A new oxygen microsensor has an internal guard cathode that removes all oxygen diffusing toward the sensor from the internal electrolyte. It exhibits unprecedented signal stability and is easy to construct. The high stability may make the use of such microsensors advantageous for routine environmental applications.

Cryptic Sulfur Cycling: Aerobic bacteria and ocean circulation patterns control the formation and distribution of oxygen-minimum zones at moderate depth in the oceans. These habitats host microorganisms that thrive on other metabolic substrates in the absence of oxygen—most commonly, metabolizing thermodynamically favorable nitrogen compounds like nitrate. Off the coast of Chile, however, Canfield et al. (p. 1375 , published online 11 November; see the Perspective by Teske ) suggest that bacteria may often reduce sulfate as well. Metagenomic sequencing revealed the presence of both sulfate-reducing and sulfide-oxidizing bacteria. With the coincidence of sulfate and nitrate reduction, the sulfur and nitrogen cycles may be intimately linked; for example, sulfate reduction could provide nitrogen-rich ammonium for bacteria that ultimately transform it into nitrogen gas.

The thickness of diffusive boundary layers and their role for the oxygen uptake of sediments and detritus were studied by the use of microelectrodes. Gradients of oxygen were always detectable within the boundary layer, which varied in thickness from 0.2 mm to > 1 mm. The thickness depended on the flow velocity of the water and on the roughness of the solid surface. Oxygen diffused through the boundary layer with a mean diffusion time of 1.2–9 min. The diffusive boundary layer constituted a transfer resistance for oxygen flux across the solid‐water interface which limited the oxygen flux at high uptake rates. Sediments or detritus exposed to aerated water could therefore be almost anoxic at the surface, provided that they had sufficiently high rates of oxygen uptake. This can explain the occurrence of microaerophilic or anaerobic bacteria on exposed sediments where fully oxic conditions would intuitively have been expected.