Antoniades D., Giralt S., Geyer A., Álvarez-Valero A.M., Pla-Rabes S., Granados I., Liu E.J., Toro M., Smellie J.L., Oliva M. (2018) The timing and widespread effects of the largest Holocene volcanic eruption in Antarctica. Scientific Reports. 8: 0-0.EnllaçDoi: 10.1038/s41598-018-35460-x
The caldera collapse of Deception Island Volcano, Antarctica, was comparable in scale to some of the largest eruptions on Earth over the last several millennia. Despite its magnitude and potential for far-reaching environmental effects, the age of this event has never been established, with estimates ranging from the late Pleistocene to 3370 years before present. Here we analyse nearby lake sediments in which we identify a singular event produced by Deception Island’s caldera collapse that occurred 3980 ± 125 calibrated years before present. The erupted tephra record the distinct geochemical composition of ejecta from the caldera-forming eruption, whilst an extreme seismic episode is recorded by lake sediments immediately overlying the collapse tephra. The newly constrained caldera collapse is now the largest volcanic eruption confirmed in Antarctica during the Holocene. An examination of palaeorecords reveals evidence in marine and lacustrine sediments for contemporaneous seismicity around the Antarctic Peninsula; synchronous glaciochemical volcanic signatures also record the eruption in ice cores spread around Antarctica, reaching >4600 km from source. The widespread footprint suggests that this eruption would have had significant climatic and ecological effects across a vast area of the south polar region. © 2018, The Author(s).
Margalef O., Álvarez-Gómez J.A., Pla-Rabes S., Cañellas-Boltà N., Rull V., Sáez A., Geyer A., Peñuelas J., Sardans J., Giralt S. (2018) Revisiting the role of high-energy Pacific events in the environmental and cultural history of Easter Island (Rapa Nui). Geographical Journal. : 0-0.EnllaçDoi: 10.1111/geoj.12253
Pacific islands are spread over thousands of kilometres of the Pacific Basin and are characterised by similar ecological features but very diverse geologic origins, from steep volcanoes to flat coral atolls. Several climatic phases have been shared across the region within the last 1,000 years. Numerous and abrupt societal and cultural changes during the same period have been described for islands separated by thousands of kilometres. Conspicuous societal changes have been exclusively attributed to the main climatic patterns (changes in precipitation and temperature). The possible role of tsunamis and the occurrence of large volcanic eruptions as regional societal modulators, however, have traditionally received little attention from archaeologists, mainly due to the difficulty of recognising them in the sedimentary and geomorphological records. We explore the potential influence of the most important high-energy events in the Pacific on Polynesian societal changes, with a special focus on Easter Island. For example, the extreme Samalas eruption in AD 1257 may have been an indirect driver of the sudden population decline, land degradation and decreased food resources on many Pacific islands between AD 1250 and 1300, and the Kuwae eruption in AD 1450 may have triggered the synchronous end of long voyaging expeditions across the Pacific. Important palaeo-tsunamis have had unquestionable impacts on coastal and seafaring societies. A direct effect of the main eruptions of the last millennia (AD 1257 and 1453) on Easter Island has not yet been identified by any record, but we have calculated the likelihood of destructive tsunamis with an estimated period of recurrence for large events of less than a century. This insight is new and needs to be taken into account to complement what we already know about Easter Island's cultural history and archaeological sites, especially those in vulnerable coastal locations. © 2018 Royal Geographical Society (with the Institute of British Geographers).
Pla-Rabés S., Catalan J. (2018) Diatom species variation between lake habitats: implications for interpretation of paleolimnological records. Journal of Paleolimnology. 60: 169-187.EnllaçDoi: 10.1007/s10933-018-0017-0
A sample of a sediment record contains diatom species that have grown in disparate habitats and eventually accumulated in a deep part of the lake. The original habitats may differ in substrate, depth location, and availability of resources. Identifying the species characteristic of each habitat should improve our ecological and environmental interpretation of the sediment record by distinguishing habitat specific responses. With this aim, we studied the benthic diatom communities of a deep oligotrophic lake across several habitats. The main source of variation in the diatom composition was the substrate type; particularly, sediment biofilms. Depth was the second factor. The thermocline defined a shift in diatom communities that also included changes in the dominant lifeforms. A third factor was the mesoscale heterogeneity (i.e., rock sides). Although most species were present in many habitats, characteristic species were identified for all the main habitats and used for an improved interpretation of the deep sediment record. Appropriate standardization showed increasing species richness and diversity from epilimnetic epilithic samples to hypolimnetic sediment samples. We estimate that more than 5000 valve counts are required for appropriate comparisons. Consequently, in sediment records with lower counts per sample, one has to amalgamate samples—losing temporal resolution—to achieve reliable analyses of diversity changes over time. Deep sediment samples are representative of the gamma-diversity of the lake diatom metacommunity, which result from the local alpha diversity of the habitats and the beta-diversity of the variability in composition among them. This double source of diversity has to be taken into account when using the sediment record for estimating lake biodiversity changes. On the other hand, we show that an estimation of the spatial (habitat) heterogeneity of a reconstructed environmental variable can be achieved using subsets of species characteristic of each habitat. We demonstrate the procedure by reconstructing the pH fluctuations during the last 200 years in several habitats from a single sediment record. The results are coherent with the expected differences between predominantly trophogenic or tropholithic habitats. © 2018, Springer Science+Business Media B.V., part of Springer Nature.
Pérez-Rodríguez M., Margalef O., Corella J.P., Saiz-Lopez A., Pla-Rabes S., Giralt S., Cortizas A.M. (2018) The role of climate: 71 ka of atmospheric mercury deposition in the southern hemisphere recorded by Rano Aroi Mire, Easter Island (Chile). Geosciences (Switzerland). 8: 0-0.EnllaçDoi: 10.3390/geosciences8100374
The study of mercury accumulation in peat cores provides an excellent opportunity to improve the knowledge on mercury cycling and depositional processes at remote locations far from pollution sources. We analyzed mercury concentrations in 150 peat samples from two cores from Rano Aroi (Easter Island, 27◦ S) and in selected vegetation samples of present-day flora of the island, in order to characterize the mercury cycling for the last ~71 ka BP. The mercury concentrations showed values ranging between 35 and 200 ng g−1, except for a large maxima (~1000 ng g−1) which occurred at the end of the Last Glacial Maximum (LGM, ~20 ka cal BP) in both peat cores. Low temperatures during the LGM would accelerate the atmospheric oxidation of Hg(0) to divalent mercury that, coupled with higher rainfall during this period, most likely resulted in a very efficient surface deposition of atmospheric mercury. Two exceptional short-lived Hg peaks occurred during the Holocene at 8.5 (350 ng g−1) and 4.7 (1000 ng g−1) ka cal BP. These values are higher than those recorded in most peat records belonging to the industrial period, highlighting that natural factors played a significant role in Hg accumulation—sometimes even more so than anthropogenic sources. Our results suggest that wet deposition, linked to atmospheric oxidation, was the main process controlling the short-lived Hg events, both in the mire and in the catchment soils. © 2018 by the authors. Licensee MDPI, Basel, Switzerland.
Blanco, S., Pla-Rabès, S., Wetzel, C.E., Granados, I. (2017) A New Psammothidium Species (Bacillariophyta, Achnanthidiaceae) from Cimera Lake (Gredos Mountain Range), Central Spain. Cryptogamie, Algologie. 38: 17-29.EnllaçDoi: 10.7872/crya/v38.iss1.2017.17
Hernández-Almeida I., Grosjean M., Pla-Rabes S., Filipiak J., Bonk A., Tylmann W. (2017) Influence of inter-annual environmental variability on chrysophyte cyst assemblages: Insight from a 2-years sediment trap study in lakes from northern Poland. Journal of Limnology. 76: 409-423.EnllaçDoi: 10.4081/jlimnol.2017.1604
Quantitative paleonvironmental studies using transfer functions are developed from training sets. However, changes in some variables (e.g., climatic) can be difficult to identify from short-term monitoring (e.g., less than one year). Here, we present the study of the chrysophyte cyst assemblages from sediment traps deployed during two consecutive years (November 2011-November 2013) in 14 lakes from Northern Poland. The studied lakes are distributed along a W-E climatological gradient, with very different physical, chemical and morphological characteristics, and land-uses. Field surveys were carried out to recover the sediment trap material during autumn, along with the measurement of several environmental variables (nutrients, major water ions, conductivity, pH, dissolved oxygen and chlorophyll-a). During the study, one year experienced mild seasonal changes in air temperature (November 2011-November 2012; TS1), typical of oceanic climate, while the other year was characterized by colder winter and spring (November 2012-November 2013; TS2), and higher summer temperatures, more characteristic of continental climate. Other environmental variables (e.g., nutrients) did not show great changes between both years. Multivariate statistical analyses (RDA and DCA) were performed on individual TS1 and TS2 datasets. Water chemistry and nutrients (pH, TN and TP) explained the largest portion of the variance of the chrysophyte data for the individual years. However, analyses of the combined TS1 and TS2 datasets show that strong changes between summer and autumn (warm period, ice-free period with thermal stratification) and winter and spring (cold period, ice-cover period) play the most important role in the inter-annual variability in the chrysophyte assemblages. We show how inter-annual sampling maximizes ecological gradients of interest, particularly in regions with large environmental diversity, and low climatic variability. This methodology could help to identify distinct seasonal and inter-annual changes of biological communities to improve its application in paleoclimate studies. © 2017, Page Press Publications All rights reserved.
Peñuelas, J., Sardans, J., Filella, I., Estiarte, M., Llusià, J., Ogaya, R., Carnicer, J., Bartrons, M., Rivas-Ubach, A., Grau, O., Peguero, G., Margalef, O., Pla-Rabés, S., Stefanescu, C., Asensio, D., Preece, C., Liu, L., Verger, A., Barbeta, A., Achotegui-Castells, A., Gargallo-Garriga, A., Sperlich, D., Farré-Armengol, G., Fernández-Martínez, M., Liu, D., Zhang, C., Urbina, I., Camino-Serrano, M., Vives-Ingla, M., Stocker, B.D., Balzarolo, M., Guerrieri, R., Peaucelle, M., Marañón-Jiménez, S., Bórnez-Mejías, K., Mu, Z., Descals, A., Castellanos, A., Terradas, J. (2017) Impacts of global change on Mediterranean forests and their services. Forests. 8: 0-0.EnllaçDoi: 10.3390/f8120463
Cañellas-Boltà N., Rull V., Sáez A., Margalef O., Pla-Rabes S., Valero-Garcés B., Giralt S. (2016) Vegetation dynamics at Raraku Lake catchment (Easter Island) during the past 34,000years. Palaeogeography, Palaeoclimatology, Palaeoecology. 446: 55-69.EnllaçDoi: 10.1016/j.palaeo.2016.01.019
Easter Island is a paradigmatic example of human impact on ecosystems. The role of climate changes in recent vegetation shifts has commonly been rejected without proper assessment. A palynological study of a long sediment core from Raraku Lake documents the vegetation dynamics for the last 34 ka and investigates their driving forces, particularly the effects of climate variability on vegetation changes. Significant relationships between pollen assemblage changes and sedimentary and geochemical proxies demonstrate the rapid response of vegetation to lake crater basin hydrology and climatic changes. The lake surroundings were occupied by an open mixed palm grove during the Last Glacial period. Poaceae and Sophora increased at the expense of palms and Triumfetta, and Coprosma practically disappeared, in response to slightly wetter and/or colder climate during the Last Glacial Maximum. Palms and Triumfetta thrived in a warmer and/or drier climate during the deglaciation. Minor vegetation changes (a slight increase in Sophora and a drop in Asteraceae and Poaceae) occurred between 13.2 and 11.8 cal. ka BP and can be related to rapid changes in the Younger Dryas chronozone. The increase in herbaceous taxa indicates a gradual shallowing of the lake and development of a mire during the Holocene, caused by sediment infilling and warmer and drier climate. Relatively rapid vegetation changes in the Holocene were caused by climate and by plant succession on the expanding mire. The rates of vegetation change observed in the mire were similar to those at the initial stages of human impact identified in a previous study. These results reveal significant vegetation changes prior to human presence, due to the interplay of climate variations (temperature and moisture), changes in lake basin form by infilling and intrinsic dynamics of plant succession. Hence, the potential contribution of these factors in vegetation shifts during the period of human presence should not be neglected. © 2016 Elsevier B.V.
Oliva M., Antoniades D., Giralt S., Granados I., Pla-Rabes S., Toro M., Liu E.J., Sanjurjo J., Vieira G. (2016) The Holocene deglaciation of the Byers Peninsula (Livingston Island, Antarctica) based on the dating of lake sedimentary records. Geomorphology. 261: 89-102.EnllaçDoi: 10.1016/j.geomorph.2016.02.029
The process of deglaciation in the Antarctic Peninsula region has large implications for the geomorphological and ecological dynamics of the ice-free environments. However, uncertainties still remain regarding the age of deglaciation in many coastal environments, as is the case in the South Shetland Islands. This study focuses on the Byers Peninsula, the largest ice-free area in this archipelago and the one with greatest biodiversity in Antarctica. A complete lacustrine sedimentary sequence was collected from five lakes distributed along a transect from the western coast to the Rotch Dome glacier front: Limnopolar, Chester, Escondido, Cerro Negro and Domo lakes. A multiple dating approach based on 14C, thermoluminescence and tephrochronology was applied to the cores in order to infer the Holocene environmental history and identify the deglaciation chronology in the Byers Peninsula. The onset of the deglaciation started during the Early Holocene in the western fringe of the Byers Peninsula according to the basal dating of Limnopolar Lake (ca. 8.3 cal. ky BP). Glacial retreat gradually exposed the highest parts of the Cerro Negro nunatak in the SE corner of Byers, where Cerro Negro Lake is located; this lake was glacier-free since at least 7.5 ky. During the Mid-Holocene the retreat of the Rotch Dome glacier cleared the central part of the Byers plateau of ice, and Escondido and Chester lakes formed at 6 cal. ky BP and 5.9 ky, respectively. The dating of the basal sediments of Domo Lake suggests that the deglaciation of the current ice-free easternmost part of the Byers Peninsula occurred before 1.8 cal. ky BP. © 2016 Elsevier B.V.
Peñuelas, J., Sardans, J., Filella, I., Estiarte, M., Llusià, J., Ogaya, R., Carnicer, J., Bartrons, M., Rivas-Ubach, A., Grau, O., Peguero, G., Margalef, O., Pla-Rabés, S., Stefanescu, C., Asensio, D., Preece, C., Liu, L., Verger, A., Rico, L., Barbeta, A., Achotegui-Castells, A., Gargallo-Garriga, A., Sperlich, D., Farré-Armengol, G., Fernández-Martínez, M., Liu, D., Zhang, C., Urbina, I., Camino, M., Vives, M., Nadal-Sala, D., Sabaté, S., Gracia, C., Terradas, J. (2016) Assessment of the impacts of climate change on Mediterranean terrestrial ecosystems based on data from field experiments and long-term monitored field gradients in Catalonia. Environmental and Experimental Botany. : 0-0.EnllaçDoi: 10.1016/j.envexpbot.2017.05.012
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