Lovasoa Ranivoharimanana's research while affiliated with University of Antananarivo and other places

Publications (17)

Article
The 4.2 ka event at the Mid- to Late-Holocene transition is often regarded as one of the largest and best documented abrupt climate disturbances of the Holocene. The event is most clearly manifested in the Mediterranean and Middle East as a regional dry anomaly beginning abruptly at 4.26 kyr BP and extending until 3.97 kyr BP. Yet the impacts of th...
Article
The spatial pattern of Holocene climate anomalies is crucial to determining the mechanisms of change, distinguishing between unforced and forced climate variability, and understanding potential impacts on past and future human societies. The 4.2 ka event is often regarded as one of the largest and best documented abrupt climate disturbances of the...
Article
Migration of the inter-tropical convergence zone, driven by changes in seasonal insolation and high northern latitude temperatures, is the primary control on tropical rainfall on geologic timescales. We test this paradigm using the timing of growth of stalagmites from southwest Madagascar to infer the timing of expansion of the ITCZ to the south at...
Article
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Madagascar experienced a major faunal turnover near the end of the first millenium CE that particularly affected terrestrial, large-bodied vertebrate species. Teasing apart the relative impacts of people and climate on this event requires a focus on regional records with good chronological control. These records may document coeval changes in rainf...
Preprint
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The decline of the Mature Harappan period of the Harappan civilization in and around the Indus Valley between 4.3 and 3.9 kyr BP, its transition to the Late Harappan and subsequent abandonment by 3.0 kyr BP are frequently attributed to a reduction in summer monsoon rainfall associated with the 4.2 kyr event (4.26–3.97 kyr BP). Yet while the 4.2 kyr...
Preprint
Full-text available
The 4.2 kyr event is regarded as one of the largest and best documented abrupt climate disturbances of the Holocene. Drying across the Mediterranean and Middle East is well established and is linked to societal transitions in the Akkadian, Egyptian and Harappan civilizations. Yet the impacts of this regional drought are often extended to other regi...
Article
Full-text available
The extent to which Madagascar’s Holocene extinct lemurs fell victim to nonhuman predators is poorly understood. Madagascar’s Holocene predator guild included several now-extinct species, i.e., crocodiles, carnivorans, and raptors. Here we focus on mammalian carnivory, specifically the roles of Cryptoprocta spelea and its still-extant but smaller-b...
Article
Full-text available
The global paleomonsoon concept predicts an antiphase response of monsoon rainfall in the Northern and Southern Hemispheres at timescales where there is asymmetric solar forcing and/or asymmetric hemispheric temperature changes. However, as different monsoon systems have different sensitivities to local, regional, and global forcing, rainfall respo...
Article
Trematosaurids form a very large and remarkable clade of Triassic tetrapods (Temnospondyli: Stereospondyli) with a worldwide geographical distribution. Compared with specimens from Europe, Australia or North America, they remain relatively scarce in African rocks, where they are mainly known in the Early Triassic of Madagascar and South Africa. Lon...
Article
Paleoclimate studies of tropical rainfall have led to a recognition of a predominant pattern of anti-phase behavior between the Northern and Southern hemispheres at both orbital and millennial timescales. Less certain is how regional tropical rainfall patterns have changed in the late Holocene, under boundary conditions and on timescales which are...

Citations

... At the onset of HS4, a longer adjustment interval is needed for the transition of climate change in the low latitudes responding to HS4 via the interaction between ocean-atmosphere systems, because of the gradual modulation of heat storage in the tropical oceans (Stocker and Johnsen, 2003;Pedro et al., 2018). The interhemispheric thermal gradient, particularly the north-south equator thermal gradient, is the driving force for the shifts of ITCZ (McGee et al., 2014, 2018Burns et al., 2022). The process of cooling of the tropical oceans and changes in the interhemispheric/north-south equatorial temperature gradient are not as dramatic as the temperature variations in the NH high latitude Skinner et al., 2020), resulting in the gradual southward shift of the ITCZ during HS4 onset (Guillevic et al., 2014). ...
... Water is a limiting resource in southern Madagascar and constrains the extent of forest habitat elsewhere on the island. While NW Madagascar was likely generally more mesic during the Holocene 22-24 , speleothem records from SW Madagascar suggest that the early Holocene was arid 25,26 and that the mid to late Holocene was punctuated by arid intervals 27,28 . A marine transgression and subsequent regression during the late Holocene can also account for lowering coastal water tables 29,30 . ...
... Scroxton et al., [93] reported that there were two prominent drought spell during pre-Meghalayan era. The first spell was abrupt 300-year long westerlies based with giving precipitation during winter months, (i.e. ...
... This transition window between the middle and late-Holocene has been recognized as a period of extreme climate change, which includes the events 5200 BP (Magny and Haas, 2004) and 4200 BP (Kathayat et al., 2017), characterized by global cooling and drought, which had drastic global effects on human civilizations (Booth et al., 2005;Cullen et al., 2000;Kathayat et al., 2017Kathayat et al., , 2018Liu and Feng, 2012;Magny and Haas, 2004;Roland et al., 2014;Scroxton et al., 2020). ...
... Moreover, if C 4 grasses were equally abundant historically, then we would also expect to see evidence for consumption of C 4 foods by both people and animals in the past. However, if C 4 grasses were less abundant in the past, particularly prior to the advent of pastoralism and the arrival of domesticated ungulates approximately 1,000 years ago(Godfrey et al., 2019), then we would expect to see evidence for more reliance on C 3 foods, particularly by endemic animals. A better quantification of reliance on C 4 resources over time and space by both animals and people would help resolve the longstanding dilemma of the historic regional extent of C 4 grasses and would also be extremely informative for decisions regarding land management on Madagascar. ...
... Actually, knowledge of extreme climate shifts and boundary conditions is necessitated for assessing potential forcing mechanisms in the climate system Barker and Diz, 2014). When the transitional conditions reach a threshold state, the climatic driving factors present abrupt feedback and are unstable over a short period (Scroxton et al., 2019). Abrupt changes in some GIS events during climate transitions are a critical for reflection of large-scale atmospheric circulation variations, which can reveal dynamic mechanisms for extreme climate change. ...
... Among the most fully aquatic temnospondyls rank the trematosaurids, which appear to have been able swimmers with elongate, laterally compressed tails, poorly ossified limbs and slen-der skulls (Hellrung 1987;Hammer 1987). Some of these forms evolved extreme longirostry that was unparalleled among lower tetrapods (Welles 1993;Fortuny et al. 2018;Maisch 2020). These probable fish-eaters must have originated and diversified during latest Permian time, because they are fully established in Lower Triassic rocks in a wide range of deposits across Pangaea (Schoch & Milner 2000). ...
... Other large-bodied nesomyine species may have gone extinct, but the absence of paleontological data in the Neogene of Madagascar and the scarcity of the Quaternary material hinders any detailed interpretation of past nesomyine diversity and evolution. Among Madagascar endemic mammals, there were giants forms, all extinct in the Late Pleistocene-Holocene, such as Hypogeomys australis, of about 2 kg; lemurs, Archaeoindris up to 200 kg, and a carnivoran, Cryptoprocta spelea, the largest Holocene land predator of Madagascar [63,66,67]. Today, the extant Hypogeomys antimena only reaches a maximum body mass of slightly greater than 1 kg [43]. ...
... However, recent proxy-, observational-, and modeling-based studies have challenged the mean position shift hypothesis, suggesting instead that ITCZ responses to external forcing are likely region specific and more strongly characterized by changes in its width and/or strength. For example, Campos et al. (20) and Asmerom et al. (21) suggest that the ITCZ became wider and perhaps weaker in the neotropics during the LIA, and Yan et al. (22) and Griffiths et al. (23) show that the ITCZ did not shift southward in the western Pacific during the LIA but rather retracted equatorward (i.e., became narrower), while Scroxton et al. (24) show that similar precipitation changes occurred on both sides of the equator in the western Indian basin during the last millennium. The mean position shift hypothesis also does not appear to explain trends observed over the satellite era (1979 to present), during which the ITCZ has instead strengthened, become more narrow, and exhibited only a slight and statistically insignificant northward shift (3). ...
... Thus we consider the period of established and continuous human habitation to be the time frame encompassing~2500 years BP onward [3][4][5]32,33 , when the human population expanded and started to have a strong impact on the island's ecosystems. Third, there is uncertainty about whether the recent extinctions were mainly caused by humans, natural changes or a combination of both 6,[34][35][36][37] . For some species, an anthropogenic cause of extinction has been suggested 38 . ...