Particulate organic carbon (POC) exported from the surface ocean fuels deep-sea ecosystems, yet whether surface productity signals are preserved during export to depth remains poorly constrained. Here we use size-fractionated (1-51 μm and >51 μm) particulate amino acids to examine how bioavailable particle pools retain surface-productivity gradient across a latitudinal (28~42°N) transect in the northwestern Pacific Ocean. Particulate amino acid concentrations in the euphotic zone closely followed the south-to-north increase in chlorophyll-a. This spatial structure extended into the deep ocean, but diverged strongly between particle size fractions. The small size fraction retained a consistent latitudinal gradient from surface to 2500 m depth, whereas the large size fraction lost this structure below ~1000 m. Compositional analyses showed more continuous transformation in small particles and greater heterogeneity in large particles at depth. These results identify small suspended particles as an underappreciated pathway for preserving and transmitting surface-derived carbon to the deep ocean.