A novel technology to understand environmental changes in marine sediments

It is well established that the ocean is of enormous importance as it has an impact on climate, weather, global food security, public health and the economy; however, currently the increasing pressure on the ocean results in unseen levels of pollution and alterations of globally important chemical cycles. From the coast to the deep sea the ocean floor is largely covered by loosely aggregated sediments. These sediments form one of the largest bioreactors on Earth and play a crucial role in the state and health of the marine environment as they convert, store and release chemical compounds that affect and control life. For example, they promote the production of potent greenhouse gases and are a major sink for oxygen, but also recycle nutrients and retain pollutants. These biogeochemical reactions lead to steep gradients of chemical compounds in the upper centimetre to decimetre of the sediments, which can be used to understand the processes proceeding in the sediment, their effects on the global biogeochemical cycles and their impact on the marine environment. However, with traditional analysis methods these gradients can often not be properly resolved, both spatially and temporally, and they are often disturbed during the collection of the sediment; in addition, these measurements are costly and time-consuming.

In the SANDMAN project I will develop a new instrument to measure gradients of important biogeochemical compounds, such as nutrients (nitrate, phosphate), metals (iron) and carbonate system parameters (total alkalinity) directly within the seafloor sediment, in particular the porewater, by combining cutting-edge Lab-on-Chip sensors with deep sea platform technology that can operate in extreme environments in the oceans over longer periods of time. The Lab-On-Chip sensors, which use miniaturized standard laboratory analyses on an automated microfluidic platform, are developed at the National Oceanography Centre and only recently became available for longer-term applications. These sensors are ideal for measuring the chemistry of porewater directly in the sediment as they are very energy efficient and can be deployed for up to a year and only use very little sample volume, hence the steep gradients in the sediment can easily be resolved. During the SANDMAN project I will lead the sensor adaptation and adjustment of the hardware for conditions in sediments, the design of a fluid sampling system to separate the porewater from the solid phase of the sediment and the combination of these components in a unique seafloor instrument. The functionality of this instrument will first be tested in a controlled laboratory environment, then in a costal test station and afterwards it will be used to answer scientifically important questions about the processes linked to nutrient and metal recycling and carbon degradation in currently underexplored areas such as permeable costal sediments and deep-sea trenches.

This unique observing instrument can transform our capacity for the urgently needed benthic biogeochemical analysis from a human-dependent, single-point and costly sampling to a technology-based long-term, high-quality and reliable approach for remote biogeochemical measurements. The SANDMAN system will be widely applicable from the coast to the deep sea and from pole to pole for marine monitoring and industrial applications. Thus it will pave the way to novel synoptic seafloor observations, providing data to support and inform stakeholders, such as government/non-governmental organisations, industries, scientists and the general public, on environmental health and potential hazards.