The biogeochemical structuring role of horizontal stirring: Lagrangian perspectives on iron delivery downstream of the Kerguelen Plateau
|Author(s)||D'Ovidio F.1, Della Penna A.1, 2, 3, Trull T. W.4, Nencioli F.5, Pujol M. -I.6, Rio M.-H6, Park Y. -H.1, Cotte C.1, Zhou M.7, Blain S.8, 9|
|Affiliation(s)||1 : Univ Paris 06, Univ Paris 04, CNRS IRD MNHN, LOCEAN Lab, F-75005 Paris, France.
2 : CSIRO, UTAS Quantitat Marine Sci Program, IMAS, Hobart, Tas 7001, Australia.
3 : Univ Paris Diderot Cite, Paris, France.
4 : Univ Tasmania, CSIRO Oceans & Atmosphere, Antarctic Climate & Ecosyst Cooperat Res Ctr, Hobart, Tas 7001, Australia.
5 : Plymouth Marine Lab, Remote Sensing Grp, Plymouth PL1 3DH, Devon, England.
6 : CLS, Toulouse, France.
7 : Univ Massachusetts, Coll Sci & Math, Sch Environm, Boston, MA 02125 USA.
8 : Observ Oceanol, Lab Oceanog Microbienne, UMR CNRS 7621, F-66650 Banyuls Sur Mer, France.
9 : Univ Paris 06, Univ Paris 04, Observ Oceanol, Lab Oceanog Microbienne,UMR7621, F-66650 Banyuls Sur Mer, France.
|Source||Biogeosciences (1726-4170) (Copernicus Gesellschaft Mbh), 2015 , Vol. 12 , N. 19 , P. 5567-5581|
|WOS© Times Cited||56|
|Note||Special issue : KEOPS2: Kerguelen Ocean and Plateau Study 2Editor(s): S. Blain, I. Obernosterer, B. Queguiner, T. Trull, and G. Herndl|
|Abstract||Field campaigns are instrumental in providing ground truth for understanding and modeling global ocean biogeochemical budgets. A survey however can only inspect a fraction of the global oceans, typically a region hundreds of kilometers wide for a temporal window of the order of (at most) several weeks. This spatiotemporal domain is also the one in which the mesoscale activity induces through horizontal stirring a strong variability in the biogeochemical tracers, with ephemeral, local contrasts which can easily mask the regional and seasonal gradients. Therefore, whenever local in situ measures are used to infer larger-scale budgets, one faces the challenge of identifying the mesoscale structuring effect, if not simply to filter it out. In the case of the KEOPS2 investigation of biogeochemical responses to natural iron fertilization, this problem was tackled by designing an adaptive sampling strategy based on regionally optimized multisatellite products analyzed in real time by specifically designed Lagrangian diagnostics. This strategy identified the different mesoscale and stirring structures present in the region and tracked the dynamical frontiers among them. It also enabled back trajectories for the ship-sampled stations to be estimated, providing important insights into the timing and pathways of iron supply, which were explored further using a model based on first-order iron removal. This context was essential for the interpretation of the field results. The mesoscale circulation-based strategy was also validated post-cruise by comparing the Lagrangian maps derived from satellites with the patterns of more than one hundred drifters, including some adaptively released during KEOPS2 and a subsequent research voyage. The KEOPS2 strategy was adapted to the specific biogeochemical characteristics of the region, but its principles are general and will be useful for future in situ biogeochemical surveys.|