Algal lipids reveal unprecedented warming rates in alpine areas of SW Europe during the industrial period

Abstract

Abstract. Alpine ecosystems of the southern Iberian Peninsula are among the most vulnerable and the first to respond to modern climate change in southwestern Europe. While major environmental shifts have occurred over the last ∼1500 years in these alpine ecosystems, only changes in the recent centuries have led to abrupt environmental responses, but factors imposing the strongest stress have been unclear until now. To understand these environmental responses, this study, for the first time, has calibrated an algal lipid-derived temperature proxy (based on long-chain alkyl diols) to instrumental historical data extending alpine temperature reconstructions to 1500 years before present. These novel results highlight the enhanced effect of greenhouse gases on alpine temperatures during the last ∼200 years and the long-term modulating role of solar forcing. This study also shows that the warming rate during the 20th century (∼0.18 ∘C per decade) was double that of the last stages of the Little Ice Age (∼0.09 ∘C per decade), even exceeding temperature trends of the high-altitude Alps during the 20th century. As a consequence, temperature exceeded the preindustrial record in the 1950s, and it has been one of the major forcing processes of the recent enhanced change in these alpine ecosystems from southern Iberia since then. Nevertheless, other factors reducing the snow and ice albedo (e.g., atmospheric deposition) may have influenced local glacier loss, since almost steady climate conditions predominated from the middle 19th century to the first decades of the 20th century.

New insights into Holocene hydrology and temperature from lipid biomarkers in western Mediterranean alpine wetlands

“…However, these expected LCD-algae producers in freshwater environments have not previously been identified in the study site (Barea-Arco et al, 2001;Sánchez-Castillo, 1988). In addition, the distribution of the relative abundances of the different diol isomers in LdRS seems to differ from the diol signature observed in previous studies suggesting that other potential diol producers might have been the source of LCDs in this alpine lake (García-Alix et al, 2020). Therefore, the obtained calibration equation in LdRS is a region-specific calibration for local alpine environments in the Sierra Nevada or for other lakes with similar LCD distribution as LdRS (García-Alix et al, 2020).…”

“…Different LCD indices such as the long-chain diol index (LDI: Eq. 4) or the multiple linear regression analysis on LCD distributions have been tested as annual and/or seasonal temperature loggers in both freshwater and marine environments (García-Alix et al, 2020;Lattaud et al, 2018;Rampen et al, 2014;Rampen et al, 2012;Smith et al, 2013). The presence of LCDs in the LdRS sedimentary record allowed the assessment of these different indices as paleotemperature proxies for the Sierra Nevada alpine wetlands.…”

“…Nevertheless, since this was the first LCD temperature calibration approach in an alpine lake, the reference temperature time-series (∼100 years) used in the calibration might not accurately reflect cold extreme past temperatures in LdRS (e.g., during the Little Ice Age -LIA-). Therefore, temperatures reconstructed from LDI values lower than 0.1 could present higher uncertainties than the mean standard error of the calibration (±0.3ºC) (García-Alix et al, 2020). In the marine environment there are a number of algal taxa producing LCD, including diatoms of the genus Proboscia Sundström (Sinninghe Damsté et al, 2003) and the unicellular phytoflagellate Apedinella radians (Lohmann) Campbell (Rampen et al, 2011), among others.…”

“…These fragile sites, occurring primarily above 2500m elevation, are in-vivo laboratories for ecological studies and their biogeochemical responses are very sensitive to climatic and environmental variations (Jiménez et al, 2018;Mladenov et al, 2011;Pulido-Villena et al, 2005;Reche et al, 2009). This also makes them sensitive to past environmental and climatic changes, as it has been shown from pollen, charcoal, major and trace elements, and organic proxies, among others (Anderson et al, 2011;Garcia-Alix et al, 2017;García-Alix et al, 2018;García-Alix et al, 2012b;García-Alix et al, 2020;Jiménez et al, 2019;Jiménez et al, 2018;Jiménez-Espejo et al, 2014;Jiménez-Moreno and Anderson, 2012;Jiménez-Moreno et al, 2013;Mesa-Fernández et al, 2018;Ramos-Román et al, 2016). These studies determined that warm and wet climates occurred during the early-middle Holocene, with the highest Holocene lake levels in the Sierra Nevada and a minimal influence of aeolian Saharan dust inputs, followed by an aridity trend during the middle-to-late Holocene.…”

“…It has a maximum depth of ~3 m, a surface area of 0.42 ha, and a small catchment basin (9.9 ha) (Morales-Baquero et al, 1999). Previous studies from the LdRS sediment record include a detailed age model, pollen, charcoal, major and trace elements, and carbon and nitrogen isotopic analyses (Anderson et al, 2011;García-Alix et al, 2018;Garcia-Alix et al, 2013;Jiménez et al, 2019;Jiménez et al, 2018;Jiménez-Espejo et al, 2014), as well as a high resolution long-chain diol study throughout the Common Era (García-Alix et al, 2020). Therefore, the results from the organic geochemical biomarkers discussed in this paper compare, contrast, and add value to those from the previously studied proxies in the same record, providing new insights into drivers of change in these high-altitude ecosystems.…”