The extreme northern jet of the Antarctic Circumpolar Current

Abstract

We analyze the location of the extreme northern jet of the Antarctic Circumpolar Current based on the measurements in cruise 79 of the R/V Akademik Mstislav Keldysh to the region of the Drake Passage in February-March 2020. The jet occupies a position over the slope of Tierra del Fuego Island over a depth range of 400-600 m based on the measurements along four sections using the shipborne SADCP and CTD/LADCP casts. The width of this coastal jet is about 15-20 km. It penetrates to the depths of 200-300 m. The jet follows the direction of isobaths. Velocities in the jet reach 40 cm/s. It is likely that this jet is a local one and does not continue along the entire circle around Antarctica, but based on the satellite data of the absolute dynamical topography (ADT) this jet continues into the shallow region between Tierra del Fuego and Falkland Islands.

Structure of the bottom water flow in the Vema Channel based on the measurements from the R/V Akademik Sergey Vavilov

“…The bottom Ekman friction induces secondary helical circulation relative to the general current, which displaces the coldwater core to the right (to the east if the current is directed to the north) in the Southern Hemisphere [Johnson et al, 1976]. In the Southern Hemisphere, the Ekman friction is directed to the right of the flow, which agrees with the modeling results of [Frey et al, 2017b[Frey et al, , 2019bJungclaus and Vanicek, 1999;Morozov et al, 2020b].…”

“…Many times, this section was extended to the west beyond the western slope of the channel. In addition to the strong flow of bottom wa- ter along the bed of the channel, another jet is found over the western slope of the channel approximately 300-400 m shallower than the deepest one [Morozov et al, 2018[Morozov et al, , 2020aTarakanov et al, 2020]. The cold core of this flow is displaced to the west relative to the center of the channel.…”

“…Current velocities were measured by a Lowered Acoustic Doppler Current Profiler (LADCP, RDI WH Sentinel, 300 kHz) mounted together with the CTD on the SBE 32 rosette (Carousel Water Sampler). The measurements stopped at a distance of 3-7 m above the bottom double checked by an altimeter (model Benthos PSA-196) and a pinger (Benthos Co) [Frey et al, 2017a;Morozov et al, 2020b].…”

“…The bottom waters of Antarctic origin flow from the Argentine Basin to the Brazil Basin along three pathways: through the Vema Channel, through the Hunter Channel, and over the Santos Plateau. Among them, the Vema Channel is the main pathway for the flow of AABW [Morozov et al, 2020a]. The depths of the Vema Channel exceed 4600 m, while the background depths of the Santos Plateau and Hunter Channel are approximately 4000-4200 m. The Vema Channel is a narrow passage between two terraces with a minimum width slightly greater than 15 km.…”