RRS Discovery Cruise 321, 24 Jul-23 Aug 2007. Biophysical interactions in the Iceland Basin 2007

• Main Author: Allen, J.T.
• Other Authors: Painter, S.C.
• Format: Book
• Language: English
• Published: National Oceanography Centre 2008
• Subjects: Iceland
• Online Access: https://eprints.soton.ac.uk/50095/; https://eprints.soton.ac.uk/50095/1/nocscr023.pdf

D321 was the first of three National Oceanography Centre ‘process study’ research cruises to be run by the Ocean Biogeochemistry and Ecosystems research group under the NERC Oceans 2025 research programme. The scientific work began by carrying out some of the extended Ellett Line stations on the way out to our study region; which centred around the historical JGOFS Ocean Weather Station India site (~ 59° N, ~ 19° W) and the northward turn of the extended Ellett line at 20° W. The Iceland Basin, like much of the N. Atlantic subpolar gyre, is characterised by a ‘bloom and bust’ seasonal cycle. Spring stratification triggers a major diatom dominated bloom event. This bloom is short lived, limited by silicate (orthosilicic acid) exhaustion (Brown et al., 2003). Two community succession pathways commonly follow the demise of the diatom bloom; typically through dinoflagellate and/or coccolithophore production. The spring bloom is dominated by eddy scale (several 10's of km) patchiness, driven by the upward and downward pumping effect of eddies on the newly forming spring stratification. However these eddy structures have another, more important, impact on phytoplankton production (Allen et al., 2005). In the release of potential energy, eddies effect a real three dimensional exchange of water across the thermocline bringing new dissolved nutrients from deeper waters up into the photic zone and transporting biogenic particles into the deep ocean. Thin ribbon like structures around the edges of eddies are clearly seen in ocean colour satellite images. The four repeated surveys carried out during D321 observed the evolution of an ‘eddy dipole’ in a background ocean full of eddies and other turbulent motions. Daily, near real-time, satellite images and in-situ vessel mounted acoustic current profiling were used to determine the movement of the eddy centres and the dipole central jet. Targeted nets and water collection within the various components of the eddy dipole enabled the assessment of its biological impacts. Since ...