Speleothem records decadal to multidecadal hydroclimate variations in southwestern Morocco during the last millennium

https://doi.org/10.1016/j.epsl.2017.07.045Get rights and content

Highlights

  • High resolution reconstruction of hydroclimate variability during the last millennium in Southwestern Morocco.

  • Coherent regional climate signals showing dry conditions during the MCA and the CWP and wetter conditions during the LIA.

  • Substantial responses to the AMO, NAO and Sahara Low over the hydroclimate variability in Southwestern Morocco.

Abstract

This study presents the first well-dated high resolution stable isotope (δ18O and δ13C) and trace element (Mg and Sr) speleothem records from southwestern Morocco covering the last 1000 yrs. Our records reveal substantial decadal to multidecadal swings between dry and humid periods, consistent with regional paleorecords with prevailing dry conditions during the Medieval Climate Anomaly (MCA), wetter conditions during the second part of the Little Ice Age (LIA), and a trend towards dry conditions during the current warm period. These coherent regional climate signals suggest common climate controls. Statistical analyses indicate that the climate of southwestern Morocco remained under the combined influence of both the North Atlantic Oscillation (NAO) and the Atlantic Multidecadal Oscillation (AMO) over the last millennium. Interestingly, the generally warmer MCA and colder LIA at longer multidecadal timescales probably influenced the regional climate in North Africa through the influence on Sahara Low which weakened and strengthened the mean moisture inflow from the Atlantic Ocean during the MCA and LIA respectively.

Introduction

Southwestern Morocco is located in a semi-arid region and is thus highly sensitive to climate change on interannual to multidecadal timescales. Most rainfall in this area occurs during the winter season, whereas summers are generally dry. The regional climate is characterized by pronounced year to year variations in precipitation, which are highly correlated with the winter NAO index (Knippertz et al., 2003, López-Moreno et al., 2011). At decadal scale, it was found that large oscillations of North Atlantic sea surface temperature (SST) (i.e. the AMO) have impacts on the regional climate in the North Atlantic region (Knight et al., 2006, Gastineau and Frankignoul, 2014). Although Knight et al. (2006) indicate that the effect of AMO on SW Moroccan climate is very small, only little is known about the long-term influence of AMO during the last millennium. Superimposed on those variations at interannual to multi-decadal scales, climate projections predict a substantial increase of extreme heats and droughts during the coming decades in this region, which is already under severe water stress (Bouchaou et al., 2011). It is however not clear what can be attributed to natural climate variability and to anthropogenic forcing as hydroclimate variations observed in areas such as southwestern Morocco are highly influenced by the North Atlantic climate modes, like NAO and possibly AMO.

Since observational data sets are too short to resolve properly natural modes of variability acting on decadal to multidecadal timescales, high resolution paleoclimate reconstructions are the only alternative to reconstruct climate variability in the remote past (Novello et al., 2012). Hydroclimate reconstructions during the last millennium from various natural archives in the North of Morocco have shown regionally consistent climate features during the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA) (Esper et al., 2007, Détriché et al., 2009, Wassenburg et al., 2013). These paleorecords show that the MCA was generally drier in Northern Morocco as compared to the LIA, which was characterized by a recovery to wetter conditions. These very low frequency hydroclimate variations have been interpreted as being the result of a persistent positive (negative) state of the NAO during the MCA (LIA) (Trouet et al., 2009, Olsen et al., 2012, Baker et al., 2015). However, Wassenburg et al. (2013) indicated that the MCA was characterized by more frequent positive phases of the NAO and a recent proxy NAO reconstruction shows no persistent positive NAO conditions during the MCA (Ortega et al., 2015).

Thus, the climate processes explaining the MCA and LIA in northern Africa are still poorly understood because of the lack of well-dated and high-resolution paleoclimate records, which are able to resolve the climate variation at a multi-year timescale. Moreover, apart from the sediment core SST reconstruction off the Moroccan coast by McGregor et al. (2007), all the previous Moroccan paleoclimate studies are located in Northern Morocco. Therefore, the investigation of hydroclimate variations during the last millennium in Southwestern Morocco is certainly required. Hence, we present here the first continental paleoclimate record in Southwestern Morocco based on a well-dated speleothem from Ifoulki cave in the Western High Atlas Mountains (Fig. 1). The Ifoulki cave record spans the last 1200 yrs with a high resolution. This allows exploring the hydroclimate variability at multi-annual to centennial timescales. In addition, the Ifoulki paleorecord is discussed in the light of existing continental and marine paleoclimate proxies from Morocco in order to find potential relationships between atmospheric and oceanic large-scale climate modes and reconstructed dry/wet periods.

Section snippets

Study area and modern climatology

The Ifoulki cave (N30°42′29″; W09°19′39″; 1256 m.a.s.l.) is located in the Western High Atlas Mountains of southwestern Morocco within the karstified Tasroukht plateau. The Tasroukht plateau is a mature karst without dense vegetation cover and the litter is virtually absent (Junger and Faille, 2011). The karstic network of the cave, with a length of 433 meters (Fig. S1), is developed within white dolomitic limestones from the Upper Jurassic. The abundance of exo-karstic forms at the surface of

Material and methods

Stalagmite “IFK1” (∼10 cm tall) was collected from the bottom of Ifoulki cave, in order to make sure that the stalagmite has grown under conditions of minimal temperature fluctuations and highest relative humidity. The analysis of two powdered samples with X-Ray Diffraction indicates that the sample is calcitic. The stalagmite is macroscopically translucent. A mosaic fabric (typical for secondary calcite) or acicular fabric/needle like crystals (associated with aragonite) are not observed.

Stable isotope composition of precipitation and groundwater

A Local Meteorological Water Line (LMWL) is defined based on δ18O and δ2H analyses of 28 event-based rainwater samples (Fig. 3) sampled at two stations (Agadir and Wintimdouine) nearby Ifoulki cave between October 2014 and October 2015. The isotopic δ18O signature of rainwater samples in Ifoulki cave area ranges from −0.67 to −8.69‰, recorded between August and November respectively, suggestive of a seasonal effect on δ18O in precipitation. The LMWL presents a slope of 7.8, which is very

Comparison with regional paleoclimate records

A comparison between the IFK1 records and another trace element (Mg and Sr) speleothem record, by Wassenburg et al. (2013), (hereafter named “GP5”) from Piste cave (known as “Grotte de Piste”; 34°N, 04°W, 1260 m.a.s.l.) in Northern Morocco is shown in Fig. 6, where the increase (decrease) of Sr (Mg) is interpreted as a result of increasing precipitation and vice-versa (Wassenburg et al., 2013), although Mg is not incorporated into the crystal lattice of aragonite speleothems (like GP5) and may

Conclusions

A new high resolution U–Th dated stalagmite stable isotope and trace element record is investigated in this study. The speleothem was collected from the Ifoulki cave in southwestern Morocco where rainfall occurs mainly during the winter in relation to NAO in the modern period. The new stalagmite δ18O and 1st principal component based on IFK1 Mg and δ13C, covering the last 1200 yrs, suggests that southwestern Morocco is currently undergoing drought conditions which began in the early 20th

Acknowledgments

This work was supported by the CLIMACTE Tripartite Cooperative Project (IRD-France/CNPq-Brazil/APGMV-Africa grant 457400/2012-9), the PRIMO: IRD-CNPq project, and the German Research Foundation (DFG; WA3532/1-1) and the strong collaboration between the Laboratory of Speleological studies at the Institute of Geoscience in the University of Sao Paulo (Brazil), the Isotope Laboratory in the University of Minnesota (U.S.A.), the Institute of Global Environmental Change in Xi'an Jiaotong University

References (64)

  • M.S. Lachniet

    Climatic and environmental controls on speleothem oxygen-isotope values

    Quat. Sci. Rev.

    (2009)
  • F. Lehner et al.

    Testing the robustness of a precipitation proxy-based North Atlantic Oscillation reconstruction

    Quat. Sci. Rev.

    (2012)
  • J.I. López-Moreno et al.

    Effects of the North Atlantic Oscillation (NAO) on combined temperature and precipitation winter modes in the Mediterranean mountains: observed relationships and projections for the 21st Century

    Glob. Planet. Change

    (2011)
  • A. Moreno et al.

    The Medieval Climate Anomaly in the Iberian Peninsula reconstructed from marine and lake records

    Quat. Sci. Rev.

    (2012)
  • C. Mühlinghaus et al.

    Modelling fractionation of stable isotopes in stalagmites

    Geochim. Cosmochim. Acta

    (2009)
  • D. Romanov et al.

    δ13C profiles along growth layers of stalagmites: comparing theoretical and experimental results

    Geochim. Cosmochim. Acta

    (2008)
  • D. Scholz et al.

    StalAge – an algorithm designed for construction of speleothem age models

    Quat. Geochronol.

    (2011)
  • M. Schulz et al.

    REDFIT: estimating red-noise spectra directly from unevenly spaced paleoclimatic time series

    Comput. Geosci.

    (2002)
  • J.A. Wassenburg et al.

    Climate and cave control on Pleistocene/Holocene calcite-to-aragonite transitions in speleothems from Morocco: elemental and isotopic evidence

    Geochim. Cosmochim. Acta

    (2012)
  • J.A. Wassenburg et al.

    Moroccan speleothem and tree ring records suggest a variable positive state of the North Atlantic Oscillation during the Medieval Warm Period

    Earth Planet. Sci. Lett.

    (2013)
  • J.A. Wassenburg et al.

    Determination of aragonite trace element partition coefficients from speleothem calcite–aragonite transitions

    Geochim. Cosmochim. Acta

    (2016)
  • F. Abrantes et al.

    Climate of the last millennium at the southern pole of the North Atlantic Oscillation: an inner-shelf sediment record of flooding and upwelling

    Clim. Res.

    (2011)
  • A. Baker et al.

    A composite annual-resolution stalagmite record of North Atlantic climate over the last three millennia

    Sci. Rep.

    (2015)
  • L. Bouchaou et al.

    The underground river of Win Timdouine (Agadir region, High Atlas): a contribution to the inventory of the geological heritage in Morocco

  • L. Bouchaou et al.

    Climate change and its impacts on groundwater resources in Morocco: the case of the Souss-Massa basin

  • H. Celle

    Caractérisation des précipitations sur le pourtour de la Méditerranée occidentale : approche isotopique et chimique

    (2000)
  • I. Couchoud

    Les isotopes stables de l'oxygène et du carbone dans les spéléothèmes : des archives paléoenvironnementales

    Quaternaire

    (2008)
  • H. Craig

    Isotopic variations in meteoric waters

    Science

    (1961)
  • M. Deininger et al.

    Coherency of late Holocene European speleothem δ18O records linked to North Atlantic Ocean circulation

    Clim. Dyn.

    (2016)
  • T.L. Delworth et al.

    Observed and simulated multidecadal variability in the northern hemisphere

    Clim. Dyn.

    (2000)
  • D.B. Enfield et al.

    Secular and multidecadal warmings in the North Atlantic and their relationships with major hurricane activity

    Int. J. Climatol.

    (2010)
  • J. Esper et al.

    Long-term drought severity variations in Morocco

    Geophys. Res. Lett.

    (2007)
  • Cited by (31)

    • Climate controls on tufa deposition over the last 5000 years: A case study from Northwest Africa

      2022, Palaeogeography, Palaeoclimatology, Palaeoecology
      Citation Excerpt :

      Therefore, it is suggested that the development of buttresses and macrocrystalline laminae was favored during the RCO. Otherwise, the high-frequency facies fluctuation between Lo and C at the upper part of the highstand interval may mirror (at least partially) the dry/cold periods within the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA) reported from regional studies (Fig. 12) (Esper et al., 2007; Wassenburg et al., 2013; Ait Brahim et al., 2017, 2018; Abdellah et al., 2021). By examining the long-term trend, tufa deposits have shown a high sensibility level to the millennial timescale climate forcing.

    • Evidence for anthropogenic, climatic and oceanographic variability off southwestern Morocco during the last three millennia

      2022, Palaeogeography, Palaeoclimatology, Palaeoecology
      Citation Excerpt :

      Long-term dinocyst changes of core GeoB9064 from the Gulf of Cadiz show an increase of L. machaerophorum during periods of negative NAO phases and high fluvial input, which is supported by coccoliths and biomarker records (Mertens, 2009). For the past 1000 years, the speleothem record from the Ifoulki Cave near Cape Ghir (Ait Brahim et al., 2017) indicates more precipitation in southwestern Morocco between ca. 1600 and 1900 CE relative to the period between 1000 and 1600 CE. The absolute abundances and the distribution pattern of Gymnodinium catenatum and G. nolerii suggest similar ecological preferences such as fluvial input and seasonal upwelling (Holzwarth et al., 2010a).

    • Hydroclimate variability during the last 2700 years based on stalagmite multi-proxy records in the central-western Mediterranean

      2021, Quaternary Science Reviews
      Citation Excerpt :

      But the absence of hydrological records for the last few millennia precludes the assessment of its sensitivity to recent natural climate variability. Most paleoclimate studies of Mediterranean and Southern European have focused on pre-Holocene hydroclimate or have only partial coverage for the last 3 kyr (e.g.: Bar-Matthews et al., 2003; Frisia et al., 2003, 2005, 2006; McMillan et al., 2005; Mangini et al., 2005; Martín-Chivelet et al., 2011; Railsback et al., 2011; Wassenburg et al., 2013; Cheng et al., 2015; Ait Brahim et al., 2017, 2018, 2019; Budsky et al., 2019). In the context of Mallorca, speleothem studies have been based on phreatic overgrowths and reconstruction of past sea-levels (Vesica et al., 2001; Polyak et al., 2018; Dumitru et al., 2019) or paleoclimate reconstructions from periods prior to the Last Glacial Maximum (Hodge, 2004; Hodge et al., 2008; Dumitru et al., 2018; Torner et al., 2019).

    View all citing articles on Scopus
    View full text