Abrupt Microplankton Regime Shift Revealed by Two Decades of Arctic Fjord Monitoring
Year: 2026
Type: conference-abstract
Abstract: Arctic marine ecosystems are changing, and increasing evidence suggests that these changes can occur as abrupt regime shifts rather than gradual transitions. Plankton communities, which form the base of marine food webs that support critical fisheries, are particularly sensitive to climate-driven environmental changes, including warming, sea-ice loss, and altered freshwater input. Due to their rapid response to environmental change and short generation times, they are strong indicators of climatic forcing. Compounding these stressors is the poleward expansion of boreal taxa, which introduces new competitors and alters trophic interactions. While the ecological impacts of these pressures are increasingly recognized, long-term biological observations from the Arctic remain scarce.We present results from two decades of marine monitoring in southwest Greenland (Nuup Kangerlua), comprising seasonal hydrographic and microplankton observations (Vonnahme et al., 2025). Around 2013, microplankton species richness declined abruptly after a period of relatively high diversity. This shift coincided with a reduced influence of Atlantic-type water, warmer surface temperatures, and reduced nitrate + nitrite (NOX) concentrations in the upper water column, suggesting that altered nutrient conditions and the influx of warmer water masses drove the decline.A comparison of Arctic fjords indicates that similar community-level changes are emerging across high-latitude fjord systems (Chitkara et al., 2024). Phytoplankton variability across Arctic fjords is strongly shaped by glacial meltwater, stratification, and light availability. Collectively, these studies suggest that when multiple hydrographic thresholds are crossed, abrupt biological responses can occur, underscoring the importance of sustained long-term observations to detect and interpret such nonlinear ecological change.Our study highlights the ecological vulnerability of Arctic fjord systems and emphasizes the critical importance of long-term, high-resolution marine monitoring. Abrupt shifts in microplankton communities may have cascading implications for food-web dynamics, biogeochemical cycling, and the resilience of marine ecosystems to ongoing climate change. Continued integrative monitoring and cross-regional synthesis will be essential to detect, quantify, and predict ecological transformations in a rapidly warming Arctic. This work is part of the Greenland Ecosystem Monitoring (GEM) program, the FACE-IT project (EU Grant no. 869154) and the MicroFUN project.
DOI: 10.5194/wbf2026-331
Institutions: Grønlands Naturinstitut, University Centre in Svalbard
Language: English
Subfield: Oceanography
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: gold
OpenAlex ID: W7134884868