Oceanographic atlas of the International Indian ocean expedition

The Agulhas Current Transports Signals of Local and Remote Indian Ocean Nitrogen Cycling

“…These waters occupy a similar density range but have different formation histories, making them easily distinguishable by salinity and AOU, as well as by their physical partitioning across the Agulhas Current core (Figures 3–5; Table 1; Beal et al., 2006). TTW underlies Tropical Surface Water (TSW; σ θ < 24.5 kg.m −3 ), with both water masses forming in the warm, fresh tropical latitudes (approximately 5–25°S) where precipitation exceeds evaporation and fresh Indonesian Through Flow waters are supplied by the South Equatorial Current (SEC; Figure 1) (Gordon, 1987; Gordon et al., 1997; Wyrtki, 1971). STTW underlies Subtropical Surface Water (STSW; σ θ < 25.5 kg.m −3 ), with both water masses forming in the more saline subtropical gyre (25–35°S, east of 90°E) where evaporation exceeds precipitation (Beal et al., 2006; Gordon, 1987; Wyrtki, 1971).…”

“…TTW underlies Tropical Surface Water (TSW; σ θ < 24.5 kg.m −3 ), with both water masses forming in the warm, fresh tropical latitudes (approximately 5–25°S) where precipitation exceeds evaporation and fresh Indonesian Through Flow waters are supplied by the South Equatorial Current (SEC; Figure 1) (Gordon, 1987; Gordon et al., 1997; Wyrtki, 1971). STTW underlies Subtropical Surface Water (STSW; σ θ < 25.5 kg.m −3 ), with both water masses forming in the more saline subtropical gyre (25–35°S, east of 90°E) where evaporation exceeds precipitation (Beal et al., 2006; Gordon, 1987; Wyrtki, 1971). TTW is thus a comparatively fresh thermocline water mass (salinity of 35.4–35.6 g.kg −1 ) compared to its subtropical counterpart (salinity >35.7 g.kg −1 ) (Figures 2a and 3).…”

“…Surface waters : At formation, TSW ( σ θ < 24.5 kg.m −3 ) is particularly fresh (salinity <35.0 g.kg −1 ). During the westward transit of TSW to the Mozambique Channel, the incorporation of Arabian Sea surface waters increase its salinity, such that in the western channel, TSW is characterized by salinities ≥35.3 g.kg −1 (mean of 35.4 ± 0.05 g.kg −1 ; Figure 3 and Table 2) (DiMarco et al., 2002; Donohue & Toole, 2003; Wyrtki, 1971). TSW salinity is further increased to 35.6 ± 0.51 g.kg −1 inshore of the Agulhas Current (Figure 3 and Table 1), likely also due to the lateral entrainment of more saline STSW by southward propagating Mozambique Channel eddies.…”

Environmental Controls of Size Distribution of Modern Planktonic Foraminifera in the Tropical Indian Ocean

“…Within the TIO (31°N, 31°S, 20–120°E), mean annual SST ranges from 18°C (southern part; July–October) to >30°C (northern part; April–May) (Locarnini et al., 2018; L. V. G. Rao & Ram, 2005). Meanwhile, sea surface salinity ranges from 30 to 36 psu, dissolved oxygen concentration ranges from 189 to 255 μmol kg −1 , surface Chl‐a concentration ranges from 0.1 to 0.5 mg m −3 , and carbonate ion content of surface waters ranges from 200 to 280 μmol kg −1 , with an average of >220 μmol/kg (Broecker & Sutherland, 2000; Garcia et al., 2018a; Lovenduski et al., 2015; L. V. G. Rao & Ram, 2005; Wyrtki, 1971; Zweng et al., 2018).…”

“…Due to its proximity to the Persian Gulf and Red Sea, the Arabian Sea has an upper layer of highly saline waters and experiences more evaporation than precipitation (Levitus, 1982; L. V. G. Rao & Ram, 2005). The Bay of Bengal receives high freshwater inputs via river discharge from abundant precipitation during the southwest (summer) monsoon, resulting in a low‐salinity upper layer and a stratification dominated by salinity gradients rather than temperature gradients (L. V. G. Rao & Ram, 2005; Wyrtki, 1971). In the Arabian Sea, wind‐driven coastal upwelling in the west is strong during the southwest monsoon and vertical mixing is also enhanced during the northeast monsoon, promoting higher productivity (Barber et al., 2001).…”