Location map of Saqqarleq Fjord-Saqqarliup Sermia system (composite image from the U.S. Geological Survey and Google Earth, 2019). The inset shows the location in central-west Greenland.

Location map of Saqqarleq Fjord-Saqqarliup Sermia system (composite image from the U.S. Geological Survey and Google Earth, 2019). The inset shows the location in central-west Greenland.

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Abstract. Meltwater and sediment-laden plumes at tidewater glaciers, resulting from the localized subglacial discharge of surface melt, influence submarine melting of the glacier and the delivery of nutrients to the fjord's surface waters. It is usually assumed that increased subglacial discharge will promote the surfacing of these plumes. Here, at...

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... Fjord (SF) is the southernmost branch of the intricate system of fjords connected to Jakobshavn Isfjord (JI) over a 125 m-depth sill, in central-west Greenland (Fig. 1). It is a mid-sized fjord and is approximately 35 km long and 6 km wide in https://doi.org/10.5194/tc-2019-264 Preprint. Discussion started: 15 January 2020 c Author(s) 2020. CC BY 4.0 ...
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... next consider the modeled plume temperature and salinity at NBD and MHD and compare these with observed properties 230 within the jets flowing down fjord. Plume-model properties at NBD in 2012 are characterized by í µí±† í µí°ánd í µí¼Ž Θ of 30.4 g kg⁻¹ and 0.8 ºC, respectively, while they are 31.0 g kg⁻¹ and 0.9 ºC in 2013 (Fig. 10). The fresher value in 2012 is due to the greater volume of freshwater present in the fjord in 2012 (Figs. 5 and 6), which is entrained into the plume. The properties at MHD (Fig. 10) are warmer and fresher than at NBD, since the plume has by then mixed in some of the warmer and fresher waters from the upper water column (Figs. 3 and ...
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... properties at NBD in 2012 are characterized by í µí±† í µí°ánd í µí¼Ž Θ of 30.4 g kg⁻¹ and 0.8 ºC, respectively, while they are 31.0 g kg⁻¹ and 0.9 ºC in 2013 (Fig. 10). The fresher value in 2012 is due to the greater volume of freshwater present in the fjord in 2012 (Figs. 5 and 6), which is entrained into the plume. The properties at MHD (Fig. 10) are warmer and fresher than at NBD, since the plume has by then mixed in some of the warmer and fresher waters from the upper water column (Figs. 3 and 5). The properties of the jets, ~ 1.5 km from the calving front, are in both years 235 considerably warmer, fresher and lighter than at MHD in the plume (Fig. 10). The outflowing jet is ...
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... the plume. The properties at MHD (Fig. 10) are warmer and fresher than at NBD, since the plume has by then mixed in some of the warmer and fresher waters from the upper water column (Figs. 3 and 5). The properties of the jets, ~ 1.5 km from the calving front, are in both years 235 considerably warmer, fresher and lighter than at MHD in the plume (Fig. 10). The outflowing jet is also significantly fresher in 2012 than in ...
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... section 2.3.3). For simplicity we do not separately account for the highly stratified top layer. Table 1 show the results of fitting curves of the form in Eq. (2) to the results from the plume model. Included 245 are both the plume extents and the vertically integrated submarine melt rate. The power law captures plume vertical extent very well (Fig. 11a), with both neutral buoyancy depth and maximum height scaling with stratification raised to the power https://doi.org/10.5194/tc-2019-264 Preprint. Discussion started: 15 January 2020 c Author(s) 2020. CC BY 4.0 License. It is also notable that the power law scalings for characteristic plume heights (Fig. 11a) perform well even in the ...
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... plume vertical extent very well (Fig. 11a), with both neutral buoyancy depth and maximum height scaling with stratification raised to the power https://doi.org/10.5194/tc-2019-264 Preprint. Discussion started: 15 January 2020 c Author(s) 2020. CC BY 4.0 License. It is also notable that the power law scalings for characteristic plume heights (Fig. 11a) perform well even in the absence of the 'point source correction'; an additional term that is often added to the scaling to account for the finite size of the source of subglacial runoff (Slater et al., 2016;Straneo and Cenedese, ...
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... integrated submarine melt rates (i.e. the total volume of submarine melting resulting from the plume) may also be 255 expressed as a simple function of stratification and runoff ( Fig. 11b and Table 1). The stratification exponent is similar to that for the characteristic plume heights. The runoff exponent is however twice that of NBD and MHD, indicating that total melt rate is twice as sensitive to runoff as NBD and MHD. This reflects the fact that submarine melt rate depends on plume velocity, which also scales ...
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... plume model also suggests that for the plume to reach the 265 surface in 2012, the rate of subglacial discharge would have had to be three times that needed in 2013. The fact that the estimated neutral buoyancy depth is deeper in 2012 (~ 25 m, Fig. 9) than the very fresh layer at the fjord surface (~ 15 m, Fig. 5) suggests that it is not just the fresh surface waters that are influencing plume dynamics but that the differences are also due to the stratification of the intermediate layer. ...
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... 2012. The simulated NBD is deeper in 2012 than in 2013, and shows reasonable agreements with the depths at which we observe jets ~ 1.5 km away from the glacier (Fig. 9). Lastly, the temperature and salinity properties of the plume at the fjord surface in 2012 and 2013 lie close to those observed by expendable probes dropped close to the glacier (Fig. 10), indicating that the mixing of the plume and ambient water is reasonably captured by the model. The model/observations agreement is improved with respect to previous 275 studies of Saqqarleq ( Mankoff et al., 2016;Stevens et al., 2016), likely due to their use of a conical rather than line plume model of appropriate width (Jackson et ...
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... results also show that the observed (or modeled) plume properties -i.e. the properties observed within 150 m of the glacier face which the plume model can reproduce given the observed stratification and estimated discharge -are very different from those of the waters exported as a jet observed 1.5 km away from the glacier (Fig. 10). The fact that the properties of the jet, in 280 both years, are considerably warmer, fresher and lighter than the observed/modeled plume properties is indicative of significant mixing with the surface waters which must occur as waters from the plume sink and flow away from the glacier. We stress that plume model does not include this ...
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... lastly generalized our results by using the plume model to fit a scaling between stratification ( í µí± 2 ), subglacial discharge (í µí±„ í µí± í µí±” ), and characteristic plume heights NBD and MHD. We found that both characteristic plume heights scaled with í µí± 2 raised to the power −0.4 and í µí±„ í µí± í µí±” raised to the power 0.26 (Fig. 11a), which are similar to those obtained by Slater et 310 al. (2016). This means that a doubling of subglacial runoff will increase plume vertical extent (NBD and MHD) by 18% while a doubling of stratification decreases plume vertical extent by 25%. While the net impact on plume vertical extent depends on the intrinsic variability of ...
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... on the intrinsic variability of runoff and stratification, this scaling taken together with our observations shows that stratification plays a dominant role in setting plume vertical extent. In contrast, a doubling of runoff increases total submarine melting by 40% while a doubling of stratification decreases total submarine melting by 26% (Fig. 11b). For submarine melting therefore, 315 stratification is not dominant, but still plays an important role that is worth considering in bulk submarine melt rate ...
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... water (PW) occupies the surface layer and extends to as deep as 200 m, overlying warmer and saltier Atlantic Water (AW) at depth ( Straneo et al., 2012;Straneo 320 and Cenedese, 2015). SF is relatively shallow, having a maximum depth of 230 m, and is separated from the open ocean by sills at 70 m to Tasiusaq Fjord and 125 m to Ilulissat Icefjord (Fig. 1). As such we do not see AW in Saqqarleq Fjord, rather we see cooler Ilulissat Icefjord waters (IIW, Stevens et al., 2016). Our CTD profiles from SF show three well-differentiated layers during summer (Fig. 5). The bottom layer (below 100 m depth) is homogeneous with properties likely controlled by shear mixing over sills Gladish et al., ...
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... stratification likely impacts on circulation more widely in the fjord, though this is beyond what we can quantify with a simple plume model. Our oceanographic observations of the jet show that due to increased stratification in 2012 compared to 2013, the jet that carries plume waters away from the glacier is deeper (Fig. 7) and fresher (Fig. 10) in 2012 than in ...

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