William J. Fletcher

William J. Fletcher
The University of Manchester · Department of Geography

PhD

About

95
Publications
33,662
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
3,417
Citations
Introduction
University lecturer and researcher in Physical Geography and Quaternary Science, specialising in the study of the Mediterranean region and North Africa
Skills and Expertise

Publications

Publications (95)
Article
Full-text available
A diatom record from Moss Lake, Washington, USA spans the last 14,500 cal year and revealed Holocene climate change in the Pacific Northwest (PNW), including evidence for periodicities related to ocean-atmosphere teleconnections and/or variations in solar output. Three main climate phases were identified: (i) Late Pleistocene to early Greenlandian...
Article
Full-text available
The grazing lands of the High Atlas are vulnerable to climate change and the decline of traditional management practices. However, prior to the mid-20th century, there is little information to examine historical environmental change and resilience to past climate variability. Here, we present a new pollen, non-pollen palynomorph (NPP) and microchar...
Article
Full-text available
Around 4000 cal yr BP, Scots pine ( Pinus sylvestris) suffered a widespread demise across the British Isles. This paper presents new information about P. sylvestris populations found in the Welsh Marches (western central Britain), for which the long-term history and origins are poorly known. Two new pollen records were produced from the Lin Can Mos...
Chapter
Stephen C. Porter was an international leader in Quaternary science for several decades, having worked on most of the world’s continents and having led international organizations and a prominent interdisciplinary journal. His work influenced many individuals, and he played an essential role in linking Chinese Quaternary science with the broader in...
Article
Full-text available
The Eurasian (née European) Modern Pollen Database (EMPD) was established in 2013 to provide a public database of high-quality modern pollen surface samples to help support studies of past climate, land-cover and land-use using fossil pollen. The EMPD is part of, and complementary to, the European Pollen Database (EPD) which contains data on fossil...
Article
Full-text available
There are no glaciers today in the High Atlas, Morocco. However, there is evidence that niche glaciers and late-lying snowpatches in the High Atlas were present as recently as the last century and there are at least four sites where snowpatches appear to survive some summer seasons today. Many other sites also support non-perennial late-lying snow...
Preprint
Full-text available
Abstract. The Eurasian (née European) Modern Pollen Database (EMPD) was established in 2013 to provide a public database of high-quality modern pollen surface samples to help support studies of past climate, land-cover and land-use using fossil pollen. The EMPD is part of, and complementary to, the European Pollen Database (EPD) which contains data...
Article
Full-text available
Quantitative climate reconstructions from pollen typically rely on empirical relationships between pollen abundances or assemblages and climate, such as the modern analogue technique. However, these techniques may be problematic when applied to fossil sequences, as they cannot separate anthropogenic from climatic influence on pollen assemblages. He...
Article
Full-text available
The aim of this work is to reconstruct the periods of growth and decline of human populations in Morocco and their potential impacts on the landscape over the past 10,000 years. In order to estimate the trends in the human population size between 10,000 and 3000 years ago, we used a summed probability distribution (SPD) of radiocarbon dates from a...
Article
Full-text available
Widespread forest dieback is a phenomenon of global concern that requires an improved understanding of the relationship between tree growth and climate to support conservation efforts. One priority for conservation is the Atlas cedar (Cedrus atlantica), an endangered species exhibiting dieback throughout its North African range. In this study, we e...
Article
Full-text available
Gerard C. Bond established a Holocene series of North Atlantic ice-rafted debris events based on quartz and haematite-stained grains recovered from subpolar North Atlantic marine cores. These so-called “Bond events” document nine large-scale and multi-centennial North Atlantic cooling phases that might be linked to a reduced thermohaline circulatio...
Data
The data set represents an improved Holocene δ18O record from Lake Sidi Ali Middle Atlas, Morocco). We add 82 new δ18O data of adult ostracod shell material from the closely related species Fabaeformiscandona sp. and Candona sp. to improve the chronological resolution of the previous oxygen isotope record (Zielhofer et al., 2017 Quaternary Science...
Article
The Earth has experienced large changes in global and regional climates over the past one million years. Understanding processes and feedbacks that control those past environmental changes is of great interest for better understanding the nature, direction and magnitude of current climate change, its effect on life, and on the physical, biological...
Article
Pollen grains are highly suitable for radiocarbon dating as they contain a closed pool of carbon derived from the atmosphere via photosynthesis, are highly resilient in a range of sedimentary environments, and can be identified in terms of the source vegetation types. Dating pollen requires the preparation of pollen concentrates in the laboratory,...
Article
Precise chronologies that allow direct correlation of paleoclimate archives are a prerequisite for deciphering the spatiotemporal characteristics of short-term climate variability. Such chronologies can be established through the analysis of tephra layers that are preserved in the respective sedimentary archives. Here we explore the yet untapped te...
Preprint
Full-text available
Gerald C. Bond established a Holocene series of North Atlantic ice rafted debris events based on quartz and hematite stained grains recovered from subpolar North Atlantic marine cores. These so-called 'Bond events' document nine large-scale and multi-centennial North-Atlantic cooling phases that might be linked to a reduced thermohaline circulation...
Article
We present a pollen record for last 28 cal kyr BP from the eastern basin of Lake Karakul, the largest lake in Tajikistan, located in the eastern Pamir Mountains at 3915 m asl, a geographically complex region. The pollen record is dominated by Artemisia and Chenopodiaceae, while other taxa, apart from Poaceae, are present in low quantities and rarel...
Article
Full-text available
It is well-known that the Holocene exhibits a millennial-scale climate variability. However, its periodicity, spatio-temporal patterns and underlying processes are not fully deciphered yet. Here we focus on the central and western Mediterranean. We show that recurrent forest declines from the Gulf of Gaeta (central Tyrrhenian Sea) reveal a 1860-yr...
Article
Full-text available
Sporopollenin is a complex biopolymer which is the main component of the pollen grain exine and is partly composed of the aromatic compounds para-coumaric acid (pCA) and ferulic acid (FA). These compounds absorb ultraviolet-B radiation (UV-B, 280–315 nm), and their abundance in pollen and spores has been shown to increase in response to increased U...
Article
Full-text available
Pollen from deep-sea sedimentary sequences provides an integrated regional reconstruction of vegetation and climate (temperature, precipitation, and seasonality) on the adjacent continent. More importantly, the direct correlation of pollen, marine and ice indicators allows comparison of the atmospheric climatic changes that have affected the contin...
Data
List of the 129 deep-sea pollen records distributed over the world.
Article
Full-text available
In semi-arid regions subject to rising temperatures and drought, palaeoecological insights into past vegetation dynamics under a range of boundary conditions are needed to develop our understanding of environmental responses to climatic changes. Here, we present a new high-resolution record of vegetation history and fire activity spanning the last...
Article
Full-text available
Quaternary records provide an opportunity to examine the nature of the vegetation and fire responses to rapid past climate changes comparable in velocity and magnitude to those expected in the 21st-century. The best documented examples of rapid climate change in the past are the warming events associated with the Dansgaard–Oeschger (D–O) cycles dur...
Article
Full-text available
The Sahara is the world's largest dust source with significant impacts on trans-Atlantic terrestrial and large-scale marine ecosystems. Contested views about a gradual or abrupt onset of Saharan aridity at the end of the African Humid Period dominate the current scientific debate about the Holocene Saharan desiccation. In this study, we present a 1...
Article
Full-text available
The morphology and size variability of pollen grains of Cedrus atlantica were investigated using a novel approach employing laser diffraction granulometry. We provide new insights into size variability and present high-quality light microscopy (LM) and scanning electron microscopy (SEM) imagery of Cedrus atlantica pollen. Grains have an average siz...
Article
In lake sediments where terrestrial macrofossils are rare or absent, AMS radiocarbon dating of pollen concentrates may represent an important alternative solution for developing a robust and high resolution chronology suitable for Bayesian modelling of age-depth relationships. Here we report an application of the heavy liquid density separation app...
Article
Full-text available
Stable carbon isotope analysis of pollen provides potential for reconstruction of past moisture availability in the environment on longer time-scales compared to isotope analysis of plant tissue. Here we show that pollen, sporopollenin, leaf and stem δ¹³C values of Cedrus atlantica are strongly related. Untreated pollen δ¹³C has a significant linea...
Article
Full-text available
Climate evolution of the Mediterranean region during the Holocene exhibits strong spatial and temporal variability, which is notoriously difficult for models to reproduce. We propose here a new proxy-based climate synthesis synthesis and its comparison – at a regional (∼ 100 km) level – with a regional climate model to examine (i) opposing northern...
Article
Full-text available
Quaternary records provide an opportunity to examine the nature of the vegetation and fire responses to rapid past climate changes comparable in velocity and magnitude to those expected in the 21st century. The best documented examples of rapid climate change in the past are the warming events associated with the Dansgaard-Oeschger (D-O) cycles dur...
Article
Full-text available
The limited availability of high-resolution continuous archives, insufficient chronological control, and complex hydro-climatic forcing mechanisms lead to many uncertainties in palaeo-hydrological reconstructions for the Western Mediterranean. In this study we present a newly recovered 19.63 m long core from Lake Sidi Ali in the North African Middl...
Article
Full-text available
Ce travail est, pour le Maroc, les premières études détaillées des diatomées de séquences lacustres de l’Holocène (Aguelmame Sidi Ali & Tigalmamine) continues et datées. Cette présente étude porte sur les diatomées de l’Holocène du lac Aguelmame Sidi Ali (33° 03'N, 5° 00'E, 2080 m) situé dans le Moyen Atlas, au Maroc. Dans le cadre d’un projet inte...
Article
Palynology is a crucial proxy for understanding Quaternary environmental change. A range of laboratory preparation techniques has been developed to deal with the extraction of pollen in different sedimentary contexts. Here, we present a comparison of the conventional hydrofluoric acid method and the dense-media separation method using sodium polytu...
Article
Full-text available
Climate evolution of the Mediterranean region during the Holocene exhibits strong spatial and temporal variability. The spatial differentiation and temporal variability, as evident from different climate proxy datasets, has remained notoriously difficult for models to reproduce. In light of this complexity, we examine the previously described evide...
Article
The Assif n'Imserdane valley, located in the Jebel Toubkal area of the High Atlas, Morocco, is a highly dynamic geomorphological setting. The valley was glaciated during the Late Pleistocene, and subsequently experienced a catastrophic rock avalanche leading to the formation of one of the largest mass movement landforms in North Africa. Recent rese...
Article
Full-text available
High-resolution palaeoecological analyses (stratigraphy, tephra geochemistry, radiocarbon dating, pollen and ordination) were used to reconstruct a Holocene vegetation history of a watershed in the Pacific Northwest of America to evaluate the effects and duration of tephra deposition on a forest environment and the significance of these effects com...
Article
Thirty-three modern surface samples were collected in the environmentally and climatologically contrasting regions of the Middle and High Atlas Mountains, Morocco. Samples representing forest and steppe montane environments (1935–2760 m above sea level) are clustered around study sites at Lake Tislit (High Atlas, semi-arid oro-Mediterranean bioclim...
Article
High-resolution palaeoecological analyses (stratigraphy, tephra geochemistry, radiocarbon dating, pollen and ordination) were used to reconstruct a Holocene vegetation history of a watershed in the Pacific Northwest of America to evaluate the effects and duration of tephra deposition on a forest environment and the significance of these effects com...
Conference Paper
Full-text available
Aguelmane Sidi Ali (33°05 ′N, 005°00 ′W) (Figure 1) is a natural lake at high altitude (2080 m) in Moroccan Middle Atlas, without surface outlet, determined by the dam of a basalt flow. With an apparent catchment of 15.6 km2, it is fed by runoff and karst springs. The site comprises two basins which are periodically separated by a basalt ridge. Sid...
Article
Full-text available
Since the first pollen analyses from core material in the 1960s, the limnotelmatic sequence of Tenaghi Philippon, located within the subsurface of the Drama Basin of NE Greece, has been recognized as an exceptional archive of terrestrial climate and ecosystem dynamics for the Quaternary in Europe. The polleniferous sequence covers the last ~1.35 Ma...
Conference Paper
Full-text available
This study concerns Diatom study of core from Lake Aguelmane Sidi Ali (33° 03’N, 5° 00’E, 2080 m a.s.l.) located in the Middle Atlas, Morocco. Sediments consist are of horizontally bedded, faintly laminated, organic silts, with aquatic fossils. Diatoms analyses give information on the water-level fluctuations and on changes in water chemistry. The...
Article
Since the first pollen analyses from core material in the 1960s, the limnotelmatic sequence of Tenaghi Philippon, located within the subsurface of the Drama Basin of NE Greece, has been recognized as an exceptional archive of terrestrial climate and ecosystem dynamics for the Quaternary in Europe. The polleniferous sequence covers the last ∼ 1.35 M...
Article
The variability of Quaternary landforms preserved in the Tabernas basin of SE Spain raises numerous questions concerning the roles of external forcing mechanisms (e.g. tectonics and / or climate) and internal landscape properties (e.g. lithological controls) in the evolution of the basin-wide fluvial system over late Quaternary timescales. In this...
Conference Paper
A long core 20 m by 38 m deep in the southwestern basin of Lake aguelmane Sidi Ali was obtained by an international team (English-German-Belgian-Moroccan) using the coring device UWITEC. This core provided a continuous Holocene record, was analyzed diatoms contained in the sediments. An oligosaline lake occupied the core site during the Holocene, w...
Conference Paper
Full-text available
Le lac aguelmane de Sidi Ali d’origine volcanique est situé à 2080 m d’altitude dans le Moyen Atlas marocain. Une carotte de 20 mètres de longueur sous 38 mètres de profondeur dans le sud-ouest du bassin a été obtenue par une équipe internationale (anglais-allemand-belgo-marocain) en utilisant le dispositif de sondage UWITEC. Les sédiments représen...
Article
Surface modification processes leading to large debris accumulations in high-relief mountain areas are important for understanding landscape evolution, especially in some of Earth's most active orogens. The Arroumd rock avalanche at the foot of the NW face of Mount Aksoual (3912 m above sea level [masl]) in the Jebel Toubkal area of the High Atlas,...
Article
The influence of precession on the redistribution of insolation on the top of the atmosphere predicts that climate change in the low latitudes is out of phase between the hemispheres. We test this prediction by the most direct approach, the analysis of terrestrial climate records, as they provide direct information on regional changes in the atmosp...
Article
In this paper we explore the evidence for Holocene Rapid Climate Changes (RCCs) in Western Mediterranean records, examining similarities and differences in the timing and nature of impacts on different components of the natural environment (vegetation, fluvial and coastal sedimentation, fire activity, soil formation). Marine, lacustrine, and fluvia...