Naslov
2400-year multi-proxy reconstruction of environmental change: the Blue Lake (Modro jezero, Imotski) sediment record

Autori
Miko, Slobodan ; Ilijanić, Nikolina ; Jarić, Anja ; Brenko, Tomislav ; Hasan, Ozren ; Šparica Miko, Martina ; Čućuzović, Helena ; Stroj, Andrej

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

Izvornik
5. HRVATSKI GEOLOŠKI KONGRES s međunarodnim sudjelovanjem/5th CROATIAN GEOLOGICAL CONGRESS with international participation Osijek 23.– 25.09.2015. Knjiga Sažetaka/Abstracts Book / Marija Horvat & Lara Wacha - Zagreb : Hrvatski geološki institut, 2015, 177-178

ISBN
978-953-6907-50-2

Skup
5. HRVATSKI GEOLOŠKI KONGRES s međunarodnim sudjelovanjem/5th CROATIAN GEOLOGICAL CONGRESS with international participation

Mjesto i datum
Osijek, Hrvatska, 23.09.2015. - 25.09.2015

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Domaća recenzija

Ključne riječi
karst lake; sediment record; paleoenvironmental reconstruction; drought periods

Sažetak
Blue Lake (Modro jezero) near Imotski has a long history of variations between drought and high water level periods. The recent drought period provided access to the lake bottom and possibility of drilling an 8 meter long core. Modro jezero is a karst lake formed as a collapse doline. The lake was formed, together with a neighboring Crveno jezero, at the edge of a late Miocene lake. Located in Dalmatia (southern Croatia), it is surrounded by the town Imotski. The wider area is inhabited since Neolitic. The lake bottom is located at 242 m a.s.l., and is 195 x 75 m wide. The highest recorded water level was at 345 m a.s.l. Through the 20th century the lake has dried out 7 times. The drought period, which started in summer 2011, provided the access to the lake bottom, and therefore a possibility for a drilling campaign, performed in January 2012. A 8, 2 meter long undisturbed sediment core was extracted from a Lake bottom. The core bottom was dated to be 2400 years old. After the field work, laboratory work was conducted. Following methods were performed: color analysis (L*a*b*), magnetic susceptibility (MS), dating with AMS 14C, microphisiography, grain size and nitrogen and organic carbon analysis. All mentioned analyses were conducted in order to construct a detailed paleolimnological reconstruction. It was possible to connect the parameter L* and organic carbon with the drought periods. By combining aforementioned parameters with discontinuances in sedimentation, it was possible to reconstruct environmental changes. The core covers the whole Subatlantic period (Fig. 1) it starts with a shallow-water sequence interrupted by several deep water phases and indicates evolution from a wetland prior to 1800 cal BP (lithological zone A). A deeper, carbonate producing lake forms from 1800 to 1300 cal BP (zone B) with frequent drought periods. A deep lake with no visible terminations of sedimentation lasts for the next 600 years (zone C). During the Little Ice Age and modern period (zones D and E) the frequency of drying out of the lake increased but their duration was much shorter without significant organic carbon accumulation. This period is accompanied by elevated influx of terrigenous material into the carbonate producing lake. The appearance of the mineral vivianite (Fig. 2) in the wetland sediment sequence indicates a reducing environment. Several faults, which are in correlation to earthquakes in the time of sedimentation, were detected within the core indicating tectonic activity of the wide area of southern Dalmatia. The lake deposits, which cover the time-span from ca 2400 cal BP to the present, show that the hydrological balance dominated by groundwater flow. The Blue lake with its unique position within a karst aquifer and high sedimentation rate will allow the construction of a simplistic climate-hydrology model in which variations in groundwater generation within the lake are recorded in sediments at a three year resolution.

Izvorni jezik
Engleski

Znanstvena područja
Geologija

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