Browsing by Author "Santos, Ricardo N."
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- Leaf wax biomarkers of a high-mountain lake area in western iberia—Implications for environmental reconstructionsPublication . Santos, Ricardo N.; Schefuß, Enno; Cordeiro, Lívia; Oliveira, Dulce; Hernández, Armand; Ramos, Alexandre M.; Rodrigues, TeresaLeaf wax n-alkane biomarkers are widely used to infer past vegetation dynamics and hydroclimate changes. The use of these compounds strongly relies on the characterization of modern plants. However, few studies have explored leaf waxes of modern plants and their application to reconstructing climate and environmental changes in the Iberian Peninsula, a region known for its high vulnerability to climate change. In this study, we characterize the distributions and compound-specific isotopic compositions of the leaf waxes of dominant plants in the vegetation cover, soil, and surface sediment of the Lake Peixao area, a high-mountain glacial lake in Serra da Estrela (central Portugal). Our results show that the modern oro-Mediterranean (subalpine) vegetation of the study area is dominated by C-3 grasses/herbs and shrubs that preferentially produce long-chain leaf waxes (& GE;C-27). The C-31 n-alkane display the overall highest concentration, produced by some grasses and shrubs, but especially Erica sp (heather), which is highlighted as a major source for the total n-alkane pool in the lake sediments. C-29 is the second-most abundant and the most equally produced n-alkane of the vegetation cover; C-25 and C-27 homologs are mainly associated with aquatic-related grasses/herbs, while C-33 and C-35 are particularly linked to cold-drought tolerant Juniperus sp. shrubs. Shrubs show higher but proportional values than grasses/herbs in the isotopic space, suggesting a directly proportional physiological adaptation of the two ecological forms to the prevailing climatic and environmental factors of the study area. C-29 is pointed as the most representative (or less plant-biased) leaf wax n-alkane in the lake sediments. Thus, delta D of C-29 n-alkane is interpreted as a robust terrestrial hydrological indicator (delta D-terr), which signal is believed to be strongly influenced by the mean air temperature and/or precipitation amount. Despite the sparse vegetation and small catchment area, the apparent hydrogen fractionation factor, determined from delta D-terr of the lake surface sediment, is in line with the modeled global mean values for the latitude of the study area. The different molecular and compound-specific signatures of the studied oro-Mediterranean species have the potential to support future interpretations of leaf wax biomarkers in the Iberian Peninsula.
- The timing of the deglaciation in the Atlantic Iberian mountains: Insights from the stratigraphic analysis of a lake sequence in Serra da Estrela (Portugal)Publication . Hernández, Armand; Sáez, Alberto; Santos, Ricardo N.; Rodrigues, Teresa; Martin‐Puertas, Celia; Gil‐Romera, Graciela; Abbott, Mark; Carballeira, Rafael; Costa, Pedro; Giralt, Santiago; Gomes, Sandra D.; Griffore, Melissa; Ibañez‐Insa, Jordi; Leira, Manel; Moreno, João; Naughton, Filipa; Oliveira, Dulce; Raposeiro, Pedro M.; Trigo, Ricardo M.; Vieira, Gonçalo; Ramos, Alexandre M.Understanding the environmental response to the last glacial termination in regions located in transitional climate zones such as the Atlantic Iberian mountains is crucial to estimate potential changes in regions affected by current glacial melting. We present an 8.5 m-long, solid last deglaciation and Holocene chronostratigraphic record including detailed sediment analysis from Lake Peixao, a pro-glacial lake in the Serra da Estrela (Central Portugal). The age-depth model relies on a Bayesian approach that includes 16 AMS C-14 dates and Pb-210-(CS)-C-137 measurements, robustly dating the lake formation at 14.7 +/- 0.32 cal. ka BP. This chronological reconstruction shows an average sedimentation rate of ca. 0.07 cm yr(-1) (15 yr cm(-1)), enabling proxy analyses at decadal timescales. The sediment sequence is composed of five lithological units: (U1) coarse and unsorted fluvioglacial lacustrine deposits; (U2) massive fluvioglacial lacustrine deposits (863-790 cm below surface [bsf]; 14.7 +/- 0.32-13.8 +/- 0.12 cal. ka BP); (U3) water current fluvioglacial lacustrine deposits (790-766 cm bsf; 13.8 +/- 0.12-12.9 +/- 0.29 cal. ka BP); (U4) laminated/banded lacustrine deposits characterized by terrigenous deposits from ice-covered lake periods and episodic events of ice and snow melting (766-752 cm bsf; 12.9 +/- 0.29-11.7 +/- 0.15 cal. ka BP); and (U5) massive muddy lacustrine deposits (752-0 cm bsf; 11.7 +/- 0.15 cal. ka BP-present). The occurrence of U2 to U4 deposits defines the transition from glacial cold (U1) to net warm postglacial conditions (U5). These climate transitions are marked by changes in sediments and the presence of very low sedimentation rate periods, possibly related to the Intra-Allerod Cold Period and the coldest phase of the Younger Dryas. Our results support the previously proposed timing of the retreat of the Serra da Estrela glaciers ca. 13.8 +/- 0.12 cal. ka BP. The robust chronology of Lake Peixao highlights the potential of Iberian pro-glacial lakes for dating deglaciation processes and will lead to unprecedented decadal-to-centennial timescale palaeoclimate reconstructions in this region since the last glacial-interglacial transition.
- Understanding the Atlantic influence on climate and vegetation dynamics in western Iberia over the last 2000 yearsPublication . Santos, Ricardo N.; Rodrigues, Teresa; Naughton, Filipa; Schefuß, Enno; Oliveira, Dulce; Moreno, João; Raposeiro, Pedro M.; Gil-Romera, Graciela; Morgan, Alistair; Leira, Manel; Gomes, Sandra D.; Ladd, S. Nemiah; Trigo, Ricardo M.; Ramos, Alexandre M.; Hernández, ArmandPredicting the environmental impact of climate change in extremely sensitive areas, like western Iberia, requires an understanding of the long-term interactions between climate and vegetation. Here we present a novel hightemporal resolution multiproxy analysis, including plant-wax n-alkane isotope data, pollen analysis, macrocharcoal identification, chironomid and diatom records of sediments from a mountain lake in central Portugal. We examined the evolution of the Atlantic and Mediterranean climate influences over the last two millennia, exploring their connection with major atmospheric patterns and impacts on the climatic signal and vegetation dynamics in this understudied region. During the Roman Period (RP; ca. -200 – 500 AD), the study area was characterized by grass dominance, with high temperatures indicated by chironomid composition and microcharcoal content. The increase in plant-wax δ2 H values during this period suggests a shift from wet to dry conditions. The Early Middle Ages (EMA; ca. 500–900 AD) were characterized by colder and a transition to wetter conditions, as indicated by the vegetation and plant-wax n-alkane isotope data. The Medieval Climate Anomaly (MCA; ca. 900–1300 AD) was generally warm, with a short initial lake level drop. This period exhibits the maximum expansion of the Mediterranean forest over the last 2 ka and possibly proximal moisture sources. During the Little Ice Age (LIA; 1300–1850 AD), a reduction of the Mediterranean forest and a strong depletion of plant-wax δ2 H values suggest cold and wet conditions with strong influence of remote Atlantic moisture, with the coldest and wettest phase of the last 2 ka detected between 1550 and 1900 AD. The post-LIA period, from 1900 AD onwards, shows a change to the present warmer and drier conditions, in a highly anthropized landscape. We also demonstrate that major changes in climate have influenced vegetation patterns, with these changes mainly controlled by large-scale atmospheric dynamics. This underscores the sensitivity of western Iberian ecosystems to climate shifts, enriches the current regional understanding of climate-vegetation interplay, and offers valuable insights for future climate change projections.