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Abstract

A novel high resolution planar optode (HiPO) for two dimensional oxygen and light‐field imaging is presented. Optical cross‐talk effects, limiting the precision and resolution of conventional planar optode setups, could be strongly reduced by the use of a fiber optic faceplate as sensing window. The new device, therefore, allows for accurate calculation of oxygen fluxes and respiration rates from oxygen concentration images, especially for measurements on small scales. In addition, the setup can be used to estimate the distribution of scalar irradiance within illuminated sediments or mats, thus directly linking local light availability to oxygen dynamics at high resolution. Irradiance values obtained with the HiPO were found to be in good agreement with scalar irradiance microsensor measurements in sandy sediment, and a spatial resolution of ~120 µm could be achieved. The performance of the HiPO for oxygen measurements was tested experimentally and the theoretical limit of spatial (~100 µm) and temporal (~10 s) resolution, governed by oxygen diffusion within the sensing layer, was determined by mathematical modeling. Rates of primary production and respiration in sandy sediments were calculated from the transient oxygen concentrations after perturbations in light condition showing a highly patchy distribution on submillimeter scale. These heterogeneities were clearly correlated to local irradiance within the sediment. Spatial correlations of photosynthesis and respiration were strongly dependent on incident irradiance.