An uncertainty-focused database approach to extract spatiotemporal trends from qualitative and discontinuous lake-status histories

Abstract

Changes in lake status are often interpreted as palaeoclimate indicators due to their dependence on precipitation and evaporation. The Global Lake Status Database (GLSDB) has since long provided a standardised synopsis of qualitative lake status over the last 30,000 14 C years. Potential sources of uncertainty however are not recorded in the GLSDB. Here we present an updated and improved relational-database framework that incorporates uncertainty in both chronology and the interpretation of palaeoenvironmental data. The database uses peerreviewed palaeolimnological studies to produce a consensus on qualitative lake-status histories, whose chronologies are revised and standardized through the recalibration of radiocarbon dates and the application of Bayesian age-depth modelling for stratigraphic archives. Quantitative information on absolute water-level elevation is preserved if available from geomorphological sources. We also propose a new probabilistic analytical framework that accounts for these uncertainties to reconstruct synoptic, integrated environmental signals. The process is based on a Monte Carlo algorithm that iteratively samples individual lake-status histories within the limits of their uncertainties to produce many possible scenarios. We then use Recursively-Subtracted Empirical Orthogonal Function analysis to extract dominant patterns of lake-status variability from these scenarios. As a proof of concept, we apply this framework to 67 sites in eastern and southern Africa whose lake-status histories cover part of the late Pleistocene and/or Holocene. We show that, despite the sometimes large temporal and interpretation uncertainties, and the inclusion of highly discontinuous lake-status time series, identifying the major known millennial-scale climatic phases during the last 20,000 years is possible. Our framework was also able to identify an antiphased response between the lake basins in eastern and interior southern Africa to these changes. We propose that our new database and methodology framework serves as a template for efficient lakestatus data synthesis, encourages the incorporation of lake-status data in more palaeoclimate syntheses, and expands the possibilities for the use of such data in the evaluation of climate models.

Dryland dunes and other dryland environmental archives as proxies for Late Quaternary stratigraphy and environmental and climate change in southern Africa

“…Figure 4. Proxy records for the northern Kalahari for the past 190 ka, arranged broadly west to east, and the central Kenyan Rift Lake level records for comparison, where: (a) Etosha lake (site 26) levels, solid is lake 21 to 24 m deep and striped is low (a few meters) (Hipondoka et al 2014), and (b) Etosha lake (site 26) classes, where left to right is 6 (highest) to 1 (lowest) (De Cort et al, 2021), (c) speleothem growth phases combined from Aikab and Aigama (site 28) and Guinas Meer (site 29) cenotes (Brook et al, 1999), (d) Dante Cave (site 30) speleothem δ 18 O (Sletten et al, 2013), (e) dune accumulation ages for the northwestern (NWK) dunefield Kalahari (site 32) (see individual citations in Thomas and Burrough, 2016), (f) speleothem growth phases at Drotsky's Cave (site 36) and Bone Cave (site 37) (Brook et al, 1998), (g) mega-lake Makgadikgadi (sites 39 to 42) , (h) dune accumulation ages for the northeast (NE) (site 38) and eastern (EK) (site 43) dunefields in the northern Kalahari (see individual citations in Thomas and Burrough, 2016), and (i) central Kenyan Rift lakes outside the region of interest for comparison (combined within Trauth et al, 2003). Figure 5.…”