ABSTRACT
Both intra-pore hydrate morphology and inter-pore hydrate distribution influence the physical properties of hydrate-bearing sediments, yet there has been no pore-scale observations of hydrate habit under pressure in preserved pressure core samples so far. We present for the first time a pore-scale micro-CT study of natural hydrate-bearing cores that were acquired from Green Canyon Block 955 in UT-GOM2-1 Expedition and preserved within hydrate pressure-temperature stability conditions throughout sub-sampling and imaging processes. Measured hydrate saturation in the sub-samples, taken from units expected to have in-situ saturation of 80% or more, ranges from 3 ± 1% to 56 ± 11% as interpreted from micro-CT images. Pore-scale observations of gas hydrate in the sub-samples suggest that hydrate in silty sediments at the Gulf of Mexico is pore-invasive rather than particle displacive, and hydrate particles in these natural water-saturated samples are pore-filling with no evidence of grain-coating. Hydrate can form a connected 3D network and provide mechanical support for the sediments even without cementation. The technical breakthrough to directly visualize particle-level hydrate pore habits in natural sediments reported here sheds light on future investigations of pressure- and temperature-sensitive processes including hydrate-bearing sediments, dissolved gases, and other biochemical processes in the deep-sea environment.
Subject(s)
Geologic Sediments , Methane , Gases/chemistry , Geologic Sediments/chemistry , Methane/chemistry , Temperature , X-Ray MicrotomographyABSTRACT
Following the distribution characteristics of Larix gmelinii in Daxing'anling Mountains, nine sampling sites along a latitude gradient were set up to analyze the spatial difference and temporal dynamic in the responses of radial growth of L. gmelinii to climate. Overall, the radial growth of L. gmelinii was positively correlated with the standardized precipitation evapotranspiration index (SPEI) in summer (June to August), summer precipitation, February SPEI, and February preci-pitation, but was negatively correlated with the March temperature. Spatially, in the southern area of the region with higher annual average temperature, the radial growth of L. gmelinii had a significant positive correlation with February SPEI. In the northern area with lower annual average tempera-ture, the radial growth of L. gmelinii was negatively correlated with the temperature in March. Temporally, the growth-climate relationship for L. gmelinii was unstable. In the area with higher annual average temperature, the positive effects of SPEI and precipitation, as well as the negative effects of temperature in summer on growth significantly enhanced with climate warming. In the area with lower annual average temperature, the negative response of growth to March temperature enhanced more obviously. Such a result indicated that climate change would alter growth-climate relationship, with great spatial variations. Our results suggested that radial growth of L. gmelinii would be limited in the future climate of warm and dry in the Daxing'anling Mountains. The growth of L. gmelinii might obviously decline in south due to summer water deficit and winter drought, and might be inhibited in north because of warm and dry winter.
