A comparative study of the particle size spectra for Arctic, North Atlantic and Southern Ocean spring blooms: implications for POC export and sinking velocity.

Feliciano C de Soto1, Elena Ceballos-Romero2, Morten H. Iversen3 and Maria Villa-Alfageme2, (1)Universidad Pablo Olavide, Physical, Chemical and Natural Systems, Seville, Spain, (2)Universidad de Sevilla, Applied Physics II, Sevilla, Spain, (3)Alfred Wegener Institute Helmholtz-Center for Polar and Marine Research Bremerhaven, Polar Biological Oceanography, Bremerhaven, Germany
Abstract:

In order to correctly evaluate the efficiency of the Biological Carbon Pump it is important to quantify the mechanisms controlling the export of particulate organic carbon (POC) from the euphotic zone to the mesopelagic and deep ocean. However how sinking velocities and particle size distribution are connected and related to export and vary with depth, location or season it is not fully understood.
In this work we analyse the measurements of particle size spectrum obtained through the use of submersible digital holographic cameras (LISST-HOLO). This camera system has been employed to measure the abundance of particles in the size range 25-2500 \mu m equivalent spherical diameter (ESD) at different depths (from 50 m to 250 m) for three contrasting sites: Arctic, Porcupine Abyssal Plain (PAP) and the Southern Ocean during the spring bloom.
In-situ measurements of the particle size distributions are used to model and quantify particle distributions in depth using variable fractal dimensions. Particle size contribution to key parameters in the study of the carbon export, such as flux and particle sinking velocity is evaluated in the three scenarios.
Furthermore we will include a typical distribution of particle sizes in a time-dependent microscopic simulation [deSoto2018] of organic particles production, sinking and degradation.This will serve as sensitivity model to asses the role played by particles of different sizes on POC export or sinking velocities over the whole productive season. Finally, it is discussed the importance of using properly normalized particles size spectra to improve the accuracy of the export evaluation.

F. de Soto, E. Ceballos-Romero, M. Villa-Alfageme. Geochimica et Cosmochimica Acta 239 (2018) 136–158

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