Sedimentary Phytopigments in the St. Anna Trough and Adjacent Waters: Spatial Patterns and Environmental Drivers

Rapid Atlantification is altering primary productivity and benthic-pelagic coupling in the Eurasian Arctic. This study assessed sedimentary pigments as indicators of exported production in the poorly studied St. Anna Trough, a critical conduit between the Barents and Kara seas. Sediment samples were collected at 20 stations in autumn 2023, and phytopigment concentrations were analyzed spectrophotometrically alongside hydrological data. Multivariate analysis revealed two distinct benthic regimes separated by the Marginal Ice Frontal Zone. The southern sector, influenced by thick seasonal warm water masses (WWM) in the subsurface layer, exhibited mesotrophic conditions with mean chlorophyll-a + pheophytin-a concentrations of 30.28 ± 6.51 µg g−1. The northern sector, dominated by Arctic-origin water masses, was oligotrophic (4.45 ± 0.54 µg g−1). Redundancy analysis identified WWM thickness as the primary driver, explaining 60.5% of the total variance in pigment contents, followed by ice-cover duration (9.8% negative effect). Pigment indices and high pheophytin proportions indicated predominantly detrital organic matter, though stations near the Barents Sea inflow showed fresher material. The prevalence of chlorophyll-b in the north suggested ice-associated green algae, while chlorophyll-c dominated the diatom-rich southern inflow. These findings establish a crucial baseline for monitoring climate-driven shifts in pelagic-benthic coupling as sea ice retreat continues.