Influence of Shelf Break Processes on the Transport of Warm Waters Onto the Eastern Amundsen Sea Continental Shelf.

The heat transported onto the continental shelf by Circumpolar Deep Water (CDW) is the main driver of ice shelf basal melting in the Amundsen Sea. Here, we investigate the slope current system and the variability of the heat transported through the Pine Island‐Thwaites central and eastern troughs using data from five moorings deployed in the region between 5 March 2012 and 7 February 2016. Substantial variability on intermonthly time scales (3–4 months) is observed in the onshore heat flux, driven primarily by zonal wind stress north of the shelf break. Heat content, onshore flow, and heat flux are highly correlated between central and eastern troughs, which are most likely dynamically linked by the zonal wind stress forcing. This is the first time this dynamic link between troughs is observed. In the eastern the Amundsen Sea, during the El Niño of 2015/2016, strong eastward winds led to lower temperatures over the continental shelf while the onshore heat flux is intensified. We hypothesize that this anti‐correlation between heat content and heat flux results from a strengthened eastward undercurrent leading to upwelling of a colder and deeper CDW variety. These results highlight the complex and heterogeneous response of this region to environmental and the importance of velocity data for understanding the dynamics in this region. It also suggests that the hypothesized link between large‐scale atmospheric forcing (e.g., El Niño‐Southern Oscillation) and ice‐shelf melt is not produced via changes in heat content, but instead via changes in onshore heat flux. Plain Language Summary: Heat stored in the ocean is the main reason that floating ice attached to the glaciers that surround the Amundsen Sea is melting. We investigate how the strength of coastal currents and the amount of heat transported by them toward the Antarctic shore vary in time. We use continuous measurements for up to 4 yr of ocean currents at five different locations in the Amundsen Sea. The amount of heat transported by a relatively warm current varies mostly with a 3–4 months period, which is influenced by local surface winds. These are the first observations showing consistency in the variability of heat transported toward the shore across different locations in this region. Moreover, we show that changes in the local winds related to the El Niño event of 2015/2016 led to a period of low ocean temperatures and enhanced transport of heat toward the shore. We explain this contradictory behavior as a result of a stronger flow of deeper, colder waters influenced by stronger westerly winds. This suggests that the rate at which heat is transported toward the shore is likely more important than the temperature of the water in determining the melting of glaciers around the Amundsen Sea. Key Points: Zonal wind stress changes north of the shelf break drive different Circumpolar Deep Water (CDW) varieties onto the eastern Amundsen Sea continental shelfHeat content, on‐shore flow, and heat flux co‐vary strongly between central and eastern continental troughsThe 2015/2016 El Niño led to stronger onshore heat flux, despite the lower onshore temperatures due to upwelling of colder CDW variety [ABSTRACT FROM AUTHOR]