Year 2 Antarctica -Photosynthesis in the Southern Ocean

Photosynthesis in Southern Ocean

The Southern Ocean surrounding Antarctica is a surprising biological hotspot with an extensive biodiversity. The nearshore waters along the “tail” of Antarctica, known as the Western Antarctic Peninsula (WAP), remain a popular study site due to the high productivity and concentration of large sea animals such as whales, seals, penguins, and other sea birds. However, much of the rest of the Southern Ocean remains devoid of microscopic photosynthetic organisms that sit at the base of the Antarctic food web. Why are there so few photosynthesizing phytoplankton, called phytoplankton, growing offshore in the Southern Ocean? We know there is plenty of light there in the summer, when the ice melts, and vigorous circulation brings a constant supply of macronutrients, such as nitrate and phosphate, to the surface ocean, allowing phytoplankton to grow. In 1990 we discovered that the so-called “high nutrient, low chlorophyll” regions such as the Southern Ocean have such low phytoplankton biomass due to growth limitation by insufficient iron supply. Iron is a crucial micronutrient required for photosynthesis, and the major supply route of iron to the ocean is terrestrial sources such as dust and continental sediments. Without adequate iron, no life will grow. This is especially important in the context of the global carbon cycle and global climate. During photosynthesis, phytoplankton use carbon dioxide (CO2) and light to make their energy. More photosynthesis means more draw down of CO2 from the atmosphere, resulting in massive storage of carbon within the ocean. This carbon can stay in the water column or sink to the ocean floor where it can remain sequestered in the sediments for millions of years. The Southern Ocean accounts for ~25% of this oceanic carbon uptake globally. This has been On the Ocean, a program made possible by the Department of Oceanography and a production of KAMU-FM on the campus of Texas A&M University in College Station. For more information and links, please go to ocean.tamu.edu and click “On the Ocean”.

Script Author: Laramie Jensen

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CO2 is being drawn down in Antarctic ocean waters