scholarly journals Ninety years of change on a low wooded island, Great Barrier Reef

2019 ◽  
Vol 6 (6) ◽  
pp. 181314 ◽  
Author(s):  
S. M. Hamylton ◽  
R. McLean ◽  
M. Lowe ◽  
F. A. F. Adnan
Keyword(s):  
Great Barrier Reef ◽  
Reef Flat ◽  
Barrier Reef ◽  
Carbonate Sand ◽  
Specific Nature ◽  
Vegetation Growth ◽  
Wave Dynamics ◽  
Relative Contribution ◽  
Carbonate Budget ◽  
Variable Nature

We assess 90 years of change on a Low Wooded Island (Low Isles, Great Barrier Reef), employing drones and topographic profiling to accurately survey ramparts, mangroves, the reef flat and the sand cay. A comparison with maps from the 1928–1929 Great Barrier Reef Expedition revealed the redistribution of an outer rampart and inward movement of shingle ridges. Remarkable lateral expansion of the mangrove woodland some 400 m has occurred as carbonate sand deposition has increased reef flat elevation, obscuring coral microatolls. The sand cay has stayed relatively constant in size, moving approximately 44 m in a northeasterly direction and rotating slightly. We conclude that the existing configuration of landforms probably represents an equilibrium with local biophysical conditions, including sea level, wave dynamics, vegetation growth, storms and cyclones. The variable nature of ramparts and the presence of a trough that prevents the continuous spread of mangroves across a uniformly flat colonization surface precludes the interpretation of landform changes with respect to a geomorphic evolutionary sequence. Moreover, longer-term implications of environmental change for these landforms can only be evaluated once the specific nature of the local carbonate budget, including the relative contribution of corals, foraminifera and Halimeda has been elucidated.

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.

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.

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.

Influence of hydrodynamic energy on Holocene reef flat accretion, Great Barrier Reef

2016 ◽  
Vol 85 (1) ◽  
pp. 44-53 ◽  
Author(s):  
Belinda Dechnik ◽  
Jody M. Webster ◽  
Luke Nothdurft ◽  
Gregory E. Webb ◽  
Jian-xin Zhao ◽  
...  
Keyword(s):  
Great Barrier Reef ◽  
Reef Flat ◽  
Wind Wave ◽  
Great Variability ◽  
Barrier Reef ◽  
The Past ◽  
Accretion Rates ◽  
Main Driver ◽  
Reef Zones ◽  
Hydrodynamic Energy

AbstractThe response of platform reefs to sea-level stabilization over the past 6 ka is well established for the Great Barrier Reef (GBR), with reefs typically accreting laterally from windward to leeward. However, these observations are based on few cores spread across reef zones and may not accurately reflect a reef's true accretional response to the Holocene stillstand. We present a new record of reef accretion based on 49 U/Th ages from Heron and One Tree reefs in conjunction with re-analyzed data from 14 reefs across the GBR. We demonstrate that hydrodynamic energy is the main driver of accretional direction; exposed reefs accreted primarily lagoon-ward while protected reefs accreted seawards, contrary to the traditional growth model in the GBR. Lateral accretion rates varied from 86.3 m/ka–42.4 m/ka on the exposed One Tree windward reef and 68.35 m/ka–15.7 m/ka on the protected leeward Heron reef, suggesting that wind/wave energy is not a dominant control on lateral accretion rates. This represents the most comprehensive statement of lateral accretion direction and rates from the mid-outer platform reefs of the GBR, confirming great variability in reef flat growth both within and between reef margins over the last 6 ka, and highlighting the need for closely-spaced transects.

The influence of sea level and cyclones on Holocene reef flat development: Middle Island, central Great Barrier Reef

Coral Reefs ◽  
2016 ◽  
Vol 35 (3) ◽  
pp. 805-818 ◽  
Author(s):  
E. J. Ryan ◽  
S. G. Smithers ◽  
S. E. Lewis ◽  
T. R. Clark ◽  
J. X. Zhao
Keyword(s):  
Great Barrier Reef ◽  
Sea Level ◽  
Reef Flat ◽  
Barrier Reef ◽  
Holocene Reef

scholarly journals Measurements of the local energy balance over a coral reef flat, Heron Island, southern Great Barrier Reef, Australia

2010 ◽  
Vol 115 (D19) ◽  
Author(s):  
Hamish A. McGowan ◽  
Andrew P. Sturman ◽  
Melissa C. MacKellar ◽  
Andrew H. Wiebe ◽  
David T. Neil
Keyword(s):  
Coral Reef ◽  
Energy Balance ◽  
Great Barrier Reef ◽  
Reef Flat ◽  
Local Energy ◽  
Barrier Reef

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

2013 ◽  
Vol 10 (5) ◽  
pp. 7641-7676 ◽  
Author(s):  
R. Albright ◽  
C. Langdon ◽  
K. R. N. Anthony
Keyword(s):  
Coral Reef ◽  
Great Barrier Reef ◽  
Reef Flat ◽  
Global Scale ◽  
Barrier Reef ◽  
Carbonate Chemistry ◽  
Net Community Production ◽  
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 natural trends in carbonate chemistry of the Davies Reef flat in the central Great Barrier Reef on diel and seasonal timescales 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 timescales. 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 36 ± 19 mmol C m−2 h−1 in summer and 33 ± 13 mmol C m−2 h−1 in winter; nighttime ncp averaged −22 ± 20 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 positively correlated with Ωarag for both seasons. Linear correlations of nec and Ωarag indicate that the Davies Reef flat may transition from a state of net calcification to net dissolution at Ωarag values of 3.4 in summer and 3.2 in winter. Diel trends in Ωarag indicate that the reef flat is currently below this calcification threshold 29.6% of the time in summer and 14.1% of the time in winter.

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