Chironomid-based Holocene summer temperature dynamics from southern Spain

Holocene summer temperature reconstruction based on a chironomid record from Sierra Nevada, southern Spain

This study presents a reconstruction of Holocene mean July air temperatures based on chironomid assemblages preserved in the sedimentary record of Laguna de la Mosca (LdlMo), an alpine lake in the Sierra Nevada of southern Spain. The LdlMo record reveals that the highest temperatures occurred during the Early and early-Middle Holocene, between 8500 and 7000 cal yr BP, followed by a significant cooling event. During the Middle Holocene, temperatures stabilized, but a second major cooling event occurred at approximately 4200 cal yr BP, possibly associated with the 4.2 kyr event. Throughout the Late Holocene, temperatures generally remained low, punctuated by warming episodes between 2300–1600 cal yr BP during the Iberian Roman Humid Period (IRHP) and around 1000 cal yr BP during the Medieval Climate Anomaly (MCA). The lowest temperatures were recorded at the end of the Little Ice Age (LIA), circa 1800 CE. Since ~1955 CE, a rapid and pronounced warming trend of 2.5°C has been observed, driven by anthropogenic climate change. This study shows the amplification of recent warming at high elevations, highlighting the vulnerability of these fragile and unique alpine environments to the impact of climate change.This work was funded by grants BIOD22_001 and BIOD22_002, funded by Consejería de Universidad, Investigación e Innovación and Gobierno de España and Unión Europea – NextGenerationEU and PID2021-125619OB-C21 funded by the Ministerio de Ciencia e Innovacion of Spain, the Agencia Estatal de Investigacion and the Fondo Europeo de Desarrollo Regional FEDER MCIN/AEI/10.13039/501100011033/FEDER, UE

A stable isotope record of Holocene precipitation dynamics in the Baltic region from Lake Nuudsaku, Estonia

We obtained a 15 m drill core from Deukryang Bay on the southwest coast of Korea, which is now an area of reclaimed land used for agriculture. We investigated changes in the depositional environment and hydrological climate responses to sea level changes using sedimentary facies, radiocarbon ages, grain-size analysis, total organic carbon (TOC), total sulfur (TS), and stable carbon isotopes (δ13C). Sediment deposition began at 12,000 cal yr BP and was divided into four stages based on changes from fluvial to intertidal environments related to Holocene marine transgression events. Stage 1 (>10,000 cal yr BP) is represented by fluvial sediments; Stage 2 (10,000–7080 cal yr BP) is represented by the deposition of mud facies in an intertidal zone in response to sea level rise; Stage 3 (7080–3300 cal yr BP) was a period of gradually descending sea level following the Holocene maximum sea level and is characterized by gradual changes in TOC, TS, and C/S ratios compared with the mud facies of Stage 2. Stage 4 (3300 to present) was deposited in a supratidal zone and contains low TS and an abundance of TOC. Based on our TS and C/S ratio results, the south coast of Korea was mainly affected by sea level rise between 7000 and 3000 cal yr BP, during the middle Holocene. At 3000 cal yr BP, sea level began to stabilize or gradually decrease. In addition, changes in δ13C values are clearly observed since ca. 5000 cal yr BP, in particular, large hydrological changes via freshwater input are confirmed in 4000–3000 cal yr BP. We consider these shifts in freshwater input indicators of an increased influence of El Niño and La Niña conditions, related to the weakening of the East Asian Summer Monsoon (EASM) and changes in sea surface temperature (SST) of the Western Pacific Ocean during the middle Holocene climatic optimum (between 7800 and 5000 cal yr BP). The cooling periods of SST in East Asia between 8400 and 6600 cal yr BP reported from the west coast of Korea are related closely to changes in vegetation (as evidenced by δ13C) from 7700 cal yrs BP to the present in the southwest coast of Korea. We interpret the freshwater input events at 4000–3000 cal yr BP to be related to changes in SST in response to the weakening of the EASM on the southwest coast of Korea. However, additional research is needed to study the southward migration effect of the westerly jet related to SST and atmospheric circulation controlling terrestrial climate in the middle Holocene.

Late Pleistocene–Holocene vegetation and Indian summer monsoon record from the Lahaul, Northwest Himalaya, India

Understanding the spatiotemporal monsoonal variability during the Holocene helps in understanding the rise and fall of many civilizations. In this study, a 2.65 m high palaeo lake sedimentary profile from the Kumaun Lesser Himalaya, Uttarakhand State, India was pollen analysed to reconstruct the variability in the monsoonal precipitation during the Middle Holocene. The study revealed that between ~7522 and 7216 cal yr BP, conifers dominated mixed broad-leaved forests occurred around the landscape of the study area, indicating a less cold and dry climate with decreased monsoon precipitation. Broad-leaved taxa during this phase show increased values considerably, indicating amelioration in climatic condition, which could be, in global perspective, broadly falling within the time-interval of the Holocene Climate Optimum (HCO; 7000–4000 BP). Between ~7216 and 6526 cal yr BP, dense conifers-dominated mixed broad-leaved forests transformed the conifers-dominated broad-leaved forests around the study area under a cold and drier climate with further reduction in monsoon precipitation. Subsequently, between ~6526 and 5987 cal yr BP, conifers-dominated broad-leaved forests continued to grow, but with lesser frequencies, around the study area under a comparatively less cold and dry climate with reduced monsoon precipitation. Finally, between ~5987 and 5817 cal yr BP, the frequencies of conifers-dominated broad-leaved forests further decreased around the landscape of the study area under a comparatively lesser cold and dry climate, probably indicating decreased monsoonal precipitation. Hence, the present study mainly showed the dominance of conifers forests around the study area between ~7522 and 7216 cal yr BP, ~7216 and 6526 cal yr BP, ~6526 and 5987 cal yr BP and between ~5987 and 5817 cal yr BP; however, broad-leaved forests also demonstrated increasing tendency between ~7522 and 7216 cal yr BP in the milieu of cold and dry climates. Moreover, the study also revealed that a lake was formed around 7522 cal yr BP along the Kulur River, a tributary of Saryu River around the study area and existed until 5817 cal yr BP.

A 3300 year-long reconstruction of paleoenvironmental moisture conditions was constructed from a sediment core from North Gate Bog (NGB) in the northern section of Range Creek Canyon within the Colorado Plateau. The methods used to analyze the record include loss on ignition (LOI), magnetic susceptibility (MS), elemental analysis with X-ray fluorescence (XRF), charcoal influx, isotopic analysis, elemental ratios and pollen percentages, influx, and ratios. This study adds two new insights to the paleoenvironmental record of the northern section of the Colorado Plateau. First, four climatic zones were established. Zone 1 (3300–2750 cal yr BP) had 100-year wet to dry variations with droughts recorded from 3300–3200, 3000–2900, and 2800–2700 cal yr BP. Zone 2 (2750–1600 cal yr BP) had an overall dry period with an 800-year transition to increased warmth and winter moisture. Zone 3 (1600–850 cal yr BP) had an overall warm, wet, summer precipitation climate conducive to the establishment of Zea Mays and Pinus edulis, two staple foods of the Fremont culture. The Medieval Climate Anomaly (MCA) registered warm and wet in this part of the Colorado Plateau. Zone 4 (850–0 cal yr BP) had a sharp transition to a drier climate from 850 to 400 cal yr BP. During the Little Ice Age (LIA), wetter climate taxon increases such as Artemisia, Cyperaceae, and Pinus edulis. The second overall finding in this study was that NGB was a place of human activity including Fremont farming. The identification of a Zea mays pollen grain confirms the archeological presumptions that this higher elevation site was used to farm corn along with other sites in Range Creek Canyon (RCC). The post Fremont occupation period was marked by a sharp increase in organic material and a return of pinyon-juniper woodlands.

Times are changing: A new chronology for Holocene volcanic events and hydro-sedimentary history recorded in the Sarliève marsh (central France)

Here we provide the first chironomid record and associated summer air-temperature (TVII) reconstruction between ca. 16,800–9100 cal yr BP from Lake Saint Anne (SZA), situated in the Eastern Carpathians. SZA was formed by the youngest volcanic eruption of Ciomadul volcano at ca. 29,600 cal yr BP. Our main goals in this study are to test whether warming after Heinrich event 1 (H1; ca. 16,200 cal yr BP) had similar amplitude to the late glacial warming, while Younger Dryas (YD) summers remained relatively warm in this region of Europe. We found the most remarkable chironomid assemblage change with a TVIIincrease of ~3.5–3.8°C at ca. 16,350 cal yr BP at SZA, followed by another slight TVIIincrease of ~0.8–1.0°C at ca. 14,450 cal yr BP. Only very minor temperature variations were recorded between 14,450 cal yr BP and 11,700 cal yr BP, with an unexpected TVIIdecrease in the Early Holocene. Variations in water depth together with increasing analogue problems and paludification from ca. 14,200 cal yr BP onwards may have influenced the reliability of our paleotemperature record obtained from SZA. In addition,Sphagnum-indicated decreasing pH, and hence decreasing nutrient level, likely overrode the effect of summer air-temperature changes during the Early Holocene, and this may explain the bias in the chironomid-inferred summer air-temperature reconstruction in the Early Holocene section.

Response of prehistoric human activity to environmental changes since 7,000 cal yr BP in Nenjiang River Basin, northeast China

We analyzed faunal remains from two rockshelters in the far western Bonneville basin of eastern Nevada: Bonneville Estates Rockshelter and Siblings East Shelter. The analysis focused on paleobiogeographic changes between 17,500 and 5500 cal yr BP. Bonneville Estates Rockshelter contains faunal remains dating to the Heinrich 1 Stadial (18,000 to 14,700 cal yr BP), whereas both shelters contain faunal remains dating to the Bølling-Allerød Interstadial (14,700 to 12,900 cal yr BP), Younger Dryas Stadial (12,900 to 11,700 cal yr BP), Early Holocene (11,700 to 9300 cal yr BP), and Middle Holocene (9300 to 5500 cal yr BP). Identified faunal remains from these records indicate cool and either moist or dry climate compared to today between 17,500 and 10,200 cal yr BP, and increasingly warm temperatures impacting animal biogeographies beginning in the latter stages of the Younger Dryas and first one-half of the Early Holocene, culminating in xeric-adapted species like today by 9300 cal yr BP. Bonneville Estates Rockshelter also contains specimens of either gray wolf (Canis lupus) or the extinct dire wolf (Aenocyon dirus) and one felid phalanx of either puma/cougar (Puma concolor) or the extinct North American “cheetah” (Miracinonyx trumani), whereas Siblings East Shelter contains a rib of an extinct large horse of the genus Equus. Radiocarbon dated faunal remains were found directly atop Lake Bonneville beach gravels deposited inside Siblings East Shelter on the Provoterrace of Lake Bonneville, suggesting the lake dropped from this elevation prior to 14,300 cal yr BP.

Holocene vegetation, fire and climate history of the Sawtooth Range, central Idaho, USA

Lateglacial and Holocene changes in vegetation and human subsistence around Lake Zhizhitskoye, East European midlatitudes, derived from radiocarbon-dated pollen and archaeological records

In order to study the stability and dynamics of highly biodiverse mountain rain forest and paramo ecosystems, the late Pleistocene and Holocene climate and fire variability as well as human impact in the Podocarpus National Park region, the first comprehensive palaeoenviremental study from the southeastern Ecuadorian Andes will be presented. An initial study of recent vegetation/modern pollen rain relationship on an altitudinal transects between 1800 and 3200 m elevation in the mountain forest and (sub)-paramo vegetation of the ECSF (Estacion Cientifica San Francisco) research area provide important background information in the interpretation of late Quaternary pollen records. Cluster analysis on the pollen rain data by CONISS, clearly reflects the zonation of the different vegetation units, lower mountain forest (LMF), upper mountain forest (UMF) and (sub)-paramo. A relatively high number of pollen taxa correspond to the altitudinal distribution of genera and families of modern vegetation. The modern tree line in the research area is at ca. 2790 m, which is pointed out by an increase of (sub)-paramo taxa and a decrease of mountain forest taxa in the pollen rain data. Palaeoenvironmental changes, inferred from 9 lake, peat bog and soil deposits, collected at different elevations between ca. 2000 and 3300 m, were investigated by pollen, spores and charcoal analysis, in combination with XRF- and magnetic susceptibility-scanning on the lake sediment cores. During the late Pleistocene from ca. 21,000 to 11,200 cal yr BP, grass-paramo vegetation occurred at the Tiro-Pass (2810 m), reflecting cold and moist climatic conditions as well as a shift of vegetation zones into lower elevation during this period. During the transition from late Pleistocene to early Holocene from ca. 14,500 to 9700 cal yr BP, arboreal taxa, mainly Weinmannia strongly increase at Laguna Cocha Caranga (2710 m), reflecting a raise in temperature. The early Holocene from ca. 11,200 to 8900 cal yr BP (El Tiro-Pass) is characterised by an increase of temperature and moisture, as well as a shift of vegetation zones into higher elevation. During the mid Holocene period, from ca. 8900 to 3300 cal yr BP, upper mountain forest vegetation developed at the El Tiro-Pass, where subparamo vegetation occurred in recent times, suggesting a warmer climate than present day at this elevation. XRF-scanning data from Laguna Rabadilla de Vaca (3310 m) reflects a drier period from ca. 8990 to 6380 cal yr BP and a wetter period from ca. 6380 to 3680 cal yr BP. The green algae Botryococcus braunii, Isoetes and Cyperaceae were used to reconstruct Holocene wet/dry phases at Laguna Cocha Caranga. Drier climatic conditions occurred from ca. 9700 to 6900 cal yr BP and from ca. 4200 to 1300 cal yr BP. From ca. 6900 to 4200 cal yr BP and from ca. 1300 cal yr BP to modern time"s wetter climatic conditions occurred. During the late Holocene, modern climatic conditions, as well as recent vegetation established since ca. 3680 cal yr BP at Laguna Rabadilla de Vaca and since ca. 3300 cal yr BP at the El Tiro-Pass. An increase of fire intensity during the early to mid Holocene period after ca. 9700 cal yr BP at Laguna Cocha Caranga and after about 7500 cal yr BP at the El Tiro-Pass reflects beginning human impact on the ecosystem in the Podocarpus National Park region. High occurrence of grasses document, that past fires have markedly influenced the floristic composition of the mountain rain forest and paramo ecosystems during the mid to late Holocene period. The reduction of fire intensity coupled with a decrease of grasses after ca. 1300 cal yr BP (Laguna Cocha Caranga) and between ca. 970 to 400 cal yr BP (Upper Rio San Francisco valley), coupled with a missing of Zea mais pollen, suggests a reduction and/or absence of human activities, may be as a result of political unrest. After the reduction and/or absence of human influence the mountain forest vegetation starts to recover.

Late-Glacial and Holocene forest dynamics at Steregoiu in the Gutaiului Mountains, Northwest Romania