Arctic Ocean is experiencing dramatic weight loss due to increasing freshwater storage

The freshwater cycle in the Earth System is a delicate balance between the net loss (i.e., evaporation > precipitation) in the warm tropical-subtropical oceans, the net gain (i.e., precipitation > evaporation) in the cold polar oceans, and the net poleward transport by the atmosphere. These processes maintain the tropical-subtropical oceans salty and the polar oceans fresh. In return, the ocean transports the freshwater equatorward, thereby closing the freshwater budget. A significant change in one of these components may result in a disruption in the global freshwater cycle, potentially leading to regional drought, flooding, and changes in the global atmosphere-ocean-biogeochemistry. A recent study published in Geophysical Research Letters shows how the freshwater system is changing in the Arctic Ocean (Jahn and Laiho, 2020). The study used large ensemble simulations from a state‐of‐the‐art climate model to show that a large increase in Arctic liquid freshwater storage over the past decades is driven by anthropogenic climate changes and associated increases in the freshwater fluxes into the Arctic Ocean (e.g. Bering Strait flux, and river runoff). The model experiments also provided a sequence of emergence of forced signals in different elements of the Arctic freshwater system. In general, the emergence of the forced Arctic freshwater fluxes occurs earlier for oceanic fluxes than for atmospheric or land fluxes. In particular, the forced freshwater flux signal occurs first at Nares Strait in the Canadian Arctic Archipelago (in the 2000s), then at Davis Strait (in the 2010s), then at Fram Strait (first for liquid flux in the 2030s, then for solid flux in the 2060s). The increasing freshwater fluxes into the Labrador Sea and the Greenland-Iceland-Norwegian (GIN) Seas through Davis and Fram Straits may result in an increase in the upper ocean stratification, thereby reducing the deep ocean convection that drives the Atlantic Meridional Overturning Circulation (AMOC).

Figure 1. from Jahn and Laiho (2020): Arctic domain and Climatological FW budget. (a) Ocean gateways (labeled in red) and the Arctic Ocean domain used here (shaded; showing the simulated liquid FW column (in m) over 1980–2000). BSO stands for Barents Sea Opening. (b) Climatological ensemble‐mean Arctic FW budget terms for the late 20th century (1980–2000) and the late 21st century (2080‐2100), with the late 21st century shown under both low warming (CESM LW; green) and high warming (CESM LE; purple). The values of the flux terms are shown on the left y-axis, the values of the FW storage terms on the right y-axis. Note that Davis Strait is shown here for reference, as it has been used in several other studies of the Arctic FW budget (e.g., Haine et al., 2015), but is not part of the Arctic FW budget/domain used here.

Jahn, A., & Laiho, R. (2020). Forced changes in the Arctic freshwater budget emerge in the early 21st century. Geophysical Research Letters, 47, e2020GL088854.

Haine, T. W. N. (2020). Arctic Ocean freshening linked to anthropogenic climate change: All hands on
deck. Geophysical Research Letters, 47, e2020GL090678.

Haine, T.W. N., Curry, B., Gerdes, R., Hansen, E., Karcher, M., Lee, C., et al. (2015). Arctic freshwater export: Status, mechanisms, and prospects. Global and Planetary Change, 125, 13–35.

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