Late Quaternary hydrological change from fluvial archives in southwestern Africa and the palaeoclimate implications

Fluvial sedimentary sequences provide important archives of late Quaternary palaeoenvironmental change. In drylands, these stores of information in fluvial landforms can be found in regions that are commonly scarce in long-term palaeoproxy records due to low levels of precipitation and poor organic preservation. In southwestern Africa, proposed drivers of Quaternary climate change carry with them a suite of hypotheses with respect to patterns of precipitation variability, yet poor coverage of palaeoclimate archives has to date made it challenging to assess model-based predictions. Here, fluvial archives offer the potential to provide the spatial and temporal coverage of palaeorecords that is required. Whilst it is well-established that dryland fluvial systems respond to hydroclimate changes on Quaternary timescales, deciphering the palaeoenvironmental histories they preserve is often complex. To date, the utility of records from fluvial archives in southwestern Africa has been hindered by low-resolution chronologies, limited use of robust methods to interrogate the context of sediment deposition, and a focus on individual studies with limited consideration of regional controls.
This thesis addresses these challenges through: i) the production of a new fluvial record from the Huab River using a detailed assessment of stratigraphic, compositional, and sedimentological changes and a high-resolution luminescence chronology; ii) the construction of a chronological database to compile and analyse quality-assessed fluvial histories from southwestern Africa; and iii) an empirical-model data comparison to interrogate these fluvial records in the context of other palaeorecords and palaeoclimate model simulations to test hypotheses of the spatial patterning of late Quaternary precipitation. The new Huab River record spans the entirety of the Holocene, recording evidence of distinct flow regimes at 12 to 9 ka, 7 to 5 ka, 4 to 1 ka, and 1 ka to present. The database collates a scattered fluvial literature and has enabled an assessment of controls on fluvial archive preservation and interpretation. The timing and nature of phases of river flow are consistent between the Huab and nearby records, and patterns of fluvial activity across southwestern Africa map onto patterns of precipitation anomalies inferred from other palaeorecords and those simulated by a suite of climate models. These data indicate spatial differences in rainfall response between coastal and inland southwestern Africa, supporting hypotheses of a difference in the dynamics of the tropical rainbelt over the ocean and land, the role of ocean-atmosphere feedbacks, and the role of westerly-derived rainfall. Together, these findings demonstrate the utility of robust fluvial archives for reconstructing palaeoenvironmental change and have allowed for recommendations to be made for priorities for future research on fluvial archives, both in southwestern Africa and beyond.

Keywords: Southern Africa
fluvial sediments
palaeoclimate
quaternary
dryland
palaeoenvironment
Advisor: Thomas, D
Burrough, S