Evolución de la vegetación en el sector biogeográfico Castellano Cantábrico durante el Cuaternario Final, a través del registro tobáceo

En esta memoria de Tesis Doctoral se aborda el estudio paleobotánico de seis yacimientos tobáceos situados en las localidades burgalesas de Tubilla del Agua, Sedano, Herrán, Tobera y Frías, y en la alavesa de Ocio. El registro fósil encontrado en estos afloramientos se analiza de forma conjunta con el objetivo de conocer la evolución de la vegetación en el sector biogeográfico Castellano Cantábrico. Este sector se considera el territorio para el cual los hallazgos paleobotánicos son representativos y extrapolables, en tanto que constituye una región homogénea desde el punto de vista florístico, que abarca todos los yacimientos prospectados. El contexto temporal en el que se enmarca este estudio es el final del Cuaternario, desde el Pleistoceno Medio hasta la actualidad. Este intervalo se ha establecido a partir de la edad de los depósitos estudiados, la cual ha sido determinada —para los yacimientos de los que no se disponía de edades fiables— mediante la datación de muestras extraídas de las diferentes unidades litológicas identificadas. Para ello han sido empleadas las técnicas de carbono-14, desequilibrio de las series del uranio y racemización de aminoácidos. Los resultados geocronológicos obtenidos junto con el análisis geomorfológico de los yacimientos han permitido vincular la génesis de las 13 unidades litológicas identificadas con diferentes estadíos climáticos. Estos abarcan un amplio rango de condiciones ambientales, desde las más extremas del Último Máximo Glacial, hasta las más benignas de los Estadíos Isotópicos Marinos interglaciares 1 y 5. Como resultado de la prospección de los depósitos de toba fueron recuperados 1.820 fósiles, la mayoría impresiones foliares, pero también moldes de estróbilos femeninos, ramas y corteza, así como 42 carbones y restos subfósiles de Pinus sp. La identificación taxonómica de estos restos se ha realizado fundamentalmente a partir del análisis de caracteres diagnósticos morfológicos. Como resultado de ello, han sido descritos 28 taxones pertenecientes a las subclases Bryidae, Polypodiidae, Pinidae y Magnoliidae. La flora de los yacimientos estudiados se puede clasificar en tres grupos en función de sus requerimientos ecológicos: (i) uno formado por dos especies de alta tolerancia a la continentalidad —Pinus nigra y Quercus faginea—, las cuales aparecen bien representadas en la mayoría de los depósitos; (ii) otro constituido fundamentalmente por un conjunto de árboles y arbustos que habitualmente tienen el papel de especies acompañantes en los bosques ibéricos submediterráneos y eurosiberianos; y (iii) un tercer grupo compuesto por taxones hidrófitos o edafohigrófilos asociados al ecosistema del fitohermo activo y la vegetación de ribera. En el capítulo de Discusión se propone y analiza la hipótesis de que P. nigra y Q. faginea habrían sido las especies protagonistas de la vegetación zonal del sector Castellano Cantábrico durante el Cuaternario Final. Estas podrían haber persistido como tal incluso durante las épocas más frías, debido a su amplia valencia ecológica y a la capacidad de reproducirse vegetativamente en el caso del quejigo. Por el contrario, los taxones mesofíticos y eurosiberianos pudieron haber sufrido la expansión y retracción de sus poblaciones al ritmo de las oscilaciones climáticas. Sin embargo, la orografía diversa del sector Castellano Cantábrico proporciona emplazamientos en los que se combinan las diversas variables fisiográficas, de tal forma que pudieron haber existido microrrefugios en los que encontraron cobijo algunos taxones mesotérmicos y eurosiberianos durante los periodos glaciales. Por último, la historia evolutiva reciente de la vegetación de este territorio ha estado marcada por la acción antrópica, la cual empezó a ser manifiesta a partir del Neolítico. Esta se tradujo en la degradación y reducción de la cubierta forestal, así como en la extinción del pino laricio del Sector Castellano Cantábrico en los dos últimos milenios. ABSTRACT This PhD Dissertation focuses in the study of six tufa formations located nearby the villages of Tubilla del Agua, Sedano, Herrán, Tobera y Frías, all of them in the province of Burgos, and Ocio, which belongs to the province of Álava. We analyze the palaeobotanical archives of these sites with the purpose of unveiling and understanding the evolution of the vegetation of the Castilian Cantabrian biogeographical sector. This area is considered to be the territory that is represented in the palaeobotanical sample of the studied tufa archives. It is the homogeneous phitogeographical area with the lowest rank that include all the sites. The time frame of this study is the last part of the Quaternary, since the Middle Pleistocene to the present time. This interval is defined by the age of the tufa deposits, which were dated —for the ones that there were not available datings— throughout the analysis of 20 tufa samples taken from the 13 identified lithostratigraphic units. The age of the samples has been determined by using the methods of radiocarbon, U-Th dating and amino acid racemization. Chronological results, along with the chronostratigraphic study of the sites has allowed us to relate the build-up of the 13 identified lithostratigraphic units with different climatic stages. These structures were deposited in a wide range of climatic conditions, from the most extreme ones of the Last Glacial Maximum, to the warmer ones of the Marine Isotopic Stages 1 and 5. A total of 1,820 fossils were recovered from the tufa deposits, most of them were leaf impressions, but also pine cones, branches and bark moulds, along with charcoal and Pinus nigra macro remains. The taxonomical identification of these remains has been done mainly through the analysis of morphological traits. As a result of this process, 28 taxa belonging to the subclass of Bryidae, Polypodiidae, Pinidae and Magnoliidae were identified. The persistency of some taxa can be traced along different climatic stages in this fossil record. This fossil flora can be classified in three different groups: (i) the first one would be composed of two species with high continental climate tolerance —Pinus nigra y Quercus faginea—, which can be found in most of the deposits, (ii) the second group would be mostly formed by trees and shrubs that usually grow in the Iberian forests as an accessory species and (iii) the third one is composed of hydrophytes or hydrophilic taxa associate to the streams, riparian zones or the active tufa ecosystem. In the Discussion chapter we propose and analyse the hypothesis that P.nigra and Q. faginea were the main species of the zonal vegetation of the Castilian Cantabrian biogeographical sector during the last part of the Quaternary. This species could have persisted due to their wide ecological amplitude and also due to the capacity of asexual reproduction in the cases of the oak. On the other hand, mesophitic taxa could have suffered the retraction and expansion of their population following the climate oscillations. However, the diverse orography of the Castilian Cantabrian biogeographical sector provides a variety of combinations of physiographic variables, which could have been suitable refuges for some of the mesophitic taxa. The recent evolutionary history of the vegetation in this territory has been affected by human activities, which started to be relevant since the Neolithic. This led to a reduction of the forests and eventually, to the extinction of P. nigra in the Castilian Cantabrian biogeographical sector in the last two thousands of years.

U-series dating of Locality 15 at Zhoukoudian, China, and implications for hominid evolution

This paper reports U-series dates on speleothem samples from Locality 15 at Zhoukoudian, one of the richest Paleolithic sites in northern China. The age of the lower part of Layer 2 is securely bracketed between 155,000 and 284,000 yr. The underlying Layer 3 dates back at least 284,000 yr. Layer 4, further below, should be older still, possibly by a cycle on the SPECMAP time scale before 284,000 yr ago. These ages, much greater than the previous estimates of 110,000-140,000 yr from U-series and electron spin resonance dating of fossil teeth, suggest that Locality 15 was broadly contemporaneous with Locality 4 (New Cave) and with the uppermost strata of Locality 1 (Peking Man site). The physical evolution and cultural development evidenced by the timing of the Zhoukoudian localities are in line with the opinion of Chinese anthropologists for a regional transition from Homo erectus to archaic Homo sapiens. (C) 2004 University of Washington. All rights reserved.

Integrating JERS-1 imaging radar and elevation models for mapping tropical rainforest communities in far North Queensland, Australia

The Wet Tropics World Heritage Area in Far North Queens- land, Australia consists predominantly of tropical rainforest and wet sclerophyll forest in areas of variable relief. Previous maps of vegetation communities in the area were produced by a labor-intensive combination of field survey and air-photo interpretation. Thus,. the aim of this work was to develop a new vegetation mapping method based on imaging radar that incorporates topographical corrections, which could be repeated frequently, and which would reduce the need for detailed field assessments and associated costs. The method employed G topographic correction and mapping procedure that was developed to enable vegetation structural classes to be mapped from satellite imaging radar. Eight JERS-1 scenes covering the Wet Tropics area for 1996 were acquired from NASDA under the auspices of the Global Rainforest Mapping Project. JERS scenes were geometrically corrected for topographic distortion using an 80 m DEM and a combination of polynomial warping and radar viewing geometry modeling. An image mosaic was created to cover the Wet Tropics region, and a new technique for image smoothing was applied to the JERS texture bonds and DEM before a Maximum Likelihood classification was applied to identify major land-cover and vegetation communities. Despite these efforts, dominant vegetation community classes could only be classified to low levels of accuracy (57.5 percent) which were partly explained by the significantly larger pixel size of the DEM in comparison to the JERS image (12.5 m). In addition, the spatial and floristic detail contained in the classes of the original validation maps were much finer than the JERS classification product was able to distinguish. In comparison to field and aerial photo-based approaches for mapping the vegetation of the Wet Tropics, appropriately corrected SAR data provides a more regional scale, all-weather mapping technique for broader vegetation classes. Further work is required to establish an appropriate combination of imaging radar with elevation data and other environmental surrogates to accurately map vegetation communities across the entire Wet Tropics.

Biodiversity values of timber plantations and restoration plantings for rainforest fauna in tropical and subtropical Australia

It has been suggested that timber plantations could play an important role in the conservation of biodiversity in cleared rainforest landscapes, not only because of their potential to cost-effectively reforest large areas of land, but also because they may provide habitat for rainforest plants and animals. However, this last claim is largely untested. In this study, we surveyed the occurrence of a range of animal taxa in monoculture and mixed species timber plantations and restoration plantings in tropical and subtropical Australia. We used the richness of ‘rainforest-dependent’ taxa (i.e., birds, lizards and mites associated with rainforest habitats) in reforested sites as our measure of their ‘biodiversity value’. We also examined whether the biodiversity value of reforested sites was correlated with habitat attributes, including plant species richness and vegetation structure and, further, whether biodiversity value was affected by the proximity of reforested sites to intact rainforest.

Activity of isotopes of U, Th and Pa versus depth in bottom sediments from Core ML1_66

A sediment core from the European Basin with alternation of biogenic calcareous oozes and terrigenous sediments is studied by several methods. Isotopic age is determined by 230Th-ex and 231Pa-ex and by the radiocarbon method. Surface water paleotemperatures are reconstructed from complexes of planktic foraminifera and oxygen isotope ratios in their shells, and the ratio of biogenic and terrigenous components are investigated. Stages 1-8 of the oxygen-isotope scale are identified. Fluctuations in paleooceanic conditions in the area of coring are discussed.

He isotope, U/Th isotope, Calcium carbonate, biogenic opal, rare earth element concentrations, and grain size distribution measured on core-top sediments during SONNE cruise SO202 (INOPEX)

Eolian dust is a significant source of iron and other nutrients that are essential for the health of marine ecosystems and potentially a controlling factor of the high nutrient-low chlorophyll status of the Subarctic North Pacific. We map the spatial distribution of dust input using three different geochemical tracers of eolian dust, 4He, 232Th and rare earth elements, in combination with grain size distribution data, from a set of core-top sediments covering the entire Subarctic North Pacific. Using the suite of geochemical proxies to fingerprint different lithogenic components, we deconvolve eolian dust input from other lithogenic inputs such as volcanic ash, ice-rafted debris, riverine and hemipelagic input. While the open ocean sites far away from the volcanic arcs are dominantly composed of pure eolian dust, lithogenic components other than eolian dust play a more crucial role along the arcs. In sites dominated by dust, eolian dust input appears to be characterized by a nearly uniform grain size mode at ~4 µm. Applying the 230Th-normalization technique, our proxies yield a consistent pattern of uniform dust fluxes of 1-2 g/m**2/yr across the Subarctic North Pacific. Elevated eolian dust fluxes of 2-4 g/m**2/yr characterize the westernmost region off Japan and the southern Kurile Islands south of 45° N and west of 165° E along the main pathway of the westerly winds. The core-top based dust flux reconstruction is consistent with recent estimates based on dissolved thorium isotope concentrations in seawater from the Subarctic North Pacific. The dust flux pattern compares well with state-of-the-art dust model predictions in the western and central Subarctic North Pacific, but we find that dust fluxes are higher than modeled fluxes by 0.5-1 g/m**2/yr in the northwest, northeast and eastern Subarctic North Pacific. Our results provide an important benchmark for biogeochemical models and a robust approach for downcore studies testing dust-induced iron fertilization of past changes in biological productivity in the Subarctic North Pacific.

Biogenic opal, biogenic barium, calcium carbonate and U/Th isotope data from core-top sediments of SONNE cruise SO202 (INOPEX)

Sedimentary proxies used to reconstruct marine productivity suffer from variable preservation and are sensitive to factors other than productivity. Therefore, proxy calibration is warranted. Here we map the spatial patterns of two paleoproductivity proxies, biogenic opal and barium fluxes, from a set of core-top sediments recovered in the Subarctic North Pacific. Comparisons of the proxy data with independent estimates of primary and export production, surface water macronutrient concentrations and biological pCO2 drawdown indicate that neither proxy shows a significant correlation with primary or export productivity for the entire region. Biogenic opal fluxes, when corrected for preservation using 230Th-normalized accumulation rates, show a good correlation with primary productivity along the volcanic arcs (tau = 0.71, p = 0.0024) and with export productivity throughout the western Subarctic North Pacific (tau = 0.71, p = 0.0107). Moderate and good correlations of biogenic barium flux with export production (tau = 0.57, p = 0.0022) and with surface water silicate concentrations (tau = 0.70, p = 0.0002) are observed for the central and eastern Subarctic North Pacific. For reasons unknown, however, no correlation is found in the western Subarctic North Pacific between biogenic barium flux and the reference data. Nonetheless, we show that barite saturation, uncertainty in the lithogenic barium corrections and problems with the reference datasets are not responsible for the lack of a significant correlation between biogenic barium flux and the reference data. Further studies evaluating the factors controlling the variability of the biogenic constituents in the sediments are desirable in this region.