George A. Brook’s research while affiliated with University of Georgia and other places

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Publications (142)


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Three distinct Holocene intervals revealed in NW Madagascar: evidence from two stalagmites from two caves, and implications for ITCZ dynamics
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January 2017

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550 Reads

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4 Citations

Climate of the Past Discussions

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L. Bruce Railsback

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George A. Brook

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[...]

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Marie Olga Madison Razanatseheno

Petrographic features, mineralogy, and stable isotopes from two stalagmites collected from Anjohibe and Anjokipoty Cave allow distinction of three intervals of the Holocene in northwestern Madagascar. The Malagasy early Holocene interval (between ca. 9.8 and 7.8 ka) was wet, and vegetation changes seem to have been controlled by changes in climate. The Malagasy late Holocene interval (after ca. 1.6 ka) also records evidence of wet conditions, but changes in vegetation were influenced by anthropogenic effects, as suggested by the stalagmite δ¹³C shift. The Malagasy middle Holocene interval seems to be characterized by drier conditions, relative to the early and late Holocene. The alternating wet/dry/wet conditions in northwestern Madagascar during each of these Holocene intervals could be linked to the long-term migration of the Inter-Tropical Convergence Zone (ITCZ). Higher southern hemisphere (SH) insolation and globally colder conditions drove the ITCZ's mean position further south, bringing more rainfall to northwestern Madagascar. This condition was favorable for stalagmite deposition. In contrast, higher northern hemisphere (NH) insolation and globally warmer conditions displaced the ITCZ further north, bringing less rainfall to northwestern Madagascar. This condition was not favorable for stalagmite deposition. The linkage between global cooling and wet conditions in regions of the SH, in response to the southward migration of the ITCZ, is further exemplified at centennial scale by the negative δ¹⁸O and δ¹³C values in northwestern Madagascar during the 8.2 ka cold event when the Atlantic Meridional Overturning Circulation (AMOC) weakened. Weakening of the AMOC led to an enhanced temperature gradient between the two hemispheres, i.e. cold NH and warm SH, shifting the mean position of the ITCZ further south. This brought wet conditions in the SH monsoon regions, such as northwestern Madagascar, and dry conditions in the NH monsoon regions, including the Asian Monsoon and the East Asian Summer Monsoon. This climatic relationship is useful to test for climate models that are used to predict changes in future climate.

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Multiple proxy analyses of a U/Th-dated stalagmite to reconstruct paleoenvironmental changes in northwestern Madagascar between 370CE and 1300CE

January 2017

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233 Reads

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50 Citations

Palaeogeography Palaeoclimatology Palaeoecology

The timing and causes of paleoenvironmental changes in Madagascar have been debated, specifically in respect to human activity following the settlement in the late Holocene. Here we present δ¹⁸O, δ¹³C, layer-bounding surfaces, layer-specific width, mineralogy, and distribution of macroholes from Stalagmite MA3 from Anjohibe Cave to provide a detailed understanding of the paleoenvironmental changes in northwestern Madagascar between 370 CE and 1300 CE. The stable isotope records of Stalagmite MA3 are compared with stable isotope records of Stalagmites ANJ94-5 and MA2.



A multi-proxy stalagmite record from northwestern Namibia of regional drying with increasing global-scale warmth over the last 47 kyr: The interplay of a globally shifting ITCZ with regional currents, winds, and rainfall

August 2016

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1,590 Reads

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24 Citations

Palaeogeography Palaeoclimatology Palaeoecology

Stalagmite Orum-1 from a cave near Orumana in northwestern Namibia provides a multi-proxy record of regional drying with increasing global-scale warmth over the last 47 kyr, in a region with few long well-dated location-specific paleoclimate records. Data from Stalagmite Orum-1 include carbon and oxygen stable isotope ratios, proportions of aragonite and calcite, pronouncedly differing petrographic fabrics, positions of layer-bounding surfaces, variation in layer-specific width, and changes in layer thickness, all of which combine to support change from wetter to drier conditions. Combined with fourteen U-Th ages, they suggest that climate was wetter in northwestern Namibia during globally cold MIS 3 than it is today, and with more grass than is present today. The climate at Orumana became drier during the deglacial transition after the Last Glacial Maximum, but carbon isotope data indicate that C4 grasses persisted. In the Holocene, even greater aridity led to a reduction in grass cover and to the present C3-dominated vegetation. Hiatuses in Stalagmite Orum-1 suggest even drier conditions during the Bølling-Allerød and during the early Holocene thermal maximum.


Stalagmite multi-proxy evidence of wet and dry intervals in northeastern Namibia: Linkage to latitudinal shifts of the Inter-Tropical Convergence Zone and changing solar activity from AD 1400 to 1950

July 2016

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167 Reads

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32 Citations

The Holocene

Multiple proxies using variation in δ¹⁸O, δ¹³C, mineralogy, and petrography in a newly generated high-resolution record of Stalagmite DP1 from Dante Cave indicate a linkage between changes in hydroclimate in northeastern Namibia and changes in solar activity and changes in global temperatures. The record suggests that during solar minima and globally cooler conditions (ca. 1660–1710 and ca. 1790–1830), wetter periods (reflecting longer summer seasons) in northeastern Namibia were linked to advances of the Inter-Tropical Convergence Zone (ITCZ) and the Inter-Ocean Convergence Zone (IOCZ) southwestward. A slight southward push of the Angola–Benguela Front (ABF) during such intervals could also be expected, bringing more rainfall inland. On the other hand, drier and warmer periods in northeastern Namibia, inferred from the increasing δ¹⁸O trend in Stalagmite DP1 after AD 1715, coincide with globally warmer conditions, and thus a northeastward migration of the ITCZ, specifically with more warming of the Northern Hemisphere (NH). This finding agrees with reducing precipitation observed in the summer rainfall zone of southern Africa since ca. 1900. Therefore, predictions of warming in high-latitude regions of the NH in the next century should suggest that the presently semi-arid climate of northern Namibia may become even drier.


An extended and higher-resolution record of climate and land use from stalagmite MC01 from Macal Chasm, Belize, revealing connections between major dry events, overall climate variability, and Maya sociopolitical changes

July 2016

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477 Reads

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60 Citations

Palaeogeography Palaeoclimatology Palaeoecology

The stalagmite MC01 was recovered from Macal Chasm cave on the Vaca Plateau of Belize in 1995, and an initial paleoclimate interpretation was published in 2007. Additional uranium-thorium ages have extended the paleoenvironmental record back from 3250 to 5250 cal yr BP, and the stable isotope (δ¹⁸O and δ¹³C) record is dramatically improved by 660 new values. A series of major dry events (MDEs) evident in stable isotopes, ultraviolet-stimulated luminescence, and petrography began ~ 3100 cal yr BP, and the initiation of these events coincides with an increase in El Niño dominance and southern shift in the Intertropical Convergence Zone. Three MDEs, centered at 1750 cal yr BP (200 CE), 1100 cal yr BP (850 CE), and 850 cal yr BP (1100 CE) and found in other regional climate records, coincide with Maya sociopolitical changes. Residuals from regression of δ¹³C versus δ¹⁸O are interpreted as a proxy for maize cultivation and land clearing, with residual values gradually increasing at the start of Preclassic Period settlement (3950 cal yr BP/2000 BCE), peaking after 2250 cal yr BP (300 BCE) during major Maya development in the Late Preclassic and Classic Periods, and dropping to pre-Preclassic values after regional land abandonment (~ 850 cal yr BP/1100 CE). Regional Maya population growth and cultural expansion may have been aided by abnormally low precipitation variability, as stable isotope variability suggests the Late Preclassic through the Late Classic was the most stable precipitation regime of the past 4000 years. This additional research on MC01 complements other regional paleoenvironmental records that suggest that MDEs coincided with disruptions in Maya society from the Preclassic through the Postclassic Periods. Although it is clear that not all significant sociopolitical changes can be attributed to the MDEs, these events likely played an antagonistic role in social stability.


The Kalahari During MIS 6-2 (190–12 ka): Archaeology, Paleoenvironment, and Population Dynamics

March 2016

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153 Reads

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28 Citations

We present a synthesis of archaeological and paleoenvironmental information for the period MIS 6-2 in the Kalahari. Discussion centers on the implications of nine new, internally consistent OSL ages obtained from White Paintings Rock Shelter. These dates provide a better understanding of the Middle Stone Age (MSA) and Late Stone Age (LSA) sequence. In addition, the revised chronology dates 11 buried soil A-horizons that were formed during wetter periods. The buried A-horizons, along with dated speleothems and high lake levels in the Kalahari correlate with Antarctic warming events (A) and North Atlantic Heinrich events (H). We also discuss the implications of the Kalahari megalake, paleolake Makgadikgadi , for human populations and compare dated changes in the archaeological sequence at WPS with dates established in Khoisan genetic evolutionary studies.


Changes in lithic technology and environment in southern continental Patagonia: The Chico and Santa Cruz River basins

January 2016

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90 Reads

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23 Citations

Quaternary International

Changes in artifact technology and environment during the Holocene are documented, within an organization of technology framework, for three different regions of Patagonia. Possible relationships between environmental changes and changes in artifact technology are explored. We examine past vegetation and geomorphic evidence of Holocene climate conditions in the three regions studied and what technologies were used during particular wetter and drier intervals. Our results suggest that many of the observed changes in technology use occurred at times of rapid climate change, particularly towards much drier conditions.



Late Holocene Stalagmite and Tufa Climate Records for Wonderwerk Cave: Relationships Between Archaeology and Climate in Southern Africa

December 2015

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427 Reads

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29 Citations

African Archaeological Review

Horizontal cores from a large stalagmite and two tufa deposits in the entrance to Wonderwerk Cave, South Africa, dated by radiocarbon methods, have provided climate proxy data on late Holocene environments near the cave. The δ18O and δ13C time series from stalagmite Core WW1–3 and tufa Core WW3 correlate well with isotope records for other sites in the summer rainfall zone of southern Africa and suggest that late Holocene warm periods in the Northern Hemisphere, including the Medieval Warm period, Roman Warm period, and Minoan Warm period, were times of increased moisture in this rainfall zone. In contrast, late Holocene cold intervals in the Northern Hemisphere, including the Dark Ages Cold period and Sub-Atlantic Cold period, were times of drier climate in the summer rainfall zone. Comparison of the Wonderwerk records with information on human settlement patterns, agricultural expansion or decline, and population growth or decline, shows that growth occurred preferentially during wetter climate periods and declines, including the abandonment of the important town of Mupungubwe in the Shashe-Limpopo area of northeast South Africa and the fall of Great Zimbabwe, which occurred during periods of low precipitation.


Citations (86)


... Techniques in which landscape features were used in hunting also occurred in the Upper Pleistocene. At the 77 ka open-air site #Gi in the Kalahari, MSA points are associated with significant quantities of zebra and extinct hartebeest teeth and this likely indicates an area where prey was ambushed at the margins of the lake (Robbins et al., 2023). A dense concentration of extinct wildebeest-like remains with butchery marks and lithics at Bovid Hill, Kenya, dating to around 70 ka, also suggests tactical hunting (Thompson et al., 2023a). ...

Reference:

The Upper Pleistocene (late Pleistocene) archaeology of sub-Saharan Africa (MSA and LSA)
Tsodilo Hills, NW Kalahari Desert, Botswana
  • Citing Chapter
  • August 2023

... Strong similarities are evident in the stable nitrogen isotope records (interpreted as a reflection of water availability) from middens recovered from Aba Huab/Austerlitz , Spitzkoppe (Chase et al., 2009(Chase et al., , 2019, Zizou (Chase et al., 2019), and Pella (Chase et al., 2019), indicating a generally common climate response signal across a 900-km transect of the Namib Desert (Fig. 1). Evidence of associated changes in vegetation, however, is often restricted to the Holocene (Scott et al., 1991(Scott et al., , 2022Scott, 1996;Gil-Romera et al., 2006, with the only indications of glacial-age vegetation coming from the continuous 50-kyr record from Pella (Lim et al., 2016), and shorter MIS 2-3 time slices from the Brandberg (Scott et al., 2004) and Mirabib (Scott et al., 2018). While each record expresses changes specific to its environmental context, evidence from all of these sites contrasts markedly with pollen records recovered from marine cores off the coast of Namibia (Shi et al., 2000(Shi et al., , 2001Urrego et al., 2015). ...

Holocene environmental change along the central Namib Desert escarpment derived from hyrax and owl dung
  • Citing Article
  • August 2022

Review of Palaeobotany and Palynology

... The flickering wet-dry events prior to major climate transitions, which seem to recur throughout the~620 kyr Chew Bahir record, combined with the HadCM3 modeling results presented here, confirm the existence of precursor events prior to a tipping point, previously predicted only in theory. data sets showing excursions at the termination and flickering during the AHP include a lake record from Lake Dendi 33 , a lake record from Lake Abiyata 34 , and a record from Congo stalagmites 35 . The discovery of flickering prior to and during the transition from wet to dry conditions in Africa has significant implications for interpreting the relationship between climate change, cultural developments, and human migrations in those regions. ...

Episodic deposition of stalagmites in the northeastern Democratic Republic of the Congo suggests Equatorial Humid Periods during insolation maxima
  • Citing Article
  • June 2022

Quaternary Science Reviews

... Presentan un frente casi vertical, muy cuarteado, con numerosos fragmentos de roca al pie y un faldeo que se prolonga suavemente hacia el centro del cañadón, desembocando en un pequeño arroyo. Se encuentra aproximadamente 40 km al oeste del extremo sur del Macizo del Deseado, donde se localizaron ocupaciones humanas discontinuas comprendidas entre la transición Pleistoceno-Holoceno y el Holoceno tardío (Brook et al. 2018;Franco et al. 2010Franco et al. , 2020, y a unos 45 km de los espacios al aire libre de 17 de Marzo (Fig. 1), en los que la ocupación humana ha sido datada en el Holoceno tardío . ...

Nueva información referida a la transición Pleistoceno-Holoceno y al Holoceno temprano en el extremo sur del Macizo del Deseado (Patagonia, Argentina)

Revista del Museo de La Plata

... There is therefore a compelling need to understand drought, and rainfall variability in general, at the Mid-to Late-Holocene transition, along with any potential association with the 4.2 ka event and societal change. This is particularly true in the tropics and southern hemisphere where there have been only a few detailed studies (Marchant and Hooghiemstra, 2004;Railsback et al., 2018Railsback et al., , 2022. In the tropics, there may be conflation of the 4.2 ka event and what is now a widely recognised shift in tropical climate at 4.0 kyr BP (Denniston et al., 2013;Gagan et al., 2004;Giosan et al., 2018;Li et al., 2018;MacDonald, 2011;Marchant and Hooghiemstra, 2004;Toth and Aronson, 2019). ...

Additional multi-proxy stalagmite evidence from Northeast Namibia supports recent models of wetter conditions during the 4.2 ka event in the Southern Hemisphere
  • Citing Article
  • November 2021

Palaeogeography Palaeoclimatology Palaeoecology

... Outcropping salt karst has been reported from the Mt. Sedom diapir in Israel (Frumkin, 1994a(Frumkin, , 1994b(Frumkin, , 1998Frumkin and Ford, 1995), the Cordillera de la Sal Mts., Atacama, Chile (De Waele et al., 2020), the Cardona diapir in Spain (Lucha et al., 2008), and the Vrancea Hills in Romania (Giurgiu, 2005). The most extensive outcropping salt karst occurs in the Zagros Mts. and along the Persian Gulf in southern and southwestern Iran (Bruthans et al., 2010;Abirifard et al., 2017). ...

Holocene evolution of halite caves in the Cordillera de la Sal (Central Atacama, Chile) in different climate conditions
  • Citing Article
  • August 2020

Geomorphology

... ka BP (Burney, 1987a(Burney, , 1987cStraka, 1996). Similar trends have been recorded almost across the entire island, for instance in the Southwest (Razanatsoa et al., 2022), and in the Northwest suggesting climate and human activities (Railsback et al., 2020;Voarintsoa et al., 2017a) as drivers. ...

Relationships between climate change, human environmental impact, and megafaunal extinction inferred from a 4000-year multi-proxy record from a stalagmite from northwestern Madagascar
  • Citing Article
  • April 2020

Quaternary Science Reviews

... No obstante, se pueden reconocer sectores con mayor abundancia de elementos cerámicos que otros. Entre éstos, cabe señalar los espacios localizados al NE costero y NW pericordillerano de la provincia de Santa Cruz, incluyendo la porción chilena, al este de la cordillera de los Andes (Cassiodoro & Tchilinguirian, 2007;Chaile et al. 2020;Cirigliano et al. 2019 y citas allí incluidas; Mena & Jackson, 1991;Roumec et al. 2020;Zilio et al. 2018; entre otros). La frecuencia de este registro es menor en los espacios localizados al sur del río Santa Cruz (Martinic & Prieto, 1998), donde sólo se identificaron elementos cerámicos en muy pocos sectores. ...

Hallazgos cerámicos y su cronología en el área comprendida entre el extremo sur del macizo del deseado y la cuenca del Río Santa Cruz (Patagonia Sur, Argentina)

Magallania (Punta Arenas)

... Early reconstructions of palaeoclimatic conditions during the Holocene in the Namib Desert and surroundings were based on microfaunal studies, geomorphological research and radiocarbon dating of inclusions in riverine deposits and dunes (e.g., Brain and Brain, 1977;Heine, 1982;Vogel and Rust, 1987;Lancaster and Teller, 1988;Vogel, 1989), followed by studies on Atlantic Ocean pollen from marine boreholes (Fig. 1), dust geochemistry, isotopes and micropalaeontology (Scott et al., 1991;Shi et al., 1998Shi et al., , 2000Shi et al., , 2001Stuut et al., 2002;Farmer et al., 2005;Dupont et al., 2008) and terrestrial records like stalagmites, geomorphology, and archaeology (e.g., Stokes et al., 1997;Stute and Talma, 1998;Brook et al., 1999Brook et al., , 2011Brook et al., , 2015Thomas and Shaw, 2002;Eitel et al., 2005;Heine, 2005;Srivastava et al., 2005;Chase et al., 2009Chase et al., , 2011Thomas and Burrough, 2012;Sletten et al., 2013;Marais et al., 2015;Railsback et al., 2016Railsback et al., , 2018Railsback et al., , 2019Voarintsoa et al., 2017;Kinahan, 2018;Schüller et al., 2018). These studies have added critical information on past hydrological regimes of southern Africa, especially rainfall ( Fig. 1), which is one of the major shifting climate features in the subcontinent. ...

Control of insolation on stalagmite growth, rainfall, and migration of the tropical rain belt in northern Namibia over the last 100 kyr, as suggested by a rare MIS 5b-5c stalagmite from Dante Cave
  • Citing Article
  • August 2019

Palaeogeography Palaeoclimatology Palaeoecology

... Testimonian la colonización temprana por Homo sapiens en regiones de diferentes continentes, como el sudeste asiático (Aubert et al., 2017;Standish et al., 2020), el norte de Australia (David et al., 2013;Ross et al., 2016), la región Franco-Cantábrica (Quiles et al., 2016) y el cono sur de Sudamérica, (Gradin et al., 1979;Carden y Miotti 2020) 1 . En su gran mayoría, estos motivos son el producto de prácticas desarrolladas por sociedades cazadoras-recolectoras, lo cual explica su larga perduración en Australia y la región patagónica, donde este modo de vida perduró hasta momentos de contacto con los europeos (Bradley et al., 2021;Brook et al., 2018;McDonald, 2005;Morwood, 2002;Mulvaney, 1996Mulvaney, , 2013. ...

Pigments, binders, and ages of rock art at Viuda Quenzana, Santa Cruz, Patagonia (Argentina)
  • Citing Article
  • October 2018

Journal of Archaeological Science Reports