Barbara Maher - Academia.edu (original) (raw)
Papers by Barbara Maher
Atmospheric Environment, Oct 1, 2022
Documenting the Earth’s magnetic field variations through time is fundamental for several discipl... more Documenting the Earth’s magnetic field variations through time is fundamental for several disciplines. However, current geomagnetic models heavily rely on datasets biased towards mid- and high northern latitudes, whereas data from Africa and surrounding oceans are particularly underrepresented. In this study, we present a new record of paleo-secular variations (PSV) in geomagnetic field inclinations during the last 23 ka from Lake Chala, situated at 3° S near Mt Kilimanjaro in eastern equatorial Africa. This deep groundwater-fed crater lake is characterized by a high sedimentation rate (ca. 1 cm/10 years) and a particularly well-constrained age model based on 210Pb and 14C dating; and rock magnetic analyses have demonstrated the magnetic stability of the sediments. The Chala dataset is linked to PSV records from Lake Malawi and Lake Victoria using a sequence slotting technique to generate a composite PSV record for East Africa. The Lake Chala PSV record not only represents an import...
In well-buffered modern soils, higher annual rainfall is associated with enhanced soil ferrimagne... more In well-buffered modern soils, higher annual rainfall is associated with enhanced soil ferrimagnetic mineral content, especially of ultrafine particles that result in distinctive observable rock magnetic properties. Hence, paleosol magnetism has been widely used as a paleoprecipitation proxy. Identifying the dominant mechanism(s) of magnetic enhancement in a given sample is critical for reliable inference of paleoprecipitation. Here we use high-resolution magnetic field and electron microscopy to identify the grain-scale setting and formation pathway of magnetic enhancement in two modern soils developed in higher (~580 mm/y) and lower (~190 mm/y) precipitation settings from the Qilianshan Range, China. We find both soils contain 1-30 µm aeolian Fe-oxide grains with indistinguishable rock magnetic properties while the higher-precipitation soil contains an additional population of ultrafine (<150 nm), magnetically distinct magnetite grains. We show that the in situ precipitation of...
Environmental Research, 2020
Environmental Pollution, 2021
Environmental Research, 2020
Science of The Total Environment, 2021
Environmental Research, 2020
Science of The Total Environment, 2021
Environmental Science & Technology, 2019
Environmental Research, 2019
Funding: In part by SEP-CONACYT 255956. Funding source had no involvement in study design; collec... more Funding: In part by SEP-CONACYT 255956. Funding source had no involvement in study design; collection, analysis and interpretation of data; in the writing of the report; and in the decision to submit the article for publication.
Quaternary Science Reviews, 2016
Whether during past climate stages or into a progressively warming world, changes in precipitatio... more Whether during past climate stages or into a progressively warming world, changes in precipitation constitute a key component of climatic change. Quantitative proxies for palaeo-precipitation are relatively rare. The magnetic properties of the windblown loess units and interbedded palaeosols of the famous Chinese Loess Plateau provide key palaeo-precipitation data for this populous, monsoondominated region. The loess/palaeosol sediments record rainfall totals, directly complementing the oxygen isotope records of Chinese speleothems. These isotopic records predominantly reflect moisture source, and hence large-scale atmospheric circulation changes. The two major Asian monsoon systems appear to display antiphase behaviour. Dominance of the Indian summer monsoon system seems associated with minimum precession/maximum northern hemisphere summer heating; dominance of the East Asian summer monsoons with maximum precession. At~2.8 Ma, more intense development of the East Asian winter monsoon initiated major increases in dust deposition rates, and formation of relatively unweathered loess layers. Glacial-stage loess units then interleaved with interglacial/ interstadial-stage palaeosols throughout the Quaternary period. Decoupling of the loess/palaeosol rainfall records from the Chinese cave records of moisture source shows that the Indian and East Asian monsoon winds were continuously driven by precessional forcing while summer monsoonal rainfall was greatly suppressed during cool, glacial stages. The timing of these East Asian climatic transitions, the subsequent intensification of northern hemisphere glaciations, and the association between monsoon circulation changes and North Atlantic temperatures, indicates a possibly leading global role for these monsoonal changes via alterations in the poleward distribution of heat and moisture.
Desertification in Europe, 1986
The watershed-ecosystem concept provides a spatially bounded framework within which many aspects ... more The watershed-ecosystem concept provides a spatially bounded framework within which many aspects of material flux and consequent ecological change can be characterized and quantified, and their interactions studied on a wide range of temporal and spatial scales. Thus in any analysis of the environmental aspects of desertification, lakes and near-shore marine environments provide some of the most favourable opportunities available. This is especially so with the advent of several new techniques using magnetic and short lived radioisotope measurements. The present account focuses on these new techniques and their applications. ‘Mineral’ magnetic measurements can be used to (i) speed and enhance quantitiative estimates of both past and present sediment yields in eroding catchments (ii) identify past and present sediment sources (iii) establish areas of soil depletion and redeposition and characterize associated slope processes (iv) provide a basis for active tracing experiments on slopes and in river channels, lakes and coastal environments and (iv) characterize atmospheric dusts and ascribe them to source type. Studies using the short lived natural radio-isotope lead-210 (half life 22.26/yr) can provide chronologies of sedimentation for the last 100 to 150 years. Used in conjunction, these methods, alongside more conventional geomorphological, sedimentological, palaeoecological and geochemical techniques, can form the core of an integrated multidisciplinary study of desertification and erosion processes on all relevant temporal and spatial scales.
Journal of Geophysical Research: Solid Earth, 1999
Geological Society, London, Special Publications, 1999
Geological Society, London, Special Publications, 1995
Science of The Total Environment, 2021
Atmospheric Environment, Oct 1, 2022
Documenting the Earth’s magnetic field variations through time is fundamental for several discipl... more Documenting the Earth’s magnetic field variations through time is fundamental for several disciplines. However, current geomagnetic models heavily rely on datasets biased towards mid- and high northern latitudes, whereas data from Africa and surrounding oceans are particularly underrepresented. In this study, we present a new record of paleo-secular variations (PSV) in geomagnetic field inclinations during the last 23 ka from Lake Chala, situated at 3° S near Mt Kilimanjaro in eastern equatorial Africa. This deep groundwater-fed crater lake is characterized by a high sedimentation rate (ca. 1 cm/10 years) and a particularly well-constrained age model based on 210Pb and 14C dating; and rock magnetic analyses have demonstrated the magnetic stability of the sediments. The Chala dataset is linked to PSV records from Lake Malawi and Lake Victoria using a sequence slotting technique to generate a composite PSV record for East Africa. The Lake Chala PSV record not only represents an import...
In well-buffered modern soils, higher annual rainfall is associated with enhanced soil ferrimagne... more In well-buffered modern soils, higher annual rainfall is associated with enhanced soil ferrimagnetic mineral content, especially of ultrafine particles that result in distinctive observable rock magnetic properties. Hence, paleosol magnetism has been widely used as a paleoprecipitation proxy. Identifying the dominant mechanism(s) of magnetic enhancement in a given sample is critical for reliable inference of paleoprecipitation. Here we use high-resolution magnetic field and electron microscopy to identify the grain-scale setting and formation pathway of magnetic enhancement in two modern soils developed in higher (~580 mm/y) and lower (~190 mm/y) precipitation settings from the Qilianshan Range, China. We find both soils contain 1-30 µm aeolian Fe-oxide grains with indistinguishable rock magnetic properties while the higher-precipitation soil contains an additional population of ultrafine (<150 nm), magnetically distinct magnetite grains. We show that the in situ precipitation of...
Environmental Research, 2020
Environmental Pollution, 2021
Environmental Research, 2020
Science of The Total Environment, 2021
Environmental Research, 2020
Science of The Total Environment, 2021
Environmental Science & Technology, 2019
Environmental Research, 2019
Funding: In part by SEP-CONACYT 255956. Funding source had no involvement in study design; collec... more Funding: In part by SEP-CONACYT 255956. Funding source had no involvement in study design; collection, analysis and interpretation of data; in the writing of the report; and in the decision to submit the article for publication.
Quaternary Science Reviews, 2016
Whether during past climate stages or into a progressively warming world, changes in precipitatio... more Whether during past climate stages or into a progressively warming world, changes in precipitation constitute a key component of climatic change. Quantitative proxies for palaeo-precipitation are relatively rare. The magnetic properties of the windblown loess units and interbedded palaeosols of the famous Chinese Loess Plateau provide key palaeo-precipitation data for this populous, monsoondominated region. The loess/palaeosol sediments record rainfall totals, directly complementing the oxygen isotope records of Chinese speleothems. These isotopic records predominantly reflect moisture source, and hence large-scale atmospheric circulation changes. The two major Asian monsoon systems appear to display antiphase behaviour. Dominance of the Indian summer monsoon system seems associated with minimum precession/maximum northern hemisphere summer heating; dominance of the East Asian summer monsoons with maximum precession. At~2.8 Ma, more intense development of the East Asian winter monsoon initiated major increases in dust deposition rates, and formation of relatively unweathered loess layers. Glacial-stage loess units then interleaved with interglacial/ interstadial-stage palaeosols throughout the Quaternary period. Decoupling of the loess/palaeosol rainfall records from the Chinese cave records of moisture source shows that the Indian and East Asian monsoon winds were continuously driven by precessional forcing while summer monsoonal rainfall was greatly suppressed during cool, glacial stages. The timing of these East Asian climatic transitions, the subsequent intensification of northern hemisphere glaciations, and the association between monsoon circulation changes and North Atlantic temperatures, indicates a possibly leading global role for these monsoonal changes via alterations in the poleward distribution of heat and moisture.
Desertification in Europe, 1986
The watershed-ecosystem concept provides a spatially bounded framework within which many aspects ... more The watershed-ecosystem concept provides a spatially bounded framework within which many aspects of material flux and consequent ecological change can be characterized and quantified, and their interactions studied on a wide range of temporal and spatial scales. Thus in any analysis of the environmental aspects of desertification, lakes and near-shore marine environments provide some of the most favourable opportunities available. This is especially so with the advent of several new techniques using magnetic and short lived radioisotope measurements. The present account focuses on these new techniques and their applications. ‘Mineral’ magnetic measurements can be used to (i) speed and enhance quantitiative estimates of both past and present sediment yields in eroding catchments (ii) identify past and present sediment sources (iii) establish areas of soil depletion and redeposition and characterize associated slope processes (iv) provide a basis for active tracing experiments on slopes and in river channels, lakes and coastal environments and (iv) characterize atmospheric dusts and ascribe them to source type. Studies using the short lived natural radio-isotope lead-210 (half life 22.26/yr) can provide chronologies of sedimentation for the last 100 to 150 years. Used in conjunction, these methods, alongside more conventional geomorphological, sedimentological, palaeoecological and geochemical techniques, can form the core of an integrated multidisciplinary study of desertification and erosion processes on all relevant temporal and spatial scales.
Journal of Geophysical Research: Solid Earth, 1999
Geological Society, London, Special Publications, 1999
Geological Society, London, Special Publications, 1995
Science of The Total Environment, 2021