Optical imaging of mesopelagic particles indicates deep carbon flux beneath a natural iron-fertilized bloom in the Southern Ocean

• Published in: Limnology and Oceanography
• Main Authors: Jouandet, M, Trull, Tw, Guidi, L, Picheral, M, Ebersbach, F, Stemmann, L, Blain, S
• Format: Article in Journal/Newspaper
• Language: English
• Published: Amer Soc Limnology Oceanography 2011
• Subjects: Earth Sciences; Oceanography; Chemical Oceanography; Kerguelen; Kerguelen Island; Southern Ocean
• Online Access: https://doi.org/10.4319/lo.2011.56.3.1130; http://ecite.utas.edu.au/76927

We recorded vertical profiles of size distributions of particles (ranging from 0.052 to several mm in equivalentspherical diameter) in the natural iron-fertilized bloom southeast of Kerguelen Island (Southern Ocean) and insurrounding high-nutrient, low-chlorophyll (HNLC) waters with an Under Water Video Profiler during theKerguelen Ocean and Plateau Compared Study cruise (JanFeb 2005). Total particle numerical abundance andtotal particle volume (TPV) in the 0200-m layer were respectively 3-fold and 20-fold higher in the bloom, andintegrated TPV was correlated to integrated chlorophyll concentration. The difference persisted well into theocean interior with a 10-fold higher TPV at 400-m depth beneath the natural iron-fertilized bloom. Below 400 m,increases in TPV values at the bloom stations reflect the suspension of bottom sediments. Bloom waters had agreater proportion of large particles from the surface to 400 m and also exhibited an increase of this proportionwith depth compared to HNLC waters. Multiple visits to the bloom reference Sta. A3, suggest preferentialremoval of large particles as the bloom declined. Comparing our particle abundance size spectra with thoseobserved previously in polyacrylamide gel-filled sediment traps allows us to estimate mesopelagic particle sinkingrates. These results suggest that particles sink faster in the HNLC waters than beneath the bloom. The fact thatsinking speeds were not a simple monotonic function of particle size and varied spatially highlights the need to gobeyond parameterizations of sinking rate as a function of size alone.