Sensitivity of two Iberian lakes to North Atlantic atmospheric circulation modes

Hernandez A., Trigo R.M., Pla-Rabes S., Valero-Garces B.L., Jerez S., Rico-Herrero M., Vega J.C., Jambrina-Enriquez M., Giralt S. (2015) Sensitivity of two Iberian lakes to North Atlantic atmospheric circulation modes. Climate Dynamics. : 0-0.
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Doi: 10.1007/s00382-015-2547-8

Resum:

The North Atlantic Oscillation (NAO) exerts a major influence on the climate of the North Atlantic region. However, other atmospheric circulation modes (ACMs), such as the East Atlantic (EA) and Scandinavian (SCAND) patterns, also play significant roles. The dynamics of lakes on the Iberian Peninsula are greatly controlled by climatic parameters, but their relationship with these various ACMs has not been investigated in detail. In this paper, we analyze monthly meteorological and limnological long-term datasets (1950–2011 and 1992–2011, respectively) from two lakes on the northern and central Iberian Peninsula (Sanabria and Las Madres) to develop an understanding of the seasonal sensitivity of these freshwater systems to the NAO, EA and SCAND circulation modes. The limnological variability within Lake Sanabria is primarily controlled by fluctuations in the seasonal precipitation and wind, and the primary ACMs associated with the winter limnological processes are the NAO and the SCAND modes, whereas only the EA mode appears to weakly influence processes during the summer. However, Lake Las Madres is affected by precipitation, wind and, to a lesser extent, temperature, whereas the ACMs have less influence. Therefore, we aim to show that the lakes of the Iberian Peninsula are sensitive to these ACMs. The results presented here indicate that the lake dynamics, in some cases, have a higher sensitivity to variations in the ACMs than single local meteorological variables. However, certain local features, such as geography, lake morphology and anthropic influences, are crucial to properly record the signals of these ACMs. © 2015 Springer-Verlag Berlin Heidelberg

Llegeix més

Expanding the tephrostratigraphical framework for the South Shetland Islands, Antarctica, by combining compositional and textural tephra characterisation

Liu E.J., Oliva M., Antoniades D., Giralt S., Granados I., Pla-Rabes S., Toro M., Geyer A. (2015) Expanding the tephrostratigraphical framework for the South Shetland Islands, Antarctica, by combining compositional and textural tephra characterisation. Sedimentary Geology. : 0-0.
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Doi: 10.1016/j.sedgeo.2015.08.002

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Tephra layers preserved in lake sedimentary sequences provide valuable isochrons with which to synchronise palaeoclimatic records. However, in regions where tephra inputs are dominated by a single volcanic source, overlapping chemical compositions can preclude unambiguous correlation of tephra layers. In this study, we characterise multiple visible (macrotephra) layers within sedimentary sequences from three lakes in Byers Peninsula, Antarctica. By combining compositional analyses with additional constraints from textural componentry, we identify three distinct tephra isochrons-T1, T2, and T3-each with distinct textural properties. The relative proportion of glassy compared to crystal-rich grains varies from ~. 50% (T3) to ~. 3% (T1) of the total sample. Although the proportion of dense to vesicular grains differs only slightly between all sampled tephra layers, the dominant vesicle shape varies from spherical (T3) to irregular and polylobate (T1/T2). These textural differences can be related to variations in the eruptive processes occurring at the Deception Island source volcano. This study highlights the efficacy of a correlative approach based on both chemical and physical tephra properties for deconvolving the tephra stratigraphy in regions where chemical compositions are non-unique. © 2015 Elsevier B.V.

Llegeix més

Late Holocene vegetation dynamics and deforestation in Rano Aroi: Implications for Easter Island's ecological and cultural history

Rull V., Canellas-Bolta N., Margalef O., Saez A., Pla-Rabes S., Giralt S. (2015) Late Holocene vegetation dynamics and deforestation in Rano Aroi: Implications for Easter Island's ecological and cultural history. Quaternary Science Reviews. 126: 219-226.
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Doi: 10.1016/j.quascirev.2015.09.008

Resum:

Easter Island (Rapa Nui) has been considered an example of how societies can cause their own destruction through the overexploitation of natural resources. The flagship of this ecocidal paradigm is the supposed abrupt, island-wide deforestation that occurred about one millennium ago, a few centuries after the arrival of Polynesian settlers to the island. Other hypotheses attribute the forest demise to different causes such as fruit consumption by rats or aridity but the occurrence of an abrupt, island-wide deforestation during the last millennium has become paradigmatic in Rapa Nui. We argue that such a view can be questioned, as it is based on the palynological study of incomplete records, owing to the existence of major sedimentary gaps. Here, we present a multiproxy (pollen, charcoal and geochemistry) study of the Aroi core, the first gap-free sedimentary sequence of the last millennia obtained to date in the island. Our results show changing vegetation patterns under the action of either climatic or anthropogenic drivers, or both, depending on the time interval considered. Palm forests were present in Aroi until the 16th century, when deforestation started, coinciding with fire exacerbation -likely of human origin- and a dry climate. This is the latest deforestation event recorded so far in the island and took place roughly a century before European contact. In comparison to other Easter Island records, this record shows that deforestation was neither simultaneous nor proceeded at the same pace over the whole island. These findings suggest that Easter Island's deforestation was a heterogeneous process in space and time, and highlights the relevance of local catchment traits in the island's environmental and land management history. © 2015 Elsevier Ltd.

Llegeix més

The effects of the NAO on the ice phenology of Spanish alpine lakes

Sanchez-Lopez G., Hernandez A., Pla-Rabes S., Toro M., Granados I., Sigro J., Trigo R.M., Rubio-Ingles M.J., Camarero L., Valero-Garces B., Giralt S. (2015) The effects of the NAO on the ice phenology of Spanish alpine lakes. Climatic Change. : 0-0.
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Doi: 10.1007/s10584-015-1353-y

Resum:

Three Spanish alpine lakes located in the Central Range (Peñalara Lake and Cimera Lake) and the Pyrenees (Redon Lake) are selected to understand the effects of the North Atlantic Oscillation (NAO) on ice phenology. A conceptual lake model is formulated based on Pearson’s correlation coefficients obtained between season-scale time series of the NAO index, climatic data (i.e., precipitation, air temperature and snow data) and limnological variables (ice phenology records). The results suggest that the effects of the NAO are only reflected in the thawing process via the air temperature and the insulating effect of snow accumulation on the ice cover. An altitude component is evident in our survey because the effects of the NAO on Peñalara Lake (the lowest altitude studied lake) are restricted to winter, whereas for Redon Lake (the highest altitude studied lake), the effects extend into spring. A latitudinal component is also clear when comparing our data with northern European lakes. Snow accumulation primarily depends on the air temperature at high latitudes, and both precipitation and the air temperature control snow accumulation at lower latitudes. Consequently, in northern Europe, the NAO signal is primarily reflected in lake ice phenology via the air temperature, whereas our results confirm that in southern Europe, the strong dependence of precipitation on the NAO determines the importance of the NAO for lake ice cover. © 2015 Springer Science+Business Media Dordrecht

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