Seasonality of Warm Water Intrusions Onto the Continental Shelf Near the Totten Glacier

Abstract

Warm Modified Circumpolar Deep Water (MCDW) from the Southern Ocean drives rapid basal melt of the Totten Ice Shelf on the Sabrina Coast (East Antarctica), affecting the mass balance of the grounded Totten Glacier. Recent observations show that MCDW intrudes onto the continental shelf through a depression at the shelf break. Here we investigate such intrusions by combining (1) new oceanographic and bathymetric observations collected for two consecutive years by profiling floats in the depression south of the shelf break, (2) oceanographic measurements collected by conductivity‐temperature‐depth‐instrumented seals on continental slope, and (3) an ocean model. The depression provides a pathway for persistent inflow of warm (0‐1°C) MCDW to the inner shelf. In austral autumn and early winter MCDW intrusions were up to 0.5°C warmer and were ~75 m thicker than in spring and summer. The seasonality of the flow on the continental slope explains the seasonality of the intrusions. The MCDW layer on the continental slope is warmer and thicker to the east of the depression than to the west. In autumn and early winter a strong, top‐to‐bottom westward current (Antarctic Slope Current) transports the warmer and thicker MCDW layer along the slope and is diverted poleward at the eastern entrance of the depression. A bottom‐intensified eastward current (Antarctic Slope Undercurrent) develops in other months, allowing cooler and thinner intrusions to enter the depression from the west. Our study illustrates how circulation on the Antarctic slope regulates the ocean heat delivery to the continental shelf and ultimately to the ice shelves.

Wind-Driven Processes Controlling Oceanic Heat Delivery to the Amundsen Sea, Antarctica

“…A narrow eastward undercurrent has been documented in several areas around Antarctica, at the shelf break and continental slope, by closely spaced hydrographic measurements and high-resolution models (Heywood et al 1998;Smedsrud et al 2006;Nuñez-Riboni and Fahrbach 2009;Chavanne et al 2010;Silvano et al 2019). Based on our results and previous works (e.g., Walker et al 2013;Kimura et al 2017;Webber et al 2019), it may be concluded that this undercurrent feature is an important element of the oceanic heat delivery toward the ice shelves.…”

Aurora Basin, the Weak Underbelly of East Antarctica

“…Li et al () reported a mass loss from Totten of 6.8±2.2 Gt/year with an acceleration of 0.55±0.27 Gt/year 2 between 1989 and 2015. This acceleration in grounded ice flux has been linked to intrusions of warm Modified Circumpolar Deep Water (0–1 °C) into Totten's subice shelf cavity (Greenbaum et al, ; Li et al, ; Mohajerani et al, ; Rintoul et al, ; Silvano et al, , ). Additionally, a 1‐ to 3‐km retreat of the southernmost portion of Totten's grounding line was observed between 1996 and 2013, concurrent with changes in subshelf ocean temperature (Li et al, ).…”

Aurora Basin, the weak underbelly of East Antarctica

“…Li et al (2016) reported a mass loss from Totten of 6.8 ± 2.2 Gt/year with an acceleration of 0.55 ± 0.27 Gt/year 2 between 1989 and 2015. This acceleration in grounded ice flux has been linked to intrusions of warm Modified Circumpolar Deep Water (0-1 • C) into Totten's subice shelf cavity (Greenbaum et al, 2015;Li et al, 2016;Mohajerani et al, 2018;Rintoul et al, 2016;Silvano et al, 2017Silvano et al, , 2019. Additionally, a 1-to 3-km retreat of the southernmost portion of (total 36) that predict at least 1-m grounded ice thinning by 2100.…”