Lake Chala 2k: the last two millennia of environmental change in equatorial East Africa

2021 ◽  
Author(s):  
Inka Meyer ◽  
Irina Papadimitriou ◽  
Dirk Verschuren ◽  
Marc De Batist
Keyword(s):  
East Africa ◽  
Large Scale ◽  
Western Europe ◽  
Environmental Changes ◽  
Temporal Trends ◽  
Ice Age ◽  
Future Climate Change ◽  
East African ◽  
The North ◽  
Temperature And Precipitation

<p>In order to disentangle natural climate variability from anthropogenically caused variations, environmental reconstructions of the past 2000 years have gained renewed scientific interest during the last ~20 years. Whereas climatic and environmental changes during this period, such as the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA) are fairly well expressed in western Europe and the North Atlantic area, knowledge about equivalent changes in African climate and environment (e.g. changes in temperature and precipitation, monsoonal activity and resulting vegetation feedbacks) can be much improved. Here we present new results from Lake Chala, a crater lake in equatorial East Africa, based on sedimentary grain-size distributions. Notwithstanding the relatively minor clastic mineral component, we are able to discriminate between different aeolian and fluviatile sources of terrigenous material and to reconstruct temporal trends in their contribution to the sediment. This can be linked to both local environmental dynamics and changes in the large-scale monsoonal systems over the East African landmass. Our findings point to arid conditions during the MCA and humid conditions during the LIA, in support of regional hydroclimate history as reconstructed from other moisture-balance proxies. The results of this study form an important piece of the puzzle to better understand past changes in African environments, which is a key aspect in the debate about future climate change in one of the most climate-sensitive regions on the planet.</p>

scholarly journals Expressions of climate perturbations in western Ugandan crater lake sediment records during the last 1000 years

2014 ◽  
Vol 10 (4) ◽  
pp. 1581-1601 ◽  
Author(s):  
K. Mills ◽  
D. B. Ryves ◽  
N. J. Anderson ◽  
C. L. Bryant ◽  
J. J. Tyler
Keyword(s):  
East Africa ◽  
Late Holocene ◽  
Large Scale ◽  
Environmental Changes ◽  
Spatial Scales ◽  
Ice Age ◽  
Climate Forcing ◽  
Diatom Community ◽  
Community Responses ◽  
Indirect Response

Abstract. Equatorial East Africa has a complex regional patchwork of climate regimes, sensitive to climate fluctuations over a variety of temporal and spatial scales during the late Holocene. Understanding how these changes are recorded in and interpreted from biological and geochemical proxies in lake sedimentary records remains a key challenge to answering fundamental questions regarding the nature, spatial extent and synchroneity of climatic changes seen in East African palaeo-records. Using a paired lake approach, where neighbouring lakes share the same geology, climate and landscape, it might be expected that the systems will respond similarly to external climate forcing. Sediment cores from two crater lakes in western Uganda spanning the last ~1000 years were examined to assess diatom community responses to late Holocene climate and environmental changes, and to test responses to multiple drivers using redundancy analysis (RDA). These archives provide annual to sub-decadal records of environmental change. Lakes Nyamogusingiri and Kyasanduka appear to operate as independent systems in their recording of a similar hydrological response signal via distinct diatom records. However, whilst their fossil diatom records demonstrate an individualistic, indirect response to external (e.g. climatic) drivers, the inferred lake levels show similar overall trends and reflect the broader patterns observed in Uganda and across East Africa. The lakes appear to be sensitive to large-scale climatic perturbations, with evidence of a dry Medieval Climate Anomaly (MCA; ca. AD 1000–1200). The diatom record from Lake Nyamogusingiri suggests a drying climate during the main phase of the Little Ice Age (LIA) (ca. AD 1600–1800), whereas the diatom response from the shallower Lake Kyasanduka is more complex (with groundwater likely playing a key role), and may be driven more by changes in silica and other nutrients, rather than by lake level. The sensitivity of these two Ugandan lakes to regional climate drivers breaks down in ca. AD 1800, when major changes in the ecosystems appear to be a response to increasing cultural impacts within the lake catchments, although both proxy records appear to respond to the drought recorded across East Africa in the mid-20th century. The data highlight the complexity of diatom community responses to external drivers (climate or cultural), even in neighbouring, shallow freshwater lakes. This research also illustrates the importance of, and the need to move towards, a multi-lake, multi-proxy landscape approach to understanding regional hydrological change which will allow for rigorous testing of climate reconstructions, climate forcing and ecosystem response models.

scholarly journals Crustal variability along the rifted/sheared East African margin: a review

2021 ◽  
Vol 41 (2) ◽  
Author(s):  
Maren Vormann ◽  
Wilfried Jokat
Keyword(s):  
East Africa ◽  
Shear Zone ◽  
Structural Changes ◽  
The South ◽  
East African ◽  
The North ◽  
Rifted Margins ◽  
Continental Block ◽  
Seismic Lines ◽  
Southeastern Madagascar

AbstractThe East African margin between the Somali Basin in the north and the Natal Basin in the south formed as a result of the Jurassic/Cretaceous dispersal of Gondwana. While the initial movements between East and West Gondwana left (oblique) rifted margins behind, the subsequent southward drift of East Gondwana from 157 Ma onwards created a major shear zone, the Davie Fracture Zone (DFZ), along East Africa. To document the structural variability of the DFZ, several deep seismic lines were acquired off northern Mozambique. The profiles clearly indicate the structural changes along the shear zone from an elevated continental block in the south (14°–20°S) to non-elevated basement covered by up to 6-km-thick sediments in the north (9°–13°S). Here, we compile the geological/geophysical knowledge of five profiles along East Africa and interpret them in the context of one of the latest kinematic reconstructions. A pre-rift position of the detached continental sliver of the Davie Ridge between Tanzania/Kenya and southeastern Madagascar fits to this kinematic reconstruction without general changes of the rotation poles.

scholarly journals A high-resolution model of the 100 ka ice-age cycle

1997 ◽  
Vol 25 ◽  
pp. 58-65 ◽  
Author(s):  
L. Tarasov ◽  
W. R. Peltier
Keyword(s):  
Large Scale ◽  
Climate Model ◽  
Relaxation Times ◽  
Ice Age ◽  
Adjustment Process ◽  
Glacial Cycle ◽  
Ice Dynamics ◽  
Last Glacial ◽  
The North ◽  
The Last Glacial

Significant improvements to the representation of climate forcing and mass-balance response in a coupled two-dimensional global energy balance climate model (EBM) and vertically integrated ice-sheet model (ISM) have led to the prediction of an ice-volume chronology for the most recent ice-age cycle of the Northern Hemisphere that is close to that inferred from the geological record. Most significant is that full glacial termination is delivered by the model without the need for new physical ingredients. In addition, a relatively close match is achieved between the Last Glacial Maximum (LGM) model ice topography and that of the recently-described ICE-4G reconstruction. These results suggest that large-scale climate system reorganization is not required to explain the main variations of the North American (NA) ice sheets over the last glacial cycle. Lack of sea-ice and marine-ice dynamics in the model leaves the situation over the Eurasian (EA) sector much more uncertain.The incorporation of a gravitationally self-consistent description of the glacial isostatic adjustment process demonstrates that the NA and EA bedrock responses can be adequately represented by simpler damped-relaxation models with characteristic time-scales of 3–5ka and 5 ka, respectively. These relaxation times agree with those independently inferred on the basis of postglacial relative sea-level histories.

scholarly journals Trends in compound extremes of air temperature and precipitation in Eastern Europe

2021 ◽  
Author(s):  
Elena Vyshkvarkova ◽  
Olga Sukhonos
Keyword(s):  
Eastern Europe ◽  
North Atlantic Oscillation ◽  
Air Temperature ◽  
North Atlantic ◽  
Large Scale ◽  
The North ◽  
Temperature And Precipitation ◽  
Atmosphere System ◽  
Daily Data ◽  
The North Atlantic Oscillation

Abstract The spatial distribution of compound extremes of air temperature and precipitation was studied over the territory of Eastern Europe for the period 1950–2018 during winter and spring. Using daily data on air temperature and precipitation, we calculated the frequency and trends of the four indices – cold/dry, cold/wet, warm/dry and warm/wet. Also, we studying the connection between these indices and large-scale processes in the ocean-atmosphere system such as North Atlantic Oscillation, East Atlantic Oscillation and Scandinavian Oscillation. The results have shown that positive trends in the region are typical of the combinations with the temperatures above the 75th percentile, i.e., the warm extremes in winter and spring. Negative trends were obtained for the cold extremes. Statistically significant increase in the number of days with warm extremes was observed in the northern parts of the region in winter and spring. The analysis of the impacts of the large-scale processes in oceans-atmosphere system showed that the North Atlantic Oscillation index has a strong positive and statistically significant correlation with the warm indices of compound extremes in the northern part of Eastern Europe in winter, while the Scandinavian Oscillation shows the opposite picture.

Chrysophyte microfossils record marked responses to recent environmental changes in high- and mid-arctic lakes

2001 ◽  
Vol 79 (6) ◽  
pp. 747-752 ◽  
Author(s):  
Alexander P Wolfe ◽  
Bianca B Perren
Keyword(s):  
Environmental Changes ◽  
Arctic Lakes ◽  
Ice Age ◽  
Algal Community ◽  
North Coast ◽  
Baffin Island ◽  
Lake Ecosystems ◽  
The North ◽  
Ecological Changes ◽  
Community Shifts

Rapid stratigraphic changes are recorded in recent assemblages of subfossil Chrysophyceae from the sediments of two highly contrasted arctic lakes, one situated in the polar desert of west-central Ellesmere Island, and the other on eastern Baffin Island in the mid-Arctic climatic zone. In Sawtooth Lake on the Fosheim Peninsula, concentrations of chrysophycean stomatocysts increase dramatically in sediments deposited since AD 1920. Only trace abundances of stomatocysts are encountered in older sediments. In Kekerturnak Lake, on the north coast of Cumberland Peninsula, scales of Mallomonas spp., previously absent from the sediment record, appear suddenly in the upper 5.5 cm of sediment and subsequently become ubiquitous in the top 1.0 cm. These results corroborate diatom stratigraphic data from other sites in the Canadian Arctic Archipelago, together suggesting that unprecedented ecological changes are presently occurring across this vast region. In all likelihood, these abrupt algal community shifts reflect the response of arctic lake ecosystems to well-documented climate warming since the Little Ice Age, with the implications that recent rates of environmental change are unprecedented in the context of the Holocene.Key words: Paleolimnology, arctic lakes, Chrysophyceae, stomatocysts, Mallomonas.

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

2013 ◽  
Vol 9 (5) ◽  
pp. 5183-5226 ◽  
Author(s):  
K. Mills ◽  
D. B. Ryves ◽  
N. J. Anderson ◽  
C. L. Bryant ◽  
J. J. Tyler
Keyword(s):  
Environmental Change ◽  
East Africa ◽  
Environmental Changes ◽  
Sediment Cores ◽  
Ice Age ◽  
Ecosystem Response ◽  
Large Lakes ◽  
Crater Lakes ◽  
Continental Scale ◽  
Western Uganda

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. 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. 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.

Quaternary Climatic Changes and Landscape Evolution

2005 ◽  
Author(s):  
Jürgen Ehlers
Keyword(s):  
Climatic Change ◽  
Large Scale ◽  
Western Europe ◽  
Ice Sheets ◽  
Climatic Changes ◽  
Mountain Glaciers ◽  
Marine Deposits ◽  
The North ◽  
Terrestrial Sediments ◽  
International Geological Congress

The last 2–3 Ma have witnessed climatic changes of a scale unknown to the preceding 300 Ma. In the cold periods vegetation was reduced to a steppe, giving rise to large-scale aeolian deposition of sand and loess and river sands and gravels. In the warm stages, flora and fauna recolonized the region. Parts of Europe were repeatedly covered by mountain glaciers or continental ice sheets which brought along huge amounts of unweathered rock debris from their source areas. The ice sheets dammed rivers and redirected drainage towards the North Sea. They created a new, glacial landscape. This chapter presents an outline of the climatic history, and in particular the glacial processes involved in shaping the landscapes of western Europe. By convention, geologists generally tend to draw stratigraphical boundaries in marine deposits because they are more likely to represent continuous sedimentation and relatively consistent environments in comparison to terrestrial sediments. However, marine deposits from the period in question are relatively rarely exposed at the surface. According to a conclusion of the International Geological Congress 1948 the Tertiary/Quaternary boundary was defined as the base of the marine deposits of the Calabrian in southern Italy. In the Calabrian sediments fossils are found that reflect a very distinct climatic cooling (amongst others the foraminifer Hyalinea baltica). This climatic change roughly coincides with a reversal of the earth’s magnetic field; it is situated at the upper boundary of what is called the Olduvai Event. Consequently, it is relatively easy to identify; its age is today estimated at 1.77 Ma (Shackleton et al. 1990). However, in contrast to the older parts of the earth’s history, the significant changes within the Quaternary are not changes in faunal composition but changes in climate. For reasons of long-term climatic evolution the base of the Calabrian is not a very suitable global boundary. Its adoption excludes some of the major glaciations from the Quaternary. Therefore, in major parts of Europe another Tertiary/Quaternary boundary is in use, based on the stratigraphy of the Lower Rhine area (e.g. Zagwijn 1989). Here the most significant climatic change is already recorded as far back as the Gauss/Matuyama magnetic reversal (some 2.6 Ma ago).

scholarly journals A high-resolution model of the 100 ka ice-age cycle

1997 ◽  
Vol 25 ◽  
pp. 58-65 ◽  
Author(s):  
L. Tarasov ◽  
W. R. Peltier
Keyword(s):  
Large Scale ◽  
Climate Model ◽  
Relaxation Times ◽  
Ice Age ◽  
Adjustment Process ◽  
Glacial Cycle ◽  
Ice Dynamics ◽  
Last Glacial ◽  
The North ◽  
The Last Glacial

Significant improvements to the representation of climate forcing and mass-balance response in a coupled two-dimensional global energy balance climate model (EBM) and vertically integrated ice-sheet model (ISM) have led to the prediction of an ice-volume chronology for the most recent ice-age cycle of the Northern Hemisphere that is close to that inferred from the geological record. Most significant is that full glacial termination is delivered by the model without the need for new physical ingredients. In addition, a relatively close match is achieved between the Last Glacial Maximum (LGM) model ice topography and that of the recently-described ICE-4G reconstruction. These results suggest that large-scale climate system reorganization is not required to explain the main variations of the North American (NA) ice sheets over the last glacial cycle. Lack of sea-ice and marine-ice dynamics in the model leaves the situation over the Eurasian (EA) sector much more uncertain.The incorporation of a gravitationally self-consistent description of the glacial isostatic adjustment process demonstrates that the NA and EA bedrock responses can be adequately represented by simpler damped-relaxation models with characteristic time-scales of 3–5ka and 5 ka, respectively. These relaxation times agree with those independently inferred on the basis of postglacial relative sea-level histories.

scholarly journals Simulating the spatiotemporal variations in aboveground biomass in Inner Mongolian grasslands under environmental changes

2021 ◽  
Vol 21 (4) ◽  
pp. 3059-3071
Author(s):  
Guocheng Wang ◽  
Zhongkui Luo ◽  
Yao Huang ◽  
Wenjuan Sun ◽  
Yurong Wei ◽  
...  
Keyword(s):  
Climate Change ◽  
Aboveground Biomass ◽  
Large Scale ◽  
Environmental Changes ◽  
Regional Scale ◽  
Future Climate Change ◽  
Desert Steppe ◽  
Meadow Steppe ◽  
Grassland Type ◽  
Spatiotemporal Changes

Abstract. Grassland aboveground biomass (AGB) is a critical component of the global carbon cycle and reflects ecosystem productivity. Although it is widely acknowledged that dynamics of grassland biomass is significantly regulated by climate change, in situ evidence at meaningfully large spatiotemporal scales is limited. Here, we combine biomass measurements from six long-term (> 30 years) experiments and data in existing literatures to explore the spatiotemporal changes in AGB in Inner Mongolian temperate grasslands. We show that, on average, annual AGB over the past 4 decades is 2561, 1496 and 835 kg ha−1, respectively, in meadow steppe, typical steppe and desert steppe in Inner Mongolia. The spatiotemporal changes of AGB are regulated by interactions of climatic attributes, edaphic properties, grassland type and livestock. Using a machine-learning-based approach, we map annual AGB (from 1981 to 2100) across the Inner Mongolian grasslands at the spatial resolution of 1 km. We find that on the regional scale, meadow steppe has the highest annual AGB, followed by typical and desert steppe. Future climate change characterized mainly by warming could lead to a general decrease in grassland AGB. Under climate change, on average, compared with the historical AGB (i.e. average of 1981–2019), the AGB at the end of this century (i.e. average of 2080–2100) would decrease by 14 % under Representative Concentration Pathway (RCP) 4.5 and 28 % under RCP8.5. If the carbon dioxide (CO2) enrichment effect on AGB is considered, however, the estimated decreases in future AGB can be reversed due to the growing atmospheric CO2 concentrations under both RCP4.5 and RCP8.5. The projected changes in AGB show large spatial and temporal disparities across different grassland types and RCP scenarios. Our study demonstrates the accuracy of predictions in AGB using a modelling approach driven by several readily obtainable environmental variables and provides new data at a large scale and fine resolution extrapolated from field measurements.

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