Month: March 2019

In the last blog post, Elin wrote that I called her with bad news from Dronning Maud Land, because the ice didn’t allow us to deploy the mooring. But what was actually our aim with that mooring? What did we want to learn? For that I need to tell you about the Southern Ocean and ice shelf ocean interaction…

The Southern Ocean is very important for the global system for different reasons:

• Cold temperatures and high salinities close to the Antarctic coast form very dense water masses. They sink down to the bottom of the ocean and drive the whole global ocean circulation.
• The ocean can melt ice shelves – the floating extensions of the ice sheet. Consequently, more of the Antarctic Ice Sheet flows into the ocean and causes sea level rise.

Regarding the ice shelves, they are mainly melting because “warm” water reaches the ice. “Warm” in this sense is not really warm… It only means warmer than the freezing point, which can go Down below -1.9^oC in salt water and under higher pressure at depth. It is very difficult to measure temperatures and currents under an ice shelf. But 10 years ago, one of our oceanographers on board, Tore Hattermann from NPI, went to the ice shelf Fimbulisen here in Dronning Maud Land to drill holes in the ice shelf and install moorings underneath. Since then, those mooring have been measuring temperature, salinity, oxygen and the current speed underneath the ice, where we otherwise can’t measure anything Those are really impressive data!

So what did Tore find out?
There are three different ways how warm water can reach an ice shelf (Hattermann et al., 2012):

• Water that is a the freezing point at the surface cannot melt ice at the surface. But ones it sinks further down, the freezing point decreases because of the higher pressure, so the water is warmer than the local freezing point and can actually melt the ice.
• Warm Deep Water (T < 0.6^oC), which is off the continental shelf break and in greater depths can spill over the continental shelf break in short pulses. It flows then into the ice shelf cavity on the bottom as Modified Warm Deep Water.
• In summer, the surface heats up by the sun. The Winds can then press the surface heated water Down to Depths where it can enter the ice shelf cavity.

However, the heat entering the cavity through those processes is relatively small in the case of Fimbulisen and the melt rate beneath  the ice shelf is low. But what does it have to do with our cruise?
We want to know, how the water masses in front of the ice shelf, at the continental shelf break change with time. Therefore we wanted to install more moorings that could measure the depth of the Warm Deep Water etc. Maybe the winds change with time and consequently also the currents? Also changes in the sea ice can change the density of the water and cause a change in water masses.

It would have been very interesting to study those processes in an area, where so good data from the ice shelf cavity and ice shelf melt exist. We were therefore quite sad, that we couldn’t reach far enough south due to the sea ice restrictions. Luckily, we managed to install two other mooring that the oceanographers from NPI brought, although we had to place them further north than intended. We’ll find out in two years if the data are interesting! And keep the fingers crossed that the instruments won’t get overrun by icebergs or break for other reasons!

On the way to our intensive study area in Dronning Maud Land, the work package leaders on RV Kronprins Haakon constantly have to keep the cruise plan updated with the time schedule and with sea ice conditions, weather and whatever interesting is coming up on the way.

In one location, the observers on board spotted more than 100 whales, compared to about 5 on other days. The whales are there for one reason: food! And the food chain starts all the way down with primary producers that are the food for krill. The Antarctic krill has an estimated biomass of around 389 000 000 tonnes, which is more than the global population of humans! More than 50% of this mass fuels the ecosystem: the whales, seals, penguins, squid and fish.

Primary production in the Southern Ocean is generally low despite high nutrient concentrations. This is due to low iron concentrations. It increases close to islands, coasts, sea ice edge and icebergs. In Dronning Maud Land, many processes that increase primary production come together and green sea ice filaments can even be seen on satellite images.

Finally, we have reached our study area in Dronning Maud Land. Since we left Punta Arenas 10 days ago, we have been sailing non-stop through the Southern Ocean. You may wonder what we have been doing the whole day on board?

First of all, our instruments and gears were piled up in huge containers and had to be unloaded. Labs had to be prepared and packed into plastic to avoid contamination, bottles had to be sorted and all equipment had to be stored securely to not fly around ones we hit high waves. The group leaders used the transit time to plan our tracks in more detail, decide where to take samples and where to do measurements. Some of us already started taking measurements during the transit!

Otherwise the days are quite similar to home when we work on our computers, just that once in a while someone shouts: Iceberg! Whale! Or, watch that beautiful petrel outside! Of course, we also have to take time to clean our own workspace and do the laundry.

Before we went on board, most people didn’t know each other, and now we have to share the cabin with another person. You better hope for someone who is not snoring! However, we already made new friends and spend some time with social activities. On Fridays it’s quiz-night, on Saturdays we play twister, every evening after dinner we do HIIT on the Helideck and we watch movies together, play table tennis, basketball etc…. The work at the stations will work much better if we know each other well!

Now, we have finally deployed a Seaglider (Autonomous Underwater Vehicle) and took the first CTD (Conductivity-temperature-depth) section, which was our first station. You will soon hear more about that and other work on board!

BTW, there is also more about our adventure on the UiB webpage!