Spassimir Tonkov

Validation of climate model-inferred regional temperature change for late-glacial Europe

Comparisons of climate model hindcasts with independent proxy data are essential for assessing model performance in non-analogue situations. However, standardized paleoclimate datasets for assessing the spatial pattern of past climatic change across continents are lacking for some of the most dynamic episodes of Earths recent past. Here we present a new chironomid-based paleotemperature dataset designed to assess climate model hindcasts of regional summer temperature change in Europe during the late-glacial and early Holocene. Latitudinal and longitudinal patterns of inferred temperature change are in excellent agreement with simulations by the ECHAM-4 model, implying that atmospheric general circulation models like ECHAM-4 can successfully predict regionally diverging temperature trends in Europe, even when conditions differ significantly from present. However, ECHAM-4 infers larger amplitudes of change and higher temperatures during warm phases than our paleotemperature estimates, suggesting that this and similar models may overestimate past and potentially also future summer temperature changes in Europe.

The European Modern Pollen Database (EMPD) project

Modern pollen samples provide an invaluable research tool for helping to interpret the quaternary fossil pollen record, allowing investigation of the relationship between pollen as the proxy and the environmental parameters such as vegetation, land-use, and climate that the pollen proxy represents. The European Modern Pollen Database (EMPD) is a new initiative within the European Pollen Database (EPD) to establish a publicly accessible repository of modern (surface sample) pollen data. This new database will complement the EPD, which at present holds only fossil sedimentary pollen data. The EMPD is freely available online to the scientific community and currently has information on almost 5,000 pollen samples from throughout the Euro-Siberian and Mediterranean regions, contributed by over 40 individuals and research groups. Here we describe how the EMPD was constructed, the various tables and their fields, problems and errors, quality controls, and continuing efforts to improve the available data.

Pollen and plant macrofossil analyses of radiocarbon dated mid-Holocene profiles from two subalpine lakes in the Rila Mountains, Bulgaria

Pollen analysis, plant macrofossil determination and radiocarbon dating were performed on profiles of Holocene age obtained from two subalpine lakes (2320-2340 m a.s.l.) in the Central Rila Mountains, Bulgaria. The palaeovegetational reconstruction dates back to the mid-Atlantic (6500-6700 cal. BP). The plant macrofossil record revealed that groups of Pinus mugo and Juniperus sibirica were distributed in the subalpine zone. The treeline was shaped by Pinus sylvestris and Pinus peuce and was higher (up to 2200-2300 m a.s.l.) compared with the present-day. A change to cooler summers and warmer winters after 6700 cal. BP, characterized by a rise in humidity and precipitation, stimulated the formation of a coniferous vegetation belt dominated by Pinus sylvestris, Pinus peuce and Abies alba. The pollen assemblages also indicated a dominance of deciduous trees (Quercetum mixtum-Corylus phase) at low altitudes until c. 6000 cal. BP. The sub-Boreal was characterized by a wider distribution of Abies alba in the lower part of the coniferous belt and a gradual enlargement of the areas occupied by Fagus sylvatica and Picea abies after 3800-3500 cal. BP. The macrofossil finds of Picea abies testify to its expansion after 2800 cal. BP when average temperatures dropped and precipitation increased. Traces of human disturbance in the subalpine area are continuously registered in the pollen and plant macrofossil records since 3770 cal. BP, indicating livestock-grazing, burning of dwarf-pine (Pinus mugo) for new pasture land and lowering of the treeline.

Holocene palaeovegetation of the Northwestern Pirin Mountains (Bulgaria) as reconstructed from pollen analysis

Pollen analysis and radiocarbon dating were performed on a sequence 150 cm deep from a peat bog (Mozgovitsa, 1800 m above sea-level) in the Northwestern Pirin Mountains, Bulgaria. The palaeovegetational reconstruction focused on the main stages of forest development starting from approximately 8700 years BP. The vegetational response to the amelioration of the climate in the Early Holocene until 7500 cal BP resulted in the spread of birch forests (Betula pendula) that occupied large areas at high altitudes forming the upper tree-line together with pine (Pinus sylvestris, Pinus peuce, Pinus mugo), juniper (Juniperus), alder (Alnus), and willow (Salix). Below them were mixed deciduous oak forests with some Ulmus, Tilia, Corylus, Carpinus, and Acer. The continuous Early Holocene pollen record of mesophyllous demanding trees (Abies alba, Fagus sylvatica and Picea abies), though in low frequencies, suggests that groups of these trees survived in environmentally favourable habitats with sufficient moisture such as deep mountain valleys. The most important change in the vegetation cover started ca. 7500 cal BP when birch forests declined and coniferous vegetation dominated by Pinus sylvestris, Pinus peuce and Abies alba invaded the slopes. The spread of the conifers and the expansion of their areas presume an increase in humidity and precipitation, and the development of soils with humic horizons. The last trees to establish after ca. 4000 cal BP in the study area were Picea abies and Fagus sylvatica. Their expansion in the Northwestern Pirin Mountains started at the Subboreal/Subatlantic transition ca. 3000 cal BP when average temperatures dropped and precipitation increased. Deforestation in historic times resulted in the appearance of new pasture land and the lowering of the upper tree-line.

Palynological study of Holocene sediments from Lake Doirani in northern Greece

A palynological investigation was conducted on two cores with Holocene sediments collected from the northeastern littoral part of the border Lake Doirani in northern Greece. The radiocarbon dates indicated that the analyzed sediments accumulated during the last 5000 yrs. The pollen-stratigraphic record revealed the environmental changes in the catchment area, starting from a natural undisturbed landscape to one modified by increasing anthropogenic influences. The tree vegetation dominated by Quercus woods in the lowlands and byPinus, Abies, and Fagus at higher altitudes, lasted for the period 2900 - 830 cal. B.C. Subsequently it was replaced by xerothermic herb and tree vegetation as a result of intensive human activity - and farming and stock-breeding. The accumulation of sediments with more sand and gravel in historical time was the result of increased erosion.

Towards the vegetation and settlement history of the southern Dobrudza coastal region, north-eastern Bulgaria: a pollen diagram from Lake Durankulak

Palynological investigation and radiocarbon dating of a 6-m core from lake Durankulak, north-eastern Bulgaria, enables vegetation development and human occupation from ca. 5500–5300 cal. B.C. onwards to be traced. Steppe vegetation that included with groves of deciduous trees asQuercus, Ulmus, Carpinus belulus andCorylus changed to a forest-steppe after 4000 cal. B.C. The archaeopalynological record indicates three distinct phases of human activity as follows: (1) 5300–4200 cal. B.C. (late Neolithic and Eneolithic) during which farming, that included a substantial arable component, was pursued, (2) 3500–3000 cal. B.C. (transition to early Bronze Age) when stock rearing appears to have dominated, and (3) after 1300 cal. B.C. (late Bronze Age) when arable farming again assumed importance. The palynological data correlate well with the rich archaeological record for human settlement that is available for the region from late Neolithic times onwards.

Postglacial vegetation history as recorded from the subalpine Lake Ribno (NW Rila Mts), Bulgaria

A pollen analysis conducted on a 600 cm core from Lake Ribno (2184 m) in the Northwestern Rila Mountains, supplemented by 13 radiocarbon dates, has revealed the basic stages in its postglacial vegetation dynamics. The lateglacial vegetation, composed of Artemisia, Chenopodiaceae and Poaceae, with stands of Pinus and Juniperus-Ephedra shrubland, dominated in the stadials and partly retreated during the Bølling/Allerød interstadial (14700–12900 cal. yrs. BP). The afforestation in the early Holocene (11600–7800 cal. yrs. BP) started with pioneer Betula forests, with groups of Pinus and Juniperus at mid-high altitudes, and Quercus forests with Tilia, Ulmus, Fraxinus, Corylus below the birch zone. A coniferous belt composed of Pinussylvestris, P. peuce and Abies was shaped under the conditions of a more humid climate (7800–5800 cal. yrs. BP). The last trees that invaded the study area were Fagus after 4300 cal. yrs. BP and Picea abies after 3400 cal. yrs. BP. Evidence for destructive changes in the vegetation and indications of agricultural and stock-breeding activities (pollen of Triticum, Secale, Plantago lanceolata, Rumex, Juglans) was continuously recorded since the Late Bronze Age (3400–3200 cal. yrs. BP). The postglacial vegetation history in the Northwestern Rila Mountains demonstrated close similarities with that of the Northern Pirin Mountains.

14. Lake Sedmo Rilsko (Bulgaria): Lateglacial vegetation history

Site details The glacial Lake Sedmo Rilsko (42◦ 12′ 39.64′ ′ N, 23◦ 19′ 36.73′ ′ E; 2095 m a.s.l.) is situated in the lower part of the subalpine vegetation belt above the present tree-line in the north-western Rila Mountains in the cirque of the Seven Rila Lakes, Bulgaria. The lake collects water from all upper lakes. The shore is flat and only the south-eastern slope is steep and rocky. The lake is about 330 m long and 180 m wide, with a maximum water depth of 11 m. It is surrounded by groups of Pinus mugo Turra and Juniperus sibirica Burgsd. within patches of herb vegetation. Not far away to the north, single trees of Pinus peuce Griesb., Pinus sylvestris L. and Picea abies (L.) Karst. are found (Bozilova & Tonkov, 2000). Geologically, the Rila Mountains are complex and composed of metamorphic (crystalline schist and marble) and intrusive (granite) rocks. The activity of Pleistocene glaciers has resulted in the formation of cirques, numerous lakes, different types of moraines, and trough valleys (Stoičev & Petrov, 1980). The climate above 1000 m is montane and at 1800–1900 m, at the present tree-line, the mean January temperature is –6 ◦C and the mean August temperature is +11.4 ◦C. The highest precipitation, much of it snow, reaches 2000 mm in the 1300–2400 m zone (Velev, 2002).

Lateglacial to Holocene vegetation development in the Central Rila Mountains, Bulgaria

The vegetation history of the Central Rila Mountains for the last 14,000 years was reconstructed by means of pollen analysis and radiocarbon chronology of a core retrieved from Lake Manastirsko-2 (2326 m). The Lateglacial landscape was dominated by open herb vegetation composed of Artemisia, Chenopodiaceae, Poaceae, and other cold-resistant herbs (14,000–11,700 cal. yr BP). Stands of Pinus, Betula, and Juniperus–Ephedra shrubland partly enlarged during the Lateglacial interstadial. Pioneer forests of Betula with Pinus and Juniperus occupied barren soils in the early Holocene (11,700–7900 cal. yr BP), while mixed oak forests with Tilia, Ulmus, Acer, and later on Corylus spread at lower elevations. A coniferous forest belt with Pinus sylvestris, Pinus peuce, and Abies developed after 7900 cal. yr BP in the conditions of milder winters, cooler summers, and increase in precipitation. The late Holocene dynamic vegetation changes were associated with the invasion of Picea abies after 3400 cal. yr BP, while Fagus communities slightly enlarged in the river valleys. Indications of human activities are visible in the pollen diagram since the ‘Late Bronze Age’ (3400–3200 cal. yr BP). The vegetation development in the study area followed a similar pattern when compared with palynological and macrofossil records from other parts of the Rila and the adjacent Northern Pirin Mountains. On a larger geographical scale, the postglacial vegetation history of the Rila Mountains displays common features with sites in the Romanian Carpathians, whereas the differences observed are result of the location of tree refugia, competing abilities, climate changes, and human activities.

6. Peat-bog Begbunar (Osogovo Mountains, south-west Bulgaria): Four millennia of vegetation history

The peat-bog Begbunar (42°09¢ N, 22° 33¢ E; 1750 m a.s.l.) is located in the central treeless zone of the Osogovo mountains, which are situated at the border between south-western Bulgaria and the north-eastern former Yugoslav Republic of Macedonia. This bog was formed near a freshwater spring on a north-western slope, which continues into a steep, deep ravine where isolated stands of beech (Fagus sylvatica L.) exist. The modern mountain vegetation consists of several vegetation belts: the oak-hornbeam belt (up to 1000 m), the compact beech belt (1000 – 1900 m) with fragments of conifers (Pinus nigra J. F. Arnold and Abies alba Mill.) and the subalpine belt, which is occupied by plant communities of Juniperus sibirica Burgsd., Vaccinium myrtillus L., Bruckenthalia spiculifolia (Salisb.) Rchb., Chamaecytisus absinthioides Janka (Kuzm.), Nardus stricta L., and scattered groups of Pinus sylvestris L., etc. The present-day vegetation composition has been strongly influenced by the long-lasting anthropogenic impact, including ore-mining industry and erosion caused by deforestation (Velcev & Tonkov, 1986; Tonkov, 2003). Geologically, the massif is composed mainly of Palaeozoic metamorphic and intrusive rocks, while geomorphological evidence suggests that small valley glaciers existed in the highest parts during Quaternary glaciations. The climate above 1000 m is typical montane with a mean annual precipitation of 700–900 mm. The basic soil types are cinnamomic-forest, brown forest and mountainous-meadow (Velcev et al., 1994).