CHEMINI: CHEmical MINIaturised analyser for in situ monitoring of macronutrients and bioactive metals in marine waters

Surveys of macronutrients and metal concentrations in the ocean waters are crucial to distinguish between natural signature and that linked to anthropogenic perturbation. However, the distribution of these chemical elements vary a lot and episodic events can be missed out if sampling and analysis frequencies are not adequate ¹. Nowadays the scientific community is trying to identify relevant information about the spatial and temporal distribution of these key chemical species. Acquiring such knowledge requires the use of in situ instrumentation, a serious challenge in the marine environment, as the areas of interest are sometimes difficult to reach and as some chemical concentrations, in particular metals, can be extremely low in seawater ².

Throughout the last 15 years, Ifremer has developed, optimised and operated CHEMINI (CHEmical MINIaturised analyser ³), an in situ sensor based on flow injection analysis with fluorescence and colorimetric detection. Our results focus on deployments of the CHEMINI surface version on an oyster nursery station (ammonium, 1 month 2005), a coastal buoy (nitrate, silicate, 7 months 2009, 4 months 2011) and on instrumented benthic chambers (ammonium, nitrate, phosphate, 24H, 2018, 2019). The results are discussed against reference laboratory methods, to provide congruous and comparable data sets.

Deep sea versions of CHEMINI, implemented on various vehicles (31 oceanographic cruises) and seafloor observatories to monitor the variability of iron concentrations close to hydrothermal vents will be discussed in a second time ⁴. An average of 5 months/per year of iron concentrations (4 times/day, 2010-on going) were recorded in the Atlantic Ocean (-1690m EMSO Azores, ⁵) and while in the Pacific, analyses run for 4 months in 2012 (Ocean Networks Canada, 2190 m⁶). Technical and analytical challenges and will be discussed in this presentation.