Deep‐Ocean Circulation in the Southwest Pacific Ocean Interior: Estimates of the Mean Flow and Variability Using Deep Argo Data

• Published in: Geophysical research letters Vol. 47; no. 13
• Main Authors: Zilberman, N. V., Roemmich, D. H., Gilson, J.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 16-07-2020
• Subjects: Abyssal circulation; Abyssal plains; Abyssal zone; Boundary currents; Circulation; Deep Argo; deep‐ocean circulation; Depth profiling; Drifters; Ekman pumping; Floats; Ocean circulation; Ocean currents; Ocean floor; Ocean surface; Oceanic trenches; Oceans; Profiles; Return flow; Sampling; Sea surface; Seasonal variations; Seasonality; Southwest Pacific Basin; Spatial data; Variability; Water circulation; Asia-Pacific region; Tonga
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2020GL088342

The spatial structure and time variability of the global deep‐ocean circulation are poorly understood due to limited sampling below 2,000‐m depth. A Deep Argo array deployed in 2016 has significantly increased oceanic measurements from the ocean surface to near the sea floor in the Southwest Pacific Basin interior. Deep Argo profiles collected between 2016 and 2019 show that 4.3–4.7 Sv between 1,500 and 4,800 m, relative to 4,800 m, of the Deep Western Boundary Current flowing along the Tonga Kermadec Ridge is redirected southward over the abyssal plain between the Tonga Kermadec Ridge and the East Pacific Rise. The southward recirculation of the Deep Western Boundary Current exhibits seasonality that may be influenced by Ekman pumping.
Plain Language Summary
Observations of the deep‐ocean circulation are important for understanding long‐term changes in fundamental ocean properties, including temperature and salinity. A newly developed technology, Deep Argo profiling floats, has been deployed in the Southwest Pacific Basin to increase oceanic sampling from the ocean surface to the sea floor. Using this new data set, the circulation in the abyssal Southwest Pacific Basin is mapped outside the Deep Western Boundary Current. Our study shows that part of the deep current flowing northward along the 2,000‐km long Tonga Kermadec trench, between the northern tip of New Zealand and the Samoan islands, is redirected southward in the basin interior between 1,500–4,800 m depth. The southward deep return flow may be influenced by the wind‐forcing on the sea surface, whose effects are seen to penetrate into the deep‐ocean.
Key Points
Part of the deep western boundary current flowing northward along the Tonga Kermadec Ridge is redirected southward between 1,500 and 4,800 m
Seasonal fluctuations in the upper 2,000 m of the Southwest Pacific Basin are continued into the abyssal ocean with decreasing amplitude
Deep Argo provides estimates of the deep‐ocean circulation complementary to repeat hydrography and moored observations