Direct visual observations of nanoparticles in the Celtic Sea

Dagmara Rusiecka1,2, Martha Gledhill2, Eric P. Achterberg3, Christine Elgy4 and Douglas Connelly5, (1)National Oceanography Centre Southampton, Ocean and Earth Sciences, Southampton, United Kingdom, (2)GEOMAR Helmholtz Centre for Ocean Research, Chemistry, Kiel, Germany, (3)Geomar - Hemholtz Centre for Ocean Research, Chemical Oceanography, Kiel, Germany, (4)FENAC, University of Birmingham, School of Geography, Earth and Environmental Sciences, Birmingham, United Kingdom, (5)National Oceanography Centre, NERC, Southampton, United Kingdom
Shelf seas are a substantial source of dissolved iron and other biologically essential dissolved trace metals (dTM) to the open ocean. The concentration of dTM in seawater is strongly influenced by their physico-chemical forms. The role of submicron colloids on the stabilization and transport of dTM in the soil porewaters has already been recognized. However, the influence of nanoparticles (NP) on dTM stabilization in marine systems and consequently on their long range off-shelf transport is still very poorly constrained.

The characterization of marine NP is fundamental to understand their chemical behaviour. Here, we report the first direct visual investigation into the formation, water column size distribution and seasonal variation of NP in the Celtic Sea with supportive examination of particle morphology.

Samples were collected from surface (depth range), intermediate (depth range) and deep (depth range) waters in December 2014, April 2015 and July 2015. Nanoparticles (>3 KDa) were concentrated by stirred cell ultrafiltration and imaged using Atomic Force Microscopy and Transmission Electron Microscopy. NP size distributions from the spring cruise showed that they mainly existed in the smallest 0.4-1 nm fraction in surface- and bottom-waters, whereas the summer season was dominated by 0.4-1 nm fraction at all depths. In winter NP in bottom-waters were found predominantly in bigger 1-2 nm fraction.