Formation of marine barite in the deep-sea environment: Evidence from sinking particles in the challenger deep, Mariana Trench

A description of the morphology and an understanding of the formation processes of barite in deep waters are lacking. Sinking particles were sampled in a water column at 2000 m, 4000 m and 6000 m in 2016 in the Challenger Deep, Mariana Trench. Sinking barite (BaSO4) crystal particles at different depths and seasons were systematically observed by scanning electron microscopy (SEM), and the chemical composition was determined by energy dispersive X-ray spectrometry (EDS) and inductively coupled plasma mass spectrometry (ICP-MS). The barite particle size ranges from 1 to 6 mu m, and most of the barite particles exhibit good crystal shape, and are in the initial phase of nucleation. The crystal morphologies were mainly ovoid, followed by rounded, hexagons and polyhedrons. The complete shapes of barite under direct observation by SEM show that they mostly formed in the deep-sea environment. The new findings of this paper provide direct microscopic evidence for the two previous views that diatoms and extracellular polymeric substances (EPS) play an important mediating role in barite precipitation. Affected by the funneling effect of the trench, the barite content in sinking particles increases with depth. The East Asian winter monsoon brings large amounts of Asian dust into the ocean in March, this can promote the growth of diatoms and other marine organisms, and thus make the content of barite in March higher than that in August. (C) 2021 Elsevier B.V. All rights reserved.