Isotopes in Biogenic Silica 2024
Evolution of particles composition along a glacier-ocean continuum
by Mathis Guyomard | Damien Cardinal | Sandrine Caquineau | Edwin Cotard | LOCEAN – Laboratoire
d’Océanographie et du Climat : Expérimentations et Approches Numériques (Sorbonne Université,
CNRS, IRD, MNHN) | LOCEAN – Laboratoire d’Océanographie et du Climat : Expérimentations et
Approches Numériques (Sorbonne Université, CNRS, IRD, MNHN) | LOCEAN – Laboratoire
d’Océanographie et du Climat : Expérimentations et Approches Numériques (Sorbonne Université,
CNRS, IRD, MNHN) | LOCEAN – Laboratoire d’Océanographie et du Climat : Expérimentations et
Approches Numériques (Sorbonne Université, CNRS, IRD, MNHN)
Topic: session 2: Biogeochemical Cycling in the Oceans
Presenter Name: Mathis GUYOMARD
Presenter Preference: Oral presentation
Silicon (Si) is a key element for silicifying marine organisms. In the Southern
Ocean, diatoms are the main phytoplanktonic group, in particular around the Kerguelen
plateau with seasonal blooms, an area naturally enriched in iron. Diatoms plays a major role
on the carbon cycle through the biological carbon pump (BCP) and Si cycle via their
frustules made of biogenic silica (BSi). Silicic acid (DSi) supply from water below the
surface generally controls the production of diatoms, but since few years, some studies
report subglacial amorphous silica (ASi) as a potential source of DSi to the polar oceans.
Since ASi can be both biogenic and non-biogenic, it is difficult to identify the Si source. In
addition, clay particles can play a role in the DSi pool via Si adsorption - desorption along
the salinity gradient in estuaries. The identification and nature of particles (primary,
secondary mineral and ASi) is essential to assess the bioavailability of silicon. Different
freshwater, estuarine, coastal and oceanic environments were sampled in late summer 2024
during the MARGO campaign around the Kerguelen plateau. Filtration at 3μm and 0.2μm
was processed in order to study the coarse and fine particles by scanning electron
microscopy (SEM) and X-Ray diffraction (XRD). Different chemical leaching steps were also
tested with the aim of measuring Si isotopes. We will discuss the evolution of the particulate
fraction composition along the glacier-ocean continuum with samples collected from a
melting glacier (glacial flour), glacial and non-glacial lakes, estuary and coast.