Háskóli Íslands

On Tuesday 13th of November at 15.30 Ulf Hauptfleisch is going to defend his PhD thesis "High-resolution palaeolimnology of Lake Mývatn, Iceland". The lecture will be held in room 132 in Askja.
The opponents are Dr. Svante Björck, professor at the University of Lund, Sweden, and Dr. Bent V. Odgaard, professor at the University of Aarhus, Denmark.
Supervisor of the PhD was Dr. Árni Einarsson, guestprofessor at the Faculty of Life and Environmental Sciences, University of Iceland, and Dr. Hreggviður Norðdahl, research scholar/scientist at the Faculty of Earth Sciences.
Magnús Tumi Guðmundsson, professor and Head of the Faculty of Earth Sciences, will conduct the ceremony.

Abstract:
The recent ecosystem of eutrophic Lake Mývatn in Northern Iceland is marked by extreme and rapid fluctuation of its main food web components. This study uses subannual core records of microfossils, inorganic element geochemistry and magnetic susceptibility, supported by historical data to detect and understand fluctuations of the lake food web over a period of ca. 170 years. The thesis also addresses two important issues of palaeo-limnology: (1) How closely do changes in a variable in the lake sediment reflect real changes in the lake or its catchment? (2) Do post depositional processes bias the primary sediment record?

Chronology of the lake sediment was established by a combination of tephrochronology and 137Cs-dating. The age of Lake Mývatn was estimated by radiocarbon dating of charred wood from below the lava flow which formed the lake. The result narrows the age interval, estimated earlier by local tephrochronology and conventional radiocarbon dating.

The results of the tephrochronological research improved the dating of the Viking age landnám tephra sequence in Lake Mývatn. The landnám tephra sequence is of importance for establishing chronologies in the North Atlantic and is widely used in palaeolimnology, marine geology and archaeology.

The microfossil results show a good correspondence between the fluctuations of chironomids and Cladocera observed by an ongoing monitoring programme and the microfossil record from the most recent part of the lake sediment. The usefulness of chironomid egg capsules in palaeolimnological studies was established.

Comparison of fossil remains of the filamentous green alga Aegagropila linnaei with meteorological data, and also with fossil and recent biological data, was used to test hypotheses which might explain a recent decline of the species in Lake Mývatn. The species forms the well known lake balls and until recently Lake Mývatn hosted a large colony of lake balls. The observed fluctuations and decline of A. linnaei seem to be driven by a combination of wind and cyanobacterial blooms.

The geochemical and the magnetic susceptibility records indicate that the primary minerogenic core record is at least partly altered by diagenetic processes. The geochemical and microfossil record and historical wildlife data from the nineteenth to the early 20th century show distinct fluctuations with periods of high benthic productivity, good duck egg harvest and high Arctic charr (Salvelinus alpinus) catches interrupted by shorter periods of low benthic productivity, anoxic conditions, Cyanobacteria blooming and high numbers of three-spined stickleback (Gasterosteus aculeatus). The driver of the observed fluctuations could be the cascading impact of fish and Cyanobacteria, on the food web. Climate warming after 1920 may have changed the character of the food web interactions.

Ulf Hauptfleisch was born 3 November 1972 in Magdeburg, Germany. He passed the Vordiplom exam in geology from the Technical University of Berlin in 1996 and a Diplom exam in geology from the same university in 1999. Ulf worked as environmental geologist and project manager in an engineering office in  Magdeburg from 2000-2004. During his PhD he worked at the Mývatn Research Station. Ulf is married with Karin Ulrike Deibele, they have two children, Annika Jórunn and Erik Ísleifur.

Link to event calendar: http://english.hi.is/events/ulf_hauptfleisch_will_defend_his_phd_thesishigh_resolution_palaeolimnology_lake_myvatn

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