Global quantification of methane hydrates

• Main Author: Kretschmer, Kerstin
• Format: Thesis
• Language: English
• Published: 2013
• Subjects: Course of study: MSc Climate Physics; Methane hydrate; Sea ice
• Online Access: https://oceanrep.geomar.de/id/eprint/22795/; https://oceanrep.geomar.de/id/eprint/22795/1/M.Sc.%202013%20Kretschmer,%20K.pdf

Large amounts of methane hydrate are thought to be stored in marine sediments. Natural methane hydrate deposits have been found along the world's continental margins as the prevailing low ocean temperatures and high pressures guarantee their stability. Climate change could induce a destabilization of marine hydrates due to changes in bottom water temperatures and/or sea level. Once the hydrates are destabilized they could release methane into the water column and potentially into the atmosphere, enhancing global warming. In this study a comprehensive model analysis is performed to evaluate the impact of destabilizing methane hydrates onto global climate within the next century. Additionally, the focus is set on changing bottom water temperatures to infer the response of the global methane hydrate inventory to future climate change. This study provides a new estimate of the global methane hydrate inventory based on a transfer function, which was recently developed by Wallmann et al. (2012). Global bottom water temperatures and their future evolution are analyzed in detail, as over the past few decades bottom water temperatures changed considerably along the continental margins, owing to natural, but also to anthropogenic climate variability. The current variability of the global bottom water temperatures is investigated in a hindcast simulation of the global ocean-sea ice model configuration ORCA025. The future temperature trend is analyzed by using an ensemble of 22 100-year-long global warming experiments of the Kiel Climate Model (KCM). The resulting warming trend is found to be mostly confined to shallow and mid-depth regions. Especially the warming at mid-depth could destabilize methane hydrates. As a consequence, methane could be released into the ocean and could potentially reach the atmosphere, leading to a strong positive carbon climate feedback. Based on the temperature analyses the changes in the global abundance and distribution of methane hydrates under future climate conditions are inferred. By ...