Onboard the Oden we have the RV Skidbladner, a 6.4 m long aluminum boat equipped with a bow mounted high-resolution multibeam echo sounder and sub-bottom profiler. The name Skidbladner is derived from Norse mythology. Skidbladner was the god Frej’s magic ship that could be folded to fit in a pocket when not needed and could sail over both land and sea with the wind always from behind no matter the wind direction. All the gods from Valhalla fit inside Skidbladner. This magic ship was built by the sons of Ivaldes, ruler of the dwarfs of the underground. We need these magic ship capabilities as we are released from Oden into the pack ice to map the unknown seafloor along the mysterious and dramatic shores of the Petermann Fjord and nearby.

Skidbladner sänks ner i havet från Oden. Foto: Björn Eriksson

Our specific Skidbladner targets have been the outlet glaciers that calve icebergs and act as sediment providers to the fjord. Oden has kept a distance of about 1–2 nautical miles from the extremely steep walls of the Petermann Fjord and the outlet glaciers. Apart from the multibeam echo soundings collected in the fjord by U.S. icebreaker Healy and Canadian Amundsen 2003 and 2012 respectively, most seafloor was unmapped before we began the expedition. For this reason, we had to map with Oden systematically from the deep central part and outwards towards the shores. With Skidbladner we are able to go up next to the glaciers and map the seafloor and water column properties directly at their margins.

The procedure with a Skidbladner operation starts with placing a RTK (Real Time Kinematic) GPS reference station somewhere on the nearby shore. From the RTK station information is sent by radio to Skidbladner’s GPS that uses this to increase the accuracy from meters to centimeters. In addition, we are able to use the GPS height information to correct for the tide variations during our survey. Once the RTK station is mounted and we verified that we are able to receive information onboard Skidbladner, it is launching time. The launch procedure has gone extremely smooth, although we were forced to cancel launches on a few occasions when the wind was too strong. Once Skidbladner is launched, we climb onboard and off we go to map our targets!

Sven Stenvall, Kallax Flyg, och Björn Eriksson, Stockholms universitet, förbereder RTK (Real Time Kinematic) GPS-stationen på ett berg i Hall Land utanför Petermannfjorden. Foto: Martin Jakobsson

All five Skidbladner missions have been mesmerizing experiences. Once down at the sea level, away from everything, the glaciers and icebergs grow in dimension. We went up to the glacier fronts, but with a steady hand on the throttle in the event that some ice would decide to break away. The advantage with a small boat is that one can move away really quickly if needed. One of the more difficult parts has been to navigate between the sea-ice flows since we do not get the “birds view” one get from the 23 m high bridge on Oden. We do not easily locate all openings between flows that off course are impenetrable for us anyway. At moments it was necessary to climb up on the roof to sufficiently see our path through the ice. While larger flows are easy to pass around if a passage exist, the greatest challenge has been to make sure we do not run into smaller pieces of ice with the bow-mounted sonar. For this reason, we have had one person on guard all the time at the bow.

Undersökning med Skidbladner längs en utloppsglaciär i Petermannfjorden. Kevin Jerram från Center for Coastal and Ocean Mapping, University of New Hampshire, njuter av utsikten. Foto: Martin Jakobsson

Kartläggning med Skidbladner längs kanten av shelfisen. Shelfiskantens tjocklek varierar och det här är en av de tunnare delarna. Rezwann Mohammad från Stockholms universitet vaktar det flerstråliga ekolodet i fören. Foto: Martin Jakobsson

The final Skidbladner mission aimed to explore the entrance to Bessels Fjord, a completely unmapped fjord where, to our knowledge no boat has ever previously entered, at least not to map. Bessels Fjord is extremely narrow with steep walls and run parallel to Petermann Fjord. There is an island at the fjord mouth made of what appears to be a terminal moraine. The fjord must have hosted a smaller ice stream at one point. We are interested in Bessels Fjord since it must have acted, and still is, as a huge sediment trap and thus its bottom should contain a thick pack of sediments of high temporal resolution that could be cored for environmental studies. However, since no one has previously measured the sill depth next to the island we were not able to enter with Oden and take sediment cores. Next to the island, sea ice and icebergs from the smaller outlet glaciers calving into the fjord have become stuck and accumulated in masses. The tidal currents across the sill were strong and ice moved like crazy. What appeared to be a relatively clear entrance with openings in between the ice flows during the morning’s first helicopter was rather clogged by ice when we arrived. Regardless, we made an attempt to drive in with Skidbladner, much like playing the good old computer game Asteroids where we had to avoid the ice blocks and flows that moved towards us swiftly. We managed to get passed the island and up onto the sill, and successfully map across from the island to the northern shore of Bessels Fjord. It was much shallower than expected! The deepest point we crossed was only 15 m, but the main cross section was generally shallower than 10 m. To take a big ship like Oden drafting 8 m across this sill would likely have ended in a disaster! The first part of the Bessels Fjord mission was completed; we now know that a big ship cannot just enter the fjord and take sediment cores!

Skidbladners besättning, från vänster: Mikael Molin, forskningstekniker, Polarforskningssekretariatet, Larry Mayer, professor, Center for Coastal and Ocean Mapping, University of New Hampshire, Kelly Hogan Pires de Matos, British Antarctic Survey. Foto: Martin Jakobsson

After the fjord sill was investigated we mapped the outside of the fjord entrance to look for signs of an ice stream that at one time may have flowed out from Bessels Fjord. The mapping went superbly well, although there were no direct signs of ice streams imprinted in the seafloor. However, the seafloor is so extremely scoured in this area that old traces may also have been erased. The finale consisted of a nearly complete mapping around a grounded piece of the ice shelf that broke off from the Petermann Glacier August 2 and had run aground outside of Bessels Fjord. The mapping allowed us to measure the ice shelf draft and get a fresh image of a large iceberg scour in the seafloor. What a superb ending to a spectacular day!

3D-bild av insamlad batymetrisk data utanför Bessels fjord. Ett 400 m långt isberg har gått på grund efter att ha orsakat ett 3 m djupt plogspår på havsbotten. Vi kunde kartlägga runt om isberget genom att försiktigt passera väldigt nära med Skidbladner.

Ett hörn av det kartlagda isberget som kommer från Petermannglaciären. Foto: Martin Jakobsson