Data collection in Petermann Fjord

10 August 2012

After a short night I woke up this morning for regular breakfast hours between 7 and 8 am. It became clear that we would not be taking measurements in at least the next few hours, so I took the opportunity to catch up on some sleep. After about two hours I was woken up in a not-so-gently manner by the ship’s crushing the thick multi-year ice in the southwestern part of the Petermann Fjord entrance. After an ice reconnaissance flight by helicopter the captain had decided that it was safe to go into the fjord, provided the ice flights were repeated every hour to make sure the ice island did not rotate southwards and close off the whole entrance. This was the first time I saw the boat in action as a real ice breaker: breaking ice. Quite an experience I must say! Thick floes of ice were crushed by the ship’s bow and pushed sideward. The landscape around us is breathtaking: steep cliffs on both sides of the fjords, on top of the cliffs theGreenland ice sheet, large ice bergs that have calved off from Petermann Glacier in the ocean around us, smaller glaciers flowing into the fjord, and the rest of the ocean around us covered in thick ice floes. The wideness and calmness is amazing. The passengers on the helicopter flights today get a real treat. Apart from the amazing landscape a large group of narwhals (whales with long pointy noses) is spotted. I stay on deck for a long time just to admire in silence.

It takes to halfway the afternoon for the boat to break its way through the ice to the vicinity of the edge of the glacier tongue, where we start a CTD/rosette section across the fjord. I asked Humfrey to add some stations to the schedule, even it would only be the top few hundred meters, to better resolve possible finer structures in the fjord. He agreed and added a ‘shallow’ station in between every planned station, warning us though that the whole operation would then take up to 1 or 2 o’clock in the morning. As I really wanted this data I was willing to stay up that late. Apart from the CTDs and rosettes, which tell us something about the water properties and currents in the fjord, we also want to know what the underwater topography (known as bathymetry) looks like. The only information we have is from previous ships in this area, and that information is extremely limited. We basically don’t know more than that the fjord is at least over 1100m deep and that around the entrance the deep part is separated from Nares Strait by a shallow sill, probably no deeper than 450m deep. Therefore we zigzag from station to station, while recording the depth soundings from the ships. The ship’s echo sounder sends a sound signal out to the bottom and waits till this signal returns. From the time it takes to go to the bottom and back, combined with the speed of sound through the water, the depth of the water under the ship is calculated. So, while covering as much ground as we can, we basically map the bathymetry of Petermann Fjord. Knowledge about the bathymetry is of vital importance to be able to make reliable computer models of the ocean circulation in the fjord.

CCGS Henry Larsen in Petermann Fjord in 2009

The zigzagging had one minor disadvantage: it took almost an hour to get from one station to the next. Most of the science team had gone off to bed or for a drink at the bar around 10 o’clock in the evening, while Andreas handled the winch and I monitored the CTD-recordings on the computer screen. Humfrey was also still dedicated to the science being done, but after being satisfied that the depth recordings of the bridge went well around 3 am, he went to bed as well. Although the deep stations were a bit boring to perform (looking at a wire unrolling for 20 min, and then rolling up for 20 min), the data was very exciting and we spent the time in between stations plotting the data, discussing, and going back and forth between the processed data and the rough profiles to see what features were real and which ones may be an artificial side effect of the plotting procedure used. When the last station was finally completed and we finished moving equipment into the container, it was 5 o’clock in the morning (slightly later than the scheduled end time). I decided skipping breakfast in the morning would be an excellent idea and went to bed for a good morning of sleep.

CTD section across the fjord in 2009, prior to the two major calving events. The data is plotted as if you are looking into the fjord, with the northeast side of the fjord on the left.

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  1. Pingback: Nares Strait 2012: Renske’s Blog on Data Collection (and other adventures) | Icy Seas

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