Author: Carlos  Muñoz Nevado,   (University of Seville)

Designation: 

Description:
COMICS (Controls over Ocean Mesopelagic Carbon Storage) project (UK) studies how especial conditions influence the sequestration of carbon from surface to the deep ocean through the action of the Biological Carbon Pump (BCP). COMICS I targeted the north of South Georgia island during the austral spring bloom of 2017 (P3), where the Subantarctic Circumpolar Current Front introduces iron to the water column increasing the diatoms productivity. COMICS II targeted Benguela North (BN) and South (BS) in the low oxygen region offshore Namibia coast. Particle sinking velocities (SV), POC flux at the base of the Euphotic depth (Ez) and export efficiency (ExpEff) are compared using radioactive pairs disequilibrium (²³⁸U-²³⁴Th and ²¹⁰Pb-²¹⁰Po). The SV at SG ranged from 60 to 140 m d^-1, while in Benguela SV ranged from 40 to 240 m d^-1. POC fluxes at SG ranged from 150 to 350 mgC m^-2 d^-1, and are higher than in Benguela, 13 (BN) - 210 (BS) mgC m^-2 d^-1. We define ExpEff as the ratio POC flux at Ez to satellite-derived NPP provided by VGPM. ExpEff ranged 12 - 38% at SG and at Benguela, 3% (BN) - 35% (BS). Overall, the results obtained from the radioactive pair disequilibrium analysis confirm that the combination of the naturally iron fertilized area and a bloom stage in SG exports more POC into the mesopelagic zone than the nutrient upwelling of Benguela. However, despite significantly higher POC fluxes in SG, similar ExpEff is found in both sites. The simultaneous estimation of POC flux and particle sinking velocities allows a better understanding of the biological processes implicates.

Category: Scientific Program Abstract > Special Sessions > SS17 Unravelling the ecology and biogeochemistry of the mesopelagic zone