Phytoplankton - Environmental Controversy

Environmental Controversy

A 2010 study published in Nature reported that marine phytoplankton have declined substantially in the world's oceans over the past century. Phytoplankton concentrations in surface waters were estimated to have decreased by about 40% since 1950 alone, at a rate of around 1% per year, possibly in response to ocean warming. The study generated debate among scientists and led to several communications and criticisms, also published in Nature. That study has not been substantiated so far.

Indicators which may be considered contraindicative to that magnitude of decline in the basis of the marine food web having occurred include not observing a comparable percentage decline in fish species which feed on phytoplankton. Another global ocean primary productivity study found a net increase in phytoplankton, as judged from measured chlorophyll, when comparing observations in 1998-2002 to those conducted during a prior mission in 1979-1986. The airborne fraction of CO2 from human emissions, the percentage neither sequestered by photosynthetic life on land and sea nor absorbed in the oceans abiotically, has been almost constant over the past century, and that suggests a moderate upper limit on how much a component of the carbon cycle as large as phytoplankton may have declined, if such declined in recent decades. In the example of the northeast Atlantic, a case where chlorophyll measurements extend particularly far back, the location of the Continuous Plankton Recorder (CPR) survey, there was net increase over a 1948 to 2002 period examined. During 1998-2005, global ocean net primary productivity rose during 1998 followed by primarily decline during the rest of that period, although still slightly higher at its end than at its start. Using six different climate model simulations, a large multi-university study of ocean ecosystems predicts, by 2050 A.D., "a global increase in primary production of 0.7% at the low end to 8.1% at the high end," although with "very large regional differences" including "a contraction of the highly productive marginal sea ice biome by 42% in the Northern Hemisphere and 17% in the Southern Hemisphere."