SPBM v2.0: Extension of a 1-D sea-ice biogeochemical model with ice–algal ecophysiology and zooplankton seasonal vertical migration for coupled ice–pelagic ecosystem simulations in Antarctic coastal seas

Abstract. We present SPBM v2.0, an extension of the one-dimensional Sympagic–Pelagic–Benthic Model for the coupling of sea-ice and pelagic ecosystems in Antarctic coastal seas. The extension introduces a temperature-gated, bottom-accumulating ice-algal ecophysiology; a water-only zooplankton formulation with continuous overwintering; and a two-species seasonal vertical migration scheme for krill and copepods, together with corrections to the solar forcing and to the ERSEM iron cycle required for iron-sensitive Southern Ocean applications. A single biogeochemical parameter set is applied at three sites spanning 6.5° of latitude — Terra Nova Bay (TNB, Ross Sea), the western Antarctic Peninsula (WAP), and the Amundsen Sea polynya (ASP) — so that inter-site differences emerge under site-specific physical forcing and prescribed initial iron inventories, without site-specific biological tuning. Evaluated against the ASPeCT circumpolar ice-core database, the model reproduces the observed spring and autumn chlorophyll magnitude at TNB and the summer magnitude at ASP, while underestimating chlorophyll during summer and winter at TNB and across seasons at WAP. The central result is that the strength of ice–pelagic coupling emerges under contrasting physical forcing and initial iron inventories rather than being prescribed through site-specific biological tuning: thick, cold ice at TNB sustains a strong ice-algal bloom whose released biomass contributes to the pelagic community and is associated with a krill-dominated grazer community, whereas the thinice WAP site develops a water-column-dominated regime. These contrasting environmental regimes are also associated with different zooplankton community structures, with krill dominance at TNB and ASP and copepod dominance at WAP. The weak simulated bloom at WAP also highlights a limitation of the one-dimensional framework, which omits lateral nutrient and iron exchange.