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A listing of all my recent publications, links to download them and the associated data is below. You can also see my work on ORCID:

Bell B.A., Fletcher W.J., Hughes P.D., Cornelissen H.L., Fink D., Rhoujjati A., Hanich L and Braithwaite R.J. (2022). Climate of the Marrakech High Atlas, Morocco: Temperature lapse rates and precipitation gradient from piedmont to summits. Arctic, Antarctic, and Alpine Research.

Abstract: Understanding mountain climates poses many challenges, because difficult terrain leads to a sparsity of weather stations and therefore poor data availability, meaning the detailed information required to understand these complex systems is lacking. Here, we analyze eleven years of half-hourly climate observations from the Joint International Laboratory LMI-TREMA (Télédétection et Ressources en Eau en Méditerranée semi-Aride) network of weather stations in the Marrakech High Atlas, Morocco, providing detailed information about the climate in this area. Our analysis shows the mean annual near-surface temperature lapse rate is -4.63°C km-1, with an uncertainty range of -4.39 to -4.85°C km-1, lower than the standard environmental temperature lapse rate. Mean temperature lapse rates vary from -3.67°C to -5.21°C km-1 monthly, and throughout the day from -2.75°C to -7.1°C km-1, which has important implications for understanding snowpack variations at the highest elevations. Understanding precipitation is inherently complex, but our analysis shows that mean annual precipitation increases by 166 mm km-1 (150.6 to 183.7 mm km-1) with a significant snow component at the highest elevations. This analysis improves our understanding of the mountain climate system with new regional temperate lapse rates and precipitation gradients, having the potential to improve gridded climatologies and climate models, with relevance for the wider High Atlas region.

Availability: Open Access

Data: Associated research data is available open access with the paper.

DOI: 10.1080/15230430.2022.2046897

Bell B.A., Fletcher W.J., Hughes P.D., Cornelissen H.L., Fink D., and Rhoujjati A. (2022). Palynological evidence from a sub-alpine marsh of enhanced Little Ice Age snowpack in the Marrakech High Atlas, North Africa. Vegetation History and Archaeobotany.

Abstract: 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 microcharcoal record from a sub-alpine marsh (pozzine) at Oukaïmeden, located in the Marrakech High Atlas, Morocco. The record reveals a history of grazing impacts with diverse non-arboreal pollen assemblages dominant throughout the record as well as recurrent shifts between wetter and drier conditions. A large suite of radiocarbon dates (n=22) constrains the deposit to the last ~1,000 years although multiple reversed ages preclude development of a robust age-depth model for all intervals. Between relatively dry conditions during the Medieval period and in the 20th century, intervening wet conditions are observed, which we interpret as a locally enhanced snowpack during the Little Ice Age. Hydrological fluctuations evidenced by wetland pollen and NPPs are possibly associated with centennial-scale precipitation variability evidenced in regional speleothem records. The pollen record reveals an herbaceous grassland flora resilient against climatic fluctuations through the last millennium, possibly supported by sustainable collective management practices (agdal), with grazing indicators suggesting a flourishing pastoral economy. However, during the 20th century, floristic changes and increases in charcoal accumulation point to a decline in management practices, diversification of land-use (including afforestation) and intensification of human activity.

Availability: Open Access

Data: Associated research data is available open access with the paper.

DOI: 10.1007/s00334-021-00837-y

Hughes, P.D, Fletcher W.J., Bell B.A., Braithwaite R.J, Cornelissen H.L., Fink D., and Rhoujjati A. (2020). Late Pleistocene glaciers to present-day snowpatches: a review and research recommendations for the Marrakech High Atlas. Mediterranean Geoscience Reviews.

Availability: Open Access

DOI: 10.1007/s42990-020-00027-4

Bell B.A., Fletcher W.J., Cornelissen H.L., Campbell J.F.E., Ryan P., Grant H. and Zielhofer C. (2019). Stable carbon isotope analysis on fossil Cedrus pollen shows summer aridification in Morocco during the last 5000 years. Journal of Quaternary Science.

Abstract: 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. Here, we reconstruct Mid‐ to Late Holocene summer aridity in the Middle Atlas, Morocco, using stable carbon isotope analysis of isolated fossil Cedrus pollen. This approach is based on well‐documented plant physiological responses to moisture stress and is therefore independent of vegetation composition. We find that there has been a general long‐term trend of increasing summer aridity in the region during the last 5000 years to the present day. The gradual decline of Cedrus atlantica forest in the Late Holocene follows this aridity trend. Additionally, we show how isolating a specific pollen type for carbon isotope analysis yields a robust climate signal, versus using pollen concentrates or bulk sediment. Our findings indicate that climate has become drier in the region and confirms the Mid‐ to Late Holocene aridification trend observed more widely in the western Mediterranean, using a novel proxy for this region with good potential for wider application in other environments.

Availability: Open Access

Data: Associated research data is available open access with the paper. The data can also be accessed for free from Mendeley Data.

DOI: 10.1002/jqs.3103

Bell B.A., Fletcher W.J., Seddon A.W.R., Wogelius R.A., Ryan P. and Ilmen R. (2018). UV-B-absorbing compounds in modern Cedrus atlantica pollen: The potential for a summer UV-B proxy for Northwest Africa. The Holocene. 28.9, 1382-1394.

Abstract: 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 UV-B flux. Here, we show that the relative abundance of UV-B-absorbing compounds (UACs) measured using Fourier Transform Infrared Spectrometry (FTIR) in modern pollen of autumn-pollinating Cedrus atlantica trees increases in response to summer UV-B flux. This relationship was observed in native Moroccan samples (r2 = 0.84, p < 0.0001), but not across a larger environmental gradient including non-Moroccan samples (r2 = 0.00, p = 0.99). For non-Moroccan samples of known provenance, the abundance of UACs is similar to the abundance of UACs found in samples from their place of origin. The FTIR spectra of these samples also closely resemble the FTIR spectra of samples from their place of origin. This unexpected finding suggests there could be a heritable component to UAC production possibly associated with epigenetic memory, an important adaptive mechanism in conifers. Our results indicate that the relative abundance of UACs in Cedrus atlantica pollen could be used as a proxy to reconstruct historic summer UV-B flux in Northwest Africa during at least the Holocene and Late Glacial period while also highlighting how UV-B proxies should be established using pollen samples from specimens growing in their native range or environment.

Availability: Open Access

Data: Associated research data is available open access with the paper. The data can also be accessed for free from Mendeley Data.

DOI: 10.1177/0959683618777072

Bell B.A., Bishop T.H., Fletcher W.J., Ryan P. and Ilmen R. (2018). Cedrus atlantica pollen morphology and investigation of grain size variability using laser diffraction granulometry. Palynology. 42.3, 339-353.

Abstract: 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 size of 59.1 ± 4.0 µm, measured on millions of grains from 91 samples. Analysis showed there is high variability of grain size within individual samples, although variability between samples is not significant. We found no significant relationships between grain size and climate (including temperature, precipitation and aridity), and suggest that grain size of fossil Cedrus pollen would not be a good proxy for climate reconstruction. Grain size may be influenced by a number of complex factors such as genome size or adaptations to support wind pollination, while variability within individual samples may result from the irregular development of pollen. The laser diffraction method produced repeatable, robust measurements on millions of pollen grains which are highly correlated with measurements taken using LM (r = 0.91, p = 0.002). Where grain size information is crucial for pollen identification, for developing isolation techniques for geochemical analysis, for investigating climatic and environmental influence, or for investigating links between genomes and grain size, particle size analysis by laser diffraction provides a reproducible and robust method for quickly determining pollen grain size on many samples.

Availability: Open Access

Data: All associated research data is available open access with the paper. High resolution photographs of pollen (SEM and LM) can be found on Mendeley Data.

DOI: 10.1080/01916122.2017.1356760

Bell B.A., Fletcher W.J., Ryan P., Grant H. and Ilmen R. (2017). Stable carbon isotope analysis of Cedrus atlantica pollen as an indicator of moisture availability. Review of Palaeobotany and Palynology. 244, 128-139.

Abstract: 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 the carbon isotopic compositions (δ13C) of pollen, sporopollenin, leaf and stem tissues of Cedrus atlantica are strongly related. Untreated pollen δ13C has a significant linear relationship with sporopollenin δ13C (r2 = 0.97, p < 0.0001) which is relatively depleted in 13C by an average 1.5‰. Carbon isotope discrimination (Δ13C) by sporopollenin (derived from pollen δ13C values) is related to mean annual (r2 = 0.54, p < 0.001) and summer precipitation (r2 = 0.63, p < 0.0001). A 100 mm increase in mean annual precipitation results in sporopollenin Δ13C increasing by 0.52‰, or by 1.4‰ per 100 mm summer precipitation. There is a stronger relationship between sporopollenin Δ13C and long-term annual scPDSI (r2 = 0.86, p < 0.0001) and summer scPDSI (r2 = 0.86, p < 0.001) aridity indexes, with reduced Δ13C as aridity increases. These relationships suggest that stable carbon isotope analysis of C. atlantica fossil pollen could be used as a quantitative proxy for the reconstruction of summer moisture availability in Northwest Africa.

Availability: Open Access

Data: All associated research data is available open access with the paper.

DOI: 10.1016/j.revpalbo.2017.04.008

Bell B.A. and Fletcher W.J. (2016). Modern surface pollen assemblages from the Middle and High Atlas, Morocco: insights into pollen representation and transport. Grana. 55(4), 286–301.

Abstract: 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 bioclime) and Lake Sidi Ali and Michliffen (Middle Atlas, sub-humid montane Mediterranean bioclime). Good discrimination between regional pollen spectra is evident, with Middle Atlas samples reflecting higher arboreal cover (Cedrus and evergreen Quercus) and High Atlas samples with high abundances of non-arboreal taxa, including Artemisia and Fabaceae. These four taxa (Cedrus, evergreen Quercus, Artemisia and Fabaceae) are furthermore shown to be reliable indicators of local source vegetation within a 100 m2 quadrat, taking into account threshold abundances of 7%, 20%, 4% and 10%, respectively. Deciduous Quercus, Olea and Phillyrea show long-distance pollen dispersal across both regions, contributing to non-trivial arboreal pollen (AP) values of up to 35% (typically 20–30%) in the High Atlas spectra. In the Middle Atlas, AP values of 40 to 50% occur in open sampling locations and > 60% under forest canopy cover. These insights should be taken into account when interpreting ancient pollen spectra from regional lakes and bogs for palaeoenvironmental reconstruction.

Availability: Published version available via subscription to the journal. Please email me if you would like a free copy.

AAM version available Open Access from Manchester University

Data: All associated research data is available with the paper. Data is also freely available from Mendeley Data

DOI: 10.1080/00173134.2015.1108996

Bell B.A.,

Abstract: ...

Availability: Open Access

Data: All associated research data is available open access with the paper.