Physical and optical properties of Arctic marine snow

• Main Author: Verin, Gauthier
• Other Authors: Institut des Géosciences de l’Environnement (IGE), Institut de Recherche pour le Développement (IRD)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes 2016-2019 (UGA 2016-2019 ), Université Grenoble Alpes, Université Laval (Québec, Canada), Michel Fily, Marcel Babin
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: HAL CCSD 2019
• Subjects: Radiative transfer; Marine snow; Albedo; Transmittace; Impurities; Ice algae; Transfert radiatif; Neige marine; Albédo; Transmittance; Impuretés; Algues de glace; [SDU.STU.GL]Sciences of the Universe [physics]/Earth Sciences/Glaciology; Arctic; Arctic Ocean; albedo; Arctique*; banquise; Global warming; ice algae; polar night; Sea ice
• Online Access: https://theses.hal.science/tel-02268971; https://theses.hal.science/tel-02268971/document; https://theses.hal.science/tel-02268971/file/VERIN_2019_diffusion.pdf

The Arctic ocean shows a very strong seasonality trough the permanent presence of sea ice whose extent varies from 6 to 15 millions km2. As an interface, sea ice limits ocean - atmosphere interactions and impacts the global energy budget by reflecting most of the short-wave incoming radiations. The snow cover, at the surface, is a key element contributing to the optical properties of sea ice. Snow enhances further the surface albedo and thus delays the onset of the ice melt. In addition, snow is the main responsible for the vertical light extinction in sea ice. However, after the polar night, this low light transmitted to the water column is a limiting factor for primary production at the base of the oceanic food web. The snow cover, through the temporal evolution of its physical properties, plays a key role controlling the magnitude and the timing of the phytoplanktonic bloom. In the actual global warming context, sea ice undergoes radical changes including summer extent reduction, thinning and shifts in snow thickness, all of which already alter Arctic primary production on a regional and global scale.This PhD thesis aims to better constrain the snow cover contributions to the radiative transfer of sea ice and its impact on Arctic primary production. It is based on a dataset collected during two sampling campaigns on landfast sea ice. Physical properties of snow such as snow specific surface area (SSA) and density allow a precise modeling of the radiative transfer which is then validated by optical measurements including albedo, transmittance through sea ice and vertical profiles of irradiance in the snow.During the melt season, marine snow which shows strong spatial heterogeneity evolves fol- lowing four distinctive phases. The melting, which first appears at the surface and gradually propagates to the entire snowpack, is characterized by a decrease in SSA from 25-60 m2kg-1 to less than 3 m2kg-1 resulting in a decrease in albedo and an increase in sea ice transmittance. This is a chaotic period, where optical ...