Hydroclimate variability was the main control on fire activity in northern Africa over the last 50,000 years

North Africa features some of the most frequently burnt biomes on Earth, including the semi-arid grasslands of the Sahel and wetter savannas immediately to the south. Natural fires are fuelled by rapid biomass production during the wet season, its desiccation during the dry season and ignition by frequent dry lightning strikes. Today, fire activity decreases markedly both to the north of the Sahel, where rainfall is extremely low, almost eliminating biomass over the Sahara, and to the south where forest biomes are too wet to burn. Over the last glacial cycle, rainfall and vegetation cover over northern Africa varied dramatically in response to gradual astronomically-forced insolation change, changes in atmospheric carbon dioxide levels, and abrupt cooling events over the North Atlantic Ocean associated with the reorganisation of Meridional Overturning Circulation (MOC). Here we report the results of a study into the impact of these climate changes on fire activity in northern African over the last 50,000 years (50 kyr). Our reconstructions come from marine sediments with strong age control that provide an uninterrupted record of charcoal particles exported from the African continent. We studied three sites on a latitudinal transect along the northwest African margin between 21 and 9°N. Our sites exhibit a distinct latitudinal relationship between past changes in rainfall and fire activity. At the southernmost site (GeoB9528-3, 9°N), fire activity decreased during intervals of increasing humidity, while our northernmost site (ODP Site 658, 21°N) clearly demonstrates the opposite relationship. The site in the middle of our transect, offshore of the present day southern Sahel today (GeoB9508-5, 15°N), exhibits a “Goldilocks” relationship between fire activity and hydroclimate, wherein charcoal fluxes peak under intermediate rainfall climate conditions and are supressed by transition to more arid or more humid conditions. Our results are remarkably consistent with the predictions of the intermediate fire-productivity hypothesis developed in conceptual macroecological models and supported by empirical evidence of modern day fire activity. Feedback processes operating between fire, climate and vegetation are undoubtedly complex but temperature is suggested to be the main driver of temporal change in fire activity globally, with the precipitation-evaporation balance perhaps a secondary influence in the Holocene tropics. However, there is only sparse coverage of Africa in the composite records upon which those interpretations are based. We conclude that hydroclimate (not temperature) exerted the dominant control on burning in the tropics of northern Africa well before the Holocene (from at least 50 ka).publishedVersio

Malaria in pregnancy.

Recently, there has been a resurgence of malaria in densely populated areas of the United States secondary to human migration from endemic areas where factors such as cessation of vector control, vector resistance to insecticides, disease resistance to drugs, environmental changes, political instability, and indifference, have played a role for malaria becoming an overwhelming infection of these tropical underdeveloped countries. It is important for health care providers of gravida to be alert of the disease and its effects on pregnancy

Geochemical response of the mid-depth Northeast Atlantic Ocean to freshwater input during Heinrich events 1 to 4

PublishedArticleHeinrich events are intervals of rapid iceberg-sourced freshwater release to the high latitude North Atlantic Ocean that punctuate late Pleistocene glacials. Delivery of fresh water to the main North Atlantic sites of deep water formation during Heinrich events may result in major disruption to the Atlantic Meridional Overturning Circulation (AMOC), however, the simple concept of an AMOC shutdown in response to each freshwater input has recently been shown to be overly simplistic. Here we present a new multi-proxy dataset spanning the last 41,000 years that resolves four Heinrich events at a classic mid-depth North Atlantic drill site, employing four independent geochemical tracers of water mass properties: boron/calcium, carbon and oxygen isotopes in foraminiferal calcite and neodymium isotopes in multiple substrates. We also report rare earth element distributions to investigate the fidelity by which neodymium isotopes record changes in water mass distribution in the northeast North Atlantic. Our data reveal distinct geochemical signatures for each Heinrich event, suggesting that the sites of fresh water delivery and/or rates of input played at least as important a role as the stage of the glacial cycle in which the fresh water was released. At no time during the last 41 kyr was the mid-depth northeast North Atlantic dominantly ventilated by southern-sourced water. Instead, we document persistent ventilation by Glacial North Atlantic Intermediate Water (GNAIW), albeit with variable properties signifying changes in supply from multiple contributing northern sources.This research used samples provided by the Integrated Ocean Drilling (Discovery) Program IODP, which is sponsored by the US National Science Foundation and participating countries under management of Joint Oceanographic Institutions, Inc. We thank Walter Hale and Alex Wülbers for help with sampling, Kirsty Crocket for providing additional samples and Matt Cooper, Andy Milton, Mike Bolshaw and Dave Spanner for analytical support. Heiko Pälike, David Thornalley and Rachel Mills are thanked for productive discussions and comments on earlier versions of this work. We also thank three anonymous reviewers for their constructive feedback, which greatly improved the manuscript. Funding for this project was provided by NERC studentships to A.J.C. (grant NE/D005728/2) and T.B.C. (NE/I528626/1), with additional funding support from a Royal Society Wolfson Research Merit Award and NERC grants NE/F00141X/1 and NE/I006168/1 to P.A.W. and NE/D00876X/2 to G.L.F

Coupling of the cryosphere and ocean during intervals of rapid climate change in the palaeo record: a multi-proxy study of the Heinrich events of the last glacial from the Northeast Atlantic

Determining the response of the global thermohaline circulation to freshwater perturbations is of vital importance for future climate modelling efforts. The Heinrich events of the last glacial provide classic case studies, with major episodic inputs of freshwater associated with large numbers of icebergs flooding the North Atlantic Ocean. Climate modelling experiments and proxy reconstructions have both indicated a significant decrease in the strength of the meridional overturning circulation in response to this fresh water input to the ocean during each Heinrich event. Here, I present high resolution, multi-proxy reconstructions of cryospheric and surface and deep ocean behaviour over the last 40,000 years from Ocean Drilling Project (ODP) Site 980 in the northeast Atlantic, incorporating Heinrich events 1 to 4. Oxygen, carbon and neodymium isotope reconstructions of bottom water chemistry show a unique signature at this site for every Heinrich event, indicating the influence of a different water mass during each event. Bulk sediment leachate neodymium isotope values are strongly offset towards more radiogenic values than both planktonic foraminifera and fish debris throughout the Holocene, however, the agreement between the substrates is much closer under glacial conditions. This observed offset is attributed to modification of the leachate signal by fine material transported by strengthened bottom current activity in the Holocene, suggesting that bulk sediment leachates may not always record bottom water chemistry faithfully at sediment drift sites. Rare earth element profiles suggest that foraminifera without their ferromanganese coatings removed do not undergo significant diagenetic modification in the sediment, making these a better choice for reconstructions of bottom water neodymium isotope signatures. Each Heinrich event shows a different sequence of changes in the lithologies of ice-rafted debris, which argues against a simple repeating pattern of ice sheet destabilisation at each Heinrich event. The high degree of spatial variability in IRD patterns between sites in close proximity, however, suggests that surface ocean properties and circulation likely exerted a strong control over the IRD flux records, and hence the phasing of the circum-Atlantic ice sheets cannot be simply deduced from any single sedimentary record. Evidence of perturbation in bottom water properties can be seen prior to the deposition of the main ice-rafted debris layer during some of the Heinrich events at Site 980, suggesting that circulation changes may have played a role in the destabilisation of ice sheets, though the nature of these precursor changes differs between events. These findings show that Heinrich events are not simple, repeating events. Instead, differences in fresh water input and in surface ocean properties and circulation between Heinrich events likely give rise to different patterns of middepth North Atlantic circulation. The observed contrasts in bottom water chemistry at Site 980 between different Heinrich events highlights the sensitivity of the overturning circulation to fresh water inputs and argues against a simplistic model of thermohaline circulation cessation at each Heinrich event

Dust source activation frequency in the Horn of Africa

Mineral dust aerosols play an important role in Earth's climate through interactions with incoming solar radiation, clouds, and the atmosphere. However, dust sources in the Horn of Africa (HoA) and controls on their activation are poorly documented. Here, we use fifteen-minute Meteosat Second Generation Spinning Enhanced Visible and Infrared Imager dust index images to identify HoA dust source areas and to quantify their activation frequency in 1° × 1° resolution from 2006 to 2010. Around half of all recorded dust events occur in boreal summer, mostly between 8:00 and 16:00 local time. They are driven by meso- to regional scale meteorological mechanisms including the breakdown of the nocturnal low-level jets, land-sea breezes, and haboobs. By far the most dust-active region in the HoA is the Afar Triangle (>77% of all recorded dust events) which features the Afar and Danakil depressions and is fed by the Awash River. Despite experiencing strong and persistent southwest summer monsoon winds, dust activation on the Somali Peninsula is less significant. A composite of our map with data for North Africa and westernmost Asia shows that the HoA is a striking latitudinal anomaly with dust activation extending deep into the equatorial belt. Our data also reveal that dust activation is unusually seasonal with ∼40% of events occurring in June and July. Our findings show that aridity and mean wind strength alone are poor predictors of dust activation and underscore the strong control exerted by the availability of readily deflated unconsolidated riverine and lacustrine sediments

Dataset supporting the University of Southampton Doctoral Thesis "Dust sources to the Arabian Sea and their record of continental hydroclimate"

Dataset supporting the University of Southampton Doctoral Thesis &quot;Dust sources to the Arabian Sea and their record of continental hydroclimate&quot;. The data includes the supplementary information (Appendix C) for Chapter 4 of the Doctoral Thesis above. It has supplementary Tables C1, C2, C3, C4 and C5. See more detailed description of all data in Doctoral Thesis (Appendix C). The data is presented in excel files. Related projects/Funders: Natural Environment Research Council. Grant Number: NE/L002531/1</span

Late Pleistocene δ¹¹B based carbon dioxide levels from ODP Site 154-926

Earth's climate cooled markedly during the Late Miocene from 12 to 5 million years ago, with far-reaching consequences for global ecosystems. However, the driving forces of these changes remain controversial. A major obstacle to progress is the uncertainty over the role played by greenhouse gas radiative forcing. Here we present boron isotope compositions for planktonic foraminifera, which record carbon dioxide change for the interval of most rapid cooling, the Late Miocene Cooling event between 7 and 5 Ma. Our record suggests that CO₂ declined by some 100 ppm over this two-million year-long interval to a minimum at approximately 5.9 Ma. Having accounted non-CO₂ greenhouse gasses and slow climate feedbacks, we estimate global mean surface temperature change for a doubling of CO₂ - Equilibrium Climate Sensitivity - to be 3.9˚C (1.8–6.7 ˚C at 95% confidence) based on comparison of our record of radiative forcing from CO₂ with a record of global mean surface temperature change. We conclude that changes in CO₂ and climate were closely coupled during the latest Miocene and that Equilibrium Climate Sensitivity was within range of estimates for the late Pleistocene, other intervals of the Cenozoic, and the 21st century as presented by the Intergovernmental Panel on Climate Change

Chemical isolation and isotopic analysis of terrigenous sediments with emphasis on effective removal of contaminating marine phases including barite

The radiogenic isotope composition (e.g. 87Sr/ 86Sr and ε Nd) of the terrigenous fraction is commonly used to determine the provenance and transport history of sediments. In ocean sediments, the terrigenous fraction must be isolated prior to analysis to avoid contamination by marine phases. While the removal of calcium carbonate, organic matter, biogenic opal, authigenic coatings and adsorbed cations is widely advised, steps to remove all these phases are not consistently employed, and there is no standard procedure for the effective removal of marine barite. Marine barite is found throughout the world's oceans, particularly in regions of high export production, is highly enriched in strontium (Sr) and therefore has the potential to bias measurements of terrigenous 87Sr/ 86Sr towards seawater. Here we present results from sequential leaching experiments on marine sediments from the Atlantic and the Pacific Oceans to quantitatively determine the contaminating effect on 87Sr/ 86Sr and ε Nd exerted by the presence of barite and develop a protocol to successfully isolate the terrigenous fraction. Our results show that marine barite can skew measurements of terrigenous 87Sr/ 86Sr by &gt;0.01 towards the 87Sr/ 86Sr value of seawater, and we highlight the importance of assessing the location-specific impact of barite contamination on terrigenous 87Sr/ 86Sr. Our results show that marine barite can severely contaminate terrigenous 87Sr/ 86Sr, even where marine barite accumulation rates are modest (&lt; ~5 mg/m 3/yr and &lt;~20 g C/m 2/yr, respectively). Barite contains Nd in very low concentrations so barite contamination of terrigenous ε Nd is not a major concern but an important aspect of our protocol is that it has minimal effect on terrigenous ε Nd, allowing 87Sr/ 86Sr and ε Nd to be analysed on identically cleaned aliquots. Our systematic graduated approach will help standardise 87Sr/ 86Sr data, allow for robust comparisons between sites, and will contribute to an improved understanding of the provenance, transport and weathering histories of windblown continental dust and riverine sediments. </p

Sr, Nd and Pb isotope characterisation of the sources and sinks of terrigenous material in the North American Southwest and California Borderland Basins

Strontium, neodymium and lead isotopic signatures were measured on the carbonate-free lithogenic fraction of a suite of terrestrial and marine sediments from the North American Southwest. We present radiogenic isotope data from 1) surface sediments from nine different playa lakes in the Mojave Desert, 2) Late Quaternary silt mantles which drape the bedrock of Anacapa and San Clemente Islands offshore California and 3) fluvially-derived and hemipelagic sedimentary horizons in Late Quaternary age marine sediments from Ocean Drilling Project sites 893 and 1015 in the California Borderland Basins. We also present a compilation of measurements of bedrock Sr, Nd and Pb isotopic composition across the North American Southwest from the published literature. These datasets allow us to identify the isotopic signature of aeolian material exported from the North American Southwest and explore the contribution of dust to the California Borderland Basins