Quantifying the role of estuarine discharge in modulating landfast sea-ice regime in Hudson Bay and James Bay

Arctic and subarctic estuaries are unique environments where flowing river water influences the freezing and melting of ice in complex ways. This study examined the impact of river discharge on the formation and persistence of landfast ice in Hudson Bay and James Bay, utilizing ice charts and satellite imagery. The results showed that landfast ice around eight major river mouths in Hudson Bay and James Bay formed later and melted earlier than near adjacent non-estuarine coastlines with minimal river impact. The degree to which ice forms later and melts earlier in river mouths compared to non-estuarine coastlines varied proportionately with the intensity of river discharge volume, implying discharge volume is a crucial factor in determining ice persistence. Furthermore, it was seen that from the start of the seasonal temperature transition, the break-up event at river mouths happened after 21 days on average, compared to 32 days in the case of ice at the adjacent coastlines. Ice at rivers with higher discharge volumes experienced earlier break-up and delayed freeze-up compared to other rivers. A crucial contribution of this study is highlighting that landfast ice break-up is either predominantly thermodynamic, with ice loss due to melting, or predominantly dynamic, with ice loss due to disintegration and flushing out of the ice due to dynamic forcings like river flow and wind.