Variations in modern pollen distribution in sediments from nearby upland lakes: implications for the interpretation of paleoecological data

Financiado para publicación en acceso aberto: Universidade de Vigo/CISUGTo determine whether modern pollen content in sediments from upland lake systems reflects the factual regional and extra-local vegetation composition, we analysed twenty-five samples focusing on aspects such as pond size and morphology, relative position in the catchment, local vegetation, canopy configuration and seasonality of the water table. The average pollen percentages of all sediment samples studied allows a fairly good reconstruction of the main vegetation units in the area, but major differences between the average samples obtained in each sedimentary system, and also between some samples taken from the same system are found. The main factors explaining those differences are the size of the pond, its tree canopy and the seasonality of the water table, which strongly determines the Ericaceae and Pinus percentages. A high-resolution multiproxy palaeoecological record from a small upland lake is re-evaluated in light of the new experimental evidence, and it is concluded that the interpretation of the importance of heathland and pinewoods in the Late Glacial landscape using pollen data may be magnified by the transport of both pollen types through water flows and their accumulation in the basin. Furthermore, anomalous Pinus pollen peaks occur in dry periods when the water table remains low. The sediment can also be depleted of some high-buoyancy pollen types (tetrads and saccate) when the water level is high and effluents are active. These effects may also be important in fluvio-marine systems in which Ericaceae and Pinus pollen are often overrepresented.Ministerio de Educación y Ciencia | Ref. CGL2012-33584Xunta de Galicia | Ref. ED431C 2019/28Xunta de Galicia | Ref. GRC 2015/02

Holocene landscapes in the Serra de Arga (NW Portugal)

El diagrama polínico obtenido permite conocer la dinámica de la vegetación y los cambios en el paisaje durante el Holoceno en el entorno de la Serra de Arga. Las fechas obtenidas, permiten situar el inicio de la secuencia en relación con el evento climático GH-8.2 registrado en las secuencias de hielo de Groenlandia. Tras esta fase de regresión se registra una recuperación del bosque correlacionable con el óptimo climático de Holoceno y en la cual se constata el predominio de los robledales. Tras un corto episodio en el que se produce un hiato sedimentario, la secuencia se reanuda en una fase de marcada deforestación tras la cual se registra un fuerte incremento de Pinus relacionado con la proliferación de plantaciones forestales.The pollen diagram obtained allow us to understand the dynamics of vegetation and landscape changes during the Holocene in the vicinity of the Serra de Arga. The dates obtained are used to place the beginning of the sequence in relation to GH-8.2 climate event recorded in Greenland ice cores. After this phase of regression there is a forest recovery coincident with the Holocene climatic optimum in which notes the predominance of oak. After a short episode in which there is a sedimentary hiatus, the sequence is resumed in a phase of marked deforestation after which records a sharp increase in Pinus associated with the proliferation of forest plantations.Fundação Calouste Gulbenkia

Organic-walled dinoflagellate cyst assemblages in surface sediments of the Ría de Vigo (Atlantic margin of NW Iberia) in relation to environmental gradients

Organic-walled dinoflagellate cyst assemblages were analysed in 31 surface sediment samples from the Ría de Vigo (NW Iberia) to obtain supporting evidence for the interpretation of past environmental signals from sediment cores. Complementarily, the totals of pollen (and pollen from riparian taxa), foraminiferal linings and freshwater algae were also considered to test their value as (palaeo)environmental indicators in fluvio-marine sedimentary environments. Abundances of foraminiferal linings gradually increased towards the ría's mouth, which supports its use as a proxy to infer the degree of marine influence in the sediment record. The ratio of dinoflagellate cysts to pollen and spores (D/P) increased with distance to the main river's mouth (and water depth) in the inner ( 20 m) parts of the ría. Total pollen concentrations decreased with water depth in the outer part but did not show any clear trend in the rest of the ría. No clear pattern in the distributions of pollen from riparian plants and spores from freshwater microalgae was detected. Multivariate analyses (clustering and RDA) performed on dinoflagellate cyst records and environmental data reflected a marked inshore-offshore distribution pattern mainly controlled by a fluvio-marine environmental gradient. Increasing abundances of cysts of Gymnodinium species and heterotrophic cysts as well as higher cyst diversity characterised the deeper environments of the outer ría. These observations suggest a relationship with increased shelf influence and are compatible with the heterotroph upwelling signal described in previous works. A very different cyst association with a predominance of autotrophic cysts characterised the intermediate and inner parts of ría, where exceptionally high cyst abundances of Lingulodinium polyedra (∼ 56–99% and ∼ 200–114,000 cysts.g−1) were reported. Abundances of cysts of L. polyedra positively correlated with shallower and higher river-influenced environments characterised by higher sea-surface temperature. Our results agree with previous studies and reinforce the value of this species as an indicator of warmer and stratified conditions. Moreover, cysts of L. polyedra positively correlated with winter sea-surface nitrate contents, which is compatible with the nutrient enrichment signal (natural or anthropogenic) that has already been described in other deep and stratified estuarine environments and is consistent with historical cyst records obtained in the Ría de Vigo. However, further research is needed to disentangle the nutrient enrichment signal from the influence of other environmental factors.Ministerio de Educación y Ciencia | Ref. CGL2012-33584Xunta de Galicia | Ref. GRC 2015/020Xunta de Galicia | Ref. ED431C 2019/28Xunta de Galicia | Ref. ED481B-2019-074Universidade de Vigo/CISU

Holocene environmental change on the Atlantic coast of NW Iberia as inferred from the Ponzos wetland sequence

The intertidal environment of the Ponzos beach (NW Iberian Peninsula) hosts a sedimentary sequence (including large wood fragments) deposited during the first half of the Holocene in a hygrophilous continental wetland. Pollen and macrofossil data alongside radiocarbon dating allow reconstruction of the changes that occurred during the Early and Middle Holocene in the landscape of the NW Iberia coastal lowlands, as well as the local wetland plant communities, in response to the climate variations and the eustatic sea-level oscillations. The sequence represents the evolution of a coastal wetland from its initial phases as a hygrophilous wetland towards the subsequent installation of a freshwater lagoon. Pollen data show the dominant role of Atlantic (mainly deciduous) woody taxa, the scarcity of conifers and the lack of Mediterranean elements in the coastal landscapes around the Ponzos site. The presence and abundance of some taxa such as deciduous Quercus, Castanea, Fagus, Tilia and Ulmus during the Early Holocene provides further support for the occurrence of glacial refuges in the Cantabrian-Atlantic area during the Last Glaciation. The diverse vegetation that characterizes the modern landscapes in this territory established later, spreading from these glacial reservoirs of biodiversity. In this sense, the notable and early presence of Fagus at the beginning of the Holocene, a tree also previously recorded during several phases of the Last Glacial Cycle on the NW Iberia coasts, is noteworthy. In addition, during the Early and Middle Holocene are recorded other trees that are currently extirpated as natural taxa in the area, such as Pinus, Tilia and CarpinusS

Millennial land use explains modern high‐elevation vegetation in the submediterranean mountains of Southern Europe

Aim Pinewood decline and scrubland expansion are major features of Late Holocene vegetation history in the Cantabrian Range. However, the drivers of this remarkable vegetation shift remain to be investigated. Here, we aim at disentangling the role of past land use and climate in shaping the high-elevation Cantabrian landscape during the past two millennia. Location Cantabrian Range (northern Iberia). Taxa Pinus sylvestris, Betula, Ericaceae, Juniperus, Poaceae. Methods We conducted high-resolution multiproxy palaeoecological analyses (pollen, plant macrofossils, microscopic charcoal and dung fungi) on lake sediments from Lago del Ausente to reconstruct vegetation, fire occurrence and grazing through time. The chronology is based on 14C (terrestrial plant macrofossils) and 210Pb dating, and Bayesian age-depth modelling (‘rbacon’). We carried out cross-correlation analysis to quantify vegetation responses to fire. Results Between 250 and 900 CE, the vegetation above 1700 m a.s.l. consisted of subalpine scrubland and scattered P. sylvestris trees/stands. Pinewoods with Betula were widespread at slightly lower elevation. This vegetation was resilient to moderate fire disturbance associated with limited pastoral activities. In contrast, enhanced fire occurrence alongside heavier pastoralism led to the demise of pinewoods and their replacement with Betula stands, subalpine scrublands, and meadows between 900 and 1100 CE. Later, the subalpine scrubland-birch tree line did not respond to Little Ice Age cooling. However, further intensification of transhumant herding between 1300 and 1860 CE (‘La Mesta’) triggered birch decline and the establishment of the modern treeless landscape. Main conclusions The extant high-elevation vegetation of the Cantabrian Range is largely the legacy of intensive land use starting more than one millennium ago. Recurrent and severe fires to promote pasturelands led to the regional extirpation of the previously widespread Pinus sylvestris. Future management should aim at preserving the valuable cultural open landscape of mountain scrubland and meadows and also at restoring patches of ancient pine-birch woodlands

Holocene distribution of woody taxa at the westernmost limit of the Circumboreal/Mediterranean boundary: evidence from wood remains

Información paleoecológica relativa a la distribución de táxones arbóreos durante el holoceno, basado en restos fósiles leñosos

Cambio climático y dinámica del paisaje en Galicia

Las secuencias polínicas, y en concreto las obtenidas a partir de sedimentos limnéticos, se han revelado como la herramienta más eficaz a la hora de valorar los cambios climáticos cuaternarios a nivel regional y su incidencia sobre los ecosistemas. Una parte importante de los registros obtenidos en el NW ibérico, presenta una antigüedad menor de 3.000; las secuencias continuas de más de 6.000 años, que alcanzan cronologías de 10.000 o 12.000 años, se limita a grandes turberas de zonas de montaña; finalmente, los periodos de más de 17.000 años, únicamente aparecen representados en sedimentos fosilizados, en los que se han obtenido registros continuos de 10.000 o 20.000 años y excepcionalmente periodos de más de 50.000. Las más de 200 secuencias disponibles para el NW ibérico, permiten realizar una correcta evaluación de la incidencia de los cambios climáticos y de la influencia antrópica sobre los ecosistemas, a lo largo de los últimos 100.000 años. La abundancia de datos, accede a reconocer la diferente influencia de estos cambios sobre las distintas áreas biogeográficas del territorio

The Eurasian Modern Pollen Database (EMPD), version 2

The Eurasian (née European) Modern Pollen Database (EMPD) was established in 2013 to provide a public database of high-quality modern pollen surface samples to help support studies of past climate, land cover, and land use using fossil pollen. The EMPD is part of, and complementary to, the European Pollen Database (EPD) which contains data on fossil pollen found in Late Quaternary sedimentary archives throughout the Eurasian region. The EPD is in turn part of the rapidly growing Neotoma database, which is now the primary home for global palaeoecological data. This paper describes version 2 of the EMPD in which the number of samples held in the database has been increased by 60 % from 4826 to 8134. Much of the improvement in data coverage has come from northern Asia, and the database has consequently been renamed the Eurasian Modern Pollen Database to reflect this geographical enlargement. The EMPD can be viewed online using a dedicated map-based viewer at https://empd2.github.io and downloaded in a variety of file formats at https://doi.pangaea.de/10.1594/PANGAEA.909130 (Chevalier et al., 2019)Swiss National Science Foundation | Ref. 200021_16959

New multiproxy data obtained from the sedimentary fill of the Ría de Ferrol, NW Iberia

Financiado para publicación en acceso aberto: Universidade de Vigo/CISUGSeveral gravity cores and vibro-cores were recovered from selected sites in the inner sector of Ría de Ferrol, NW Iberia (Muñoz Sobrino et al., 2021) [1]. These sediment cores were obtained during the surveys ECOMER-2014 and ECOMER-2015, developed from 2014 to 2015 on-board the R/V Mytilus (Consejo Superior de Investigación Científica) and the Amarradores Mil (Amarradores del Puerto y Ría de Ferrol, S.L.), respectively. Sedimentary and other multiproxy data presented here belong to four selected sediment cores located in the innermost part of the study area. Two were recovered using a gravity corer and another two using a vibro-corer. The depth of the cores and samples obtained is referred to the NMMA (the mean sea level in Alicante), which is the Spanish orthometric datum. One half of each core was subjected to non-destructive analysis using an ITRAX core scanner providing X-ray fluorescence (XRF) elemental data. Particle size distribution was characterised by laser diffraction. For radiocarbon dating, well-preserved articulated valves, small remains of wood and very organic bulk sediment from one location free of biogenic gas were selected. Palynological analyses were performed on selected sections of the sediment. All samples were spiked with Lycopodium spores for absolute palynomorph estimation and analysed using 400x and 600x magnifications. The ratio of dinoflagellate cyst concentrations to pollen, fern spore and dinoflagellate cyst concentrations (D/P ratio, ranging between 0 and 1) was calculated for each sample to show the temporal variation. Combined seismic, lithological, elemental, chronological and palynological data enable reconstructing the environmental changes that occurred during the local marine transgression. Besides, the combination of evidence identified may also be applied to other areas or periods in order to perform local reconstructions of changing coastal ecosystems. This type of high-resolution spatial-temporal reconstructions of past changes in estuarine environments may be a valuable tool for modelling, predicting and managing the changes and threats linked to the global warming and sea-level rise associated.Ministerio de Economía y Competitividad | Ref. CGL2012-33584Ministerio de Economía y Competitividad | Ref. BES-2013-066901Xunta de Galicia | Ref. ED431C 2019/2