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Being an XBerT
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By Christopher Jacobs, DST/NRF Intern, SAEON Egagasini Node
As part of the Ship Of Opportunity Program (SOOP) implemented by the National Oceanic and Atmospheric Administration (NOAA), I had the opportunity of participating on the AX08 transect* between Cape Town, South Africa and Newark, New Jersey in the United States of America from 26 August to 30 September 2014.
The AX08 transect is a high-density expendable bathythermograph (XBT) cruise which monitors both the tropical South and North Atlantic oceans, the currents and fronts contained within. The data gathered on the AX08 transect is collected from instruments deployed from the cargo/container vessels, usually the Maersk Vilnius or the Maersk Visby, two of the V class vessels owned by transporting company, Maersk.
The success of this 28-day voyage across the Atlantic depends on the high-density deployment of XBT, a small missile-like probe which measures temperature down to a depth of approximately 900 m while the ship is underway. A single XBT is deployed approximately every hour, 24/7 throughout the voyage, resulting in a high-resolution transect with a spacing of approximately 25 km between each XBT drop. Along with this, is the deployment of Argo floats and drifter buoys at various predetermined positions. These positions are usually within the equatorial currents, and thus the monitoring and observation of the currents are made possible.
Why is this done?
The Atlantic Ocean plays an important role within the global ocean thermohaline circulation, through the interocean and interhemispheric exchanges of water, heat, salt and vorticity. The Meridional Overturning Circulation (MOC) in the subpolar North Atlantic is driven by the formation of the North Atlantic Deep Water (NADW), with a formation rate and properties that are highly influenced by climate changes on the decadal and interdecadal time scales. These climate changes affect the air-sea buoyancy flux in the subpolar basin, where warm-to-cold water transformation processes take place.
Recent results indicate that the formation of the NADW is the cause of strong traces of the North Atlantic Oscillation (NAO), a leading signal in decadal time-scale climate changes in the Atlantic. The MOC in the subtropical North Atlantic is mostly affected by changes in momentum, air-sea fluxes and salinity. However, the processes by which they cause changes in the ocean dynamics are not completely known, particularly at decadal and longer time scales.
This programme is designed to measure the upper ocean thermal structure in key regions of the Atlantic Ocean. The seasonal to interannual variability in upper ocean heat content and transport is monitored to understand how the ocean responds to changes in atmospheric and oceanic conditions and how the ocean response may feed back to the important climate fluctuations such as the NAO. This increased understanding is crucial to improving climate prediction models.
How often is this AX08 transect undertaken?
The AX08 transect is undertaken four to five times a year depending on the opportunity available whenever one of the allocated vessels sails. This is usually dependent on the export demands of the goods containers. This opportunity to traverse across the Atlantic is seized as often as possible and is seen as an opportunity to collect data albeit opportunistically. The AX08 transect is undertaken throughout the year, thus seasonal comparisons are possible.
Duties aboard the AX08
The purpose of the scientist or technical rider is to be of as little inconvenience as possible and not demand too much of the captain or crew of the vessel as XBTs are deployed every hour.
Because this is a cargo ship, the scientist/technical rider has to monitor the deployment of each XBT from the auto-launcher mounted at the aft of the vessel throughout the day and reload the auto launcher once all the canisters are spent. This involves reloading the auto-launcher, sometimes during the early hours of the morning, and also ensuring that the deployments, which take place every hour, are successful. This happens all through the day and night.
At night, this means waking up every hour to observe the deployment from the laptop in your cabin and ensure that there were no issues during the deployment, a process which takes up to five minutes every hour. As a result, sleep becomes a rare commodity, but is sacrificed all in the name of science.
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Aside from scientific duties, the scientist/technical rider also has a role to play during emergency and muster drills and has to be ready to help out during life boat drills. Apart from all of this, the scientist rider has the duty of making the cruise enjoyable by interacting with the captain and crew and participating in various activities which may take place.
Life at sea
Whether on a research vessel or a container vessel; life at sea can be very demanding and challenging. The first major challenge is overcoming sea sickness and becoming accustomed to the pitching and rolling of the vessel. Once leaving port in Cape Town, there’s not much to see at sea except ocean to left and right.
Life at sea may be challenging but as soon as you think there’s nothing to see and do besides science and catch up on your favourite series, the sun begins to set and creates the perfect backdrop, like a scene from an epic Hollywood movie. Close to the Equator, the doldrums, a region with very little to no wind, set up calm sailing for vessels and certainly one of the smoothest rides you will ever endure. If you are really observant, you may also hear and see the fluttering of flying fish and possibly a whale or two as the ship steams towards its destination.
Crossing the Equator is an adventure on its own. The traditional line crossing ceremony takes place for any newbies to be initiated by King Neptune (usually played by the Captain) and his cohort, which builds good team spirit between the captain, crew, officers and scientist. This is always good for the crew, who often spend about eight months at sea.
The crew aboard the vessel is comprised of a mixed group of people, with many of the crew members being Filipino or Chinese as the vessel hails from Singapore. There were also Indian cadets onboard who were part of the Maersk cadet training programme. This cultural difference, although vast, makes for some interesting meal times, however the team spirit and comradery is kept up with karaoke evenings, table tennis in the conference room, basketball tournaments on the aft deck and, of course, Bingo nights.
All in all, life at sea while doing the AX08 is quite tough and tiring, with very little sleep, lots of work and loads of deployments, but the experience of traversing the Atlantic, crossing the Equator and gaining cruise experience is very much worth it. This long but enjoyable cruise is definitely not for the faint of heart but is unquestionably one of the best experiences a sea-going physical oceanographer can have.
* The data collected and a detailed report from the AX08 transect are freely available for download at http://www.aoml.noaa.gov/phod/hdenxbt/ax_mmmyy.php
