365 Days of Climate Awareness 50 - Phytoplankton

Phytoplankton (more Greek: phyton = plant, and planktos = wanderer) are autotrophic (self-feeding) primary producers, marine organisms which rely on photosynthesis. Though they account for roughly 1% of oceanic biomass, it is estimated that they produce 50-80%  of the oxygen created each year. It is not a strict biological category, as they comprise many organisms from three distinct biological kingdoms (there are seven kingdoms: Archaea, Bacteria, Chromista, Protozoa, Plantae, Fungi, and Animalia). Photosynthesizing archea, bacteria and algae (protists) are considered phytoplankton.

This broad category includes everything from free-floating cyanobacteria, single-celled to the massive species of kelp which form underwater forests around the world. The common characteristic among these organisms is that they sustain themselves using inorganic chemicals and the light of the sun, and synthesize both their own organic cell material and the byproduct which helps define our atmosphere and most terrestrial and marine ecosystems: oxygen.

Annual average sea chorophyll (SeaWIFS satellite).

Phytoplankton play an important role in the global carbon cycle, consuming roughly one half of the more than 30 Gt (gigatons) of carbon dioxide emitted globally each year. But even increased phytoplankton activity poses a longer-term issue for the global ocean. Increased phytoplankton biomass leads to increased rates of decomposition, which creates more carbon dioxide and acidifies the deeper layers of the ocean, which will affect food webs everywhere (as well as demonstrating that the ocean is not a long-term carbon sink).

As primary producers phytoplankton are the foundation of marine food webs, from the antarctic to the tropics. Since oxygen levels are highest in cold waters, free-floating phytoplankton are most common near the poles, where they support an ecosystem which includes huge mammals like whales. The main factors which affect phytoplankton aboundance are insolation (incoming solar energy), CO₂ concentration, water temperature, and nutrient access. In this way plankton can form part of a negative feedback on global warming, where additional CO₂ improves their productivity, but another aspect is the increasing acidity of the global ocean due to carbon dioxide becoming carbonic acid in the ocean. Lowered marine pH adversely affects the exoskeletons (tests) of many phytoplankton, and might harm them in other ways.

Tomorrow: the cryosphere.

Be well!