16 Mar - Pine Island Bay
RRS James Clark Ross Diary
Noon Position: 70° 13.0 S, 113° 19.7 W)
Distance Travelled since Grimsby: 26909.5 Nautical Miles
Air temperature @ Noon today: -1.8°C
Sea temperature @ Noon today : -1.0°C
Weather: Cold and windy!
Pine Island Bay: Closed for the winter!
This week the JCR has been cracking through the ice in the Amundsen Sea. The aim has been to get to Pine Island Glacier at the heart of Pine Island Bay. However the going has been made difficult thanks to large amounts of sea ice and bergs in the area. Pine Island Bay is a deep bay with many fast flowing glaciers entering it which produce a huge number of particularly tall icebergs that flow out into the Admunsen Sea. Many of these bergs ground on the relatively shallow ocean shelf. To the east of Pine Island Bay there is lots of pack ice that is at the mercy of the ocean currents and especially the wind. This ice moves at up to several knots with a strong wind behind it and can be blown together making it very dense and impossible to sail through. The JCR receives satellite images of the ice conditions and despite being of low resolution they can help in following the movements of ice.
Bearing these factors in mind the JCR sailed south towards Pine Island Bay assessing the ice conditions along the way. Please see the map above. We found a long line of huge tabular bergs, each up to 8 miles long, leading towards the Thwaites Glacier and probably grounded on the seabed. This effectively produced a solid barrier. We then sailed northeast to assess the density and extent of the area of ice pack to the east of Pine Island Bay. All the time we were sailing through new ice that was forming around the ship all the time. With temperatures of -10°C the sea was literally freezing and while this didn't hinder the ship it suggested that at this late stage in the season, new ice was forming all the time.
We found the east edge of the pack about 20 miles to the east of the line of bergs. This meant that there was an ice corridor leading into Pine Island Bay of thin new ice that the JCR could penetrate. However things were not quite that simple. The concern was that the heavy pack and loose ice would be blown to the south west and would effectively close the corridor. If that happened and the pack was compacted against the line of grounded bergs there would be a risk of the JCR getting trapped in the Bay by a barrier of dense pack ice. At this stage of the season the ice is freezing and becoming solid and the risk was of the JCR becoming stuck in the bay for the winter!! The JCR is not a formal ice breaker and cannot break through heavy compacted pack. With these serious risks of entrapment the JCR held off and retreated north, out of ice towards the open sea. During the week we watched the pack ice being blown west and effectively closing the corridor that was open. Clearly the right decision had been made by Captain Elliott not to enter Pine Island Bay. So while we are disappointed not to get to Pine Island Bay it leaves the JCR working with Autosub along the edge of the pack ice and performing other oceanographic and glaciological work.
The chart above shows the relevant features. The coloured track shows the movements of the JCR with each colour corresponding to a different day. The arrow shows the movements of the heavy pack during the week. The loose pack is pushed infront of the heavy pack and the ice already within the ice corridor would be compressed. The small flags along the line of the JCR track are CTD stations.
Cute animal corner
Whilst passing through the ice, we did manage to spot adélie penguins and also a few emperor penguins sitting on the floes. Sorry the pictures of the emperor penguins are not as good as those produced from Halley. It is difficult to take pictures from a ship that is moving at 5 knots and bouncing around against ice floes! Thanks to Dave for his efforts.
This far south we haven't seen much bird life as the normal petrels and albatross didn't follow us this far south. We have seen a number of snow and Antarctic petrels that follow the ship for a time. Some land on the ship, probably for a rest or because they are confused by the lights, but have great difficulty getting off. They cannot fly over the bulwark and so end up trapped on deck looking decidedly sorry for themselves. In the morning we have to comically chase them around the snowy deck before picking up these bedraggled birds releasing them back over the side. Below is Lester having his finger chewed by an very ungrateful Antarctic Petrel!
We have a problem.....charts.....
Since the area we are going is so remote and rarely visited there are NO charts of Pine Island Bay. So how do we know where we have been, are and are going?
Most places in the world are covered by British Admiralty Charts which map the worlds ocean and are accessible to the public. There are none for Pine Island.
Next we turn to the Admiralty's Antarctic chart section and request specialist charts of the area. There are none of these either for Pine Island Bay. No British ship has ever been there before!
Finally we request a 'collector' sheet from the Admiralty. A collector sheet is a blank chart and we have to mark all information on it as we find it! It has a lattice of latitude and longitude with the approximate coastline marked out and that's all. However even the coastline is not regarded as accurate as it is taken from satellite data which has difficulty in mapping the coast when it is covered in ice. Icebergs can look remarkably like islands hence the aptly named 'Probable Island' in the middle of Pine Island Bay! Even aerial photography is inaccurate in these conditions. There are no contours for sea depths and we will plot them on as we find them.
So armed with only a blank chart and a rough idea of where the coastline is the JCR boldly edges towards Pine Island Bay. Fortunately the ship is armed with several mapping tools that can be used to ensure we don't hit any islands or underwater hazards:
- Global Positioning System (GPS): the most accurate prediction of our position is the ships GPS system and can estimate our position down to 20 metres. This at least allows us to know where we are on the blank chart and tells us where we have been.
- Radar: the ship is equipped with two radar and these can 'see' most things on the surface of the sea including land and most icebergs. The radar can accurately tell the size, distance and bearing from the ship of an object up to 50 miles away depending on it's height. Pack ice can be detected up to 3 miles away, large icebergs up to 20 and high mountains up to 50 miles from the ship. When coastline or islands are seen, position and size can be recorded by taking multiple radar observations of the object. The radar image shown by 'clicking here' reveals multiple icebergs seen as the yellow blobs on the screen.
Below the water the JCR is equipped with three devices for mapping of the seabed and any dangers that lurk below the waves:
- Sonar: We have a sonar device onboard that is direction specific. This means it can be pointed away from the ship in any direction and so can take readings of the seabed infront of the ship. This device allows us the chart the sea floor infront of the ship and so hopefully avoid any hazards.
- Echosounder: All ships have echosounders that send a 'ping' straight down below the ship and the time it takes for it to be reflected off the seabed is measured. Knowing the speed of sound in water allows calculation of the depth of water the ship is currently in. The JCR has a particularly accurate hydrographic echosounder that can record extremely deep oceans. This runs continuously and is automatically recorded in conjunction with the GPS position and the information is logged and plotted.
- Swathbathymetry: Special to the JCR is an extremely complex and accurate swath system that records the depths of the ocean floor in an arc around the ship. Computer analysis of the data gives accurate 3D pictures of the sea floor in wide transects either side of the ship.
All of these systems allow the ship to see and chart features around it. Any new information that the ship sees is recorded in a 'note' that is then sent to the Admiralty. All ships record navigation 'notes' when ever they see features that a different from established charts. When these notes have been verified and checked to ensure their accuracy, the Admiralty sends out 'chart corrections' that are then drawn in by hand onto the ships existing charts. In the current situation the JCR will submit the 'collector' sheet back to the Admiralty who may then make a new chart depending on the amount of new information gathered. New charts are only released relatively rarely in the Antarctic compared to every 6 weeks in the Thames Estuary. The JCR has over 500 charts covering the Antarctic, Atlantic and Arctic but this is few compared to ship trading all over the world that may carry many more and must cover all the oceans.
The accuracy of modern navigation systems has revealed that in many cases the old charts are wrong. Often the shape and size of the land is accurate but the whole island is in the wrong position. When tied up at Grytviken in South Georgia, the JCR used to appear on the top of Mount Hodges on the chart! Don't worry, it has now been changed. This season when sailing down the Washington Channel near Signy, Coronation Island was noted to be half a mile from where it should have been using the GPS. The coastline was the right shape but the whole island had been 'shifted' half a mile one way!
Man of the week
Congratulations this week to Richard Turner, our excellent chief cook. Much to the disappointment of everyone's stomach onboard, Richard has got a new job this week and will be leaving Captain Elliott's crew. Don't worry he won't be going far as he has got the purser's job on the JCR but under Captain Burgan's crew. It all means that he won't be in the kitchen any more after this trip and we won't be treated to his wonderful cuisine (but still get his evil circuit training! - Ed). We wish him well in his new role as 'grocer'.
Thankyou this week: to Andy Liddel and Tobi for the chart info.
Coming up next week: CTDs and Autosub missions.....