Properties of Antarctic Bottom Water in the Western Gap (Azores-Gibraltar Fracture Zone, Northeast Atlantic) in 2021

Abstract

We present the results of measurements of thermohaline and dynamical structures, as well as hydrochemical parameters of near-bottom water in the Western Gap (Azores-Gibraltar Fracture Zone, Northeast Atlantic). The data were collected during cruise 59 of the research vessel Akademik Ioffe in October 2021. The results of the analysis showed that water with potential temperatures lower than 2.00 °C had crossed the Entrance Sill, but was not detected inside the interior basin of the Western Gap. The velocities of currents at the Entrance Sill were high (up to 30 cm/s) leading to mixing of the water overflowing the sill. While Antarctic Bottom Water (AABW) flows from the Entrance Sill to the Exit Sill it is subjected to modification. Bottom water becomes less dense after the sill due to mixing during overflow and in addition not all cold water overflows the sill. The dissolved oxygen concentration in the bottom layer increases from the Entrance Sill (239–242 μmol/kg) to the Exit Sill (241–248 μmol/kg) indicating the transformation of AABW as it circulates in the Western Gap and mixes with North Atlantic Deep Water propagating from the north. All velocity measurements indicate that north velocity component is a characteristic property of the bottom flow. Thus, water with specific chemical composition of AABW is transported to the Iberian Basin despite that its potential temperature becomes higher than 2 °C.