Southern Hemisphere controls on ITCZ variability in southwest Madagascar over the past 117,000 years

Burns, Stephen J.; McGee, David; Scroxton, Nick; Kinsley, Christopher W.; Godfrey, Laurie R.; Faina, Peterson; Ranivoharimanana, Lovasoa

doi:10.1016/j.quascirev.2021.107317

Cited by 11 publications

(7 citation statements)

References 71 publications

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“…Holocene climate shifts are also documented by both stalagmites and sediment cores in the ST, but they were not necessarily in sync with those observed elsewhere on the island (Virah‐Sawmy et al, 2016; Godfrey et al, 2021; Faina et al, 2021; Burns et al, 2022; Hixon, Curtis, et al, 2021). In the ST, dry conditions prevailed for most of the Holocene (Burns et al, 2022; Godfrey et al, 2021), but there was a wetter period from ca. 3200 to 1600 years BP followed by a drought that ended ca.…”

Section: Introductionmentioning

confidence: 85%

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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Section: Introductionmentioning

confidence: 85%

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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“…This region is dominated by Madagascar's northwestern monsoon which is largely driven by northwesterly winds advecting moisture to the island from the tropical western Indian Ocean due to the sensible heating of Madagascar's land surface (Jury, 2016). The ITCZ is located over northern Madagascar during austral summer (Jury et al., 1995) as indicated by outgoing longwave radiation (OLR) minima (Burns et al., 2022), making Anjohibe an ideal study site for reconstructing past changes in the local monsoon and ITCZ over the southwest Indian Ocean (Figure 1). In austral winter, dry conditions prevail at Anjohibe due to the rain shadow cast by Madagascar's central mountains blocking prevailing easterlies and causing orographic rainfall along the island's eastern coast (Scroxton et al., 2017).…”

Section: Contemporary Hydroclimatementioning

confidence: 99%

Zonal Indian Ocean Variability Drives Millennial‐Scale Precipitation Changes in Northern Madagascar

Tiger,

Burns,

Dawson

et al. 2023

Paleoceanog and Paleoclimatol

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The low latitude Indian Ocean is warming faster than other tropical basins, and its interannual climate variability is projected to become more extreme under future emissions scenarios with substantial impacts on developing Indian Ocean rim countries. Therefore, it has become increasingly important to understand the drivers of regional precipitation in a changing climate. Here we present a new speleothem record from Anjohibe, a cave in northwest (NW) Madagascar well situated to record past changes in the Intertropical Convergence Zone (ITCZ). U‐Th ages date speleothem growth from 27 to 14 ka. δ18O, δ13C, and trace metal proxies reconstruct drier conditions during Heinrich Stadials 1 and 2, and wetter conditions during the Last Glacial Maximum and Bølling–Allerød. This is surprising considering hypotheses arguing for southward (northward) ITCZ shifts during North Atlantic cooling (warming) events, which would be expected to result in wetter (drier) conditions at Anjohibe in the Southern Hemisphere tropics. The reconstructed Indian Ocean zonal (west‐east) sea surface temperature (SST) gradient is in close agreement with hydroclimate proxies in NW Madagascar, with periods of increased precipitation correlating with relatively warmer conditions in the western Indian Ocean and cooler conditions in the eastern Indian Ocean. Such gradients could drive long‐term shifts in the strength of the Walker circulation with widespread effects on hydroclimate across East Africa. These results suggest that during abrupt millennial‐scale climate changes, it is not meridional ITCZ shifts, but the tropical Indian Ocean SST gradient and Walker circulation driving East African hydroclimate variability.

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“…Yan et al 48 also pointed out that the latitudinal range of ITCZ rainfall in the Western Pacific contracted over decadal to centennial timescales in response to a cold climate during the Little Ice Age (LIA). Stalagmite record from southwest Madagascar have also shown that the tropical rain-belt simultaneously expands or contracts in both hemispheres in the past 49 .…”

Section: Resultsmentioning

confidence: 98%

A contracting Intertropical Convergence Zone during the Early Heinrich Stadial 1

et al. 2023

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Despite the fact that the response of tropical hydroclimate to North Atlantic cooling events during the Heinrich Stadial 1 (HS1) has been extensively studied in African, South American and Indonesia, the nature of such responses remains debated. Here we investigate the tropical hydroclimate pattern over the Indo-Asian-Australian monsoon region during the HS1 by integrating hydroclimatic records, and examining a δ18Oseawater record from Globigerinoides ruber (white) in the tropical Indian Ocean. Our findings indicate that tropical hydrological conditions were synchronously arid in both hemispheres during the early HS1 (~18.3-16.3 ka) in the Indo-Asian-Australian monsoon region, except for a narrow, wet hydrological belt in northern low latitudes, suggesting the existence of a contracted tropical precipitation belt at that time. This study reveals that the meltwater discharge and resulting changes in global temperatures and El Niño exerted a profound influence on the tropical hydroclimate in the Indo-Asian-Australian monsoon region during the early HS1.

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Southern Hemisphere controls on ITCZ variability in southwest Madagascar over the past 117,000 years

Cited by 11 publications

References 71 publications

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

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

Zonal Indian Ocean Variability Drives Millennial‐Scale Precipitation Changes in Northern Madagascar

A contracting Intertropical Convergence Zone during the Early Heinrich Stadial 1

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Southern Hemisphere controls on ITCZ variability in southwest Madagascar over the past 117,000 years

Cited by 11 publications

References 71 publications

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

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

Zonal Indian Ocean Variability Drives Millennial‐Scale Precipitation Changes in Northern Madagascar

A contracting Intertropical Convergence Zone during the Early Heinrich Stadial 1

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

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