New capabilities for measuring organic matter degradation in the deepest oceans on Earth

The hadal zone, with depths of 6000-11000 m, accounts for nearly half of the ocean's depth range, but has only recently been recognized as potential hotspot for organic carbon turnover and microbial activity. To understand the carbon mineralization and the related biogeochemical processes in hadal sediments is of global importance as carbon recycling in sediments can have critical implications for ocean chemistry, redox conditions, nutrient availability and hence for life in the oceans and on land. Due to inherent difficulties of retrieving samples for later analyses from hadal depths, a key element to make step changes in this field of research is the ability to use sensor technology to measure the important biogeochemical parameters directly in the hadal sediments and water column, i.e. without retrieving samples. The National Oceanography Centre (NOC) are world-leaders in developing autonomous miniaturized chemical sensors for use in the open ocean. Their existing technology has been tested to 6000 m depth and can measure a wide range of chemicals in environments from the polar regions to the tropics. This project will bring together NOC experts with researchers from the newly created centre of excellence for ultra-deep sea research: the Danish Center for Hadal Research (HADAL) at the University of Southern Denmark (SDU) to jointly improve our knowledge about the processes governing organic carbon degradation in deep-sea trenches. In order to achieve this, we will share resources with the HADAL Center participants, to: i) conduct a knowledge exchange and a collaborative design workshop with both partners to decide on required sensor adaptations ii) test the sensors at the HADAL pressure testing facility to depths > 6000 m to study their limitations and required improvements, and iii) develop the first proof of concept data set of nutrients measured directly in hadal sediments during joint field work to a deep-sea trench off Japan. The outcomes of this project will answer exciting research questions about organic carbon degradation processes in deep-sea trenches and their impact on the surrounding ecosystem and will provide a proof-of-concept data set that will position us to strengthen the collaboration by writing joint proposals for future collaborations.