Limits in detecting acceleration of ice sheet mass loss due to climate variability

The Greenland ice sheet presently accounts for ~70% of global ice sheet mass loss. Because this mass loss is associated with sea-level rise at a rate of 0.7 mm/year, the development of improved monitoring techniques to observe ongoing changes in ice sheet mass balance is of paramount concern. Spaceborne mass balance techniques are commonly used; however, they are inadequate for many purposes because of their low spatial and/or temporal resolution. We demonstrate that small variations in seismic wave speed in Earth’s crust, as measured with the correlation of seismic noise, may be used to infer seasonal ice sheet mass balance. Seasonal loading and unloading of glacial mass induces strain in the crust, and these strains then result in seismic velocity changes due to poroelastic processes. Our method provides a new and independent way of monitoring (in near real time) ice sheet mass balance, yielding new constraints on ice sheet evolution and its contribution to global sea-level changes. An increased number of seismic stations in the vicinity of ice sheets will enhance our ability to create detailed space-time records of ice mass variations.

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A century of climate variability and climate gradients from coast to ice sheet in west greenland

Geografiska Annaler Series A Physical Geography ◽

10.1111/j.0435-3676.2004.00226.x ◽

2004 ◽

Vol 86 (2) ◽

pp. 217-224 ◽

Cited By ~ 14

Author(s):

Andrea Taurisano ◽

Carl Egede Billionøggild ◽

Håkon Gjessing Karlsen

Keyword(s):

Climate Variability ◽

Ice Sheet ◽

West Greenland ◽

Climate Gradients

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Natural variability and recent warming in central Greenland ice cores

10.5194/egusphere-egu21-12914 ◽

2021 ◽

Author(s):

Maria Hoerhold ◽

Thomas Münch ◽

Stefanie Weißbach ◽

Sepp Kipfstuhl ◽

Bo Vinther ◽

...

Keyword(s):

Climate Variability ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Ice Cores ◽

Natural Variability ◽

The Arctic ◽

Last Millennium ◽

Recent Warming ◽

Temperature Reconstructions ◽

Firn Core

Climate variability of the Arctic region has been investigated by means of temperature reconstructions based on proxies from various climate archives around the Arctic, compiled over the last 2000a in the so called Arctic2k record. However, the representativeness of the Arctic2k reconstruction for central Greenland remains unclear, since only a few ice cores have been included in the reconstruction, and observations from the Greenland Ice Sheet (GIC) report ambiguous warming trends for the end of the 20th and the beginning of the 21st century which are not displayed by Arctic2k. Today, the GIC experiences periods with temperatures close to or above the freezing point at high elevations, area-wide melting and mass loss. In order to assess the recent warming as signature of global climate change, records of past climate changes with appropriate temporal and spatial coverage can serve as a benchmark for naturally driven climate variability. Instrumental records for Greenland are short and geographically sparse, and existing temperature reconstructions from single ice cores are noisy, leading to an inconclusive assessment of the recent warming for Greenland.Here, we provide a Greenland firn-core stack covering the time span of the last millennium until the first decade of the 21st century in unprecedented quality by re-drilling as well as analyzing 16 existing firn core sites. We find a strong decadal to bi-decadal natural variability in the record, and, while the record exhibits several warming events with trends that show a similar amplitude as the recent one, we find that the recent absolute values of stable oxygen isotope composition are unprecedented for the last 1000 years.&#160;Comparing our Greenland record with the Arctic 2k temperature reconstruction shows that the correlation between the two records changes throughout the last millennium. While in the periods of 1200-1300 and 1400-1650 CE the records correlate positively, between 1300 and 1400 and 1650-1700 CE shorter periods with negative correlation are found. Since then the correlation is characterized by alternation between positive and zero correlation, with a drop towards negative values at the end of the 20th century. Including re-analysis data, we hypothesize that the climate on top of the GIC was decoupled from the surrounding Arctic for the last decades, leading to the observed mismatch in observations of warming trends.We suggest that the recently observed Greenland temperatures are a superposition of a strong natural variability with an anthropogenic long-term trend. Our findings illustrate that global warming has reached the interior of the Greenland ice sheet, which will have implications for its surface mass balance and Greenland&#8217;s future contribution to sea level rise.Our record complements the Arctic 2k record to a profound view on the Arctic climate variability, where regional compilations may not be representative for specific areas.

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A new approach for simulating the paleo-evolution of the Northern Hemisphere ice sheets

Geoscientific Model Development ◽

10.5194/gmd-11-2299-2018 ◽

2018 ◽

Vol 11 (6) ◽

pp. 2299-2314 ◽

Cited By ~ 5

Author(s):

Rubén Banderas ◽

Jorge Alvarez-Solas ◽

Alexander Robinson ◽

Marisa Montoya

Keyword(s):

Climate Variability ◽

Ice Core ◽

Ice Sheets ◽

Ice Sheet ◽

Temperature Reconstruction ◽

Anomaly Field ◽

Temperature Anomalies ◽

Ice Volume ◽

Index Approach ◽

Millennial Scale

Abstract. Offline forcing methods for ice-sheet models often make use of an index approach in which temperature anomalies relative to the present are calculated by combining a simulated glacial–interglacial climatic anomaly field, interpolated through an index derived from the Greenland ice-core temperature reconstruction, with present-day climatologies. An important drawback of this approach is that it clearly misrepresents climate variability at millennial timescales. The reason for this is that the spatial glacial–interglacial anomaly field used is associated with orbital climatic variations, while it is scaled following the characteristic time evolution of the index, which includes orbital and millennial-scale climate variability. The spatial patterns of orbital and millennial variability are clearly not the same, as indicated by a wealth of models and data. As a result, this method can be expected to lead to a misrepresentation of climate variability and thus of the past evolution of Northern Hemisphere (NH) ice sheets. Here we illustrate the problems derived from this approach and propose a new offline climate forcing method that attempts to better represent the characteristic pattern of millennial-scale climate variability by including an additional spatial anomaly field associated with this timescale. To this end, three different synthetic transient forcing climatologies are developed for the past 120 kyr following a perturbative approach and are applied to an ice-sheet model. The impact of the climatologies on the paleo-evolution of the NH ice sheets is evaluated. The first method follows the usual index approach in which temperature anomalies relative to the present are calculated by combining a simulated glacial–interglacial climatic anomaly field, interpolated through an index derived from ice-core data, with present-day climatologies. In the second approach the representation of millennial-scale climate variability is improved by incorporating a simulated stadial–interstadial anomaly field. The third is a refinement of the second one in which the amplitudes of both orbital and millennial-scale variations are tuned to provide perfect agreement with a recently published absolute temperature reconstruction over Greenland. The comparison of the three climate forcing methods highlights the tendency of the usual index approach to overestimate the temperature variability over North America and Eurasia at millennial timescales. This leads to a relatively high NH ice-volume variability on these timescales. Through enhanced ablation, this results in too low an ice volume throughout the last glacial period (LGP), below or at the lower end of the uncertainty range of estimations. Improving the representation of millennial-scale variability alone yields an important increase in ice volume in all NH ice sheets but especially in the Fennoscandian Ice Sheet (FIS). Optimizing the amplitude of the temperature anomalies to match the Greenland reconstruction results in a further increase in the simulated ice-sheet volume throughout the LGP. Our new method provides a more realistic representation of orbital and millennial-scale climate variability and improves the transient forcing of ice sheets during the LGP. Interestingly, our new approach underestimates ice-volume variations on millennial timescales as indicated by sea-level records. This suggests that either the origin of the latter is not the NH or that processes not represented in our study, notably variations in oceanic conditions, need to be invoked to explain millennial-scale ice-volume fluctuations. We finally provide here both our derived climate evolution of the LGP using the three methods as well as the resulting ice-sheet configurations. These could be of interest for future studies dealing with the atmospheric or/and oceanic consequences of transient ice-sheet evolution throughout the LGP and as a source of climate input to other ice-sheet models.

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On the recent contribution of the Greenland ice sheet to sea level change

The Cryosphere ◽

10.5194/tc-10-1933-2016 ◽

2016 ◽

Vol 10 (5) ◽

pp. 1933-1946 ◽

Cited By ~ 212

Author(s):

Michiel R. van den Broeke ◽

Ellyn M. Enderlin ◽

Ian M. Howat ◽

Peter Kuipers Munneke ◽

Brice P. Y. Noël ◽

...

Keyword(s):

Mass Loss ◽

Mass Balance ◽

Sea Level ◽

Pore Space ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Sea Level Change ◽

Recent Contribution ◽

Surface Mass ◽

Level Change

Abstract. We assess the recent contribution of the Greenland ice sheet (GrIS) to sea level change. We use the mass budget method, which quantifies ice sheet mass balance (MB) as the difference between surface mass balance (SMB) and solid ice discharge across the grounding line (D). A comparison with independent gravity change observations from GRACE shows good agreement for the overlapping period 2002–2015, giving confidence in the partitioning of recent GrIS mass changes. The estimated 1995 value of D and the 1958–1995 average value of SMB are similar at 411 and 418 Gt yr−1, respectively, suggesting that ice flow in the mid-1990s was well adjusted to the average annual mass input, reminiscent of an ice sheet in approximate balance. Starting in the early to mid-1990s, SMB decreased while D increased, leading to quasi-persistent negative MB. About 60 % of the associated mass loss since 1991 is caused by changes in SMB and the remainder by D. The decrease in SMB is fully driven by an increase in surface melt and subsequent meltwater runoff, which is slightly compensated by a small ( <  3 %) increase in snowfall. The excess runoff originates from low-lying ( <  2000 m a.s.l.) parts of the ice sheet; higher up, increased refreezing prevents runoff of meltwater from occurring, at the expense of increased firn temperatures and depleted pore space. With a 1991–2015 average annual mass loss of ∼  0.47 ± 0.23 mm sea level equivalent (SLE) and a peak contribution of 1.2 mm SLE in 2012, the GrIS has recently become a major source of global mean sea level rise.

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Constraining GRACE-derived cryosphere-attributed signal to irregularly shaped ice-covered areas

The Cryosphere ◽

10.5194/tc-7-1901-2013 ◽

2013 ◽

Vol 7 (6) ◽

pp. 1901-1914 ◽

Cited By ~ 3

Author(s):

W. Colgan ◽

S. Luthcke ◽

W. Abdalati ◽

M. Citterio

Keyword(s):

Monte Carlo ◽

Mass Loss ◽

Mass Balance ◽

Spherical Harmonic ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Ice Caps ◽

Ice Coverage ◽

Ice Sheet Mass Balance ◽

Harmonic Representation

Abstract. We use a Monte Carlo approach to invert a spherical harmonic representation of cryosphere-attributed mass change in order to infer the most likely underlying mass changes within irregularly shaped ice-covered areas at nominal 26 km resolution. By inverting a spherical harmonic representation through the incorporation of additional fractional ice coverage information, this approach seeks to eliminate signal leakage between non-ice-covered and ice-covered areas. The spherical harmonic representation suggests a Greenland mass loss of 251 ± 25 Gt a−1 over the December 2003 to December 2010 period. The inversion suggests 218 ± 20 Gt a−1 was due to the ice sheet proper, and 34 ± 5 Gt a−1 (or ~14%) was due to Greenland peripheral glaciers and ice caps (GrPGICs). This mass loss from GrPGICs exceeds that inferred from all ice masses on both Ellesmere and Devon islands combined. This partition therefore highlights that GRACE-derived "Greenland" mass loss cannot be taken as synonymous with "Greenland ice sheet" mass loss when making comparisons with estimates of ice sheet mass balance derived from techniques that sample only the ice sheet proper.

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Decadal-scale onset and termination of Antarctic ice-mass loss during the last deglaciation

Nature Communications ◽

10.1038/s41467-021-27053-6 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Michael E. Weber ◽

Nicholas R. Golledge ◽

Chris J. Fogwill ◽

Chris S. M. Turney ◽

Zoë A. Thomas

Keyword(s):

Mass Loss ◽

Sea Level Rise ◽

Sea Level ◽

Ross Sea ◽

Ice Sheet ◽

Rate Of Change ◽

Last Deglaciation ◽

Decadal Scale ◽

Ice Sheet Modeling ◽

Global Sea Level

AbstractEmerging ice-sheet modeling suggests once initiated, retreat of the Antarctic Ice Sheet (AIS) can continue for centuries. Unfortunately, the short observational record cannot resolve the tipping points, rate of change, and timescale of responses. Iceberg-rafted debris data from Iceberg Alley identify eight retreat phases after the Last Glacial Maximum that each destabilized the AIS within a decade, contributing to global sea-level rise for centuries to a millennium, which subsequently re-stabilized equally rapidly. This dynamic response of the AIS is supported by (i) a West Antarctic blue ice record of ice-elevation drawdown >600 m during three such retreat events related to globally recognized deglacial meltwater pulses, (ii) step-wise retreat up to 400 km across the Ross Sea shelf, (iii) independent ice sheet modeling, and (iv) tipping point analysis. Our findings are consistent with a growing body of evidence suggesting the recent acceleration of AIS mass loss may mark the beginning of a prolonged period of ice sheet retreat and substantial global sea level rise.

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