Efficient measurement of marine sedimentary porewater pH and oxygen concentrations using optical sensors

Layla CREAC'H , Wytze Lenstra, Marcus Gutjahr, Manuel Ruben, Huang Huang, Patrick Blaser 

Porewater oxygen concentrations and pH exert substantial influence on sediment diagenesis and potentially towards the reliability of palaeoceanographic records. However, these fundamental chemical parameters are not systematically measured during sea-going expeditions. This study presents an easy, inexpensive and effective method to measure marine sediment porewater oxygen and pH levels using optical sensors. The method was tested with multi-cores during expedition EASI-2 / PS140 onboard RV Polarstern from 22 locations in the Southern Ocean, spanning diverse environments from 0.5 to 4.5 km water depth. The results show that rapid measurements with non-invasive sensors can offer precise and accurate porewater oxygen and pH measurements at a high spatial resolution downcore. This method allows to rapidly identify sedimentary geochemical redox gradients, which would offer valuable information for marine geochemists and paleoceanographers.