Limnological changes and chironomid-inferred summer air temperature from the Late Pleniglacial to the Early Holocene in the East Carpathians

Here we provide the first chironomid record and associated summer air-temperature (T VII ) 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 T VII increase of ~3.5-3.8°C at ca. 16,350 cal yr BP at SZA, followed by another slight T VII increase 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 T VII decrease 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

Holocene treeline and timberline changes in the South Carpathians (Romania): Climatic and anthropogenic drivers on the southern slopes of the Retezat Mountains

Two high-altitude lake-sediment sequences (Lake Lia, 1910 m a.s.l. and Lake Bucura, 2040 m a.s.l.) from the Retezat Mountains (South Carpathians, Romania) were analysed using multi-proxy methods to study responses of treeline, timberline and alpine/subalpine vegetation to climate change and human impact during the past 16,000 years. Woody species (Pinus mugo, Pinus cembra, Picea abies and Juniperus communis) reached Lake Lia between 12,000 and 11,800 cal. yr BP, whereas P. mugo colonised the shores of Lake Bucura at 9600 cal. yr BP. Lake Lia was in the timberline ecotone between 8000 and 3200 cal. yr BP, in semi-open P. cembra and Picea abies woodland, probably mixed with P. mugo on the steeper slopes. Lake Bucura was surrounded by the upper part of the krummholz zone during the mid-Holocene. The increase in P. cembra after c. 6000 cal. yr BP around Lake Lia suggests that the composition of the timberline forest changed. The disappearance of P. cembra and Picea abies around Lake Lia at ~3000 cal. yr BP reflects descent of the timberline. A large mean July temperature decline between 3300 and 2800 cal. yr BP may have driven or at least contributed to the descent of the Picea abies?P. cembra forests. An increase in human indicator pollen types in Lake Bucura around 4200 cal. yr BP may reflect human impact in the naturally open alpine zone in the Late Bronze Age. In contrast, human impact likely appeared considerably later, around 2650 cal. yr BP (Early Iron Age) around Lake Lia in the upper subalpine zone. Human impact likely intensified after 2200 cal. yr BP at both sites that resulted in the lowering of the krummholz zone. We conclude that climate change and human impact both played an important role in the lowering of the treeline and timberline in the late-Holocene

Holocene fire-regime changes near the treeline in the Retezat Mts. (Southern Carpathians, Romania)

To investigate Holocene vegetation and fire-disturbance histories in the treeline ecotone, macroscopic charcoal, plant-macrofossil, and pollen records from two lacustrine sediment records were used. Lake Lia is on the southern slope and Lake Brazi is on the northern slope of the west-east-oriented Retezat Mountain range in the Romanian Carpathians. The records were used to reconstruct Holocene fire-return intervals (FRIs) and biomass burning changes. Biomass burning was highest at both study sites during the drier and warmer early Holocene, suggesting that climate largely controlled fire occurrence. Fuel load also influenced the fire regime as shown by the rapid biomass-burning changes in relation to timberline shifts. Overall, the number of inferred fire episodes was smaller on the northern than on the southern slope. FRIs were also comparatively longer (1000-4000 years) on the northern slope where Picea abies-dominated woodlands persisted around Lake Brazi throughout the Holocene. On the southern slope, where Pinus mugo was more abundant around Lake Lia, FRIs were significantly shorter (80-1650 years). A period of frequent fire episodes occurred around 1900-1300 cal yr BP on the southern slope, when chironomid-inferred summer temperatures increased and the pollen record documents increased anthropogenic activity near the treeline. However, the forest clearance by burning to increase grazing land was subdued in comparison to other European regions. © 2016 Elsevier Ltd and INQUA

Plant macrofossils from lake sediment as the material to assess ancient genetic diversity: Did deforestation influence Norway spruce ( Picea abies ) in the South Carpathians?

How genetic diversity of populations reacts to neutral or adaptive processes such as population bottlenecks, immigration or local adaptation are central questions of population genetics. They may be directly answered through ancient DNA analysis, however such studies in plants are remarkably scarce, owing to the difficulty of gaining population-scale samples with good DNA preservation. Plant macrofossils are abundant in lake sediments, and here we assessed if they can be valuable material for population genetic studies. We extracted ancient DNA from early to late Holocene seed and needle remains of Norway spruce (Picea abies L. Karst) recovered from the sediment of a lake in the Retezat Mts. (South Carpathians). We aimed to reveal whether deforestations starting in the late Holocene and reaching maximum in the 19th and early 20th centuries have caused decreased genetic diversity in the modern Norway spruce population of the Retezat Mts. In a combined approach, we sequenced two plastid regions and generated detailed paleobotanical data to reconstruct the population history of Norway spruce. Our results show that genotyping success of the ancient material was high in samples younger than c. 2000-year-old, but was very low in early Holocene samples, and needles allowed genotyping with higher success compared to seeds. We discovered macrofossil samples that contained DNA from more than a single Norway spruce individual. This phenomenon, together with the possible multiple sampling of the same individual needs to be kept in mind when interpreting the genetic data obtained from macrofossils. Our results overall indicate a genetic diversity decrease during the late Holocene. We demonstrate that macrofossils preserved in sediments are invaluable material for population genetic studies

Terrestrial and aquatic ecosystem responses to early Holocene rapid climate change (RCC) events in the South Carpathian Mountains, Romania

As demonstrated by an increasing number of palaeoclimatic and palaeoecological studies, rapid climate change events (RCCs) occurred frequently in the Holocene and their timing correlates well in the European records. Changes in vegetation composition and environmental conditions were significant during these RCC events. In this study we use high resolution pollen, stomata, micro- and macrocharcoal, macrofossil, siliceous algae, biogenic silica and organic content analyses from two alpine lake sediments (Lake Brazi, 1740 m a.s.l.; Lake Gales, 1990 m a.s.l.) in the Retezat Mts, South Carpathian Mountains, Romania. Our aim is to study ecosystem responses to RCCs between 12,000 and 7000 cal yr BP using high-resolution proxy analyses of the relevant sediment sections. We detected several significant changes in the terrestrial vegetation composition and aquatic ecosystems in case of both lakes. Complex ecosystem responses were found in connection with the early Holocene RCC intervals. Most prominently, the 10.2 ka climatic change likely fostered the extinction of Larix decidua from the shore of Lake Brazi, while climatic change during the 8.2 ka event facilitated the establishment of Carpinus betulus in the lower deciduous mixed oak forests, due to decreasing growing season temperatures, frequent summer droughts and associated recurrent fire events. Taken together, most of the significant pollen compositional changes reflected the periodic spread of pioneer deciduous tree taxa (mainly Fraxinus excelsior and Corylus avellana) during the early Holocene RCCs. In all cases, this change was connectable to increased regional fire activity and the temporary increase of herbs. The most significant change in the lake-ecosystems was often the short-lived spread of various planktonic diatom species, mainly the members of genus Aulacoseira. Sudden appearance and large-scale percentage increase of these taxa suggested higher water-depth and/or intensified water turbulence

Drivers of Holocene treeline and timberline changes in the Retezat Mountains (South Carpathians, Romania)

Four high-altitude lake sediment sequences (Lake Brazi, 1740 m .as.l., Lake Gales 1990 m a.s.l., Lake Bucura, 2040 m a.s.l. and Lake Lia, 1910 m a.s.l.) were analyzed using multi-proxy methods (pollen, stomata, plant macrofossil and micro- and macrocharcoal) in order to study responses of treeline and alpine/subalpine vegetation to climate change and human impact during the last 15000 years. Observing and reconstructing the changes of the position and structure of the treeline can provide valuable information on biotic and other factors such as human activities. Sediment cores were taken from two lakes on the northern slope (Lake Brazi and Lake Gales) and two lakes from the southern slope (Lake Lia and Lake Bucura) in the Retezat Mountains, South Carpathians (Romania).</p

Warm Younger Dryas summers and early late glacial spread of temperate deciduous trees in the Pannonian Basin during the last glacial termination (20-9 kyr cal BP)

This paper focuses on the last glacial termination vegetation and climate reorganization of the Eastern Pannonian Plain via the multi-proxy paleoecological analysis of Kokad mire in Eastern Hungary. Grains size, sediment chemistry and magnetic susceptibility records are compared with the pollen and plant macrofossil records on the basis of which biome and quantitative summer mean temperature reconstructions are provided and discussed with other climate records of the region. Biome assignments indicated (graminoid and forb) tundra vegetation from 19,440 cal yr BP with the local presence of Betula pendula, B. pubescens, B. nana, and Pinus sylvestris. A rapid biome shift to cool coniferous forest took place at 16,200 cal yr BP, and a second biome shift was identified at 14,740 cal yr BP when cool mixed forest developed and persisted into the Early Holocene. The most prominent feature of the record was the early post last glacial maximum (LGM) establishment (17,700 cal yr BP) and expansion (14,700 cal yr BP) of elm (Ulmus) and hazel (Corylus) supporting the phylogeographical evidence for extra-Mediterranean refugia in the Pannonian Basin. The fungal spore record indicated the presence of large grazing mammals locally after the LGM until ∼16,780 cal yr BP. Their disappearance predated the biome shift to cold coniferous forest and the final increase of forest fires. Pollen based summer temperature reconstruction suggested relatively warm summers (∼14.5 °C) by 19,440 cal yr BP, and buffered July mean temperature fluctuations throughout the last glacial termination in this region with < 1 °C decrease in summer mean temperatures during the Younger Dryas stadial, and ∼2.2 °C warming in the Early Holocene. Our comprehensive summary of the basin’s Late Pleniglacial (24,000–14,600 cal yr BP) and late glacial paleoenvironmental and paleoclimate records showed a partially wooded landscape with higher woody cover in Western Hungary. Several loess and lake archives confirmed that in this region of Europe the warming after Heinrich event 1 (around 16,200 cal yr BP) had similar amplitude to the late glacial warming