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To appraise the application of isoprenoid glycerol dialkyl glycerol tetraethers (isoGDGTs) as paleoclimate proxies in small lakes we investigated the effect of seasonal variability in temperature and dissolved oxygen concentration (DO) on the GDGT contents and its proxy in the water column of an oligotrophic karst lake in the Catalan pre-Pyrenees (Lake Montcortes). From October 2013 to November 2014, we collected suspended particulate matter (SPM) monthly at three depths and retrieved the sediment from a trap located at 20 m below the lake surface. The GDGT contents in the SPM and sediment trap presented a marked seasonal variation, showing the highest values in summer and autumn. In addition, the isoGDGT proxy TEX86 in SPM and sediment trap showed a marked seasonal variability which matched the temperatures of the upper water column and fit the published global trend between TEX86 and mean annual lake surface temperature (LST). However, in the hypolimnion where oxygen was depleted for most of the study period, we found that TEX86 co-varied with DO. This further confirms previous claims with seasonal field data that the sedimentary TEX86 LST signal may be confounded by DO conditions. Consequently, the application of TEX86 to estimate LST should be carefully appraised in environments with depleted DO conditions., This work was supported by the Spanish Ministry of Research through projects TETRACLIM (ref. CGL2010-15000), Montcortes-500 (ref. CGL-2012-33665); and ICTA-UAB's Maria de Maeztu award (MDM-2015-0552); and a pre-doctoral research studentship to MCT (FPI, BES2013-065846). MC was funded with a doctoral research studentship from the China Scholarship Council (CSC). Fieldwork was performed with the collaboration of E. Safont, N. Canellas and J. Goma. BES2013-065846Fieldwork permits were provided by the Territorial Service of the department of Agriculture, Livestock, Fishing and Natural Environment of Catalunya. Meteorological data in Pobla de Segur were provided by J. Sigro. We also thank N. Moraleda, C. Huguet and the UAB Analytical Service for technical support.

A high-resolution (average 6 years/sampling interval) palaeoenvironmental reconstruction using pollen, charcoal and non-pollen palynomorphs was carried out on annually laminated sediments of Lake Montcortès (southern Pyrenean flank). The results were combined with historical data to better understand landscape evolution and human interaction during the last 500 years. Our results show that human activities (cropping, livestock breeding and hemp cultivation and retting) have been the most important factors responsible for vegetation changes with highest intensity between 1530 and 1900 CE. By means of a sub-decadal study we have been able to evaluate short-lasting events at local and regional scales related to climate (heavy rainfall events and, high-land forest fluctuations) or to historical and well-dated and documented socio-economic events (i.e., crop promotions (hemp) or land abandonment-population emigration). The temporal extent (400 years) and continuity of Cannabis pollen peak have been confirmed, and new evidence of water quality changes, likely as a consequence of hemp retting practices between the mid-17th to late 19th century, are provided. This is the first high-resolution palaeoenvironmental study carried out in a varved lake on the Iberian Peninsula so far. With these data we hope to contribute to filling the gap in high-resolution palaeoenvironmental data. © 2018 Elsevier B.V., This work was funded by the Ministry of Economy, Industry and Competitiveness (project MONT-500; reference CGL2012-33665 with an associated pre-doctoral research grant (FPI; BES-2013-065846 ); PI: Teresa Vegas-Vilarrúbia). We would like to thanks people that participated and helped during fieldwork: Elisabet Safont, Núria Cañellas-Boltà, Teresa Buchaca, Joan Gomà. The authors are grateful to the Council of Baix Pallars and the Cultural Association Lo Vent do Port for their continuous support, and to the Busseing Pallars Company for their implication and maintenance of field devices. Fieldwork permits were provided by the Territorial Service of the department of Agriculture, Livestock, Fishing and Natural Environment of Catalonia.

Coastal wetlands have been proposed as highly threatened by the ongoing and future climatic change, including projected sea-level changes as an additional forcing factor compared to more inland locations. The limited knowledge generated to date in this topic has been primarily focused on those areas attaining a high population density, and rarely deals with long-term (>50 years) dynamics. Here we present the first Holocene palaeoecological study carried in the Orinoco Delta, in NE Venezuela. The record presented here contains sediments from the last 6200 years and is located in a river-shore swamp dominated by the palm Mauritia flexuosa. Current human occupation is almost restricted to small settlements of the Warao indigenous culture, closely related to the use of M. flexuosa and other palm species present in the zone. The results show the occurrence of three well-distinguished palynological zones: (i) from 6200 to 5200 cal yr BP, characterised by mixed rainforest and other taxa related to salinity (coastal-like), low (negative) values of magnetic susceptibility and magnetic grain size, absence of transported clays, and the highest macrocharcoal particles abundance; (ii) from 5200 to 2950 cal yr BP, marked by a replacement of the mangrove-like vegetation by a more inland mixed-swamp forest community with low levels of charcoal, and (iii) from 2950 cal yr BP to present-day, characterised by the establishment of the current vegetation community, dominated by M. flexuosa, and an increasing trend in the charcoal curve since the last 700 years. A combination of regional (climatic changes) and local (sediment ontogeny) has been proposed as the key drivers influencing the vegetation succession recorded. The stabilisation of the sea-level that occurred during the mid-Holocene would have favoured the transgression of the coastal line, with the migration of the coastal-like vegetation seawards. Synchronous to this event, a trend towards drier conditions has been reported in the close Cariaco record, that could have also influenced the vegetation replacement. Between 3800 and 2800 years ago, the increased ENSO variability registered in Cariaco may have played a key role in the expansion of the Mauritia palm community. It is suggested that in our location, the potential inhabiting human populations were differently influenced by these environmental changes. First, the disappearance of the coastal resources could have favoured land abandonment, whereas the increase in the abundance of the palm might be influential for the arrival of other inland cultures that were previously used to manage Mauritia. This sequence shows the importance of the ecosystem services for the location inhabitants, highlighting the abandonment of the mid-Holocene culture coeval with the disappearance of its ecosystem. These results also provide information about the sensitivity and resilience in facing external stressors of both humans and vegetation, and will be valuable tools for managing the future of this ecosystem. © 2019 Elsevier Ltd, This study has been funded by BBVA Foundation (ref. BIOCON 08-031 ) to V. Rull, and the Spanish Ministry of Economy and Competitivity (Juan de la Cierva Incorporación contract, ref. IJCI-2015-24273 ) and the Catalan Agency for Universities and Research AGAUR and the EU programme Marie Curie COFUND (Beatriu de Pinós – Marie Curie COFUND fellowship, ref.: 2014 BP-B 00094 ) to E. Montoya.

After decades of human-deterministic explanations for the collapse of the ancient Rapanui culture that inhabited Easter Island (Rapa Nui) before European contact (1722 CE), paleoecological studies developed over the last decade have provided sound evidence of climate changes and their potential socioecological impacts. Especially significant is the occurrence of a century-scale drought (1570–1720 CE) during the Little Ice Age (LIA). Freshwater is a critical resource on Easter Island that heavily depends on rain, which maintains the only three permanent surficial freshwater sources on the island: two lakes (Rano Kao and Rano Raraku) and a marsh (Rano Aroi). Under these conditions, the LIA drought could have significantly affected human life; however, the Rapanui society remained healthy, showing remarkable resilience. There are two main hypotheses on how the ancient Rapanui could have obtained freshwater to guarantee their continuity. One of these hypotheses proposes that Lake Kao was a permanent source of freshwater, even during the LIA drought, which led to some intraisland cultural and population reorganizations. The coastal groundwater hypothesis dismisses the use of lakes and other surficial freshwater sources to maintain the water-stressed Rapanui population and contends that the only routine freshwater sources during the LIA drought were the abundant and widespread coastal seeps fed by fresh/brackish groundwater. The pros and cons of these two hypotheses are discussed on the basis of the available archeological and paleoecological evidence, and it is concluded that given the present state of knowledge, neither can be rejected. Therefore, these two proposals could be complementary rather than mutually exclusive., The author’s Easter Island research was funded by the Spanish Ministry of Education and Science, through projects LAVOLTER (CGL2004-00683) and GEOBILA (CGL2007-60932/BTE).