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Widespread hypoxia occurs seasonally across the Oregon continental shelf, and the duration, intensity, and frequency of hypoxic events have increased in recent years. In hypoxic regions, iron reduction can liberate dissolved Fe(II) from continental shelf sediments. Fe(II) was measured in the water column across the continental shelf and slope on the Oregon coast during summer 2022 using both a trace metal clean rosette and a high‐resolution benthic gradient sampler. In the summer, Fe(II) concentrations were exceptionally high (40–60 nM) within bottom waters and ubiquitous across the Oregon shelf, reflecting the low oxygen condition (40–70 μM) at that time. The observed inverse correlation between Fe(II) and bottom water oxygen concentrations is in agreement with expectations based on previous work that demonstrates oxygen is a major determinant of benthic Fe fluxes. Rapid attenuation of Fe(II) from the benthic boundary layer (within 1 m of the seafloor) probably reflects efficient cross‐shelf advection. One region, centered around Heceta Bank (~ 44°N) acts a hotspot for Fe release on the Oregon continental shelf, likely due to its semi‐retentive nature and high percent mud content in sediment. The results suggest that hypoxia is an important determinant of the inventory of iron is Oregon shelf waters and thus ultimately controls the importance of continental margin‐derived iron to the interior of the North Pacific Basin. [ABSTRACT FROM AUTHOR]

THE vast reservoirs of organic carbon in marine sediments1–3 have the potential to influence the properties of organic matter in the overlying water column. For example, it has been suggested that marine sediments are a possible source of the old, refractory dissolved organic carbon (DOC) found in deep water3–4. Natural radiocarbon and stable carbon isotope ratios (Δ14C and δ13C) can be used to constrain the role of sediments in the ocean carbon cycle5–8. Here we report the distributions of Δ14C and δ13C associated with dissolved organic and inorganic carbon in sediment pore water, together with those of the particulate sedimentary organic carbon, from two geochemically distinct marine environments. Concentration gradients of dissolved organic and inorganic carbon across the sediment–water interface imply significant diffusive fluxes of these solutes from the sediment to the water column. But the DOC fraction in the sediments is greatly enriched in 14C compared with that in the overlying sea water (by as much as 370%), indicating that the DOC supplied by sediments to ocean waters must be relatively young, and that its remnant ages in the water column itself. © 2015 Nature Publisher Group.

The conversion of organic detritus found in sea floor sediments into a source of electrical energy is examined. Research indicates that a seawater cathode and an electrode buried in sediments could provide power for oceanographic instruments. Accompanying charts and graphs provide additional statistical data.

Data from potentiometric pH and PCO2 microelectrodes can be used to determine reliable concentrations of dissolved inorganic carbon (DIC) in pore waters and accurate DIC diffusive fluxes across the sediment-water interface. Very steep or spatially heterogeneous pH and PCO2 gradients can cause mismatching of measurements or disequilibrium of the CO2 system, however.

A direct relationship was found between the bottom water oxygen concentration and core top organic carbon content to benthic oxygen flux for deep sea areas in the Pacific Ocean. This equation was derived from observations of the above factors in the northeast Pacific and may also be applied to other deep sea areas. It shows clearly how the concentrations of organic carbon and oxygen influence the benthic oxygen consumption rate in the ocean.

Marine heatwave (MHW) events have led to acute decreases in primary production and phytoplankton biomass in the surface ocean, particularly at the mid latitudes. In the Northeast Pacific, these anomalous events have occasionally encroached onto the Oregon shelf during the ecologically important summer upwelling season. Increased temperatures reduce the density of offshore waters, and as a MHW is present offshore, coincident downwelling or relaxation may transport warmer waters inshore. As an event persists, new upwelling‐driven blooms may be prevented from extending further offshore. This work focuses on MHWs and coincident events that occurred off Oregon during the summers of 2015–2023. In late summer 2015 and 2019, both documented MHW years, coastal phytoplankton biomass extended on average 6 and 9 km offshore of the shelf break along the Newport Hydrographic Line, respectively. During years not influenced by anomalous warming, coastal biomass extended over 34 km offshore of the shelf break. Reduced biomass also occurs with reduced upwelling transport and nutrient flux during these anomalous warm periods. However, the enhanced front associated with a MHW aids in the compression of phytoplankton closer to shore. Over shorter events, heatwaves propagating far inshore also coincide with reduced chlorophyll a and sea‐surface density at select cross‐shelf locations, further supporting a physical displacement mechanism. Paired with the physiological impacts on communities, heatwave‐reinforced physical confinement of blooms over the inner‐shelf may have a measurable effect on the gravitational flux and alongshore transport of particulate organic carbon. [ABSTRACT FROM AUTHOR]

The decomposition of marine plankton in two-chamber, seawater-filled microbial fuel cells (MFCs) is examined and is related to resulting chemical changes, electrode potentials, current efficiencies and microbial diversity. The results have shown that higher current efficiencies are achieved by optimizing plankton-fed MFCs for direct electron transfer from organic matter to electrodes, which has included the microbial precolonization of high-surface-area electrodes and pulsed flowthrough additions of biomass.