Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Vanuatu: The coral reef, record of a 23,000 year history

04.12.2003


A research team from the IRD "Tropical Palaeo-environments and climatic variability" research unit and their American co-workers (1) have succeeded in retracing over a 23 000 year period the history of a coral reef of the Island of Urelapa, in Vanuatu. This fossil reef bears the record of the longest continuous growth – 17 000 years – ever studied by scientists (2). For the first time, researchers have at their disposal uninterrupted records of environmental data on the whole of the deglaciation period, which began around 20 000 years ago (3). A major finding is that the Urelapa reef changed growth strategy, in response to environmental changes which occurred during the post-glacial sea-level rise. More broadly, this research has brought new key information which contributes to a better understanding of the influence of climatic change on the coral reefs of the Pacific, which are the most complex ecosystems of the marine environment.



In the course of the last glacial maximum, around 20 000 years B.P., sea levels reached their lowest point, at 120 to 130 metres below the present level. The subsequent ice-cap melting induced a gradual rise of the oceans up to current levels. In the tropical regions, these large-amplitude fluctuations have contributed to the formation and growth of coral reefs.

IRD researchers at Noumea, in conjunction with scientists from three American universities (1), have just reconstructed the history of the oldest post-glacial reef ever studied in the Pacific which has grown under the influence of sea-level oscillations. This reef is situated at Urelapa, off the island of Espiritu Santo in the Vanuatu group in the South-West Pacific. It shows the longest recorded continuous growth, at 17 000 years, between 23 000 and 6 000 years B.P.. (2). The scientists thus have at their disposal environmental data (sea-levels, quantity of nutrients, temperatures, and so on) covering the entire period of deglaciation (3).


Core samples from five boreholes made on the island were analysed. Data was taken on the sedimentology, palaeontology, radiochronology (dating of the corals) and palaeoecology (study of communities of fossil organisms like corals, algae and molluscs). Character and morphological analysis of the corals (whether tabular, branched, massive or foliaceous) and the calcareous algae species which are associated with them gave clues which put together produced a reconstruction of the different stages of the reef’s development (4). These corals reveal a strong ability to adapt. The reef developed according to two different and successive growth processes, in response to variations in environmental conditions and, in particular, to sea-level changes.

From 23 000 to about 11 300 years B.P., the reef developed continuously, keeping to the shallow marine habitats. The corals thus followed the rise in the oceans very closely. The associations of ramified corals, including species of the Acropora genus, with red encrusting algae, as coralgal assemblages, forming the basis of the reef frameworks, found at horizons dating from this period, are specific to shallow well-lit, high wave-energy environments (at depths less than 6 m), ideal conditions for reef growth.

However, from 11 300 to 6 000 years B.P. the coral colony morphology, consisting mainly of massive Porites species, and changes observed in the associations of organisms show a deeper, calm water (i.e. low wave-energy) habitat (10 to 20 m), where light penetration is poorer. Coral reef growth slowed during this period and did not keep up with the rising sea level. In fact, an acceleration of deglaciation and of the rise in sea level are known to have occurred 11 300 B.P. They indeed led to changes in the environmental conditions. These induced in the reef a change-over from a keep-up mode of growth geared to keeping pace with sea-level rise to a catch-up mode. The reef could no longer keep up to the surface. It was temporarily completely submerged, before it could succeed in catching up with the water level. This reef-sequence study showed that the reef nevertheless managed to grow throughout the deglaciation period by modifying its structure and morphology. It did this by favouring species capable of adapting to new environmental conditions.

Coral reef development depends on external factors (sea water temperatures, salinity, nutrient content and input, tectonic activity, the nature of the rock substrate, and so on). The respective roles of these parameters in determining which of the two types of growth process prevails are still not really known. Further drilling investigations in different environments of the Pacific, such as some which have been conducted in New-Caledonia, Tahiti and Vanuatu, should reveal more about the impact of each factor and allow assessment of their variations for all parts of that ocean. The aim of this research is to gain better understanding of the influence of climatic changes on these marine complex ecosystems. Fundamental information that can be obtained on the installation, formation and development of coral reefs in the tropical zone should make it possible in the long run to elaborate models of their growth.

(1) Department of geology and geophysics of the University of Minnesota, Department of physics of the University of Arizona (Tucson) and Institute of Geophysics of the University of Texas (Austin).
(2) The longest continuous growth -14 000 years- known up to now had been found on the barrier reef of Tahiti in 1999. See scientific bulletin n° 106 (January 2000)
(3) They had hitherto, for the tropical zone, only fragmented reef growth data which was spread too widely over time. Reconstitution enabled them only to gather information for the past 22 000 years, with no guarantee of a real continuity.
(4) As the community structure of fossil fauna and flora species is closely bound to the water depth, degree of light penetration and to calm or rough conditions, it is a valuable indicator of the type of reef growth prevailing at a given time.

Bénédicte Robert | EurekAlert!
Further information:
http://www.paris.ird.fr/

More articles from Earth Sciences:

nachricht Huge stores of Arctic sea ice likely contributed to past climate cooling
21.02.2020 | University of Massachusetts Amherst

nachricht First research results on the "spectacular meteorite fall" of Flensburg
18.02.2020 | Westfälische Wilhelms-Universität Münster

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: A step towards controlling spin-dependent petahertz electronics by material defects

The operational speed of semiconductors in various electronic and optoelectronic devices is limited to several gigahertz (a billion oscillations per second). This constrains the upper limit of the operational speed of computing. Now researchers from the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg, Germany, and the Indian Institute of Technology in Bombay have explained how these processes can be sped up through the use of light waves and defected solid materials.

Light waves perform several hundred trillion oscillations per second. Hence, it is natural to envision employing light oscillations to drive the electronic...

Im Focus: Freiburg researcher investigate the origins of surface texture

Most natural and artificial surfaces are rough: metals and even glasses that appear smooth to the naked eye can look like jagged mountain ranges under the microscope. There is currently no uniform theory about the origin of this roughness despite it being observed on all scales, from the atomic to the tectonic. Scientists suspect that the rough surface is formed by irreversible plastic deformation that occurs in many processes of mechanical machining of components such as milling.

Prof. Dr. Lars Pastewka from the Simulation group at the Department of Microsystems Engineering at the University of Freiburg and his team have simulated such...

Im Focus: Skyrmions like it hot: Spin structures are controllable even at high temperatures

Investigation of the temperature dependence of the skyrmion Hall effect reveals further insights into possible new data storage devices

The joint research project of Johannes Gutenberg University Mainz (JGU) and the Massachusetts Institute of Technology (MIT) that had previously demonstrated...

Im Focus: Making the internet more energy efficient through systemic optimization

Researchers at Chalmers University of Technology, Sweden, recently completed a 5-year research project looking at how to make fibre optic communications systems more energy efficient. Among their proposals are smart, error-correcting data chip circuits, which they refined to be 10 times less energy consumptive. The project has yielded several scientific articles, in publications including Nature Communications.

Streaming films and music, scrolling through social media, and using cloud-based storage services are everyday activities now.

Im Focus: New synthesis methods enhance 3D chemical space for drug discovery

After helping develop a new approach for organic synthesis -- carbon-hydrogen functionalization -- scientists at Emory University are now showing how this approach may apply to drug discovery. Nature Catalysis published their most recent work -- a streamlined process for making a three-dimensional scaffold of keen interest to the pharmaceutical industry.

"Our tools open up whole new chemical space for potential drug targets," says Huw Davies, Emory professor of organic chemistry and senior author of the paper.

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

70th Lindau Nobel Laureate Meeting: Around 70 Laureates set to meet with young scientists from approx. 100 countries

12.02.2020 | Event News

11th Advanced Battery Power Conference, March 24-25, 2020 in Münster/Germany

16.01.2020 | Event News

Laser Colloquium Hydrogen LKH2: fast and reliable fuel cell manufacturing

15.01.2020 | Event News

 
Latest News

Active droplets

21.02.2020 | Medical Engineering

Finding new clues to brain cancer treatment

21.02.2020 | Health and Medicine

Beyond the brim, Sombrero Galaxy's halo suggests turbulent past

21.02.2020 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>