Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Climate variation in the tropical Pacific: coral provides proof

07.05.2004


IRD scientists have revealed, in an article just published in Nature, that the cooling event known in the Northern Hemisphere as the Younger Dryas (about 12 000 years B.P.) was expressed in the Pacific by the absence of any South Pacific Convergence Zone activity and the movement of tropical waters closer to the Equator. This observation shows the interaction which occurs between the low and high latitudes and provides boundaries relevant for building ocean-atmosphere climatic models. Geochemical analyses (determining strontium/calcium ratios and oxygen isotope levels) were performed on a coral core sample from Vanuatu. The fossil coral, belonging to a single species, Diploastrea heliopora, bears a record that is a key to tracing fluctuations in sea-surface temperature and salinity and in rainfall over that cold period.



The Younger Dryas period, about 12 000 years ago, was marked by a sharp cooling event in the Northern Hemisphere. Temperatures there fell by between 2 and 10°C. The East Antarctic in contrast experienced an episode of warming. Data have up to now been insufficient or too inconclusive to enable palaeoclimatologists to track this climatic event in the southern temperate regions and the tropics. An IRD researcher campaign took a 2 m drill core sample from the isle of Espiritu Santo, Vanuatu, found to contain a giant fossil coral of a single species, Diploastrea heliopora, well preserved in a condition of growth. The specimen age was estimated at between 12 449 and 11 719 calendar years, a span covering nearly the entire Younger Dryas. This unique fossil provides clear evidence of the spatial signature this major climatic cooling event left in the tropics.

Mineral skeleton growth of these corals is a steady few millimetres per year over many centuries, which offers a precise record of ancient environmental conditions. Fossil skeleton concentrations in chemical elements such as strontium or oxygen isotopes indicate the sea surface temperature (SST) on which they depended when the corals were alive. Corals of the genus Porites, which which grow by about 1 cm per year, are the type most used as paleothermometers, but the Diploastrea used in this study have the advantage of growing more slowly. Moreover, there is only one species of this marker, Diploastrea heliopora, which eliminates any inter-specific differences, always a source of uncertainty.


The IRD researchers, working with Australian and American colleagues (1), first compared SSTs, data obtained by way of Sr/Ca ratio analyses in the Diploastrea and modern Porites originating respectively from New Caledonia and Indonesia. Similarity of the figures obtained both validated the use of Diploastrea as a palaeothermometer and allowed calibration of the data acquired from this coral in modern times, before applying it as a palaeoclimatic marker on fossil forms from Vanuatu.

The temperature curves drawn from fossil Diploastrea data show that during the Younger Dryas period the STT around Vanuatu was on average 4.5°C lower than at present (2). The data furthermore indicate large interdecadal variations. The periods during which the SSTs were relatively warm coincides with annual amplitudes of about 3°C, similar to those currently observed in Vanuatu. However, cooler periods were marked by greater amplitudes, of about 5 to 6°C, like those observed at present in New Caledonia, 7 to 10° of latitude further South of Vanuatu. These data indicate an upward movement of the thermocline (3) and suggest that the Younger Dryas cooling resulted from compression of Pacific tropical waters towards the Equator.

In addition, coupled analysis of Sr/Ca and of 18O/16O isotope ratios at biannual and monthly time-scales provided information on the ocean-atmosphere exchanges operating during this period, and especially on the evaporation/precipitation ratio. The 18O level in the corals depends on the SST and surface water salinity. It is an expression of seasonal variations linked with rainfall, poor in 18O compared with sea water. At present in Vanuatu, the sea surface 18O concentration and salinity declines as the temperature rises. This stems from the intense activity, during the Southern hemisphere summer, of the South Pacific trades convergence zone (SPTCZ) which brings strong precipitation. Conversely, in the South-West Pacific subtropical area, unaffected by rainfall coming from the SPTCZ, the SST and surface water salinity are positively correlated. This is why in the subtropical oceanic environments, where evaporation largely exceeds precipitation, the salinity and 18O concentration rise with the SST. This situation is similar to that observed in Vanuatu during the Younger Dryas period, but quite different to the present prevailing situation. The data drawn from Diploastrea samples therefore suggest strongly that the South Pacific Convergence Zone did not exist in the Younger Dryas. This climatic scenario is similar to conditions seen in the present during an El Niño event, during which the west Pacific warm pool contracts towards the Equator, the SPTCZ then moving towards the North to fuse with the intertropical convergence zone. These results should also lead to improvements in climatological modelling and to better understanding of ocean-atmosphere exchanges and the processes influencing the activity of convergence zones.


(1) IRD research unit UR055 "Palaeotropics", Research School of Earth Sciences, Australian National University, Canberra, Australia and NSF Arizona AMS Facility, University of Arizona, Tucson, USA
(2) This deviation is similar to the one observed in earlier studies made on Porites core samples from Vanuatu, but greater than the cooling calculated for the tropical Pacific zones closer to the Equator.
(3) Thermocline: a zone of steep temperature gradient within the oceanic water layer which marks the transition between warm surface waters and the colder waters at deeper levels.



FOR FURTHER INFORMATION

Contacts : Thierry Corrège, IRD UR055 "Paléo-environnements tropicaux et variabilité climatique (Paléotropique)", BP A5 Nouméa cedex, New Caledonia. In 2004 : Research School of Earth Sciences, Australian National University, Canberra, ACT 0200 Australia. Tel. : 61-2-61-25-41-75, Fax: 61-2-61-25-03-15. Email: thierry.correge@anu.edu.au, thierry.correge@noumea.ird.nc
Or Guy Cabioch, Email : guy.cabioch@noumea.ird.nc

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

More articles from Earth Sciences:

nachricht Modeling magma to find copper
13.01.2017 | Université de Genève

nachricht What makes erionite carcinogenic?
13.01.2017 | Friedrich-Schiller-Universität Jena

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

Im Focus: How to inflate a hardened concrete shell with a weight of 80 t

At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).

Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...

Im Focus: Bacterial Pac Man molecule snaps at sugar

Many pathogens use certain sugar compounds from their host to help conceal themselves against the immune system. Scientists at the University of Bonn have now, in cooperation with researchers at the University of York in the United Kingdom, analyzed the dynamics of a bacterial molecule that is involved in this process. They demonstrate that the protein grabs onto the sugar molecule with a Pac Man-like chewing motion and holds it until it can be used. Their results could help design therapeutics that could make the protein poorer at grabbing and holding and hence compromise the pathogen in the host. The study has now been published in “Biophysical Journal”.

The cells of the mouth, nose and intestinal mucosa produce large quantities of a chemical called sialic acid. Many bacteria possess a special transport system...

Im Focus: Newly proposed reference datasets improve weather satellite data quality

UMD, NOAA collaboration demonstrates suitability of in-orbit datasets for weather satellite calibration

"Traffic and weather, together on the hour!" blasts your local radio station, while your smartphone knows the weather halfway across the world. A network of...

Im Focus: Repairing defects in fiber-reinforced plastics more efficiently

Fiber-reinforced plastics (FRP) are frequently used in the aeronautic and automobile industry. However, the repair of workpieces made of these composite materials is often less profitable than exchanging the part. In order to increase the lifetime of FRP parts and to make them more eco-efficient, the Laser Zentrum Hannover e.V. (LZH) and the Apodius GmbH want to combine a new measuring device for fiber layer orientation with an innovative laser-based repair process.

Defects in FRP pieces may be production or operation-related. Whether or not repair is cost-effective depends on the geometry of the defective area, the tools...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

Nothing will happen without batteries making it happen!

05.01.2017 | Event News

 
Latest News

Solar Collectors from Ultra-High Performance Concrete Combine Energy Efficiency and Aesthetics

16.01.2017 | Trade Fair News

3D scans for the automotive industry

16.01.2017 | Automotive Engineering

Nanoparticle Exposure Can Awaken Dormant Viruses in the Lungs

16.01.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>