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Abstract Under the supposition that organisms inhabiting physically dynamic marine environments are better able to survive hypoxic conditions than those experiencing little turbulent or advective augmentation of oxygen fluxes, we evaluated summertime benthic macrofauna communities, in situ aquatic eddy covariance measurements, and ex situ sediment core incubations from 5 latitudinally distinct mid‐shelf locations off Oregon–Washington, USA. Despite bottom water dissolved oxygen (DO) concentrations averaging from 17 to 75 μmol L⁻¹, invertebrate faunal collections contained mixtures of 11 to 28 taxa per 0.1 m²box core and increased in richness and abundance at sites with greater velocity variation. Eddy covariance velocity records of 18‐30 hours regularly showed the arrivals of internal waves. Oxygen fluxes, derived in 15‐min intervals, correlated with multiple flow parameters assessed from velocity components. Daily averages of the oxygen fluxes to the sediment were determined to range from −3.5 to −23 mmol m⁻² d⁻¹, and these fluxes, assumed to fully represent seabed respiration, were 2 to 5 times greater than rates of DO uptake by sediment cores from the same locations. Velocity profiles measured from 0.3 to 2.5 m above the seafloor at a subset of sites were consistent with a wave‐current boundary layer modulated by ocean swell. These findings illustrate how natural physical processes can relieve the stress of hypoxia exposure on the benthos. Physical dynamics play critical roles in supplying DO and determining sediment grain size, permeability, and the activities of benthic organisms. Thus, these factors need consideration when predicting the impacts of low DO concentrations in coastal regions. 

Abstract Cross‐shelf exchange at Greenland's continental margins transports warm waters toward the glacier margins and freshwater offshore into the convective basins of the North Atlantic and Nordic Seas. Several studies have suggested that the exchange is enhanced by the presence of deep, glacial troughs, but observations from Greenland's troughs are scarce. This work presents data from a ship‐based survey at Narsaq Trough, a wide, branched trough in southwest Greenland, during the summer of 2022. We use Conductivity‐Temperature‐Depth‐Oxygen profiles, water samples for nutrient analysis, and underway current profiles to compare the water mass properties and distribution inside and outside the trough, describe the flow‐field in and around the trough, and estimate mixing in the trough. Narsaq Trough is found to provide a pathway for warm, salty Atlantic Water to intrude onto the continental shelf where these waters are mixed with the overlying cold, fresh Polar Water. As a result, waters in the trough are fresher, oxygen‐enriched, macronutrient‐depleted, and at times colder, relative to the unmodified Atlantic Water offshore. This trough‐modified water has the potential to freshen and oxygenate the flow on the shelf‐break and/or reduce the thermal forcing of waters in the adjacent fjord, limiting ice melt. 

Abstract Starting in 2012, the eastern subpolar North Atlantic experienced the strongest surface freshening in the past 120 years. It is yet unknown whether this salinity anomaly propagated downward into the water column and affected the properties of the boundary currents of the subpolar gyre, which could slow down the overturning. Here, we investigate the imprint of this salinity anomaly on the warm and saline Irminger Current (IC) in the decade thereafter. Using daily mooring data from the IC covering the period 2014–2022 combined with hydrographic sections across the adjacent basins from 1990, the evolving signal of the salinity anomaly over the water column and its imprint on the transport variability is studied. We find that due to the salinity anomaly, the northward freshwater transport of the IC increased by 10 mSv in summer 2016 compared to summer 2015. In 2018, the salinity anomaly covered the water column down to 1,500 m depth. Hydrographic sections across the basin showed that this recent freshening signal spread across the Irminger Sea. Overall, the freshwater transport of the IC increased by a factor of three between 2014–2015 and 2021–2022. The associated density decrease over the upper 1,500 m of the water column resulted in an increase in the northward transport of waters lighter thanσ₀ = 27.55 kg m⁻³from 1.7 to 4.2 Sv. This change in northward IC transport by density class may impact the characteristics of the overturning in the Northeastern Atlantic, its strength and the density at which it peaks.