The rapidly warming Arctic and its effects on sea ice extent, hydrology, and nutrient availability influence terrestrial and marine carbon cycles in a number of interrelated ways. While these changes likely have shared effect on adjacent land and ocean systems, we often study them in isolation, making it difficult to understand response patterns and trajectories in these carbon cycle hotspots. Using almost two decades of remotely-sensed Gross Primary Productivity (GPP) in Arctic coastal margins, we test how the magnitude and direction of change in productivity covary. We observed that coastal marine productivity is four times that of coastal tundra productivity in the pan-Arctic. From 2003-2020, GPP in both the coastal land and ocean increased by approximately 12%. This common trajectory seems to be a product of increasing open water conditions, increased terrestrial water balance, and nutrient availability as driven by the regional warming. On a sectoral scale, we proposed a Coastal Synchrony Index (CSI) to compare the rate of change of ocean productivity relative to land productivity and show that ocean productivity is increasing faster than land in inflow margins of Barents, Bering, and Okhotsk, outflow margins of Canadian Arctic Archipelago (CAA) and Greenland/Iceland, and in interior margin of Eurasia. Additionally, we see strong coherence between land and ocean GPP on 4–5-year cycles illustrating that coastal synchrony observed over decadal timescales is mirrored over interannual timescales. These cycles align with variations in open water duration, emphasizing the pivotal role of reducing shorefast ice on terrestrial and marine productivity trajectories.

Open watersheds and their rivers play a pivotal role in biogeochemical cycles, forming crucial links between land and ocean ecosystems. This study utilized remotely sensed and reanalysis datasets to investigate the land-ocean Gross Primary Productivity (GPP) dynamics of 15 major watersheds: Mississippi, Nelson, St. Lawrence, Amazon, Parana, Congo, Zambezi, Niger, Orange, Ganges Brahmaputra, Yangtze, Huang He, Amur, Danube, and Murray Darling. It looked at the dynamics and vulnerabilities of major watersheds to identify the influences of land use and land management, moisture balance, and temperature on the patterns of how primary producers absorb CO2 from the atmosphere. Intensive human interventions, particularly in agriculture-dominant watersheds like Mississippi, Ganges Brahmaputra, Yangtze, Huang He, and Murray Darling, were observed to substantially influence land productivity, with consequent cascading effects on adjoining ocean ecosystems. In contrast, the vast rainforests of Amazon and Congo illuminated their intrinsic vulnerability to moisture dynamics, accentuating potential threats under shifting climatic regimes. Watersheds like the Parana and Zambezi offered insights into ecosystem susceptibilities arising from temperature variations. As climatic anomalies continue to redefine land-ocean interactions, our study not only underscores the imperative for adaptive conservation strategies but also to study adjacent land and marine systems as intricately linked entities.