Expressions of Climate Perturbations in Western Ugandan Crater Table 3
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EGU Journal Logos (RGB) Open Access Open Access Open Access Advances in Annales Nonlinear Processes Geosciences Geophysicae in Geophysics Open Access Open Access Natural Hazards Natural Hazards and Earth System and Earth System Sciences Sciences Discussions Open Access Open Access Atmospheric Atmospheric Chemistry Chemistry and Physics and Physics Discussions Open Access Open Access Atmospheric Atmospheric Measurement Measurement Techniques Techniques Discussions Open Access Open Access Biogeosciences Biogeosciences Discussions Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Open Access Open Access Clim. Past Discuss., 9, 5183–5226, 2013 Climate www.clim-past-discuss.net/9/5183/2013/ Climate CPD doi:10.5194/cpd-9-5183-2013 of the Past of the Past © Author(s) 2013. CC Attribution 3.0 License. Discussions 9, 5183–5226, 2013 Open Access Open Access This discussion paper is/has been under review for the journal ClimateEarth of the System Past (CP). Earth System Expressions of Please refer to the corresponding final paper in CP if available. Dynamics Dynamics climate perturbations Discussions in western Ugandan Open Access ExpressionsGeoscientific of climate perturbationsGeoscientific inOpen Access crater Instrumentation Instrumentation K. Mills et al. western UgandanMethods and crater lake sedimentMethods and Data Systems Data Systems records during the last 1000 yr Discussions Open Access Open Access Title Page Geoscientific 1,2 1Geoscientific 1 3 4 K. Mills , D. B. Ryves , N. J. Anderson , C. L. BryantModel, and Development J. J. Tyler Abstract Introduction Model Development Discussions 1 Department of Geography, Loughborough University, Loughborough, LE11 3TU, UK Conclusions References 2 Open Access School of Science and Engineering, UniversityOpen Access of Ballarat, 3350 Ballarat, Australia 3NERC Radiocarbon FacilityHydrology (Environment), and Scottish Enterprise TechnologyHydrology Park, and Tables Figures East Kilbride, G75 0QF, Scotland,Earth System UK Earth System 4 School of Earth and EnvironmentalSciences Sciences, University of Adelaide, Sciences J I Adelaide, SA 5001, Australia Discussions Open Access Open Access J I Received: 15 August 2013 – Accepted: 3 September 2013 – Published:Ocean 10 Science September 2013 Ocean Science Back Close Correspondence to: K. Mills ([email protected]) Discussions Published by Copernicus Publications on behalf of the European Geosciences Union. Full Screen / Esc Open Access Open Access Solid Earth Printer-friendly Version Solid Earth Discussions Interactive Discussion Open Access 5183 Open Access The Cryosphere The Cryosphere Discussions Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Abstract CPD Equatorial East Africa has a complex, regional patchwork of climate regimes, with multi- ple interacting drivers. Recent studies have focussed on large lakes and reveal signals 9, 5183–5226, 2013 that are smoothed in both space and time, and, whilst useful at a continental scale, 5 are of less relevance when understanding short-term, abrupt or immediate impacts Expressions of of climate and environmental changes. Smaller-scale studies have highlighted spatial climate perturbations complexity and regional heterogeneity of tropical palaeoenvironments in terms of re- in western Ugandan sponses to climatic forcing (e.g. the Little Ice Age [LIA]) and questions remain over the crater spatial extent and synchroneity of climatic changes seen in East African records. 10 Sediment cores from paired crater lakes in western Uganda were examined to as- K. Mills et al. sess ecosystem response to long-term climate and environmental change as well as testing responses to multiple drivers using redundancy analysis. These archives pro- vide annual to sub-decadal records of environmental change. The records from the Title Page two lakes demonstrate an individualistic response to external (e.g. climatic) drivers, Abstract Introduction 15 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 Conclusions References Anomaly (MCA; 1000–1200 AD) and a relatively drier climate during the main phase of Tables Figures the LIA (1500–1800 AD); though lake levels in western Uganda do fluctuate. The rela- tionship of Ugandan lakes to regional climate drivers breaks down c. 1800 AD, when J I 20 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. J I The data highlight the complexity of individual lake response to climate forcing, in- dicating shifting drivers through time. This research also highlights the importance of Back Close using multi-lake studies within a landscape to allow for rigorous testing of climate re- Full Screen / Esc 25 constructions, forcing and ecosystem response. Printer-friendly Version Interactive Discussion 5184 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 1 Introduction CPD The climate of East Africa exhibits high inter-decadal variability during the last 2000 yr, whilst high magnitude and abrupt climate events characterise the short instrumental 9, 5183–5226, 2013 record (e.g. rainfall variability as a result of short-term climatic perturbations, such as 5 El Niño-Southern Oscillation; Nicholson, 1996, 2000; Nicholson and Yin, 2001; Con- Expressions of way, 2002). Previous studies within East Africa have shown that some of these past climate perturbations climatic events are synchronous across the region. However, a number of more recent in western Ugandan studies have suggested spatial complexity (Verschuren et al., 2000; Ssemmanda et crater al., 2005; Stager et al., 2005; Ryves et al., 2011), and thus regional heterogeneity of 10 tropical palaeoenvironments in terms of responses to climatic forcing (e.g. the Little K. Mills et al. Ice Age; Russell et al., 2007). Current palaeoclimatic research in Africa is of immense importance as it has the means to provide an historical and pre-colonial perspective on past variability (both natural and anthropogenic). The last 1000 yr is a crucial pe- Title Page riod in East African history during which time there were major societal transformations Abstract Introduction 15 and political changes, which have often been linked to fluctuations in climatic condi- tions (e.g. Taylor et al., 2000; Robertshaw and Taylor, 2000; Verschuren et al., 2000; Conclusions References Robertshaw et al., 2004; Doyle, 2006). In addition to this, the last 1000 yr provides Tables Figures one of the most challenging time frames in which to understand regional climatic and environmental changes from lake sediment records in East Africa due to the issues J I 20 associated with the dating of sediments spanning this period as well as increasing modification of many of the catchments by anthropogenic activity, especially in terms J I of agriculture (with the development of nucleated, permanent settlements) and the im- plementation of new technologies (e.g. iron technology and associated forest clearance Back Close for the production of charcoal). Full Screen / Esc 25 More recently, research has focussed upon compiling continent wide, historical and proxy temperature records from a range of archives to understand past variations in Printer-friendly Version climate of the last 2000 yr (Nicholson et al., 2013). However, given that equatorial East Africa has a complex, regional patchwork of climate regimes, with a general eastward Interactive Discussion 5185 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | trend of increasing aridity, there are clearly multiple interacting drivers that appear to have a causal relationship with long-term trends in temperature, rainfall and lake levels, CPD but which are overlain by the cultural signals. The causes of century- to millennial-scale 9, 5183–5226, 2013 climate variability in tropical Africa and the drivers of some of the significant climatic 5 perturbations (e.g. Mediaeval Climate Anomaly – MCA – and Little Ice Age – LIA) are poorly understood (Russell and Johnson, 2005), though several climatic scenarios Expressions of (hypotheses) have been suggested. Recent high-resolution studies that have focussed climate perturbations on large lakes reveal signals that are smoothed in both space and time which whilst in western Ugandan useful at a continental scale, are of less relevance when addressing short term, abrupt crater 10 or immediate impacts of climate and environmental change at a scale that is relevant to people and policy. K. Mills et al. There is a growing body of literature on high temporal resolution palaeolimnological records of Ugandan crater lakes spanning the last c. 1000 yr (Ssemmanda et al., 2005; Title Page Russell et al., 2007; Bessems et al., 2008; Ryves et al., 2011) which have suggested 15 that some of these lakes are particularly sensitive to short-term (decadal to century- Abstract Introduction scale) rainfall variability (Russell et al., 2007; Bessems et al., 2008), due to the lake water-balance which is primarily driven by effective moisture (precipitation: evapora- Conclusions References tion ratio), even in open systems. In addition to this, the relatively small catchment to Tables Figures lake ratio increases the lake’s sensitivity to shifts in precipitation (hydrological connec- 20 tivity) as well as catchment changes (as a result of disturbance). However, whilst these J I studies explore