Abstract
AbstractSubmarine melting has been implicated as a driver of glacier retreat and sea level rise, but to date melting has been difficult to observe and quantify. As a result, melt rates have been estimated from parameterizations that are largely unconstrained by observations, particularly at the near‐vertical termini of tidewater glaciers. With standard coefficients, these melt parameterizations predict that ambient melting (the melt away from subglacial discharge outlets) is negligible compared to discharge‐driven melting for typical tidewater glaciers. Here, we present new data from LeConte Glacier, Alaska, that challenges this paradigm. Using autonomous kayaks, we observe ambient meltwater intrusions that are ubiquitous within 400 m of the terminus, and we provide the first characterization of their properties, structure, and distribution. Our results suggest that ambient melt rates are substantially higher (×100) than standard theory predicts and that ambient melting is a significant part of the total submarine melt flux. We explore modifications to the prevalent melt parameterization to provide a path forward for improved modeling of ocean‐glacier interactions.
Highlights
Mass loss from marine-terminating glaciers is increasing the freshwater flux into the ocean and contributing to rising sea levels (Bamber et al, 2018; Dieng et al, 2017; Shepherd et al, 2018)
Our results suggest that ambient melt rates are substantially higher (×100) than standard theory predicts and that ambient melting is a significant part of the total submarine melt flux
The near-ice velocity has rarely been measured and is impossible to resolve in most models, so a common approach for deriving these velocities and associated melt rates is to couple buoyant plume theory with a submarine melt parameterization (Holland & Jenkins, 1999) to create a coupled plume-melt parameterization (Jenkins, 2011; MacAyeal, 1985)
Summary
Mass loss from marine-terminating glaciers is increasing the freshwater flux into the ocean and contributing to rising sea levels (Bamber et al, 2018; Dieng et al, 2017; Shepherd et al, 2018). The near-ice velocity has rarely been measured and is impossible to resolve in most models (due to the small-scale, nonhydrostatic dynamics of plumes), so a common approach for deriving these velocities and associated melt rates is to couple buoyant plume theory (which describes the evolution of a turbulent plume; Ellison & Turner, 1959; Morton et al, 1956) with a submarine melt parameterization (Holland & Jenkins, 1999) to create a coupled plume-melt parameterization (Jenkins, 2011; MacAyeal, 1985) Using this plume-melt framework, the large upwelling velocities from subglacial discharge plumes are expected to drive high melt rates, while the weak velocities of ambient melt plumes produce low melt rates. These near-glacier observations were complemented by downstream shipboard measurements of velocity, temperature, and salinity, with 10 cross-fjord transects occupied between 0.5 and 2 km from the glacier over the same surveying period. (See supporting information for sampling details.)
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