Distribution of marine snow and copepods vary between two Arctic fjords with contrasting ice cover and stratification regimes

Glacial meltwater is a major contributor to stratification in polar waters, particularly in glacial fjords where it is contained by fjord topography. Stratification from glacial meltwater input impacts both light and nutrient availability, altering the timing and magnitude of phytoplankton blooms and peak in secondary productivity. Ice conditions can further impede near-surface circulation and trap low-density meltwater plumes, amplifying stratification. Whilst stratification is a critical process in the initiation of phytoplankton blooms, reduced mixing can impede nutrient resupply in the euphotic zone, reduce productivity, and alter the formation processes of marine snow. Here, using a combination of optical and acoustic instrumentation, we investigated how different stratification conditions in two adjacent fjords of northwest Greenland (Petermann Fjord, PF, and Sherard Osborn Fjord, SOF) impact the vertical distribution of two key components of Arctic pelagic ecosystems: marine snow and copepods. We show that the amplified stratification caused by ice damming outside SOF was associated with lower indices of primary and secondary production. Stratification also reduced concentrations of marine snow and resulted in an altered vertical distribution of small sphere particles that were likely fecal pellets in the top 100 m of SOF. Zooplankton distributions in both fjords were centered below the fluorescence peak but were more tightly coupled with the chlorophyll maximum in SOF than in the well-mixed PF. Feeding conditions in SOF were poorer, while in the more productive PF zooplankton were distributed deeper where risks of predation are likely reduced. Although small and large copepod densities were comparable between fjords, the low numbers of nauplii in SOF further suggest mismatch conditions not suitable for their survival. We demonstrate that sea ice conditions are linked to local physical water column stratification that has cascading effects on productivity and the abundance, distribution, and types of marine snow and copepods. Future conditions in glacial fjords are not clear because thermal stratification and glacier runoff will increase, but the number of ice damming events could decrease.