Increasing subtropical North Pacific Ocean nitrogen fixation since the Little Ice Age

Nature. 2014 Jan 2;505(7481):78-81. doi: 10.1038/nature12784. Epub 2013 Dec 15.


The North Pacific subtropical gyre (NPSG) plays a major part in the export of carbon and other nutrients to the deep ocean. Primary production in the NPSG has increased in recent decades despite a reduction in nutrient supply to surface waters. It is thought that this apparent paradox can be explained by a shift in plankton community structure from mostly eukaryotes to mostly nitrogen-fixing prokaryotes. It remains uncertain, however, whether the plankton community domain shift can be linked to cyclical climate variability or a long-term global warming trend. Here we analyse records of bulk and amino-acid-specific (15)N/(14)N isotopic ratios (δ(15)N) preserved in the skeletons of long-lived deep-sea proteinaceous corals collected from the Hawaiian archipelago; these isotopic records serve as a proxy for the source of nitrogen-supported export production through time. We find that the recent increase in nitrogen fixation is the continuation of a much larger, centennial-scale trend. After a millennium of relatively minor fluctuation, δ(15)N decreases between 1850 and the present. The total shift in δ(15)N of -2 per mil over this period is comparable to the total change in global mean sedimentary δ(15)N across the Pleistocene-Holocene transition, but it is happening an order of magnitude faster. We use a steady-state model and find that the isotopic mass balance between nitrate and nitrogen fixation implies a 17 to 27 per cent increase in nitrogen fixation over this time period. A comparison with independent records suggests that the increase in nitrogen fixation might be linked to Northern Hemisphere climate change since the end of the Little Ice Age.

Publication types

  • Historical Article
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acids / chemistry
  • Animals
  • Anthozoa / chemistry
  • Anthozoa / metabolism
  • Aquatic Organisms / metabolism*
  • Climate Change
  • Ecosystem
  • Hawaii
  • History, 15th Century
  • History, 16th Century
  • History, 17th Century
  • History, 19th Century
  • History, 20th Century
  • History, 21st Century
  • History, Ancient
  • History, Medieval
  • Ice Cover*
  • Nitrates / analysis
  • Nitrogen Fixation*
  • Nitrogen Isotopes / analysis
  • Pacific Ocean
  • Plankton / metabolism
  • Radiometric Dating
  • Seawater / chemistry
  • Time Factors
  • Tropical Climate


  • Amino Acids
  • Nitrates
  • Nitrogen Isotopes