young sea ice that is safe to walk on
day 9 | June 24, 2023
“Sikuliaq” translates to “young sea ice that is safe to walk on” in Iñupiaq, the language spoken by the Iñupiat peoples native to the Seward Peninsula, Northwest Arctic/Alaska, and parts of Western Canada. Our entire journey aboard the Sikuliaq is within their waters — waters that have been stewarded for millennia & continue to hold significant meaning, provide sustenance and home for the Iñupiat peoples to this day. It is with upmost respect that we travel aboard this vessel and I feel extremely honored to be able to experience first-hand this young sea ice that is safe to walk on.
So yes, as you might have gathered we are a little over a week into this cruise and have finally ventured out into (and onto) the sea ice! The Sikuliaq is capable of breaking through ice up to a meter thick, meaning all the ice we are venturing into is young or first-year ice that forms each winter and melts in the summer (multi-year ice up by the North Pole can reach thicknesses upwards of 20 meters!). In fact, most of the sea ice we are surrounded by right now will likely be melted by the time our cruise ends in late July (crazy I know). Aside from being really cool to sail through and walk out on, this sea ice is also a critical component of our research mission on this cruise.
As you may have gathered by now (through the profile photo, instagram handle or just generally talking to one of us), this cruise is focused on polar plankton – more specifically we are investigating the fate of phytoplankton within the Chukchi Sea. The term “plankton” refers to any (typically small) organism that is free-floating within the ocean, meaning they have limited ability to move themselves and are at the whim of the ocean’s waves, currents and tides. Phytoplankton are particularly important as they are the base of the marine food chain. The prefix “phyto-” means plant and similar to the plants we have on land, phytoplankton also practice photosynthesis, or the process of converting light into energy.
In order to conduct photosynthesis, phytoplankton require two main ingredients: nutrient-rich waters (full of nitrogen & iron among others) and light. When conditions allow, phytoplankton typically become plentiful all at once – in large aggregations called blooms. There is plenty of light in the summer months of the Arctic (the sun quite literally never sets) & there are also plentiful nutrients as the shallow basin of the Chukchi Sea (it’s only ~50 meters deep, practically a bathtub in comparison to the Pacific who’s average depth is 4,000 meters) and outflow of rivers from nearby landmasses provides a steady stream of nitrogen into well-mixed waters. So it would seem as though the Chukchi sea should be full of phytoplankton. However, when looking at satellite images of this region – chlorophyll levels (used as a proxy to determine phytoplankton concentrations) seem to be surprisingly low.
How do you determine chlorophyll from satellite imagery? – in simple terms by looking at the color of the sea’s surface, chlorophyll rich waters will be darker & allow less light to pass through than waters with less chlorophyll. For example – the dark blue waters off the coast of California compared to the turquoise clear waters of the Caribbean, the first is full of chlorophyll & phytoplankton while the second not so much…
However, there is one thing that satellite images can’t capture – the chlorophyll/phytoplankton concentration underneath sea ice! On past research cruises, the Arrigo lab has determined that the Chukchi Sea is home to a plethora of under sea ice phytoplankton blooms – meaning something about the protection & conditions provided by the sea ice are allowing phytoplankton to thrive in these waters. By investigating a number of properties both within, under and around the sea ice – we are hoping to gain a little more clarity on why these under-ice blooms occur.
So you might be wondering… what exactly do we do out on the ice?
The first most important step for any ice station is polar bear watch. As cute and cuddly polar bears might be from afar, they can actually be quite aggressive and something we only want to see from the safety of the ship. Therefore, each ice station begins with 2 hours of polar bear watch where a rotating team of scientists & crew survey the area for any signs of off-white movement and continue looking out until the last person is safely back on the ship.
There are many moving parts to an ice station — but the main goal is to get as much information as we can about the composition of the ice itself as well as what lies below (and above) it. One of the primary ways that we do this is by collecting ice cores, or cylindrical tubes of ice. These ice cores allow us to determine the depths at which algae are found within the ice floe (conducting similar processes to phytoplankton, algae within an ice floe are technically not ‘planktonic’ as they aren’t free-floating within the water). We then saw these ice cores into ~10cm thick chunks and bring them back into the lab to melt and filter/process the water.
In addition to ice cores, we do a number of other operations on the ice, such as fly a drone to image the structure of the ice floes.
Drill a large hole to place a sediment trap & wave buoy, both instruments that must be left for ~48 hours to collect data and have GPS-trackers that will allow us to come back and collect them.
We even drive an ROV (remotely operated vehicle) underneath the surface of the ice to image the structure and view the algal coverage.
And most importantly, take a drink from the melt pond. Formed in late spring/summer due to the melting of surface layer snow and ice, melt ponds are shallower than the sea ice floes that they rest upon. The one pictured below was about a meter deep, less than half of the ~2.25 meter thick sea ice surrounding it.
The differential freezing properties of ice and water (when sea ice freezes it expels salt crystals) and the fact that these shallow melt ponds never come into contact with the salty ocean water beneath them mean that these melt ponds are filled with freshwater! Making them the perfect source for a refreshing drink after a long ice station.
In other news – we’ve had some super successful walrus and polar bear watching & have all mostly settled into the schedule of life at sea. Due to heavy ice, our route has been a little all over the place but we’re making progress and have collected data from 26 different points so far.
