Molar gas ratios and stable oxygen and nitrogen isotopes of air entrapped in ice, North America

The molar ratios of atmospheric gases change during dissolution in water due to differences in their relative solubilities. We exploited this characteristic to develop a tool to clarify the origin of ice formations in permafrost regions. Extracted from ice, molar gas ratios can distinguish buried glacier ice from intrasedimental ground ice formed by freezing groundwaters. An extraction line was built to isolate gases from ice by melting and trapping with liquid He, followed by analysis of N2, O2, Ar, 18O-O2 and 15N-N2, by continuous flow mass spectrometry. The method was tested using glacier ice, aufeis ice (river icing) and intrasedimental ground ice from sites in the Canadian Arctic. O2/Ar and N2/Ar ratios clearly distinguish between atmospheric gas in glacial ice and gases from intrasedimental ground ice, which are exsolved from freezing water. 615NN2 and 618OO2 in glacier ice, aufeis ice and intrasedimental ground ice do not show clear distinguishing trends as they are affected by various physical processes during formation such as gravitational settling, excess air addition, mixing with snow pack, and respiration.

Degradation of [14C]GlcDGD in the marine sediment by monitoring radioactivity in the aqueous and gas phase using liquid scintillation counting (LSC) techniques

An experiment was conceived in which we monitored degradation of GlcDGD. Independent of the fate of the [14C]glucosyl headgroup after hydrolysis from the glycerol backbone, the 14C enters the aqueous or gas phase whereas the intact lipid is insoluble and remains in the sediment phase. Total degradation of GlcDGD then is obtained by combining the increase of radioactivity in the aqueous and gaseous phases. We chose two different sediment to perform this experiment. One is from microbially actie surface sediment sampled in February 2010 from the upper tidal flat of the German Wadden Sea near Wremen (53° 38' 0N, 8° 29' 30E). The other one is deep subsurface sediments recovered from northern Cascadia Margin during Integrated Ocean Drilling Program Expedition 311 [site U1326, 138.2 meters below seafloor (mbsf), in situ temperature 20 °C, water depth 1,828 m. We performed both alive and killed control experiments for comparison. Surface and subsurface sediment slurry were incubated in the dark at in situ temperature, 4 °C and 20 °C for 300 d, respectively. The sterilized slurry was stored at 20 °C. All incubations were carried out under N2 headspace to ensure anaerobic conditions. The sampling frequency was high during the first half-month, i.e., after 1, 2, 7, and 14 d; thereafter, the sediment slurry was sampled every 2 months. At each time point, samples were taken in triplicate for radioactivity measurements. After 300 d of incubation, no significant changes of radioactivity in the aqueous phase were detected. This may be the result of either the rapid turnover of released [14C] glucose or the relatively high limit of detection caused by the slight solubility (equivalent to 2% of initial radioactivity) of GlcDGD in water. Therefore, total degradation of GlcDGD in the dataset was calculated by combining radioactivity of DIC, CH4, and CO2, leading to a minimum estimate.

Heat flow measurements in the Weddell Sea

From January to March 1987, heat flow measurements were tried at four sites (Sites 689, 690, 695, and 696) during ODP Leg 113, in the Weddell Sea, Antarctica. At Site 690 (Maud Rise), a convex upward shaped temperature vs. depth profile was observed. This profile cannot be explained by steady-state conduction through solid materials only. We conclude that the minimum heat flow value at Site 690 is 45 mW/m2. A prominent bottom simulating reflector (BSR) was observed at 600 mbsf at Site 695. However, the observed temperature is too high to explain the BSR as a gas hydrate. The origin of the BSR remains unknown, although it is probably of biogenic origin as observed in the Bering Sea during DSDP Leg 19. After correcting for the effects of sedimentation, heat flow values at Sites 695 and 696 are 69 and 63 mW/m2, respectively. Furthermore, we compiled heat flow data south of 50°S. In the Weddell Sea region, the eastern part shows relatively low heat flow in comparison with the western part, with the boundary between them at about 15°W longitude.

Heat flow measurements on METEOR cruise M86/5

Mud volcanoes (MV) are sources of mass and energy, transported from deeper levels of the sediment pile to the surface. Together with fluid and gas, thermal energy is emitted through these structures. Therefore heat flow determination is a sensible tool to detect and quantify the amount of convective flow. In the Gulf of Cadiz several mud volcanoes can be found along major tectonic lines (SWIM faults). We employ geothermal measurements to observe the activity of mud volcanoes and possible leakage at the faults apart from pronounced structures.