Description: Large amounts of methane hydrate locked up within marine sediments are vulnerable to climate change. Changes in bottom water temperatures may lead to their destabilization and the release of methane into the water column or even the atmosphere. In a multimodel approach, the possible impact of destabilizing methane hydrates onto global climate within the next century is evaluated. The focus is set on changing bottom water temperatures to infer the response of the global methane hydrate inventory to future climate change. Present and future bottom water temperatures are evaluated by the combined use of hindcast high-resolution ocean circulation simulations and climate modeling for the next century. The changing global hydrate inventory is computed using the parameterized transfer function recently proposed by Wallmann et al. (2012). We find that the present-day world's total marine methane hydrate inventory is estimated to be 1146Gt of methane carbon. Within the next 100years this global inventory may be reduced by ∼0.03% (releasing ∼473Mt methane from the seafloor). Compared to the present-day annual emissions of anthropogenic methane, the amount of methane released from melting hydrates by 2100 is small and will not have a major impact on the global climate. On a regional scale, ocean bottom warming over the next 100years will result in a relatively large decrease in the methane hydrate deposits, with the Arctic and Blake Ridge region, offshore South Carolina, being most affected.

Description: The microbial benthic methane filter of the ocean floors globally retains approximately 80-90% of the ascending greenhouse gas methane through anaerobic oxidation of methane (AOM). However natural and catastrophic fluctuations of methane fluxes (caused e.g. by gas hydrate melting, earthquakes, slope failure) can challenge the capability of this greenhouse gas sink. We ask: How efficient can the methanotrophic community adapt its activity to methane flux changes, what is its response time and what is the efficiency of the benthic filter in this time. To answer these questions, a new sediment-flow-through-system was developed. The system holds intact sediment cores and simulates natural condition of seepage with a diffusive supply of sulfate from the top and an advective transport of methane from the bottom. Sampling holes allow monitoring the key parameters (sulfate, sulfide, pH, Redox, Total Alkalinity) over the entire sediment depth. For our experiments, sediment from three different methane-rich environments were used: (1) gassy sediments from Eckernförde Bay (German Baltic) without naturally occurring advective fluid transport, (2) sediments with high advective transport from a methane seep within an oxygen minimum zone on the continental margin (Quepos Slide, Costa Rica), and (3) methane-seep sediments from the center of a mud volcano (North Alex Mud Volcano, Eastern Mediterranean Sea). Two different advective methane flow rates (15.3 and 153 mmol CH4 cm-'yr-1, fluid flow 10.9 and 109 cm yr-1) were applied for replicate sediment cores (upper 20cm) of the respective environments. The poster will present results of the long-term experiment and compare the response of the different sediment types to the varying methane and fluid flow rates.

Description: 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 applying the transfer function of Wallmann et al. (2012) the present-day world's total methane hydrate inventory is estimated to be 1146 Gt of methane carbon. In a worst-case scenario, where steady state is reached by 2100, the global inventory could be reduced by ~0.6%, resulting in an additional average annual methane flux of ~89 Mt from the seafloor. Based on the results of this study, the amount of methane released from melting hydrates by 2100 will not have a major impact on the global climate.

Description: Fossil shells of planktonic foraminifera serve as the prime source of information on past changes in surface ocean conditions. Because the population size of planktonic foraminifera species changes throughout the year, the signal preserved in fossil shells is biased toward the conditions when species production was at its maximum. The amplitude of the potential seasonal bias is a function of the magnitude of the seasonal cycle in production. Here we use a planktonic foraminifera model coupled to an ecosystem model to investigate to what degree seasonal variations in production of the species Neogloboquadrina pachyderma may affect paleoceanographic reconstructions during Heinrich Stadial 1 (∼ 18–15 cal ka B.P.) in the North Atlantic Ocean. The model implies that during Heinrich Stadial 1 the maximum seasonal production occurred later in the year compared to the Last Glacial Maximum (∼ 21–19 cal ka B.P.) and the preindustrial era north of 30°N. A diagnosis of the model output indicates that this change reflects the sensitivity of the species to the seasonal cycle of sea ice cover and food supply, which collectively lead to shifts in the modeled maximum production from the Last Glacial Maximum to Heinrich Stadial 1 by up to 6 months. Assuming equilibrium oxygen isotopic incorporation in the shells of N. pachyderma, the modeled changes in seasonality would result in an underestimation of the actual magnitude of the meltwater isotopic signal recorded by fossil assemblages of N. pachyderma wherever calcification is likely to take place.