Sugar Blobs & Stressed Out Algae
The distributed network is set up! Buoys and sensors are installed in an intricate pattern for 20-30 miles around the main ice camp. We will likely circle back around to do a bit of final maintenance on the larger sites since we still have cooperative weather and are ahead of schedule. However we have to be careful not to accidentally run the icebreaker through any of the sites where we've already set up buoys. They are drifting with ocean currents and winds. The first floes we put buoys and sensors on have moved more than 50 kilometers (30 miles) since the equipment was deployed. People are working hard to map out their new location so we can avoid them as we make our way around the Distributed Network. Later this week, we'll reunite with Polarstern to exchange people and equipment, and then return to Tromso.
Now, the data collection begins. With this data, MOSAiC is hoping to help answer many questions. Some of my favorite questions revolve around the ecology of the region and the life that exists here.
Oceanographic research instrument. This CTD measures conductivity (which tells us how salty the water is), temperature, and density. It also contains sampling bottles which are closed at different depths, capturing water. The water is analyzed for things like dissolved oxygen and nutrients like nitrogen. It also can be filtered to look more closely at phytoplankton present and chlorophyll concentrations. It is an important tool for studying phytoplankton and environmental factors in the ocean. (Photo courtesy of ARCUS.)
I spoke with a phytoplankton ecophysiologist yesterday. He studies how environmental factors affect the way that phytoplankton functions over small time scales. For example, how do the plankton respond to an increase in the saltiness of the water?
It is fascinating work! On land, his job is to grow phytoplankton and change one environmental factor. The goal is to see if this stresses out the plankton, and how much. Temperature, salinity, nutrients, light, and the amount of carbon dioxide in the water are all environmental factors that are changing in the Arctic Ocean. The impacts of these changes can be studied individually in the lab, but it is especially important to understand how they combine to affect phytoplankton. Basically he tries to stress out the plankton by doing something like growing them at warmer temperatures, and then adds a stressor of a different type (like lowering the nutrient availability) to see what happens.
For example, ocean acidification is a concern in the Arctic Ocean. Carbon dioxide in the atmosphere mixes into ocean water; with increasing amounts of carbon dioxide in the atmosphere, more mixes into the ocean. Through a chain of chemical reactions, additional carbon dioxide in the water drops the pH to a more acidic level. Colder waters can hold more carbon dioxide, so the chemical consequences of ocean acidification are faster and stronger in the Arctic Ocean.
Currently, most surface ocean waters are slightly alkaline, with a pH of around 8.2. Models project that this will drop to 7.9 or 7.8 pH over the coming decades, becoming less alkaline and getting closer to being acidic. This seems like a small shift, but it is actually a significant change and can have major impacts. When people think about ocean acidification, usually they worry about organisms that use calcium carbonate to form shells. And ocean acidification does impact shell formation and maintenance for many animals. But that isn't the only way ocean acidification impacts living things in the ocean.
Most phytoplankton only have a thin, single membrane that separates their cell interiors from the outside water. For them, changes in the pH of the water quickly permeate their cells. At significantly lower pH levels, this may have many impacts that are still not well understood. But for most phytoplankton, the more direct effect is a step back from ocean pH. Increased carbon dioxide in the water impacts their rates of photosynthesis.
At low light intensity, some species of phytoplankton actually benefit from having more carbon dioxide in the water. They are able to use this carbon dioxide to photosynthesize more. They grow faster and reproduce more often. But at high light intensity with more carbon dioxide in the water, they are stressed. There is just too much light and carbon dioxide for them to handle. Chlorophyll and other pigments used in photosynthesis become overexcited. The pigments themselves can be damaged, as can important enzymes and the overall cell.
So most phytoplankton benefit from increased carbon dioxide in the water at low light levels. But switch the light to brighter, and the carbon dioxide increase becomes a problem. This is really significant in a changing Arctic. Overall, sea ice is becoming thinner and the extent of it is decreasing. Whether or not there is ice covering the ocean really matters for how much light reaches the phytoplankton. In places where ice persists, the thickness of the ice also can impact how much light penetrates to the under-ice ecosystem. These of course are not the only factors that affect light levels, but it is likely that the Arctic Ocean of the future will be one with higher light levels.
Ice edge with bearded seal. As the Arctic changes, there will likely be more areas where sea ice melts early in the summer season. This may change the timing of phytoplankton growth, with impacts throughout the food web and on the way that carbon moves through the environment. Photo by Bill Schmoker (PolarTREC 2015), Courtesy of ARCUS.
Changes in light availability may also significantly impact the phenology (timing of life history events) of phytoplankton growth. In the past, growth of phytoplankton in the Arctic Ocean was mostly limited by light. There was usually plenty of nitrogen, phosphorous, silica, and other nutrients for phytoplankton to grow during the season of summer light. Before they ran out of nutrients, they ran out of light. In the future, though, changes in ice extent and thickness will likely mean that phytoplankton will experience higher light availability sooner. They'll grow and reproduce quickly, creating what is called a bloom of phytoplankton. With a longer growing season, they may exhaust (use up) key nutrients before summer is over.
If there is still lots of light the phytoplankton will keep creating sugars through photosynthesis. But to use these sugars, they need nitrogen and phosphorous to build proteins and RNA. If nutrients are depleted (used until only small amounts are left), the phytoplankton needs to do something else with the sugars. Some of the sugar can be converted to fat or lipid and saved for later, but there isn't much storage space inside a single-celled organism. If they keep photosynthesizing without enough nutrients, the phytoplankton eventually have to get rid of the excess sugars.
They exude (push out) chains of sticky sugar into the water around them. These sugar chains tend to come together in sticky blobs, and aggregate other bits of organic matter floating in the water. The aggregates are a great meal for many types of bacteria. Lots of bacteria produce methane as they consume the sticky sugar blobs, so this has major connections to the cycling of methane in the Arctic. The aggregates also sink quickly through the water column. Phytoplankton that die also drift down through the water column; diatoms which have a heavy silica case sink faster than most other types of phytoplankton. What isn't consumed by bacteria or zooplankton ends up at the bottom of the ocean. Some of these aggregates and other plankton detritus(bits of dead stuff) gets buried in the bottom sediments. This process can sequester (store away) carbon. This part of the carbon cycle is important for understanding climate feedback loops in a changing Arctic.
These cycles of carbon and nutrients are pretty amazing when you think about it. My body contains many, many, many, many, many atoms of carbon (to be specific, the average human body contains about 7,000,000,000,000,000,000,000,000 atoms of carbon!). Carbon is a basic building block for life. On earth, carbon has been cycling for billions of years. Chances are, I have carbon atoms in my body that were once part of a dinosaur. You do too! And we definitely have carbon atoms in our bodies that have been part of Arctic phytoplankton.
Ocean water with bits of detritus. During and after a bloom of phytoplankton, detritus like this is often observable in the water column. This may be chains of living or dead phytoplankton, or aggregates of exuded sugars and other detritus colonized by bacteria. Though the picture isn't that exciting to look at, it is a really important part of carbon cycling! (Photo courtesy of ARCUS.)
These big elemental cycles have existed since life began on Earth. They are massively important. And these cycles were set in motion by the smallest living things: microbes (single-celled organisms like bacteria and phytoplankton). To this day, carbon and nutrient cycling are largely maintained and altered by these tiny life forms. As the phytoplankton researcher explained to me, "The power of microbes cannot be overestimated. They are everywhere and they are involved in everything." Larger organisms, like polar bears and Arctic cod, are cool. But microbes make the world (or at least, carbon and nutrients) go 'round.
Word of the Day
The Russian word of the day was kolbasa or sausage. I already knew this one, so I asked our translators the Russian word for phytoplankton. And it is ... fitoplankton. Many scientific words based on Latin or Greek are quite similar across English and Russian languages. But things encountered more commonly in daily life tend to be more different across languages, for example: plant and rasteme.
Education Extension
There is so much to investigate and learn about with phytoplankton! If you have access to the ocean, doing a net tow for plankton and observing it with microscopes is a fantastic learning experience! For really young learners, even looking at the plankton sample with their eyes or a magnifying glass can be interesting. This [Plankton Studies] (https://adaptalaska.org/wp-content/uploads/2019/02/Plankton-Studies.pdf) lesson from the Center for Alaskan Coastal Studies is a great guide to a plankton field trip and lab activity. If you don't have a special net for plankton samples, don't worry. You can build your own plankton net!
After observing plankton with microscopes, Plankton Races is a fun follow-up activity. It can also work on its own if you are unable to do your own net tow or plankton observations. In this hands-on, watery activity, students engineer models of plankton to explore the concept of neutral buoyancy and the adaptations plankton have to achieve this.
This plankton coloring book from the Kachemak Bay National Estuarine Research Reserve is a fun resource for younger learners. It is based around species found in the temperate estuary of Kachemak Bay, Alaska, rather than an arctic ecosystem. However, some of the phytoplankton are incredibly similar in these different locations.
Once learners know that plankton exist, you can zoom out to the way phytoplankton interacts with larger ocean, ice, and atmosphere processes. For younger students this might just be thinking about what phytoplankton need to grow. List these needs, and work together to predict patterns of which seasons phytoplankton will be "big and happy" and which seasons are harder for them. For high school students, check out the Being Productive in the Arctic Ocean component of the Arctic Ocean Exploration unit from NOAA. In this lesson, students analyze sea ice cover, nutrient, and primary productivity data to understand factors that may limit primary productivity in the Arctic Ocean.
You could also dive into activities around Ocean Acidification. The Alaska Ocean Acidification Network has compiled a number of lessons, labs, and other resources for educators that are definitely worth checking out.
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