Reference: Wu, N., Grieve, S.W.D., Manning, A.J., & Spencer, K.L. (2024). "Marine snow as vectors for microplastic transport: Multiple aggregation cycles account for the settling of buoyant microplastics to deep-sea sediments." Abstract (High-Level Summary): This code simulates how buoyant microplastics become incorporated into marine snow aggregates and are transported downward in a one-dimensional water column (0–5100 m), following multiple cycles of aggregation and disaggregation as described in the paper. Key Points: 1) Particle class (both microplastic and marine snow). 2) Collision frequencies (shear- and settling-induced). 3) Marine snow size attenuation below the euphotic zone. 4) Residence times in different layers of the ocean. 5) Multiple aggregation cycles: A buoyant microplastic is incorporated into settling marine snow, transported downward, then released (if the marine snow degrades), and can be re-incorporated again while rising. Implementation note: in line 212, the settling kernel, this is the collector-limited and the speed term uses |v_a|+|v_agg| rather than |Δv| as one is settling and another is rising. Note: This version might not be perfect for everyone to read clearly, and an updated version will be coming soon.