Naslov
RESPONSE OF CARBONATE DEPOSITS OF PLITVICE LAKES, CROATIA, TO THE BOMB-PRODUCED 14C

Autori
Sironić, Andreja ; Barešić, Jadranka ; Horvatinčić, Nada ; Krajcar Bronić, Ines ; Felja, Igor ; Nikolov, J. ; Todorović, N. ; Hansman, J. ; Krmar, M.

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
Geochronometria, Conference Abstracts Series / Pazdur, Anna - Gliwice : Silesian University of Technology, 2016, 85-86

ISBN
978-83-904783-3-3

Skup
Methods of Absolute Chronology

Mjesto i datum
Gliwice, Poljska, 11.05.2016. - 13.05.2016

Vrsta sudjelovanja
Poster

Vrsta recenzije
Nije recenziran

Ključne riječi
Carbonate sediments; Plitvice Lakes; 14C bomb peak

Sažetak
Global contamination of the atmosphere by thermonuclear bomb-produced 14C in the 1960s has been reflected in Earth’s natural environment such as tree-rings, soils, speleothems, lake sediments, corals, but with different intensity and with some delay depending on length of carbon exchange processes in the nature. In this work we studied recent lake sediments (in the last ~ 150 yr) and tufa (in the last ~ 40 yr) collected in the Plitvice Lakes, Croatia. Activity of radioactive isotopes 14C, 137Cs and 210Pb as well as ratio of stable isotopes 13C/12C were measured in lake sediments, top 40 cm, of two big lakes Prošće and Kozjak (~0.8 km2, max depth 37 m and 46 m, respectively) and two small lakes: Gradinsko (~0.08 km2, max depth 8 m) and Kaluđerovac (~0.02 km2, max depth 14 m). Frozen sediment cores were cut out into 1 to 2 cm-thick fragments and dried prior to analyses. a14C and δ13C were measured separately in carbonate and organic fraction. Recent tufa deposit was collected in the stream of the Korana River which outflows from the Plitvice Lakes. a14C and δ13C in tufa deposit were measured along 20 cm, on points ~2 cm apart, following the natural tufa lamination. Sedimentation rates of the lake sediments were estimated based on the unsupported 210Pb and 137Cs activity. The starting point for the tufa deposition was determined as the time a wooden pillar on which the tufa grew was submerged in water. The 13C values showed that the carbonate fraction in sediments was mostly authigenic, i.e. precipitated from dissolved inorganic carbonate. Distribution of a14C showed simultaneous increase to the depth of ~10 cm in big lakes and to the depth of ~20 cm in small lakes in both carbonate and organic fractions. It can be interpreted as a delayed and damped response to the bomb-produced 14C in the atmosphere. The a14C increase/peak was also observed in the tufa sample from the Korana River. The delay of the atmospheric 14C signal was 25 years in the Korana River, 28 and 32 years in lakes Gradinsko and Kaluđerovac and ~36 years in lakes Prošće and Kozjak. The peak increase of a14C in carbonate sediments was 12 % in the big lakes, 15 % in the small lakes and 20 % in tufa. The delay and dampening intensity of the atmospheric 14C bomb peak response in the sediments/tufa increased exponentially with the lakes’ size, i.e. the sampling depth. Since the water of Plitvice lakes shows seasonal temperature stratification, this is probably a result of the vertical seasonal mixing of the lake waters. Thermocline is observed in water of big/deep lakes Prošće and Kozjak (during summer-autumn) and in small/shallow lakes Gradinsko and Kaluđerovac the water is well mixed during all seasons. The autogenic calcite that precipitates mostly in euphotic zone of the lake waters takes time to deposit in water column. Along with the influence of seasonal water mixing, the newly deposited calcite is mixed with calcite produced during a previous season/s, resulting in delaying and dampening of 14C signal from the atmosphere, which is emphasized in the big and deeper lakes, not as well-mixed as the small and shallower. The work was performed within the project with the Plitvice Lakes National Park and within the HRZZ project 1623 financed by Croatian Science Foundation.

Izvorni jezik
Engleski

Znanstvena područja
Geologija

POVEZANOST RADA