The Role of Thermodynamics on Northern Labrador Sea Ice Trends and Variability

Long-term changes and year-to-year variability in sea ice conditions on the northern Labrador (Nunatsiavut) coast and shelf have important influences on regional climate, marine ecosystems, and coastal communities. The drivers of sea ice variability in this region are poorly understood despite being critical for planning for future changes. Here, we evaluate the spatial and temporal trends and variability of sea ice area, concentration, thickness, and volume over the Labrador Shelf between 1979 and 2021 based on Canadian Ice Service sea ice charts. We characterise the seasonal cycle into two phases: a growth phase (December to January) and a peak phase (February to April). We then use Empirical Orthogonal Function analysis on mean ice thickness to identify the dominant modes of variability, and use correlations and simple physical models to investigate the relationships between these modes and thermodynamic forcing variables. Around 68% of the total variability can be explained by the first two modes (Mode 1: 52.6%; Mode 2: 15.2%). The first mode represents sea ice volume changes across the entire shelf, mainly driven by remote air temperature variations, with a smaller but non-negligible influence from local anomalies. The second mode represents a cross-shelf dipole structure that may be linked to the dynamic effects of winds and ocean currents.