The 2008 North Atlantic Spring Bloom Experiment I: Overview and Strategy
Abstract
The 2008 North Atlantic Spring Bloom Experiment (NAB08) aimed to understand carbon export from this globally important event by combining a new generation of autonomous floats and gliders equipped with a new generation of sensors, and traditional and modern shipboard observational methods. Measurements were made from early April to late June 2008 in a region southeast of Iceland near the JGOFS and MLML sites. Although Sverdrup's classical explanation for the bloom is probably broadly correct, previous observations have revealed a large degree of spatial and temporal variability, often on scales of a few kilometers, which have made detailed tests of Sverdrup's hypothesis difficult. The experiment was designed to continuously sample the bloom and its temporal and spatial 'patchiness' from the pre-bloom, wintertime conditions through the Spring and early Summer. The spatial scales were sampled by 4 Seagliders operating together as a mobile array. Measurements were made in a Lagrangian, water-following coordinate system which minimized the effects of horizontal advection and most clearly separated temporal and spatial scales. The coordinate system was defined by two Lagrangian Floats, one of which was chosen as the center of the Seaglider array. Proper measurement of the bloom by the autonomous vehicles required a robust and redundant array of sensors measuring key physical, chemical and biological variables including temperature, salinity, spectral light, oxygen, multiple optical proxies for carbon (chlorophyll fluorescence, beam-c attenuation and optical backscatter coefficients) and nitrate. Redundant measurements were made whenever possible, with nearly identical sensors on many platforms and multiple sensors measuring similar quantities on the same platform. Such care is clearly necessary, since the current generation of biogeochemical sensor require considerable efforts in calibration and interpretation. The autonomous platforms provided good coverage in space and time, but could not sample the entire range of processes that control the bloom. More detailed measurements and multiple calibrations of the autonomous platforms were made on 4 cruises, particularly a 21-day Knorr cruise in May 2008 that included collaborators from five US and five international institutions. These measurements included nutrients; particulate organic carbon and nitrogen; characterization of plankton composition and physiology by size, imaging, genomics, HPLC pigments, absorption spectra, 14C-primary productivity, and variable fluorescence; particle flux from floating sediment traps; and ADCP and CTD measurements. The experiment clearly demonstrated the ability of autonomous platforms to make biogeochemically relevant measurements of blooms. Its success, however, required intensive shipboard support for sensor calibration and interpretation. Further development of sensor technology, validation protocols, and understanding is clearly required if these measurements are to made routinely and easily.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFMOS24A..08D
- Keywords:
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- 0428 Carbon cycling (4806);
- 4805 Biogeochemical cycles;
- processes;
- and modeling (0412;
- 0414;
- 0793;
- 1615;
- 4912);
- 4806 Carbon cycling (0428);
- 4894 Instruments;
- sensors;
- and techniques