Seasonal patterns of pollen sedimentation in Lake Montcortès (Central Pyrenees) and potential applications to high-resolution paleoecology: a 2-year pilot study

14 páginas, 2 tablas, 10 figuras.Lakes with varved sediments are especially well suited for paleoecological study, from annual to even seasonal resolution. The interpretative power of such high-resolution paleoenvironmental reconstructions relies on the availability of modern analogs with the same temporal resolution. We studied seasonal pollen sedimentation in varved Lake Montcorte`s, Central Pyrenees (Spain), as a modern analog for highresolution reconstruction of Late Holocene vegetation and landscape dynamics. Seasonal samples were obtained from sediment traps that were submerged near the maximum water depth for a 2-year period (fall 2013 to fall 2015). Seasonal pollen sedimentation was compared with meteorological variables from a nearby weather station. Bulk pollen sedimentation, dominated by Pinus (pine) and Quercus (oak), followed a clear seasonal pattern that peaked during the spring/summer, coinciding with maximum temperature and precipitation, minimum relative humidity and moderate winds from the SSE. Pollen sedimentation lags (PSL) were observed formost pollen types, as substantial amounts of pollen were found in the traps outside of their respective flowering seasons. Two pollen assemblages were clearly differentiated by their taxonomic composition, corresponding to spring/summer and fall/winter. This pattern is consistent with existing interpretation of the sediment varves, specifically, that varves are formed by two-layer couplets that represent the same seasonality as pollen. We concluded that pollen sedimentation in Lake Montcorte`s exhibits a strong seasonal signal in the quantity of pollen, the taxonomic composition of the pollen assembalges, and relationships between the pollen and meteorological variables. Thus, varved sediments provide a potentially powerful tool for paleoecological reconstruction at seasonal resolution. This method could be used not only to identify paleoenvironmental trends, but also to identify annual layers and therefore date sediments, even in the absence of evident sediment laminations. A satisfactory explanation of PSL will require further studies that examine internal lake dynamics and pollen production/dispersal patterns.This work was funded by the Ministry of Economy and Competitivity (project MONT-500; reference CGL2012-33665; PI: Teresa Vegas-Vilarru´bia).Peer reviewe

Seasonal patterns of pollen sedimentation in Lake Montcortès (Central Pyrenees) and potential applications to high-resolution paleoecology: a two-year pilot study.

Lakes with varved sediments are especially well suited for paleoecological study, from annual to even seasonal resolution. The interpretative power of such high-resolution paleoenvironmental reconstructions relies on the availability of modern analogs with the same temporal resolution. We studied seasonal pollen sedimentation in varved Lake Montcorte`s, Central Pyrenees (Spain), as a modern analog for highresolution reconstruction of Late Holocene vegetation and landscape dynamics. Seasonal samples were obtained from sediment traps that were submerged near the maximum water depth for a 2-year period (fall 2013 to fall 2015). Seasonal pollen sedimentation was compared with meteorological variables from a nearby weather station. Bulk pollen sedimentation, dominated by Pinus (pine) and Quercus (oak), followed a clear seasonal pattern that peaked during the spring/summer, coinciding with maximum temperature and precipitation, minimum relative humidity and moderate winds from the SSE. Pollen sedimentation lags (PSL) were observed for most pollen types, as substantial amounts of pollen were found in the traps outside of their respective flowering seasons. Two pollen assemblages were clearly differentiated by their taxonomic composition, corresponding to spring/summer and fall/winter. This pattern is consistent with existing interpretation of the sediment varves, specifically, that varves are formed by two-layer couplets that represent the same seasonality as pollen. We concluded that pollen sedimentation in Lake Montcorte`s exhibits a strong seasonal signal in the quantity of pollen, the taxonomic composition of the pollen assembalges, and relationships between the pollen and meteorological variables. Thus, varved sediments provide a potentially powerful tool for paleoecological reconstruction at seasonal resolution. This method could be used not only to identify paleoenvironmental trends, but also to identify annual layers and therefore date sediments, even in the absence of evident sediment laminations. A satisfactory explanation of PSL will require further studies that examine internal lake dynamics and pollen production/dispersal patterns

Ecology of the collapse of Rapa Nui society

Collapses of food producer societies are recurrent events in prehistory and have triggered a growing concern for identifying the underlying causes of convergences/divergences across cultures around the world. One of the most studied and used as a paradigmatic case is the population collapse of the Rapa Nui society. Here, we test different hypotheses about it by developing explicit population dynamic models that integrate feedbacks between climatic, demographic and ecological factors that underpinned the sociocultural trajectory of these people. We evaluate our model outputs against a reconstruction of past population size based on archaeological radiocarbon dates from the island. The resulting estimated demographic declines of the Rapa Nui people are linked to the long-term effects of climate change on the island's carrying capacity and, in turn, on the 'per-capita food supply'

Vegetación y paisaje alrededor del lago de Montcortès (Prepirineos catalanes) como instrumento para el estudio paleoecológico de los sedimentos lacustres

15 p., gráf., fot.[EN]Lake Montcortès (42º 19′ N, 0º 59′ E; 1027 m elevation) is an excellent target for high resolution palaeoecological studies because its annually-laminated sediments extending back to the early-middle Holocene. The detailed knowledge of present vegetation patterns around the lake and the pollen they release to lake sediments is essential for a reliable interpretation of past vegetation dynamics. This study aims to identify and map the vegetation types currently growing around the lake. For this purpose, a quadrangular area of ca. 48 ha was defined. The floristic study resulted in a catalogue of 534 species. Vegetation analysis was based on 42 phytosociological inventories used to synthesise and map the relevant plant landscape units. As a result, we obtained 52 vegetation units as expressions of the CORINE habitats previously defined for Catalonia. Each of these habitats was described in floristic, physiognomic, phytogeographic, environmental and human-use terms. The next step will be the palynological study of the more representative species of the described vegetation types, as a means to optimise future palynological interpretations.[ES]El lago de Montcortès (42º 19′ N, 0º 59′ E; 1027 m altitud) posee sedimentos con laminaciones anuales, ideales para estudios paleoecológicos de alta resolución. Para el análisis palinológico de estos sedimentos, es necesario conocer en detalle la vegetación local, como fuente del polen sedimentario. El objetivo de este estudio es reconocer y cartografiar los tipos de vegetación presentes alrededor del lago, para lo cual se delimitó un área rectangular de unas 48 ha. Del estudio florístico de este espacio resultó un catálogo de 534 especies, que sirvió de base para el análisis de vegetación. Para ello, se llevaron a cabo 42 inventarios fitosociológicos, que se utilizaron para elaborar una síntesis del paisaje vegetal mediante cartografía digital. Como resultado, se obtuvieron 52 unidades de vegetación, expresión concreta de los hábitats CORINE definidos en la lista de los hábitats de Cataluña. Cada una de estas unidades se describió con criterios florísticos, fisionómicos, fitogeográficos, ambientales y de uso humano. La siguiente etapa consistirá en el estudio palinológico de las especies más representativas de los tipos de vegetación y hábitats establecidos aquí, con el fin de optimizar las interpretaciones paleoecológicas futurasThis research is supported by projects POLMONT (V. Rull and J. Vigo, responsible investigators), funded by the Institut d’Estudis Catalans (IEC), and MONTCORTÈS-500 (CGL2012-33665; T. Vegas-Vilarrúbia, responsible investigator), funded by the Spain’s Ministry of Economy and Competitiveness. The study is sponsored by the Ajuntament del Baix Pallars, at Gerri de la Sal.Peer reviewe

First records and potential palaeoecological significance of Dianella (Xanthorrhoeaceae), an extinct representative of the native flora of Rapa Nui (Easter Island).

Easter Island, a remote island in the Pacific Ocean, is currently primarily covered by grasslands, but palaeoecological studies have shown the former presence of different vegetation. Much of its original biota has been removed during the last two millennia, most likely by human activities, and little is known about the native flora.Macrofossil and pollen analyses of a sediment core from the Raraku crater lake have revealed the occurrence of a plant that is currently extinct from the island: Dianella cf. intermedia/adenanthera (Xanthorrhoeaceae), which grew and disappeared at the Raraku site long before human arrival. The occurrence of Dianella within the Raraku sedimentary sequence (between 9.4 and 5.4 cal. kyr B.P.) could have been linked to the existence of favorable palaeoenvironmental conditions (peatland rather than the present-day lacustrine environment) during the early to mid Holocene. This finding contributes new knowledge about indigenous plant diversity on Easter Island and reinforces the usefulness of further macrofossil and pollen analyses to identify native species on Easter Island and elsewhere

Seasonal patterns of pollen sedimentation in Lake Montcortès (Central Pyrenees) and potential applications to high-resolution paleoecology: a two-year pilot study.

Lakes with varved sediments are especially well suited for paleoecological study, from annual to even seasonal resolution. The interpretative power of such high-resolution paleoenvironmental reconstructions relies on the availability of modern analogs with the same temporal resolution. We studied seasonal pollen sedimentation in varved Lake Montcorte`s, Central Pyrenees (Spain), as a modern analog for highresolution reconstruction of Late Holocene vegetation and landscape dynamics. Seasonal samples were obtained from sediment traps that were submerged near the maximum water depth for a 2-year period (fall 2013 to fall 2015). Seasonal pollen sedimentation was compared with meteorological variables from a nearby weather station. Bulk pollen sedimentation, dominated by Pinus (pine) and Quercus (oak), followed a clear seasonal pattern that peaked during the spring/summer, coinciding with maximum temperature and precipitation, minimum relative humidity and moderate winds from the SSE. Pollen sedimentation lags (PSL) were observed for most pollen types, as substantial amounts of pollen were found in the traps outside of their respective flowering seasons. Two pollen assemblages were clearly differentiated by their taxonomic composition, corresponding to spring/summer and fall/winter. This pattern is consistent with existing interpretation of the sediment varves, specifically, that varves are formed by two-layer couplets that represent the same seasonality as pollen. We concluded that pollen sedimentation in Lake Montcorte`s exhibits a strong seasonal signal in the quantity of pollen, the taxonomic composition of the pollen assembalges, and relationships between the pollen and meteorological variables. Thus, varved sediments provide a potentially powerful tool for paleoecological reconstruction at seasonal resolution. This method could be used not only to identify paleoenvironmental trends, but also to identify annual layers and therefore date sediments, even in the absence of evident sediment laminations. A satisfactory explanation of PSL will require further studies that examine internal lake dynamics and pollen production/dispersal patterns

Ecology of the collapse of Rapa Nui society: Population collapse of Rapa Nui society

Collapses of food producer societies are recurrent events in prehistory and have triggered a growing concern for identifying the underlying causes of convergences/divergences across cultures around the world. One of the most studied and used as a paradigmatic case is the population collapse of the Rapa Nui society. Here, we test different hypotheses about it by developing explicit population dynamic models that integrate feedbacks between climatic, demographic and ecological factors that underpinned the socio-cultural trajectory of these people. We evaluate our model outputs against a reconstruction of past population size based on archaeological radiocarbon dates from the island. The resulting estimated demographic declines of the Rapa Nui people are linked to the long-term effects of climate change on the island's carrying capacity and, in turn, on the 'per-capita food supply'.Data accessibility. The data is available from the Dryad Digital Repository: https://doi.org/10.5061/dryad.bk3j9kd7j [69]. Authors’ contributions. Conceptualization: M.L., E.M.G., S.A.E., C.L. and N.C.S. Data curation: E.M.G., N.C.-B., O.M., S.G., A.S. and S.P.-R. Formal analysis: M.L., S.A.E. and E.M.G. Investigation: M.L., E.M.G., S.A.E., C.L., C.M.S., N.C.-B., O.M., S.G., A.S., S.P.-R. and N.C.S. Methodology: M.L., S.A.E., N.C.-B. and E.M.G. Validation: M.L., E.M.G. and S.A.E. Visualization: M.L. and S.A.E. Writing— original draft: M.L., E.M.G., S.A.E., C.L., C.M.S. and N.C.S. Writing—review and editing: M.L., E.M.G., S.A.E., C.L., S.G., A.S., O.M. and S.P.-R. Competing interests. We declare we have no competing interests. Funding. M.L., E.M.G. and S.A.E. acknowledge financial support from the Center of Applied Ecology and Sustainability (CAPES; ANID PIA/BASAL FB0002) and FONDECYT proposal no. 1180121—2018. We also thank ANID FONDAP and PIA grant nos 15110009 (to CR2) and AFB170008 (to the IEB) for additional funding

Ecology of the collapse of Rapa Nui society

Collapses of food producer societies are recurrent events in prehistory and have triggered a growing concern for identifying the underlying causes of convergences/divergences across cultures around the world. One of the most studied and used as a paradigmatic case is the population collapse of the Rapa Nui society. Here, we test different hypotheses about it by developing explicit population dynamic models that integrate feedbacks between climatic, demographic and ecological factors that underpinned the socio-cultural trajectory of these people. We evaluate our model outputs against a reconstruction of past population size based on archaeological radiocarbon dates from the island. The resulting estimated demographic declines of the Rapa Nui people are linked to the long-term effects of climate change on the island's carrying capacity and, in turn, on the 'per-capita food supply'

Modern Analogue Approach Applied to High-Resolution Varved Sediments—A Synthesis for Lake Montcortès (Central Pyrenees)

Este artículo contiene 23 páginas, 10 figuras.In Quaternary paleosciences, the rationale behind analogical inference presupposes that former processes can be explained by causes operating now, although their intensity and rates can vary through time. In this paper we synthesised the results of di erent modern analogue studies performed in a varved lake. We discuss their potential value to obtain best results from high resolution past records. Di erent biogeochemical contemporary processes revealed seasonality and year-to-year variability, e.g., calcite precipitation, lake oxygenation, production and deposition of pollen and phytoplankton growth. Fingerprints of the first two of these processes were clearly evidenced in the varve-sublayers and allow understanding related to past events. Pollen studies suggested the possibility of identifying and characterizing seasonal layers even in the absence of varves. Marker pigments in the water column were tightly associated with phytoplankton groups living today; most of them were identified in the sediment record as well. We observed that 50% of these marker pigments were destroyed between deposition and permanent burying. In another study, seasonality in the production/distribution of branched glycerol dialkyl glycerol tetraethers (brGDGTs) and derived temperature estimates were investigated in catchment soils and particles settling in the lake. The signatures of brGDGTs in depositional environments mainly were representative of stable conditions of soils in the catchment that last over decades; no brGDGTs seemed to be produced within the lake. The main contribution of this review is to show the advantages and limitations of a multiproxy modern-analogue approach in Lake Montcortès as a case study and proposing new working hypotheses for future research.Research funding was granted by the Spanish Ministry of Economy and Competitivity (MINECO/FEDER) with the projects MONT-500, ref. CGL2012-33665; GLOBALKARST, ref. CGL2009-08145), the Institute of Catalan Studies with the projects PIRIMOD and POLMONT, and the Catalan University and Research Management Agency (AGAUR) with the projects 2014 SGR 1207, 2017 SGR 1116).Peer reviewe