Antarctic Sea‐Ice Extent Anomalies Impact Interannual Variability of Phytoplankton Chlorophyll‐a in Southern Ocean Frontal Zones

Abstract The influence of sea‐ice variability on Southern Ocean phytoplankton productivity across frontal zones remains poorly quantified. Using 26 years (1998–2023) of satellite data, we quantified how sea‐ice extent anomalies (SIEA) impact surface phytoplankton Chlorophyll‐a (Chl‐a) anomalies across three frontal zones. The annual minimum (February) and annual maximum (September) sea‐ice extent declined over 1998–2023 (Sen's slope = −19,088 and −28,858 km 2 yr −1 ; Mann–Kendall p = 0.0198 and 0.0230, respectively), with a faster relative decline at the annual minimum (−0.87% yr −1 ) than at the annual maximum (−0.18% yr −1 ). Lagged correlations show positive SIEA precede enhanced Chl‐a (36%–40%, p < 0.01) in coastal and Southern Boundary zones. Post‐2015, SIEA declined by 8.1% (from 11.88 to 10.91 million km 2 , with −17.4% anomaly in 2023), and Chl‐a declined by 2.6%–6.7% across zones, indicating a low‐ice, low‐productivity regime. Unlike basin‐wide studies, we resolve frontal‐scale lagged effects linking SIEA and Chl‐a variability across frontal zones.