The Role of the Russian Shelf and Eurasian Basin on the Beaufort Gyre and Arctic Freshwater Content
Abstract
The Arctic Ocean is characterized by its strong stratification structure, primarily determined by salinity variations. Freshwater has changed more frequently in the Arctic Ocean in recent years due to differing rate of sources/transport pathways and exports especially within the Beaufort Gyre (BG). The BG serves as a large freshwater reservoir within the Arctic Ocean, where its accumulation and retention are influenced by wind forcing, surface currents among ice-ocean stress, and eddy-induced circulation and diffusivity. The BG, an ocean current that circulates in a clockwise motion, encompasses a large amount of the total freshwater in the Arctic Ocean. Depending on changes in the gyre#s characteristics such as its strength and vertical movement, the amount of freshwater added can increase or decrease. In the last few decades (years), the BG has experienced anomalous freshening followed by its stabilization between 2007-2008. However, there is limited understanding of the role that the Russian Arctic Shelf and Eurasian basin plays in the Arctic Ocean#s FWC. This region has often been overlooked in terms of FWC. The Russian Arctic Shelf exhibits a wide range of salinity variability due to seasonal sea ice advance and retreat as well as discharge from major rivers. The largest three rivers are the Ob and Yenisei (flowing into the Kara Sea), and Lena (flowing into the Laptev Sea) that combined contribute ~2,300 km3/yr; this is roughly half of total discharge from all rivers flowing into the Arctic Ocean. The Russian Shelf contributes around 16% of freshwater content to the Arctic Ocean#s storage with a decreasing trend that is mainly influenced by the Kara and Laptev Seas. Notably, the Russian Shelf experienced a significant decrease in freshwater content during 2007, when the BG coincidentally accumulated a large amount of fresh water, possibly owing to a change in ocean currents. Neglecting the Russian Shelf creates an error of up to 25% in assessing Arctic Ocean freshwater volume change across the 2007 regime transition. For investigating the subsurface mixing processes in BG, we will use the rescaled potential vorticity (PV) along water mass trajectories in the BG. When calculated within an isopycnal layer, PV is conserved adiabatically through the impermeability theorem. This allows us to combine calculations of PV with calculations of the Richardson number to determine what changes in PV must have been due to different diabatic processes, including diapycnal mixing and friction with the boundaries. In this proposed project we will employ this technique in conjunction with Lagrangian particle tracking, allowing us to project the transport pathways of specific water masses, such as the front between the Chukchi Sea water and the BG water, forward and backward in time across the Russian Arctic Shelf, the BG, and the rest of the Arctic Ocean and export pathways beyond. By performing this analysis in each of our models as well as in in-situ measurements where possible, we will be able to diagnose the sources and strengths of water mass mixing and FWC alterations throughout time and space, accounting for climatological shifts in salinity and temperature. This project highlights the drawbacks and advantages of utilizing ocean model simulations (ECCO, MIZMAS, HYCOM, NEMO) and Reanalysis products (ORAS5, GLORYS12 and SODA3) for a comprehensive understanding of the Arctic Ocean#s physical dynamics. In addition to FWC in the BG, we also investigate the strength, structure, and variability of the BG using the altimetry Dynamic Ocean Topography (including recently launched NASA#s Surface Water Topography Mission (SWOT) altimetry data) and model simulations, and transport pathways of water in the Arctic Ocean using these suite of model simulations and reanalysis products. The rescaled isopycnal PV is also used in the context of Lagrangian particle tracking in this study.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Nov 08, 2024
- Source ID
- N000142412635
Entities
People
- Bulusu Subrahmanyam
Organizations
- Office of Naval Research
- United States Navy
- University of South Carolina