Phytoplankton community structure and variability at the landfast ice–water column interface in Terra Nova Bay, Ross Sea (Antarctica)

Abstract

Landfast ice in Terra Nova Bay represents a dynamic ecological interface where sea-ice structure, meltwater inputs, and platelet-ice processes interact to shape microalgal communities across the ice–ocean boundary. During the austral spring–summer 2015/2016, we examined how seasonal transitions—from early-season to progressive melting and stratification—modulate the development of sympagic assemblages and their connection with the underlying water column. By integrating sea-ice thermodynamics, pigment signatures, nutrient variability, and water-column profiles, we describe how physical forcing and biogeochemical gradients interact to shape community composition and functional structure. Surface salinity decreased from a maximum of 36.67 to a minimum of 30.67, while surface chlorophyll a exceeded 40 µg L - ¹ during the early-December biomass maximum and subsequently declined to below 1 µg L - ¹ in late December and January. The pigment record showed changes in the relative contribution of fucoxanthin, 19′-hexanoyloxyfucoxanthin (19′HF), and chlorophyll c2, while the multivariate analysis identified a significant vertical effect (PERMANOVA, F = 1.7188, R² = 0.1629, p = 0.0003), with sampling date accounted for as a temporal blocking factor. Together, these findings highlight the meltwater-influenced layer beneath landfast ice as a biologically relevant interface linking sea-ice processes with phytoplankton dynamics in Antarctic coastal waters.