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Pregled bibliografske jedinice broj: 493199

Determination of initial 14C activity Of speleothem from Modrič Cave, Croatia


Surić, Maša; Krajcar Bronić, Ines; Obelić, Bogomil
Determination of initial 14C activity Of speleothem from Modrič Cave, Croatia // Sažeci radova / Abstracts, Prvi hrvatski speleološki kongres s međunarodnim sudjelovanjem / Garašić, Mladen ; Kovačević, Meho Saša (ur.).
Zagreb: Hrvatski speleoški savez, 2010. str. 28-30 (predavanje, nije recenziran, sažetak, znanstveni)


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Naslov
Determination of initial 14C activity Of speleothem from Modrič Cave, Croatia

Autori
Surić, Maša ; Krajcar Bronić, Ines ; Obelić, Bogomil

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

Izvornik
Sažeci radova / Abstracts, Prvi hrvatski speleološki kongres s međunarodnim sudjelovanjem / Garašić, Mladen ; Kovačević, Meho Saša - Zagreb : Hrvatski speleoški savez, 2010, 28-30

ISBN
978-953-56438-0-7

Skup
Prvi hrvatski speleološki kongres s međunarodnim sudjelovanjem

Mjesto i datum
Poreč, Hrvatska, 24.-27.11.2010

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Nije recenziran

Ključne riječi
speleothem; initial 14C activity (A0); Modrič Cave; Croatia

Sažetak
Radiocarbon (14C) is widely applied for dating of various types of samples including carbonate cave deposits. Since carbon of different origins takes part in speleothem formation, it is essential to know the initial activity (A0) of the 14C in the moment of carbonate formation in order to determine the age of the speleothem. A0 is sometimes called also the dead carbon proportion (dcp), dcp = 100 – A0, where both dcp and A0 are expressed in percent of modern carbon (pMC) (GENTY et al., 2001, KRAJCAR BRONIĆ et al., 1992). Speleothem carbon originates from (a) the seepage water dissolved inorganic carbon (mainly HCO3−) originated from limestone carbon, having 14C activity of 0 pMC, and (b) CO2 of the soil above the cave derived from plant root respiration, having 14C activity similar to that of the atmosphere (fast response), and from microbial decomposition of soil organic matter, which can be slow (decomposition of dead roots, leaf veins etc.). If organic matter is old, CO2 resulting from its decomposition can have a much lower 14C activity than that of atmosphere, but if the decomposed organic matter was formed in the 1960s, during the nuclear weapon test period, the activity may be higher (GENTY et al., 1998). A comprehensive study of isotopic and geochemical characteristics of carbonate sediments has been performed in the continental karst areas of Croatia (KRAJCAR BRONIĆ et al., 2010). It was found that A0 varies between 65 pMC and 90 pMC, depending on local conditions. However, carbonates from caves in the coastal area of Croatia have not been systematically studied. Modrič Cave is shallow horizontal cave located 120 m from the coastline on the foothill of Velebit Mt (44°15' N, 15°32' E). It consists of two channels with total length of 829 m (KUHTA et al., 1999) formed in Cenomanian-Turonian well bedded limestone (MIKO et al., 2002). The cave is rich in speleothems, both fossil and active ones, in all its parts. Overlying bedrock (1 to 27 m thick) is heavily fractured and covered by typical Mediterranean maquis with thin sporadic terra rossa soil, resulting in absence of surface flows and fast direct infiltration into the underground (MIKO et al., 2002). In order to determine initial 14C activity (A0) of the Modrič Cave spelean calcite, 14C activity was measured on modern carbonate sample (MOD 8) which had been collecting on a nylon sheet from 1999 to 2007. 14C measurement was preformed at Radiocarbon Laboratory of Ruđer Bošković Institute, Zagreb, by liquid scintillation counter (LSC) Quantulus 1220TM. The carbonate sample MOD 8 showed 14C activity of 106.2 ± 1.1 pMC. The value is normalized by using δ13C = -8.17‰ (SURIĆ et al., 2010). For the initial activity estimation we used equation where a14Cm is the measured activity of calcite sample, and a14Catm is the mean atmospheric 14C activity of the period covering calcite formation. However, the influence of the age of decomposing organic matter in the soil above the cave must be taken into account when determining the later value. Namely, 14C bomb input was registered in Belgian and Slovenian speleothems with delay of 6-25 and 10 ± 5 years, respectively, and decrease of post-bomb 14C activity was much slower than in atmosphere, demonstrating the damping effect of the soil carbon reservoir (GENTY et al., 1998). That is the reason for modern calcite 14C activity (106.2 ± 1.1 pMC) being higher than the mean atmospheric 14C activity for the 1999 – 2007 period in Zagreb (105.6 pMC) (KRAJCAR BRONIĆ et al., 2010). If we presume similar soil carbon reservoir effect as in Postojna Cave (Slovenia), i.e. delay of ca. 10 years, we would deal with atmospheric 14C activity in the period 1989 – 1997 of 112.5 pMC (LEVIN et al., 2008). Thus, according to above equation, the initial 14C activity in spelean calcite would be 94.4 pMC. Furthermore, the 14C activity of the resulting calcite can be influenced by 'old' storage water (GENTY & MASAULT, 1997). Due to the low thickness of the overlaying bedrock, location under the hill peak, observed increased drip rate within day or two after the heavy rain above Modrič Cave site, and as the most important, overlapping δ18O and δ2H dripwater values with local meteoric water lines (LMWL), being similar to average rainwater δ18O and δ2H (SURIĆ et al., 2010), we assume that residence time of the water is very short and there is no mixing with the older storage water, so that kind of interference into calcite 14C activity can be neglected. Supposing that the same (or similar) mechanism had supported the calcite formation in the past, we can suggest the use of A0 = 94.4 pMC value in age calculation of older speleothem from Modrič Cave. This value can be used also for radiocarbon dating of speleothems from other Croatian shallow coastal caves. However, more studies concerning the present-day isotopic composition of speleothems should be performed to better understand the processes of carbonate precipitation in coastal karts areas and to derive reliable palaeoenvironmental data.

Izvorni jezik
Engleski

Znanstvena područja
Fizika, Geologija



POVEZANOST RADA


Projekti:
098-0982709-2741 - Prirodni radioizotopi u istraživanju krških ekosustava i datiranju (Horvatinčić, Nada, MZOS ) ( POIROT)
119-1191152-1169 - Recentni sedimenti i fosilni okoliši jadranskog priobalja (Juračić, Mladen, MZOS ) ( POIROT)
269-2693084-1177 - Geografske osnove razvoja litoralnih regija Hrvatske (Magaš, Damir, MZOS ) ( POIROT)

Ustanove:
Institut "Ruđer Bošković", Zagreb,
Prirodoslovno-matematički fakultet, Zagreb,
Sveučilište u Zadru

Profili:

Avatar Url Maša Surić (autor)

Avatar Url Bogomil Obelić (autor)

Avatar Url Ines Krajcar Bronić (autor)


Citiraj ovu publikaciju:

Surić, Maša; Krajcar Bronić, Ines; Obelić, Bogomil
Determination of initial 14C activity Of speleothem from Modrič Cave, Croatia // Sažeci radova / Abstracts, Prvi hrvatski speleološki kongres s međunarodnim sudjelovanjem / Garašić, Mladen ; Kovačević, Meho Saša (ur.).
Zagreb: Hrvatski speleoški savez, 2010. str. 28-30 (predavanje, nije recenziran, sažetak, znanstveni)
Surić, M., Krajcar Bronić, I. & Obelić, B. (2010) Determination of initial 14C activity Of speleothem from Modrič Cave, Croatia. U: Garašić, M. & Kovačević, M. (ur.)Sažeci radova / Abstracts, Prvi hrvatski speleološki kongres s međunarodnim sudjelovanjem.
@article{article, author = {Suri\'{c}, Ma\v{s}a and Krajcar Broni\'{c}, Ines and Obeli\'{c}, Bogomil}, year = {2010}, pages = {28-30}, keywords = {speleothem, initial 14C activity (A0), Modri\v{c} Cave, Croatia}, isbn = {978-953-56438-0-7}, title = {Determination of initial 14C activity Of speleothem from Modri\v{c} Cave, Croatia}, keyword = {speleothem, initial 14C activity (A0), Modri\v{c} Cave, Croatia}, publisher = {Hrvatski speleo\v{s}ki savez}, publisherplace = {Pore\v{c}, Hrvatska} }
@article{article, author = {Suri\'{c}, Ma\v{s}a and Krajcar Broni\'{c}, Ines and Obeli\'{c}, Bogomil}, year = {2010}, pages = {28-30}, keywords = {speleothem, initial 14C activity (A0), Modri\v{c} Cave, Croatia}, isbn = {978-953-56438-0-7}, title = {Determination of initial 14C activity Of speleothem from Modri\v{c} Cave, Croatia}, keyword = {speleothem, initial 14C activity (A0), Modri\v{c} Cave, Croatia}, publisher = {Hrvatski speleo\v{s}ki savez}, publisherplace = {Pore\v{c}, Hrvatska} }




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