Kallel Nejib

No Thumbnail Available
Last Name
Kallel
First Name
Nejib
ORCID

Filters

2016 - 2017 2
1 1
2
Reset filters

Settings

Search Results

Now showing 1 - 2 of 2
  • Preprint
    Exploring the oxygen and carbon isotopic composition of the Mediterranean red coral (Corallium rubrum) for seawater temperature reconstruction
    ( 2016-07) Chaabane, Sonia ; Lopez Correa, Matthias ; Montagna, Paolo ; Kallel, Nejib ; Taviani, Marco ; Linares, Cristina ; Ziveri, Patrizia
    Here we provide first evidence that the stable oxygen and carbon isotopic composition (δ18O, δ13C) of the high-magnesium calcite skeleton red coral Corallium rubrum can be used as a reliable seawater temperature proxy. This is based upon the analyses of living colonies of C. rubrum from different depths and localities in the Western Mediterranean Sea. The assessment of the growth rates has been established through the analysis of growth band patterns. The δ18O and δ13C compositions show large variability with a significant difference between the branches and the bases of the colonies. In both coral portions, the δ18O and δ13C values are highly correlated and show well-defined linear trends. Following the “lines technique” approach developed by Smith et al. (2000) for scleractinian aragonitic deep-water corals, our data have been combined with published values for the deep-sea gorgonian corals Isididae and Coralliidae from Kimball et al. (2014) and Hill et al. (2011) resulting in the following δ18O temperature equation: T (°C) = 38 -5.05 ± 0.24 x (δ18Ointercept) + 14.26 ± 0.43 (R² = 0.962, p value < 0.0001) The error associated with this equation is ± 0.5 °C at the mean temperature of the data set, ± 0.7 °C for corals living in 2 °C water and ± 1 °C for coral living in warmer water (17 °C). The highly significant δ18Ointercept vs. temperature relationship combined with the “lines technique” method can be reliably applied to the calcitic skeleton to obtain calcification temperature estimates in the past, although this approach requires the knowledge of the past δ18O and δ13C composition of seawater and it is labor and time intensive.
  • Article
    Hydrological variations of the intermediate water masses of the western Mediterranean Sea during the past 20 ka inferred from neodymium isotopic composition in foraminifera and cold-water corals
    (Copernicus Publications on behalf of the European Geosciences Union, 2017-01-10) Dubois-Dauphin, Quentin ; Montagna, Paolo ; Siani, Giuseppe ; Douville, Eric ; Wienberg, Claudia ; Hebbeln, Dierk ; Liu, Zhifei ; Kallel, Nejib ; Dapoigny, Arnaud ; Revel, Marie ; Pons-Branchu, Edwige ; Taviani, Marco ; Colin, Christophe
    We present the neodymium isotopic composition (εNd) of mixed planktonic foraminifera species from a sediment core collected at 622 m water depth in the Balearic Sea, as well as εNd of scleractinian cold-water corals (CWC; Madrepora oculata, Lophelia pertusa) retrieved between 280 and 442 m water depth in the Alboran Sea and at 414 m depth in the southern Sardinian continental margin. The aim is to constrain hydrological variations at intermediate depths in the western Mediterranean Sea during the last 20 kyr. Planktonic (Globigerina bulloides) and benthic (Cibicidoides pachyderma) foraminifera from the Balearic Sea were also analyzed for stable oxygen (δ18O) and carbon (δ13C) isotopes. The foraminiferal and coral εNd values from the Balearic and Alboran seas are comparable over the last  ∼  13 kyr, with mean values of −8.94 ± 0.26 (1σ; n =  24) and −8.91 ± 0.18 (1σ; n =  25), respectively. Before 13 ka BP, the foraminiferal εNd values are slightly lower (−9.28 ± 0.15) and tend to reflect higher mixing between intermediate and deep waters, which are characterized by more unradiogenic εNd values. The slight εNd increase after 13 ka BP is associated with a decoupling in the benthic foraminiferal δ13C composition between intermediate and deeper depths, which started at  ∼  16 ka BP. This suggests an earlier stratification of the water masses and a subsequent reduced contribution of unradiogenic εNd from deep waters. The CWC from the Sardinia Channel show a much larger scatter of εNd values, from −8.66 ± 0.30 to −5.99 ± 0.50, and a lower average (−7.31 ± 0.73; n =  19) compared to the CWC and foraminifera from the Alboran and Balearic seas, indicative of intermediate waters sourced from the Levantine basin. At the time of sapropel S1 deposition (10.2 to 6.4 ka), the εNd values of the Sardinian CWC become more unradiogenic (−8.38 ± 0.47; n =  3 at  ∼  8.7 ka BP), suggesting a significant contribution of intermediate waters originated from the western basin. We propose that western Mediterranean intermediate waters replaced the Levantine Intermediate Water (LIW), and thus there was a strong reduction of the LIW during the mid-sapropel ( ∼  8.7 ka BP). This observation supports a notable change of Mediterranean circulation pattern centered on sapropel S1 that needs further investigation to be confirmed.