Abstract
Weakly nonlinear (i.e., finite but small amplitude) propagation of plane progressive pressure waves in compressible water flows uniformly containing many spherical bubbles is theoretically ...studied. Drag force acting bubbles and translation of bubbles are newly considered by introducing in momentum conservation equations in a two fluid model and the bubble dynamics equation for volumetric oscillations, respectively. Although these assumptions are the same as our previous paper, in this study, the energy conservation equation for each bubble describing a thermal conduction inside bubble is introduced. By using the method of multiple scales, the Korteweg–de Vries–Burgers equation for low-frequency long wave was derived from the set of basic equations in the two-fluid model. As a result, the dissipation effect was described by two types of terms, i.e., one was the second-order partial derivative owing to the liquid compressibility and the other was the term without differentiation owing to the drag force and the thermal conduction. Finally, we clarified that the dissipation owing to the drag force was smaller than that owing to the thermal conduction.
A freshwater plume from the Fly River, Papua New Guinea, stretched to the south-west over a distance of more than 150km from the estuary towards Torres Strait. The highly turbid freshwater was mixed ...with the relatively clear water of the Gulf of Papua, producing a sharp boundary around 23 salinity. Sediment concentrations were typically more than 50mg l−1inside the turbid water mass, and were rapidly reduced to a few milligrams per litre in the area where salinity was still as low as 26. The area had relatively high levels of phytoplankton (>1μg chl l−1), resulting in rapid depletion of nitrate and phosphate. Biological as well as physico-chemical (flocculation) processes seemed responsible for the rapid removal of sediments from the plume. Settling particles collected near the estuary consisted largely of fine sediments bound loosely by flocculant organic matter, and contained very few plankton and their remains. Further away from the estuary, however, settling particles were dominated by colonies of phytoplankton, fecal pellets and macroscopic aggregates of apparently biological origin. Fine sediments were found firmly attached to or embedded in these settling particles. The area of high biological activities in the plume probably functions as a barrier, limiting a further offshore transport of sediments.
The CO
2 fugacity (
fCO
2) measurements in offshore and lagoonal surface waters were carried out along a ship track of more than 2000 km in and around the Great Barrier Reef (GBR). The surface water ...in the lagoon of the GBR exhibited higher
fCO
2 than oceanic water by about 15 μatm, which was mainly due to the on-going calcification in the reef. The transition zones between the lagoonal and offshore waters varied from less than 10 km to over 100 km in width, which might be related to the development of reef, width of passage, and mesoscale seawater circulation. Estimate of net CO
2 flux associated with reef calcification was available from independent data sets:
fCO
2 measurements of the present study and Kinsey and Hopley's Palaeogeogr., Palaeoclimatol., Palaeoecol. 89 (1991) 363. estimate of bulk calcium carbonate deposition. These two estimates were of the same order. Consideration of similar results from coral reefs developed around oceanic islands in the Indo-Pacific region, including Majuro Atoll, South Male Atoll, and Palau Barrier Reef, together with our observations at the GBR allowed us to draw the conclusion that coral reefs are a potential source for atmospheric CO
2.
The effect of phytoplankton size on feeding rates of planktonic larvae of the crown-of-thorns starfish Acanthaster planci (L.) was evaluated by examining their gut contents under an epifluorescence ...microscope. Concentrations of coccoid cyanobacteria in natural seawater ranged between 1.73 and 5.33 x 10 super(5) cells ml super(-1) and were three to four orders of magnitude greater than that of eukaryotes. Under these conditions, A. planci larvae ingested similar or smaller numbers of cyanobacteria than eukaryotes. Consequently, clearance rates of A. planci larvae on cyanobacteria were approximately three orders of magnitude lower than those on eukaryotes. Cyanobacteria and eukaryotes in the gut of A. planci larvae had mean equivalent spherical diameter (ESD) of 1-2 mu m and 3.6-4.6 mu m, respectively. Thus, the volume of cyanobacteria ingested was less than 10% of the volume of eukaryotes ingested. Acanthaster planci larvae were fed cultured phytoplankton Dunaliella tertiolecta and suspensions of three different sizes of plastic beads with fluorescence labelling. There was no significant difference in clearance rates on 6 and 20 mu m plastic beads. Clearance rates on 1 mu m plastic beads were, however, much lower than those on 6 and 20 mu m plastic beads. Apart from particle size, this result shows that feeding of A. planci larvae is influenced by other properties of potential food particles.
There has been a debate over whether the growth and development of the larvae of the crown-of-thorns starfish Acanthaster planci are severely food-limited. This debate has raised a range of ...questions, including the one relating to the role of heterotrophic bacteria in the nutrition of larvae. In this study, the feeding rate of larvae on bacteria as well as on other ultraplankton (<5 μm) was determined by counting the number of the fluorescence-labeled cells (FLC) in the gut after short incubation. Preliminary experiments showed no detrimental effect of the fluorescence dye (5-(4,6-dichlorotriazin-2-yl) aminofluorescein) on the development of larvae and demonstrated the usefulness of FLC in feeding experiments as food particles analogous to living cells of ultraplankton. There was no evidence that larvae ingested bacteria. Larvae did ingest two strains of photosynthetic cyanobacteria, which had equivalent spherical diameters (ESD) of 1 and 1.8 μm, but these tiny cells were cleared more than 10 times slower than the larger algae Phaeodactylum tricornutum (4.7 μm ESD) and Dunaliella tertiolecta (5.1 μm ESD). Regardless of the size of FLC used, the clearance rate (volume of water cleared per animal per unit time) increased by 50-120%, as larvae developed from the late bipinnaria stage to the late brachiolaria stage. These results show that larvae may derive a sizable proportion of their nutrition from ultraplankton, but not from bacteria.
Nutrient concentrations were measured at a fixed station in the lagoon of Davies Reef, the central Great Barrier Reef, Australia, monthly between January and December 1990. The day-to-day variation ...in nutrient concentration inside and outside the lagoon was determined in May. The average dissolved inorganic nitrogen (DIN) (sum of NO sub(3), NO sub(2), and NH sub(4)) concentration for the pooled data in each of 11 monthly observations ranged between 0.34 and 1.84 mu M. There was only a two-fold variation in average PO sub(4) concentration. Average SiO sub(4) concentration showed a magnitude of variation similar to that of DIN concentration. DIN concentration was significantly higher in the lagoon than in the surrounding open water, suggesting that the significant DIN flux results from internal sources. There were no clear inside-outside differences in PO sub(4) and SiO sub(4) concentrations. N:P ratios in the lagoon were usually < 16:1, suggesting the possibility of N limitation.
In total, ten dilution experiments were conducted to determine growth and grazing mortality rates of picoplanktonic cyanobacteria. Concentrations of nitrogenous nutrients (NO
3 + NO
2 + NH
4) and ...phosphate (PO
4) were relatively low, being in the range between 0.09–0.82 μM and between 0.05–0.11 μM, respectively. Specific growth and grazing mortality rates of cyanobacteria were estimated as 0.0101–0.0424 h
−1 and < 0–0.0069 h
−1, respectively. The reliability of these estimates were, however, rather questionable. One of the critical assumptions in the dilution technique is that phytoplankton growth rates are identical in diluted and undiluted water. This assumption was not always valid for cyanobacterial populations sampled. In seven of ten experiments, the day-time peak of the frequency of dividing cells (FDC) of cyanobacteria was lower in diluted water than in undiluted water, with the difference in mean value being in the range between 1.3–3.9%. No such difference was, however, observed in nutrient enriched treatments. This suggests the likelihood of nutrient limitation and the need for including nutrient enriched treatments in the experimental design. Incorporating FDC measurements into the experimental design is also a worthwhile practice as an independent check of the reliability of growth and grazing mortality rate estimates, particularly those for cyanobacterial populations in oligotrophic tropical waters.
The Great Barrier Reef (GBR) is the largest reef system in the world. During winter (dry season), a relative increase of CO2 fugacity, together with a depletion in total alkalinity, was evident in ...the GBR lagoon water. This suggests the release of CO2 due to CaCO3 production in the lagoon. But, in detail, significant contribution from organic matter oxidation was also identified. Despite the dissolved carbon losses as carbonate, total dissolved inorganic carbon (DIC) concentration normalized at constant salinity was relatively uniform throughout the study area. This indicates the presence of external carbon input to the lagoon. The most likely source is river discharge, which carries sizeable amounts of dissolved and particulate organic carbon as well as DIC. The marine CO2 system of the GBR lagoon highlights the nature of tropical carbonate shelves as a strong alkalinity sink and a net oxidation site of land‐derived organic carbon.
Phytoplankton biomass, production and grazing mortality were measured in Exmouth Gulf, a shallow embayment on the arid, tropical coast of Western Australia. In the Gulf, chlorophyll
a concentrations ...were typically 0.2–0.3 mg m
−3 and phytoplankton production rates were mostly below 25 mg of C m
−3 d
−1. The low phytoplankton biomass and production in the Gulf are seemingly related to the aridity of the region and hence the small terrestrial runoff of nutrients. In dilution experiments, which complemented
14C incorporation experiments, the proportion of potential primary production grazed ranged from 79 to 155% in the fluorometric analysis of chlorophyll
a and from 73 to 191% in the HPLC analysis of chlorophyll
a. There may be some excess phytoplankton production on the relatively well flushed, western side of the Gulf. On the eastern side of the Gulf, however, the estimated grazer biomass ranged between 4.6–8.8 mg of C m
−3, not much less than the estimated phytoplankton biomass (6–15 mg of C m
−3), and this grazer population appeared to consume more organic matter than the phytoplankton population could produce. The disproportionally large grazer biomass and the relatively high grazing mortality of phytoplankton may be due to the supply of additional organic matter from benthic macroalgal communities and/or mangrove and salt flat systems present on the eastern side of the Gulf.
The Great Barrier Reef (GBR) is the largest reef system in the world. During winter (dry season), a relative increase of CO sub(2) fugacity, together with a depletion in total alkalinity, was evident ...in the GBR lagoon water. This suggests the release of CO sub(2) due to CaCO sub(3) production in the lagoon. But, in detail, significant contribution from organic matter oxidation was also identified. Despite the dissolved carbon losses as carbonate, total dissolved inorganic carbon (DIC) concentration normalized at constant salinity was relatively uniform throughout the study area. This indicates the presence of external carbon input to the lagoon. The most likely source is river discharge, which carries sizeable amounts of dissolved and particulate organic carbon as well as DIC. The marine CO sub(2) system of the GBR lagoon highlights the nature of tropical carbonate shelves as a strong alkalinity sink and a net oxidation site of land-derived organic carbon.
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