This project has developed and validated five genera-specific ddPCR eDNA assays for indigenous kelp (Carpophyllum, Cystophora, Ecklonia, Lessonia, Macrocystis), conducted controlled degradation experiments, and executed a major field campaign across the Marlborough Sounds–Cook Strait–Cook Strait Canyon system (10–2,980 m). In total, 280 sediment eDNA samples, 62 water eDNA samples, and 175 sediment isotope samples were collected from 29 sites. eDNA detections in sediments were frequent (≈85% positive in Cook Strait), while water-column detections were sparser and genus-dependent (e.g., Macrocystis detected at 47% of water-column sites).

Despite strong assay sensitivity (four assays to 1:1,000; Macrocystis to 1:10,000), a robust quantitative relationship between kelp DNA and sediment organic carbon has not yet been established, limiting direct conversion of eDNA to sequestration rates. Preliminary 210Pb results (Sept 2025) provide the first sedimentation-rate constraints for Cook Strait Canyon cores; integrated with hydrodynamic particle tracking, these support a “near-source deposition + lateral focusing to canyons” pathway governed by sinking rates and shelf hydrodynamics.

A synthesis of published and project-inferred sinking rates (mean ≈0.029 m s⁻¹) implies much POC may sink near production zones, with canyon-ward advection concentrating material that becomes preservable in deep-sea sediments.

Priority next steps: calibrating eDNA to carbon with additional biomarkers, expanding species and shelf coverage (including outer-shelf transects away from canyon feeders), and running ROMS particle tracking across a realistic range of sinking velocities to bound sequestration fluxes below the euphotic zone.