scholarly journals Ice front change of marine-terminating outlet glaciers in northwest and southeast Greenland during the 21st century

2018 ◽  
Vol 64 (246) ◽  
pp. 523-535 ◽  
Author(s):  
CHARLIE BUNCE ◽  
J. RACHEL CARR ◽  
PETER W. NIENOW ◽  
NEIL ROSS ◽  
REBECCA KILLICK
Keyword(s):  
Temporal Variability ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Spatial And Temporal Variability ◽  
Spatial And Temporal Patterns ◽  
Negative Mass ◽  
Position Change ◽  
Specific Factors ◽  
Enhanced Surface

ABSTRACTThe increasingly negative mass balance of the Greenland ice sheet (GrIS) over the last ~25 years has been associated with enhanced surface melt and increased ice loss from marine-terminating outlet glaciers. Accelerated retreat during 2000–2010 was concentrated in the southeast and northwest sectors of the ice sheet; however, there was considerable spatial and temporal variability in the timing and magnitude of retreat both within and between these regions. This behaviour has yet to be quantified and compared for all glaciers in both regions. Furthermore, it is unclear whether retreat has continued after 2010 in the northwest, and whether the documented slowdown in the southeast post-2005 has been sustained. Here, we compare spatial and temporal patterns of frontal change in the northwest and southeast GrIS, for the period 2000–2015. Our results show near-ubiquitous retreat of outlet glaciers across both regions for the study period; however, the timing and magnitude of inter-annual frontal position change is largely asynchronous. We also find that since 2010, there is continued terminus retreat in the northwest, which contrasts with considerable inter-annual variability in the southeast. Analysis of the role of glacier-specific factors demonstrates that fjord and bed geometry are important controls on the timing and magnitude of glacier retreat.

The Prominent Role of GRACE in the Series of IMBIE Studies: Future Plans and Prominent Issues

2020 ◽  
Author(s):  
Erik Ivins ◽  
Andrew Shepherd
Keyword(s):  
Mass Balance ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Glacial Isostatic Adjustment ◽  
Isostatic Adjustment ◽  
General Plan ◽  
Ice Mass Balance ◽  
Grace Mission ◽  
Phase I And Ii

<p>The Ice Mass Balance Intercomparison Exercize  (IMBIE) was initiated in 2011 with the intent of better reconciling the various reports  on the Greenland ice sheet (GrIS)  and Antarctic ice sheet (AIS) mass balance during the 2000’s. The focused study was funded and promoted by both ESA and NASA to better understand the origins of  contradictory results using space observations for a 20 year-long period: 1990-2010. Here we review some of the main results of phase I and II of IMBIE and the strength of the GRACE mission results.  For 20-year long trends (2002-2021) trends are influenced by glacial isostatic adjustment (GIA) in Greenland, but with more profound consequence for Antarctica. IMBIE-I determined a mass balance trend for 1992-2011: -142 ± 49 and -71 ± 83 Gt/yr, for GrIS and AIS, respectively.  IMBIE-II was open to a wider sampling of international  investigative teams and the results for GrIS over 1992-2018 changed to -150 ± 13 Gt/yr. Most notably the 1-sigma formal errors reported in IMBIE-II were 25% of those reported in the earlier IMBIE-I study for GrIS. For Antarctica the most notable contrast in results was the total value of the trend over 1992-2017 (IMBIE-II) in contrast 1992-2011 (IMBIE-I) (-109 ± 56 vs -71 ± 83 Gt/yr, respectively). The loss estimate for AIS rose by 67% and the error also reduced by about 33%. Glacial isostatic adjustment (GIA) estimates for Antarctica cluster around + 54 Gt/yr (meaning their correction adds to the negativity of the mass balance result for GRACE and GRACE-FO).  The East Antarctica Ice Sheet (EAIS) has trend errors for the estimate 1992-2017 (IMBIE-II) that continue to dwarf the uncertainty: +5 ± 46 Gt/yr. Beneath EAIS, GIA is also most uncertain and models have the greatest spread. We discuss the general plan for IMBIE-III that is currently forming.</p>

scholarly journals <i>Brief communication</i> "Important role of the mid-tropospheric atmospheric circulation in the recent surface melt increase over the Greenland ice sheet"

2013 ◽  
Vol 7 (1) ◽  
pp. 241-248 ◽  
Author(s):  
X. Fettweis ◽  
E. Hanna ◽  
C. Lang ◽  
A. Belleflamme ◽  
M. Erpicum ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Circulation Type ◽  
Atmospheric Flow ◽  
The North ◽  
Surface Melt ◽  
The North Atlantic Oscillation ◽  
June July ◽  
Atmospheric Heat

Abstract. Since 2007, there has been a series of surface melt records over the Greenland ice sheet (GrIS), continuing the trend towards increased melt observed since the end of the 1990's. The last two decades are characterized by an increase of negative phases of the North Atlantic Oscillation (NAO) favouring warmer and drier summers than normal over GrIS. In this context, we use a circulation type classification based on daily 500 hPa geopotential height to evaluate the role of atmospheric dynamics in this surface melt acceleration for the last two decades. Due to the lack of direct observations, the interannual melt variability is gauged here by the summer (June–July–August) mean temperature from reanalyses at 700 hPa over Greenland; analogous atmospheric circulations in the past show that ~70% of the 1993–2012 warming at 700 hPa over Greenland has been driven by changes in the atmospheric flow frequencies. Indeed, the occurrence of anticyclones centred over the GrIS at the surface and at 500 hPa has doubled since the end of 1990's, which induces more frequent southerly warm air advection along the western Greenland coast and over the neighbouring Canadian Arctic Archipelago (CAA). These changes in the NAO modes explain also why no significant warming has been observed these last summers over Svalbard, where northerly atmospheric flows are twice as frequent as before. Therefore, the recent warmer summers over GrIS and CAA cannot be considered as a long-term climate warming but are more a consequence of NAO variability affecting atmospheric heat transport. Although no global model from the CMIP5 database projects subsequent significant changes in NAO through this century, we cannot exclude the possibility that the observed NAO changes are due to global warming.

scholarly journals Spatial and temporal variability of water-filled crevasse hydrologic states along the shear margins of Jakobshavn Isbrae, Greenland

2017 ◽  
Author(s):  
Casey A. Joseph ◽  
Derrick J. Lampkin
Keyword(s):  
Temporal Variability ◽  
Large Strain ◽  
Water Injection ◽  
Greenland Ice Sheet ◽  
Spatial And Temporal Variability ◽  
Strain Rates ◽  
Ice Streams ◽  
Lower Elevation ◽  
Melt Water ◽  
The Impact

Abstract. The impact of melt water injection into ice streams over the Greenland Ice Sheet is not well understood. Water-filled crevasses along the shear margins of Jakobshavn Isbræ are known to fill and drain, resulting in weakening of the shear margins due to reduced basal friction. Seasonal variability in the hydrologic dynamics of these features has not been quantified. In this work, we characterize the spatial and temporal variability in the hydrological state (filled or drained) of these water-filled crevasse systems. A fusion of multi-sensor optical satellite imagery was used to examine hydrologic states from 2000 to 2015. The monthly distribution of crevasse systems observed as water filled is unimodal with peak number of filled days during the month of July at 329 days, while May has the least at 15. Over the study period the occurrence of drainage within a given season increases. Inter-seasonal drain frequencies over these systems ranged from 0 to 5. The frequency of multi-drainage events are correlated with warmer seasons and large strain rates. Over the study period, summer temperatures averaged from −1 and 2 °C and tensile strain rates have increased to as high as ~ 1.2 s-1. Intermittent melt water input during hydrofracture drainage responsible for transporting surface water to the bed is largely facilitated by high local tensile stresses. Drainage due to fracture propagation may be increasingly modulated by ocean-induced calving dynamics for the lower elevation ponds. Water-filled crevasses could expand in extent and volume as temperatures increase resulting in regional amplification of ice mass flux into the ice stream system.

North Atlantic footprint of summer Greenland ice sheet melting on interannual to interdecadal timescales: A Greenland blocking perspective

2021 ◽  
pp. 1-52
Keyword(s):  
North Atlantic ◽  
High Latitude ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Zonal Winds ◽  
Event Frequency ◽  
The North ◽  
Poleward Shift ◽  
The North Atlantic

Abstract Recent rapid melting of summer Greenland ice sheet (GrIS) and its impact on the Earth’s climate has attracted much attention. In this paper, we establish a connection between the melting of GrIS and the variability of summer sea surface temperature (SST) anomalies over North Atlantic on interannual to interdecadal timescales through changes in sub-seasonal Greenland blocking (GB). It is found that the latitude and width of GB are important for the spatial patterns of the GrIS melting. The melting of GrIS on interdecadal timescales is most prominent for the positive Atlantic Multidecadal Oscillation phase (AMO+) because the high latitude GB and its large width, long lifetime and slow decay are favored. However, the North Atlantic mid-high latitude warm-cold-warm (cold-warm-cold) tripole or NAT+ (NAT−) pattern on interannual timescales tends to strengthen (weaken) the role of AMO+ in the GrIS melting especially on the northern or northeastern periphery of Greenland by promoting (inhibiting) high-latitude GB and increasing (decreasing) its width. It is further revealed that AMO+ (NAT+) favors the persistence and width of GB mainly through producing weak summer zonal winds and small summer meridional potential vorticity gradient (PVy) in the North Atlantic mid-high latitudes 55°-70°N (55°-65°N) compared to the role of AMO− (NAT−). The event frequency and zonal width of GB events and their poleward shift are favored by the combination of NAT+ with AMO+. In contrast, the combination of NAT− and AMO+ tends to suppress reduced summer zonal winds and PVy, thus inhibiting the event frequency of GB events and their poleward shift and zonal width.

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