29 Dec - White Christmas
Noon Position : 580 22" 1' S 560 21" 3' W
Distance Travelled since Grimsby : 16,602 nautical miles
Air temperature @ Noon today : 5.7 0 C
Sea temperature @ Noon today : 3.4 0 C
Weather : Moderate/Poor, South, 1-2, 1013.5
We started Christmas week with a couple of days cargo whilst at Rothera and dispatched 1000m3 before leaving. We also dropped of a great bunch FIDs going into Rothera for the summer. One evening we managed to persuade the locals to take us up for another evening of skiing up on the slopes behind the base. There were downhill, cross country skiers, snow boarders and also those who chose to go down the hill on a giant rubber inner tube! It was great to get out and practice again and appreciate the amazing views. Thanks to the GAs who took us up in the snowcat and skidoos.
On Christmas eve we left Rothera to their celebrations and steamed north up the peninsula on a gorgeous afternoon. The mountains looked spectacular and formed a beautiful backdrop to the sea ice. We basked in the sun as we watched seals and penguins playing on the passing floes. It was totally calm and quite balmy as we steamed through the afternoon and wondered what Santa was going to bring us later.
We awoke to fog on Christmas morning but it looked like Santa had just managed to squeeze his sledge on the aft deck during the night. None of the night watch had seen him though. By 6am it was
already snowing and we were still dodging icebergs and almost unbelievably it was the first white Christmas for some onboard. After a morning of presents and the ubiquitous Christmas CD's, everyone
onboard put on their smartest uniforms and sat down to a delicious blow-out Christmas dinner with all the trimmings. Seven courses required an obligatory post prandial walk amongst the gentoo
penguins on Port Lockroy, where we had called in to say hello and let Amanda do some washing on the ship. Some odd fellow even dressed up like a penguin for the occasion but the locals didn't seem
very impressed and just passively watched sitting on their own little Christmas presents. I guess it was the yellow boots that gave him away!
To get rid of the last remains of our Christmas lunch, 3 lunatics went in for a quick swim. The water was a balmy 0.50C with a bracing wind to add to the atmosphere when Jo the cadet, Johnny the computer and Alex the doc each dived into the penguin infested waters. Total body submersion was mandatory to join the latest branch of the Antarctic Swimming Association. Despite severe shrinkage of certain body organs it proved be a very effective method for hangover removal! Even Santa turned up to watch.
So far it all looks to be a bit of a jolly week for the JCR but we have been doing some proper work in between the fun.............
This week we have been doing a bit of science in the Drake Passage. Steve and Mike hail from POL (Proudman Oceanographic Lab), which is part of NERC (Natural Environmental Research Council) and is based on Merseyside.
The oceans are fundamental in the distribution of heat around the globe and into the atmosphere.
The circumpolar current is a sea movement that runs west to east in a giant circle around Antarctica.
This current transfers water between the Pacific, Atlantic and Indian Oceans.
The current passes through a narrow gap called the Drake Passage and this is a key choke point for the flow of water.
The sea is not flat.
The flow of water through the Drake Passage is a complicated system but may provide an insight into ocean currents and heat transfer around the globe and therefore help with prediction of global warming and climate control.
POL have been measuring the flow of water through the Drake Passage for 12 years (current speed variability). Data is collected continuously from buoys that are left in a various locations and recovered every year or two for the data to be downloaded. These buoys don't float on the surface, they sink to the bottom of the sea and settle on the bottom. Each has a range of sensors that monitor the pressure of water ie the weight of water above them. Other sensors monitor the amount of heat in the water above them using an echo sounder. Three buoys are deployed in the Drake Passage. One to the north, one in the middle and a third to the south near Elephant Island. Each buoy is placed in an exact location for two reasons. Firstly is so that it can be found again and the data collected. Secondly it is placed within the track of a satellite called ENVISAT that measures the height of water from space and therefore allows comparison of the results of the two measurements. The north and south buoys are 1000m below the surface and the middle buoy is 3500m below the waves. They are specially designed to withstand the huge pressures involved.
Downloading data from each of the 3 buoys, tells us the height of water above them over the last year. Differences in height of water in the different areas will indicate how the current speeds are changing. The difference in height is variable across the Drake Passage but in the order of tens of centimetres.
The Tricky Bit
Retrieval of the data as one can imagine is difficult from something that has been left 3.5km under the water. To solve this problem we can 'talk' to the buoy because it is constantly listening
for us coming back. After sending a specific 'ping' of sound down, the buoy knows to release itself from the bottom and float back up to the surface. To achieve this it burns through a
pyro-explosive device that connects it to weights on the seafloor and its natural buoyancy brings it back up to the surface. Once there Mike and Steve get out a special directional radio receiver
that picks up a radio message from the buoy on the surface. Once it is spotted we pick it up, download the data, service it and then redeploy it over the side.
Where are the buoys
Below is map showing where the buoys are. They are arranged north to south across the Drake Passage not west to east. This is because of the Coriolis Effect. The water current is moving round a sphere and therefore in a circle. Coriolis moves westward flowing water (or air) to the north in the Southern Hemisphere. Therefore the northern buoy will have a higher water height than the southern buoy. Also the faster the current the greater the difference. Land based tide gauges also measure water height and can be used in the analysis and such measurements are taken at Rothera and Stanley by POL.
The Results so far
POL have a data for the Drake Passage for 12 years and so far can say that......the circumpolar current is changing. It's becoming more variable due to changes in atmospheric winds but that more work needs to be done.
When can you call an iceberg an iceberg?
Being a landlubber at heart I didn't realize just how naive I was when I got very excited and called a piece of ice floating in the water an 'iceberg'. It was greeted with howls of laughter and lashings of derision. In vein as the slightly arbitrary division of ships and boats (It's obvious - boats go on ships! - Ed), floating bits of ice can be often confused as icebergs. For my own education and so all at home don't make this easy mistake, I have included a cadet report from Jo explaining the finer points of ice classification. It's also a chance to put in some nice bergy photos.
Ice formation and classification
When classifying ice the first task is to determine if the ice has originated from the land or sea. The first type of ice that will be discussed is ice of sea origin, i.e. that which forms when sea water reaches its freezing point. The freezing point of sea water depends on the salinity but is approximately -1.30C. When sea ice first begins to develop it will be in the form of small pieces of ice up to 2.5cm, which float on the sea surface and are known frazil ice. When large accumulations of these pieces are present the sea gains an oily appearance, and when they combine form grease ice. Frazil ice and grease ice are both classed as new ice.
The next stage is the development ice rind and nilas. Ice rind and nilas form when further cooling takes place. Ice rind forms when water of low salinity freezes slowly, forming a thin layer of ice which is almost free of salt, whereas nilas forms when water of high salinity freezes quickly. If nilas or ice rind are broken up by the action of wind or sea it forms pancake ice. The next stage of development occurs when the pancake ice freezes together and thickens producing what is known as young ice. The ice can then continue to develop and thicken forming thin, medium and thick first year ice. If this ice survives the summer it is termed second year ice, and after subsequent years multi year ice. As the ice ages the salt content decreases until all salt is lost. By this stage the ice takes on a blue-green colour and is extremely hard. 'Good tea' can be made from ice that is 10 months old but it doesn't become as 'fresh as rain water' until it is 2 years old.
The following table details the different types of sea ice, the thickness of ice, and a description of the main characteristics.
|New ice||Frazil ice||<2.5cm||Ice spicules|
|Grease ice||Soupy layer on sea surface giving matt appearance|
|Nilas||<10cm||Thin elastic crust of ice with matt surface|
|Ice rind||<5cm||Brittle shiny crust of ice|
|Young ice||Grey ice||10-15cm||Dark grey or light grey, becoming whiter with age. Can break in swell causing pieces to override one another|
|Grey white ice||15-30cm||Thicker and harder than grey ice|
|First year ice||Thin||30-70cm||White/ milky white in colour|
|Medium||70-120cm||Gradually changes colour as it ages, acquiring greenish tint after 1 year|
|Old ice||2nd year ice||>250cm||Thicker than 1st year ice, generally smoother. Small puddles produced by summer melting|
|Multiyear ice||>300cm||Smoother, almost salt free, large interconnecting puddles|
When sea ice accumulates it is termed pack ice. When referring to pack ice the concentration of ice to water is used with a scale ranging from open water at 0/10, to consolidated pack 10/10 where there is no water visible. The following pictures show the varying concentrations of pack ice:
Ice of land origin (glacier ice)
The second type of ice encountered during my time on the JCR was ice of land origin. Ice calving away from the Antarctic continent can come from ice shelves or glaciers. Glacial icebergs are usually of high density and resistant to weathering. They frequently show bands of silt, sand and other debris picked up when part of a glacier. Grouped into the term glacier ice are icebergs, bergy bits and growlers. The following pictures show the 3 types of glacier ice:
The most common form of berg is a tabular berg that has calved from an iceshelf. A flat topped iceberg the length can vary from a few metres up to 80miles. Their height is generally between 10 and 35metres. They appear a peculiar white colour (as if made from plaster of paris) due to their high air content.
Additional ice terminology
The ice types mentioned previously are only a small selection of those that may be encountered. The following pictures show a selection of additional ice types and forms encountered during my time on the JCR.
An underwater ice projection. Its formation is usually due to more intense melting and erosion of the unsubmerged part.
Dark streaks on the underside of low clouds, indicating the presence of open water in the vicinity of sea ice. Can been seen in the distance in the picture below as the JCR heads towards the open sea.
Predominantly circular pieces of ice from 30cm to 3m in diameter, with raised edges due to striking one another. Usually formed from grease ice, ice rind or nilas. Here it is seen with a growler.
Sea ice that forms and remains fast along the coast, where it is attached to the shore. It may extend for a few meters or several hundred miles from the shore. If it is thicker than about 2m above sea level then it is called an ice shelf.
Thanks Jo for that insight.
Thankyou this week to all the lads who laid on such a great Christmas dinner.
Coming up next week......Stanley, a new crew and a new year!