A record of rapid Holocene climate change preserved in hyrax middens from southwestern Africa

Abstract

The discovery of sensitive paleoenvironmental proxies contained within fossilized rock hyrax middens from the margin of the central Namib Desert, Africa, is providing unprecedented insight into the region's environmental history. High-resolution stable carbon and nitrogen isotope records spanning 0-11,700 cal (calibrated) yr B.P. indicate phases of relatively humid conditions from 8700-7500, 6900-6700, 5600-4900, and 4200-3500 cal yr B.P., with a period of marked aridity occurring from 3500 until ca. 300 cal yr B.P. Transitions between these phases appear to have occurred very rapidly, often within <200 years. Of particular importance are: (1) the observed relationship between regional aridifi cation and the decline in Northern Hemisphere insolation across the Holocene, and (2) the signifi cance of suborbital scale variations in climate that covary strongly with fl uctuations in solar forcing. Together, these elements call for a fundamental reexamination of the role of orbital forcing on tropical African systems, and a reconsideration of what factors drive climate change in the region. The quality and resolution of these data far surpass any other evidence available from the region, and the continued development of this unique archive promises to revolutionize paleoenvironmental studies in southern Africa.on June 8, 2015 geology.gsapubs.org Downloaded from

Stable isotope analyses of rock hyrax faecal pellets, hyraceum and associated vegetation in southern Africa: Implications for dietary ecology and palaeoenvironmental reconstructions

“…This is consistent with existing observations (Lensing, 648 1983;Fourie, 1983;Scott and Vogel, 2000), but the wider geographic spread of our data suggests such 649 inferences are generally valid for much of the hyrax's habitat. This is also consistent with some 650 interpretations of hyrax midden δ 13 C records from the Savanna Biome, whereby a model of greater 651 wet season C4 grass consumption was extended to consider longer-term fluctuations in the 652 duration/intensity of the wet season (Chase et al 2009;. broader impact of this latter factor is difficult to assess as it can be anticipated that the animal is able 663 to meet its protein needs and at most sites (perhaps excepting Zizou) this can be achieved through 664 varying the proportions of (fresh) graze and browse through time.…”

“…Changes in hyraceum isotopic signals have 34 been inferred to largely relate to the stable isotope composition of the animal's diet and thus, to 35 environmental controls on plant isotopic composition in the midden environs (Chase et al, 2012). It 36 has been argued that this interpretation is supported by facets of the midden geochemistry (Carr et 37 al., 2010) and by: 1) the close correlations in temporal isotopic trends between discrete midden 38 (colony) records ; 2) correlations of such trends with independent 39 palaeoenvironmental archives, which furthermore show the isotopically opposite responses to those 40 predicted by dominantly metabolic controls on urine stable isotope composition (Chase et al, 2009;41 20112015b); and 3) good correlations between isotope and pollen data from the same midden 42 (Chase et al, 2015a;Chase et al 2015b). 43 Notwithstanding, the fundamental isotope systematics of the diet-herbivore system within 44 rock hyrax habitats remain to be fully elucidated.…”

“…Several studies have developed palaeoclimatic records using 31 sequential analysis of stable carbon and nitrogen isotopes through stratified hyraceum, the 32 crystallised urinary material (cf. faecal pellets) that forms many hyrax middens (Scott and Vogel, 2000; 33 Chase et al, 2009;2011;2015a;2015b). Changes in hyraceum isotopic signals have 34 been inferred to largely relate to the stable isotope composition of the animal's diet and thus, to 35 environmental controls on plant isotopic composition in the midden environs (Chase et al, 2012).…”

Vegetation response to the &quot;African Humid Period&quot; termination in Central Cameroon (7° N) – new pollen insight from Lake Mbalang

“…3500 until ca. 300 cal yr BP (Chase et al, 2009). If some slight discrepancies can be observed in timing, mode and amplitude of vegetation response in the different Holocene records during the AHP termination, it is mainly due to location and peculiar environment of the study sites (cf.…”

Southern Hemisphere anticyclonic circulation drives oceanic and climatic conditions in late Holocene southernmost Africa

“…In the past, it was relatively uncontroversial that long term (glacial-interglacial timescale) climate variations in southernmost Africa are directly forced by local insolation (Daniau et al, 2013;Simon et al, 2015). However, recently several paleorecords have emerged showing either no evidence of direct insolation as a climatic driver (Chase et al, 2009(Chase et al, , 2010Dupont et al, 2011) or evidence for opposing trends (i.e., synchrony with the Northern Hemisphere) (Tierney et al, 2008;Stager et al, 2012;Truc et al, 2013). Furthermore, on shorter timescales, recent datasets reveal strong indications for a highly complex local climate system.…”