Strong export of Antarctic Bottom Water east of the Kerguelen plateau

Abstract

The horizontal coherence and duration of the array allowed accurate estimates of the transport and structure of the Kerguelen DWBC.The DWBC forms a narrow (~50 km wide), intense, bottom-intensified flow to the northwest over the lower flank of the plateau, with a flow to the southeast further offshore (Fig. 2). The currents are remarkably strong for these depths: maximum two-year mean speed exceeds 20 cm s -1 at ~3500 m depth at M6 (the largest DWBC speeds yet observed at similar depths; Supplementary Table 1 The similarity between the moored results and the synoptic snapshots indicates that the limited vertical resolution of the moored instruments is sufficient to capture the DWBC structure.The daily velocity and potential temperature data are used to calculate the 4 AABW transport per unit width (Fig. 3a). The northwestward transport of AABW is concentrated between M4 and M6, with the largest value observed at M5 where the velocities are large and the AABW layer is thick (Fig. 2). Northwestward transport is commonly observed to extend offshore as far as M3 (~38 km is within the 95% confidence intervals of the mean after 9 months, indicating that the records are of sufficient length to establish a stable mean. The overall impression is of a narrow, intense and relatively steady deep boundary current, modulated by topographic waves and the episodic influence of fronts and meanders of the ACC.This DWBC is associated with a mean temperature transport of -2.52±0.26 Sv °C 5 northwestward.Snapshot estimates based on CTD/ADCP measurements are in agreement with the observations from the moored array, with the exception of the deployment cruise (Fig. 3b, Supplementary Table 2). However, these estimates sampled periods of larger than average transport (Fig. 3b) Several factors make it difficult to assess the relative contribution of the Kerguelen DWBC to the Southern Ocean overturning. These include the presence of recirculation gyres, interaction between the DWBC and other circulation regimes (e.g., the ACC and subpolar gyres) 8 , the fact that mixing and entrainment change the volume and properties of AABW along the export pathway 13 , and the lack of coherent long-term observations in other DWBCs. The only previous coherent current meter measurements of AABW export by a DWBC south of 45°S were obtained north of the Falkland Plateau, where a net transport of 1.9 Sv of Weddell Sea Deep Water (θ < 0.2°C) was found to enter the Argentine Basin (the difference between 8.2 Sv westward and 6.3 Sv recirculating to the east) 8 . In comparison, the net transport of water with θ < 0.2°C by the Kerguelen DWBC is 8.0 Sv (16.4 Sv to the northwest and an 8.4 Sv recirculation to the southeast). Incoherent multi-year moored measurements in the northwest Weddell Sea reveal relatively weak currents (deep mean flows < 7 cm s -1 ) 11 . Combining these 6 current-meter data with CTD sections gives a net export of 3.8 Sv of AABW (θ < 0°C) from the Weddell Sea 14 ; based on an inverse model, an additional 4.7 Sv may leave the Weddell Sea ac...

Influence of Ross Sea Bottom Water changes on the warming and freshening of the Antarctic Bottom Water in the Australian-Antarctic Basin

“…At I8S section across the western side of the basin at 82-93 • E, the repeated sections were within 2 to 3 months of each other. This section is the furthest from the source regions (over 2500 km) and so we expect the seasonal variability to be negligible, as reported for a two-year mooring array close to I8S section by Fukamachi et al (2010). Decadal changes in the AA-AABW are examined by comparing the meridional variation of potential temperature ( • C), salinity, neutral density (γ n kg m −3 ) and apparent oxygen utilization (AOU µmol kg −1 ) averaged over a 100 m-thick layer at the bottom (Fig.…”

“…AA-AABW flows westward over the continental slope and rise of Wilkes Land towards the Kerguelen Plateau, where it turns north along the plateau (e.g. Fukamachi et al, 2010) until it joins the lower part of the Antarctic Circumpolar Current (ACC) that flows to the east (Orsi et 1999). AA-AABW exits the basin through the Princess Elisabeth Trough (PET) and the Australian-Antarctic Discordance (e.g.…”

The Southern Ocean and Its Climate in CCSM4

“…In the ocean, AABW is transported to the global abyssal ocean in deep western boundary currents east of the Kerguelen Plateau (Fukamachi et al 2010) and off the Antarctic Peninsula in the Weddell Sea (Gordon et al 2001;Fahrbach et al 2001). The CCSM4 features a strong northward current off the Kerguelen Plateau in the Australian-Antarctic Basin (AAB; not shown).…”

“…Entrainment processes increase the volume and modify the properties of the dense shelf water masses as they overflow off the Antarctic continental shelves into the abyssal ocean (Legg et al 2009). AABW is transported to the global abyssal ocean in deep western boundary currents east of the Kerguelen Plateau (Fukamachi et al 2010) and off the FIG. 1.…”

Late Oligocene obliquity-paced contourite sedimentation in the Wilkes Land margin of East Antarctica: implications for paleoceanographic and ice sheet configurations

“…Several authors have postulated that oxygen-depleted 610 Antarctic Bottom Water (AABW) occupying the abyssal zones of the oceans can change the redox conditions in the sediment, trapping and preserving dissolved and particulate organic matter and, consequently reducing and dissolving both, biogenic and detrital magnetite (Florindo et al, 2003;Hepp et al, 2009;Korff et al, 2016). At present, Site U1356 is influenced by AABW forming in the adjacent Wilkes Land shelf (Orsi et al, 1999;Fukamachi et al, 2000) and in the Ross Sea spilling over to the 615 Wilkes Land continental shelf (Fukamachi et al, 2010) (Fig. 1).…”