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1.

001-es BibID:BIBFORM080901
Első szerző:Braun Mihály (vegyész, analitikus)
Cím:Using linear discriminant analysis (LDA) of bulk lake sediment geochemical data to reconstruct lateglacial climate changes in the South Carpathian Mountains / M. Braun, K. Hubay, E. Magyari, D. Veres, I. Papp, M. Bálint
Dátum:2013
ISSN:1040-6182
Megjegyzések:A multi-proxy approach is widely used for reconstructing climatic change in alpine lake sediments. This study applied bulk sediment geochemistry to reconstruct lateglacial and early Holocene climatic change in a glacial lake (Lake Brazi, 1740 m a.s.l.) in the Retezat Mts. (South Carpathians, Romania). The lowermost 1 m part of a 4.9-m long sediment core, covering the period between 9950 and 15,750 cal BP, was used for high resolution bulk analysis of major elements (Al2O3, SiO2, TiO2, CaO, MgO, K2O, Na2O, Fe2O3, MnO, SO3). Linear discriminant analysis (LDA) was used to compare a priori classified main chemical groups. Subsamples from the core were priory ordered to "warm" and "cold" groups respectively, according to their age and evidence of cold and warm events in the record, as suggested by proxy correlation with the lateglacial event stratigraphy of North Greenland Ice Core Project (NGRIP). The discriminant function was calculated using concentrations of Al2O3, TiO2, CaO, MgO, K2O, Na2O, Fe2O3, and MnO after log ratio transformation. Loss-on-ignition, silicon and sulphur concentrations were not used for the discriminant analysis, but regarded as comparison proxies for checking up the validity of outputs. Sediments deposited during "cold" and "warm" events were separated significantly by the LDA function; 85.1% of the originally grouped cases were correctly classified under the LDA analysis. The calculated discriminant scores indicated four "cold" and four "warm" events. Sediments ordered into the "warm" group contained larger amounts of organic matter and sulphur, while sediment samples of the "cold" group were characterized by the overall predominance of major oxides bound into inorganic silicates. The discriminant scores showed strong correlation with the NGRIP ?18O data (r = 0.8135) and with the pollen percentage sum of trees and shrubs (r = 0.9460). Loss-on-ignition showed a somehow weaker, but still conclusive linear relationship with the discriminant scores (r = 0.7505). Discriminant analyses of bulk sediment major oxide chemical data may be a useful tool to identify the impact of climatic events upon the nature and composition of materials delivered to a lake basin.
Tárgyszavak:Természettudományok Földtudományok idegen nyelvű folyóiratközlemény külföldi lapban
Megjelenés:Quaternary International. - 293 (2013), p. 114-122. -
További szerzők:Hubay Katalin (1985-) (biológus, környezetkutató) Magyari Enikő (1973-) (biológus) Veres Dániel Papp István (1980-) (vegyész) Bálint Miklós
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2.

001-es BibID:BIBFORM084457
Első szerző:Buczkó Krisztina (biológus)
Cím:Diatom-inferred lateglacial and Holocene climatic variability in the South Carpathian Mountains (Romania) / Buczkó Krisztina, Magyari Enikő Katalin, Braun Mihály, Bálint Miklós
Dátum:2013
Megjegyzések:Climatic and environmental changes were studied using siliceous algae (diatoms and chrysophycean cysts) analyses in a mountain lake in the South Carpathian Mountains for the lateglacial and Holocene. Lake Brazi (1740 a.s.l.) is a small, shallow lake in the Retezat Mountains. According to the basal radiocarbon dating of the core, the lake was formed around 15,750 cal BP and sediment accumulation has been continuous ever since. High resolution diatom analyses were carried out together with loss-on-ignition and biogenic silica measurements. Total epilimnetic phosphorus (TP) concentrations and pH were reconstructed quantitatively. Ten statistically significant zones were distinguished, six of which appeared in the lateglacial and Early Holocene suggesting the instability of diatom assemblages after deglaciation. The uppermost zone covered six thousand years, which suggests that diatom assemblages remained quite stable during the second half of the Holocene. High lake level occurred between 9500 and 9000 cal BP. After 6300 cal BP the lake level gradually increased again until 5800 cal BP. A further increase was detected at 3000 cal BP, while after 1500 cal BP water level decreased. Although there is limited knowledge regarding the environmental constraints of several diatom taxa present in the sequence (e.g. Aulacoseira laevissima), which makes the precise environmental interpretation of the diatom record more difficult, the available data provide an important new insight into the environmental history of Lake Brazi and the Carpathian Mountains. The most remarkable changes in the aquatic ecosystem were observed at 6000 cal BP in the Holocene and 12,800 cal BP, at the onset of the Younger Dryas. Marked changes were also detected at 10,500-10,300; 9800; 9500-9000; 8900-8800; 8300; 6300-5800 and 3100-3000 cal BP.
Tárgyszavak:Természettudományok Kémiai tudományok idegen nyelvű folyóiratközlemény külföldi lapban
folyóiratcikk
Megjelenés:Quaternary International. - 293 (2013), p. 123-135. -
További szerzők:Magyari Enikő (1973-) (biológus) Braun Mihály (1966-) (vegyész, analitikus) Bálint Miklós
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3.

001-es BibID:BIBFORM079443
Első szerző:Buczkó Krisztina (biológus)
Cím:Diatom-based evidence for abrupt climate changes during the Late Glacial in the Southern Carpathian Mountains / Buczkó Krisztina, Magyari Enikő K., Soróczki-Pintér Éva, Hubay Katalin, Braun Mihály, Bálint Miklós
Dátum:2009
ISSN:1788-2281 1789-3348
Megjegyzések:A high-resolution paleolimnological record from Lake Brazi (TDB-1; 45?23'47"N, 22-54'06"E, 1740 m a.s.l.), a small, glacial lake in the Retezat (South Carpathian Mountains, Romania) provides a sensitive record of the impacts of late glacial climatic change on siliceous algal assemblages. The sequence, ranging from 15,700 cal yr BP to 9500 cal yr BP, suggests that the most significant changes in diatom assemblages took place at 12,800 and 10,400 cal yr BP, when alkaliphilous fragilarioid taxa were replaced by acidophilous diatoms. Altogether eight zones were distinguished with sharp and rapid changes of diatom assemblages. The paper discusses the application of siliceous algae in multi-proxy paleolimnological analyses, demonstrates the advantages and disadvantages of this proxy and presents the story of floristic discovery of unique diatom assemblages, the closest recent analogs of which are found in the arctic region.
Tárgyszavak:Természettudományok Környezettudományok idegen nyelvű folyóiratközlemény hazai lapban
diatoms
glacial lakes
Megjelenés:Central European Geology. - 52 : 3-4 (2009), p. 249-268. -
További szerzők:Magyari Enikő (1973-) (biológus) Soróczki-Pintér Éva Hubay Katalin (1985-) (biológus, környezetkutató) Braun Mihály (1966-) (vegyész, analitikus) Bálint Miklós
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4.

001-es BibID:BIBFORM079444
Első szerző:Magyari Enikő (biológus)
Cím:Radiocarbon chronology of glacial lake sediments in the Retezat Mts (South Carpathians, Romania): a window to Late Glacial and Holocene climatic and paleoenvironmental changes / Magyari Enikő K., Braun Mihály, Buczkó Krisztina, Kern Zoltán, László Péter, Hubay Katalin, Bálint Miklós
Dátum:2009
ISSN:1788-2281 1789-3348
Megjegyzések:As a first piece in a series of Late Quaternary paleoecological studies on the glacial lake sediments of the Retezat Mountains, this study discusses radiocarbon chronology and sediment accumulation rate changes in two sediment profiles in relation to lithostratigraphy, organic content, biogenic silica and major pollenstratigraphic changes. A total of 25 radiocarbon dates were obtained from sediments of two lakes, Lake Brazi (TDB-1; 1740 m a.s.l.) and Lake Gales (Gales-3; 1990 m a.s.l.). Age-depth modeling was performed on TDB-1 using calibrated age ranges from BCal and various curve-fitting methods in psimpoll. Our results suggest that sediment accumulation began between 15,124?15,755 cal yr BP in both lakes and was continuous throughout the Late Glacial and Holocene. We demonstrated that local ecosystem productivity showed delayed response to Late Glacial and Early Holocene climatic changes in the subalpine and alpine zones most likely attributable to the cooling effect of remnant glaciers and meltwater input. However, regional vegetation response was without time lag and indicated forestation and warming at 14,450 and 11,550 cal yr BP, and cooling at ca. 12,800 cal yr BP. In the Holocene one major shift was detected, starting around 6300 cal yr BP and culminating around 5200 cal yr BP. The various proxies suggested summer cooling, shorter duration of the winter ice-cover season and/or increasing size of the water body, probably in response to increasing available moisture.
Tárgyszavak:Természettudományok Környezettudományok idegen nyelvű folyóiratközlemény hazai lapban
folyóiratcikk
Late Glacial
radiocarbon dating
loss-on-ignition
pollen
glacial lake sediments
rapid climate change
Megjelenés:Central European Geology. - 52 : 3-4 (2009), p. 225-248. -
További szerzők:Braun Mihály (1966-) (vegyész, analitikus) Buczkó Krisztina (1962-) (biológus) Kern Zoltán László Péter Hubay Katalin (1985-) (biológus, környezetkutató) Bálint Miklós
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5.

001-es BibID:BIBFORM018141
Első szerző:Magyari Enikő (biológus)
Cím:Population dynamics and genetic changes of Picea abies in the South Carpathians revealed by pollen and ancient DNA analyses / Enikő K Magyari, Ágnes Major, Miklós Bálint, Judit Nédli, Mihály Braun, István Rácz, Laura Parducci
Dátum:2011
ISSN:1471-2148
Megjegyzések:Background Studies on allele length polymorphism designate several glacial refugia for Norway spruce (Picea abies) in the South Carpathian Mountains, but infer only limited expansion from these refugia after the last glaciation. To better understand the genetic dynamics of a South Carpathian spruce lineage, we compared ancient DNA from 10,700 and 11,000-year-old spruce pollen and macrofossils retrieved from Holocene lake sediment in the Retezat Mountains with DNA extracted from extant material from the same site. We used eight primer pairs that amplified short and variable regions of the spruce cpDNA. In addition, from the same lake sediment we obtained a 15,000-years-long pollen accumulation rate (PAR) record for spruce that helped us to infer changes in population size at this site. Results We obtained successful amplifications for Norway spruce from 17 out of 462 pollen grains tested, while the macrofossil material provided 22 DNA sequences. Two fossil sequences were found to be unique to the ancient material. Population genetic statistics showed higher genetic diversity in the ancient individuals compared to the extant ones. Similarly, statistically significant Ks and Kst values showed a considerable level of differentiation between extant and ancient populations at the same loci. Lateglacial and Holocene PAR values suggested that population size of the ancient population was small, in the range of 1/10 or 1/5 of the extant population. PAR analysis also detected two periods of rapid population growths (from ca. 11,100 and 3900 calibrated years before present (cal yr BP)) and three bottlenecks (around 9180, 7200 and 2200 cal yr BP), likely triggered by climatic change and human impact. Conclusion Our results suggest that the paternal lineages observed today in the Retezat Mountains persisted at this site at least since the early Holocene. Combination of the results from the genetic and the PAR analyses furthermore suggests that the higher level of genetic variation found in the ancient populations and the loss of ancient allele types detected in the extant individuals were likely due to the repeated bottlenecks during the Holocene; however our limited sample size did not allow us to exclude sampling effect. This study demonstrates how past population size changes inferred from PAR records can be efficiently used in combination with ancient DNA studies. The joint application of palaeoecological and population genetics analyses proved to be a powerful tool to understand the influence of past population demographic changes on the haplotype diversity and genetic composition of forest tree species.
Tárgyszavak:Természettudományok Biológiai tudományok idegen nyelvű folyóiratközlemény külföldi lapban
Megjelenés:BMC Evolutionary Biology. - 11 : 66 (2011), p. 1-16. -
További szerzők:Major Ágnes Bálint Miklós Nédli Judit (1980- ) (biológus) Braun Mihály (1966-) (vegyész, analitikus) Rácz István András (1949-) (biológus) Parel, Serge P.
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