Posted on behalf of Jane Qiu
Science journalist Jane Qiu is at the Palmer ecological research station on the Antarctic Peninsula, joining researchers investigating how climate change has affected the region in recent decades. Please check back for her dispatches from the bottom of the world.
“There is a bloom right now,” says Edgar Woznica, a sense of excitement palpable. Wozinica and Alice Alpert, newly graduated college students who are spending the austral summer at the Palmer ecological research station in the western Antarctic Peninsula, have been busy collecting samples from coastal and open waters around the station to study their bacterial communities. They want to know the extent of the bacterial bloom and what may be causing it.
For each water sample, the researchers, of the Marine Biological Laboratory (MBL) in Woods Hole, Massachusetts, determine the size distribution of the bacteria and measure the total bacterial mass and how fast they grow.
Meanwhile, another research team from, led by Oscar Schofield of Rutgers University in New Brunswick, New Jersey, measures the composition, weight and the rate of photosynthesis of phytoplankton, microscopic plants that are the starting point of the marine food chain.
Together, the scientists will be able to deduce the amount of carbon that goes into so-called heterotrophic bacteria that feed on dissolved organic matter (DOM) released by phytoplankton and other organisms.
Such experiments have been carried out twice a week between October and April every year since 2001. Ultimately, the researchers want to have a better handle on the role of bacteria in the carbon cycle in the Antarctic and how it may respond to a changing environment.
Largely driven by phytoplankton photosynthesis, the oceans absorb about a quarter of the carbon dioxide in the atmosphere – 20% of that carbon production takes place in polar regions. “Bacteria counteract that storage process by decomposing the organic matter back to carbon dioxide,” says Hugh Ducklow, also of MBL, who leads the bacteria study.
Heterotrophic bacteria are able to use dissolved organic matter at extremely low concentrations – nanomolar, or parts per billion – that no other organisms are capable of. They convert a quarter of the carbon content into their biomass, available for small grazers to use, and pump the rest back to the atmosphere in form of carbon dioxide – a byproduct of respiration, in which nutrients are turned into useful energy in the cell.
Ducklow’s team was surprised to find that bacterial production in coastal waters in the region constitutes only 5% of the primary production – compared to 15-30% elsewhere in the global ocean – making the western Antarctic Peninsula an important region of carbon storage.
This cannot be explained by a slower growth rate – because bacteria in the Antarctic grow just as fast as those at the Equator do, says Hugh. The researchers suspect that the Antarctic food web may produce less dissolved organic carbon – due to the ecosystem structure in the region – so bacterial growth is limited by the amount of food available.
The key question, however, is what will happen in the future. As the ocean gets warmer, the food web may become more similar to its low-latitude counterparts – resulting in more dissolved organic carbon, an increase in bacterial production and more carbon-dioxide emission through decomposition.
“We may have a potential positive feedback,” says Hugh. Further studies of the bacterial communities at Palmer and other parts of the Antarctic will shed light on whether these invisible carbon pumps may change the fate of the global carbon cycle – and ultimately the fate of the white continent itself.
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Probing ocean acidification
Image: Edgar Woznica studies bacteria and phytoplankton / Jane Qiu