Stratification in a small lagoon in the Great Barrier Reef

1984 ◽  
Vol 35 (3) ◽  
pp. 273 ◽  
Author(s):  
JC Andrews ◽  
WC Dunlap ◽  
NF Bellamy
Keyword(s):  
Great Barrier Reef ◽  
Time Scales ◽  
Wind Stress ◽  
Thermal Stratification ◽  
Bottom Water ◽  
Reef Flat ◽  
Low Frequency ◽  
Wind Vector ◽  
Barrier Reef ◽  
Lunar Synchronization

Temperatures were measured in a small lagoon in the windward reef flat of Davies Reef in the central Great Barrier Reef and examined on three time scales to gain three perspectives on thermal stratification and the trapping of bottom water. Profiling for stratification and dye revealed layering where bottom water was trapped and released by the successive capping and uncapping of the lagoon by a diurnal thermocline. A 1-month monitoring array revealed a solar synchronization, with the temperature of reef-flat water exceeding temperatures of lagoon water by up to 1 5�C within 1 h of midday, and lagoon stratification lagging this by 1 h. There was also a lunar synchronization with mixing proceeding during nocturnal rising tides. Lagoon surface and bottom temperatures were also monitored for 11 months. The amplitude of the diurnal stratification showed no coherence either with the amplitude of the tide (marked spring-neap tides) or with scalar wind stress. The low frequency amplitude of the diurnal oscillation was coherent with the longshore wind vector at periods near 3 6 days and in a band approximately from 10 to 40 days. Daily stratification increased when winds were poleward and decreased when winds were equatonvard. Events of flushing were separated on average by 9 h, but the most frequently observed separation was 5 h and only 10% of separations exceeded 18 h during the 11 months.

Water circulation around Britomart Reef, Great Barrier Reef, during July 1979

1980 ◽  
Vol 31 (4) ◽  
pp. 415 ◽  
Author(s):  
E Wolanski ◽  
M Jones
Keyword(s):  
Great Barrier Reef ◽  
Sea Level ◽  
Central Region ◽  
Reef Flat ◽  
Water Circulation ◽  
Barrier Reef ◽  
Trade Winds ◽  
Sea Breezes ◽  
Coral Sea ◽  
Sea Level Oscillations

Weather and currents at eight sites were measured and drogue trajectories obtained in July 1979 at Britomart Reef, a middle reef located at 18�16'S.,146� 38'E. in the central region of the Great Barrier Reef province. The longest current records (3 weeks) were obtained at two sites in passes between the Coral Sea and the Great Barrier Reef Lagoon where westerly currents modulated by tides were observed. Analysis of residuals also showed the importance of wind-driven secondary circulation. Non-tidal sea-level oscillations were very small. Shorter current records (1-10 days) at six sites in the lagoon and on the reef flat showed a predominant northerly flow, also modulated by tides and wind. A residual anticlockwise water circulation existed in the lagoon where flushing was controlled more by winds than by tides. The rise in sea level over the reef flat as a result of waves breaking was negligible. Temperature differences between air and water accounted for the cooling of the water column during the expedition. Constant south-east trade winds were experienced at the reef, while on land the wind was weaker. more variable, and often dominated by land-sea breezes.

Population structure and trophic composition of the free-living nematodes inhabiting carbonate sands of Davies Reef, Great Barrier Reef, Australia

1986 ◽  
Vol 37 (5) ◽  
pp. 609 ◽  
Author(s):  
DM Alongi
Keyword(s):  
Population Structure ◽  
Great Barrier Reef ◽  
Reef Flat ◽  
Detrended Correspondence Analysis ◽  
Reef Crest ◽  
Barrier Reef ◽  
Back Wall ◽  
Free Living ◽  
Shallow Lagoon ◽  
Reef Zones

Population structure and trophic composition of free-living nematodes from carbonate sands within different functional zones (reef crest, reef flat and lagoon) of Davies Reef in the Great Barrier Reef were examined. At the reef crest (station C) and at a shallow lagoon area unprotected by the back wall of the reef flat (station G), sediments were subjected to intense wave action and supported significantly (P < 0.05) lower mean nematode densities (<60 individuals per 10 cm2) than sands within the other reef zones (100-400 individuals per 10 cm2). Mean nematode densities and numerical species richness were highest (P < 0.05) in a shallow lagoon habitat protected from hydrodynamic- induced disturbances by the back wall of the reef flat (station H). Differences in population densities among the reef zones were not related to water depth or sediment granulometry. Species diversity was low within the reef, with only six species present in deep lagoon sands co-inhabited by actively bioturbating ghost shrimps (Callianassa spp.). Normal classification, nodal analysis and detrended correspondence analysis indicated that faunal groups were distinct among the different reefal zones. Very coarse to medium sands at the reef crest and across the reef flat were inhabited primarily by omnivorous and epistrate-feeding nematodes. Most nematodes within the very fine to fine sands of the lagoon were non-selective or selective deposit feeders. Nematode community structure from the reef crest to the shallow lagoon appears to be determined primarily by sediment granulometry as controlled by reef hydrodynamics, whereas in the deep lagoon nematode communities are negatively affected by the presence of thalassinid ghost shrimps.

Water circulation and shelf waves in the northern Great Barrier Reef lagoon

1981 ◽  
Vol 32 (5) ◽  
pp. 721 ◽  
Author(s):  
E Wolanski ◽  
B Ruddick
Keyword(s):  
Great Barrier Reef ◽  
Sea Level ◽  
Low Frequency ◽  
Current Data ◽  
Barrier Reef ◽  
Sea Levels ◽  
The North ◽  
Level Data ◽  
Shelf Wave ◽  
Salinity Water

Currents and sea levels were measured at a number of locations in the Great Barrier Reef (GBR) lagoon from about 10 to 13� S., during the period October-December 1979. A strong non-tidal, low-frequency modulation of all sea-level and current data was found. The currents nearshore were driven northward by the wind, and then at least partially blocked by the dense network of reefs to the north of 10� s. The water then flowed southward in deeper water adjacent to the reef, driven by a longshore pressure gradient. The low- frequency sea-level data, though not the current records, showed northward phase propagation at speeds characteristic of a first-mode shelf wave trapped in the lagoon between the shore and the reef. Data are presented revealing the intrusion of low-salinity water, through Bligh Entrance, in the GBR lagoon, as a result of river discharges in the Gulf of Papua. It is suggested that low-frequency longshore currents may periodically flush these river plumes from the GBR lagoon and enhance interaction between reefs. In the Coral Sea in front of reef passages, the large horizontal velocities may result in forces upwelling by selective withdrawal and jet entrainment.

Water masses, nutrient levels and sesonal drift on the outer central Queensland shelf (Great Barrier Reef)

1983 ◽  
Vol 34 (6) ◽  
pp. 821 ◽  
Author(s):  
JC Andrews
Keyword(s):  
Surface Water ◽  
Great Barrier Reef ◽  
Bottom Water ◽  
Chlorophyll Concentration ◽  
Central Zone ◽  
Shelf Break ◽  
Barrier Reef ◽  
Oxygen Utilization ◽  
Phosphate Nitrate ◽  
Reef Zone

A series of 19 cruises in 19 months in the central zone of the Great Barrier Reef was made in 1980-1 981 to examine the seasonal thermohaline cycles and nutrient distributions. The reefs occupy the outer 60 km of the shelf and the mixing there of Lagoon Water, Coral Sea Surface Water, Shelf-break Water and Subtropical Lower Water is examined using thermohaline data. Current meters and thermistors were moored from mid-1980 to mid-1982 to obtain seasonal drift and subseasonal temperature fluctuations. Subtropical Lower Water upwells through the reef zone to create a year-round thermal contrast between Shelf-break and Lagoon Waters, and vertical density stratification reflects this temperature contrast on the shelf Salinity variations reflect monsoonal rainfall and winter evaporation; rainfall and salinity show an interannual variation. The drifts of bottom water over the outer lagoon and of surface water over the continental slope follow the isobaths poleward. In the reef zone between the lagoon and the shelf break, there is a substantial cross-isobath, onshore flow of bottom water. Surface waters exhibit no significant averaged gradients in phosphate, nitrate, nitrite or oxygen utilization aross the reef zone. Surface chlorophyll concentration is high amongst the reefs. Subsurface chlorophyll levels are similarly high inside the shelf break, and subsurface phosphate, nitrate and oxygen utilization increases markedly, seaward across the reefs, particularly near the shelf break.

Continental shelf waves and their influence on the circulation around the Great Barrier Reef

1983 ◽  
Vol 34 (1) ◽  
pp. 23 ◽  
Author(s):  
E Wolanski ◽  
AF Bennett
Keyword(s):  
Continental Shelf ◽  
Great Barrier Reef ◽  
Sea Level ◽  
Atmospheric Pressure ◽  
Low Frequency ◽  
Internal Tides ◽  
Wind Component ◽  
Barrier Reef ◽  
Longshore Current ◽  
Shelf Waves

Winds and atmospheric pressure, sea level and water currents were measured at several locations over the continental shelf, both east and west of the Great Barrier Reef, between 14.5�s. and 20�S., from June to November 1980. The dominant wind direction changed from westward over the Coral Sea to north- westward (roughly parallel to the shore) over the shelf. A strong non-tidal low-frequency signal in all sea- level and longshore current data was found, highly coherent from site to site and strongly correlated with the longshore wind component over the shelf, though not with the atmospheric pressure. A model of wind- driven barotropic shelf waves is used to explain a number of observations, such as the invariance of temporal fluctuations of longshore current with distance from shore, and the northward longshore propagation of oceanic disturbances at a speed equal to twice that of the first-mode barotropic free shelf wave, a speed one order of magnitude smaller than that of the wind system. The low-frequency current fluctuations resulted in large water displacements, up and down the coast. Low-frequency cross-shelf currents were much weaker and less coherent. Two upwelling mechanisms are internal tides and internal Kelvin waves coupled to the barotropic shelf waves.

Upwelling by internal tides and kelvin waves at the continental shelf break on the Great Barrier Reef

1983 ◽  
Vol 34 (1) ◽  
pp. 65 ◽  
Author(s):  
E Wolanski ◽  
GL Pickard
Keyword(s):  
Continental Shelf ◽  
Great Barrier Reef ◽  
Low Frequency ◽  
Kelvin Waves ◽  
Shelf Break ◽  
Internal Tides ◽  
Wind Component ◽  
Barrier Reef ◽  
Tidal Period ◽  
Continental Shelf Break

A time series of 50 days duration was obtained of sea levels and winds and of temperature and currents at six depths from 27 to 104 m at 18�19'S.,147�21'E. on the continental shelf break between the Great Barrier Reef and the Coral Sea. The sea-level signal had a predominantly mixed solar and lunar semidiurnal tidal period. The currents consisted of a semidiurnal tidal component oriented primarily cross-shelf, except near the sea floor, superimposed on a low-frequency, predominantly longshore, southward component, coherent with depth, in geostrophic balance, and modulated by the longshore wind component Large fluctuations in temperature were observed, consisting of a low-frequency component, possibly generated by internal Kelvin waves, and iiucruarions of predominantiy solar semidiurnai iidai period. The latter fiiictuations are interpreted as evidence of internal tides of amplitude up to 110 m that may be generated by the interaction of the longshore currents with topographic irregularities in the shelf. It is suggested that, during any long-term studies of water properties near the shelf break, some additional monitoring of short-term temporal variations should be carried out to avoid data aliasing by internal tides. The bottom boundary layer appears to be very active in vertical mixing. Internal tides may be very important in introducing other water components, e.g. nutrients, to the outer Great Barrier Reef.

scholarly journals Time Scales of Southern Ocean Eddy Equilibration

2016 ◽  
Vol 46 (9) ◽  
pp. 2785-2805 ◽  
Author(s):  
Anirban Sinha ◽  
Ryan P. Abernathey
Keyword(s):  
Southern Ocean ◽  
Time Scales ◽  
Wind Stress ◽  
Time Scale ◽  
High Frequency ◽  
Channel Model ◽  
Large Fraction ◽  
Low Frequency ◽  
Amplitude Response ◽  
Relative Conversion

AbstractStratification in the Southern Ocean is determined primarily by a competition between westerly wind-driven upwelling and baroclinic eddy transport. This study investigates the time scales of equilibration of the Southern Ocean in response to changing winds through an idealized channel model. An analytical framework describing the energetic pathways between wind input, available potential energy (APE), eddy kinetic energy (EKE), and dissipation provides a simple theory of the phase and amplitude response to oscillating wind stress. The transient ocean response to variable winds lies between the two limits of Ekman response (high frequency), characterized by the isopycnal slope responding directly to wind stress, and “eddy saturation” (low frequency), wherein a large fraction of the anomalous wind work goes into mesoscale eddies. The crossover time scale is the time scale of meridional eddy diffusive transport across the Antarctic Circumpolar Current (ACC) front. For wind variability with a period of 3 months (high-frequency forcing), the relative conversion of wind work to APE/EKE is 11, while for a period of 16 years (low-frequency forcing), the relative conversion to APE/EKE reduces to 3. The system’s frequency response is characterized by a complex transfer function. Both the phase and amplitude response of EKE and APE predicted by the linear analytic framework are verified using multiple ensemble experiments in an eddy-resolving (4-km horizontal resolution) isopycnal coordinate model. The results from the numerical experiments show agreement with the linear theory and can be used to explain certain features observed in previous modeling studies and observations.

scholarly journals The contribution of coral reef-derived dimethyl sulfide to aerosol burden over the Great Barrier Reef: a modelling study

2021 ◽  
Author(s):  
Sonya Fiddes ◽  
Matthew Woodhouse ◽  
Steve Utembe ◽  
Robyn Schofield ◽  
Joel Alroe ◽  
...  
Keyword(s):  
Coral Reef ◽  
Great Barrier Reef ◽  
Time Scales ◽  
Dimethyl Sulfide ◽  
Regional Scale ◽  
Cloud Formation ◽  
Barrier Reef ◽  
Anthropogenic Aerosol ◽  
Daily Time

Abstract. Coral reefs have been found to produce the sulfur compound dimethyl sulfide (DMS), a climatically relevant aerosol precursor predominantly associated with phytoplankton. Until recently, the role of coral reef-derived DMS within the climate system had not been quantified. A study preceding the present work found that DMS produced by corals had negligible long-term climatic forcing at the global-regional scale. However, at sub-daily time scales more typically associated with aerosol and cloud formation, the influence of coral reef-derived DMS on local aerosol radiative effects remains unquantified. The Weather Research and Forecasting – chemistry model (WRF-Chem) has been used in this work to study the role of coral reef-derived DMS at sub-daily time scales for the first time. WRF-Chem was run to coincide with an October 2016 field campaign over the Great Barrier Reef, Queensland, Australia, against which the model was evaluated. After updating the DMS surface water climatology, the model reproduced DMS and sulfur concentrations well. The inclusion of coral reef-derived DMS resulted in no significant change in sulfate aerosol mass or total aerosol number. Subsequently, no direct or indirect aerosol effects were detected. The results suggest that the co-location of the Great Barrier Reef with significant anthropogenic aerosol sources along the Queensland coast prevents coral reef derived-aerosol from having a modulating influence on local aerosol burdens in the current climate.

scholarly journals Dynamics of seawater carbonate chemistry, production, and calcification of a coral reef flat, central Great Barrier Reef

2013 ◽  
Vol 10 (10) ◽  
pp. 6747-6758 ◽  
Author(s):  
R. Albright ◽  
C. Langdon ◽  
K. R. N. Anthony
Keyword(s):  
Coral Reef ◽  
Coral Reefs ◽  
Great Barrier Reef ◽  
Reef Flat ◽  
Global Scale ◽  
Barrier Reef ◽  
Carbonate Chemistry ◽  
Saturation State ◽  
Diel Cycles ◽  
Seawater Carbonate Chemistry

Abstract. Ocean acidification is projected to shift coral reefs from a state of net accretion to one of net dissolution this century. Presently, our ability to predict global-scale changes to coral reef calcification is limited by insufficient data relating seawater carbonate chemistry parameters to in situ rates of reef calcification. Here, we investigate diel and seasonal trends in carbonate chemistry of the Davies Reef flat in the central Great Barrier Reef and relate these trends to benthic carbon fluxes by quantifying net ecosystem calcification (nec) and net community production (ncp). Results show that seawater carbonate chemistry of the Davies Reef flat is highly variable over both diel and seasonal cycles. pH (total scale) ranged from 7.92 to 8.17, pCO2 ranged from 272 to 542 μatm, and aragonite saturation state (Ωarag) ranged from 2.9 to 4.1. Diel cycles in carbonate chemistry were primarily driven by ncp, and warming explained 35% and 47% of the seasonal shifts in pCO2 and pH, respectively. Daytime ncp averaged 37 ± 19 mmol C m−2 h−1 in summer and 33 ± 13 mmol C m−2 h−1 in winter; nighttime ncp averaged −30 ± 25 and −7 ± 6 mmol C m−2 h−1 in summer and winter, respectively. Daytime nec averaged 11 ± 4 mmol CaCO3 m−2 h−1 in summer and 8 ± 3 mmol CaCO3 m−2 h−1 in winter, whereas nighttime nec averaged 2 ± 4 mmol and −1 ± 3 mmol CaCO3 m−2 h−1 in summer and winter, respectively. Net ecosystem calcification was highly sensitive to changes in Ωarag for both seasons, indicating that relatively small shifts in Ωarag may drive measurable shifts in calcification rates, and hence carbon budgets, of coral reefs throughout the year.

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