A Deep Eastern Boundary Current Carrying Indian Deep Water South of Australia

• Published in: Journal of geophysical research. Oceans 2019-03, Vol.124 (3), p.2218-2238
• Main Authors: Tamsitt, V., Talley, L. D., Mazloff, M. R.
• Format: Article
• Language: English
• Subjects: Antarctic Circumpolar Current; Basins; Boundaries; Boundary currents; Carbon; Carbon exchange; Continental slope; deep ocean; Deep water; Deep western boundary currents; Eastern boundary currents; Flinders Current; Geophysics; Heat exchange; hydrography; Indian Ocean; Lagrangian particle tracking; Mineral nutrients; Ocean currents; Ocean models; Oceans; Oxygen; Sea currents; Sea surface; Ships; Southern Hemisphere; Transport; Volume transport; Water flow; water masses; Western boundary currents
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1029/2018JC014569

In the Southern Hemisphere, the ocean's deep waters are predominantly transported from low to high latitudes via boundary currents. In addition to the Deep Western Boundary Currents, pathways along the eastern boundaries of the southern Atlantic, Indian, and Pacific transport deep water poleward into the Southern Ocean where these waters upwell to the sea surface. These deep eastern boundary currents and their physical drivers are not well characterized, particularly those carrying carbon and nutrient‐rich deep waters from the Indian and Pacific basins. Here we describe the poleward deep eastern boundary current that carries Indian Deep Water along the southern boundary of Australia to the Southern Ocean using a combination of hydrographic observations and Lagrangian experiments in an eddy‐permitting ocean state estimate. We find strong evidence for a deep boundary current carrying the low‐oxygen, carbon‐rich signature of Indian Deep Water extending between 1,500 and 3,000 m along the Australian continental slope, from 30°S to the Antarctic Circumpolar Current southwest of Tasmania. From the Lagrangian particles it is estimated that this pathway transports approximately 5.8 ± 1.3 Sv southward from 30°S to the northern boundary of the Antarctic Circumpolar Current. The volume transport of this pathway is highly variable and is closely correlated with the overlying westward volume transport of the Flinders Current. Plain Language Summary Heat and carbon exchange between the atmosphere and the ocean has a big impact on our climate. It is important to understand the routes by which the ocean delivers heat and carbon to the sea surface. In the Southern Hemisphere, deep waters (below 1,000‐m depth) flow southward toward Antarctica along the boundaries of the Atlantic, Indian, and Pacific Oceans. In the Indian and Pacific Oceans, the eastern boundaries carry old, carbon‐rich waters south until they reach the sea surface in the Southern Ocean. However, many aspects of the deep southward flow from the eastern Indian Ocean are not well understood. Although this flow was identified in observations from ships in the 1990's, there are few observations and the importance of this deep flow has not been fully appreciated. The goal of this study is to describe the Indian deep eastern boundary current by revisiting observations from ships and tracking virtual particles in an ocean model. The results show that deep water from the Indian Ocean flows along the southern coast o