Abstract
In this special collection, new studies reveal that fjords serve as vital estuarine transition zones between terrestrial ecosystems and the open ocean. Primarily found at high latitudes, fjords are highly sensitive to climate change, which fundamentally reshapes their land and marine inputs. As glaciers retreat, the influx of freshwater, nutrients, and sediments shifts, altering the chemical and biological makeup of fjord waters. While glaciers currently drive the upwelling of nutrient‐rich waters that support primary productivity, glacial retreat onto land may increase stratification and shift ecosystems toward microbial dominance. Fjords also play a critical role in the global climate system as disproportionate hotspots for organic carbon burial. However, warming and melting permafrost threaten to remobilize this stored carbon, potentially changing fjords from carbon sinks into sources of CO2 emissions. Because of these complex and interacting stressors, fjords are increasingly viewed as “Aquatic Critical Zones” that require urgent interdisciplinary research and management.