Phytoplankton Levels in Oceans Crashed during the 20th Century

According to EurkeAlert!  a new study conducted by researchers at Dalhousie University in Canada, have found that phytoplankton, unicellular organisms that form the basis of the marine food chain, have been declining globally at dramatic rates over the 20th century.

Using an unprecedented collection of historical and recent oceanographic data, a team from Canada's Dalhousie University documented phytoplankton declines of about 1% of the global average per year. This trend is particularly well documented in the Northern Hemisphere and after 1950, and would translate into a decline of approximately 40% since 1950. The scientists found that long-term phytoplankton declines were negatively correlated with rising sea surface temperatures and changing oceanographic conditions.

Lead author of the study, Daniel Boyle, told CBC News, "We should be very concerned … it's extremely disturbing."

Phytoplankton represent a vast array of aquatic plants that live in close proximity to the ocean's surface.  Through photosynthetic activity, these organisms "produce about half the world's oxygen and remove carbon dioxide from the atmosphere."  In addition to forming the basis of marine food chains, phytoplankton are an important component of the carbon cycle and therefore are vital to the stability of the global climate.

The Christian Science Monitor provides a more detailed explanation of the methodology, which entailed three years of combining satellite based data from 1979 and physical measurements as far back as 1899.

After carving up the marine map into 10 regions, the team found a lot of year-to-year variation in phytoplankton populations, as well as regional variations in abundance. But the century-long decline was evident in 8 of 10 ocean regions and was strong enough to offset gains in two others centered in the Indian Ocean.

The overall decline in phytoplankton populations is directly correlated to increases in ocean temperatures.  As temperatures increase, thermal stratification occurs, which prevents nutrients cycling to upper surface levels and diminishes phytoplankton growth.  The findings therefore, "contribute to a growing body of scientific evidence indicating that global warming is altering the fundamentals of marine ecosystems."   Anthony Richardson of the University of Queensland in Australia explains:

The ocean absorbs 40% of the CO₂ humans emit. Phytoplankton, in turn, convert that CO₂ into oxygen or die and bury it at the bottom of the ocean. If the phytoplankton are disappearing, Richardson says, "the ocean as a carbon sink is declining, and what that means is ultimately more CO₂ will stay in the atmosphere instead of being dissolved in the ocean." That will translate into a warmer world, which will wipe out even more phytoplankton.

Human based activities including over-fishing, pollution, biodiversity loss, climate change induced acidification of the oceans, and the creation of permanent dead zones in coastal areas across the planet point to the obvious and undeniable fact that the planet's oceans are in very poor health.   When aquatic ecosystems across the globe collapse, so will terrestrial life, which is inexorability connected to the oceans through the web of life.