Aritina Haliuc

Erosion is a complex geomorphological process controlled by climate, soil and vegetation characteristics in addition to land-use. However, the interplay of these drivers is not fully understood. Here we present a 11.8 ka multi-proxy record of geochemical, mineral magnetic and grain size analyses from Lake Stiucii, in the Transylvania lowlands (CE Europe) documenting past erosional activity and the drivers of landscape change. We identify three major phases in the site’s development. The first, a lacustrine phase (11.8–10.9 cal ka BP), is characterised by open water conditions with significant river inflow and depicts a period of greater erosion under a less developed catchment vegetation cover. Between 10.9 and 4.6 cal ka BP, the lake became a wetland characterised by shallow water with a reduced drainage network under warmer climate and/or reduced rainfall. From 4.6 cal ka BP, a second lacustrine phase developed driven by enhanced stream flow and sediment input subsequently accelerated by land use change. On a millennial scale, the two significant changes in the lake-catchment system and erosion regime at 10.9 and 4.6 cal ka BP may reflect a response to fluctuations in large-scale atmospheric circulation patterns. The eight short-term erosional events identified at 10.6, 7.8 cal ka BP, between 4.4–4.1, 3.5, 3.0–2.5, 1.9, 1.5, 1.1–0.8 cal ka BP, overlap well-known climate events. However, from 4.6 cal ka BP the climate-landscape relationship is amplified by rising anthropogenic impacts. Our data provide critical information on the paleoenvironmental evolution of CE Europe’s lowlands and facilitate discussion of the effects of millennial and centennial climatic shifts as expressed in the local environment.

We present chironomid-based reconstructions of mean July air temperature changes over the last 2000 years from Lake Latoriței (1530 m a.s.l.) in the Southern Carpathians. A multi-proxy analysis was performed along a 58 cm long sediment core and two training sets were used for quantitative July air temperature reconstructions: the Eastern-European (EE, 212 lakes) and the Finnish-Polish-Carpathian (FPC, 273 lakes). The transfer functions had a coefficient of determination ( r²) 0.88 and 0.91 with a root mean squared error of prediction (RMSEP) 0.88°C and 1.02°C. Despite possible biases resulting from methodological problems and the ecological complexity of the chironomid response to both climatic and environmental changes, the agreement of the temperature reconstruction of Lake Latoriței with other alpine records suggests that the transfer function successfully reconstructed past summer temperatures between 750 and 1830 CE. Biases in the temperature reconstruction in the period before 750 and after 1830 CE were likely caused by increased abundance of rheophilic and semi-terrestrial chironomid species related to increased inflow activity before 750 CE and local land use changes after 1830 CE, which was also indicated by increasing deforestation and increasing lake productivity in the pollen and diatom records. Our results suggest that the region experienced a warm period between 750 and 1360 CE, and a cold period between 1360 and 1600 CE followed by fluctuating summer temperatures until 1830 CE. These events were associated with the so-called ‘Mediaeval Warm Period’ (MWP) and the ‘Little Ice Age’ (LIA), respectively. The inference models reconstructed a decrease in July air temperatures by 0.7°C–1.1°C during the LIA relative to the warmer MWP. We also demonstrated that the FPC training set gives better results, supporting that local/continental training sets are efficient to detect weak amplitude summer temperature changes in the Late-Holocene.

A Páreng-hegységcsoportban (Munții Parâng, Déli-Kárpátok) lévő magashegyi tó (Latorica-tó, Iezerul Latorița, 1530 m) üledékének késő glaciális és kora holocén korú szakaszán növényi makrofosszília és pollen analitikai elemzéseket végeztünk, hogy megállapítsuk a fahatár, az erdőhatár és a szubalpi vegetáció éghajlatváltozásra adott válaszreakcióit. A Latorica-tó vízgyűjtőjén és partján 15 510–14 765 kal. BP évek (Grönlandi 2-es oxigénizotóp fázis (GS-2) vége) között a gleccserek visszahúzódása nyomán nem volt, vagy csak ritka növényborítás lehetett, tehát a fahatár valószínűleg a tó alatt húzódott. Az ezt követő GI-1 fázisban (kormodellünk alapján 14 765–13 340 kal. BP évek között) bekövetkező felmelegedés hatására a tó körül kialakuló fahatár ökoton zónában törpefenyő, lucfenyő és szálanként vörösfenyő (Pinus mugo–Picea abies–Larix decidua) keveredésével jellemezhető, boreális nyílt erdő expanzióját rekonstruáltuk. A fahatár fokozatosan magasabbra húzódott, majd a GI-1 végén (13 340–12 930 kal BP évek közt) nagy intenzitású erdőtűz következhetett be a tó körül, annak vízgyűjtőjére is kiterjedve. A fiatal driász lehűlés a jelenlegi kormodell szerint 12 930 és 11 995 kal. BP évek között a tó szerves anyag produkciójának csökkenéséhez vezetett, ugyanakkor a lehűlés csak kis mértékben hatott a tó menti vegetációra. A legjelentősebb változás a havasi cirbolyafenyő (Pinus cembra) megjelenése és előretörése volt ebben az időszakban. A kora holocénben (11 995–11 300 kal. BP évek közt) a fa- és erdőhatár folyamatosan emelkedhetett, az erdőszerkezet zárult és tovább diverzifikálódott a molyhos nyír (Betula pubescens) megjelenésével: luc- (P. abies), vörösfenyő (L. decidua) és törpefenyő (P. mugo) alkotta nyílt, de a késő glaciálisnál zártabb erdők uralták a tó körüli tájat. Eredményeink alapján elmondhatjuk, hogy a késő glaciális erdőexpanzió gyorsasága közeli refúgiális populációkra utal a fenyőfélék esetében, valamint eredményeink megerősítik a Déli-Kárpátok Retyezát vonulatában kapott eredményeket, miszerint a fiatal driász lehűlés a vegetációs időszak hőösszegét csak kis mértékben csökkentette ebben a régióban (szemben Nyugat-Európával). Az éghajlatváltozás kompetíciós előnybe hozta a Déli-Kárpátok szubalpin zónájában a havasi cirbolyafenyőt (P. cembra), mely ekkor terjedt el a fahatár ökoton zónában. A kora holocén felmelegedés során a mainál kontinentálisabb klímán a vörösfenyő széles körben elterjedt a Déli-Kárpátokban a szubalpin zónában.

Fires in Africa account for more than half of global fire-carbon emissions but the long-term evolution of fire activity and its link to global climate change remains elusive. Paleofire records provide descriptive information about fire changes through time, going beyond the range of satellite observations, although fire regime characteristics are challenging to reconstruct. To address this conceptual gap, we report here the abundance and morphometric data for a large set of microscopic charcoal samples (n = 128) recovered from surface ocean sediments offshore Africa. We show that in subtropical Southern Africa, large and intense fires prevailing in open savanna-grassland ecosystems produce a high abundance of small and elongated microcharcoal particles. In contrast, in the forest ecosystems of equatorial and tropical regions of western and central Africa, low-intensity fires dominate, producing low amounts of squared microcharcoal particles. Microcharcoal concentration and morphotype in marine sediment records off Africa are thus indicative of fire regime characteristics. Applied to down-core marine charcoal records, these findings reveal that at orbital time-scale intense and large, open grassland-savanna fires occurred during wet periods in the sub-tropical areas. A strong contribution of fire carbon emissions during periods of precession and summer insolation maxima in the geological record is thus expected.

The North Atlantic region experienced abrupt high-amplitude cooling at the onset of the Younger Dryas stadial. However, due to chronological uncertainties in the available terrestrial records it is unclear whether terrestrial ecosystem response to this event was instantaneous and spatially synchronous, or whether regional or time-transgressive lags existed. Here we use new palynological results from a robustly dated lake sediment sequence retrieved from lake Hämelsee (north Germany) to show that vegetation change started at 12,820 cal. yr BP, concurrent with the onset of changes in local climate. A comparison of the Hämelsee results to a compilation of precisely dated palynological records shows instant and, within decadal-scale dating uncertainty, synchronous response of the terrestrial plant community to Late-Glacial climate change across northwest Europe. The results indicate that the environmental impact of climate cooling was more severe than previously thought and illustrates the sensitivity of natural terrestrial ecosystems to external forcing.

Fire is a pervasive component of almost every terrestrial ecosystem, but the African continent is rather unique, holding the most vulnerable ecosystems to fire which account for most of the global burned area and for more than half of fire-carbon emissions. Fire has a significant role in ecosystem functioning though our understanding of this complex process is still limited which hinders our ability to model and predict fire.Paleofire records go beyond the short instrumental records of the last decades and can provide long-term information about fire, but only at a descriptive scale and with difficulties in relating it to the fire regime. To address these limitations, we attempt to develop a quantitative calibration model based on the examination of micro-charcoal from 137 surface sediment samples collected offshore the African continent in conjunction with a set of fire parameters (burnt perimeter, fire radiative power, fire spread) derived from satellite data, environmental information (hydrographic basins, vegetation cover, climatic parameters) and a wind dispersal particle model. Our results show that changes in charcoal concentration and morphometry are linked with fire regime and the type of burnt vegetation on the adjacent continent. In (sub)tropical settings, elongated micro-charcoal particles in high concentrations relate to rare but intense fires spreading in graminoid-mixed ecosystems whereas squared particles in low concentrations are typical for frequent but low intensity fires, characteristic for tree-dominated ecosystems.This work provides the first calibration model of micro-charcoal in marine sediments which can be applied to long marine charcoal records to help reconstruct past fire regimes. This investigation addresses a key issue in unlocking specific methodological and theoretical problems related to fire research; it provides a better understanding of the local to regional processes that govern the fire signal and contextualize current and past environmental changes.

The paleoclimatic and paleoenvironmental changes inferred from shifts in lake sediment geochemistry require reliable, efficient and cost-effective methods of analysis. The available geochemical techniques, however, suggest that different analytical approaches can influence data interpretation. X-ray fluorescence core scanner analyses (XRF-CS), field portable X-ray fluorescence (FPXRF) and inductively coupled plasma optical emission spectrometry (ICP-OES) were concurrently applied to provide a multi-method geochemical appraisal of a 6000-year-long karstic sediment record (Lake Ighiel, Romania). The comparison between techniques was based on a set of elements that are widely employed in environmental reconstructions (Ti, K, Fe, Ca). Descriptive and statistical approaches were used to assess the advantages and disadvantages of each method and assess their optimal use in karstic environments. Our data display similar downcore patterns, with strong to moderate correlations between the datasets. The discrepancies observed between method-specific downcore multi element behaviour are related to the preparation steps and sampling. To best capture the complexity of past environmental changes in karstic settings, a combination of quantitative and qualitative geochemical methods would be the most appropriate approach to reliable data acquisition and subsequent paleoenvironmental interpretation of lake sediment data.

Peatlands are one of the largest terrestrial carbon sinks on the planet, yet little is known about carbon accumulation rates (CARs) of mountainous examples. The long-term variability in the size of the associated carbon sink and its drivers remain largely unconstrained, especially when long-term anthropogenic impact is also considered. Here we present a composite CAR record of nine peatlands from central-eastern Europe (Romania and Serbia) detailing variability in rates of carbon accumulation across the Holocene. We show examples of extremely high long-term rates of carbon accumulation (LORCA > 120 g C m⁻² yr⁻¹), indicating that at times, mountain peatlands constitute an efficient regional carbon sink. By comparing our data to modelled palaeoclimatic indices and to measures of anthropogenic impact we disentangle the drivers of peat carbon accumulation in the area. Variability in early and mid-Holocene CARs is linked to hydroclimatic controls, with high CARs occurring during the early Holocene and lower CARs associated with the transition to cooler and moister mid-Holocene conditions. By contrast, after 4000 years (calibrated) before present (yr BP) the trends in CARs indicate a divergence from hydroclimate proxies, indicating that other processes became the dominant drivers of peat CARs. We suggest that enhanced erosion following tree cover reduction as well as enhanced rates of long-distance atmospheric dust fallout might have played a role as both processes would result in enhanced mineral and nutrient supply to bog surfaces, stimulating peat land productivity. Surprisingly though, for the last 1000 years, reconstructed temperature is significantly correlated with CARs, with rising temperatures linked to higher CARs. We suggest under future climate conditions, predicted to be warmer in the region, peat growth may expand, but that this is entirely dependent upon the scale of human impact directly affecting the sensitive hydrological budget of these peatlands.