The Holocene Cedrus pollen record from Sierra Nevada (S Spain), a proxy for climate change in N Africa

Comprehending the effects of climate variability and disturbance on forested ecosystems is paramount to successfully managing forest environments under future climate scenarios (e.g., global warming, aridi-fication increase). Changes in fossil pollen abundance in sedimentary archives record past vegetation dynamics at regional scales, mainly related to climate changes and, in the last few millennia, to human impact. Pollen records can thus provide long databases with information on how the environment reacted to climate change before the historical record. In this study, we synthesized fossil pollen data from seven sites from the Sierra Nevada in southern Spain to investigate the response of forests in the western Mediterranean area to millennial-scale climate changes and to human impact during the Holocene. In particular, here we focused on Cedrus pollen abundances, which most-likely originated from Northern Africa and were carried to Sierra Nevada by wind. Cedrus pollen has received little attention in the Iberian Peninsula palynological records, for it occurs in low concentrations and has an African source, and thus this article explores the potential to reconstruct its past history and climate. Although Cedrus abundances are generally lower than 1% in the studied pollen samples, a comparison with North African (Moroccan) Cedrus pollen records shows similar trends at long- and short-term time-scales. Therefore, this record could be used as a proxy for changes in this forest species in North Africa. As observed in the Sierra Nevada synthetic record, the increasing trend of Cedrus pollen during the Middle and Late Holocene closely correlates with decreasing summer insolation. This would have produced overall cooler annual temperatures in Northern Africa (Middle Atlas and Rif Mountains) as well as lower summer evaporation, benefiting the growth of this cool-adapted montane tree species while increasing available moisture during the summer, which is critical for this water-demanding species. Millennial-scale variability also characterizes the Sierra Nevada Cedrus synthetic pollen record. Cedrus abundance oscillations co-vary with well-known millennial-scale climatic variability that controlled cedar abundance and altitudinal distribution in montane areas of N Africa. (C) 2020 Elsevier Ltd. All rights reserved.Peer reviewe

Climatic control on the Holocene hydrology of a playa-lake system in the western Mediterranean

Evaporitic lakes such as playa-lakes are characteristic of many arid regions and are unique environments with respect to fauna and flora, while being very vulnerable to climate and environmental fluctuations and threatened by the current global change scenario. Water balance oscillations in these systems can trigger the precipitation or dissolution of different evaporitic minerals, negatively impacting local biodiversity and economic activities. Here, we study the sedimentary record of a small saline pond from a playa-lake complex in southwestern Iberia in order to reconstruct the paleohydrological evolution of this area and assess potential anthropogenic disturbances. The different proxies studied in the-11.9 ky old sedimentary record of the Laguna de la Ballestera suggest that the greatest lake extension and the highest water levels occurred during the Early Holocene, pointing to the wettest period of the record. Climate transitioned towards more arid conditions during the Middle Holocene, and even more dramatically during the Late Holocene. In this last stage the wetland surface and the water level largely diminished and gypsum precipitation gradually increased pointing towards a negative precipitation/ evapotranspiration balance and lowest water levels. Summer desiccation likely occurred under this scenario, especially after-1.0-0.9 cal ky BP coeval with the Medieval Climate Anomaly, when gypsum content started to rise abruptly. However, this significant gypsum precipitation was only associated with a massive drop in the siliciclastic content and scarce carbonates (dolomite and calcite) during the last-400 years. This evidence suggests a shift from a (semi) permanent to a temporal/seasonal hydrological regime. The environmental evolution of this wetland responded to the general climatic evolution of the western Mediterranean during the Holocene, being mostly controlled by changes in insolation. Our data also show that the environmental response of the studied wetland to natural climate variations was only significantly disturbed by human activities since the 20th century, especially in the second half of the century, deduced by abrupt fluctuations in the siliciclastic, gypsum and organic content in the sediments, as well as by the enhanced sedimentary accumulation rates, probably as a response to changes in the hydroperiod of the lake and in the catchment land use.Peer reviewe

Paleohydrological dynamics in the Western Mediterranean during the last glacial cycle

The transitional regions between the low and high latitudes of the Northern Hemisphere are highly vulnerable to future climate change yet most of the current climate models usually diverge in their projections. To better understand the dynamics in these regions, the reconstruction of past hydrological fluctuations and precipitation patterns is of paramount importance to accurately constrain present and future climate scenarios. In this study, we investigated paleohydrological dynamics in the western Mediterranean region, a transitional zone between low-mid latitudes and Atlantic - Mediterranean realms. We reconstruct precipitation and moisture source changes during the last -35 ka in order to propose the potential mechanisms driving these oscillations. To do so, we use hydrogen isotopes from sedimentary leaf waxes, more specifically the C31 n-alkane homologue, and a precipitation proxy based on previously published pollen data from a sedimentary core (Padul-15-05) in southern Iberia (Padul wetland -37-N). With this combination we disentangle the coupled effect of precipitation amount and source on the hydrogen isotopic signature of the studied C31 n-alkane record. Our results show three main periods characterized by different precipitation patterns. Low precipitation, mainly linked to a significant contribution from an isotopically-enriched Mediterranean precipitation source, occurred from -30 to -15.5 ka BP and during the last -5 ka, whereas enhanced precipitation with a predominant isotopically-depleted Atlantic precipitation source prevailed from -15.5 to -5 ka BP. This latter stage is here defined as the Western Mediterranean Humid Period (WMHP). In addition, some occasional millennial-scale opposite precipitation patterns can be observed during these climatically distinct periods. These changes in the source of precipitation were likely coupled to a shift in the main rainy season from winter, when Atlantic precipitation prevailed, to late winter-early spring, when the contribution of Mediterranean moisture is higher. Comparison between the studied mid-latitude terrestrial Padul-15-05 core and a low-latitude marine record offshore of northwestern Africa shows clear long-term synchronous responses of both western Mediterranean precipitation and western African monsoon systems to northern Hemisphere atmospheric dynamics, ultimately controlled by orbital forcing and ice-sheets fluctuations.Peer reviewe

Paleoclimatic influence on bottom currents in the East Bransfield Basin during the late Holocene (Antarctic Peninsula)

Póster en INSTANT SCAR Conference 2023, September 11-14, in Trieste (Italy

Paleoenvironmental evolution of Laguna Seca lake (Sierra Nevada, southern Iberia) since the Late Glacial

Comunicación oral en XXI INQUA Congress. Rome (Italy). 14-20th july 2023Laguna Seca lake at 2259 masl has provided the longest alpine sedimentary record in southern Iberia, registering the last ~18 kyr in a ~14-meter-long sediment core. The oldest part of the sedimentary record represents a phase of subaerial debris flows and a small glacier/nivation hollow. The sediment characteristics abruptly changed at ~15.7 cal kyr BP, when a lake environment was established. A multi-proxy approach (magnetic susceptibility, organic geochemical analyses in bulk sediment, XRF core scanner data, and algae identification) has allowed the characterization of three different environmental phases in this lake. Deep lake conditions are identified from ~15.7 to ~10.6 cal kyr BP, agreeing with overall increasing precipitation in southern Iberia coinciding with augmenting summer insolation. This part of the record is characterized by grey lutites with high total organic carbon (TOC) content, high algae productivity, high vascular plant inputs (high C/N ratio) from the catchment and low Fe/S ratio, suggesting low oxygen conditions in the water-sediment interphase. Between ~10.6 and 8.2-8.0 cal kyr BP higher TOC and low Fe/S ratio are also recorded as well as higher algae content and low C/N ratio suggesting high aquatic production and more algae contribution to the local organic matter pool. This period registered the highest lake levels agreeing with summer insolation maximum and highest precipitation in southern Iberia. An abrupt lowering of the lake level is recorded after 8.0 cal kyr BP in the area. This is deduced by the decrease in TOC and algae in the sediments and more siliciclastic contribution from the catchment basin, evidenced by a high increase in siliciclastic elements (Si, Al, K, Ti, among others), with increased oxic conditions in the water-sediment interphase pointed out by the high increase in Fe/S ratio. Additionally, a potential increase in north African aeolian inputs (rich in Fe cations and Fe compounds) can be interpreted for the Middle and Late Holocene, evidenced by high Fe/Al values. This environmental change agrees with an aridification trend previously observed in the southern Iberian Peninsula

Millennial-scale cyclical environment and climate variability during the Holocene in the western Mediterranean region deduced from a new multi-proxy analysis from the Padul record (Sierra Nevada, Spain)

A high-resolution multi-proxy approach, integrating pollen, inorganic and organic geochemical and sedimentological analyses, has been carried out on the Holocene section of the Padul sedimentary record in the southern Iberian Peninsula reconstructing vegetation, environment and climate throughout the last ~ 11.6 cal kyr BP in the western Mediterranean. The study of the entire Holocene allows us to determine the significant climate shift that occurred during the middle-to-late Holocene transition. The highest occurrence of deciduous forest in the Padul area from ~ 9.5 to 7.6 cal kyr BP represents the Holocene humidity optimum probably due to enhanced winter precipitation during a phase of highest seasonal anomaly and maximum summer insolation. Locally, insolation maxima induced high evaporation, counterbalancing the effect of relatively high precipitation, and triggered very low water table in Padul and the deposition of peat sediments. A transitional environmental change towards more regional aridity occurred from ~ 7.6 to 4.7 cal kyr BP and then aridification enhanced in the late Holocene most likely related to decreasing summer insolation. This translated into higher water levels and a sedimentary change at ~ 4.7 cal kyr BP in the Padul wetland, probably related to reduced evaporation during summer in response to decreased in seasonality. Millennial-scale variability is superimposed on the Holocene long-term trends. The Mediterranean forest regional climate proxy studied here shows significant cold-arid events around ~ 9.6, 8.5, 7.5, 6.5 and 5.4 cal kyr BP with cyclical periodicities (~1100 and 2100 yr) during the early and middle Holocene. A change is observed in the periodicity of these cold-arid events towards ~1430 yr in the late Holocene, with forest declines around ~ 4.7–4, 2.7 and 1.3 cal kyr BP. The comparison between the Padul-15-05 data with published North Atlantic and Mediterranean paleoclimate records suggests common triggers for the observed climate variability, with the early and middle Holocene forest declines at least partially controlled by external forcing (i.e. solar activity) and the late Holocene variability associated with internal mechanisms (oceanic-atmospheric).This work was supported by the project P11-RNM-7332 funded by Consejería de Economía, Innovación, Ciencia y Empleo de la Junta de Andalucía, the project ( CGL2013-47038-R ) funded by Ministerio de Economía y Competitividad of Spain and fondo Europeo de desarrollo regional FEDER and the research group RNM0190 (Junta de Andalucía). M. J. R.-R. acknowledges the predoctoral and postdoctoral funding provided by Consejería de Economía, Innovación, Ciencia y Empleo de la Junta de Andalucía ( P11-RNM-7332 ). J.C. acknowledges the PhD funding provided by Ministerio de Economía y Competitividad ( CGL2013-47038-R ). J.S.C. acknowledges the support of projects CGL-BOS-2012-34717 , CGL-BOS 2015-68604 , and Fundación Séneca 19434/PI/14. A.G.-A. was also supported by a Ramón y Cajal Fellowship RYC-2015-18966 of the Spanish Government (Ministerio de Economía y Competividad)

Summer temperatures during the Holocene inferred from a chironomid record from Sierra Nevada, southern Spain

XXI INQUA 2023. Rome. july 14-20 2023Accurate and continuous quantitative paleotemperature records from the past are rare in southern Iberia, mostly due to the scarcity of continuous sedimentary sequences in terrestrial environments from that area. In this study we show the first Holocene mean July air temperature reconstruction based on fossil chironomids from a sedimentary sequence obtained from Laguna de Río Seco, an alpine lake in Sierra Nevada, southern Spain. Reconstructed summer temperatures agree with changes in summer insolation and other palaeotemperature records from alpine environments from southern Europe and show the Holocene thermal maximum between 10 to 8.0 ka (1 ka = 1000 cal yr BP). Rapid cooling occurred after the warmest maximum and between ~8.0-7.0 ka and temperatures stabilized between ~6.5 and 3.0 ka. A further cooling trend started ~3.0 ka, and coldest summer conditions were reached at 1.4 ka (~550 CE) and ~0.2 ka (~1750 CE), coinciding with the Dark Ages and Little Ice Age, respectively. This record also shows relatively warmer summer temperature conditions during the Iberian-Roman Humid Period ~2.0 ka and during the Medieval Climate Anomaly at ~0.9 ka. Summer climate warming of more than two degree Celsius is observed in the last decades showing that recent warming is amplified in high alpine environments

Earliest evidence of pollution by heavy metals in archaeological sites

Homo species were exposed to a new biogeochemical environment when they began to occupy caves. Here we report the first evidence of palaeopollution through geochemical analyses of heavy metals in four renowned archaeological caves of the Iberian Peninsula spanning the last million years of human evolution. Heavy metal contents reached high values due to natural (guano deposition) and anthropogenic factors (e.g. combustion) in restricted cave environments. The earliest anthropogenic pollution evidence is related to Neanderthal hearths from Gorham's Cave (Gibraltar), being one of the first milestones in the so-called "Anthropocene". According to its heavy metal concentration, these sediments meet the present-day standards of "contaminated soil". Together with the former, the Gibraltar Vanguard Cave, shows Zn and Cu pollution ubiquitous across highly anthropic levels pointing to these elements as potential proxies for human activities. Pb concentrations in Magdalenian and Bronze age levels at El Pirulejo site can be similarly interpreted. Despite these high pollution levels, the contaminated soils might not have posed a major threat to Homo populations. Altogether, the data presented here indicate a long-term exposure of Homo to these elements, via fires, fumes and their ashes, which could have played certain role in environmental-pollution tolerance, a hitherto neglected influence.Francisco J. Jiménez Palacios and to the Analytical Chemistry Department (Sevilla University) are gratefully acknowledged for their help in the use of Carbolite electric oven. A.G.-A. was supported by a Marie Curie Intra-European Fellowship of the 7th Framework Programme for Research, Technological Development and Demonstration (European Commission). R.B. is a Beatriu de Pinós-A post-doctoral fellowship recipient (Generalitat de Catalunya and COFUND Marie Curie Actions, EU-FP7). This work also was partially financed by projects 19434/PI/14 Fundación Séneca, HARP2013-44269P, , CGL2012-38434-C03-03 and CGL2012-38358 Ministerio de Economía y Competitividad, 2014 SGR 900 and 2014/100573 Generalitat de Catalunya-AGAUR, RNM 432 Research Group 179 (Junta de Andalucia) and MEXT-Japan

Reconstruction of Past Environment and Climate Using Wetland Sediment Records from the Sierra Nevada

Understanding the effects of climate change and human activities on fragile mountain ecosystems is necessary to successfully managing these environments under future climate scenarios (e.g., global warming, enhanced aridity). This can be done through the study of paleoecological records, which can provide long paleoenvironmental databases containing information on how ecosystems reacted to climate change and human disturbances before the historical record. These studies can be particularly interesting when focusing on especially warm and/or dry past climatic phases. Biotic (pollen, charcoal) and abiotic (physical, geochemistry) analyses from wetland sediment records from the Sierra Nevada, southern Spain record changes in vegetation, fire history and lake sedimentation since ~11,700 years (cal yr BP). This multiproxy paleoecological study indicates that maxima in temperature and humidity occurred in the area in the Early and Middle Holocene, with a peak in precipitation between ~10,500 and 7000 cal yr BP. This is deduced by maxima in water runoff, the highest abundance of tree species and algae and high total organic carbon values recorded in the alpine wetland’s sedimentary records of the Sierra Nevada during that time period. In the last 7000 cal yr BP, and especially after a transition period between ~7000 and 5000 cal yr BP, a progressive aridification process took place, indicated by the decrease in tree species and the increase in xerophytic herbs in this region and a reduction in water runoff evidenced by the decrease in detritic input in the wetland sedimentary records. An increasing trend in Saharan dust deposition in the Sierra Nevada wetlands is also recorded through inorganic geochemical proxies, probably due to a coetaneous loss of vegetation cover in North Africa. The process of progressive aridification during the Middle and Late Holocene was interrupted by millennial-scale climatic oscillations and several periods of relative humid/droughty conditions and warm/cold periods have been identified in different temperature and/or precipitation proxies. Enhanced human impact has been observed in the Sierra Nevada in the last ~3000 cal yr BP through the increase in fires, grazing, cultivation, atmospheric pollution as well as reforestation by Pinus and the massive cultivation of Olea at lower altitudes.This study was supported by projects CGL2013-47038-R and CGL2017-85415-R funded by Ministerio de Economía y Competitividad of Spain and Fondo Europeo de Desarrollo Regional FEDER; Séneca Project 20788/PI/18; Junta de Andalucía I+D+i Junta de Andalucía 2020 Retos P-20-00059, FEDER Project B-RNM-144-UGR18, UGR-FEDER B-RNM-144-UGR18 Proyectos I + D + i del Programa Operativo FEDER 2018 and the research group RNM-190 (Junta de Andalucía). M.J.R.R. acknowledges the postdoctoral funding provided by the European Commission/H2020 (ERC-2017-ADG, project number 788616). J.C. acknowledges the postdoctoral funding provided by the Academy of Finland (project number 316702). A.G.-A. acknowledges the Ramón y Cajal fellowship RYC-2015-18966 provided by the Ministerio de Economía y Competitividad of the Spanish Government. M.R.G. acknowledges funding by the Juan de la Cierva-Incorporación program in the University of Granada (IJCI-2017-33755) from Secretaría de Estado de I+D+i, Spain. RSA acknowledges several travel grants from Northern Arizona University to support this work

Salt production by ignition during the prehistory in the Iberian Peninsula with special focus on the archaeological site of Espartinas (Ciempozuelos, Spain)

One of the prehistoric techniques of salt production consisted of using ceramic vessels, known as briquetage, for the artificial evaporation of salt water. This paper summarizes all the archaeological sites throughout the Iberinan Peninsula where briquetage has been described to date, with special focus on the well-studied archaeological site of Espartinas saltworks. At Espartinas we found the use of two different kinds of ceramics, which points to a two-step process also involving halfah or esparto grass, which may well have been used for transport or/and as an insulating layer between the vessels walls and the mass of salt to facilitate the extraction of whole salt cakes. Palaeoenvironmental conditions at Espartinas have also been described based on local and regional pollen records and compared with the dry conditions associated to the so-called “4.2 cal kyr BP abrupt climatic event”. Despite the reduced amount of radiocarbon dating, the briquetage appears have been present in the studied region from the Late Neolithic to at least the Bronze Age. However, we cannot discard the fact that it might have reached the early Roman period, when salt evaporation ponds replaced this laborious technique. Moreover, briquetage distribution has been compared with evaporite outcrops throughout the Iberian Peninsula and it has been observed a characteristic pattern with a preference for peripheral, near to coast regions, with the exception of from Aranjuez-Getafe lower-Miocene lacustrine evaporites in central Iberia. Briquetage spread also shows a marked correlation with sites characterized by the presence of Atlantic halberds the first true metal weapon ever made in Western Europe and part of the warrior panoply of Late Copper Age/Early Bronze Age elites. At least during this period, these findings suggest that briquetage was used to obtain solid salt cakes easily transportable to medium and large distances by Atlantic and intra-Iberian trade exchange networks, which confirms previous studies that associate Bell Beaker phenomenon with salt circulation.This work is funded by the Ministry of Science and Innovation of the Government of Spain, Agencia Estatal de Investigaci´on/10.13039/501100011033/and Fondo Europeo de Desarrollo Regional – A way of making Europe, in particular the grant number PID2021-125619OB-C22 (authors F.J.J.-E. and A.G-R.). The University of Groningen project Salt and Power: Early States, Rome and Resource Control financed by the Dutch Research Council (Nederlandse Organisatie voor Wetenschappelijk Onderzoek), funding n. 406.20.HW.013. (author F.B.). Also to project PID2019-105690 GB-I00.Peer reviewe