Environment Counts | Change in plankton responsible for rapidly increasing nutrient production in North Pacific since 1850 :
The North Pacific subtropical gyre (NPSG) is a major source of carbon and other nutrients to the deep ocean. Primary production in the NPSG has increased in recent decades due to a shift in the dominant forms of plankton to nitrogen-fixing. As a proxy for nitrogen-supported nutrient production in the NPSG, the authors analyze records of the isotopic ratio of nitrogen-15 (Î´15N) in the skeletons of long-lived deep-sea corals near Hawaii. From 1000â€‰ AD to 1850â€‰AD, Î´15N showed no long-term trend. Then, beginning at the end of the Little Ice Age (1850â€‰ad), Î´15N began to decrease dramatically to levels not seen for 5000 years.
Nitrogen isotope ratios from coral
The total shift in Î´15N over this period is comparable to the total change in global mean sedimentary Î´15N at the end of the last ice age 11,700 years ago, but it is happening 10 times faster. Nature (2013) doi:10.1038/nature12784