Sandy proximal sediments underlying Zostera marina meadows near Poel Island (SW Baltic Sea) were cored to a depth of ~ 60 cm and studied for the nature and amount of particulate organic carbon. Special emphasis was placed on the questions (i) whether seagrass coverage would lead to an enhanced C sequestration in this high-energy depositional setting, and (ii) whether the organic matter stored in these sediments has a seagrass origin or derives from other, marine or terrestrial sources. We observed that the C sequestration in the rhizosphere of seagrass vegetated areas is currently very low and similar to unvegetated areas. However, our analyses of selected lipid biomarkers (sterols, ω-hydroxyacids, and α,β-dihydroxyacids), scanning electron microscopy, ¹⁴C age dating, and a ‘heavy’ δ¹³C-value clearly identified a layer enriched in fossil seagrass biomass that has been buried about 2.500 years ago. This material now resides at a depth of 40 – 60 cm as a several cm thick organic-rich layer and contains most of the organic carbon stored in the uppermost ~ 0.5 m of the sediments near Poel Island. Thus, event-driven burial of seagrass biomass may provide a critical pathway for enabling Blue Carbon storage over relevant (10³ yrs-) timespans in coarse-grained proximal sediments.

The San Juan Basin located in the Four Corners region of the southwestern United States, has long been recognized as a prolific hydrocarbon province, with decades of oil and gas production contributing to a well-understood subsurface geology. With growing global interest in CO₂ capture and storage (CCS) as a strategy to reduce greenhouse gas emissions, this study evaluates basin potential for long-term geological storage.

We focus on Mesozoic reservoir units—particularly those historically associated with conventional and unconventional hydrocarbon production. This work assesses the reservoir quality, seal integrity, and structural configuration of the basin through analysis of well logs, 2D/3D seismic data, and existing geologic studies. Criteria for site selection and potential risk factors for leakage were also examined.

The Entrada Formation, composed of Middle Jurassic sandstones, was identified as a particularly promising reservoir, with thicknesses up to 250 ft, porosities reaching 25%, and permeabilities ranging from 180 to 450 mD. The overlying Todilto Formation, consisting of limestone and evaporites, serves as an effective local seal. Additionally, regional sealing units such as the Mancos Shale and Lewis Shale enhance long-term CO₂ storage. These findings support the viability of the San Juan Basin as a CO₂ storage site, especially in proximity to industrial emission sources such as thermal power plants.

Carbon Capture and Storage (CCS) is increasingly utilized to achieve climate goals by reducing atmospheric carbon dioxide (CO₂) levels. The long-term security of CO₂ sequestration depends on the integrity of both the reservoir and the overlying sealing units. While reservoir properties have been well studied, the transmissive properties of multi-barrier sealing systems remain less well understood and heterogeneity is rarely captured. This study investigates the sealing properties of low-permeability lithologies and well-cement, a critical factor in assessing storage site integrity. Helium was used as the primary permeant for all samples, with CO₂ additionally tested on selected samples to evaluate permeant-specific effects. Klinkenberg-corrected permeability evolution was assessed under increasing and decreasing confining pressures, considering mineralogical influences. The pressure sensitivity coefficient (γ-values) was determined to quantify permeability changes at different confining stresses. To evaluate the time required for permeability stabilization under representative in-situ stress conditions, samples were subjected to 30 MPa confining pressure, corresponding to effective stresses at approximately 2 km depth, and measured daily for 5-8 days. The results indicate that ductile lithologies exhibit a permeability reduction of approximately one order of magnitude after 3-5 days, while casing cement permeability can decrease by two orders of magnitude in 3 days. These findings highlight the necessity of allowing caprock samples to equilibrate under targeted effective stresses for at least three days to obtain reliable permeability measurements.