Glacial Isostatic Adjustment (GIA) in Greenland: A Review

Using the most recently published regional and global deglaciation histories we provide updated estimates of the Glacial Isostatic Adjustment (GIA) component of present day uplift at a suite of GPS sites in Greenland. The GIA of the solid Earth beneath Greenland contributes -6 to +10 Gt/yr to the present day mass trends observed by the Gravity Recovery and Climate Experiment (GRACE), representing <5% contribution to the observed mass trends over the last decade. Although the contribution of GIA to GRACE estimates of mass imbalance is insignificant for Greenland as a whole, differences between deglacial models reviewed here and their assumed viscoelastic Earth structures result in significantly different estimates of regional patterns and magnitudes of GIA. This means that for some areas of Greenland (e.g. the north-west, south- and north-east) the use of GNSS to estimate elastic uplift patterns is more affected by the choice of GIA correction applied

A history-matching analysis of Antarctic Ice Sheet evolution since the last interglacial

One technique to explicitly quantify uncertainties of glacial systems is a history-matching analysis (HMA) of a model against a large observational database. This is achieved by ruling out simulations that are inconsistent with an observational constraint database. A comprehensive database (“AntICE2”) was compiled for state-space estimation of past Antarctic Ice Sheet (AIS) changes and to evaluate model reconstructions. This research applies a HMA on a 3D glacial systems model (GSM) for Antarctica against the AntICE2 observational constraint database. A HMA represents a crucial steppingstone towards a comprehensive Bayesian calibration. A HMA consists of identifying model reconstructions that are consistent with observations given uncertainties in the model and data. Our HMA extensively samples model uncertainties against fits to observational data through Markov Chain Monte Carlo methods using Bayesian artificial neural network emulators of the full GSM. This methodology produced several large ensembles exceeding 40,000 simulations that were evaluated against observational constraints. The terminal large ensemble consisting of 9,293 members represents the culmination of this research. The GSM simulation output is scored against the AntICE2 database to evaluate the model reconstruction. The HMA rules simulations as being broadly inconsistent with the AntICE2 database based on being within a 3σ or 4σ threshold of each various observational data type. The simulations from the full ensemble that are tentatively not inconsistent with the observational constraint database are classified as the not-ruled-out-yet (NROY) sub-ensemble. The HMA of the AIS since the last interglacial and the resulting NROY sub-ensemble addresses several outstanding research questions. Considering the extent to which uncertainties across the glacial system and data were incorporated in the HMA, the NROY sub-ensemble should approximately bracket the past evolution of the actual ice sheet. The NROY simulations have excess Last Glacial Maximum (LGM) volumes ranging between 9.2 to 26.5 meters equivalent sea level. This range has upper limits that are considerably higher than past studies and this addresses in large part inferential deficits in the LGM sea-level budget. Moreover, the NROY sub-ensemble represents an envelop of chronologies which can be used as input boundary conditions for general circulation models and glacial isostatic adjustment models to better understand past atmospheric and oceanic circulation, and sea-level change

Greenland Temperature Response to Climate Forcing during the Last Deglaciation

Greenland ice core water isotopic composition (δ¹⁸O) provides detailed evidence for abrupt climate changes, but is by itself insufficient for quantitative reconstruction of past temperatures and their spatial patterns. We investigate Greenland temperature evolution during the last deglaciation using independent reconstructions from three ice cores and simulations with a coupled ocean-atmosphere climate model. Contrary to the traditional δ¹⁸O interpretation, the Younger Dryas period was 4.5±2°C warmer than the Oldest Dryas, due to increased CO₂ forcing and summer insolation. The magnitude of abrupt temperature changes is larger in central Greenland (9-14°C) than in the northwest (5-9°C), fingerprinting a North-Atlantic origin. Simulated changes in temperature seasonality closely track changes in the Atlantic overturning strength, and support the hypothesis that abrupt climate change is mostly a winter phenomenon

Mass balance of the Greenland and Antarctic ice sheets from 1992 to 2020

Ice losses from the Greenland and Antarctic ice sheets have accelerated since the 1990s, accounting for a significant increase in the global mean sea level. Here, we present a new 29-year record of ice sheet mass balance from 1992 to 2020 from the Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE). We compare and combine 50 independent estimates of ice sheet mass balance derived from satellite observations of temporal changes in ice sheet flow, in ice sheet volume, and in Earth's gravity field. Between 1992 and 2020, the ice sheets contributed 21.0±1.9g€¯mm to global mean sea level, with the rate of mass loss rising from 105g€¯Gtg€¯yr-1 between 1992 and 1996 to 372g€¯Gtg€¯yr-1 between 2016 and 2020. In Greenland, the rate of mass loss is 169±9g€¯Gtg€¯yr-1 between 1992 and 2020, but there are large inter-annual variations in mass balance, with mass loss ranging from 86g€¯Gtg€¯yr-1 in 2017 to 444g€¯Gtg€¯yr-1 in 2019 due to large variability in surface mass balance. In Antarctica, ice losses continue to be dominated by mass loss from West Antarctica (82±9g€¯Gtg€¯yr-1) and, to a lesser extent, from the Antarctic Peninsula (13±5g€¯Gtg€¯yr-1). East Antarctica remains close to a state of balance, with a small gain of 3±15g€¯Gtg€¯yr-1, but is the most uncertain component of Antarctica's mass balance. The dataset is publicly available at 10.5285/77B64C55-7166-4A06-9DEF-2E400398E452 (IMBIE Team, 2021)

A Model of the Greenland Ice Sheet Deglaciation

The goal of this thesis is to improve our understanding of the Greenland ice sheet (GrIS) and how it responds to climate change. This was achieved using ice core records to infer elevation changes of the GrIS during the Holocene (11.7 ka BP to Present). The inferred elevation changes show the response of the ice sheet interior to the Holocene Thermal Maximum (HTM; 9-5 ka BP) when temperatures across Greenland were warmer than present. These ice-core derived thinning curves act as a new set of key constraints on the deglacial history of the GrIS. Furthermore, a calibration was conducted on a three-dimensional thermomechanical ice sheet, glacial isostatic adjustment, and relative sea-level model of GrIS evolution during the most recent deglaciation (21 ka BP to present). The model was data-constrained to a variety of proxy records from paleoclimate archives and present-day observations of ice thickness and extent

Developments in Ice Core Research on Past Climate Change

IPICS 2016 Open Science Conference; Hobart, Australia, 7–11 March 2016</jats:p

Sea Level and Ice Sheet Changes During Past Warm Periods

PALSEA2 2015 Workshop; Tokyo, Japan, 22–24 July 2015</jats:p