Incubation SetupThe aggregates were placed inside the settling microcosm. The microcosm was filled with GF/F filtered, artificial seawater (32 psu) with a carbonate chemistry adjusted to the present or future conditions. This reduced the biological activity to the community originally present in the aggregates. The microcosm was continuously pressurized at a rate of 30 MPa/day, until it reached 10 MPa, the equivalent to a depth of 1000 m. The full incubation lasted 80 h. The experiment was triplicated at a pCO2 of 380 µatm and 1100 µatm. Additional incubations of similar duration were done at atmospheric pressure, with triplicates at a pCO2 of 380 µatm and 1100 µatm. These aimed at isolating the effect of the increase in hydrostatic pressure.Determination of Particle Size and Settling Velocity (ws)A Laser In Situ Scattering and Transmissiometry device (LISST-100X) was used to measure the variations in particle size distribution of the model aggregates before and after the incubations. The particle size vs. settling velocity relationship of phytodetrital aggregates was investigated by using a settling column of square cross-section [24]. The particles were back-illuminated and recorded with a digital video camera (Imageworks DFK-41F02) for determination of settling rates and particle sizes. The camera was capable of resolving particles of >11 µm diameter. The analysis of the particle sizes and settling velocities was done using the ImageJ (v.1.61) software. The resulting settling speeds were converted into m day−1 velocities, and the average speed for each of the aggregate size classes was calculated for the equivalent size classes of the LISST analysis (>63 µm, >75 µm, >88 µm, >104 µm, >122 µm, >144 µm, >170 µm, >201 µm, >237 µm, >280 µm, >331 µm, >390 µm, >460 µm).