Jan 25 - South From the Falklands
South From the Falklands
It was in this way that the ship headed on a course permanently towards the south west, across open water, towards the point furthest to the south and west it has ever travelled on this side of the Antarctic Peninsula. It was to be a beautifully smooth trip down across slight seas covered by occasionally glassy water. It was a journey of five days until sighting our first land since the Falklands. Peter 1st Island was initially seen from a distance of 85 miles, in the early hours of 18th January, though it wasn't until lunchtime on the same day that it was passed at much closer range.
The 18th was also also to be the celebration of the birthday of Tara Deen, one of the Geophysicists on board. Technically, her birthday was on the 19th, but since the ship was due to arrive in the work area that day, and people would be moving to a12 hour shift system it was decided that the festivities should be a day early. The Wednesday evening keep fit class was thus cancelled and it was a chance for all the science staff to let their hair down prior to the starting of work in earnest later the next day. It was a perfectly flat calm evening and the ship at last came into close contact with a significant amount of ice, presumably to be with us for much of the rest of the cruise. For this reason, much of the evening was spent relaxing on the Monkey Deck in perfectly calm, sunny weather, with passing wildlife for added company.
As said, the next day was to be our first day of work at the actual research site. At 10:30am the magnetometer was brought back on board, as we were getting close in towards the ice. It is towed on a cable behind the ship and would be lost if left out whilst the ship was going through pack ice. Just an hour or so later the ship actually entered the ice and headed onto the shelf. After finding a suitable area of open water a first set of sediment cores were undertaken. After this, the JCR headed back out and further west to undertake 48 hours of survey work, coring and a single CTD over a trough near the shelf edge. After this, on Sunday 22nd Jan the ship left this site and headed to around 117 degrees west in an attempt to find one of the leads that could be seen on satellite images. After just under 24 hours heading through the pack ice the ship made it to the open water, closer to the shore, that had been believed to be present, ready to make an attempt to head back east towards Pine Island Bay itself.
Science Work for the Week
with Rob Larter
Most of the first week of this research cruise was spent just getting to the study area in the Amundsen Sea. This is the southernmost part of the Pacific Ocean and lies almost half way from South America to New Zealand (see map in last week's diary entry). The remoteness of the Amundsen Sea is one of the reasons that few research vessels have visited it. Another is that it is covered by sea ice for most of the year. Even with an ice strengthened vessel like JCR, it is only possible to work here for about two months in most years, between mid January and mid March.
What are we doing in the Amundsen Sea?
The main objectives of this cruise are to investigate the glacial history of the continental shelf in the Amundsen Sea and to study present day interactions between the ocean and Antarctic ice sheet.
The few previous research cruises that have visited the Amundsen Sea have shown that the ice sheet extended a long way onto the continental shelf during the last ice age. We aim to find out exactly how far the ice sheet extended, when it retreated from the shelf, and where the fastest flowing glaciers were within in. To achieve this we are using the ship's advanced sonar systems and collecting sediment cores from the sea floor.
Below is one example of a sea floor image collected with the ship's “swath bathymetry” system. This shows very long ridges and troughs called “mega-scale glacial lineations” in an area near the edge of the continental shelf that is more than 600 m below sea level. These features were produced at the base of a fast-flowing glacier as it scraped across sediments. When such glaciers are between areas of slower flowing ice, rather than in a valley in a mountainous area, they are known as “ice streams”. Much of the continental shelf around Antarctica lies at water depths of 400–500 m, but these lineations are in the bottom of a trough that was carved by the ice stream.
Swath bathymetry image of the sea floor showing “mega-scale glacial
lineations” near the edge of the continental shelf. The deepest parts of
the sea floor are shown in dark blue and the shallowest areas are shown
in green. The surface is shaded as if illuminated by a light shining from
the northeast (top right corner). The orange lines show the position of
the ship's tracks.
We are also collecting sediment cores on the continental shelf. We will try to find out when the ice sheet retreated from the shelf by radiocarbon dating samples from the thin layer of marine sediments that overlies glacial sediments.
Present day ocean-ice sheet interactions
The main method we plan to use to study how the ocean interacts with the ice sheet is to lower instruments down to near the sea bed that measure the temperature and electrical conductivity of sea water. These measurements are called conductivity-temperature-depth casts, or CTDs for short. The CTD measurements can be used to calculate salinity. The instruments make continuous measurements as they are lowered and raised through the water, and thus show how water temperature and salinity change with depth. By carrying out CTDs at several sites along a line, it is possible to use the measurements to calculate the flow of ocean currents at different depths. Differences in temperature and salinity between water flowing onto and off the continental shelf provide information about how water is being modified on the shelf. Two important processes that modify water on the shelf are cooling through contact with ice and freshening through addition of meltwater produced where inflowing water comes into contact with the base of floating ice shelves.
Unfortunately the first location where we wanted to try to collect a line of such CTDs, across a trough near the edge of the continental shelf, was covered in sea ice and it was only possible to make a single CTD cast. However, this cast did confirm that the same water masses are present now as on the one previous occasion when CTDs were carried out at this location (3 years ago, also on JCR).
Keeping in touch by Mike Gloistein, Radio Officer.
An important part of life onboard a ship is being able to keep in touch with family and friends back home and around the world.
In the years since the ship was built (1990) communications have changed dramatically, making life easier for all those onboard.
When the ship first came into service the bulk of communications was carried out via fax, with all personnel allowed to send and receive one sheet of fax per month, resulting in messages being abbreviated in order to get as much into the allowance.
By the mid 1990’s a very simple form of e-mail service came into operation and once again there was a limit, in the region of 1000 words per month. The limit was necessary due to the high cost of sending and receiving the data, via the Inmarsat geostationary satellites, using analogue technology.
Towards the end of the 1990’s e-mail was becoming an established means of communicating and with the introduction of digital satellite services it meant that higher transfer rates were now possible and the ship was using a 64kb link. Due to the cost all mail would be ‘queued’ at the server onboard and the server at BAS Cambridge, to be transferred two or three times a day. The limit for personal messages changed with the times and everyone onboard was allowed 1Mb per month, allowing for daily messages to family and friends along with the ability to send pictures and documents also.
In the summer of 2004 a new communications package was installed, now referred to as BASNET, giving a 24/7 connection to BAS Cambridge. This link, rated at 128kb, allows us full internet access, almost instantaneous e-mail and four telephone lines (extensions to Cambridge), so a call home now is routed via Cambridge and at the UK national rate. A traditional Inmarsat call costs in the region of £2 per minute.
With the internet access there have been other benefits, the ability to use Instant Messenger for ‘live’ chatting, the ships webcam and access to such things as corrections to charts and nautical publications, obtaining technical information on products used onboard, listening to local radio stations and reading the news as it happens.
All of this is routed via the NSS-7 satellite, located over the equator in position 22° West. It has a ‘footprint’ that covers our normal working area and operates as far south as Halley Base (approx 75° South). Our current working area for the JR141 cruise has taken us to about 71° South and 113° West, and this is outside the footprint (the satellite is some 9° below the horizon!) and so we are now restricted to the Inmarsat system (which we can access worldwide via four different satellites). However Inmarsat also has a footprint and we are finding that we are working just outside of it, so that our e-mail communications are now running on an as-and-when, as opposed to a regular, schedule. Also, due to the low elevation of the satellite even a gentle ships roll of only a degree or two is enough to break the link, which is much slower than the expected 64kb.