title: An approach for particle sinking velocity measurements in the 3-400 μm size range and considerations on the effect of temperature on sinking rates.
abstract: The flux of organic particles below the mixed layer is one major pathway of carbon from the surface into the deep ocean. The magnitude of this export flux depends on two major processes-remineralization rates and sinking velocities. Here, we present an efficient method to measure sinking velocities of particles in the size range from approximately 3-400 μm by means of video microscopy (FlowCAM®). The method allows rapid measurement and automated analysis of mixed samples and was tested with polystyrene beads, different phytoplankton species, and sediment trap material. Sinking velocities of polystyrene beads were close to theoretical values calculated from Stokes' Law. Sinking velocities of the investigated phytoplankton species were in reasonable agreement with published literature values and sinking velocities of material collected in sediment trap increased with particle size. Temperature had a strong effect on sinking velocities due to its influence on seawater viscosity and density. An increase in 9 °C led to a measured increase in sinking velocities of ~40 %. According to this temperature effect, an average temperature increase in 2 °C as projected for the sea surface by the end of this century could increase sinking velocities by about 6 % which might have feedbacks on carbon export into the deep ocean.
authors.affiliation: Helmholtz-Zentrum für Ozeanforschung (GEOMAR), Düsternbrooker Weg 20, 24105 Kiel, Germany.
authors.forename: Lennart Thomas
authors.initials: LT
authors.lastname: Bach
authors.affiliation: Helmholtz-Zentrum für Ozeanforschung (GEOMAR), Düsternbrooker Weg 20, 24105 Kiel, Germany.
authors.forename: Ulf
authors.initials: U
authors.lastname: Riebesell
authors.affiliation: Helmholtz-Zentrum für Ozeanforschung (GEOMAR), Düsternbrooker Weg 20, 24105 Kiel, Germany.
authors.forename: Scarlett
authors.initials: S
authors.lastname: Sett
authors.affiliation: Helmholtz-Zentrum für Ozeanforschung (GEOMAR), Düsternbrooker Weg 20, 24105 Kiel, Germany.
authors.forename: Sarah
authors.initials: S
authors.lastname: Febiri
authors.affiliation: Helmholtz-Zentrum für Ozeanforschung (GEOMAR), Düsternbrooker Weg 20, 24105 Kiel, Germany.
authors.forename: Paul
authors.initials: P
authors.lastname: Rzepka
authors.affiliation: Helmholtz-Zentrum für Ozeanforschung (GEOMAR), Düsternbrooker Weg 20, 24105 Kiel, Germany.
authors.forename: Kai Georg
authors.initials: KG
authors.lastname: Schulz