Exchange of Water Between the Ross Gyre and ACC Assessed by Lagrangian Particle Tracking

• Published in: Journal of geophysical research. Oceans Vol. 124; no. 7; pp. 4631 - 4643
• Main Authors: Roach, Christopher J., Speer, Kevin
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01-07-2019; Wiley-Blackwell
• Subjects: Antarctic Circumpolar Current; Antarctic front; Antarctic zone; Components; Dense water; Downwelling; Exchanging; Fracture zones; Geophysics; Global climate; Ice cover; Inflow; Mathematical models; Numerical experiments; Numerical models; Ocean circulation; Ocean currents; Oceans; Particle tracking; Physics; Polar fronts; Ross Gyre; Sciences of the Universe; Sea ice; Slope currents; Southern Ocean; Transport; Upwelling; Variability; Velocity distribution; Water masses; Ross Sea; World Fracture Zones; Southern Ocean
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1029/2018JC014845

To reach upwelling and downwelling zones deep within the Southern Ocean seasonal sea ice cover, water masses must move across the Antarctic Circumpolar Current and through current systems including the Ross Gyre, Weddell Gyre, and Antarctic Slope Current. In this study we focus our attention on the Lagrangian exchange between the Ross Gyre and surrounding current systems. We conducted numerical experiments using five‐day 3‐D velocity fields from the Southern Ocean State Estimate with a particle tracking package to identify pathways by which waters move from near the Antarctic coastal margins or Antarctic Circumpolar Current into the interior of the Ross Gyre, and to identify the time scales of variability associated with these pathways. Waters from near the Antarctic margins enter the Ross Gyre along the western and northern boundaries of gyre until the gyre separates from the Pacific‐Antarctic Ridge near fracture zones. At this juncture, Antarctic Circumpolar Current‐derived inflow dominates the across‐gyre transport up to the Antarctic margin. Transport and exchange associated with different time‐average components of flow are calculated to determine the relative contributions of high‐ and low‐frequency and time‐mean components.
Plain Language Summary
Formation of cold, dense waters in the Antarctic Zone south of the Polar Front plays a key role in driving the overturning circulation, with major implications on global climate. One of the key regions of dense water formation is the Ross Sea. However, between the Ross Sea and the wider Southern Ocean lies the Ross Gyre. So we need to understand how the Ross Gyre controls exchange between the continent and the Southern Ocean. We use velocities from a numerical model to track virtual water parcels as they move into the gyre. This lets us estimate total inflow and identify pathways the water takes to enter the gyre. We find that inflow into the Ross Gyre is enough to replace outflowing dense waters from the Ross Sea. We also find that most inflow enters via exchange with Antarctic Circumpolar Current at the northern and eastern limits of the gyre through a combination of eddy activity and low‐frequency variability in the gyre boundary.
Key Points
Using numerical particle tracking we examine the location and vertical structure of inflow to the Ross Gyre
We estimate that 2.6 Sv enters the gyre from the ACC and 2.9 Sv from the AA margins
Most of the inflow from the ACC into the gyre is associated with low‐frequency variability