From The University of Sydney (AU)
4.29.24
Marcus Strom
Media Adviser
+61 423 982 485
marcus.strom@sydney.edu.au
Elevated nutrient levels in the ocean impacted reef growth.
A new study, conducted at the University of Sydney research station at One Tree Island, shows that coral reef growth wasn’t halted but just went deeper, slower.
Jack-up drill system deployed on the reef flat with a blue star fish in the foreground.
As the modern Great Barrier Reef emerged after the last ice age, it had to cope with multiple environmental stresses – rising sea levels, increased sediment from a flooding coastline, ocean turbulence and likely warming oceans.
It has been speculated that these factors inhibited the emergence of the modern Great Barrier Reef, but with little direct data. Now, for the first time, geoscientists have managed to determine how these factors, particularly water quality, contributed to the reef’s development between about eight and six thousand years ago.
Their findings, published today in Quaternary Science Reviews, confirm a long-standing idea that elevated nutrient levels impacted reef growth. In modern coral reefs, nutrient-rich waters have been observed to favour macro algae, which can outcompete corals, as well as cause increases in bio-eroders that can weaken coral skeletons.
Fig. 1. Location of One Tree and Heron Reefs, and location of One Tree Reef Holocene cores (inset) (bathymetry source (Beaman, 2010)).
See the science paper for instructive material with images.
As the modern reef emerged thousands of years ago, scientists have found that these factors led to the establishment of slower-growing and more sediment-tolerant coral communities in deeper water, rather than the more familiar shallow and clear-water species that emerged later.
Senior author Professor Jody Webster from the School of Geosciences at the University of Sydney said: “This study has given us an historical picture of how the emerging modern reef responded to huge environmental stress.
“We get the picture of a dynamic ecosystem dealing with adverse environmental conditions during the early Holocene as sea levels rose and inundated the previously exposed shelf.”
Lead author Dr Kelsey Sanborn from the Geocoastal Research Group in the School of Geosciences said: “This work demonstrates that reef communities were able to grow despite higher sediment and nutrient input to the reef. However, the types of corals that grew were more like today’s inshore, turbid reefs, as opposed to the shallow and clear-water communities common on One Tree Reef today.
“This provides evidence to understand early Holocene water quality on the southern Great Barrier Reef and demonstrates the capacity of the reef to grow under conditions that would typically be considered unsuitable.”
Overview close up of fossil reef core investigated in this study.
The research was conducted at the University of Sydney research station at One Tree Island, in collaboration with the University of Queensland, Southern Cross University and the University of Tokyo. Using a jack-up drill rig, geoscientists drilled into the reef, extracting cores from 12 sites. The extracted cores provided fossilised records of corals for examination.
Professor Webster said: “Our research establishes the first geochemical record of skeletal-bound organic nitrogen from precisely dated cores from this time. We also measured the ratio of barium to calcium in the corals.
“The elevated nitrogen and barium-to-calcium values point to increased sediment and nutrient levels on the reef.”
The team compared their results with established records of rare earth elements and yttrium as proxies for land-based sediment and nutrient concentrations on the reef.
Dr Sanborn said: “Our study provides important evidence of how the modern Great Barrier Reef emerged and withstood environmental stresses.
“Over this period of a thousand years, sea levels rose about 10 metres. Had sea levels continued to rise at this rate, we can’t be sure if the reef would have survived.
“What we do see is that only some of the more tolerant reef communities were able to continue growing slowly during this time until ocean levels and other factors stabilised.”
Professor Webster said: “The Great Barrier Reef now faces a new set of environmental stressors, many of them due to human, industrial and agricultural activity. Our work looking at the history of the reef can assist in understanding how coral communities might respond to some of that stress today.”
See the full article here .
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The University of Sydney (AU)
Our founding principle as Australia’s first university, U Sydney was that we would be a modern and progressive institution. It’s an ideal we still hold dear today.
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The University of Sydney (AU) is an Australian public research university in Sydney, Australia. Founded in 1850, it is Australia’s first university and is regarded as one of the world’s leading universities. The university is known as one of Australia’s six “sandstone universities”. Its campus, spreading across the inner-city suburbs of Camperdown and Darlington, is ranked in the top 10 of the world’s most beautiful universities by the British Daily Telegraph and the American Huffington Post. The university comprises eight academic faculties and university schools, through which it offers bachelor, master and doctoral degrees.
The QS World University Rankings ranked the university as one of the world’s top 25 universities for academic reputation, and high in the world for graduate employability. It is one of the first universities in the world to admit students solely on academic merit, and opened their doors to women on the same basis as men.
Nobel and Crafoord laureates have been affiliated with the university as graduates and faculty. The university has educated Australian prime ministers, governors-general of Australia, state governors and territory administrators, and justices of the High Court of Australia, including chief justices. The university has produced Rhodes Scholars and Gates Scholars.
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