Hydroclimate variability in the Madagascar and Southeast African summer monsoons at the Mid- to Late-Holocene transition

Scroxton, Nick; Burns, Stephen J.; McGee, David; Godfrey, Laurie R.; Ranivoharimanana, Lovasoa; Faina, Peterson; Tiger, Benjamin H.

doi:10.1016/j.quascirev.2022.107874

Cited by 9 publications

(16 citation statements)

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“…Highlighted bars indicate the wet interval (blue) and dry events (red) observed in AB13 record. From top: AB13 (this study), ANJ94-2 (Railsback et al 2020), ANJ94-5 (Wang et al 2019), and AK1 (Scroxton et al 2023a). Previously published recordsare superimposed over AB13 δ 18 O record (grey) and individual dates with error are shown above each record.…”

Section: Discussionmentioning

confidence: 83%

“…Recent results from speleothems from across Madagascar have produced high resolution, well-dated paleoclimate reconstructions, with most of these studies using speleothems from Anjohibe (Burns et al, 2016; Duan et al, 2021; Voarintsoa et al, 2017, 2019; Wang et al, 2019) or from nearby Anjohikely (Scroxton et al, 2023a). The temporal coverage of several of these studies and our AB13 record partially overlap.…”

Section: Discussionmentioning

confidence: 99%

“…One measure of the reliability of speleothem climate records is replication of the isotopic time series with other speleothems from the same approximate location (Dorale and Liu, 2009). In Figure 5 we compare our record to three previously published stalagmite records from NW Madagascar with varying temporal resolutions and dating accuracies: ANJ94-2 (Railsback et al, 2020) and ANJ94-5 (Wang et al, 2019) from Anjohibe and AK1 from Anjohikely (“little cave” in Malagasy), which is located 2.3 km southwest of Anjohibe (Scroxton et al, 2023a).…”

Section: Discussionmentioning

confidence: 99%

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A speleothem record of hydroclimate variability in northwestern Madagascar during the mid-late Holocene

Williams,

Burns,

Scroxton

et al. 2024

The Holocene

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We present a continuous high-resolution precisely dated multiproxy record of hydroclimate variability at Anjohibe cave in northwestern Madagascar using speleothem AB13. The record spans from ~4484 y BP to ~2863 y BP. Stalagmite δ18O, δ13C and Sr/Ca ratios show very similar changes in hydroclimate. The mechanism controlling Sr/Ca changes, however, from prior calcite precipitation to degree of dolomite dissolution at about 4 ky BP. Our record is also in good agreement with previously published speleothem records from the same area. This agreement and multiproxy consensus indicate that AB13 provides a robust record of hydroclimate variability, including a continuous record of hydroclimate variability across the 4.2 ka event. This 4.2 ka event in Madagascar is marked by two distinct periods of drying between ~3900 y BP to 4300 y BP. A dry 4.2 ka event at this Southern Hemisphere site helps limit possible mechanisms for the event, indicating that a meridional shift to the south in the ITCZ is not responsible for the 4.2 ka event. In addition, the 4.2 ka event does not stand out as a unique dry period in our record. The longest and driest period of the record lasted ~300 years with peak dryness at ~3000 y BP. Our record differs significantly from a speleothem record from Rodrigues Island, located ~1800 km to the east of our study area in Madagascar suggesting different climatological controls on northwest Madagascar and more oceanic sites to the east.

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Section: Discussionmentioning

confidence: 83%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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A speleothem record of hydroclimate variability in northwestern Madagascar during the mid-late Holocene

Williams,

Burns,

Scroxton

et al. 2024

The Holocene

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“…For the CH, we were able to evaluate isotopic differences for Holocene individuals from mid‐elevation sites that lived before and after a drying event beginning ca. 4300 years ago (Razafimanantsoa, 2021; Scroxton et al, 2023). Sample size for dated hippos is small.…”

Section: Resultsmentioning

confidence: 99%

“…Finally, temporal data can help clarify if there were changes over time in the degree to which hippos relied on C 4 plants. Mid‐Holocene drying is recorded in stalagmites from northwestern Madagascar and broadly across the Indian Ocean (Scroxton et al, 2023). Lake sediments from the high‐elevation western slope of the CH (ca.…”

Section: Introductionmentioning

confidence: 99%

What can hippopotamus isotopes tell us about past distributions of C₄ grassy biomes on Madagascar?

Crowley

Godfrey

Samonds

2023

Plants People Planet

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Societal Impact StatementToday, expansive C4 grassy biomes exist across central, western, and northern Madagascar. Some researchers have argued that the island's now‐extinct pygmy hippopotamuses belonged to a megaherbivore grazing guild that maintained these grasslands prior to human arrival. However, the chemistry of hippo bones indicates that C4 grasses were only a minor part of hippo diet. This, in turn, suggests that C4 grasses were present but not widespread when hippos were alive and that grasses expanded only after Malagasy people shifted from hunting and foraging to agropastoralism approximately 1000 years ago. These results have important implications for environmental reconstructions and biodiversity management.Summary Extinct hippopotamuses (Hippopotamus spp.) were part of Madagascar's megaherbivore guild. Stable carbon (δ13C) and nitrogen (δ15N) isotopes in radiometrically dated bone collagen track spatial and temporal variation in diet and habitat. If hippos helped maintain C4 grassy biomes, then they should have regularly consumed C4 grasses, which have high δ13C values. However, if expansive C4 grassy biomes are anthropogenic, then forests would have been more extensive in the past, and hippos would have predominantly consumed C3 plants with low δ13C values. Nitrogen isotopes can clarify foraging habitat (moist or dry). We assessed δ13C and δ15N values for hippos from different ecoregions of Madagascar and compared these with data for extinct herbivorous lemurs from the same ecoregions. We further explored the effects of wet/dry transitions on isotopic trends for hippos from the central highlands and spiny thicket ecoregions. Carbon isotopes suggest (1) limited C4 consumption by hippos in the central highlands, dry deciduous forest, and succulent woodland ecoregions; and (2) moderate consumption of C4 resources in the spiny thicket. Nitrogen data indicate that hippos foraged in wetter habitats than sympatric lemurs in all regions. Malagasy hippos did not regularly graze C4 grasses in dry, open habitats, even in regions blanketed by C4 grassy biomes today. Malagasy grasses are adapted to grazing and fire, but these are likely ancient adaptations that accompanied grasses when they initially spread to Madagascar. C4 grassy biomes were spatially limited in extent in the past and only expanded after the Late Holocene introduction of domesticated ungulates.

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Sea-Locked: The Cascading Effects of Seaborne Challenges to Human Security in Madagascar

Shi

2024

Advanced Sciences and Technologies for Security Applications

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This chapter presents a ‘wicked deadlock’ between human insecurity, underdevelopment, and unsustainability against the background of a more turbulent ocean environment, which can be best illustrated with the ongoing seaborne challenges on the island of Madagascar, especially those engendered by sea-originated nature hazards and man-caused maritime disruptions. It first investigates what human security means in respect of Madagascar’s position as both one of the least-developed island nations and the frontier of ocean sustainability. Then it examines how the worsening of human insecurity on the island has been accelerated recently in light of climatic and socio-ecological changes from the sea. The human security emergencies the island is confronting might have rooted partly in its oceanographic peculiarities, but they warn the world of a possible failing scenario of the sustainability-security nexus, which might have larger implications that go beyond Madagascar’s coastlines and reach to other oceanic communities.

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Hydroclimate variability in the Madagascar and Southeast African summer monsoons at the Mid- to Late-Holocene transition

Cited by 9 publications

References 95 publications

A speleothem record of hydroclimate variability in northwestern Madagascar during the mid-late Holocene

A speleothem record of hydroclimate variability in northwestern Madagascar during the mid-late Holocene

What can hippopotamus isotopes tell us about past distributions of C₄ grassy biomes on Madagascar?

Sea-Locked: The Cascading Effects of Seaborne Challenges to Human Security in Madagascar

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Hydroclimate variability in the Madagascar and Southeast African summer monsoons at the Mid- to Late-Holocene transition

Cited by 9 publications

References 95 publications

A speleothem record of hydroclimate variability in northwestern Madagascar during the mid-late Holocene

A speleothem record of hydroclimate variability in northwestern Madagascar during the mid-late Holocene

What can hippopotamus isotopes tell us about past distributions of C4 grassy biomes on Madagascar?

Sea-Locked: The Cascading Effects of Seaborne Challenges to Human Security in Madagascar

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What can hippopotamus isotopes tell us about past distributions of C₄ grassy biomes on Madagascar?