Nordvestfjord and the polynyas

The coast of Renland, seen from near the Bear Islands:  high plateau and deep incisions.

The inner reaches of the fjord.  The flanks of the fjord are heavily scoured and gently sloping.  Here, at some stages, areal scouring has affected the whole landscape during heavy ice inundation, whereas further down the fjord linear erosion and trough deepening have been the dominant processes.

Daugaard Jensens Gletscher, one of the most productive glaciers of the world, feeding into the head of Nordvestfjord

This prominent bench (with a small glacier decanting onto it) dates from a time when the fjord was wider and maybe not so deep.......

Lately I have been looking at some new satellite images of the inner reaches of Nordvestfjord. Something interesting has been going on up there. Just a reminder of the basic info:

The fjords stretch for hundreds of kilometres along the east coast, having been carved out of the landscape over millions of years by vast glaciers draining the Greenland Ice Sheet. The pattern of glacier flow has been by no means simple -- we see not just troughts carved out on the most direct routes to the coast, but highly complicated "rectilinear" patterns, with many connecting or cross-fjords running in unexpected directions. For about ten months of the year the fjords are choked with sea ice, and the only effective means of travel is by dog sled or (nowadays) by skidoos. In addition to the sea ice, vast numbers of icebergs move inexorably out towards the coast, having been calved off the big glaciers that still drain the ice sheet. 

  

Nordvest Fjord is really the mother and father of all the fjords on Planet Earth. If you go to any of the fjord sites on the web, you will find copious amounts of information about Sognefjord, Milford Sound, the fjords of Chile and even Antarctica, but very little about this one. Strange, given that it is now well known from satellite imagery, even if not very frequently visited. That's because access is very difficult. The fjord extends c 217 miles (350 km) inland from the outer coast. It's in two sections -- the outer (very broad) part is called Scoresby Sund, which is about 20 miles wide and 120 miles long, with Jameson land to the north and Milne Land and Knud Rasmussens land to the south and west, and then Nordvest Fjord proper, which pushes inland for a further 95 miles or so. In this section the fjord is mostly less than 5 miles wide, and in places as narrow as 3.5 miles from shore to shore. Access into the fjord system is often very difficult, even for ice-strengthened ships in the summer, because of the thick pack ice which congests the Scoresby Sund entrance; in some years no vessels manage to get through it, and even when access is possible, the fjord is effectively shut off again early in September.

The Nordvest Fjord - Scoresby Sund system has clearly been one of the major outlet routes for ice from the Greenland Ice Sheet, during the whole of the Pleistocene and maybe for much longer than that. Even today the Daugaard Jensens Gletscher, near the head of the fjord, is possibly the most productive glacier in the whole of Greenland. Because the ice here has been streaming so effectively in a narrow and constrained trough, the rate of downcutting has been impressive indeed. There are no proper bathymetric charts, but from the scattered soundings that have been made we see depths of 1372m, 1459m, 1372m, 1150m, 1237m, and 1290m between Eskimo Bugt and Syd Kap. The deepest sounding of all is 1508m (4,947 ft). These soundings show that the fjord is substantially deeper than Sognefjord in Norway (maximum known depth 1308m), which has just one short stretch deeper than 1200m. But here on the flanks of Nordvest Fjord the plateau ice caps and mountain summits are almost all over 2000m (6561 ft), whereas there is little land over 1600m on the flanks of Sognefjord. So the full depth of Nordvest Fjord over a distance of about 80 miles is approx 3300m or 11,000 feet. I'll let somebody else work out how much material has been eroded and removed by ice from a trough of this size....... but it is indisputable that this is the deepest, longest and most dramatic fjord system on earth.

We don't know enough about the long profile to know whether it conforms to the "ideal" long profile of Sognefjord, where we can see an incremental deepening of the trough wherever there have been supplements to the ice discharge via tributary glaciers.

The Sognefjord long profile, showing how deepening is associated with discharge supplements

I would expect something similar in the case of Nordvest Fjord.  Some very useful information is found in this publication, showing a series of connected basis separated by sills:

https://www.repository.cam.ac.uk/bitstream/handle/1810/247782/Dowdeswell%20et%20al%202015%20Geological%20Society%20of%20London.pdf?sequence=1

The deepest section of the fjord begins about 20 km from the GJ Glacier snout, and continues for about 30 km with depths around 1400m before shallowing to around 1200m; this may reflect erosive power or capacity, but it may well be that sediments are much thicker in the middle and outer sections of the fjord, with the bedrock floor maybe several hundreds of metres below the "sediment floor".  Near the exit into Hall Bredning the sediments are at least 100m thick.

What we do know is that where the narrow Nordvest Fjord opens out in the vicinity of Syd Kap and the Bear Islands, there is a sudden shallowing of the water, as the bedrock floor rises to approx 400-500m below sea level. This is very similar to the situation at the mouth of Sognefjord, where ice diffluence has been associated with a reduction in erosive capacity, as we can see on the diagram above. We don't exactly see skerries at the junction between the deep fjord and the shallow fjord, but there are some grounds and small islets which make navigation difficult and dangerous, and as in the case of Sognefjord the fjord bed rises from c 1200m to just a few tens of metres over a distance of just 4 miles. This is called the threshold, and it explains why there is relatively little water exchange in the murky depths of the fjord; vast quantities of water are simply trapped in what is in effect a gigantic elongated basin.

Link and more images:
http://www.actsofgod.cool/location.html

One interesting feature of the local geography is the occurrence of polynyas (areas of open water encircled by solid pack ice) in the Hall Bredning area -- with one which is intermittently open near the Bear Islands and another around Nordostbugt and around the mouth of the Schuchert River.  

The polynyas (horizontal bars) shown for the Syd Kap / Nordostbugt area and to the north of the Bear Islands

Ice-free water can occur here even in the depths of winter, partly because of the "ice breaking" effects of vast icebergs driven by the wind and currents, and partly because of upwellings of warmer water which occur in the neighbourhood of shallow sills -- such as that of Hall Bredning.  In the autumn and spring the polynyas can be  havens for wildlife, including narwhal, walrus, ring seals, harp seals and a vast array of seabirds.

King eiders in the early spring, in the polynya near Syd Kap

A vast concentration of narwhals, in a small polynya surrounded by sea ice.

Naturally enough, where food supplies are concentrated in this way, the polar bears will follow.  And in the past  this is where they were found in large numbers.  Hence the name of the little archipelago of islands off the coast of Renland.  And where there are polar bears there are Inuit hunters -- there are traces of ancient settlements near Syd Kap and elsewhere. When the adventurer Tristan Jones overwintered at Syd Kap he was hunted by a polar bear and had a number of close shaves.  Luckily, when we were in this area in 1962 we did not see a sign of polar bears.  Just as well, since we had no weapons with which we might have protected ourselves.......

Tourist sailing ship near the Renland coast -- this is where the polynya is located in the winter.

From the same area -- a jumble of sea ice, icebergs and mountains