| Popis: |
The marine sedimentary environment in the polar regions is different from the rest of the world’s oceans, as it is greatly influenced by the cryosphere. In the Arctic, sea ice and icebergs can transport vast amounts of sediments, delivered by extensive fluvial systems from the surrounding continents, which have been shaped by the waxing and waning of large terrestrial ice sheets during the Quaternary period. Reconstructing palaeoenvironmental changes in the Arctic Ocean during this time requires the accurate dating of marine sediment cores, something that has been more difficult than in most other marine environments. This thesis investigates and integrates less developed methods to date marine sediments in the Arctic Ocean. It focuses on applying amino acid racemization geochronology and optically stimulated luminescence dating to sediments from across the Arctic Ocean, accompanied by palaeo- and rock magnetic measurements, and sedimentological analyses. The presented results show that racemization of aspartic and glutamic acids in foraminifera follow a predictable rate at the Yermak Plateau and the Greenland and Iceland Seas, and existing calibrated age equations can be used to confidently date late Quaternary sediments in these regions. Purportedly high rates of racemization are observed in the benthic foraminifera, Cibicidoides wuellerstorfi from central Arctic sediments, confirming that the high rates cannot be attributed to taxonomic effects. Their possible causes, which include variable environmental and diagenetic conditions are considered. Optically stimulated luminescence dating of quartz grains from the Lomonosov Ridge provide much needed absolute age control for sediments from this area, further constraining the timing of glacial activity near the Siberian margin and illustrating the potentials of luminescence dating as a geochronological tool in the Arctic. Palaeomagnetic and rock magnetic analyses provide additional evidence that putative polarity reversals and excursions are not always due to geomagnetic field behaviour but are possibly linked to glacial/interglacial modulation of the magnetic mineralogy. |
