Late Quaternary dynamics of southern Africa's winter rainfall zone

Chase, Brian M.; Meadows, Michael E.

doi:10.1016/j.earscirev.2007.06.002

Cited by 515 publications

(453 citation statements)

References 119 publications

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“…These acid soils may form where MAP minus PET is negative, but where appreciable leaching still occurs because of seasonal rainfall 19 or snowmelt 3 . Additionally, geologic constraints on Ca 2+ supply may explain acid soils in regions (1) to (4), which are low-relief continental surfaces where erosion is probably limited, and where conditions were more humid during the Last Glacial Maximum [20][21][22][23] . Although the role of palaeoclimate in creating these acid soils is challenging to evaluate quantitatively, they are generally most common in both seasonal and low-relief environments (Extended Data Fig.…”

mentioning

confidence: 99%

Water balance creates a threshold in soil pH at the global scale

Slessarev

Lin

Bingham

et al. 2016

Nature

416

255

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Soil pH regulates the capacity of soils to store and supply nutrients, and thus contributes substantially to controlling productivity in terrestrial ecosystems 1 . However, soil pH is not an independent regulator of soil fertility-rather, it is ultimately controlled by environmental forcing. In particular, small changes in water balance cause a steep transition from alkaline to acid soils across natural climate gradients 2,3 . Although the processes governing this threshold in soil pH are well understood, the threshold has not been quantified at the global scale, where the influence of climate may be confounded by the effects of topography and mineralogy. Here we evaluate the global relationship between water balance and soil pH by extracting a spatially random sample (n = 20,000) from an extensive compilation of 60,291 soil pH measurements. We show that there is an abrupt transition from alkaline to acid soil pH that occurs at the point where mean annual precipitation begins to exceed mean annual potential evapotranspiration. We evaluate deviations from this global pattern, showing that they may result from seasonality, climate history, erosion and mineralogy. These results demonstrate that climate creates a nonlinear pattern in soil solution chemistry at the global scale; they also reveal conditions under which soils maintain pH out of equilibrium with modern climate.Climate controls many aspects of soil chemistry, affecting soil pH (ref. 4). Alkaline soils are known to be common in arid climates, while acid soils are known to be common in humid climates 1 . Surprisingly, however, the global-scale mechanisms governing this pattern remain broadly defined, and untested by direct observation. What are the dominant chemical equilibria that constrain soil pH? What aspect of climate defines the transition between alkaline and acid soils, and is the transition linear? The answers to these questions are fundamental to understanding soil development and surface geochemistry at the global scale. Furthermore, achieving this understanding may prove essential for representing soils in models of the terrestrial biosphere, given that soil pH controls many aspects of soil fertility 5,6 . Here we illustrate that simple geochemical and hydrological concepts can be used to build a mechanistic understanding of soil pH at the global scale.Interpretations of acid-titration experiments indicate that the soil pH is typically most strongly buffered by equilibrium with two secondary minerals: calcite (CaCO 3 ), or gibbsite (Al(OH) 3 ) 7,8 Fig. 1).Local studies of climate gradients have shown that the relative importance of these two buffers is determined by leaching, which removes Ca 2+ from the soil 2,3,8,9 . In climates where evaporative demand exceeds precipitation, leaching rates are low, and dissolved Ca 2+ accumulates as CaCO 3 -buffering soil pH near 8.2 (ref. 4). Conversely, in climates where precipitation exceeds evaporative demand, water leaches through the soil, removing Ca 2+ and allowing accumulation of relatively immobile...

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confidence: 99%

Water balance creates a threshold in soil pH at the global scale

Slessarev

Lin

Bingham

et al. 2016

Nature

416

255

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“…Various palaeoclimate studies in the winter rainfall zone of South Africa [20][21][22][23] have also contributed to the understanding of the long-term changes in climate in Namaqualand. Distinguishing local climate trends is essential as climate may not change uniformly across large areas.…”

Section: Introductionmentioning

confidence: 99%

Recent trends in the climate of Namaqualand, a megadiverse arid region of South Africa

Davis

Hoffman

Roberts³

2016

S. Afr. J. Sci.

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Namaqualand is especially vulnerable to future climate change impacts. Using a high-resolution (0.5°x0.5°) gridded data set (CRU TS 3.1) and individual weather station data, we demonstrated that temperatures as well as frequency of hot extremes have increased across this region. Specifically, minimum temperatures have increased by 1.4 °C and maximum temperatures by 1.1 °C over the last century. Of the five weather stations analysed, two showed evidence of a significant increase in the duration of warm spells of up to 5 days per decade and a reduction in the number of cool days (TX10P) by up to 3 days per decade. In terms of rainfall, we found no clear evidence for a significant change in annual totals or the frequency or intensity of rainfall events. Seasonal trends in rainfall did, however, demonstrate some spatial variability across the region. Spatial trends in evapotranspiration obtained from the 8-day MOD16 ET product were characterised by a steepening inland-coastal gradient where areas along the coastline showed a significant increase in evapotranspiration of up to 30 mm per decade, most notably in spring and summer. The increase in temperature linked with the increases in evapotranspiration pose significant challenges for water availability in the region, but further research into changes in coastal fog is required in order for a more reliable assessment to be made. Overall, the results presented in this study provide evidence-based information for the management of climate change impacts as well as the development of appropriate adaptation responses at a local scale.

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“…This area is composed of 3913 quarter-degree grid cells. The region provides an excellent case study as it is characterized by strong topographic, geologic and climatic heterogeneity (Tyson, 1986;Partridge and Maud, 2000;Chase and Meadows, 2007), which has resulted in the existence of many vegetation types, which often change rapidly over short distances. Botswana (533) Swaziland (25) Lesotho ( …”

Section: Validationmentioning

confidence: 99%

“…Using southern Africa as a study area, we consider five countries: (7) mangroves. The dashed white lines delineate the different rainfall zones as defined by Chase and Meadows (2007): the winter rainfall zone (WRZ; > 66 % winter rain), the summer rainfall zone (SRZ; < 33 % of winter rain) and the year-round rainfall zone (YRZ) in between.…”

Section: Validationmentioning

confidence: 99%

“…Southern Africa -composed of South Africa, Botswana, Lesotho, Swaziland and Namibia -is well suited for such a test as it is characterized by a strong topographic, geological and climatic heterogeneity (Tyson, 1986;Partridge and Maud, 2000;Chase and Meadows, 2007), leading ultimately to a great diversity of plant species (Goldblatt and Manning, 2002). Statistical tests were performed on climate anomalies (1) to analyse where and why the model was reliable, and (2) to measure the effects of parameters, such as the type of variable, the number of taxa used and/or the vegetation type.…”

Section: Introductionmentioning

confidence: 99%

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CREST (Climate REconstruction SofTware): a probability density function (PDF)-based quantitative climate reconstruction method

Chevalier¹,

Cheddadi²,

Chase

2014

Clim. Past

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Abstract. Several methods currently exist to quantitatively reconstruct palaeoclimatic variables from fossil botanical data. Of these, probability density function (PDF)-based methods have proven valuable as they can be applied to a wide range of plant assemblages. Most commonly applied to fossil pollen data, their performance, however, can be limited by the taxonomic resolution of the pollen data, as many species may belong to a given pollen type. Consequently, the climate information associated with different species cannot always be precisely identified, resulting in less-accurate reconstructions. This can become particularly problematic in regions of high biodiversity. In this paper, we propose a novel PDF-based method that takes into account the different climatic requirements of each species constituting the broader pollen type. PDFs are fitted in two successive steps, with parametric PDFs fitted first for each species and then a combination of those individual species PDFs into a broader single PDF to represent the pollen type as a unit. A climate value for the pollen assemblage is estimated from the likelihood function obtained after the multiplication of the pollen-type PDFs, with each being weighted according to its pollen percentage.To test its performance, we have applied the method to southern Africa as a regional case study and reconstructed a suite of climatic variables (e.g. winter and summer temperature and precipitation, mean annual aridity, rainfall seasonality). The reconstructions are shown to be accurate for both temperature and precipitation. Predictable exceptions were areas that experience conditions at the extremes of the regional climatic spectra. Importantly, the accuracy of the reconstructed values is independent of the vegetation type where the method is applied or the number of species used.The method used in this study is publicly available in a software package entitled CREST (Climate REconstruction SofTware) and will provide the opportunity to reconstruct quantitative estimates of climatic variables even in areas with high geographical and botanical diversity.

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Late Quaternary dynamics of southern Africa's winter rainfall zone

Cited by 515 publications

References 119 publications

Water balance creates a threshold in soil pH at the global scale

Water balance creates a threshold in soil pH at the global scale

Recent trends in the climate of Namaqualand, a megadiverse arid region of South Africa

CREST (Climate REconstruction SofTware): a probability density function (PDF)-based quantitative climate reconstruction method

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