Net uptake of carbon dioxide in the Atlantic Ocean north of 50 degN accounts for about 25% of the global total. The biological pump, most importantly the phytoplankton bloom occurring each spring, drives this uptake. Previous studies have shown the importance of small temporal and spatial scales, i.e. ecosystem patchiness, during the bloom, but have had limited success in resolving these scales due to the inherent limitations of ship-based research. Recent advances in autonomous platforms and sensors now enable new approaches to sustained measurement of key quantities and rates that have potentially broad impacts. In this research, PIs from the University of Washington and the University of Maine - Orono, propose a process experiment focusing on an important component of the oceanic carbon system - the North Atlantic Spring Bloom - both for its intrinsic merit and as a test-bed for developing the strategies and knowledge needed to successfully use these new methods to drive the next generation of ocean observations.
The PIs will use Lagrangian floats to follow water parcels in the mixed layer, with each float coupled with roving gliders to characterize its surroundings. The floats and gliders will measure - in three dimensions over time - the vertical and horizontal mixing rates, and key carbon system components and rates. Phytoplankton and organic carbon will be quantified through a suite of optical proxies, oxygen by two different sensors, and nitrate by UV spectrometry. Redundancy of sensors, reference measurements at 250-1000m, cross-checking among platforms and water sample analysis on three cruises will be used to maintain and verify the calibration of the autonomous sensors. Two-way communication via Iridium satellite will allow sampling strategies to evolve in response to observed conditions. Measurements will be made near 60 degN from late March 2008, before the bloom, through early July when it has ended. Primary productivity and carbon fluxes will be calculated from changes in inventories of oxygen, nitrate and biomass proxies corrected for the effects of horizontal and vertical mixing. Systematic comparison of these data with a bio-physical ecosystem model guided by adjoint analysis will be used to evaluate the appropriateness of such models for predicting both small-scale patchiness and net carbon uptake through the evolution of the bloom.
The most important broader impact will be on the technology of ocean carbon system measurement as described above. The proposed work will also support multidisciplinary training of four graduate students in ocean observing, as well as undergraduate interns. The PIs will collaborate with the COSEE-Ocean Systems to develop a "story" on the role of the North Atlantic ocean ecosystem that will resonate with non-scientists and be integrated into areas identified in the National Science Education Content Standards. Finally, the project will build international collaboration with a Canadian scientist at Dalhousie University.
