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CRP El Niño member - Mr. Luc Ortlieb
Mr. L. Ortlieb
Institut de Recherche pour le Développement
- Multidisciplinary paleo-ENSO research in Peru and Chile
- IRD research activity on Paleo-ENSO records in western South
America began while L. Ortlieb developped a cooperative project with the Instituto
Geofísico del Perú (IGP, Dr . J Macharé) on paleoclimate evolution on the coasts
of Peru. Historical and geological evidence for former El Niño manifestations were
gathered from different kinds of records. Radiocarbon data from beach-ridge series
in the northern coast of Peru provided indications for major nearshore anomalies related
to ENSO conditions (Ortlieb & Macharé, 1992; Macharé J. & Ortlieb, 1993; Ortlieb et al., 1995).
Preliminary geochemical analyses on Mid-Holocene molluscan shells which showed growth
anomalies could be related to former short-lived ENSO conditions (Perrier et al., 1994).
Documentary investigations based on abundant data available in Peruvian libraries led to
question a number of historical reconstructions proposed by W. Quinn et collaborators.
In 1992, J. Macharé and L. Ortlieb organized in Lima an international symposium on
"Former ENSO phenomena in western South America: Records of El Niño events" (Ortlieb & Macharé,
1992; Macharé J. & Ortlieb, 1993) which was attended by more than a hundred specialists of varied disciplines.
- Subsequently, L. Ortlieb developped other collaborative projects,
with Chilean universities and institutions, also oriented toward the reconstruction
of former ENSO manifestations. A high-resolution paleoceanographic study was focused
on a marine sequence preserved in a relatively shallow embayment of northern Chile,
where hypoxic conditions strongly limited bioturbation (Ortlieb et al., 2000; Vargas
et al., 2004; Valdes et al., 2004). Other studies concerned the record of meteorological
ENSO impacts on debris-flow deposits in northern Chile and southern Peru (Ortlieb & Vargas, 2003).
Another work focused upon upwelling and ENSO comparative relationships in Chile and Baja California
(Takesue et al., 2004). In parallel, L. Ortlieb continued to refine the regional reconstruction
of historical ENSO events according documentary sources from Peru and
Chile (Ortlieb, 2000; 2004, Ortlieb et al., 2002).
- Since 2003, another project (PALEOPECES), which associates IRD,
IMARPE (Instituto del Mar del Peru) and CICESE (Centro de Investigaciones y de
Enseñanza Superior de Ensenada, Ensenada, Mexico) aims to decipher marine sedimentary
sequences from the Oxygen Minimum Zone off central Peru in terms of paleoclimatic
evolution of the last 2000 years. This attempt of high-resolution reconstruction
(decadal to interannual scales) is focused upon laminated sediments and will combine
a series of geochemical, biochemical and sedimentologic proxies. The report of IMARPE
(within the same AIEA document) refers with some detail to this project.
- Coral paleoclimatology
- At IRD, the paleoclimatological studies based on coral records started
in the 1990's in collaboration with the University of Minnesota at Minneapolis
(Larry Edwards, Sarah Gray and Warren Beck presently at Tucson), the University
of Arizona at Tucson (George Burr) and the University of Texas at Austin
(Frederick Taylor) (Beck et al., 1992, 1997, Min et al., 1995). Beck et al. (1992)
provided data on Sr/Ca ratio of Porites corals from the South-West Pacific as usual
proxy of sea surface temperature (SST). In the same way, Min et al. (1995) showed
that the U/Ca ratio can be used as another SST proxy. Then, analyses of fossil
Porites coral from Vanuatu gave information on SST variation since 10,000 years
in Vanuatu (South-West Pacific). The determination of uranium to calcium and strontium
to calcium ratios in corals by Inductively Coupled Plasma Mass Spectrometry (ICP/MS)
highly improved the analytical measurements ; this methode was developed by Le Cornec and Correge (1997).
- Sr/Ca and U/Ca analysis of a Porites dated of 4,150 yr BP over
47 years of growth exhibited several cooling events and ENSO frequency SST oscillations
(Corrège et al., 2000). Analyses of a Porites from New Caledonia, covering the period
from 1701 to 1761 (during the Little Ice Age), showed a lowering of SST by 1.4°C with
respect to present-day mean SST (Corrège et al., 2001). Coupled analyses of Sr/Ca, U/Ca
and d18O in modern coral cores from Fiji were conducted by Le Bec et al. (2000) to examine
the ENSO signal of the last century.
- The use of Porites corals from the SW Pacific region as SST proxy
appeared as limited, and the IRD group looked for other coral species. Recently,
Dipoloastrea corals were calibrated with the aim to be used as SST proxy (Watanabe
et al., 2003). This provided the necessary background to analyze a fossil Diploastrea
coral that grew during the Younger Dryas (Corrège et al., 2004).
- Scleroclimatological approach on mollusc shells
- The western coast of South America, between the equator and the tropic
of Capricorn, is particularly affected by El Niño oceanographic anomalies. This is the
region where the largest ENSO-related SST anomalies are registered. Since no corals
are present on this coastal stretch, the IRD group and its Peruvian and Chilean partners
designed a project to develop the use molluscan shells as markers of ENSO impacts.
The general aim is to determine which mollusc species, among those which can survive the
strong El Niño stress, and which are commonly found within coastal archaeological middens
or Pleistocene marine terrace deposits, may provide geochemical records of ENSO manifestations.
Along the coasts of Peru, SST anomalies during strong ENSO events amount to several
degrees (up to 10° C in 1983) during several months (value to compare to the
1 to 2° ?-SST observed in the western Pacific). Perrier et al. (1994) provided
some isotopic evidence for quantification of SST anomalies on mid-Holocene shells.
These and other isotopic data on fish otoliths were vividly discussed in relation with
the problem of the onset of the modern regime of ENSO variability
(DeVries et al., 1997; Béarez et al., 2003).
- The French national Programme for the study of climate dynamics
(PNEDC) supported a project ("CONCHAS", PI L. Ortlieb) dedicated to calibration
studies for the use of mollusc shells as indicators of SST anomalies (2002-2005).
This project associates several French laboratories (LSCE, ISEM, LOCEAN besides the
IRD PALEOTROPIQUE unit) and Peruvian (IMARPE) and Chilean (Univ. of Antofagasta,
Univesity A. Prat at Iquique) institutions.
- From the end of 2004, and for 4 years, the European Community (6th PCRD, INCO)
will support a project (CENSOR) "Climate variability and El Niño Southern Oscillation:
Impacts on natural coastal Resources and management"(PI W. Arntz, Alfred Wegener Institute,
Bremerhaven, Germay) in which IRD is the French participant while several of the Peruvian
and Chilean participants (IMARPE, Univ. of Antofagasta, Univ. A. Prat, Univ. of Concepcion)
are long ago IRD's scientific partners. In this project, L. Ortlieb is Principal Scientist
for the working package dedicated to the study of climate and ENSO impacts on molluscan shell
growth (including the isotopic and elemental geochemical signature of El Niño anomalies).
Other French partners of the project include the LODYC lab (IRD-CNRS-Univ. Paris-VI-MNHN)
and the Univ. of Paris-XI. Several Chilean and Peruvian PhD and post-doc students will be
involved in the CENSOR project (including four of them working on microstructural and
isotopic studies on molluscan shells).