Highly productive, yet heterotrophic, and still pumping CO2 from the atmosphere: A land fast ice paradigm?

• Main Authors: Delille, Bruno, Van der Linden, Fanny, Conte, L, Kotovitch, Marie, Fripiat, François, Vancoppenolle, M., Champenois, Willy, Moreau, S., Carnat, G., Roukaerts, A., Dehairs, F., Haskell, T., Tison, Jean-Louis
• Other Authors: FOCUS - Freshwater and OCeanic science Unit of reSearch - ULiège
• Format: Conference Object
• Language: English
• Published: 2016
• Subjects: Physical; chemical; mathematical & earth Sciences; Earth sciences & physical geography; Physique; chimie; mathématiques & sciences de la terre; Sciences de la terre & géographie physique; Antarc*; Antarctica; McMurdo Sound; Sea ice
• Online Access: https://orbi.uliege.be/handle/2268/206780

The YROSIAE (Year Round survey of Ocean-Sea Ice-Air Exchanges) survey aimed to carry out a year-round survey of land-fast sea ice focusing on the study of sea ice physics and biogeochemistry. Ice cores, sea water, brines material were collected at regular intervals about 1 km off cape Evans in McMurdo Sound, Antarctica, from November 2011 to December 2011 and from September 2012 to December 2012. Samples were processed to characterize both the vertical distribution and temporal changes of climate gases (CO2, DMS, CH4, N2O), CO2-related parameters (ice-air CO2 fluxes, dissolved inorganic carbon, total alkalinity and CaCO3 amount), physical parameters (salinity, temperature, and ice texture), biogeochemical parameters (macro-nutrients, particulate and dissolved organic carbon, δ13C, δ30Si and δ15N) and biological parameters (chlorophyll a, primary production within sea ice derived from O2:Ar and O2:N ratios…). Very high chlorophyll a abundance was observed at the bottom of the ice, a common feature of land fast ice in McMurdo Sound. During spring, chlorophyll a exhibited a significant increase suggesting high primary production. . However, at the same time, nutrients at the bottom of the ice increased significantly suggesting high remineralization and heterotrophy. In the middle of the ice column, evolution of dissolved inorganic carbon shown a succession of autotrophic and heterotrophic phases. However, the overall increase of DIC suggests that the ice interior was rather heterotroph. This was consistent with the increase in nutrients observed at the bottom of the ice. Such sea ice system should expel CO2. Yet, strong under saturation in CO2 in surface ice, and negative air-ice CO2 fluxes suggested that sea ice was taking up CO2 from the atmosphere. Meanwhile, measurements of N2O within the sea ice suggest that the ice was releasing N2O to the atmosphere as a result of high nitrification. On the whole land fast sea ice in McMurdo Sound appears as a puzzling ecosystem. It is able to support elevated growth of ...