Paleo-environment and flooding of the Limpopo River-plain, Mozambique, between c. AD 1200–2000 (2023)


Volume 126,

March 2015

, Pages 105-116

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Multi-proxy analysis was performed on a radiocarbon-dated core, collected from a relic oxbow lake in the Limpopo River-plain, Mozambique, with the aim to reconstruct paleo-environment and past flooding of the lower river system over the past c. 800years. An additional objective was to evaluate and investigate the potential use of different proxies as recorders of paleo-flooding events and paleo-environmental variability within the floodplain. The proxies applied in this study were: mineral magnetic properties, grain-size distribution, organic carbon content and diatom microfossil assemblages. We found that sediment grain-size and mineral magnetic properties of the minerogenic fraction were the most sensitive proxies in terms of detecting signals from high-intensity river-discharge events. In the 800year long sequence, variations in sand content, magnetic susceptibility and saturation isothermal remnant magnetization suggest at least four major flooding events at the site during the reconstructed period; in the mid-1200, late-1300, mid-1500AD and during the last century. The diatom proxy reflects the development of the site from an open oxbow lake to a mainly terrestrial area. The diatom assemblage indicates that open lake conditions prevailed at the site between c. AD 1200–1400, with periodic inundation by marine water, most likely due to late Holocene sea-level changes. From c. AD 1400 and onwards, diatoms were rarely deposited at the site, which indicates drier conditions. This was a result of soil formation and gradual in-filling of the lake, a process which possibly was accentuated by a regionally dry climate situation. Our study shows that oxbow lakes and the proxies used here have great potential for reconstructing flooding events, a knowledge that is crucial for potential prediction and mitigation of flooding events in Mozambique in the future. Although chronological uncertainties limit comparisons to other paleo-environmental records, it seems that the flooding events recorded at our site occurred both during regionally wet and dry periods. Our data infer however, that flooding was probably more clearly recorded during the lake-stages than during infilled stage, probably as the terrestrial environment was more exposed to erosion.


Understanding of past climate dynamics and hydrological conditions is necessary for the evaluation of climate model predictions, as well as for quantifying corresponding climate changes and uncertainties during the present and in the future (Hegerl and Russon, 2011). General Circulation Model (GCM) predictions of future climate change remain complex and uncertain, particularly regarding humidity patterns in sub-tropical and tropical regions of Africa, where precipitation scenarios project different trend and magnitude of future change (IPCC, 2013). Therefore, there is uncertainty regarding future rainfall variability in southern Africa, both regarding its spatial and frequency distributions and the occurrence of extreme rainfall events. Rainfall events cause flooding events in southern Africa and are considered to be a serious natural hazard (Stal, 2011). A modern example of this hazard was the flooding associated with the tropical cyclone Eline, which affected parts of Mozambique, South Africa and Zimbabwe in AD 2000 (Reason and Keibel, 2004). Cardoso (2009) estimated that the peak discharge caused by the Eline cyclone has a 50-year return period. In general, severe flooding events in the region have a return period of 10–25years, while the normal or moderate flooding events have a return period of 2–5years (Cardoso, 2009). The loss of several hundred lives and damage to infrastructure, in the wake of the Eline cyclone, had serious negative effects on social and economic development of southern Mozambique. The Eline cyclone and its aftermaths, stress the importance to predict rainfall variability and the past recurrence interval of river flooding. Improved understanding of rainfall variability and flood frequencies would help society to take appropriate mitigatory actions and prepare for similar events in the future.

An increasing number of records of hydro-climate and flooding events in southern Africa are available, based on instrumental data (e.g. Dyson and Van Heerden, 2001, Mélice and Reason, 2007) and pre-instrumental reconstructions (e.g. Smith, 1991, Hattingh and Zawada, 1996, Smith and Zawada, 1990, Ekblom and Stabell, 2008, Heine and Heine, 2002, Holmgren et al., 2012). Historically documented flooding events generally coincide with those recorded in slack water sediments. However, most studies are based on discontinuous records and the dating of events is often uncertain. Moreover, most current research focuses on the causes of instrumentally recorded flood events, i.e. those that took place during the last century (e.g. Reason, 2007, Reason and Keibel, 2004). Considerably less is known about long-term frequency of flood events, as well as the magnitude of paleo-flooding events and the paleo-environment of the affected flood-plain. One reason for this knowledge gap is probably the many challenges associated with the use of river sediments as a source of paleodata in this region. For example, the preservation of micro- and macrofossils is hampered by temporary droughts (pollen, spores, seeds are oxidized) and high pH (diatoms, phytoliths are degraded). Furthermore, frequent shifts in river level may result in uneven deposition of sediments, sometimes with unknown origin, and erosive processes associated with the river flow may affect the continuity of the record, causing sediment hiatuses. Additionally, radiocarbon dating is complex due to possible reworking of macrofossils and hard water effects. Thus, there is an urgent need to evaluate different proxies that reflect flooding intensity and frequency in this area.

With this study, we address the lack of paleo-flood proxies in southern Mozambique, and make a first attempt to reconstruct past flooding events and hydrological conditions in the Limpopo River flood-plain, through a multi-proxy analysis of a sediment core retrieved from a relic oxbow lake located within the flood-plain (Fig.1). The retrieved sediment core covers the last c. 800years. An additional objective is to evaluate the different proxy methods used, and specify suitable approaches to detecting paleo-floods in river sediments in this area. More specifically, we investigate the potential of mineral magnetic properties, grain size distribution, carbon content and diatom microfossil assemblages as recorders of paleo-flooding events and paleo-environmental variability within the floodplain. Furthermore, we discuss problems involved in radiocarbon dating of river sediments in this region, and identify the most suitable approach to dating sediments that accumulated within the Limpopo River flood-plain.

The Limpopo River and its catchment are located in the south-eastern part of Africa, and cover approximately 412,000km2 (Fig.1). The catchment has a population of 13.5 million habitants, which is distributed within parts of Botswana, Mozambique, South Africa and Zimbabwe. The lower course of the river flows through southern Mozambique with a flood-plain covering about 79,600km2. The flood-plain is a flat area that extends approximately 200km in the NE–SW direction and 50km in the NE–SW direction (INGC et al., 2003). Relic oxbow lakes that have been filled with sediment are abundant as a consequence of the meandering river, with present day oxbow lakes in different stages of development. The relic oxbow lakes are seen as shallow topographical features (depressions) basins in an undulating landscape. The natural hydrology has been modified by the constructions of dams upstream since the 1940s, which probably altered the meandering activity. The river is flanked by pronounced levees that reach about 1–2m above the flood-plain. The flood-plain is fertile and used for both cultivation and grazing. At the river mouth, extensive Pleistocene dune formations impound river water on its way to the ocean (Fig.1). The narrow opening to the ocean, the altitude of the dunes (about 35ma.s.l.) and the gentle slope make the flood-plain and its habitants susceptible to the impacts of high intensity rainfall events.

The sampling site is a relic oxbow lake (24°53′28.5″S, 33°38′28.4″E) that is presently used primarily for grazing, but it can be inundated by water during flooding events. It is located approximately 60km from the river mouth (Fig.1), at an altitude of 6ma.s.l. The relic oxbow lake is approximately 3km long and 200m wide. The area is almost flat but has a gently undulating surface as a result of the lateral accretion of sediments from the meandering system of the Limpopo River. A minor topographic depression at the site suggests that re-connection to the main Limpopo River may occur during high water stands. The topography at the sampling site results in an environment where inundating floods will first erode and transport sediment downstream. During the recession of the flood, suspended sediment in the trapped flood water will be deposited on the bed of the basin.

Eleven flooding events occurred in the Limpopo River flood-plain area (including the sampling site) during the last century; AD 1915, 1937, 1955, 1967, 1972, 1975, 1977, 1981, 2000, 2012 and 2013. The first two are documented in newspapers printed in 1967, while the next six events are registered in reports from Direcção Nacional de Águas (1996) and the last three events are from recent observations. The magnitude of flooding depends mainly on amount and intensity of rainfall, in combination with the size and location of the geographical area being affected by the rain storm. Furthermore, the dam constructions upstream the Limpopo River have altered the natural hydrographic regime and can mitigate “natural” flooding events in the flood-plain. However, during events when the level of water trapped behind the dams becomes a threat to the infrastructure water will be released and potentially cause flash floods to occur in the flood-plain. Generally, the runoff is high in the upper part of the floodplain, near Chokwé, and decreases where the floodplain becomes shallower and wider. During the most recent flooding events in 2013, the majority of rainfall was received upstream of the flood-plain area, and the water level was higher near our sampling site than in the downstream Xai-Xai area. This pattern was also observed during the January 2013 flooding event, when the water source (intense rainfall) was located further upstream from the floodplain area. This resulted in high water fluxes and flooding of a large part of the Chokwé City, while, Xai-Xai City, located further downstream, was not affected. Interruptions of road connections during this flooding event made it impossible to access the sampling site and we could therefore not assess whether that area was flooded or not.

Section snippets


During fieldwork in 2007, a 4.68m long sediment core was collected using a 1.2m long gouge auger with an inner diameter of 60mm, and a piston corer, 75cm long with an inner diameter of 50mm (both corers were manufactured by Eijkelkamp). The gouge auger was used to sample the upper 2m and the piston corer was used for the remaining part of the sequence. The sediment sequence was sub-sampled at 1cm contiguous intervals.

Radiocarbon dating and calibration

Ten samples were submitted for radiocarbon dating (Table1). Dating was


The resulting age–depth model is illustrated in Fig.2, with calibrated ages plotted with their 2σ uncertainty range. The model was based on linear interpolation between the highest probability points, with the exception of Ua-35111, where the second highest probability point was considered more realistic, as accumulation rates would otherwise be inferred to be negative. The dates from the living shells did not suggest a problem of reservoir age as they were dated as modern (Table1). The bulk


The radiocarbon dating and age–depth construction reveal a significant offset between bulk sample ages and macrofossil ages (Fig.2). The age difference between these sample categories at corresponding depths ranges between c. 500 and 1000years. The relatively older age of the bulk sediment samples probably results from that secondary organic matter has been reworked from upstream and/or the effect of tertiary limestone that has been eroded and transported from old soil sequences, also from

Local development of the site: Influences of flooding and sea level change

The Indian Ocean tidal range at the mouth of Limpopo River is on the order of ±4–5m. Thus, at present, our sampling site is situated at 6ma.s.l., and is not exposed to a direct marine influence. Around AD 1200, however, the flood plain surrounding the sampling site was at a lower altitude in relation to sea level. Since the onset of our record, c. 4.5m of sediment has been accumulated (in the floodplain), indicating a lower topographic position in relation to the contemporary sea level at that


This paper reports the first stratigraphic analyses of sediments from the vast Limpopo River flood-plain, Mozambique. The major conclusions are as follows:

  • Analysis of mineral magnetic parameters and grain-size variations allowed the identification of past flooding events at the site. Magnetic susceptibility, saturation isothermal magnetization (SIRM) and sand content were the most sensitive proxies in terms of reflecting paleo-flooding.

  • Four high-magnitude flooding events were identified during


The research was funded by the SIDA/SAREC (Swedish International Development Cooperation Agency/Swedish Agency for Research Cooperation) and VR (the Swedish Research Council). Dr. Eve Arnold and Åsa Wallin, Department of Geological Sciences, Stockholm University, assisted during grain size analyses. Elidio Massuanguanhe from Department of Geology, Eduardo Mondlane University, participated in the field work. Dr. Dai G. Herbert, the Natal Museum, helped with shell identification. Hildred Crill,

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      Citation Excerpt :

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      Citation Excerpt :

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    • Research article

      Pluridisciplinary analysis and multi-archive reconstruction of paleofloods: Societal demand, challenges and progress

      Global and Planetary Change, Volume 177, 2019, pp. 225-238

      Floods are one of the gravest natural hazards for societies, worsened by population growth, unchecked development, and climate change. From a Global Change perspective, past extreme events merit particular interest because they can be linked to wider climate and environmental changes, introduce perturbations. During the last decade, knowledge of long-term flood frequency and magnitude has been improved by extracting data from different types of archive. But, despite advances in dating methods, proxies and statistical techniques and efforts to identify atmospheric drivers, some fundamental questions remain unresolved. The Special Issue entitled “Pluridisciplinary analysis and multi-archive reconstruction of paleofloods” in the journal Global and Planetary Change addresses these uncertainties and complexities by assembling a selection of studies, which were first presented at the Past Climate Changes (PAGES) Open Scientific Meeting held at Zaragoza in 2017. In this introductory paper, the guest editors outline the 17 research contributions and meta-data from the 17 paleoflood studies were systematically analyzed in terms of i) geographical distribution; ii) methodologies applied; iii) types of archives; iii) numbers of flood series compiled and iv) spatial and temporal resolution of paleoflood data. The data indicate that paleoflood studies focused on fluvial depositional environments show a higher rate of integration with other types of paleoflood archive (mean of 4.5 types of archive) than studies focused on documentary sources (mean of 3.5) and lake sediments (mean of 2.4). We suggest that this strategy of archive integration has been adapted to effectively compensate for the higher uncertainties of fluvial deposition in floodplains. Statistical processing of the meta-data shows quantitative associations between specific types of flood archive and offers a solid platform for designing the optimal approach for multi-archive paleoflood research. A qualitative review and visual comparison of the 17 paleoflood series shows some consistent trends and breaks but also notable differences within and between regions. While a trend of increased flooding since 4-5 ka BP is evident, the lack of synchronicity between breaks and the coeval increases and decreases in fluvial activity is manifest. The majority of studies in the Special Issue do denote the 19th century – including the youngest cool climate pulses during the Little Ice Age – as a particularly flood-rich period. It is more difficult to assess the 20th century because of social changes, population growth and extensive river modification. Despite the mentioned uncertainties, 10 of 14 papers do not record the 20th century as an exceptional flood period. Assessing the effects of human impact on paleoflood calendars and disentangling anthropogenic from natural drivers are major challenges in integrated paleoflood analysis.

      It is concluded that the interpretation of flood series is complex as landscapes and flood drivers are heterogeneous and systems show different sensitivities to flood control and drivers. Thus, the study of past floods, from historical and natural archives, is challenging but also offers unparalleled opportunities to document low-frequency, large-magnitude flood events, which occurred under a broad range of climate and/or environmental scenarios, and, probably, the only way to reconstruct robust paleoflood series.

    • Research article

      Soil n-alkane δD and glycerol dialkyl glycerol tetraether (GDGT) distributions along an altitudinal transect from southwest China: Evaluating organic molecular proxies for paleoclimate and paleoelevation

      Organic Geochemistry, Volume 107, 2017, pp. 21-32

      Organic molecular proxies provide a record of the hydrogen isotopic composition of ambient precipitation and paleoenvironmental temperature. In terrestrial settings, two classes of organic biomarkers are commonly utilized to reconstruct these past environmental conditions: straight-chained normal alkanes (n-alkanes) and branched glycerol dialkyl glycerol tetraethers (brGDGTs). We measured the δDn-alkane and the ratio of cyclisation and methylation indexes of branched tetraethers (CBT/MBT) from surface soils along a ∼1000km transect along the southeast margin of the Tibetan Plateau to assess how these proxies record changes in climate parameters that are related to elevation, despite variations in ecosystem. Abundance-weighted δDnC27-31 data record the δD of precipitation across the orogen and indicate minimal change in apparent fractionation (εn-alkane/water=−133‰) with elevation. n-Alkane δD mirrors the pattern of Rayleigh distillation of an air mass undergoing rainout as moisture moves from the Bay of Bengal into the SE margin of the Tibetan plateau. Soil tetraether temperatures provide a reliable measure of modern temperature with an MBT/CBT calculated temperature lapse rate (5.8°C/km) close to the moist adiabat. These data reflect “ground-level” conditions that are independent of the shape of the orogen or the source of moisture. In combination with a Rayleigh distillation model that incorporates temperature and precipitation isotope data, paired tetraether temperature and leaf wax isotope data produce a reliable record of changes in environmental conditions associated with modern elevation change across the largest orogen. However, some tetraether calibrations may impart systematic temperature bias, most notably in cold or dry climates. These calibration uncertainties can result in underestimates of paleoelevations by up to 1.5–2km. Paired isotopic and temperature paleoelevation reconstructions can minimize errors associated with an individual proxy method, however we recommend that application of tetraether temperature paleoelevation reconstruction take potential calibration biases into account in paleoelevation estimates.

    • Research article

      The Indian Ocean Zonal Mode over the past millennium in observed and modeled precipitation isotopes

      Quaternary Science Reviews, Volume 103, 2014, pp. 1-18

      The Indian Ocean Zonal Mode (IOZM) has gained considerable attention in the past decade due to its role in causing widespread flooding and droughts in the continents and islands surrounding the Indian Ocean. The IOZM has also been observed to vary on a low-frequency (multi-decadal) basis, making its behavior important to understand both for mid-range 21st century climate prediction and for paleoclimate studies. Despite efforts to reconstruct the IOZM using corals and other high-resolution proxies, nonstationarities in the response of paleoclimate proxies to the IOZM have also been noted, raising the possibility that the IOZM may be difficult to reconstruct or to predict in the long-term. It is therefore critical to assess the low-frequency component of the IOZM in observed, modeled, and paleoclimate data from the Indian Ocean region in order to identify nonstationary behavior and to assess its role in low-frequency climate variations.

      We present an analysis of low-frequency and nonstationary behavior in the IOZM on multi-decadal to centennial timescales using a combination of modeled, observed, and proxy reconstructions of δ18O/δDprecip. In order to assess multiple timescales of low-frequency variability, we focus on two key time periods: the historical period (1870–2003), and the past millennium (1000C.E.-present). We find significant nonstationarities in the relationships between the IOZM, precipitation amount, and δ18Oprecip/δDprecip during the historical period. These relationships vary on a multi-decadal basis in our model and in observed/reanalysis datasets. Air-sea interactions in the Indo-Pacific Warm Pool and teleconnections to the Pacific Ocean, as well as the phase of the IOZM itself, may contribute to this nonstationary behavior.

      We examine the potential ramifications of nonstationary IOZM behavior using a synthesis of spatially distributed proxy archives of δ18Oprecip/δDprecip from both sides of the IOZM region spanning the past millennium. Our findings indicate that during the past millennium, a strong IOZM-like connection exists in the proxy data network, with anti-correlation between East Africa and Indonesia. However, the links are spatially limited and in some cases timescale-dependent. Nonlinear behaviors in these links suggest that the IOZM may be difficult to detect on a consistent basis in proxy records from the past millennium. Based on our modeling results, the inconsistent links in the IOZM proxy network may arise from temporally and spatially variable relationships between the IOZM, precipitation, and δ18Oprecip/δDprecip. We conclude that the IOZM's potential to influence the climate of the Indian Ocean region is inconsistently reflected in proxy data, and that due to the changing strength of the IOZM/δ18Oprecip/δDprecip relationship, its spatial “footprint” may be restricted on multi-decadal to multi-centennial timescales.

    • Research article

      Cretaceous–Cenozoic sedimentary budgets of the Southern Mozambique Basin: Implications for uplift history of the South African Plateau

      Journal of African Earth Sciences, Volume 109, 2015, pp. 1-10

      In this study, data from 41 wells were used to quantify the evolution of the sedimentary budget in the Southern Mozambique passive margin basin, with a high temporal resolution for the Cenozoic period. We found that the drainage areas, which supplied sediments to the Southern Mozambique Basin, were eroded in two episodes. The first, of Mid–Late Cretaceous in age, is concordant with both thermochronological datation and sedimentary fluxes estimated by other studies in the Namibian and South African and Northern Mozambique margins. This erosion episode ended when the African surface, as defined by Burke and Gunnel (2008), had become flat and low-lying over most of the South African Plateau by ∼65Ma. Carbonate sediment deposition became more important in the shallow waters of the Mozambique basin after that time. The second erosion episode began at ∼23Ma and is likely due to an uplift event of the North-eastern part of the South African Plateau. It seems that the Limpopo catchment and the whole area sourcing the studied basin have inherited their present relief from two epeirogenic uplift pulses of Late Cretaceous and Miocene ages.

    • Research article

      Vegetation dynamics of Kisima Ngeda freshwater spring reflect hydrological changes in northern Tanzania over the past 1200years: Implications for paleoenvironmental reconstructions at paleoanthropological sites

      Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 580, 2021, Article 110607

      Kisima Ngeda (KN), a spring on the northern margin of saline Lake Eyasi, Tanzania, sustains an Acacia-Hyphaene palm woodland and Typha swamps, while the surrounding vegetation is semi-desert. To study the vegetation changes associated with this spring, which represents a plausible modern analog for the fossil springs documented in the nearby paleoanthropological and archaeological sites of Olduvai Gorge, we analyzed the pollen content of a 43cm-long sediment core that documents vegetation changes since the last ~1200years (from cal yrs. C.E. 841 to 2011). Our results show that (1) Hyphaene palms, which require meso-halophytic soil conditions were most abundant in the area of the coring site until cal yrs. C.E. ~1150 when the groundwater supplying the KN spring was likely lower than at present, allowing intrusions of saline lake waters. (2) From cal yrs. C.E. ~1200, a peat began to develop, the palm woodland was replaced by a Mimosaceae woodland, and the increased presence of Typha pollen indicates the presence of more wetlands. (3) From cal yrs. C.E. 1600, the groundwater level of the KN spring increased and reached its highest level in the last 1200years. (4) Peaks of wetland expansion, which reflect increased groundwater flow and level in response to amplified rainfall in the recharge area (Mt Oldeani, Ngorongoro Highlands), occurred at cal yrs. C.E. ~1200–1400 and ~1650–2011. These outflows of groundwater at Kisima Ngeda were linked to the intensity and frequency of positive Indian Ocean Dipole (IOD) events, which trigger heavy rains in eastern Africa. We conclude that the Kisima Ngeda hydrological system, which has been active for more than 1200years, responds rapidly to regional climate change driven by changes in the sea surface temperatures (SSTs) of the Indian Ocean. Yet, it is also capable of remaining active during dry intervals as inferred from the Kisima Ngeda record prior to cal yrs. C.E. 1200. Our results support the hypothesis that this type of system helped to maintain Plio-Pleistocene hominin populations and activities in the arid lowlands of the rift on a multi-decennial scale.

    • Research article

      Initiation of East Asia monsoon failure at the climate transition from the Medieval Climate Anomaly to the Little Ice Age

      Global and Planetary Change, Volume 128, 2015, pp. 83-89

      We have reconstructed decadally-resolved continuous sea surface temperature and seawater δ18O (hence salinity) records over the last 1300yr from alkenone and planktonic foraminiferal oxygen isotope ratio analyses of the East Sea/Japan Sea marine sediments to investigate East Asia monsoon variability. Comparisons of the records with other paleoclimate records indicate a possible connection between changes in the mid-latitude East Asia monsoon and Pacific Decadal Oscillation (PDO) over this period. The results show that during the Medieval Climate Anomaly (MCA) when the PDO index was negative, East Asia was characterized by surface warming with a strengthened summer monsoon. Summer monsoon-related precipitation increased and pluvials possibly dominated in the region at that time. Onset of Asia monsoon failure and severe drought occurred at the end of the MCA and extended to the Little Ice Age (LIA) when the PDO became positive.

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