Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Article
  • Published:

Drivers of river reactivation in North Africa during the last glacial cycle

Nature Geoscience volume 14, pages 97–103 (2021)Cite this article

Subjects

Abstract

North African greening phases, during which large rivers ran through the Sahara Desert, occurred repeatedly during the Quaternary and are regarded as key periods for the development of past human populations. However, the timing and mechanisms responsible for the reactivation of the presently dormant fluvial systems remain highly uncertain. Here we present hydroclimate changes over the past 160,000 years, reconstructed from analyses of the provenance of terrestrial sediments in a marine sediment record from the Gulf of Sirte (offshore Libya). By combining high-resolution proxy data with transient Earth system model simulations, we are able to identify the various drivers that led to the observed shifts in hydroclimate and landscapes. We show that river runoff occurred during warm interglacial phases of Marine Isotope Stages 1 and 5 due to precession-forced enhancements in the summer and autumn rainfall over the entire watershed, which fed presently dry river systems and intermittent coastal streams. In contrast, shorter-lasting and less-intense humid events during glacial Marine Isotope Stages 3 and 4 were related to autumn and winter precipitation over the Libyan coastal regions driven by Mediterranean storms. Our results reveal large shifts in hydroclimate environments during the last glacial cycle, which probably exerted a strong evolutionary and structural control on past human populations, potentially pacing their dispersal across northern Africa.

This is a preview of subscription content, access via your institution

Access options

Buy this article

  • Purchase on Springer Link
  • Instant access to full article PDF
Buy now

Prices may be subject to local taxes which are calculated during checkout

Fig. 1: Map of northern Africa with records relevant for our study.
Fig. 2: Tracers of past fluvial input into the GS.
Fig. 3: Hydroclimate records of core 64PE349-8 compared to transient simulations of precipitation.
Fig. 4: Summer and autumn precipitation as modelled by LOVECLIM during IPM and GPM.

Similar content being viewed by others

Data availability

All datasets presented here will be made freely available at the data repository PANGAEA (https://pangaea.de/) and are provided as Supplementary tables. Transient LOVECLIM simulations are available at https://climatedata.ibs.re.kr/grav/data/loveclim-784k.

References

  1. Drake, N. A., Blench, R. M., Armitage, S. J., Bristow, C. S. & White, K. H. Ancient watercourses and biogeography of the Sahara explain the peopling of the desert. Proc. Natl Acad. Sci. USA 108, 458–462 (2011).

    Article  Google Scholar 

  2. Lézine, A.-M., Hély, C., Grenier, C., Braconnot, P. & Krinner, G. Sahara and Sahel vulnerability to climate changes, lessons from Holocene hydrological data. Quat. Sci. Rev. 30, 3001–3012 (2011).

    Article  Google Scholar 

  3. Claussen, M., Dallmeyer, A. & Bader, J. Theory and Modeling of the African Humid Period and the Green Sahara Vol. 1 (Oxford Univ. Press, 2017).

  4. Hublin, J.-J. et al. New fossils from Jebel Irhoud, Morocco and the pan-African origin of Homo sapiens. Nature 546, 289–292 (2017).

    Article  Google Scholar 

  5. Scerri, E. M. L. The North African Middle Stone Age and its place in recent human evolution. Evol. Anthropol. 26, 119–135 (2017).

    Article  Google Scholar 

  6. Tjallingii, R. et al. Coherent high- and low-latitude control of the northwest African hydrological balance. Nat. Geosci. 1, 670–675 (2008).

    Article  Google Scholar 

  7. Larrasoaña, J. C., Roberts, A. P. & Rohling, E. J. Dynamics of green Sahara periods and their role in hominin evolution. PLoS ONE 8, e76514 (2013).

    Article  Google Scholar 

  8. Kutzbach, J. E. et al. African climate response to orbital and glacial forcing in 140,000-y simulation with implications for early modern human environments. Proc. Natl Acad. Sci. USA 117, 2255–2264 (2020).

    Article  Google Scholar 

  9. Ehrmann, W., Schmiedl, G., Beuscher, S. & Krüger, S. Intensity of African humid periods estimated from Saharan dust fluxes. PLoS ONE 12, e0170989 (2017).

    Article  Google Scholar 

  10. Hoffmann, D. L. et al. Timing and causes of North African wet phases during the last glacial period and implications for modern human migration. Sci. Rep. 6, 36367 (2016).

    Article  Google Scholar 

  11. Abouelmagd, A. et al. Toward a better understanding of palaeoclimatic regimes that recharged the fossil aquifers in North Africa: inferences from stable isotope and remote sensing data. Palaeogeogr. Palaeoclimatol. Palaeoecol. 329–330, 137–149 (2012).

    Article  Google Scholar 

  12. Rogerson, M. et al. Enhanced Mediterranean water cycle explains increased humidity during MIS3 in North Africa. Clim. Past 15, 1757–1769 (2019).

    Article  Google Scholar 

  13. Tierney, J. E., Pausata, F. S. R. & deMenocal, P. B. Rainfall regimes of the green Sahara. Sci. Adv. 3, e1601503 (2017).

    Article  Google Scholar 

  14. Paillou, P. et al. Mapping of a major paleodrainage system in eastern Libya using orbital imaging radar: the Kufrah River. Earth Planet. Sci. Lett. 277, 327–333 (2009).

    Article  Google Scholar 

  15. Skonieczny, C. et al. African humid periods triggered the reactivation of a large river system in Western Sahara. Nat. Commun. 6, 8751 (2015).

    Article  Google Scholar 

  16. Causse, C. et al. Humidity changes in southern Tunisia during the Late Pleistocene inferred from U–Th dating of mollusc shells. Appl. Geochem. 18, 1691–1703 (2003).

    Article  Google Scholar 

  17. Bout-Roumazeilles, V. et al. Tracking atmospheric and riverine terrigenous supplies variability during the last glacial and the Holocene in central Mediterranean. Clim. Past 9, 1065–1087 (2013).

    Article  Google Scholar 

  18. Wu, J. et al. North-African paleodrainage discharges to the central Mediterranean during the last 18,000 years: a multiproxy characterization. Quat. Sci. Rev. 163, 95–113 (2017).

    Article  Google Scholar 

  19. Osborne, A. H. et al. A humid corridor across the Sahara for the migration of early modern humans out of Africa 120,000 years ago. Proc. Natl Acad. Sci. USA 105, 16444–16447 (2008).

    Article  Google Scholar 

  20. Blanchet, C. L., Frank, M. & Schouten, S. Asynchronous changes in vegetation, runoff and erosion in the Nile river watershed during the Holocene. PLoS ONE 9, e115958 (2014).

    Article  Google Scholar 

  21. Revel, M. et al. 100,000 years of African monsoon variability recorded in sediments of the Nile margin. Quat. Sci. Rev. 29, 1342–1362 (2010).

    Article  Google Scholar 

  22. Beuscher, S. et al. End-member modelling as a tool for climate reconstruction—an Eastern Mediterranean case study. PLoS ONE 12, e0185136 (2017).

    Article  Google Scholar 

  23. Blanchet, C. L. A database of marine and terrestrial radiogenic Nd and Sr isotopes for tracing Earth-surface processes. Earth Syst. Sci. Data 11, 741–759 (2019).

    Article  Google Scholar 

  24. Schepanski, K. et al. Meteorological processes forcing Saharan dust emission inferred from MSG‐SEVIRI observations of subdaily dust source activation and numerical models. J. Geophys. Res. Atmos. 114, D10201.

  25. Weltje, G. J. End-member modeling of compositional data: numerical–statistical algorithms for solving the explicit mixing problem. Math. Geol. 29, 503–549 (1997).

    Article  Google Scholar 

  26. O’Hara, S. L., Clarke, M. L. & Elatrash, M. S. Field measurements of desert dust deposition in Libya. Atmos. Environ. 40, 3881–3897 (2006).

    Article  Google Scholar 

  27. Goudie, A. S. & Middleton, N. J. Saharan dust storms: nature and consequences. Earth Sci. Rev. 56, 179–204 (2001).

    Article  Google Scholar 

  28. Peyron, O. et al. Quantitative reconstructions of annual rainfall in Africa 6000 years ago: model–data comparison. J. Geophys. Res. Atmos. 111, D24110 (2006).

    Article  Google Scholar 

  29. Bartlein, P. J. et al. Pollen-based continental climate reconstructions at 6 and 21 ka: a global synthesis. Clim. Dyn. 37, 775–802 (2011).

    Article  Google Scholar 

  30. Coulthard, T. J., Ramirez, J. A., Barton, N., Rogerson, M. & Brücher, T. Were rivers flowing across the Sahara during the last interglacial? Implications for human migration through Africa. PLoS ONE 8, e74834 (2013).

    Article  Google Scholar 

  31. Timmermann, A. & Friedrich, T. Late Pleistocene climate drivers of early human migration. Nature 538, 92–95 (2016).

    Article  Google Scholar 

  32. Wagner, B. et al. Mediterranean winter rainfall in phase with African monsoons during the past 1.36 million years. Nature 573, 256–260 (2019).

    Article  Google Scholar 

  33. Kutzbach, J. E., Chen, G., Cheng, H., Edwards, R. L. & Liu, Z. Potential role of winter rainfall in explaining increased moisture in the Mediterranean and Middle East during periods of maximum orbitally-forced insolation seasonality. Clim. Dyn. 42, 1079–1095 (2014).

    Article  Google Scholar 

  34. Bosmans, J. H. C. et al. Precession and obliquity forcing of the freshwater budget over the Mediterranean. Quat. Sci. Rev. 123, 16–30 (2015).

    Article  Google Scholar 

  35. Rohling, E. J., Marino, G. & Grant, K. M. Mediterranean climate and oceanography, and the periodic development of anoxic events (sapropels). Earth Sci. Rev. 143, 62–97 (2015).

    Article  Google Scholar 

  36. Davis, B. A. S. & Brewer, S. Orbital forcing and role of the latitudinal insolation/temperature gradient. Clim. Dyn. 32, 143–165 (2009).

    Article  Google Scholar 

  37. Scerri, E. M. L., Drake, N. A., Jennings, R. & Groucutt, H. S. Earliest evidence for the structure of Homo sapiens populations in Africa. Quat. Sci. Rev. 101, 207–216 (2014).

    Article  Google Scholar 

  38. Gunz, P. et al. Early modern human diversity suggests subdivided population structure and a complex out-of-Africa scenario. Proc. Natl Acad. Sci. USA 106, 6094–6098 (2009).

    Article  Google Scholar 

  39. Scerri, E. M. L. et al. Did our species evolve in subdivided populations across Africa, and why does it matter? Trends Ecol. Evol. 33, 582–594 (2018).

    Article  Google Scholar 

  40. Mcbrearty, S. & Brooks, A. S. The revolution that wasn’t: a new interpretation of the origin of modern human behavior. J. Hum. Evol. 39, 453–563 (2000).

    Article  Google Scholar 

  41. Ziegler, M. et al. Development of Middle Stone Age innovation linked to rapid climate change. Nat. Commun. 4, 1905 (2013).

    Article  Google Scholar 

  42. Jacobs, Z. et al. The chronostratigraphy of the Haua Fteah cave (Cyrenaica, northeast Libya)—optical dating of early human occupation during marine isotope stages 4, 5 and 6. J. Hum. Evol. 105, 69–88 (2017).

    Article  Google Scholar 

  43. Groucutt Huw, S. et al. Rethinking the dispersal of Homo sapiens out of Africa. Evol. Anthropol. 24, 149–164 (2015).

    Article  Google Scholar 

  44. Secher, B. et al. The history of the North African mitochondrial DNA haplogroup U6 gene flow into the African, Eurasian and American continents. BMC Evol. Biol. 14, 109 (2014).

    Article  Google Scholar 

  45. Sankararaman, S., Patterson, N., Li, H., Pääbo, S. & Reich, D. The date of interbreeding between neandertals and modern humans. PLoS Genet. 8, e1002947 (2012).

    Article  Google Scholar 

  46. Drake, N. A. et al. Reconstructing palaeoclimate and hydrological fluctuations in the Fezzan Basin (southern Libya) since 130 ka: a catchment-based approach. Quat. Sci. Rev. 200, 376–394 (2018).

    Article  Google Scholar 

  47. Harris, I., Jones, P. D., Osborn, T. J. & Lister, D. H. Updated high-resolution grids of monthly climatic observations—the CRU TS3.10 dataset. Int. J. Climatol. 34, 623–642 (2014).

    Article  Google Scholar 

  48. Laskar, J. et al. A long-term numerical solution for the insolation quantities of the Earth. Astron. Astrophys. 428, 261–285 (2004).

    Article  Google Scholar 

  49. Larrasoaña, J. C., Roberts, A. P. & Rohling, E. J. Magnetic susceptibility of eastern Mediterranean marine sediments as a proxy for Saharan dust supply? Mar. Geol. 254, 224–229 (2008).

    Article  Google Scholar 

  50. De Lange, G. J. et al. Synchronous basin-wide formation and redox-controlled preservation of a Mediterranean sapropel. Nat. Geosci. 1, 606–610 (2008).

    Article  Google Scholar 

  51. Reimer, P. J. et al. IntCal13 and Marine13 radiocarbon age calibration curves 0–50,000 years cal bp. Radiocarbon 55, 1869–1887 (2013).

    Article  Google Scholar 

  52. Bronk-Ramsey, C. Bayesian analysis of radiocarbon dates. Radiocarbon 51, 337–360 (2009).

    Article  Google Scholar 

  53. De Vivo, B. et al. New constraints on the pyroclastic eruptive history of the Campanian volcanic plain (Italy). Mineral. Petrol. 73, 47–65 (2001).

    Article  Google Scholar 

  54. Grant, K. M. et al. The timing of Mediterranean sapropel deposition relative to insolation, sea-level and African monsoon changes. Quat. Sci. Rev. 140, 125–141 (2016).

    Article  Google Scholar 

  55. Lourens, L. J. Revised tuning of Ocean Drilling Program Site 964 and KC01B (Mediterranean) and implications for the δ18O, tephra, calcareous nannofossil, and geomagnetic reversal chronologies of the past 1.1 Myr. Paleoceanography 19, PA3010 (2004).

    Article  Google Scholar 

  56. Lisiecki, L. E.M. E. A Pliocene-Pleistocene stack of 57 globally distributed benthic δ18O records. Paleoceanography 20, PA1003 (2005).

    Google Scholar 

  57. Bronk Ramsey, C. Dealing with outliers and offsets in radiocarbon dating. Radiocarbon 51, 1023–1045 (2009).

    Article  Google Scholar 

  58. Barrat, J. A. et al. Determination of rare earth elements in sixteen silicate reference samples by ICP-MS after Tm addition and ion exchange separation. Geostand. Newsl. 20, 133–139 (1996).

    Article  Google Scholar 

  59. Horwitz, P. E., Chiarizia, R. & Dietz, M. L. A novel strontium selective extraction chromatographic resin. Solvent Extr. Ion Exch. 10, 313–336 (1992).

    Article  Google Scholar 

  60. Le Fèvre, B. & Pin, C. A straightforward separation scheme for concomitant Lu–Hf and Sm–Nd isotope ratio and isotope dilution analysis. Anal. Chim. Acta 543, 209–221 (2005).

    Article  Google Scholar 

  61. Tanaka, T. et al. JNdi-1: a neodymium isotopic reference in consistency with La Jolla neodymium. Chem. Geol. 168, 279–281 (2000).

    Article  Google Scholar 

  62. Jacobsen, S. B. & Wasserburg, G. J. Sm–Nd isotopic evolution of chondrites. Earth Planet. Sci. Lett. 50, 139–155 (1980).

    Article  Google Scholar 

  63. Kucera, M. & Malmgren, B. A. Logratio transformation of compositional data: a resolution of the constant sum constraint. Mar. Micropaleontol. 34, 117–120 (1998).

    Article  Google Scholar 

  64. Petschick, R. MacDiff 4.2.6 (Goethe Univ., 2001); http://go.nature.com/3oUPn1z

  65. Biscaye, P. E. Mineralogy and sedimentation of recent deep-sea clay in the Atlantic Ocean and adjacent seas and oceans. GSA Bull. 76, 803–832 (1965).

    Article  Google Scholar 

  66. Weaver, C. E. & Beck, K. C. Miocene of the SE United States: a model for chemical sedimentation in a peri-marine environment. Sediment. Geol. 17, IX–234 (1977).

    Article  Google Scholar 

  67. Goosse, H. et al. Description of the Earth system model of intermediate complexity LOVECLIM version 1.2. Geosci. Model Dev. 3, 603–633 (2010).

    Article  Google Scholar 

  68. Opsteegh, J. D., Haarsma, R. J., Selten, F. M. & Kattenberg, A. ECBILT: a dynamic alternative to mixed boundary conditions in ocean models. Tellus A 50, 348–367 (1998).

    Article  Google Scholar 

  69. Goosse, H. & Fichefet, T. Importance of ice–ocean interactions for the global ocean circulation: a model study. J. Geophys. Res. Oceans 104, 23337–23355 (1999).

    Article  Google Scholar 

  70. Brovkin, V., Ganopolski, A. & Svirezhev, Y. A continuous climate–vegetation classification for use in climate–biosphere studies. Ecol. Model. 101, 251–261 (1997).

    Article  Google Scholar 

  71. Berger, A. Long-term variations of daily insolation and Quaternary climatic changes. J. Atmos. Sci. 35, 2362–2367 (1978).

    Article  Google Scholar 

  72. Ganopolski, A. & Calov, R. The role of orbital forcing, carbon dioxide and regolith in 100 kyr glacial cycles. Clim. Past 7, 1415–1425 (2011).

    Article  Google Scholar 

  73. Timmermann, A. et al. Modeling obliquity and CO2 effects on Southern Hemisphere climate during the past 408 ka. J. Clim. 27, 1863–1875 (2014).

    Article  Google Scholar 

  74. Lüthi, D. et al. High-resolution carbon dioxide concentration record 650,000–800,000 years before present. Nature 453, 379–382 (2008).

    Article  Google Scholar 

  75. EPICA community members. Eight glacial cycles from an Antarctic ice core. Nature 429, 623–628 (2004).

    Article  Google Scholar 

  76. Friedrich, T., Timmermann, A., Tigchelaar, M., Timm, O. E. & Ganopolski, A. Nonlinear climate sensitivity and its implications for future greenhouse warming. Sci. Adv. 2, e1501923 (2016).

    Article  Google Scholar 

  77. R Core Team. R: A Language and Environment for Statistical Computing (R Foundation for Statistical Computing, 2013).

  78. Pante, E. & Simon-Bouhet, B. marmap: a package for importing, plotting and analyzing bathymetric and topographic data in R. PLoS ONE 8, e73051 (2013).

    Article  Google Scholar 

  79. Wickham, H. ggplot2: Elegant Graphics for Data Analysis (Springer, 2016).

  80. Krzywinski, M. & Altman, N. Points of significance: visualizing samples with box plots. Nat. Methods 11, 119–120 (2014).

    Article  Google Scholar 

  81. Wang, P., Tian, J. & Lourens, L. J. Obscuring of long eccentricity cyclicity in Pleistocene oceanic carbon isotope records. Earth Planet. Sci. Lett. 290, 319–330 (2010).

    Article  Google Scholar 

  82. Bouchette, F. et al. Hydrodynamics in Holocene Lake Mega-Chad. Quat. Res. 73, 226–236 (2010).

    Article  Google Scholar 

  83. Pinardi, N., Zavatarelli, M., Arneri, E., Crise, A. & Ravaioli, M. in The Sea: Ideas and Observations on Progress in the Study of Seas (eds. Robinson, A. R. & Brink, K. H.) Ch. 32 (Harvard Univ. Press, 2006).

Download references

Acknowledgements

We thank the captain, crew and scientific team of RV Pelagia cruise 64PE349 as well as P. van Gaever and R. Gieles (in memoriam) at NIOZ for analytical assistance. C.L.B. acknowledges the support of GFZ Potsdam through a reintegration grant. R.T. acknowledges financial support by NWO grants INTAX (839.08.434) and SCAN2. W.E. was supported by a grant from the Deutsche Forschungsgemeinschaft (EH89/19-1). A.T. was supported by the Institute for Basic Science (IBS) (IBS-R028-D1).

Author information

Authors and Affiliations

  1. Climate Dynamics and Landscape Evolution, Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences, Potsdam, Germany

    Cécile L. Blanchet & Rik Tjallingii

  2. GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany

    Anne H. Osborne, Warner Brückmann & Martin Frank

  3. Department Ocean Systems, Royal Netherlands Institute for Sea Research NIOZ, ‘t Horntje (Texel), The Netherlands

    Rik Tjallingii

  4. Institute for Geophysics and Geology, University Leipzig, Leipzig, Germany

    Werner Ehrmann

  5. Department of Oceanography, School of Ocean and Earth Sciences and Technology, University of Hawaii at Mānoa, Honolulu, HI, USA

    Tobias Friedrich

  6. Center for Climate Physics, Institute for Basic Science (IBS), Busan, South Korea

    Axel Timmermann

  7. Pusan National University, Busan, South Korea

    Axel Timmermann

Authors
  1. Cécile L. Blanchet
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Anne H. Osborne
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Rik Tjallingii
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. Werner Ehrmann
    View author publications

    You can also search for this author in PubMed Google Scholar

  5. Tobias Friedrich
    View author publications

    You can also search for this author in PubMed Google Scholar

  6. Axel Timmermann
    View author publications

    You can also search for this author in PubMed Google Scholar

  7. Warner Brückmann
    View author publications

    You can also search for this author in PubMed Google Scholar

  8. Martin Frank
    View author publications

    You can also search for this author in PubMed Google Scholar

Contributions

C.L.B., A.H.O. and R.T. conceived the study and organized cruise 64PE349, led by W.B. W.B. and A.H.O. retrieved the sediment cores. A.H.O. and M.F. facilitated and measured the radiogenic isotopes; R.T. measured the grain-size distributions, oxygen isotopes and carried out X-ray fluorescence core scanning; W.E. measured the clay mineral assemblages; T.F. and A.T. developed and ran the LOVECLIM simulations. C.L.B. analysed the data and wrote the manuscript with input from all co-authors. A.T., W.B. and M.F. provided logistical and financial support.

Corresponding author

Correspondence to Cécile L. Blanchet.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Peer review information Nature Geoscience thanks the anonymous reviewers for their contribution to the peer review of this work. Primary Handling Editor: James Super.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data

Extended Data Fig. 1 Extended map of North Africa showing present-day climatology and preferential dust sources (PDS).

a. Topography, climatology and marine surface currents. Location of core 64PE349-8 (red diamond) and relevant records mentioned in the text (MD04-279717, CP10BC18, SL719, MS27PT21 and GeoB77026) or used for the age model (KC0155,81, LC21 and Soreq Cave54) (green diamonds). Map background represents the topography and bathymetry (Gebco 2014 30-arcsecond grid, version 20150318, www.gebco.net), plotted with the open source software R77 and ‘marmap’ package78. Location of current Nile, Niger and Senegal rivers (blue lines) and paleo-river systems (green lines) redrawn from ref. 30 (Kufrah, Sahabi and Irharhar rivers) and ref. 15 (Tamanrasett river). The extent of the paleo-lake Chad was redrawn from ref. 82. Present-day precipitation patterns are indicated as contour lines of monthly precipitation rates in winter (February, in blue) and in summer (August, in red) (UEA CRU TS3p21 climatology c1901-2012 precipitation data47). Present-day surface marine circulation (grey lines) shows the anti-cyclonic circulation in the Gulf of Sirte83. b. Preferential dust sources (PDS) redrawn from remote sensing24 numbered 1 to 7. εNd signature of surface soils and river sediments, rocks, bivalves and deposited aerosols and contour plot of interpolated εNd signature of seafloor sediments (data from ref. 23).

Extended Data Fig. 2 Age model and identification of sapropel layers in core 64PE349-8.

Left: uncorrected core depth, section number (in roman number), line-scan image of the split core surface. a. tie-points for age-depth model shown as diamonds (red: radiocarbon age, orange: upper and lower sapropel limits, purple: tephra layer Y-5), δ18O of planktonic foraminifera G. ruber and correlation tie-points (green diamonds), intervals used to compare sediment populations (sapropel layers S1, S3-S5 and MIS3/4) (orange bars). b. marine isotope stages (MIS, black and white bars), age-depth relationship with identified tie-points and uncertainty envelop, sedimentation rates (black step curve). c. Magnetic susceptibility; d. Log-ratio of barium/aluminium (Ba/Al). The latter two records (c,d) were used to determine the boundaries of the sapropel layers (horizontal grey bars) and tephra layers (marked as ‘T’). Line-scan image, magnetic susceptibility and elemental ratios were measured using an Aavatech XRF scanner at Nioz (Texel, Netherlands).

Extended Data Fig. 3 Grain-size distribution and end-member modeling.

Left panel: Grain-size distribution of individual samples (grey) with overlaid: coefficient of determination (R2) for each grain-size fraction (dashed orange line), end-members EM1 (main mode 3 µm, blue line), EM2 (main mode 15 µm, green line) and EM3 (main modes 3 µm and 45 µm, red line). Right panel: Proportion of variance explained per number of additional end-member. Methodology for end-member modelling analysis follows ref. 6,25.

Extended Data Fig. 4 Definition of interglacial precession minima (IPM) and glacial precession minima (GPM).

a. Reconstructed global-mean surface atmospheric temperature (SAT) for the past 160 kyr76 (black) and precession parameter (green). IPM (red bars) and GPM (blue bars) are defined by time intervals when the precession index is < 0.01 and the simulated global-mean SAT-anomaly is < 1 K (glacial) or > 1 K (interglacial). These IPM and GPM intervals are reported on the simulated MAP for the Tibesti region (b) and the Libyan coastal region (c).

Extended Data Fig. 5 Comparison Model-Data and seasonality of precipitation as modelled by LOVECLIM.

a. Comparison of observed (left) and modelled (right, 0-1 ka averages) present-day seasonality of precipitation (mm/month) over Western North Africa (zonal averaging: 2.8°E-25.3°E). Observed precipitation from reanalysis CMAP Precipitation data provided by the NOAA/OAR/ESRL PSD, Boulder (USA) (https://www.esrl.noaa.gov/psd/). b. Simulated seasonality of precipitation at the LGM (25 ka BP, black), during a GPM (50 ka BP, blue) and during an IPM (125 ka BP, red) over the Libyan coast (left) and the Tibesti (right). c. Precipitation anomalies with respect to the 0-1 ka monthly averages for the same time intervals.

Extended Data Fig. 6 Simulated precipitation over the Tibesti (A–D) and coastal Libya (E–H) for full forcing run and sensitivity simulations.

a and e: Precipitation for full-forcing simulation (black) and simulation using only orbital forcing under a warm background climate (CO2 at 280 ppm, red). b and f: Black line as in a, e and simulation using only orbital forcing under a cold background climate (CO2 at 200 ppm, blue). c,g: Black line as in A, E and simulation using full-forcing except for a constant preindustrial Northern Hemisphere ice-sheet (NHIS). d and h: Black line as in a, e and simulation using full-forcing except for constant preindustrial green-house gas concentrations.

Supplementary information

Supplementary Table 1

Data for plotting regional radiogenic Nd and Sr isotopes.

Supplementary Table 2

Stable O isotopes, radiogenic Nd and Sr isotopes, clay mineral ratio and proportion of grain-size end-members.

Supplementary Table 3

Age model and sedimentary signals in core 64PE349-8.

Rights and permissions

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Blanchet, C.L., Osborne, A.H., Tjallingii, R. et al. Drivers of river reactivation in North Africa during the last glacial cycle. Nat. Geosci. 14, 97–103 (2021). https://doi.org/10.1038/s41561-020-00671-3

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/s41561-020-00671-3

This article is cited by

Search

Advanced search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing