High turnover rates indicated by changes in the fixed N forms and their stable isotopes in Antarctic landfast sea ice

François Fripiat, Daniel Mikhail Sigman, Guillaume Massé, Jean Louis Tison

Research output: Contribution to journalArticle

17 Scopus citations

Abstract

We report concentration and nitrogen and oxygen isotopic measurements of nitrate, total dissolved nitrogen, and particulate nitrogen from Antarctic landfast sea ice, covering almost the complete seasonal cycle of sea ice growth and decay (from April to November). When sea ice forms in autumn, ice algae growth depletes nitrate and accumulates organic N within the ice. Subsequent low biological activity in winter imposes minor variations in the partitioning of fixed N. In early spring, the coupling between nitrate assimilation and brine convection at the sea ice bottom traps a large amount of fixed N within sea ice, up to 20 times higher than in the underlying seawater. At this time, remineralization and nitrification also accelerate, yielding nitrate concentrations up to 5 times higher than in seawater. Nitrate δ15N and δ18O are both elevated, indicating a near-balance between nitrification and nitrate assimilation. These findings require high microbially mediated turnover rates for the large fixed N pools, including nitrate. When sea ice warms in the spring, ice algae grow through the full thickness of the ice. The warming stratifies the brine network, which limits the exchange with seawater, causing the once-elevated nitrate pool to be nearly completely depleted. The nitrate isotope data point to light limitation at the base of landfast ice as a central characteristic of the environment, affecting its N cycling (e.g., allowing for nitrification) and impacting algal physiology (e.g., as reflected in the N and O isotope effects of nitrate assimilation). Key Points: Spring accumulation of fixed nitrogen above seawater values High turnover rates of fixed N pool, including nitrate Light availability affects sea ice nitrate isotopes distribution

Original languageEnglish (US)
Pages (from-to)3079-3097
Number of pages19
JournalJournal of Geophysical Research: Oceans
Volume120
Issue number4
DOIs
StatePublished - Apr 1 2015

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Forestry
  • Oceanography
  • Aquatic Science
  • Ecology
  • Water Science and Technology
  • Soil Science
  • Geochemistry and Petrology
  • Earth-Surface Processes
  • Atmospheric Science
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science
  • Palaeontology

Keywords

  • Antarctic
  • isotopes
  • nitrogen
  • nutrients
  • sea ice

Fingerprint Dive into the research topics of 'High turnover rates indicated by changes in the fixed N forms and their stable isotopes in Antarctic landfast sea ice'. Together they form a unique fingerprint.

  • Cite this