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 Small- and mid-sized cities particularly vulnerable
29.09.2016 | Universität Stuttgart

nachricht Tracking the amount of sea ice from the Greenland ice sheet
28.09.2016 | Ca' Foscari University of Venice

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: New welding process joins dissimilar sheets better

Friction stir welding is a still-young and thus often unfamiliar pressure welding process for joining flat components and semi-finished components made of light metals.
Scientists at the University of Stuttgart have now developed two new process variants that will considerably expand the areas of application for friction stir welding.
Technologie-Lizenz-Büro (TLB) GmbH supports the University of Stuttgart in patenting and marketing its innovations.

Friction stir welding is a still-young and thus often unfamiliar pressure welding process for joining flat components and semi-finished components made of...

Im Focus: First quantum photonic circuit with electrically driven light source

Optical quantum computers can revolutionize computer technology. A team of researchers led by scientists from Münster University and KIT now succeeded in putting a quantum optical experimental set-up onto a chip. In doing so, they have met one of the requirements for making it possible to use photonic circuits for optical quantum computers.

Optical quantum computers are what people are pinning their hopes on for tomorrow’s computer technology – whether for tap-proof data encryption, ultrafast...

Im Focus: OLED microdisplays in data glasses for improved human-machine interaction

The Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP has been developing various applications for OLED microdisplays based on organic semiconductors. By integrating the capabilities of an image sensor directly into the microdisplay, eye movements can be recorded by the smart glasses and utilized for guidance and control functions, as one example. The new design will be debuted at Augmented World Expo Europe (AWE) in Berlin at Booth B25, October 18th – 19th.

“Augmented-reality” and “wearables” have become terms we encounter almost daily. Both can make daily life a little simpler and provide valuable assistance for...

Im Focus: Artificial Intelligence Helps in the Discovery of New Materials

With the help of artificial intelligence, chemists from the University of Basel in Switzerland have computed the characteristics of about two million crystals made up of four chemical elements. The researchers were able to identify 90 previously unknown thermodynamically stable crystals that can be regarded as new materials. They report on their findings in the scientific journal Physical Review Letters.

Elpasolite is a glassy, transparent, shiny and soft mineral with a cubic crystal structure. First discovered in El Paso County (Colorado, USA), it can also be...

Im Focus: Complex hardmetal tools out of the 3D printer

For the first time, Fraunhofer IKTS shows additively manufactured hardmetal tools at WorldPM 2016 in Hamburg. Mechanical, chemical as well as a high heat resistance and extreme hardness are required from tools that are used in mechanical and automotive engineering or in plastics and building materials industry. Researchers at the Fraunhofer Institute for Ceramic Technologies and Systems IKTS in Dresden managed the production of complex hardmetal tools via 3D printing in a quality that are in no way inferior to conventionally produced high-performance tools.

Fraunhofer IKTS counts decades of proven expertise in the development of hardmetals. To date, reliable cutting, drilling, pressing and stamping tools made of...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

European Health Forum Gastein 2016 kicks off today

28.09.2016 | Event News

Laser use for neurosurgery and biofabrication - LaserForum 2016 focuses on medical technology

27.09.2016 | Event News

Experts from industry and academia discuss the future mobile telecommunications standard 5G

23.09.2016 | Event News

 
Latest News

The first genome of a coral reef fish

29.09.2016 | Life Sciences

Gentle sensors for diagnosing brain disorders

29.09.2016 | Medical Engineering

Swiss space research reaches for the sky

29.09.2016 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>