Papers by Peter De Geest
Figure 8 in The first vertebrate fossil from Socotra Island (Yemen) is an early Holocene Egyptian fruit bat
Figure 8. AMS radiocarbon dating of the Socotran R. aegyptiacus skull fragments and calibration c... more Figure 8. AMS radiocarbon dating of the Socotran R. aegyptiacus skull fragments and calibration curve.
Figure 4. Socotran early Holocene R in The first vertebrate fossil from Socotra Island (Yemen) is an early Holocene Egyptian fruit bat
Figure 4. Socotran early Holocene R. aegyptiacus skull fragments: mandible in (a) dorsal and (b) ... more Figure 4. Socotran early Holocene R. aegyptiacus skull fragments: mandible in (a) dorsal and (b) frontal view; skull in (c) dorsal and (d) ventral view.
Figure 2 in The first vertebrate fossil from Socotra Island (Yemen) is an early Holocene Egyptian fruit bat
Figure 2. Hoq Cave on Socotra Island (Yemen), (a) current entrance and (b) the location of the ca... more Figure 2. Hoq Cave on Socotra Island (Yemen), (a) current entrance and (b) the location of the calcite flowstone speleothem with the embedded early Holocene Rousettus aegyptiacus remains before removal of the skull (c; arrow points to the skull). Photographs by Kay Van Damme (a), Dirk Van Damme (b) and Peter De Geest (c).
Figure 6 in The first vertebrate fossil from Socotra Island (Yemen) is an early Holocene Egyptian fruit bat
Figure 6. Bivariate plot of the examined specimens of African and Arabian fruit bat populations o... more Figure 6. Bivariate plot of the examined specimens of African and Arabian fruit bat populations of Myonycteris,Stenonycteris, Epomophorus, Eidolon and Rousettus aegyptiacus (the latter from Egypt, W Africa, S Arabia, E. Africa and the Socotra specimen; measurements in mm). (a) Greatest length of skull (LCr) against the length of upper tooth-row (CM2). (b) Condylobasal length of skull (LCb) against the neurocranium width (LaN). See Supplementary Material for details and full list of the comparative taxa.
Figure 5. Socotran early Holocene R in The first vertebrate fossil from Socotra Island (Yemen) is an early Holocene Egyptian fruit bat
Figure 5. Socotran early Holocene R. aegyptiacus, skull viewed laterally from (a) right and (b) l... more Figure 5. Socotran early Holocene R. aegyptiacus, skull viewed laterally from (a) right and (b) left; and mandible in (c) left and (d) right external lateral view.
Figure 3. Socotran early Holocene R in The first vertebrate fossil from Socotra Island (Yemen) is an early Holocene Egyptian fruit bat
Figure 3. Socotran early Holocene R. aegyptiacus remains embedded in calcite in situ. For the ful... more Figure 3. Socotran early Holocene R. aegyptiacus remains embedded in calcite in situ. For the full names of the structures, see under Abbreviations. Photo by Dirk Van Damme.
Figure 7 in The first vertebrate fossil from Socotra Island (Yemen) is an early Holocene Egyptian fruit bat
Figure 7. Bivariate plot of the examined samples of African and Arabian fruit bats (taxa as in Fi... more Figure 7. Bivariate plot of the examined samples of African and Arabian fruit bats (taxa as in Figure 6): results of the principal component analysis of skull dimensions.
Journal of Natural History, 2018
Figure 1 in The first vertebrate fossil from Socotra Island (Yemen) is an early Holocene Egyptian fruit bat
Figure 1. Locations of (a) the Socotra Archipelago (Yemen) in the western Indian Ocean near the H... more Figure 1. Locations of (a) the Socotra Archipelago (Yemen) in the western Indian Ocean near the Horn of Africa; (b) Hoq Cave on Socotra Island; and (c) the fruit bat fossil inside Hoq Cave, closest to an alternative fossil entrance leading to the plateau above.
The arid tropical island Soqotra is situated in the Indian Ocean between the Horn of Africa and t... more The arid tropical island Soqotra is situated in the Indian Ocean between the Horn of Africa and the Arabian Peninsula. Here a bi-annual rainy season is active, due to the passing of the inter-tropical convergence zone (ITCZ) twice each year, known as the Indian Ocean Monsoon system. By evaluating local meteorological data (rainfall and temperature) from the last 5 years,
Four stalagmites covering the last 7.0 ka were sampled on Socotra, an island in the northern Indi... more Four stalagmites covering the last 7.0 ka were sampled on Socotra, an island in the northern Indian Ocean to investigate the evolution of the northeast Indian Ocean Monsoon (IOM) since the mid Holocene. On Socotra, rain is delivered at the start of the southwest IOM in MayeJune and at the start of the northeast IOM from September to December. The Haggeher Mountains act as a barrier forcing precipitation brought by the northeast winds to fall preferentially on the eastern side of the island, where the studied caves are located. d 18 O and d 13 C and Mg/Ca and Sr/Ca signals in the stalagmites reflect precipitation amounts brought by the northeast winds. For stalagmite STM6, this amount effect is amplified by kinetic effects during calcite deposition. Combined interpretation of the stalagmites' signals suggest a weakening of the northeast precipitation between 6.0 and 3.8 ka. After 3.8 ka precipitation intensities remain constant with two superimposed drier periods, between 0 and 0.6 ka and from 2.2 to 3.8 ka. No link can be established with Greenland ice cores and with the summer IOM variability. In contrast to the stable northeast rainy season suggested by the records in this study, speleothem records from western Socotra indicate a wettening of the southwest rainy season on Socotra after 4.4 ka. The local wettening of western Socotra could relate to a more southerly path (more over the Indian Ocean) taken by the southwest winds. Stalagmite STM5, sampled at the fringe between both rain areas displays intermediate d 18 O values. After 6.2 ka, similar precipitation changes are seen between eastern Socotra and northern Oman indicating that both regions are affected similarly by the monsoon. Different palaeoclimatologic records from the Arabian Peninsula currently located outside the ITCZ migration pathway display an abrupt drying around 6 ka due to their disconnection from the southwest rain influence. Records that are nowadays still receiving rain by the southwest winds, suggest a more gradual drying reflecting the weakening of the southwest monsoon.
An Ordovician ostracode from Belgium
High-Resolution Speleothem Records of the Indian Ocean Monsoon Variability of the Last 6 ka and 0,5 ka From Soqotra Island, Yemen
Soqotra is an arid tropical island in the Indian Ocean, situated between the Horn of Africa and t... more Soqotra is an arid tropical island in the Indian Ocean, situated between the Horn of Africa and the Arabian Peninsula. The inter-tropical convergence zone (ITCZ) passes there twice each year, resulting in a bi-annual rainy season. High-resolution \delta18O and \delta13C ratios of speleothems from two different caves are used to reconstruct changes in the Monsoon intensity and/or variability. Based on
Data on the prehistoric biota of the Socotra Archipelago (Yemen) are scarce. We report on the fir... more Data on the prehistoric biota of the Socotra Archipelago (Yemen) are scarce. We report on the first extinct vertebrate ever recorded from this western Indian Ocean island group. An exceptionally preserved adult specimen of Egyptian fruit bat Rousettus aegyptiacus was found in a calcite flowstone in Hoq Cave on the NE coast of Socotra Island. Accelerator mass spectrometry (AMS) radiocarbon dating on bone fragments estimates the fossil at ca. 7600–7400 cal a BP (radiocarbon age 6669 ± 70 14C a BP) corresponding to an early Holocene wet period in southern Arabia and the Horn of Africa. Morphometric analysis of the skull compared to Recent specimens from the neighbouring mainlands finds the fossil morphologically most similar to Egyptian (Nile Valley and Libyan Desert), not to East African or Middle Eastern populations. The species is currently absent from the Horn of Africa (Somalia and Eastern Ethiopia). Although potentially a stray individual, we also discuss the palaeoenvironmental implications under the hypothetical scenario that the fruit bat is a remnant of an extinct resident population. If so, the extinction of an important pollinator and seed disperser may have impacted the Socotran terrestrial ecosystems.
Quaternary Science Reviews, 2013
Four stalagmites covering the last 7.0 ka were sampled on Socotra, an island in the northern Indi... more Four stalagmites covering the last 7.0 ka were sampled on Socotra, an island in the northern Indian Ocean
to investigate the evolution of the northeast Indian Ocean Monsoon (IOM) since the mid Holocene. On
Socotra, rain is delivered at the start of the southwest IOM in MayeJune and at the start of the northeast
IOM from September to December. The Haggeher Mountains act as a barrier forcing precipitation
brought by the northeast winds to fall preferentially on the eastern side of the island, where the studied
caves are located. d18O and d13C and Mg/Ca and Sr/Ca signals in the stalagmites re!ect precipitation
amounts brought by the northeast winds. For stalagmite STM6, this amount effect is ampli"ed by kinetic
effects during calcite deposition. Combined interpretation of the stalagmites’ signals suggest a weakening
of the northeast precipitation between 6.0 and 3.8 ka. After 3.8 ka precipitation intensities remain
constant with two superimposed drier periods, between 0 and 0.6 ka and from 2.2 to 3.8 ka. No link can
be established with Greenland ice cores and with the summer IOM variability.
In contrast to the stable northeast rainy season suggested by the records in this study, speleothem
records from western Socotra indicate a wettening of the southwest rainy season on Socotra after 4.4 ka.
The local wettening of western Socotra could relate to a more southerly path (more over the Indian
Ocean) taken by the southwest winds. Stalagmite STM5, sampled at the fringe between both rain areas
displays intermediate d18O values. After 6.2 ka, similar precipitation changes are seen between eastern
Socotra and northern Oman indicating that both regions are affected similarly by the monsoon. Different
palaeoclimatologic records from the Arabian Peninsula currently located outside the ITCZ migration
pathway display an abrupt drying around 6 ka due to their disconnection from the southwest rain in-
!uence. Records that are nowadays still receiving rain by the southwest winds, suggest a more gradual
drying re!ecting the weakening of the southwest monsoon.
Journal of Arid Environments, 2010
The climate of Socotra, influenced by the Indian Ocean Monsoon, is poorly known, hampering unders... more The climate of Socotra, influenced by the Indian Ocean Monsoon, is poorly known, hampering understanding of its paleoclimate and (endemic) biodiversity. Mean annual rainfall and temperature, measured in a network of meteorological stations from 2002 to 06, were 216 mm and 28.9 C. Combined with cloud cover information from satellite images, this data provides clear ideas on inter-and intra-annual variability. Precipitation derived from the northeast (NE) winter monsoon influences especially the NE plateaus and windward side of the Haggeher Mountains because of orographic effects. The southwest (SW) summer monsoon concentrates at the southern half of the island and generally produces less rainfall. During the SW summer monsoon, clouds cover the highlands and plateaus south of the Haggeher Mountains, creating fog. Preliminary measurements suggest that at higher altitudes, fogderived moisture may constitute up to two-thirds of total moisture, amounting up to 800 mm. The predominant SW aspect of the enigmatic dragonblood tree underlines the importance of fog. Long-term weather observations by Socotri put these short-term meteorological observations into a longer perspective. Socotri informants also described the drought years when livestock populations crashed, after which windows of opportunities for the regeneration of dragonblood and other grazing-sensitive trees may have occurred.
Book Chapters by Peter De Geest
Several years ago a group of Belgian speleologists of the Socotra Karst Project made a spectacula... more Several years ago a group of Belgian speleologists of the Socotra Karst Project made a spectacular discovery. Deep inside a huge cave on the island Socotra they came across a large number of inscriptions, drawings and archaeological objects. As further investigation showed, they were left by sailors who visited the island between the 1st c. BC and the 6th c. AD. The majority of the texts are written in the Indian Brahmi script, but there are also inscriptions in South-Arabian, Ethiopian, Greek, Palmyrene and Bactrian scripts and languages. This corpus of nearly 250 texts and drawings thus constitutes one of the main sources for the investigation of Indian Ocean trade networks in the first centuries of our era. The present book is the first comprehensive edition and study of this material. It comprises contributions by an international group of scholars who have been working on these new discoveries for a couple of years (in alphabetical order): Mikhail D. Bukharin (Moscow), Peter De Geest (Brussels), Hédi Dridi (Neuchâtel), Maria Gorea (Paris), Julian Jansen Van Rensburg (Brussels), Christian Julien Robin (Paris), Bharati Shelat (Ahmedabad), Nicholas Sims-Williams (London, Oxford) and Ingo Strauch (Berlin).
DE GEEST, P. and the Soqotra Karst Project. Text Box 2.2: Karst and Caves, p.28-29. In CHEUNG, C. & DE VANTIER, L., 2006. Socotra - A Natural History of the Islands and Their People. VANDAMME, K. (Science Editor).
Uploads
Papers by Peter De Geest
to investigate the evolution of the northeast Indian Ocean Monsoon (IOM) since the mid Holocene. On
Socotra, rain is delivered at the start of the southwest IOM in MayeJune and at the start of the northeast
IOM from September to December. The Haggeher Mountains act as a barrier forcing precipitation
brought by the northeast winds to fall preferentially on the eastern side of the island, where the studied
caves are located. d18O and d13C and Mg/Ca and Sr/Ca signals in the stalagmites re!ect precipitation
amounts brought by the northeast winds. For stalagmite STM6, this amount effect is ampli"ed by kinetic
effects during calcite deposition. Combined interpretation of the stalagmites’ signals suggest a weakening
of the northeast precipitation between 6.0 and 3.8 ka. After 3.8 ka precipitation intensities remain
constant with two superimposed drier periods, between 0 and 0.6 ka and from 2.2 to 3.8 ka. No link can
be established with Greenland ice cores and with the summer IOM variability.
In contrast to the stable northeast rainy season suggested by the records in this study, speleothem
records from western Socotra indicate a wettening of the southwest rainy season on Socotra after 4.4 ka.
The local wettening of western Socotra could relate to a more southerly path (more over the Indian
Ocean) taken by the southwest winds. Stalagmite STM5, sampled at the fringe between both rain areas
displays intermediate d18O values. After 6.2 ka, similar precipitation changes are seen between eastern
Socotra and northern Oman indicating that both regions are affected similarly by the monsoon. Different
palaeoclimatologic records from the Arabian Peninsula currently located outside the ITCZ migration
pathway display an abrupt drying around 6 ka due to their disconnection from the southwest rain in-
!uence. Records that are nowadays still receiving rain by the southwest winds, suggest a more gradual
drying re!ecting the weakening of the southwest monsoon.
Book Chapters by Peter De Geest
to investigate the evolution of the northeast Indian Ocean Monsoon (IOM) since the mid Holocene. On
Socotra, rain is delivered at the start of the southwest IOM in MayeJune and at the start of the northeast
IOM from September to December. The Haggeher Mountains act as a barrier forcing precipitation
brought by the northeast winds to fall preferentially on the eastern side of the island, where the studied
caves are located. d18O and d13C and Mg/Ca and Sr/Ca signals in the stalagmites re!ect precipitation
amounts brought by the northeast winds. For stalagmite STM6, this amount effect is ampli"ed by kinetic
effects during calcite deposition. Combined interpretation of the stalagmites’ signals suggest a weakening
of the northeast precipitation between 6.0 and 3.8 ka. After 3.8 ka precipitation intensities remain
constant with two superimposed drier periods, between 0 and 0.6 ka and from 2.2 to 3.8 ka. No link can
be established with Greenland ice cores and with the summer IOM variability.
In contrast to the stable northeast rainy season suggested by the records in this study, speleothem
records from western Socotra indicate a wettening of the southwest rainy season on Socotra after 4.4 ka.
The local wettening of western Socotra could relate to a more southerly path (more over the Indian
Ocean) taken by the southwest winds. Stalagmite STM5, sampled at the fringe between both rain areas
displays intermediate d18O values. After 6.2 ka, similar precipitation changes are seen between eastern
Socotra and northern Oman indicating that both regions are affected similarly by the monsoon. Different
palaeoclimatologic records from the Arabian Peninsula currently located outside the ITCZ migration
pathway display an abrupt drying around 6 ka due to their disconnection from the southwest rain in-
!uence. Records that are nowadays still receiving rain by the southwest winds, suggest a more gradual
drying re!ecting the weakening of the southwest monsoon.
Invited speaker at the 14th International Karstological School “Classical Karst” EU Marie Curie sponsored scholarship, Postojna, Slovenia, June-July 2006.
Invited speaker at the Yemen Society for the Protection of Wildlife, sponsored by the Global Environmental Facility (GEF), Sana’a, Yemen, January 2006
Invited speaker at the International Symposium: Cave Climate and Paleoclimate – Best Record of Global Change – II, Kalamos, Greece, August 2005.
Invited Chairman at Session 19: Speleogenesis and evolution of Karst Aquifers including Geology, Hydrology and Geomorphology VII at the 14th International Congress of Speleology
Invited speaker at the Past and Present: Developing Infrastructure & Current Social Issues for Soqotra meeting. University of London, London, England, September 2004