Simulated Impact of Time-Varying River Runoff and Greenland Freshwater Discharge on Sea Level Variability in the Beaufort Gyre Over 2005-2018

Global mean sea level has been rising at a rate of 3.25 +/- 0.4 mm yr-1 over 1993-2018. Yet several regions are increasing at a much faster rate, such as the Beaufort Gyre in the Arctic Ocean at a rate of 9.3 +/- 7.0 mm yr-1 over 2003-2014. At interannual to decadal time scales, the Beaufort Gyre sea level is controlled by salinity changes due to sea ice melt and wind-driven lateral Ekman convergence-divergence of freshwater. This study uses recent Greenland discharge and river runoff estimates to isolate and quantify the sea level response to freshwater fluxes variability over the period 1980-2018. It relies on sensitivity experiments based on a global ocean model including sea-ice and icebergs. These sensitivity experiments only differ by the freshwater fluxes temporal variability of Greenland and global rivers which are either seasonal climatologies or fully time varying, revealing the individual and combined impact of these freshwater sources fluctuations. Fully varying Greenland discharge and river runoff produce an opposite impact on sea level trends over 2005-2018 in the Beaufort Gyre region, the former driving an increase, while the latter, a decrease. Their combined impact leads to a fairly weak sea level trend. The sea level response is primarily driven by salinity variations in the upper 300 m, which are mainly caused by salinity advection involving complex compensations between passive, active, and nonlinear advection. This study shows that including the temporal variability of freshwater fluxes in forced global ocean models results in a better representation of regional sea level change. Sea level is rising globally but not at the same rate everywhere. In the Arctic Ocean, the Beaufort Gyre sea level has been increasing at a fast rate of 9.3 +/- 7.0 mm yr-1 over 2003-2014. At long time scales, the Beaufort Gyre sea level change is controlled by salinity, which depends mainly on continental freshwater runoff-particularly high in this region-and sea ice melt. This study uses recent estimates of Greenland discharge and river runoff in a global ocean model. The aim is to isolate and quantify the sea level response of the Beaufort Gyre to freshwater fluxes variability. We compare numerical simulations where Greenland discharge and river runoff are fully varying or set to a repeated seasonal cycle to reveal the individual and combined impacts of the variability of these freshwater sources on regional sea level. Both Greenland discharge and global river runoff impact remotely the Beaufort Gyre sea level. They induce salinity variations in the upper 300 m of the gyre through salinity advection. This study highlights the importance of the variability of continental freshwater fluxes in models in order to better represent regional sea level variability. Greenland discharge and river runoff variability contribute to sea level rise and fall in the Beaufort Gyre The positive impact of Greenland is greater than the negative impact of rivers in the 0-78-m range, and vice versa in the 78-300-m range Sea level change in the sensitivity experiments is mostly halosteric with salinity changes mainly controlled by advection

Keyword(s)

Arctic Ocean, Beaufort gyre, regional sea level change, land freshwater discharge, salinity variability

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Tajouri Soumaia, Llovel William, Sevellec Florian, Molines J. -M., Mathiot P., Penduff Thierry, Leroux S. (2024). Simulated Impact of Time-Varying River Runoff and Greenland Freshwater Discharge on Sea Level Variability in the Beaufort Gyre Over 2005-2018. Journal Of Geophysical Research-oceans. 129 (9). e2024JC021237 (21p.). https://doi.org/10.1029/2024JC021237, https://archimer.ifremer.fr/doc/00905/101734/

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