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Humid Periods (humid + period)
Selected AbstractsLate Quaternary upwelling off tropical NW Africa: new micropalaeontological evidence from ODP Hole 658C,JOURNAL OF QUATERNARY SCIENCE, Issue 3 2006Simon K. Haslett Abstract Planktonic foraminifera and radiolaria have been analysed in a Late Quaternary (40,0,ka) sediment sequence from Ocean Drilling Program (ODP) Hole 658C located under a coastal upwelling system near Cap Blanc, offshore northwest Africa, in order to document the palaeoceanographic history of the area. Temporal variations in species abundance and faunal assemblage analysis reveal a tripartite phased sequence of palaeoceanographic change through the Late Quaternary. Phase 1 spans 40,14.5,ka and is characterised by moderate upwelling, but Heinrich event 2 is distinguished as a brief episode of strengthened upwelling. Phase 2 begins with a change in a number of variables at ca. 14.5,ka and extends to ca. 5.5,ka. This phase is characterised by a general strengthening of upwelling, but may be subdivided into three minor phases including (a) the recognition of the Younger Dryas, marked by a temporary reduction in upwelling strength, followed by (b) an intensification of upwelling, and (c) upwelling and high productivity between 8 and 5.5,ka. This phase of upwelling corresponds with maximum Holocene cooling, possibly triggered by the collapse of the Laurentide ice sheet. Phase 3 extends from 5.5 to 0,ka and is characterised by weak upwelling and significant calcite dissolution. These phases are related to climatic events, particularly the African Humid Period (AHP), which is coincident with Phase 2. The AHP is characterised by increased precipitation, linked to an intensification of the African monsoon that enhances North East Trade Wind-driven coastal upwelling and is associated with the expansion of continental vegetation across North Africa. Copyright © 2006 John Wiley & Sons, Ltd. [source] Two-step vegetation response to enhanced precipitation in Northeast Brazil during Heinrich event 1GLOBAL CHANGE BIOLOGY, Issue 6 2010LYDIE M. DUPONT Abstract High resolution palynological and geochemical data of sediment core GeoB 3910-2 (located offshore Northeast Brazil) spanning the period between 19 600 and 14 500 calibrated year bp (19.6,14.5 ka) show a land-cover change in the catchment area of local rivers in two steps related to changes in precipitation associated with Heinrich Event 1 (H1 stadial). At the end of the last glacial maximum, the landscape in semi-arid Northeast Brazil was dominated by a very dry type of caatinga vegetation, mainly composed of grasslands with some herbs and shrubs. After 18 ka, considerably more humid conditions are suggested by changes in the vegetation and by Corg and C/N data indicative of fluvial erosion. The caatinga became wetter and along lakes and rivers, sedges and gallery forest expanded. The most humid period was recorded between 16.5 and 15 ka, when humid gallery (and floodplain) forest and even small patches of mountainous Atlantic rain forest occurred together with dry forest, the latter being considered as a rather lush type of caatinga vegetation. During this humid phase erosion decreased as less lithogenic material and more organic terrestrial material were deposited on the continental slope of northern Brazil. After 15 ka arid conditions returned. During the humid second phase of the H1 stadial, a rich variety of landscapes existed in Northeast Brazil and during the drier periods small pockets of forest could probably survive in favorable spots, which would have increased the resilience of the forest to climate change. [source] Current epidemiology of atopic dermatitis in south-eastern NigeriaINTERNATIONAL JOURNAL OF DERMATOLOGY, Issue 10 2004Edith N. Nnoruka MB Background, Atopic dermatitis (AD) is a common pruritic, eczematous skin disorder that runs a chronic and relapsing course. In Nigeria, it is currently on the increase, particularly amongst infants, and has created cost burdens for families. It occurs in association with a personal or family history of asthma, allergic rhinitis and conjunctivitis. Major and minor criteria exist as guidelines for arriving at a diagnosis of AD, and surveys from Western countries have shown that these features, in particular the minor features, vary with ethnicity and genetic background and can be used to aid diagnosis. African dermatologists have also voiced concern that the much used Hanifin criteria for diagnosis of AD may need some adaptation for use in Africa. Objective, To document the features and disease outcomes of AD seen amongst dermatology hospital patients in Enugu, south-eastern Nigeria, with a view to reflecting current features amongst Nigerian Blacks. Methods, A prospective study of AD patients seen over a 2-year period at a tertiary referral dermatology clinic (University of Nigeria Teaching Hospital, Enugu, Nigeria) was carried out. A total of 1019 patients aged between 4 weeks and 57 years were included in the study. Results, The prevalence of AD was 8.5%, which is much higher than the prevalence of AD reported in various parts of Nigeria 15 years ago. AD occurred before the age of 10 years in 523 (51.3%) patients, whilst 250 (24.5%) had onset after 21 years. The earliest age of onset in infants was in the first 6 weeks of life, and this was found in 129 patients (12.7%). Education and occupation of household heads were the most significant (P < 0.001) factors associated with seeking proper health care for the child's AD. Four hundred and forty-one (43.3%) patients presented with subacute atopic eczema and 326 (32%) patients with severe impeteginized eczema. Four hundred and twenty-five patients (41.7%) had at least one first-degree family member with AD (16.7%), allergic rhinitis (10.3%), asthma (14.6%) and allergic conjunctivitis (2.1%), while 55 (13.3%) of controls had a positive family history (P < 0.01) of allergy. A personal history of AD only, without concomitant respiratory allergies, was seen in 486 (47.7%) patients. The face was affected in 431 (42.3%) patients. Inverse distribution of a flexural rash was observed over the extensor aspect of the joints: the elbow in 502 patients (49.3%), the wrist joint in 183 patients (17.9%) and the knee joints in 354 patients (34.7). The commonly observed minor features included xerosis in 719 patients (71%), papular lichenoid lesions in 547 patients (54.1%), infraorbital folds in 498 patients (49.2%), palmar hyper linearity in 524 patients (51.8%) and raised peripheral blood eosinophils in 519 patients (51%), particularly for those with severe AD. Fissured heels, forehead lichenification, orbital darkening, nail pitting, sand paper-like skin lesions on the elbows/knees/lateral malleolli, knuckle dermatitis of the hands, palmar erythema and pitted keratolysis occurred more uncommonly as minor features. Infective complications were very common and included bacterial infections (folliculitis, impetiginized dermatitis and pyodermas) in 425 (41.7%) patients, fungal infections in 377 (37%) patients, parasitic infections (scabies) in 90 (8.8%) patients and viral infection (herpes simplex and molluscum contagiosum) in 29 (2.9%) patients. Thirteen of these atopics were also HIV positive. Aggravating factors most commonly reported included heat intolerance, excessive sweating, humidity, grass intolerance, thick woollen clothing and drug reactions. Only three patients had food intolerance. Three hundred and ten patients (30.4%) recalled their AD being worse in the hot humid periods and 383 (37.6%) could not recall any periods of relief or remission. Conclusions, The prevalence of AD amongst south-eastern Nigerian Blacks is on the increase, as in other areas, although it is still lower here than in other parts of the world. Many conventional minor features were found, but some occurred less frequently than in other countries, which may be attributed to ethnicity. Further studies will be required to confirm the ethnic differences in these features of AD amongst Nigerians and other Africans, to clarify the features of AD that are peculiar to Africans. [source] Phylogeography of spiny mice (genus Acomys, Rodentia: Muridae) from the south-western margin of the Sahara with taxonomic implicationsBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 1 2009VIOLAINE NICOLAS The present study aims to depict the overall pattern of Acomys history in south-western Sahara. We tested the specific predictions that: (1) several mitochondrial clades can be identified and that they coincide with the described species; (2) successive phases of desert expansion and contraction during the last 3 Myr have resulted in several phases of demographic expansion and population fragmentation in Acomys; and (3) isolation-by-distance occurs. The extent of phylogeographic patterns and molecular genetic diversity (cytochrome b gene and D-loop) were addressed in a survey of 90 individuals of Acomys from 38 localities. Our phylogeographical analyses show a strong genetic structure within western Saharan Acomys, with several phylogroups displaying non-overlapping geographic distributions. Restricted gene flow with isolation-by-distance was recorded and a signal of population expansion was detected within several clades. We suggest that during arid or semi-arid paleoclimatic periods, when large sandy areas were present, Acomys was restricted to rocky massifs, whereas, in more humid periods, when savannah and/or steppe habitat prevailed, this species was able to disperse and to survive outside rocky areas because food resources were abundant. Based on a comprehensive sampling and the use of an integrative approach (i.e. combining cytogenetic, molecular and morphological data), we firmly propose that Acomys airensis should be considered as a junior synonym of Acomys chudeaui. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98, 29,46. [source] | ||||||||||