Barotropic Kelvin Wave‐Induced Bottom Boundary Layer Warming Along the West Antarctic Peninsula

Abstract

Intrusions of warm circumpolar deep water onto the Antarctic continental shelf are thought to drive accelerated loss of Antarctic glacial ice mass by triggering melt at the ice shelf grounding line. However, the mechanisms responsible for driving on‐shelf circumpolar deep water intrusions are not well understood. Here we examine how sea surface height (SSH) anomalies propagating around the Antarctic coastline as coastal‐trapped waves can drive warm water intrusions through changes in bottom Ekman transport. A wind perturbation motivated by the recent intensification and poleward shift of the southern annular mode during its positive phase is applied over Eastern Antarctica between 20°E and 120°E in two global ocean sea‐ice models (1/4° and 1/10°) and a single‐layer shallow water model. The changes in winds generate a drop in coastal SSH that propagates around Antarctica as a barotropic Kelvin wave. The SSH drop is accompanied by a barotropic flow, which alters the bottom stress, generating an onshore transport of warm water wherever thermal gradients are favorable. We estimate the resulting anomalous bottom Ekman flow and use temperature gradients calculated from the Southern Ocean State Estimate, along with the 1/4° and 1/10° models, to evaluate the resultant heat advection. We find that this mechanism can drive warming of up to 0.7 °C along the West Antarctic Peninsula within a year, depending on the mean state of the cross‐shelf temperature gradient and the barotropic flow strength. Over longer time scales, warming eventually ceases due to saturation of the SSH field and arrest of the Ekman transport by buoyancy forces.

Control of the Oceanic Heat Content of the Getz‐Dotson Trough, Antarctica, by the Amundsen Sea Low

“…On longer time scales (e.g., decades and longer), it is possible that variations in the large‐scale winds may lead to changes in the water masses carried by the Antarctic Circumpolar Current, which could affect the margins of West Antarctica (Nakayama et al, 2018). A potential role for remote winds in shaping the on‐shelf heat content of the Amundsen Sea via propagation of coastal‐trapped waves has also been highlighted (e.g., Spence et al, 2017; Webb et al, 2019).…”

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

“…In the present work, we analyzed the local forcings and processes governing temperature variability on the Amundsen Sea continental shelf. However, one must keep in mind that remote drivers might also affect the region's heat content via changes in the pathways or properties of offshore water masses (Nakayama et al 2018), and/or the remote wind-forced generation and propagation of barotropic Kelvin waves around Antarctica (Kusahara and Ohshima 2014;Spence et al 2017;Webb et al 2019). While our results are most relevant for temperature changes in the Amundsen Sea on time scales of months to years, remote forcings are likely to exert an increasingly important influence on temperature variability on longer time scales (Spence et al 2014;Nakayama et al 2018), which may affect the ice shelves' configuration over periods of decades to centuries (Jenkins et al 2018).…”

“…Nakayama et al (2018) suggested that the offshore CDW characteristics advected from afar, that is, by the large-scale ocean circulation, might be as important as regional atmospheric forcing in setting the temperature variability on the Amundsen Sea continental shelf. Further, barotropic Kelvin waves, generated by wind forcing elsewhere around Antarctica and propagating along continental margins, have been indicated as a possible regulator of oceanic heat content off West Antarctica (Spence et al 2017;Webb et al 2019), with consequences for coastal temperatures in future wind-changing scenarios (Spence et al 2014).…”

Water Mass Characteristics of the Antarctic Margins and the Production and Seasonality of Dense Shelf Water

“…The Antarctic Circumpolar Current, the continental slope, and the Antarctic Slope Front present dynamical barriers to the intrusion of CDW onto the continental shelf, which is broken by mean (Rodriguez et al, ) and mesoscale processes that can drive CDW across these fronts (Gille et al, ; Heywood et al, ; Klinck & Dinniman, ). These processes include bottom Ekman transport (Dinniman & Klinck, ), eddies (Thompson et al, ), tides (Padman et al, ), mean transport (Stewart et al, ), cross‐slope canyon steered flow (St‐Laurent et al, ), and Kelvin wave‐driven undercurrents (Chavanne et al, ; Webb et al, ). Petty et al () used mixed‐layer models to show that atmospheric forcing plays an important role in determining CDW intrusion onto the continental shelf.…”