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Abstract The impacts of climate change on Arctic marine systems are noticeable within the scientific “lifetime” of most researchers and the iconic image of a polar bear struggling to stay on top of a melting ice floe captures many of the dominant themes of Arctic marine ecosystem change. But has our focus on open‐ocean systems and parameters that are more easily modeled and sensed remotely neglected an element that is responding more dramatically and with broader implications for Arctic ecosystems? We argue that a complementary set of changes to the open ocean is occurring along Arctic coasts, amplified by the interaction with changes on land and in the sea. We observe an increased number of ecosystem drivers with larger implications for the ecological and human communities they touch than are quantifiable in the open Arctic Ocean. Substantial knowledge gaps exist that must be filled to support adaptation and sustainability of socioecological systems along Arctic coasts. 

Abstract The seasonal behavior of fluvial dissolved silica (DSi) concentrations, termedDSi regime, mediates the timing of DSi delivery to downstream waters and thus governs river biogeochemical function and aquatic community condition. Previous work identified five distinct DSi regimes across rivers spanning the Northern Hemisphere, with many rivers exhibiting multiple DSi regimes over time. Several potential drivers of DSi regime behavior have been identified at small scales, including climate, land cover, and lithology, and yet the large‐scale spatiotemporal controls on DSi regimes have not been identified. We evaluate the role of environmental variables on the behavior of DSi regimes in nearly 200 rivers across the Northern Hemisphere using random forest models. Our models aim to elucidate the controls that give rise to (a) average DSi regime behavior, (b) interannual variability in DSi regime behavior (i.e., Annual DSi regime), and (c) controls on DSi regime shape (i.e., minimum and maximum DSi concentrations). Average DSi regime behavior across the period of record was classified accurately 59% of the time, whereas Annual DSi regime behavior was classified accurately 80% of the time. Climate and primary productivity variables were important in predicting Average DSi regime behavior, whereas climate and hydrologic variables were important in predicting Annual DSi regime behavior. Median nitrogen and phosphorus concentrations were important drivers of minimum and maximum DSi concentrations, indicating that these macronutrients may be important for seasonal DSi drawdown and rebound. Our findings demonstrate that fluctuations in climate, hydrology, and nutrient availability of rivers shape the temporal availability of fluvial DSi. 

This dataset includes monthly dissolved silicon (DSi) concentration data from 198 rivers across the Northern Hemisphere. Concentration and discharge data were sourced from public and/or published datasets and the Weighted Regressions on Time, Discharge, and Season model (Hirsch et al. 2010) was used to estimate monthly concentrations and flow-normalized concentrations for all sites over their period of record. Sites span eight climate zones, ranged from 18 degrees N to 70 degrees N, and vary in drainage area from < 1 km2 to nearly 3 million km2. These monthly concentration data were then used to cluster sites into average (i.e., average of all years) and annual (i.e., each year individually) seasonal regimes using a time-series clustering approach. The annual regimes were used to quantify how often a site moved among regimes over its period of record (i.e., stability). Site characteristics including climate zone, discharge, and concentration-discharge behavior were explored as potential drivers of cluster membership and stability.