Optical sensing technologies provide opportunities for in situ oxygen sensing capable of capturing the whole range of spatial and temporal variability. We developed a miniaturized Distributed Oxygen Sensor ("mDOS") specifically for long-term in situ application in soil and sediment. The mDOS sensor system enables the unattended, repeated acquisition of time series of in situ oxygen profiles at a subcentimeter resolution covering a depth of up to one meter. As compared to existing approaches, this provides the possibility to reveal highly variable and heterogeneous oxygen dynamics at a high, quasi-continuous resolution across both scales. The applicability of the mDOS to capture both intra- and interday fine-scale variability of spatiotemporal oxygen dynamics under varying hydrological conditions is exemplarily demonstrated. We specifically aim at estimating the dependency between oxygen dynamics and hydrologic conditions along the measured profiles. The mDOS system enables highly detailed insights into oxygen dynamics in various aquatic and terrestrial environments and in the inherent transition zones between them. It thus represents a valuable tool to capture oxygen dynamics to help disentangling the coupling between underlying hydrological and biogeochemical process dynamics.