10 results on '"Lamb, Henry"'
Search Results
2. Diatom-derived palaeoconductivity estimates for Lake Awassa, Ethiopia: evidence for pulsed inflows of saline groundwater
- Author
-
Telford, Richard J., Lamb, Henry F., and Umer Mohammed, Mohammed
- Published
- 1999
- Full Text
- View/download PDF
3. Lake evolution in a semi-arid montane environment: response to catchment change and hydroclimatic variation
- Author
-
Lamb, Henry, Roberts, Neil, Leng, Melanie, Barker, Philip, Benkaddour, Abdelfattah, and van der Kaars, Sander
- Published
- 1999
- Full Text
- View/download PDF
4. John Birks: Pioneer in quantitative palaeoecology.
- Author
-
Battarbee, Richard W, Lamb, Henry, Bennett, Keith, Edwards, Mary, Bjune, Anne E, Kaland, Peter E, Berglund, Björn E, Lotter, André F, Seppä, Heikki, Willis, Kathy J, Herzschuh, Ulrike, and Birks, Hilary H
- Subjects
- *
SCIENTISTS , *PALEOECOLOGY , *CLIMATE change , *ECOLOGY , *HOLOCENE paleoecology - Abstract
We describe the career of John Birks as a pioneering scientist who has, over a career spanning five decades, transformed palaeoecology from a largely descriptive to a rigorous quantitative science relevant to contemporary questions in ecology and environmental change. We review his influence on students and colleagues not only at Cambridge and Bergen Universities, his places of primary employment, but also on individuals and research groups in Europe and North America. We also introduce the collection of papers that we have assembled in his honour. The papers are written by his former students and close colleagues and span many of the areas of palaeoecology to which John himself has made major contributions. These include the relationship between ecology and palaeoecology, late-glacial and Holocene palaeoecology, ecological succession, climate change and vegetation history, the role of palaeoecological techniques in reconstructing and understanding the impact of human activity on terrestrial and freshwater ecosystems and numerical analysis of multivariate palaeoecological data. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
5. Oxygen and carbon isotope composition of authigenic carbonate from an Ethiopian lake: a climate record of the last 2000 years.
- Author
-
Lamb, Henry F., Leng, Melanie J., Telford, Richard J., Ayenew, Tenalem, and Umer, Mohammed
- Subjects
- *
OXYGEN , *CARBON , *ISOTOPES , *CARBONATES , *METEOROLOGICAL precipitation , *EVAPORATION (Meteorology) , *RAINFALL , *CLIMATE change , *LAKES - Abstract
The oxygen and carbon isotope composition of sedimentary carbonates formed in Lake Hayq, a closed-basin lake in northern Ethiopia, suggests marked variation in the balance between precipitation and evaporation during the last 2000 years. Diatom stratigraphy shows that the lake remained deep enough to support planktonic taxa, and was never saline. The record suggests that rainfall was higher than that of the twentieth century during most of this time, especially during two short intervals centred on AD 700 and AD 1300. Climate was drier only around AD 800, and from AD 1750–1900. Similar, but slightly moister climate than today, with high interdecadal variability, prevailed from AD 800 to AD 1200, equivalent to the European ‘Mediaeval Warm Period’. A period of high effective precipitation followed, from AD 1200 to AD 1700, during the ‘Little Ice Age’. Pollen evidence suggests that increased forest cover from AD 1400 to AD 1750 was a response to higher rainfall; forest cover may have increased evaporative loss from the catchment, contributing to a subsequent trend of increasing lakewater δ18O values. The record shows similarities in the timing and direction of changes in proxy-climatic records from Lake Naivasha (Kenya) and from the Nile. [ABSTRACT FROM AUTHOR]
- Published
- 2007
- Full Text
- View/download PDF
6. Vegetational response to Holocene climatic change: pollen and palaeolimnological data from the Middle Atlas, Morocco.
- Author
-
Lamb, Henry F. and van der Kaars, Sander
- Abstract
Pollen data from a radiocarbon-dated lake-sediment core from the Middle Atlas of Morocco show that forests of evergreen and winter-deciduous oaks (Quercus rotundifolia, Q. canariensis), present from the start of the Holocene, were invaded at 6200 BP by Cedrus atlantica in low numbers. Two thousand years later, after a short period characterized by higher deciduous oak frequency, Cedrus increased to its present abundance. These changes may have been in response to increasing effective moisture as summer temperatures decreased with declining northern-hemisphere seasonality, under the influence of precessional forcing. Palaeolimnological data from the same core show that the lake level fell sharply in five 200-400 yr-long arid intervals, but the pollen data show little or no evidence of a vegetational response. This suggests that summer (growing-season) rainfall remained adequate during the dry intervals, whereas depletion of the groundwater aquifer was the result of reduced winter precipitation. Anthropogenic exploitation since c. 1300 BP has had a greater effect on the forest ecosystem than any of the Holocene arid intervals. [ABSTRACT FROM PUBLISHER]
- Published
- 1995
- Full Text
- View/download PDF
7. Late Quaternary climate change in the north-eastern highlands of Ethiopia: A high resolution 15,600 year diatom and pigment record from Lake Hayk.
- Author
-
Loakes, Katie L., Ryves, David B., Lamb, Henry F., Schäbitz, Frank, Dee, Michael, Tyler, Jonathan J., Mills, Keely, and McGowan, Suzanne
- Subjects
- *
INTERGLACIALS - Abstract
Abstract Multi-proxy analyses of an 8 m sediment core from Lake Hayk, a closed, freshwater lake in the north-central highlands of Ethiopia, provide a record of changing lake level and inferred regional climatic change for the last 15.6 cal ka years. Between ca. 15.6–15.2 cal ka BP, a lowstand was synchronous with Heinrich Event 1 and an intense drought across Eastern Africa. At ca. 15.2 cal ka BP a lake began to develop at the core site in response to wetter conditions, at the onset of the African Humid Period (AHP). However, in contrast to other lakes in eastern Africa, Hayk lake level fell around ca. 14.8 cal ka BP, indicating a climate shift towards aridity. The lake began filling again at ca. 12.3 cal ka BP and reached maximum water depth between ca. 12.0–10.0 cal ka BP. Lake level declined slowly during the Holocene, culminating in the termination of the AHP at Hayk between ca. 5.2–4.6 cal ka BP. In the late Holocene, ca. 2.2–1.3 cal ka BP, Lake Hayk was again deep and fresh with some evidence of short-term lake level variability. The palaeo-record from Lake Hayk indicates that while it experienced, to a broad degree, the same glacial-interglacial dynamics and sub-millennial shifts in climate found in other palaeolimnological records from eastern Africa, there are offsets in timing and rate of response. These differences reflect chronological discrepancies between records, as well as the varying climate sensitivities and site-specific factors of individual lake basins. This record highlights the different responses by lakes in a climatically vulnerable area of Ethiopia. Highlights • Discrepancies in the timing of the Younger Dryas Stadial proper. • No evidence for the catastrophic shift in climate centred at 8.2 ka. • Diatom evidence suggesting relatively rapid AHP termination. • High-resolution evidence of millennial to multi-decadal variability at Lake Hayk. • Regional discrepancies in the timing and expression of climatic events. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
8. Palaeolimnology of high and low altitude sites in Ethiopia : diatom and geochemistry records from Garba Guracha and Lake Babogaya
- Author
-
Grady, David Anton Ieuan, Davies, Sarah, and Lamb, Henry
- Subjects
551.48 ,Ethiopia ,Garba Guracha ,Lake Babogaya ,palaeolimnology ,diatoms ,XRF geochemistry - Abstract
Palaeoenvironmental studies at high altitude in eastern Africa are rare. As a result, our understanding of contemporary climate change in the region is limited. This study presents high-resolution, multi-proxy (diatoms and core geochemistry) palaeolimnological reconstructions at sites located at contrasting altitudes: Garba Guracha a cirque lake >3950 m above sea level spanning the last 16,000 years, and since the mid-Holocene at Lake Babogaya a crater lake on the western escarpment of the Main Ethiopian Rift (1800 m above sea level). These palaeo-records broadly exhibit the same glacial-interglacial dynamics and sub-millennial shifts in climate found in other palaeolimnological records from across eastern Africa. However, these shifts are more muted at Garba Guracha. Furthermore, the precise timing and expression of these climatic events is not always synchronous between the Lake Babogaya and Garba Guracha records as well as other records across eastern Africa. The Garba Guracha sediment geochemistry and diatom record is typical of a dry, post-glacial and sparsely vegetated environment with the dominance of Fragilarioid taxa and high terrigenous input. Due to the poorly developed postglacial landscape at Garba Guracha, any Younger Dryas-like drying signal would have been superimposed on to high soil erosion and a poorly productive lake environment. The retreat of a nearby ice mass may also have over-ridden any catchment development related to the start of the African Humid Period. However, in response to increased moisture availability and warming at Garba Guracha after 10,250 cal BP, catchment productivity considerably increases with a large increase in diatom productivity and organic matter content and remains high for the majority of the remaining African Humid Period interval. The termination of the African Humid Period is clear in the Garba Guracha diatom record at around 5,500 cal BP, with a second phase of change to an environment similar to the modern day after 4,500 cal BP, potentially representing the Meghalayan. Drier conditions around the Meghalayan is also documented in the Lake Babogaya record with the deposition of a Gastropod shell layer. A reduction in organic matter content following the deposition of this layer likely represents reduced productivity and a destabilising catchment under a drier climate. These drier conditions culminate in the deposition of coarse grained, terrigenous material between 3,600 and 3,300 cal BP. Following high lake nutrient content and deepening of the lake between 3,300 cal BP and 1,750 cal BP, the Lake Babogaya record suggests a relatively stable, deep lake, with only brief intervals of shallower waters, until the top of the core (~600 cal BP). The diatom record after 560 cal BP at Garba Guracha is characterised by a dominance of aerophilous taxa such as Nitzschia amphibia and Cymbelloid taxa driven by an increased growing season and nutrient loading under a drier climate. These records further reinforce the reported heterogeneous pattern of climate across the region and the significance of site-specific dynamics in the responses of catchments to regional drivers. The data produced in this study may be used to inform future climate modelling and perform more complete regional downscaling, while also furthering our understanding of palaeoenvironmental change in eastern Africa, at a variety of altitudes.
- Published
- 2020
9. Generating long chronologies for lacustrine sediments using luminescence dating: a 250,000 year record from Lake Tana, Ethiopia.
- Author
-
Roberts, Helen M., Bryant, Charlotte L., Huws, Dei G., and Lamb, Henry F.
- Subjects
- *
OPTICALLY stimulated luminescence , *THERMOLUMINESCENCE dating - Abstract
Abstract The lakes of the eastern Africa Rift often contain great thicknesses of sediment that may provide continuous records of environmental change over decadal to million-year timescales. However interpretation of these changes is greatly compromised without a reliable chronology. Luminescence dating has not been used extensively in lacustrine settings; instead previous studies have often relied upon radiocarbon dating, using extrapolation beyond the upper limit of that technique, and employing opportunistic sampling of tephra and palaeomagnetic signatures where possible. This study from Lake Tana, Ethiopia, demonstrates that recent advances in luminescence methodology can provide long chronologies for lake sediments that are not dependent on the intermittent presence of dateable material, as is the case for radiocarbon and tephra-based methods. Specifically, this study generates luminescence ages that agree with independent chronology based on radiocarbon dating in the upper part of the core, and extends significantly beyond the range of radiocarbon dating to provide one of the longest independently dated lacustrine sediment records in eastern Africa, thus demonstrating the tremendous potential of luminescence for constructing lacustrine sediment chronologies over 100,000 year timescales. Highlights • Recent advances make it timely to apply luminescence methods to date lake sediments. • Luminescence dating can provide long chronologies throughout lake sediment cores. • The application of luminescence dating to sediments from Lake Tana is discussed. • One of the longest independently dated lake records in eastern Africa. • Demonstrates the contribution luminescence dating can make to lacustrine studies. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
10. An extended and revised Lake Suigetsu varve chronology from ∼50 to ∼10 ka BP based on detailed sediment micro-facies analyses.
- Author
-
Schlolaut, Gordon, Staff, Richard A., Brauer, Achim, Lamb, Henry F., Marshall, Michael H., Bronk Ramsey, Christopher, and Nakagawa, Takeshi
- Subjects
- *
INTERPOLATION algorithms - Abstract
Abstract Lake Suigetsu (Japan) is a key site for radiocarbon (14C) calibration and palaeo-environmental reconstruction in East Asia. Here we present a description of the sediment (micro)facies, which in combination with a new approach to varve interpolation allows construction of a revised varve based chronology that extends the previous 2012 varve based chronology by ∼10 ka, back to ∼50 ka BP. Challenges in varve counting and interpolation, which were previously discussed in detail only for the Last Glacial-Interglacial Transition, are described here back to ∼50 ka BP. Furthermore, the relative merits of varve counting by μXRF scanning and by thin-section microscopy are discussed. Facies analysis reveals four facies zones, their transitions driven by both local and climatic controls. The lamination quality of the sediment is highly variable and varve interpolation reveals that in the analysed time interval, on average, only 50% of the annual cycles are represented by seasonal layers. In the remaining years seasonal layers are indistinguishable, i.e. either did not form or were not preserved. For varve interpolation an advanced version of the Varve Interpolation Program was used, which enabled the construction of the longest, purely varve dated chronology published, despite long intervals of poor lamination quality. The calculated interpolation uncertainty is +8.9% and −4.6%, which is well within expectations considering the high degree of interpolation and the length of the record. Highlights • New facies and microfacies data from Lake Suigetsu are presented. • Analysis covers the time frame from 50 to 10 ka BP. • Detailed description varve characteristics for the complete analysed interval. • Discussion of μXRF as a tool for varve counting compared to microscope counting. • Detailed discussion of strength and weaknesses of the Suigetsu varve chronology. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.