Hydroclimate of the Last Glacial Maximum and deglaciation in southern Australia's arid margin interpreted from speleothem records (23–15 ka)

Abstract

Abstract. Terrestrial data spanning the Last Glacial Maximum (LGM) and deglaciation from the southern Australian region are sparse and limited to discontinuous sedimentological and geomorphological records with relatively large chronological uncertainties. This dearth of records has hindered a critical assessment of the role of the Southern Hemisphere mid-latitude westerly winds on the region's climate during this time period. In this study, two precisely dated speleothem records for Mairs Cave, Flinders Ranges, are presented, providing for the first time a detailed terrestrial hydroclimatic record for the southern Australian drylands during 23-15 ka. Recharge to Mairs Cave is interpreted from the speleothem record by the activation of growth, physical flood layering, and δ 18 O and δ 13 C minima. Periods of lowered recharge are indicated by 18 O and 13 C enrichment, primarily affecting δ 18 O, argued to be driven by evaporation of shallow soil/epikarst water in this water-limited environment. A hydrological driver is supported by calcite fabric changes. These include the presence of laminae, visible organic colloids, and occasional dissolution features, related to recharge, as well as the presence of sediment bands representing cave floor flooding. A shift to slower-growing, more compact calcite and an absence of lamination is interpreted to represent reduced recharge.

Climatic influences on the offset between d18O of cave drip waters and precipitation inferred from global monitoring data

“…Finally, speleothem  18 O records from regions with increasing aridity and higher temperatures should be expected to not preserve a record of precipitation  18 O. Our meta-analysis confirms the modern monitoring observations of Markowska et al (2016), who proposed that speleothem  18 O would be an archive of alternating paleo-aridity and paleo-recharge, and supports the interpretation of speleothem  18 O as a paleo-recharge and paleo-aridity for the Last Glacial Maximum speleothem in arid southern Australia (Treble et al, 2017). Table 1.…”

“…For example, water-limited regions where  18 O has high magnitude and frequency variability (e.g. Dennison et al, 2013;Treble et al, 2017). In waterlimited environments, several potential mechanisms have been proposed to significantly affect speleothem  18 O, including: 1) evaporative fractionation of  18 O in the soil, shallow vadose zone or cave; 2) selective recharge, whereby rainfall events with high magnitude or intensity have a distinct isotopic composition, typically low  18 O; and 3) non-equilibrium deposition during speleothem formation (Cuthbert et al, 2014;Pape et al, 2010;Dreybrodt and Scholz, 2011;Markowska et al, 2016).…”

Hydro-climatic variability in the southwestern Indian Ocean between 6000 and 3000 years ago

“…This inference, if correct, is partially in contrast with the southward shift of the ITCZ, which is often invoked to explain the weakening of the Asian monsoon since ∼ 4.2 ka (e.g. Wang et al, 2005;Kathayat et al, 2017). Thus, the observed drying trends on both the northern and southern fringes of the ITCZ in both hemispheres argue against the model of a southward shift in the mean position of the ITCZ as a viable cause of the 4.2 ka event.…”

The SISAL database: a global resource to document oxygen and carbon isotope records from speleothems

“…The distance of the speleothem from the cave entrance is provided, which, depending on the morphology of a cave, can be a useful indicator of cave ventilation (direct air advection). Ventilation is important as it can control cave air temperature, humidity, evaporation and pCO 2 levels (Fairchild and Baker, 2012;Frisia et al, 2011;Spötl et al, 2005;Tremaine et al, 2011). The entity table also contains a field to document whether any tests have been carried out to establish whether there is oxygen and carbon isotope quasi-equilibrium between the drip water (CO 2 -H 2 O system) and the speleothem (CaCO 3 ).…”