Biogeochemical dynamics in a marine storm demonstrates differences between natural and anthropogenic impacts.

This study explores the impact of a wind storm on sediment resuspension and marine biogeochemical dynamics. Additionally, the storm took place during an expedition researching bottom trawling, enabling the direct comparison of certain natural and fisheries-related disturbances. The storm was initiated by a decline in atmospheric pressure and a 2 h period of gale force winds, which was followed by over 40 h of elevated bottom currents. Storm induced turbidity, potentially a cumulative post-fishing impact, was remarkably higher compared to what was observed in a recent trawling event. Storm-induced mixing and movement of water masses led to decreased silicate and increased phosphate concentrations in the water column, accompanied by lower salinity and higher fluorescence. The erosion depth of the seabed averaged around 0.3 cm during the peak turbidity period. Trawl-induced erosion in the area has been measured at over twice that depth, and has been linked to intermittent reductions in near-bed oxygen levels. In contrast, storm-induced turbidity coincided with increased oxygen due to wave mixing, suggesting inherent differences in how trawling and storms can oxidize reduced substances. These findings suggest that storms have a greater regional impact, whereas the local impacts of bottom trawling on biogeochemistry can be more significant.

The Physical Oceanography of Ice-Covered Moons.

In the outer solar system, a growing number of giant planet satellites are now known to be abodes for global oceans hidden below an outer layer of ice. These planetary oceans are a natural laboratory for studying physical oceanographic processes in settings that challenge traditional assumptions made for Earth's oceans. While some driving mechanisms are common to both systems, such as buoyancy-driven flows and tides, others, such as libration, precession, and electromagnetic pumping, are likely more significant for moons in orbit around a host planet. Here, we review these mechanisms and how they may operate across the solar system, including their implications for ice-ocean interactions. Future studies should continue to advance our understanding of each of these processes as well as how they may act together in concert. This interplay also has strong implications for habitability as well as testing oceanic hypotheses with future missions.

Impact of off-bottom seaweed cultivation on turbulent variation in the hydrodynamic environment: A flume experiment study with mimic and natural Saccharina latissima thalli.

The seaweed industry is growing worldwide to meet future resource needs in terms of food and fuel. In the meantime, the impact of expanding off-bottom seaweed cultivation on its environment is unclear. For example, it remains poorly understood how off-bottom seaweeds affect the local hydrodynamic environment, especially concerning turbulence that is more important for nutrient transport and availability than the mean flow velocity. Here, we carried out well-controlled flume experiments with mimic seaweed thalli, which are available, controllable, and stable, to investigate the impact of off-bottom seaweed canopies on whole-depth flow velocities in terms of both mean flow and turbulence velocity profiles. A careful comparison of behavior in the flow between natural and mimic seaweed thalli was made before these experiments. The results show that the floating seaweed thalli generate a surface boundary layer and have a profound impact on the velocity structure in the bottom boundary layer. More importantly, the generation, growth and dissipation of turbulence in the seaweed thalli area deeply affect the downstream distribution of near-bed turbulent strength and associated bed shear stress. Ignoring this turbulent variation would cause inaccurate predictions of morphological changes of the seabed. Our findings suggest that expanding the seaweed cultivation area may cause high risks of bed degradation and low diffusion in the downstream cultivation area. These findings provide novel insights into the environmental influence of off-bottom seaweed cultivation, with important implications for optimizing management strategies to promote seaweed productivity while minimizing seabed destabilization.