Most of Earth’s volcanic eruptions occur underwater, and these submarine eruptions can significantly impact large-scale Earth systems (e.g., enhancing local primary production by phytoplankton). However, detecting submarine eruptions is challenging due to their remote locations, short eruption durations, lack of sea surface signature (if eruptions do not breach the surface), and the transient nature of the surface manifestations of an eruption (e.g., floating pumice clasts, hydrothermal fluids). We can utilize global satellite imagery of 10–30 m resolution (e.g., Landsat 8, Sentinel-2) to detect new eruptions; however, the large data volumes make it challenging to systematically analyze satellite imagery globally. In this study, we address these challenges by developing a new semi-automated analysis framework to detect submarine eruptions through supervised classification of satellite images on Google Earth Engine. We train our algorithm using images from rafts produced by the August 2019 eruption of Volcano F in the Tofua Arc and present a case study using our methodology on satellite imagery from the Rabaul caldera region in Papua New Guinea. We potentially find a large number of new unreported pumice rafts (in ∼16% of images from 2017–present). After analysis of the spatial pattern of raft sightings and ancillary geophysical and visual observations, we interpret that these rafts are not the result of a new eruption. Instead, we posit that the observed rafts represent remobilization of pumice clasts from previous historical eruptions. This novel process of raft remobilization may be common at near-shore/partially submarine caldera systems (e.g., Rabaul, Krakatau) and may have significant implications for new submarine eruption detection and volcanic stratigraphy.

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Staphylococcus aureus is an important nosocomial and community-acquired facultative intracellular pathogen. Many studies have reported that S. aureus infections are associated with intestinal symptoms, but little is known about the molecular mechanisms implicated in S. aureus-induced alterations of intestinal functions. In this study, we investigated the implication of lipid rafts in the interaction of S. aureus with Caco-2 cells. To assess potential alterations in the lipid raft structure and effects on the hydrolytic function, we utilized sucrase–isomaltase (SI) as the major intestinal α-glucosidase that is associated with and sorted to the apical membrane via lipid rafts. Seven days post-confluent, Caco-2 cells were infected with S. aureus Newman and further incubated for an additional 2 days. After 48 h, the levels of SI expression as well as the enzymatic function of this protein were assessed in the infected versus non-infected cells. Analysis of the sorting behavior of SI to the apical membrane constituted another crucial aspect in studying the effects of S. aureus on Caco-2 cells. For this purpose, the apical membranes or brush border membranes (BBMs; referred to as P2 fraction) were separated in both infected and non-infected cells from the basolateral and intracellular membranes (referred to as P1 fraction) by employing a cationic-based procedure using CaCl2. The data show that there is no significant change in the overall expression levels of SI in the infected versus non-infected cells as assessed by Western blotting analysis using monoclonal anti-SI antibodies. By contrast, a significant decrease in the localization as well as the specific hydrolytic activities of SI toward sucrose and isomaltose (Palatinose) was observed in the BBM (P2 fraction) in Caco-2 cells 48 h post-infection. Concomitantly, the specific SI activities increased in the basolateral membrane/intracellular fraction (P1). Noteworthy, the specific activity of SI in the BBM of infected cells was markedly reduced as compared with that of the non-infected counterparts. The data accumulated from this study strongly suggest that infections with S. aureus influence the final step in the lipid raft-associated trafficking of human SI and thereby may trigger secondary functional gastrointestinal disorders.