Fig. 4.

Topographically upwelled waters in the vicinity of the Antarctic Circumpolar Current along the SWIR. Maps of the eddy kinetic energy (EKE) at the surface (a) and at depth (b, approximately 1000 meters). The surface EKE was derived from altimetry-derived velocities (AVISO MADT daily product) over the 2003–2017 period. The deep EKE was calculated from the Argo-derived velocities during their parking depth and available in the ANDRO dataset (2000–2016). The maximum depth-integrated biomass (mg Chl a m⁻²) is also depicted according the size of the dots (triangle: float WMO 6901585 and circle: float WMO 2902130). c Maps of bathymetry of the SWIR, the Andrew Bain fracture zone (as indicated by the dashed box; http://www.marineregions.org/gazetteer.php?p=details&id=7253) and the two meridional sections at 28°E and 38°E (between latitude 47°–55°S; plain black lines) where the difference in potential density Δσ shown in panel d was determined. d Climatological difference of potential density, Δσ, between the two meridional sections at 38°E and 28°E in the upper 2000 m (between latitude 47°–55°S). Gray shading represents the mean bottom topography between 28 and 38°E, and the red arrows are provided to show the sense of downstream isopycnal adjustment at 750-m depth. The difference in Δσ is an alongstream difference across the two sections, which is converted back to latitude for ease of reading (therefore referred to as pseudo-latitude). See the Methods for more details. e–f Satellite altimetry-derived Lagrangian modeling of the iron pathways from the departure of the SWIR as shown in e age (days since having left the SWIR) and in f iron delivery. Black circles in e–f indicate the origin of the iron pathways in the surface layer. The red stars in a–c, e and f are related to the position of hydrothermal vents from Tao et al.¹⁴. The continuous and dashed gray lines indicate, respectively, the bathymetry (a, b, e and f) of the SWIR (contour levels: 2000, 3000, and 4000 m) and the isopycnals (d)