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 (δ15N) in the skeletons of long-lived deep-sea corals near Hawaii. From 1000  AD to 1850 AD, δ15N showed no long-term trend. Then, beginning at the end of the Little Ice Age (1850 ad), δ15N began to decrease dramatically to levels not seen for 5000 years.
Nitrogen isotope ratios from coral
The total shift in δ15N over this period is comparable to the total change in global mean sedimentary δ15N 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