Expressions of climate perturbations in western Ugandan crater lake sediment records during the last 1000 yr

Abstract

Equatorial East Africa has a complex, regional patchwork of climate regimes, with multiple interacting drivers. Recent studies have focussed on large lakes and reveal signals that are smoothed in both space and time, and, whilst useful at a continental scale, are of less relevance when understanding short-term, abrupt or immediate impacts of climate and environmental changes. Smaller-scale studies have highlighted spatial complexity and regional heterogeneity of tropical palaeoenvironments in terms of responses to climatic forcing (e.g. the Little Ice Age [LIA]) and questions remain over the spatial extent and synchroneity of climatic changes seen in East African records. <br><br> Sediment cores from paired crater lakes in western Uganda were examined to assess ecosystem response to long-term climate and environmental change as well as testing responses to multiple drivers using redundancy analysis. These archives provide annual to sub-decadal records of environmental change. The records from the two lakes demonstrate an individualistic response to external (e.g. climatic) drivers, however, some of the broader patterns observed across East Africa suggest that the lakes are indeed sensitive to climatic perturbations such as a dry Mediaeval Climate Anomaly (MCA; 1000–1200 AD) and a relatively drier climate during the main phase of the LIA (1500–1800 AD); though lake levels in western Uganda do fluctuate. The relationship of Ugandan lakes to regional climate drivers breaks down c. 1800 AD, when major changes in the ecosystems appear to be a response to sediment and nutrient influxes as a result of increasing cultural impacts within the lake catchments. <br><br> The data highlight the complexity of individual lake response to climate forcing, indicating shifting drivers through time. This research also highlights the importance of using multi-lake studies within a landscape to allow for rigorous testing of climate reconstructions, forcing and ecosystem response

A Tapestry of Human-Induced and Climate-Driven Environmental Change in Western Uganda: The Ndali Crater Lakes Region

“…77 The hiatus in permanent human settlements from 1000 to 1250 CE may be linked to this global climate event, though the region would not have been as severely impacted as eastern regions, such as the Lake Navaisha basin. 78 In fact, this arid period is made more complex by a gradient of severe aridity running from eastern to western East Africa. 79 The increased aridity of the eastern reaches of East Africa may have been a driver for those practicing pastoral-based economies to seek more sustainable settings in the Ndali Crater Lakes Region, initially in the form of transhumant pastoralism with some lowrainfall cropping, which left an ephemeral footprint in the area.…”

“…78 In fact, this arid period is made more complex by a gradient of severe aridity running from eastern to western East Africa. 79 The increased aridity of the eastern reaches of East Africa may have been a driver for those practicing pastoral-based economies to seek more sustainable settings in the Ndali Crater Lakes Region, initially in the form of transhumant pastoralism with some lowrainfall cropping, which left an ephemeral footprint in the area.…”

“…The difficulties of linking climate changes among the Ndali Crater Lakes is witnessed in the Kasenda catchment, where there was increased moisture at about 1400 CE, somewhat later than the 1300 CE return of high moisture at Lake Nkuruba to the north, where a return to moist conditions replicated increased water levels in Lake Victoria and Lake Edward. 84 Importantly, both the Nkuruba and Kasenda records show moisture conditions that would have been attractive to sustain dense Bigo-related settlements on the Ndali Crater Lakes landscape (Figure 9). Large Bigo-related sites are omnipresent on the landscape, usually occupying deep soils on caldera slopes or on high and flat caldera rims.…”