Noel Brice P. Y.

No Thumbnail Available
Last Name
First Name
Brice P. Y.

Search Results

Now showing 1 - 2 of 2
  • Article
    Greenland Ice Sheet flow response to runoff variability
    (John Wiley & Sons, 2016-11-12) Stevens, Laura A. ; Behn, Mark D. ; Das, Sarah B. ; Joughin, Ian ; Noel, Brice P. Y. ; van den Broeke, Michiel R. ; Herring, Thomas
    We use observations of ice sheet surface motion from a Global Positioning System network operating from 2006 to 2014 around North Lake in west Greenland to investigate the dynamical response of the Greenland Ice Sheet's ablation area to interannual variability in surface melting. We find no statistically significant relationship between runoff season characteristics and ice flow velocities within a given year or season. Over the 7 year time series, annual velocities at North Lake decrease at an average rate of −0.9 ± 1.1 m yr−2, consistent with the negative trend in annual velocities observed in neighboring regions over recent decades. We find that net runoff integrated over several preceding years has a negative correlation with annual velocities, similar to findings from the two other available decadal records of ice velocity in western Greenland. However, we argue that this correlation is not necessarily evidence for a direct hydrologic mechanism acting on the timescale of multiple years but could be a statistical construct. Finally, we stress that neither the decadal slowdown trend nor the negative correlation between velocity and integrated runoff is predicted by current ice-sheet models, underscoring that these models do not yet capture all the relevant feedbacks between runoff and ice dynamics needed to predict long-term trends in ice sheet flow.
  • Article
    Elevation change of the Greenland Ice Sheet due to surface mass balance and firn processes, 1960–2014
    (Copernicus Publications on behalf of the European Geosciences Union, 2015-11-02) Munneke, Peter Kuipers ; Ligtenberg, Stefan R. M. ; Noel, Brice P. Y. ; Howat, Ian M. ; Box, Jason E. ; Mosley-Thompson, Ellen ; McConnell, Joseph R. ; Steffen, Konrad ; Harper, Joel T. ; Das, Sarah B. ; van den Broeke, Michiel R.
    Observed changes in the surface elevation of the Greenland Ice Sheet are caused by ice dynamics, basal elevation change, basal melt, surface mass balance (SMB) variability, and by compaction of the overlying firn. The last two contributions are quantified here using a firn model that includes compaction, meltwater percolation, and refreezing. The model is forced with surface mass fluxes and temperature from a regional climate model for the period 1960–2014. The model results agree with observations of surface density, density profiles from 62 firn cores, and altimetric observations from regions where ice-dynamical surface height changes are likely small. In areas with strong surface melt, the firn model overestimates density. We find that the firn layer in the high interior is generally thickening slowly (1–5 cm yr−1). In the percolation and ablation areas, firn and SMB processes account for a surface elevation lowering of up to 20–50 cm yr−1. Most of this firn-induced marginal thinning is caused by an increase in melt since the mid-1990s and partly compensated by an increase in the accumulation of fresh snow around most of the ice sheet. The total firn and ice volume change between 1980 and 2014 is estimated at −3295 ± 1030 km3 due to firn and SMB changes, corresponding to an ice-sheet average thinning of 1.96 ± 0.61 m. Most of this volume decrease occurred after 1995. The computed changes in surface elevation can be used to partition altimetrically observed volume change into surface mass balance and ice-dynamically related mass changes.