Seasonal to Decadal Western Boundary Current Variability From Sustained Ocean Observations. Issue 12 (21st June 2022)

• Record Type: Journal Article
• Authors: Chandler, M.; Zilberman, N. V.; Sprintall, J.
• Is Part Of: Geophysical research letters. Volume 49:Issue 12(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-06-21
• Subjects: western boundary current -- East Australian Current -- Agulhas Current -- Kuroshio -- ocean observations; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2022GL097834
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Subtropical western boundary currents (WBCs) exert a substantial influence on regional climate. To improve WBC observations on seasonal‐to‐decadal timescales, and characterize their subsurface structure to 1975 m depth, we combine high‐resolution expendable bathythermograph, Argo, and satellite altimetry observations in the Agulhas Current, East Australian Current, and Kuroshio. The resulting 16 year time series (2004–2019) show a weakening trend in Kuroshio transport, but no trend in Agulhas transport or East Australian Current transport. All three WBCs have stronger transport in summer, driven mostly by changes in current speed rather than current width. This unique subsurface view of WBC variability reveals changes in the path of the Kuroshio Extension on interannual timescales, and eddy variability in the Agulhas. Our work highlights how this application of a consistent methodology to combine complementary ocean observations allows for an unprecedented direct comparison of variability between WBCs. Plain Language Summary: Western boundary currents are major ocean currents located on the western side of the world's oceans. These currents transport warm water toward the poles, which influences regional weather and climate. However, despite their importance, the fast speeds, high variability, and narrow width of these currents makes them difficult to observe. Here we examine the western boundary currents (WBCs) of the Indian Ocean (Agulhas Current) and Pacific Ocean (East Australian Current and Kuroshio) using measurements from three different ocean observing networks. The same method is applied to each current, allowing us to compare variability in the three currents. Between the start of 2004 and end of 2019 we find that transport of water has decreased in the Kuroshio but has not changed in the Agulhas or East Australian Current. We find changes in the path of the Kuroshio on interannual time scales, and shorter and irregular changes in the path of the Agulhas. On annual time periods, all three currents transport more water in summer than winter, which is related to faster speeds during the summer. These long subsurface time series can help us better understand how WBC variability impacts society at the western boundaries of the ocean. Key Points: Combining ocean observations allows estimation of western boundary current (WBC) variability between 0 m and 1975 m depth over 2004–2019 A decrease was observed in Kuroshio transport, no significant change was observed in Agulhas or East Australian Current transport Transport in all three WBCs is greatest in summer and related to coincident changes in core speed