TY  - THES
A1  - Angelopoulos, Michael
T1  - Mechanisms of sub-aquatic permafrost evolution in Arctic coastal environments
BT  - field observations and modelling of submerged ice-rich permafrost deposits and thermokarst lagoons in northeastern Siberia
N2  - Subsea permafrost is perennially cryotic earth material that lies offshore. Most submarine permafrost is relict terrestrial permafrost beneath the Arctic shelf seas, was inundated after the last glaciation, and has been warming and thawing ever since. It is a reservoir and confining layer for gas hydrates and has the potential to release greenhouse gases and affect global climate change. Furthermore, subsea permafrost thaw destabilizes coastal infrastructure. While numerous studies focus on its distribution and rate of thaw over glacial timescales, these studies have not been brought together and examined in their entirety to assess rates of thaw beneath the Arctic Ocean. In addition, there is still a large gap in our understanding of sub-aquatic permafrost processes on finer spatial and temporal scales. The degradation rate of subsea permafrost is influenced by the initial conditions upon submergence. Terrestrial permafrost that has already undergone warming, partial thawing or loss of ground ice may react differently to inundation by seawater compared to previously undisturbed ice-rich permafrost. Heat conduction models are sufficient to model the thaw of thick subsea permafrost from the bottom, but few studies have included salt diffusion for top-down chemical degradation in shallow waters characterized by mean annual cryotic conditions on the seabed. Simulating salt transport is critical for assessing degradation rates for recently inundated permafrost, which may accelerate in response to warming shelf waters, a lengthening open water season, and faster coastal erosion rates. In the nearshore zone, degradation rates are also controlled by seasonal processes like bedfast ice, brine injection, seasonal freezing under floating ice conditions and warm freshwater discharge from large rivers. The interplay of all these variables is complex and needs further research. To fill this knowledge gap, this thesis investigates sub-aquatic permafrost along the southern coast of the Bykovsky Peninsula in eastern Siberia. Sediment cores and ground temperature profiles were collected at a freshwater thermokarst lake and two thermokarst lagoons in 2017. At this site, the coastline is retreating, and seawater is inundating various types of permafrost: sections of ice-rich Pleistocene permafrost (Yedoma) cliffs at the coastline alternate with lagoons and lower elevation previously thawed and refrozen permafrost basins (Alases). Electrical resistivity surveys with floating electrodes were carried out to map ice-bearing permafrost and taliks (unfrozen zones in the permafrost, usually formed beneath lakes) along the diverse coastline and in the lagoons. Combined with the borehole data, the electrical resistivity results permit estimation of contemporary ice-bearing permafrost characteristics, distribution, and occasionally, thickness. To conceptualize possible geomorphological and marine evolutionary pathways to the formation of the observed layering, numerical models were applied. The developed model incorporates salt diffusion and seasonal dynamics at the seabed, including bedfast ice. Even along coastlines with mean annual non-cryotic boundary conditions like the Bykovsky Peninsula, the modelling results show that salt diffusion minimizes seasonal freezing of the seabed, leading to faster degradation rates compared to models without salt diffusion. Seasonal processes are also important for thermokarst lake to lagoon transitions because lagoons can generate cold hypersaline conditions underneath the ice cover. My research suggests that ice-bearing permafrost can form in a coastal lagoon environment, even under floating ice. Alas basins, however, may degrade more than twice as fast as Yedoma permafrost in the first several decades of inundation. In addition to a lower ice content compared to Yedoma permafrost, Alas basins may be pre-conditioned with salt from adjacent lagoons. Considering the widespread distribution of thermokarst in the Arctic, its integration into geophysical models and offshore surveys is important to quantify and understand subsea permafrost degradation and aggradation. Through numerical modelling, fieldwork, and a circum-Arctic review of subsea permafrost literature, this thesis provides new insights into sub-aquatic permafrost evolution in saline coastal environments.
KW  - permafrost
KW  - subsea
KW  - submarine
KW  - thermokarst
KW  - lagoons
KW  - salt diffusion
KW  - electrical resistivity
Y1  - 2020
ER  - 
TY  - THES
A1  - Feige, Katharina
T1  - Molecular ecological analysis of methanogenic communities in terrestrial and submarine permafrost deposits of Siberian Laptev Sea area
T1  - Molekular-ökologische Analyse von methanogenen Gemeinschaften im terrestrischen und submarinen Permafrost im Laptevseegebiet
N2  - Despite general concern that the massive deposits of methane stored under permafrost underground and undersea could be released into the atmosphere due to rising temperatures attributed to global climate change, little is known about the methanogenic microorganisms in permafrost sediments, their role in methane emissions, and their phylogeny. The aim of this thesis was to increase knowledge of uncultivated methanogenic microorganisms in submarine and terrestrial permafrost deposits, their community composition, the role they play with regard to methane emissions, and their phylogeny. It is assumed that methanogenic communities in warmer submarine permafrost may serve as a model to anticipate the response of methanogenic communities in colder terrestrial permafrost to rising temperatures. The compositions of methanogenic communities were examined in terrestrial and submarine permafrost sediment samples. The submarine permafrost studied in this research was 10°C warmer than the terrestrial permafrost. By polymerase chain reaction (PCR), DNA was extracted from each of the samples and analyzed by molecular microbiological methods such as PCR-DGGE, RT-PCR, and cloning. Furthermore, these samples were used for in vitro experiment and FISH. The submarine permafrost analysis of the isotope composition of CH4 suggested a relationship between methane content and in situ active methanogenesis. Furthermore, active methanogenesis was proven using 13C-isotope measurements of methane in submarine permafrost sediment with a high TOC value and a high methane concentration. In the molecular-microbiological studies uncultivated lines of Methanosarcina, Methanomicrobiales, Methanobacteriacea and the Groups 1.3 and Marine Benthic from Crenarchaeota were found in all submarine and terrestrial permafrost samples. Methanosarcina was the dominant group of the Archaea in all submarine and terrestrial permafrost samples. The archaeal community composition, in particular, the methanogenic community composition showed diversity with changes in temperatures. Furthermore, cell count of methanogens in submarine permafrost was 10 times higher than in terrestrial permafrost. In vitro experiments showed that methanogens adapt quickly and well to higher temperatures. If temperatures rise due to climate change, an increase in methanogenic activity can be expected as long as organic material is sufficiently available and qualitatively adequate.
N2  - Trotz allgemeiner Bedenken, dass auf Grund des Temperaturanstieges im Zusammenhang mit der globalen Klimaerwärmung große Mengen des in terrestrischen und submarinen Permafrostsedimenten gespeicherten Methans freigesetzt werden könnte, ist bisher wenig über die in diesen Böden lebenden methanogenen Mikroorganismen, ihre Phylogenese und sowie ihre Bedeutung hinsichtlich der Methanemissionen bekannt. Das Ziel dieser Doktorarbeit war die Erweiterung der bisherigen Kenntnisse über unkultivierte methanogene Mikroorganismen in submarinen und terrestrischen Sedimentablagerungen, die Zusammensetzung ihrer Lebensgemeinschaft, ihrer Phylogenese und ihrer Bedeutung bei der Emission von Methan. Es wird vermutet, dass methanogene Gemeinschaften submarines Permafrostes zur Erstellung von Modellen genutzt werden können, um Aussagen bezüglich potenzieller Reaktionen methanogener Gemeinschaften des kälteren terrestrischen Permafrostes auf steigende Temperaturen, zu ermöglichen. Die Zusammensetzung der methanogenen Gemeinschaft wurde in terrestrischen und submarinen Permafrostproben untersucht. Der im Rahmen dieser Forschungsarbeit untersuchte submarine Permafrost wies eine im Vergleich zum terrestrischen Permafrost um circa 10°C höhere Temperatur auf. Mittels Polymerasenkettenreaktion (PCR) wurde von jeder der Proben DNA extrahiert und mittels weiterer molekular-mikrobiologischen Methoden wie DGGE, RT-PCR und Klonierung analysiert. Des Weiteren wurden die Proben für in vitro Experimente und Zellzählungen (DAPI und FISH) verwendet. Die Analyse der Isotopenzusammensetzung von CH4 in submarinen Permafrostsedimenten ließ einen Zusammenhang zwischen Methangehalt und aktiver in situ Methanogenese vermuten. Überdies konnte aktive Methanogenese, mittels 13C-Isotopenmessungen von Methan in submarinem Permafrostsediment mit hohem TOC-Wert und hoher Methankonzentration, bewiesen werden. Im Rahmen der molekular-mikrobiologischen Untersuchungen wurden in allen submarinen und terrestrischen Permafrostproben unkultivierte Linien von Methanosarcina, Methanomicrobiales, Methanobacteriacea und den Gruppen 1.3 und Marine Benthic von Crenarchaeota gefunden. Methanosarcina war in allen submarinen und terrestrischen Permafrostproben die dominierende Gruppe der Archaeen. Die Zusammensetzung der archaealen Gemeinschaft, insbesondere die Zusammensetzung der methanogenen Gemeinschaft, variierte zwischen den submarinen und terrestrischen Proben. Des Weiteren fand sich bei der Zellzählung der Methanogenen im submarinen Permafrost eine 10-fach höhere Zellzahl als im terrestrischen Permafrost. Die in vitro Experimente zeigten, dass Methanogene sich schnell und gut an höhere Temperaturen anpassen können. Im Falle weiter steigender Temperaturen auf Grund der Klimaveränderungen, kann – bei ausreichender Verfügbarkeit und Qualität organischen Materials – mit einer Zunahme der methanogenen Aktivität gerechnet werden.
KW  - methanogene Archaea
KW  - Permafrost
KW  - submarin
KW  - terrestrisch
KW  - methanogenic archaea
KW  - permafrost
KW  - submarine
KW  - terrestrial
Y1  - 2009
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-37998
ER  -