The Atlantic Meridional Transect Ocean CO2 flux from satellite campaign (AMT28) has been at sea for over 2 weeks now on the Royal Research Ship James Clark Ross.
The installation of all of the equipment in Harwich necessary for the campaign was frenetic. With all of the materials and supplies required on board, both scientific and for the ships stores, in preparation for the voyage across the Atlantic Ocean, and also the summer season in the Antarctic, there was a continuous stream of material being winched aboard from early morning to late afternoon. In amongst the melee, AMT4OceanSatFlux scientists were being winched up the foremast to install the array of automated instrumentation that comprises the instrument package for this campaign. It includes:
- above water radiometric optical sensors that measure upwelling radiance from the sea surface for validation of satellite Ocean Colour;
- Infra-red radiometers (ISAR) that measure the skin temperature of the Ocean used to validate satellite Sea Surface Temperature;
- c-band radar which characterises wave properties that are detected by the Copernicus Sentinel 1 satellite; and
- eddy covariance which is a measure of the gas flux from the Ocean.
This involved winching Tom Bell, Bob Brewin, Werenfrid Wimmer and Louis Marie up to a height of 20 metres above the ship to install the instruments (see below). The location of the foremast is chosen so that each instrument has a clear and unimpeded view of either the sea or sky with minimal interference from the ship’s super structure. After nearly three long days in port to install the instruments, lay cables, set-up the computers and power supplies to log the data, the ship sailed into the Southern Bight of the North Sea and to Portsmouth to refuel for the 4000 mile journey ahead.
Sailing out of Portsmouth into the English Channel and the Celtic Sea, coincided with a region of high pressure and clear skies with potential match-ups with the suite of satellites orbiting overhead. Each day vertical profiles of the water column commenced to complement the underway surface measurements and to reveal more of the physical, chemical and biological changes beneath the surface lit ocean.
Giorgio Dall’Olmo deploys an optical profiler to characterise the absorption and scattering properties of both particles and dissolved organic material and is testing out a new filter system so that these measurements can be made coincidentally (see below left). Bob Brewin also deploys a Small Oceanographic Floating Device, which has a series of temperature sensors fitted to it, known as the Smartfin (see below right). It is a simple device that can be fitted to pleasure craft such as surf and paddle boards and kayaks. The idea of deploying on station during the AMT4OceanSatFlux campaign is to compare it with Werenfrid’s highly accurate ISAR system, to assess whether the Smartfin can be used with confidence over different regions of the Atlantic Ocean.
As the ship traverses further over the Celtic Sea shelf, the waters become clearer and clearer with secchi depth readings increasing from 8m to 14m to 20 m. Once the ship reaches 51°N, the secchi depth dropped right down to 25m indicative that the AMT4OceanSataFlux campaign has reached the desert gyres of the North Atlantic. As well as making vertical optical and temperature profile measurements, Giorgio is also deploying Bio-Argo floats to add to the existing network of floats already in the Atlantic Ocean.
Argo is a profiling float used to observe temperature, salinity, currents, and, recently, bio-optical properties in the Earth's oceans; it has been operational since the early 2000s. Each float weighs 20–30 kg. In most cases probes drift at a depth of 1000m; (the so-called parking depth) and, every 10 days, by changing their buoyancy, dive to a depth of 2000m and then move to the sea-surface, measuring conductivity and temperature profiles as well as pressure. The floats have been successfully deployed on previous Atlantic Meridional Transect campaigns and two of them which were deployed in 2014 had sensors on them which had failed that measure backscatter, fluorescence and irradiance. One of these was some 40-50 nautical miles off the ships course. In consultation with the Ship’s Captain, the Chief Scientist, Dr. Glen Tarran, facilitated the recovery of one of the Bio-Argo floats. The ship steamed at 13 knots towards the location of the float. Dr. Tarran describes;
‘The float had been ordered to go into "End of Life" mode, whereby it comes to the surface and periodically sends out it's position AND says "Help".’
As the ship neared the floats position, the frequency of position updates was increased to every 10 minutes. The float had been travelling SSE with the equatorial counter current at up to 0.8 knots but as the ship came closer it started swinging west. Teams of people gathered on the bow and bridge of the ship to post look outs to locate the stray float. Once located, a glider recovery cradle with long strops attached to the 10 tonne crane and a long pole with a wire lasso was used to guide the float into the cradle. It was then craned on board and removed from the cradle to a loud round of applause!!!
The ship will continue south over the equator and into the Southern Ocean whilst continually acquiring data that will be used to validate CO2 flux estimates built from a range of satellite data inputs. The RRS James Clark Ross is due to dock in the Falkland Islands, after nearly 40 days at sea, on 29 October 2018.
by Dr Gavin Tilstone
Top image: Tom Bell and Bob Brewin from Plymouth Marine Laboratory are winched up to the foremast to install the Picarro Eddy Covariance instrument that measures gas flux of the Ocean and the HyperOCR irradiance sensor that is used a reference sensor for measuring remote sensing reflectance.
Bottom image: Giorgio Dall’Olmo from Plymouth Marine Laboratory deploys the optics profiler during grey skies in the North Atlantic. Bob Brewin deploys the SmartFin in blue waters of the North Atlantic Gyre.