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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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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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001-es BibID:	BIBFORM079873
Első szerző:	Hubay Katalin (biológus, környezetkutató)
Cím:	Age-depth relationship and accumulation rates in four sediment sequences from the Retezat Mts, South Carpathians (Romania) / Hubay Katalin, Molnár Mihály, Orbán Ildikó, Braun Mihály, Bíró Tamás, Magyari Enikő
Dátum:	2018
ISSN:	1040-6182
Megjegyzések:	This study summarizes the results of radiocarbon dating and age-depth modelling in four mountain lakes (Brazi, Gales, Bucura and Lia) in the Retezat Mountains. Altogether 69 AMS 14C measurements were performed on these deposits, mostly on terrestrial plant macrofossils. In several cases, plant macrofossils, aquatic animal remains (Cladoceran eggs) and bulk sediment were measured from the same depth allowing for the comparison of various sediment components in terms of their dating potential. Age-depth models were developed using both Bayesian modelling with the BACON and smooth spline curve fitting with the CLAM software. In this study Bayesian models are applied to identify outlier 14C dates, while smooth spline models are used to model sediment accumulation age-depth relations, as these are more likely to follow natural deposition time changes of lake sediments. Changes in sediment deposition times (DT) in relation to catchment size and climate are also studied. DT varied considerably in the late glacial (LG) part of the records. The sediment sequence characterised by high deposition rates during the late glacial (DT maximum around 100?110 years cm?1) was defined by small catchment size (Lake Brazi, 6 ha; surface area: 0.5 ha). In contrast, much slower LG sediment deposition in the southern slope lake characterised by large catchment area (Lake Lia, 171 ha, 20 years cm?1), principally reflecting strong erosion in these catchment areas at times when vegetation cover was scarce. Holocene was characterised again by variable DT values, but only Lake Gales showed extreme values: 62?110 years between 10,900 and 6050 cal yr BP, followed by much slower sediment deposition in the last 6000 years (av. 29 years cm?1). Generally, sediment deposition times were largely dependent on the stability and vegetation cover of the slope in the case of high altitude deep lakes, while lower altitude, shallow lakes showed slower sediment deposition time in the early and mid-Holocene, when summer insolation was higher than today. This reflects that in these shallow lakes in-lake organic production probably increased with summer insolation, which was a significant driver in the rate of deposition.
Tárgyszavak:	Természettudományok Környezettudományok idegen nyelvű folyóiratközlemény külföldi lapban AMS 14C dating Glacial lake sediments Late glacial Holocene Carpathians
Megjelenés:	Quaternary International. - 477 (2018), p. 7-18. -
További szerzők:	Molnár Mihály Orbán Ildikó Braun Mihály (1966-) (vegyész, analitikus) Bíró Tamás Magyari Enikő (1973-) (biológus)
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001-es BibID:	BIBFORM084456
Első szerző:	Magyari Enikő (biológus)
Cím:	A 13,600-year diatom oxygen isotope record from the South Carpathians (Romania): Reflection of winter conditions and possible links with North Atlantic circulation changes / Magyari Enikő Katalin, Demény Attila, Buczkó Krisztina, Kern Zoltán, Vennemann T., Fórizs István, Vincze Ildikó, Braun Mihály, Kovács István János, Udvardi Beatrix, Veres Dániel
Dátum:	2013
ISSN:	1040-6182
Megjegyzések:	This study provides a continuous lateglacial and Holocene record of diatom silica oxygen isotope changes (?18ODIAT) in a subalpine lake sediment sequence obtained from the Retezat Mts (Taul dintre Brazi, 1740 m a.s.l.). This through-flow, shallow, high-altitude lake with a surface area of only 0.4 ha has short water residence time and is predominantly fed by snowmelt and rainwater. Its ?18ODIAT record principally reflects the oxygen isotope composition of the winter and spring precipitation, as diatom blooms occur mainly in the spring and early summer. Hence, changes in ?18ODIAT are interpreted as seasonal scale changes: in the amount of winter precipitation. Low oxygen isotope values (27-28.5?) occurred during the lateglacial until 12,300 cal BP, followed by a sharp increase thereafter. In the Holocene ?18ODIAT values ranged from 29 to 31? until 3200 cal BP, followed by generally lower values during the late Holocene (27?30?). Short-term decreases in the isotopic values were found between 10,140-9570, 9000?8500, 7800?7300, 6300?5800, 5500?5000 and at 8015, 4400, 4000 cal BP. After 3200 cal BP a decreasing trend was visible with the lowest values between 3100?2500 and after 2100 cal BP The general trend in the record suggests that contribution of winter precipitation was generally lower between 11,680 and 3200 cal BP, followed by increased contribution during the last millennia.
Tárgyszavak:	Természettudományok Kémiai tudományok idegen nyelvű folyóiratközlemény külföldi lapban folyóiratcikk
Megjelenés:	Quaternary International. - 293 (2013), p. 136-149. -
További szerzők:	Demény Attila Buczkó Krisztina (1962-) (biológus) Kern Zoltán Vennemann, Torsten Fórizs István Vincze Ildikó Braun Mihály (1966-) (vegyész, analitikus) Kovács István János Udvardi Beatrix (Budapest) Veres Dániel
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