The Quest for the Great Sea Tomato

Zach and I have been camped out in Kangerlussuaq for almost 5 weeks now, on a quest.  Our quest is of a limnological nature. We are trying to better understand one of the more ubiquitous yet perplexing features of these Arctic lakes  – the sea tomato.

A sea tomato gathering occurs at the shoreline of Sea Tomato lake.

And in case you need a little sea tomato refresher, these are a type of cyanobacteria of the genus Nostoc, which form spherical, gelatinous colonies in the water. The colonies can range from quite small (<5 mm) to very large (softball size). They typically lie on the bottom of the lake, and can occur in densities of hundreds, to hundreds of thousands per lake.

Sea tomatoes cover the lake benthos in the aptly named, “Sea Tomato Lake”

As cyanobacteria, sea tomatoes play important role in the ecosystem — they aren’t plants (they are bacteria), but they do contain special photosynthetic pigments in their cytoplasm that enable them to photosynthesize. They also have the remarkable ability to fix atmospheric nitrogen into a useable form, and this combination of metabolic features can be crucial to thriving in a nutrient-limited environment like an oligotrophic (low nutrient) Arctic lake.

BUT…WHY do sea tomatoes occur so abundantly in some lakes, and barely grow in others? Some lakes don’t have any sea tomatoes, while lakes located less than 100 meters away may have 100,000’s…

Sea tomatoes can range widely not only in size, but also in color, as seen here from an underwater shot of the lake floor.

To investigate this phenomenon, we built a research vessel…specifically designed to fit our limnological needs.

The set-up includes two modular kayaks, which each snap apart into 3 pieces so that we can load them in and out of the back of our pickup. Add some bungees, plywood, and a whole lot of Velcro, and we’ve got our research vessel: the “Sea Chickadee”.

We’ve installed an underwater sonar device to the back of the boats and we paddle transects across each lake in order to map the shape and size of the lake basins. We also measure a variety of water chemistry parameters (pH, conductivity, dissolved oxygen, temperature), and take biological samples including zooplankton, phytoplankton, and sea tomatoes, which we will use to construct species composition for each lake, and run a variety of nutrient and toxin analyses (did I mention the sea tomatoes are also producing toxins? That may call for a separate entry…).

Zach inspects the imaging of the sonar output.

We have now surveyed 19 lakes ranging from the mouth of the fjord to the edge of the ice sheet:

The Kangerlussuaq area, showing lakes (yellow stars) surveyed between the mouth of the fjord and the margin of the Greenland Ice Sheet.

One of our most interesting discoveries has been that there are a few different species of sea tomato here!

We believe the smooth, spherical species in all the photos above is Nostoc pruniforme. It is the most abundant and widespread species of sea tomato in these lakes.

This next one, however,  is bumpy, irregular in shape, contains dark patches of greenish-black, and doesn’t occur in nearly as dense quantities as N. pruniforme. We are not sure yet, but we think it may be a very rare species called Nostoc zetterstedtii.

Another species of sea tomato co-occuring here (possibly N. zetterstedtii). Note the snail hanging out on the bottom of the colony, probably cleaning some of the epiphytic material off the surface.

There are even occasions where the two are found attached…

Interesting aggregation of the two Nostoc species together.

And finally, we also came across a very dark colony of tiny spheres and much rougher texture, which we have not yet been able to identify…

Colony of Nostoc (spp. unkonwn). We have only spotted one like this in one lake here.

* I’d be very interested to hear if anyone has come across something similar to this one before.

And now in our final week, we are now focused on finishing some underwater photography, with an effort to more accurately estimate sea tomato densities across lakes.

Our eyes remain peeled, and the quest continues…

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Natural History Detective

Police departments and private detectives are not the only ones who use hidden clues to uncover events long passed. Massive amounts of natural history information are waiting to be uncovered in the landscapes around us. Using fairly simple clues, you can determine for how long areas in New Hampshire have been forested, when farming stopped, when and where blowdown events occurred, and even where fires scorched hillsides decades ago.

But you can take this even farther. In southwest Greenland, we’re particularly interested in how our study lakes were formed. We want to be able to look at a lake, and imagine the receding Laurentide Ice carving away cirques, or giant ice blocks melting in the moraine, leaving giant holes. We can do this, and it isn’t that difficult.

There are four main types of lakes (and many combinations thereof) we see around Kangerlussuaq, each with its own epic story of formation.

Cryogenic lakes are shallow dishes of water caught on top of permafrost blocks and ice-wedges. Water is held on the ground surface because the underground ice keeps it from flowing away. These lakes are extremely shallow, and usually have large cracks in the ground nearby, caused by expanding and contracting permafrost.

Cryogenic lakes near the Greenlandic Ice Sheet, with part of the Russel Glacier in the background.

Fault lakes are exactly what they sound like: large fault valleys filled with water, often due to landslide activity at either or both ends. These lakes tend to be very narrow and very deep. In Greenland, these are some of the only lakes not formed by glacial or ice activity.

These small lakes near the Sandflugtdalen all occur in the same fault valley, and are therefore probably fault lakes.

Cirque lakes are generally the most dramatic lakes we see in Greenland. Cirque lakes are formed by moving glaciers that carve out large amphitheater-shaped valleys in the landscape. They are also usually the easiest to identify, as they are almost always surrounded by steep mountains on almost all sides, and have small lips or ledges holding the water back at the outlet.

Sea Tomato Lake (the largest in this photo) is in a small cirque, and has a small moraine lip holding water back at its outlet. The bay to the upper left contains a kettle.

Kettle lakes are by far the most numerous lakes in Greenland. They are usually small, and form when a receding glacier leaves a block of ice to melt in the sediment, often over hundreds of years. These lakes often appear to occur randomly- on plains or in areas with no obvious valleys or depressions. A neat feature of kettles is that they hold the general shape of the ice block that formed them, so each one is very unique.

This lake, also near the Sandflugtdalen, is a typical kettle.

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A Brief Journey Stateside

After three fantastic weeks at Summit, our group of four (IGERTeer Ben Walker, Allison, Jim and I) will return to the US tomorrow. Our last week was very productive and full of radar surveys! Thanks to our colleagues at the Center for Remote Sensing of Ice Sheets (CReSIS), we have a spectacular, cutting-edge radar system that we are using to look at ice layers in the snow. We pull the radar across the snow using a snowmobile so that we can cover lots of ground at a set speed. We had hoped that our friend the Cool Robot would be able to tow the radar, but weighing in at over 400 pounds, the CReSIS radar system proved to be too great an adversary, and the Cool Robot could not quite make the cut on the softer snow.

Might look like a smurf, but that’s me running a radar survey with the CReSIS Snow Radar. (Photo: Allison Morlock)

The Cool Robot was able to do a special radar survey for the camp by taking a look at an old freezer trench (where food and ice cores were once stored) that had been buried several years ago. The robot drove over the freezer trench pulling the smaller radar system to see if any cavities remained where the freezer once was. Check out the glamor shot below of the Cool Robot with the Summit “Big House” in the background.

Cool Robot running a radar survey of Summit’s old freezer trench. (Photo: Tom)

In our journey homeward, we had the great fortune of catching up with Ruth, Christine, Jess and Zach in Kangerlussuaq for dinner. We enjoyed some food from the local “Polar Bear Inn” and swapped stories about our trips –ours coming to an end and theirs just beginning. The Kanger crew headed back to their camp to get ready for another big day of science on the tundra tomorrow. Our agenda for tomorrow includes a flight back to Scotia with the Air National Guard. Once I’m back in Hanover, I’ll be pulling together the data I gathered during our trip to make plans for our next visit to Summit in mid-July.

I can’t thank the Summit Station crew enough for all that they did to make our visit go so smoothly. Though a few days late at this point, the sentiments are still there–wishing everyone a happy solstice and the best of luck for the rest of the field season. Greenland, I’ll be back soon!

The crew at Summit wishing a happy solstice to all! (Photo: Katie Hess)

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