Interannual versus spatial variability in pelagic and benthic set up of particulate organic carbon in a glaciated Antarctic fjord.

Rapid warming along the Western Antarctic Peninsula (WAP) is altering glacier dynamics, freshwater inputs and biogeochemical processes. This study assessed how interannual and spatial variability influence the transfer and composition of particulate organic carbon (POC) from the pelagic to the benthic environment within a glaciated fjord of the WAP. Surveys were conducted over four consecutive years (2022-2025). Biogeochemical markers, isotopic signatures and elemental analysis were used to evaluate sources, quality and trophic status of suspended and sedimentary POC in Collins Bay. Surface suspended POC ranged from 101 to 674 μg L-1, with higher values in the inner shallow zone (ISZ) in 2025 (326.10 ± 88.18 μg L-1). Lipids were the principal component of biopolymeric carbon, with contributions up to 82%, indicating high-nutritive POC aggregates. δ13C (-26.7 to -19.2‰) and C/N (2.31-9.47) together with Bayesian Mixing models (MixSIAR) indicated predominantly marine phytoplankton sources with variable contributions from detrital-heterotrophic and minor terrestrial inputs. Interannual variability was the main driver of suspended POC composition. Sedimentary TOC ranged from 0.11 to 1.15%, with higher values in the outer deep zone (ODZ). Sediment δ13C (-25.9 to -22.8‰) and low C/N (4.25 ± 1.36) indicated mainly marine-derived, nitrogen-rich particles, with spatial differences driven by depth and sea bed characteristics linked to glacier influence. This work provides a multi-year empirical evidence of contrasting drivers between pelagic and benthic environment within an Antarctic glaciated fjord. Despite the marked interannual variability in surface-water conditions, efficient POC transfer and pelagic-benthic coupling remains strong in Collins Bay.