The Impacts of Freshwater Input and Surface Wind Velocity on the Strength and Extent of a Large High Latitude River Plume

Abstract

Arctic Ocean physical and biogeochemical properties are strongly influenced by freshwater input from land and through the Bering Strait, where the mean currents transport water northward from the Bering Sea. The Yukon River is one of the largest rivers in North America and the Arctic, contributing large quantities of freshwater and terrigenous material to the coastal ocean in the northern Bering Sea. However, a detailed analysis of the coastal hydrodynamics at the outflow of the river has not been conducted in this remote but regionally important river. A three-dimensional hydrodynamic model was built to represent the lower Yukon River and coastal ocean for the ice-free months in 7 years. On average, a large anticyclonic eddy persisted at the main outflow of the Yukon that recirculates water back toward the coast where the currents converge to form a mean northward transport along the delta. Interannual spatial variance in salinity was relatively small, while there was substantial variance in u and v current velocity. u velocity spatial variance was correlated to the volume of freshwater discharge across years, while v velocity spatial variance was correlated to the N–S wind velocity. During strong wind events, plume structure was substantially altered: southerly winds deepened the plume and enhanced northward transport, while northerly winds shoaled and strengthened the pycnocline, and reversed the flow toward the south. The variability in plume dispersion on short time scales due to wind forcing has implications for where terrigenous material is processed in and settles out of the water column.

Modelling the interannual variability of Maipo and Rapel river plumes off central Chile

“…Choi and Wilkin (2007) demonstrated the strong influence of buoyancy and wind forcing on the Hudson River plume. Similar findings were described for the Yukon River plume by Clark and Mannino (2022). The change of river plume direction caused by winds associated with the passage of low atmospheric pressure systems was investigated using the Navy Coastal Ocean Model (Cobb et al, 2008).…”

The Transformation and Export of Organic Carbon Across an Arctic River‐Delta‐Ocean Continuum

“…The coastal currents where the Yukon flows into the ocean at the southwest edge of Norton Sound drive water northward through the Bering Strait where transport and freshwater content has increased over the last two decades (Woodgate, 2018 ). There is a substantial anti‐cyclonic eddy that increases residence time in the plume and moves water into meandering currents in Norton Sound (Clark & Mannino, 2022 ). The watershed is 830,000 km 2 (Figure 1a ) and contains 24% forest, 19% grassland and 60% discontinuous + continuous permafrost (HydroATLAS; Lehner et al., 2022 ; Linke et al., 2019 ).…”

“…The hydrodynamics of the lower Yukon River and coastal ocean are simulated using a high‐resolution regional implementation of the Finite Volume Community Ocean Model (FVCOM version 4.3) (Chen et al., 2003 ; Clark & Mannino, 2022 ). FVCOM is a three‐dimensional ocean circulation model developed to predict many physical properties of ocean systems on an unstructured triangular grid (Chen et al., 2003 ).…”

Arctic biogeochemical and optical properties of dissolved organic matter across river to sea gradients

“…The YukonFVCOM hydrodynamic model (Clark and Mannino, 2022) was used to determine the proportion of the water volume measured at Pilot Station that passes through the primary river mouths and Emmonak Channel. The model assumes that on average no water is gained (lower watershed inflow) or lost (e.g., evaporation) during passage from Pilot Station to the delta.…”

“…When the plume was sampled during the Norton Sound transect about ten days later, the hydrograph had already peaked at Pilot Station (Figure 2). Because of the lag time in water transport between Pilot Station and Norton Sound (~11-13 days for plume region and ~3 days to the Yukon Delta during peak freshet (Clark and Mannino, 2022), this approximate ten-day period was likely when the greatest amount of DOM was transported from the river channels to a great distance into Norton Sound (Figures 1C and 4B).…”