Papers by Alejandra Restrepo
Ecology, 2012
A high-resolution (2-9 year sampling interval) fossil pollen record from the Galápagos Islands, w... more A high-resolution (2-9 year sampling interval) fossil pollen record from the Galápagos Islands, which spans the last 2690 years, reveals considerable ecosystem stability. Vegetation changes associated with independently derived histories of El Niño Southern Oscillation variability provided evidence of shifts in the relative abundance of individual species rather than immigration or extinction. Droughts associated with the Medieval Climate Anomaly induced rapid ecological change that was followed by a reversion to the previous state. The paleoecological data suggested nonneutral responses to climatic forcing in this ecosystem prior to the period of human influence. Human impacts on the islands are evident in the record. A marked decline in long-term codominants of the pollen record, Alternanthera and Acalypha, produced a flora without modern analogue before 1930. Intensified animal husbandry after ca. 1930 may have induced the local extinction of Acalypha and Alternanthera. Reductions in populations of grazing animals in the 1970s and 1980s did not result in the return of the native flora, but in invasions by exotic species. After ca. 1970 the trajectory of habitat change accelerated, continuously moving the ecosystem away from the observed range of variability in the previous 2690 years toward a novel ecosystem. The last 40 years of the record also suggest unprecedented transport of lowland pollen to the uplands, consistent with intensified convection and warmer wet seasons.
A table of corresponding age (AD/BC) for each of the depths sampled.
Boletín de Antropología, 2010
Proyecto académico sin fines de lucro, desarrollado bajo la iniciativa de acceso abierto
Japanese Journal of Palynology
Todo o conteúdo deste livro está licenciado sob uma Licença de Atribuição Creative Commons. Atrib... more Todo o conteúdo deste livro está licenciado sob uma Licença de Atribuição Creative Commons. Atribuição 4.0 Internacional (CC BY 4.0). O conteúdo dos artigos e seus dados em sua forma, correção e confiabilidade são de responsabilidade exclusiva dos autores. Permitido o download da obra e o compartilhamento desde que sejam atribuídos créditos aos autores, mas sem a possibilidade de alterá-la de nenhuma forma ou utilizá-la para fins comerciais.
The Galapagos Islands provided one of the first lowland paleoecological records from the Neotropi... more The Galapagos Islands provided one of the first lowland paleoecological records from the Neotropics. Since the first cores were raised from the islands in 1966, there has been a substantial increase in knowledge of past systems, and development of the science of paleoclimatology. The study of fossil pollen, diatoms, corals and compound-specific isotopes on the Galapagos has contributed to the maturation of this discipline. As research has moved from questions about ice-age conditions and mean states of the Holocene to past frequency of El Niño Southern Oscillation, the resolution of fossil records has shifted from millennial to sub-decadal. Understanding the vulnerability of the Galapagos to climate change will be enhanced by knowledge of past climate change and responses in the islands. RESUMEN Cuarenta años de paleoecología en las Galápagos. Las Islas Galápagos proporcionaron uno de los primeros registros paleoecológicos de tierras bajas en los Neotrópicos. Desde que las primeras muestras sedimentarias fueron levantadas en las islas en 1966, ha habido un incremento sustancial en el conocimiento de los sistemas del pasado, y en el desarrollo de la ciencia de paleoclimatología. El estudio en las Galápagos de los fósiles de polen, diatomeas y corales, y de los isótopos de componentes específicos ha contribuido a la maduración de esta disciplina. A medida que la investigación ha trascendido desde las preguntas sobre condiciones en la era glacial y estados promedio del Holoceno, hacia la frecuencia pasada de El Niño Oscilación del Sur, la resolución de los registros fósiles se ha refinado desde milenial a sub-decadal. La comprensión de la vulnerabilidad de las Galápagos al cambio climático mejorará con el conocimiento de pasados cambios y respuestas climáticos en las islas.
The total number of taxa found in the El Junco crater lake pollen record, 105 pollen and spores t... more The total number of taxa found in the El Junco crater lake pollen record, 105 pollen and spores types.
The Galapagos Islands provided one of the first lowland paleoecological records from the Neotropi... more The Galapagos Islands provided one of the first lowland paleoecological records from the Neotropics. Since the first cores were raised from the islands in 1966, there has been a substantial increase in knowledge of past systems, and development of the science of paleoclimatology. The study of fossil pollen, diatoms, corals and compound-specific isotopes on the Galapagos has contributed to the maturation of this discipline. As research has moved from questions about ice-age conditions and mean states of the Holocene to past frequency of El Niño Southern Oscillation, the resolution of fossil records has shifted from millennial to sub-decadal. Understanding the vulnerability of the Galapagos to climate change will be enhanced by knowledge of past climate change and responses in the islands.
Nature Geoscience, 2009
Oscillation system, climate variability in the tropical Pacific Ocean influences climate across m... more Oscillation system, climate variability in the tropical Pacific Ocean influences climate across much of the planet. But the history of temperature change in the tropical Pacific Ocean during recent millennia is poorly known: the available annually resolved records 1,2 are discontinuous and rarely span more than a few centuries. Longer records at coarser temporal resolution suggest that significant oceanographic changes, observed at multi-year to multi-century resolution, have had important effects on global climate 3-5 . Here we use a diatom record from El Junco Lake, Galápagos, to produce a calibrated, continuous record of sea surface temperature in the eastern tropical Pacific Ocean at subdecadal resolution, spanning the past 1,200 years. Our reconstruction reveals that the most recent 50 years are the warmest 50-year period within the record. Because our diatom-based sea surface temperature index resembles Northern Hemisphere temperature reconstructions, we suggest that with continued anthropogenic warming, the eastern tropical Pacific Ocean may continue to warm.
Ecological information derived from pollen analysis
in archeological excavations: constrains and ... more Ecological information derived from pollen analysis
in archeological excavations: constrains and potential
article in Spanish
Abstract. Palaeo - environmental studies have relied on pollen analysis given the amount of ecological and climatic information that this proxy brings out. However, it is primordial to distinguish the settings from which the reconstructions are carried out. Pollen analyses (sensu stricto) are relevant de- pending on the context in which the information is interpreted. This paper assesses pollen information in the context of archaeological excavations done in the southern area of Antioquia (Colombia), Neotropical palaeo-environmental reconstructions over the Holocene are used for comparisons.
Keywords: archaeology, phytoliths, pollen, micro remains, soils, sediments.
An ecological system that had been resilient to climatic change for thousands of years was transf... more An ecological system that had been resilient to climatic change for thousands of years was transformed in decades by the introduction of livestock to the Galapagos. Habitat restoration at El Junco, San Cristobal Island, has included the exclusion of cattle, removal of exotic species, and replanting with the endemic shrub, Miconia robinsoniana. M. robinsoniana was known to form a characteristic zone of near mono-dominant shrub cover at equivalent elevations on other islands. Analysis of modern and fossil pollen data from El Junco Crater Lake showed that two of the most common shrubs of the San Cristo ́bal uplands, Acalypha and Alternanthera, were the most common pollen types for more than two thousand years. In the 1930s, 30 years before the first scientific description of that habitat, the abundance of both taxa declined rapidly as live stock densities increased. The restoration target, based on the assumption that mono dominance by M. robinsoniana is the natural state, reflects a shifted baseline. Acalypha and Alternanthera should be considered for inclusion within future restoration efforts.
Abstract. A high-resolution (2–9 year sampling interval) fossil pollen record from the Gala ́ pag... more Abstract. A high-resolution (2–9 year sampling interval) fossil pollen record from the Gala ́ pagos Islands, which spans the last 2690 years, reveals considerable ecosystem stability. Vegetation changes associated with independently derived histories of El Nin ̃o Southern Oscillation variability provided evidence of shifts in the relative abundance of individual species rather than immigration or extinction. Droughts associated with the Medieval Climate Anomaly induced rapid ecological change that was followed by a reversion to the previous state. The paleoecological data suggested nonneutral responses to climatic forcing in this ecosystem prior to the period of human influence.
Human impacts on the islands are evident in the record. A marked decline in long-term codominants of the pollen record, Alternanthera and Acalypha, produced a flora without modern analogue before 1930. Intensified animal husbandry after ca. 1930 may have induced the local extinction of Acalypha and Alternanthera. Reductions in populations of grazing animals in the 1970s and 1980s did not result in the return of the native flora, but in invasions by exotic species. After ca. 1970 the trajectory of habitat change accelerated, continuously moving the ecosystem away from the observed range of variability in the previous 2690 years toward a novel ecosystem. The last 40 years of the record also suggest unprecedented transport of lowland pollen to the uplands, consistent with intensified convection and warmer wet seasons.
Conference Presentations by Alejandra Restrepo
We present preliminary results from a high-resolution palynological reconstruction from an entire... more We present preliminary results from a high-resolution palynological reconstruction from an entire Neogene sequence of sediments retrieved in Northern Venezuela. In a paleoenvionmental context, the Negeone is a period of special relevance because it includes the configuration of major mountain chains and the origin of modern ocean currents with and the subsequent establishment of current climate regimes (Zachos et al 2001, Potter and Szatmari 2009, Pound et al 2011). In the Neotropics, the uplift and closure of Central America Seaway (CAS) during the Neogene played an essential role in the Great American Biotic Interchange (Webb 2006). The uplifting of CAS has also implications on the transition towards current salinity concentrations in the Caribbean, which along with climatic gradients, leaded into the strengthening of the Atlantic Meridional Overturning Circulation and modern climate regimes (Molnar 2008; Sepulcre 2010, 2014).
The importance of the nine kilometers of sequence sediments from the Urumaco trough in Northern Venezuela resides on its time continuity. Isolated from the central region of Venezuela by the Merida Andes since the Eocene (Escalona and Mann 2006), the Urumaco region has undergone fluctuations from deltaic - marine environments to a fluvial – continental dominated system (Smith et al 2010, Quiroz and Jaramillo 2010).
The complexity of the tectonism in the Caribbean basin, intermittent marine transgressions, and the arid climatic conditions, have shaped the environmental conditions for the deposition of sediments in the Falcón basin (Fig. 2) (Kellogg 1984, Audemard 2002, Smith et al 2010, Quiroz and Jaramillo 2010). The characteristic aridity of the region is due to the influence of the Caribbean low level jet with minimal seasonal variations associated with the Intertropical Convergence Zone (ITCZ) (Peterson et al 2002).
GSA 2014 POSTER
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Papers by Alejandra Restrepo
in archeological excavations: constrains and potential
article in Spanish
Abstract. Palaeo - environmental studies have relied on pollen analysis given the amount of ecological and climatic information that this proxy brings out. However, it is primordial to distinguish the settings from which the reconstructions are carried out. Pollen analyses (sensu stricto) are relevant de- pending on the context in which the information is interpreted. This paper assesses pollen information in the context of archaeological excavations done in the southern area of Antioquia (Colombia), Neotropical palaeo-environmental reconstructions over the Holocene are used for comparisons.
Keywords: archaeology, phytoliths, pollen, micro remains, soils, sediments.
Human impacts on the islands are evident in the record. A marked decline in long-term codominants of the pollen record, Alternanthera and Acalypha, produced a flora without modern analogue before 1930. Intensified animal husbandry after ca. 1930 may have induced the local extinction of Acalypha and Alternanthera. Reductions in populations of grazing animals in the 1970s and 1980s did not result in the return of the native flora, but in invasions by exotic species. After ca. 1970 the trajectory of habitat change accelerated, continuously moving the ecosystem away from the observed range of variability in the previous 2690 years toward a novel ecosystem. The last 40 years of the record also suggest unprecedented transport of lowland pollen to the uplands, consistent with intensified convection and warmer wet seasons.
Conference Presentations by Alejandra Restrepo
The importance of the nine kilometers of sequence sediments from the Urumaco trough in Northern Venezuela resides on its time continuity. Isolated from the central region of Venezuela by the Merida Andes since the Eocene (Escalona and Mann 2006), the Urumaco region has undergone fluctuations from deltaic - marine environments to a fluvial – continental dominated system (Smith et al 2010, Quiroz and Jaramillo 2010).
The complexity of the tectonism in the Caribbean basin, intermittent marine transgressions, and the arid climatic conditions, have shaped the environmental conditions for the deposition of sediments in the Falcón basin (Fig. 2) (Kellogg 1984, Audemard 2002, Smith et al 2010, Quiroz and Jaramillo 2010). The characteristic aridity of the region is due to the influence of the Caribbean low level jet with minimal seasonal variations associated with the Intertropical Convergence Zone (ITCZ) (Peterson et al 2002).
GSA 2014 POSTER
in archeological excavations: constrains and potential
article in Spanish
Abstract. Palaeo - environmental studies have relied on pollen analysis given the amount of ecological and climatic information that this proxy brings out. However, it is primordial to distinguish the settings from which the reconstructions are carried out. Pollen analyses (sensu stricto) are relevant de- pending on the context in which the information is interpreted. This paper assesses pollen information in the context of archaeological excavations done in the southern area of Antioquia (Colombia), Neotropical palaeo-environmental reconstructions over the Holocene are used for comparisons.
Keywords: archaeology, phytoliths, pollen, micro remains, soils, sediments.
Human impacts on the islands are evident in the record. A marked decline in long-term codominants of the pollen record, Alternanthera and Acalypha, produced a flora without modern analogue before 1930. Intensified animal husbandry after ca. 1930 may have induced the local extinction of Acalypha and Alternanthera. Reductions in populations of grazing animals in the 1970s and 1980s did not result in the return of the native flora, but in invasions by exotic species. After ca. 1970 the trajectory of habitat change accelerated, continuously moving the ecosystem away from the observed range of variability in the previous 2690 years toward a novel ecosystem. The last 40 years of the record also suggest unprecedented transport of lowland pollen to the uplands, consistent with intensified convection and warmer wet seasons.
The importance of the nine kilometers of sequence sediments from the Urumaco trough in Northern Venezuela resides on its time continuity. Isolated from the central region of Venezuela by the Merida Andes since the Eocene (Escalona and Mann 2006), the Urumaco region has undergone fluctuations from deltaic - marine environments to a fluvial – continental dominated system (Smith et al 2010, Quiroz and Jaramillo 2010).
The complexity of the tectonism in the Caribbean basin, intermittent marine transgressions, and the arid climatic conditions, have shaped the environmental conditions for the deposition of sediments in the Falcón basin (Fig. 2) (Kellogg 1984, Audemard 2002, Smith et al 2010, Quiroz and Jaramillo 2010). The characteristic aridity of the region is due to the influence of the Caribbean low level jet with minimal seasonal variations associated with the Intertropical Convergence Zone (ITCZ) (Peterson et al 2002).
GSA 2014 POSTER