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Elevated Southern Hemisphere moisture availability during glacial periods

Nature volume 626, pages 319–326 (2024)Cite this article

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Abstract

Late Pleistocene ice-age climates are routinely characterized as having imposed moisture stress on low- to mid-latitude ecosystems1,2,3,4,5. This idea is largely based on fossil pollen evidence for widespread, low-biomass glacial vegetation, interpreted as indicating climatic dryness6. However, woody plant growth is inhibited under low atmospheric CO2 (refs. 7,8), so understanding glacial environments requires the development of new palaeoclimate indicators that are independent of vegetation9. Here we show that, contrary to expectations, during the past 350 kyr, peaks in southern Australian climatic moisture availability were largely confined to glacial periods, including the Last Glacial Maximum, whereas warm interglacials were relatively dry. By measuring the timing of speleothem growth in the Southern Hemisphere subtropics, which today has a predominantly negative annual moisture balance, we developed a record of climatic moisture availability that is independent of vegetation and extends through multiple glacial–interglacial cycles. Our results demonstrate that a cool-moist response is consistent across the austral subtropics and, in part, may result from reduced evaporation under cool glacial temperatures. Insofar as cold glacial environments in the Southern Hemisphere subtropics have been portrayed as uniformly arid3,10,11, our findings suggest that their characterization as evolutionary or physiological obstacles to movement and expansion of animal, plant and, potentially, human populations10 should be reconsidered.

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Fig. 1: CMI for the three main landmasses of the Southern Hemisphere subtropics and study sites.
Fig. 2: Two new speleothem proxy records of subtropical moisture in southern Australia show a cool-moist pattern.
Fig. 3: Naracoorte fossil pollen record and moisture reconstructions confirm Naracoorte KDE pattern.
Fig. 4: Southern Hemisphere subtropical hydroclimate proxy records show a widespread cool-moist pattern.
Fig. 5: Modelled responses of Southern Hemisphere hydroclimate proxy records to Southern Hemisphere temperature.
Fig. 6: Modelled responses of Southern Hemisphere hydroclimate proxy records to hemispheric temperature show the latitudinal limits of the subtropical cool-moist pattern.

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Data availability

The data that support the findings of this study are available in the Supplementary Information and at https://doi.org/10.25375/uct.24609138. Source data are provided with this paper.

Code availability

We used the R packages qgam, envirem, raster, geoChronR, astrochron, mgcv and rnaturalearth to generate Figs. 1, 5 and 6 and Extended Data Figs. 2, 3, 4, 9 and 10. The Wavemetrics Igor Pro code to calculate probabilistic KDEs, which was used in Figs. 2, 3 and 4 and Extended Data Fig. 6, is available at https://doi.org/10.25375/uct.24609138. Please cite this study when using this code.

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Acknowledgements

We acknowledge the Traditional Owners and ongoing Custodians of the Ancestral Lands of the South East and South West regions. In relation to Naracoorte caves, we acknowledge the Potaruwutij, Jardwadjali, Boandik and Meintangk Peoples. For assistance with permits, cave information and guidance in the field we thank the South Australian Department of Environment and Water (DEW), Australian Research Council (ARC) grant research partners at Naracoorte (Naracoorte Lucindale Council, DEW, Terre à Terre, Wrattonbully Wine Industries Association, South Australian Museum and the Defence Science and Technology Group), the Western Australian Government Department of Biodiversity, Conservation and Attractions and the Margaret River Busselton Tourist Association. We thank P. Valdes (Bristol) for access to HadCM3 simulations and P. Bajo, S. Paul and R. Maas for laboratory and data processing assistance. R.W. thanks R. Pickering for her support. At Naracoorte, speleothem rubble samples used in this study were collected under permit nos. M26647, E26667 and U26922. For the LN caves, samples were collected under permits from the Western Australian Government Department of Biodiversity, Conservation and Attractions and/or with permission from the Margaret River Busselton Tourist Association. This work was facilitated by ARC grants FL160100028 to J.D.W., FT130100801 to J.C.H. and LP160101249 to E.R., R.N.D. and J.C.H. R.W. acknowledges the Postgraduate Writing-Up Award supported by the Albert Shimmins Fund and the Oppenheimer Memorial Trust and VC2030 Scholar Postdoctoral Fellowship awards. J.R.B. is supported by the ARC Centre of Excellence for Climate Extremes (CE170100023).

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  1. Rieneke Weij

    Present address: Department of Geological Sciences and the Human Evolution Research Institute, University of Cape Town, Rondebosch, Western Cape, South Africa

  2. Jay Gordon

    Present address: IEEFA, Melbourne, Victoria, Australia

  3. These authors contributed equally: Rieneke Weij, J. M. Kale Sniderman

Authors and Affiliations

  1. School of Geography, Earth and Atmospheric Sciences, University of Melbourne, Melbourne, Victoria, Australia

    Rieneke Weij, J. M. Kale Sniderman, Jon D. Woodhead, John C. Hellstrom, Josephine R. Brown, Russell N. Drysdale & Jay Gordon

  2. Environnements, Dynamiques et Territoires de la Montagne, UMR CNRS, Université de Savoie-Mont, Chambéry, France

    Russell N. Drysdale

  3. School of Biological Sciences, University of Adelaide, Adelaide, South Australia, Australia

    Elizabeth Reed

  4. South Australian Museum, Adelaide, South Australia, Australia

    Elizabeth Reed

  5. Limestone Coast Landscape Board, Mount Gambier, South Australia, Australia

    Steven Bourne

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  1. Rieneke Weij
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Contributions

R.W., J.D.W., J.M.K.S., J.C.H., R.N.D. and E.R. conceived and designed the study. R.W., J.D.W., J.M.K.S., J.C.H., E.R., R.N.D., J.G. and S.B. conducted the fieldwork. R.W. and J.C.H. performed and/or contributed to the U–Th analysis and postprocessing. J.M.K.S. performed the pollen analyses. J.R.B. and J.M.K.S. analysed the climate simulations. R.W. and J.M.K.S. performed statistical analyses, wrote the manuscript and created the figures, with contributions from the other authors. All authors contributed comments and/or revisions to the manuscript.

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Correspondence to Rieneke Weij or J. M. Kale Sniderman.

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Extended data figures and tables

Extended Data Fig. 1 Spectral analyses shows coherence and typically small phase lags with Southern Hemisphere summer insolation.

a, Coherence spectra of the Naracoorte KDE, the Leeuwin-Naturaliste KDE and the seven other high-resolution Southern Hemisphere subtropical hydroclimate proxy records relative to summer insolation (21 Dec, 30°S). Thick black line is the 50th percentile of the nine coherence spectra; dark shading corresponds to the 15.9 and 84.1 percentiles, lighter shading to the 2.5 and 97.5 percentiles. Stippled line indicates non-zero coherence level at 95% confidence. Yellow bars highlight the eccentricity, obliquity and precession orbital bands. b, Coherence spectra of average HadCM3 seasonal precipitation with each spatial domain, relative to SH summer insolation. Note that only the HadCM3 precipitation simulations with the highest correlations with each record (see asterisks in Extended Data Fig. 5) are used. Thick black line is the 50th percentile of the eight coherence spectra; dark shading corresponds to the 15.9 and 84.1 percentiles, lighter shading to the 2.5 and 97.5 percentiles. Stippled line indicates non-zero coherence level at 95% confidence. Yellow bars highlight the eccentricity, obliquity and precession orbital bands. c. Phase wheels showing the phase differences in kyr between the hydroclimate proxy records and summer insolation (left wheel) and HadCM3 precipitation per region and summer insolation (right wheel). See Methods for details.

Source Data

Extended Data Fig. 2 Pollen-based quantitative climate reconstructions for Naracoorte.

1-99 percentile reconstruction envelopes for annual, summer (DJF) and winter (JJA) (a) CMI and (b) precipitation. Modern values for Naracoorte Caves shown as horizontal dashed red lines.

Source Data

Extended Data Fig. 3 Climatically sensitive plant taxa’s geographic ranges within eastern Australia.

Species occurrence data for each climatically sensitive plant taxon used for palaeoclimatic reconstruction, derived from the Atlas of Living Australia (https://ror.org/018n2ja79, see Supplementary Table 4). Filled purple circles, species occurrence data. Red diamond, location of Naracoorte Caves. Contour lines correspond to the annual CMI. Base maps created with the R package rnaturalearth114.

Source Data

Extended Data Fig. 4 Climatically sensitive plant taxa’s climatic ranges in summer and winter seasons.

Ranges of climatically sensitive plant taxa observed as fossil pollen within Naracoorte speleothems, along summer (DJF) and winter (JJA) Climatic Moisture Index axes (see Methods). Filled purple circles, species occurrence data; red diamond, modern Naracoorte Caves climate.

Source Data

Extended Data Fig. 5 Correlation plots of HadCM3 simulations vs. proxy records.

Linear correlations between simulated 0-120 ka HadCM3 DJF and JJA regional subtropical Southern Hemisphere seasonal precipitation and standardized, detrended hydroclimate proxy records within the same regions. Shaded intervals correspond to the 95% confidence interval of the linear regression lines. Records with significant (p < 0.05), or, in the case of MD96-2048 % Podocarpus, near significant (p = 0.06) positive correlations marked with an asterisk and used in Extended Data Fig. 1.

Source Data

Extended Data Fig. 6 Three subtropical lake basin hydroclimate records show a cool-moist pattern.

a, Kati Thanda/Lake Eyre Basin KDE (bandwidth = 15 kyr) based on palaeo-shoreline luminescence ages33; b, Tswaing Crater total inorganic carbon35, with reversed y-axis; and c, Salar de Uyuni natural gamma variation34. Dark and light-shaded intervals correspond to the 1 and 2 s.e.m. uncertainty envelopes on the KDE, respectively.

Source Data

Extended Data Fig. 7 Hydroclimate proxy records demonstrating the equatorward and poleward limits of the subtropical cool-wet pattern.

a, The Antarctic temperature reconstruction32; b, FR1/94-GC3 Fe/Ca37; c. U1460 Ti/Ca38; d, MD00-2361 Fe/Ca39; e, SO257-18548 terrigenous/Ca40; f, GeoB-9311 Fe/Ca41; g, Lake Malawi MAL05-1b lake level43; h, MAL05-1B % Podocarpus pollen42; i, Tanganyika KH3/4 δD44.

Source Data

Extended Data Fig. 8 Power spectra with red noise threshold reveal significant precessional frequencies.

Individual power spectra (multitaper method) of ten subtropical hydroclimate proxy time series, Southern Hemisphere summer insolation (21 Dec, 30°S) and the Antarctic temperature reconstruction32. See Methods for details.

Source Data

Extended Data Fig. 9 Naracoorte speleothem sample thickness/diameter versus sample age confirms there is no size-based preservation bias.

The thickness (flowstones) or diameter (stalagmites and stalactites) were measured for 70 individual speleothems. Note the low r2 value of the linear regression line, suggesting that there is no size-based preservation bias in our sampling at Naracoorte.

Source Data

Extended Data Fig. 10 Southern Hemisphere subtropical DJF and JJA precipitation (mm).

Data derived from Worldclim90; hydroclimate proxy sites discussed in this paper; and the six spatial domains (southwestern and southeastern South America, southwestern and southeastern Africa and southwestern and southeastern Australia) used to calculate area-averaged HadCM3 precipitation, 0-120 ka. Base maps created with the R package rnaturalearth114.

Extended Data Fig. 11 Micrographs of selected pollen and spores from Naracoorte speleothems.

a–b, Eucalyptus (Myrtaceae). c, Leptospermeae (Myrtaceae); d, Casuarinaceae; e, Asteraceae; f, Poaceae; g, Asteraceae short-spined; h, Amaranthaceae; i, Plantago (Plantaginaceae); j, Ericaceae; k-l, Banksia marginata-type (Proteaceae); m, Banksia ornata (Proteaceae); n, Pimelea (Thymelaeaceae); o, Bursaria (Pittosporaceae); p, Asparagales; q. Cichorioideae (Asteraceae); r-s, Leucopogon-type (Ericaceae); t-u, Opercularia (Anthospermeae:Rubiaceae); v, Pteris (Pteridaceae); w, Restionaceae; x-z, Monotoca-type (Ericaceae); aa, Acaena (Rosaceae); ab, Amperea (Euphorbiaceae); ac, Nertera (Anthospermeae:Rubiaceae); ad, Muehlenbeckia (Polygonaceae); ae, Grevillea/Hakea-type (Proteaceae); af, Gyrostemonaceae; ag, Myriophyllum (Haloragaceae).

Extended Data Table 1 Modern climatic data for the Naracoorte Cave Complex and the Leeuwin-Naturaliste caves in southern Australia
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Source data

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Weij, R., Sniderman, J.M.K., Woodhead, J.D. et al. Elevated Southern Hemisphere moisture availability during glacial periods. Nature 626, 319–326 (2024). https://doi.org/10.1038/s41586-023-06989-3

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