3-year period (1983–1985) on the outer shelf of the central Great Barrier Reef province and in the adjacent East Australian Current. No seasonal production cycle could be established. Estimated daily production rates in shelf and offshore waters ranged between 0.1 and 1.5 g C m −2, with most between 0.2 and 0.7 g C m −2. Annual primary production during 1983 in mid-shelf, shelf break and offshore zones was estimated to be 183, 167 and 211 g C m −2, respectively. Annual production by the<10μm size fraction at the same sites was 114, 94 and 127 g C m −2, 62, 56 and 60% of total production, respectively. Corresponding proportions of chlorophyll standing crop in the<10μm fraction were 65, 85 and 79%. In a subset of the above experiments, picoplankton (<2μm size fraction) accounted for 37–99% of total water column production and 32–85% of the chlorophyll standing crop. At first order, annual phytoplankton plus coral reef primary production on the outer shelf in the central GBR is estimated to be 404 g C m −2, with phytoplankton contributing 37%.

Global transmissivity and diffuse fraction of solar radiation for clear and cloudy skies as measured and as predicted by bulk transmissivity models

Measurements of cloudiness and of global, direct, and diffuse radiation taken over a 13 mo period at Davis, CA, are analyzed in terms of global transmission ( K t) and diffuse fraction ( K d) for clear sky conditions and for various cloudiness conditions. A number of global transmission clear sky models are compared with observations for ranges of total water column and turbidity and some are found to give representative values for the global radiation at the ground. The dependence of the diffuse fraction on global transmission is found to be best represented by linear formulae—with different dependencies found for clear and cloudy conditions. Global transmission models are also compared with observations for cloudy conditions and found to give representative values of cloud transmissivities if climatological differences in the cloudiness at the measurement site and those sites used to calibrate the cloud models are considered. These results support the use of routine instantaneous surface meteorological data to calculate the most likely instantaneous global and diffuse radiation on a horizontal surface in the absence of any radiation measurements. These calculated irradiances are best used for solar energy system dynamic modeling in which system responses to typical sequences in meteorological conditions are being examined.