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2 resultados encontrados para: AUTOR: Veer, Ron van 't
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1.
Artículo
*En hemeroteca, SIBE-Chetumal
Climatic change during the Younger Dryas chron in northern South America: a test of the evidence
Veer, Ron van 'T ; Islebe, Gerald A. (coaut.) ; Hooghiemstra, Henry (coaut.) ;
Contenido en: Quaternary Science Reviews Vol. 19, no. 17-18 (December 2000), p. 1821-1835 ISSN: 0277-3791
Nota: En hemeroteca, SIBE-Chetumal
Resumen en: Inglés |
Resumen en inglés

New AMS and palynological data are presented from the Colombian Andes to assess vegetational and climatic change during the Lateglacial–Holocene transition, with special emphasis on the Younger Dryas (YD) chronozone. The new evidence is compared and discussed with other Colombian cores and with data from other countries in the region. The Lateglacial climatic reversal in Colombia, known as the El Abra stadial, has an estimated lower boundary of 11,200 (conventional) and 10,900 (interpolated) 14C yr BP, respectively. Although the El Abra stadial is assumed to be the equivalent of the European YD, the present data suggest that the El Abra stadial is a biostratigraphical signal representing both the YD chronozone and the earliest Holocene (11,000–9000 14C yr BP). On the basis of new AMS dates and a re-evaluation of the pollen zones, we divided the Colombian El Abra biozone into two phases. From ca. 11,000 to ca. 10,500 14C yr BP there is a sharp increase of subparamo and paramo pollen, reflecting a relatively cool phase during the YD chronozone (zone Y1). After ca. 10,500 14C yr BP, a slight increase of arboreal pollen and the presence of Cactaceae (zone Z1) point toward a relatively milder but drier phase extending to ca. 9000 14C yr BP in the earliest Holocene.

Our conclusions add detail to the concept of astronomical forcing of contrasting rainfall changes in northern South America between 12,400 and 8800 14C yr BP. We propose an environmental drought during the El Abra biozone, with subsequent erosion of the sediments deposited during that period, as a major factor explaining the poor presence of YD evidence in northern South America. We conclude that at hydrologically sensitive sites without a clear lithological change around 11,000–9000 14C yr BP, a hiatus during the YD chronozone can only be detected if other cores are available with bracketed time control. We state that the start of the temperature decline in Central America and northern South America is related to the global YD cooling event. However, much work is still required to understand the duration and amplitude of the climatic reversal during the YD chronozone in this part of the globe.


2.
- Artículo con arbitraje
*Solicítelo con su bibliotecario/a
Holocene vegetation and water level history in two bogs of the Cordillera de Talamanca, Costa Rica
Islebe, Gerald A. ; Hooghiemstra, Henry (coaut.) ; Veer, Ron van 't (coaut.) ;
Contenido en: Vegetatio Vol. 124, no. 2 (Jun. 1996), p. 155-171 ISSN: 1948-1996
Nota: Solicítelo con su bibliotecario/a
Resumen en: Inglés |
Resumen en inglés

Pollen records of Holocene sediment cores from the Costa Rican Cordillera de Talamanca (La Chonta bog, 2310 m and La Trinidad bog, 2700 m) show the postglacial development of the montane oak forest zone from ca. 9500 to 1500 yr BP. During the early Holocene (ca. 9500-7000 yr BP), alder vegetation covered the La Chonta and La Trinidad bogs and their adjacent hills. The upper forest line is inferred to be at 2800-3000 m elevation. A Podocarpus-Quercus forest characterised the middle Holocene (ca. 70(0)°4500 yr BP). The upper forest line is located at >3000 m reaching the present-day altitudinal distribution. A Quercus forest characterised the late Holocene (ca. 4500-1500 yr BP). Compared to modern conditions, the early Holocene has similar average temperatures, but the moisture level was probably higher. Pollen evidence for the late Holocene indicates drier environmental conditions than today. In order to improve the paleoecological interpretation, we described the local vegetation and used moss samples as pollen traps at both montane bogs along strong soil moisture gradients.