scholarly journals Progressive seawater acidification on the Great Barrier Reef continental shelf

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Katharina E. Fabricius ◽  
Craig Neill ◽  
Erik Van Ooijen ◽  
Joy N. Smith ◽  
Bronte Tilbrook
Keyword(s):  
Coral Reefs ◽  
Continental Shelf ◽  
Great Barrier Reef ◽  
Ocean Acidification ◽  
Seawater Temperature ◽  
Barrier Reef ◽  
Saturation State ◽  
Seawater Acidification ◽  
Seawater Ph ◽  
Seawater Samples

Abstract Coral reefs are highly sensitive to ocean acidification due to rising atmospheric CO2 concentrations. We present 10 years of data (2009–2019) on the long-term trends and sources of variation in the carbon chemistry from two fixed stations in the Australian Great Barrier Reef. Data from the subtropical mid-shelf GBRWIS comprised 3-h instrument records, and those from the tropical coastal NRSYON were monthly seawater samples. Both stations recorded significant variation in seawater CO2 fugacity (fCO2), attributable to seasonal, daytime, temperature and salinity fluctuations. Superimposed over this variation, fCO2 progressively increased by > 2.0 ± 0.3 µatm year−1 at both stations. Seawater temperature and salinity also increased throughout the decade, whereas seawater pH and the saturation state of aragonite declined. The decadal upward fCO2 trend remained significant in temperature- and salinity-normalised data. Indeed, annual fCO2 minima are now higher than estimated fCO2 maxima in the early 1960s, with mean fCO2 now ~ 28% higher than 60 years ago. Our data indicate that carbonate dissolution from the seafloor is currently unable to buffer the Great Barrier Reef against ocean acidification. This is of great concern for the thousands of coral reefs and other diverse marine ecosystems located in this vast continental shelf system.

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.

Rates of nitrogen fixation on coral reefs across the continental shelf of the central Great Barrier Reef

1984 ◽  
Vol 80 (3) ◽  
pp. 255-262 ◽  
Author(s):  
C. R. Wilkinson ◽  
D. McB. Williams ◽  
P. W. Sammarco ◽  
R. W. Hogg ◽  
L. A. Trott
Keyword(s):  
Nitrogen Fixation ◽  
Coral Reefs ◽  
Continental Shelf ◽  
Great Barrier Reef ◽  
Barrier Reef

Demographic variability and long-term change in a coral reef sponge along a cross-shelf gradient of the Great Barrier Reef

2010 ◽  
Vol 61 (4) ◽  
pp. 389 ◽  
Author(s):  
R. J. Bannister ◽  
C. N. Battershill ◽  
R. de Nys
Keyword(s):  
Coral Reefs ◽  
Continental Shelf ◽  
Great Barrier Reef ◽  
Anthropogenic Impacts ◽  
Barrier Reef ◽  
Outer Reef ◽  
Reef System ◽  
Anthropogenic Inputs ◽  
Term Change ◽  
The Mean

Effects of anthropogenic inputs on corals are well documented in regard to the ecology of coral reefs. However, responses to anthropogenic changes by sponge assemblages, also a key component of coral reefs, have received less attention. This paper quantifies differences in abundance, size and distribution of the sponge Rhopaloeides odorabile across a cross-shelf reef system on the central Great Barrier Reef (GBR) from neritic to outer reef oligotrophic waters. Benthic surveys were conducted in reef habitats spatially separated across the continental shelf. The mean abundance of R. odorabile increased significantly with increasing distance from coastal habitats, with 3.5 times more individuals offshore than inshore. In contrast, the mean size (volume) of R. odorabile individuals did not differ significantly across the cross-shelf reef system. On inshore reefs, R. odorabile was restricted to depths <10 m, with a preference for shallower depths (5–6 m). On offshore reefs, R. odorabile was found as deep as 15 m and predominantly between 9 and 10 m. These demographic changes in R. odorabile populations, together with a general population size reduction from surveys made decades prior, suggest a response to anthropogenic impacts across the continental shelf of the central GBR.

scholarly journals Does ocean acidification induce an upward flux of marine aggregates?

2008 ◽  
Vol 5 (4) ◽  
pp. 1023-1031 ◽  
Author(s):  
X. Mari
Keyword(s):  
Ocean Acidification ◽  
Atmospheric Carbon Dioxide ◽  
New Caledonia ◽  
Seawater Acidification ◽  
Seawater Ph ◽  
Biogenic Carbon ◽  
Marine Aggregates ◽  
Atmospheric Carbon ◽  
Carbon Dioxide Co2 ◽  
Sedimentation Processes

Abstract. The absorption of anthropogenic atmospheric carbon dioxide (CO2) by the ocean provokes its acidification. This acidification may alter several oceanic processes, including the export of biogenic carbon from the upper layer of the ocean, hence providing a feedback on rising atmospheric carbon concentrations. The effect of seawater acidification on transparent exopolymeric particles (TEP) driven aggregation and sedimentation processes were investigated by studying the interactions between latex beads and TEP precursors collected in the lagoon of New Caledonia. A suspension of TEP and beads was prepared and the formation of mixed aggregates was monitored as a function of pH under increasing turbulence intensities. The pH was controlled by addition of sulfuric acid. Aggregation and sedimentation processes driven by TEP were drastically reduced when the pH of seawater decreases within the expected limits imposed by increased anthropogenic CO2 emissions. In addition to the diminution of TEP sticking properties, the diminution of seawater pH led to a significant increase of the TEP pool, most likely due to swollen structures. A diminution of seawater pH by 0.2 units or more led to a stop or a reversal of the downward flux of particles. If applicable to oceanic conditions, the sedimentation of marine aggregates may slow down or even stop as the pH decreases, and the vertical flux of organic carbon may reverse. This would enhance both rising atmospheric carbon and ocean acidification.

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