When I think of the word ‘plankton’, the first thing that comes to mind is the small, scheming nemesis of my childhood hero, SpongeBob SquarePants. His devious plans to steal the famous ‘Krabby Patty’ formula often made him the villain of the popular kid’s TV show but despite the bad rep, plankton are actually vital players in the marine food web.
The term plankton covers a wide range of organisms from bacteria and protists to single celled plants. Here’s an awesome collage I found, adapted from drawings and micrographs by Sally Bensusen showing just how diverse plankton can be.
Phytoplankton are a subset of plankton which contain chlorophyll meaning that they can take light energy from the sun and convert it into chemical energy. This process, photosynthesis, requires carbon dioxide and as this is usually abundant in the ocean, phytoplankton growth tends to depend on two main factors; the availability of light and the availability nutrients such as nitrate or phosphate.
In the same way that land plants are vital to the food chain on land, phytoplankton are crucial to the food web under the sea. Their ability to convert light into chemical energy makes them the primary producers of the marine world. The energy they produce is passed through all marine life as the phytoplankton are eaten by primary consumers which are then in turn eaten by other predators. From the tiniest of zooplankton to the largest of whales, phytoplankton power the ocean.
Phytoplankton are also big contributors to carbon cycling. Just like the trees in a forest take carbon dioxide from the atmosphere and convert it into oxygen, so do phytoplankton. Although individually they may be microscopic, as a whole, phytoplankton are responsible for transferring a large amount of the carbon from the atmosphere into the ocean. Much like a huge increase in deforestation would affect global carbon dioxide levels, so to would a change in the amount of phytoplankton. And as the primary producers of the marine world, any changes in phytoplankton levels could also feed back to changes in global climate, marine food webs and human supply chains. It’s important therefore to keep an eye on the state of phytoplankton and to have accurate estimates of ocean primary production.
A recent publication led by the Norwegian Polar Institute (NPI) suggests that the current estimates of primary production in the Arctic Ocean could be inaccurate due to unforeseen phytoplankton growth under the ice. Until recently, it was thought that phytoplankton blooms only occurred sporadically under sea-ice due to a lack of light making its way through to the ocean. Data from the N-ICE 2015 Arctic Expedition however suggests that phytoplankton growth is in fact possible under thick sea-ice due to the changing dynamics of the Arctic icescape.
Up until about a few decades ago, the Arctic landscape was thought to barren in the winter and early spring months. It was commonly believed that not much occurred under the thick sea-ice. Although previous papers have reported phytoplankton blooms in the Arctic, these have been during the summer months where melt ponds (like the ones on the left) occur on top of the ice. These easily allow light to pass into the water where it can be used for photosynthesis by any phytoplankton swept beneath the ice. It’s no surprise then that blooms have been recorded under these conditions.
In a recent interview, Arctic researcher Alexey Pavlov explained to me how data from the N-ICE 2015 Arctic expedition furthers this research and shows phytoplankton blooms occurring much earlier in the season ,under thick sea-ice, due to on going changes of the Arctic ice cover.
The appearance of more cracks and leads (openings) in Arctic sea-ice allows light to penetrate the sea-ice pack meaning that these blooms can be initiated and sustained much earlier in the season than initially thought possible. The paper published by the NPI also explains how the thinner, first-year ice forming in recent years allow yet more light to penetrate into the Arctic Ocean and drive these phytoplankton blooms.
The data for this paper was gathered over a 6 month expedition in the Arctic and the paper they published included contributions from over 40 authors! When asked about the importance of this work, Alexey explained how our estimations and future predictions of Arctic primary production are based on the physical and biological ocean models that we create. The more up-to-date research and information we put into these models, the more accurate our estimations will be.
As highlighted in the paper, the sea ice zone is the area with the biggest model uncertainty. One of the limitations of models of the Arctic Ocean is the lack of observations needed for their development and validation. Arctic research is usually only carried out over the summer months due to the inaccessibility of many Arctic regions in the winter. This means that the data generated is often only a snap shot of what is happening over the year. Although the N-ICE 2015 Arctic expedition was longer than a typical expedition and actually designed to gather data from some of these winter months, there is still a lot of work to be done. Thankfully the scientific community are starting to engage in longer expeditions looking at the months that we usually neglect or are unable to study.
The phytoplankton paper is just one of numerous publications to come out of this expedition but it’s certainly one of the most exciting as no one thought it was possible for phytoplankton growth to occur under such conditions. It’s also important as a better understanding of what controls primary production in ice-covered waters would help to reduce the uncertainty surrounding model performance in the ice-covered Arctic Ocean.
Particularly as global temperatures rise and Arctic sea-ice cover changes, it’s important that we survey our environment and improve our models to understand how this could impact us in the future. Blooms like the one captured by the N-ICE 2015 Arctic Expedition could become more common as the Arctic landscape changes and this could have a huge impact on the world around us. So next time someone steps on Plankton in the ‘Krusty Krab’ or flicks him back to the ‘Chum Bucket’, be sure to remember just how important he really is.
If you’d like to read the phytoplankton publication for yourself, click the link below: http://www.nature.com/articles/srep40850
(It’s actually a really nice and easy read as far as scientific papers go!)
And finally a big thank you to Alexey Pavlov for taking the time to answer my questions! In our interview we also discussed what life as an Arctic researcher was like, how Alexey got into this field of work and what Arctic research actually involves. You can find out more about Alexey and the exciting work conducted by the Norwegian Polar Institute in next week’s post.