During ANDREX-2, a whole variety of science will be conducted on board the JCR. On this page, we'll show the main bits of the physical and chemical oceanography that's part of this cruise.

Physics:

(Povl Abrahamsen, Nathan Cunningham, Allan Davies, Loic Jullion, Mike Meredith, Aurelie Persechino, Angelika Renner, Takamasa Tsuboushi, Hugh Venables, John Wymar)

CTD

Swath Bathymetry

One of the fancier systems on the RRS James Clark Ross is the multi-beam sonar, or swath bathymetry system. While a normal echo sounder will only give you a single depth reading just below the ship, the swath system covers a whole fan of depths on both sides of the ship, so you can map the seabed in large areas, and with high precision.

Normally the system just runs quietly, and the scientists on duty check on it occasionally, to make sure that everything is running well and it hasn’t lost track of the seabed. The past day’s data can then be processed and cleaned, and we will hopefully end up with a nice, clean map of the seabed depths. Besides mapping out areas that we are planning to cross while doing the ANDREX survey, we have 72 hours set aside for a more detailed survey of Orkney Passage, east of the South Orkney Islands. This is an area where BAS  (British Antarctic Survey) has deployed moorings to monitor the outflow of Antarctic Bottom Water from the Weddell Sea into the Scotia Sea – which we believe to be a major pathway into the Atlantic. So hopefully we will have filled some more of the gaps in our knowledge of the seabed in this area by the end of the cruise!

Shipboard ADCP

ADCP is short for Acoustic Doppler Current Profiler. It is an acoustic instrument that measures the velocity of the water currents underneath the ship relative to the ship speed. To do this, it sends out sound pulses (also known as 'pings') of a set frequency. The pings are reflected by particles in the water like plankton, that move essentially at the same speed as the water. The Doppler effect results in a frequency shift in the reflected ping, and using that and the speed of sound in water, we get the current velocities. The James Clark Ross has a 75 kHz instrument on board which in good conditions can reach as far as 800 m below the ship. The ADCP is one of the instruments that measure continuously throughout the cruise.

LADCP

The L in LADCP stands for Lowered. Just like the shipboard ADCP, the LADCP uses acoustics to measure water current velocities by sending out sound pulses and recording their Doppler shift. The LADCPs, however, are mounted on the CTD frame, one looking down and one looking up, and lowered with the CTD on every station. By this we get full depth current velocity profiles. The measured velocities are used to calculate water mass transports across our transects and as reference for geostrophic velocities.

ARGO floats

Chemistry

Natural and anthropogenic carbon

Dorothee Bakker¹, Mario Hoppema², Marie-José Messias¹, Pete Brown^1,3, Elizabeth Jones¹, Maciej Telszewski¹, Andrew Brousseau¹, Stephen Woodward¹, Steven Jones¹ and Shaun Scally¹

Participants of JR239 in bold

¹ School of Environmental Sciences, University of East Anglia, Norwich, UK

² Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany

³ British Antarctic Survey, Cambridge, UK

The Southern Ocean is a key area for ventilation of the deep waters of the global oceans. The Weddell Gyre is a large, elongated clockwise rotating gyre, south of the Antarctic Circumpolar Current (ACC). Deep water, rich in ‘natural’ CO₂, reaches the surface in the Weddell Gyre. Major quantities of deep and bottom waters are produced near and on the Antarctic continental shelves, which are likely to be accompanied by uptake of ‘anthropogenic’ CO₂. In the western Weddell Gyre the largest share of dense waters is produced. Part of this water leaves the gyre circulation through deep passages in the northern boundary of the gyre, while another part is transferred to the eastern gyre. In the eastern Weddell Gyre major interaction takes place with the ACC (Gouretski and Danilov, 1993). The north-eastern gyre region is important from a biogeochemical point of view and might be a significant CO₂ sink (Hoppema et al., 2000; Bakker et al., 2008).

The ANDREX section runs along the northern boundary of the Weddell Gyre from 30°E to the tip of the Antarctic Peninsula. The second ANDREX cruise (JR239) will complete the ANDREX section from the tip of the Antarctic Peninsula to 14°W from 15 March (Montevideo, Uruguay) to 25 April 2010 (Stanley, Falkland Islands) on the RRS James Clark Ross. An earlier ANDREX cruise (JC30) took place from 26 December 2008 (Cape Town, South Africa) to 30 January 2009 (Punta Arenas, Chile) on the RRS James Cook. The central goal of the ANDREX project is to measure the rates at which water masses, nutrients and carbon are transported between the Weddell Gyre and Antarctic Circumpolar Current. UEA scientists will carry out measurements of inorganic carbon parameters, chlorofluorocarbons (CFCs) and sulphur hexafluoride (SF₆). The data will be used to deliver these objectives:

• estimates of the inventory and transport of natural and anthropogenic carbon in the Atlantic sector of the Southern Ocean,
• an assessment of how these may be changing on decadal time scales,
• an overall budgeting of carbon by region that links the changes in inventories to the fluxes by water transport, biological production and air-sea fluxes
• improved estimates of overturning transport of mass, freshwater and heat as a result of the constraints that the CFC observations will place on these quantities.

For more information regarding the project, please see the ANDREX @ UEA website and links therein.

Bakker, D.C.E., M. Hoppema, M. Schröder, W. Geibert, H.J.W. de Baar (2008) A rapid transition from ice covered CO₂-rich waters to a biologically mediated CO₂ sink in the eastern Weddell Gyre. Biogeosciences 5, 1373-1386.

Gouretski, V.V., A.I. Danilov (1993) Weddell Gyre: Structure of the eastern boundary. Deep-Sea Research I 40, 561-582, 1993.

Hoppema, M., M.H.C. Stoll, H.J.W. de Baar (2000) CO₂ in the Weddell Gyre and Antarctic Circumpolar Current: Austral autumn and early winter. Marine Chemistry 72, 203-220.

Tracers

(Sophie Chollet, Ella Darlington, Sinhue Torres-Valdes)

Noble Gases

(Brice Loose, Roisin Moriarty)