1,721,125 research outputs found
Northern hemispheric land ice distribution outside of Greenland during the Quaternary
No full textFrom the combination of orbital theory with benthic δ18O it has been suggested which obliquity cycles led to interglacials during the Quaternary. Here, we use a model-based deconvolution of this benthic δ18O record to calculate northern hemispheric land ice outside of Greenland, from which an alternative distribution of glacial and interglacial periods is defined.
Model output is compared with independent reconstructions of δ18O_seawater, sea level and atmospheric CO2 concentrations.
All data plotted in the figures of the article:
Köhler, P. & van de Wal, R. S. W. Interglacials of the Quaternary defined by northern hemispheric land ice distribution outside of Greenland, Nature Communications, 2020, 11, 5124, doi:10.1038/s41467-020-18897-5.
are compiled here
Idealised steady-state and transient simulations of Miocene Antarctic ice-sheet variability using 3D thermodynamical ice-sheet model IMAU-ICE
No full textWe present results from simulations of the Miocene Antarctic ice sheet, that were performed using the 3D thermodynamical ice-sheet model IMAU-ICE (v1.1.1-MIO). Five steady-state present-day simulations were conducted for reference (PI_ref), and 12 experiments using Miocene settings. Each Miocene experiment comprises 11 steady-state and 4 transient simulations. In the README file, the experiments and simulations are listed.
IMAU-ICE was run using a 40x40km grid covering the Antarctic continent. Initial conditions were obtained from reconstructions of the Antarctic bathymetry and bedrock topography pertaining to 23 to 24 million years (Myr) ago (dataset doi:10.1594/PANGAEA.923109). The simulations were forced by climate input data obtained from GENESIS simulations with varying CO2 levels (280 to 840 ppm) and Antarctic ice sheet cover (no ice to a large East-Antarctic ice sheet), and with present-day insolation. We utilized a matrix interpolation method to construct the time-varying climate forcing, based on the prescribed CO2 levels and ice cover simulated by IMAU-ICE.
For each simulation, we provide the run script, 1D output variables including CO2 level and the sea level contribution of the Antarctic ice sheet, and 3D output variables including ice thickness, bedrock and surface height, surface mass balance, basal mass balance, ice velocities, and ice temperatures. For more information, please contact L.B. Stap at [email protected]
A simulation of CO2, benthic δ¹⁸O, sea level and global temperature over the past 5 million years
No full textMIS 5e relative sea-level changes in the Mediterranean Sea: Contribution of isostatic disequilibrium
Full text linkSea-level indicators dated to the Last Interglacial, or Marine Isotope Stage (MIS) 5e, have a twofold value. First, they can be used to constrain the melting of Greenland and Antarctic Ice Sheets in response to global warming scenarios. Second, they can be used to calculate the vertical crustal rates at active margins. For both applications, the contribution of glacio- and hydro-isostatic adjustment (GIA) to vertical displacement of sea-level indicators must be calculated. In this paper, we re-assess MIS 5e sea-level indicators at 11 Mediterranean sites that have been generally considered tectonically stable or affected by mild tectonics. These are found within a range of elevations of 2–10 m above modern mean sea level. Four sites are characterized by two separate sea-level stands, which suggest a two-step sea-level highstand during MIS 5e. Comparing field data with numerical modeling we show that (i) GIA is an important contributor to the spatial and temporal variability of the sea-level highstand during MIS 5e, (ii) the isostatic imbalance from the melting of the MIS 6 ice sheet can produce a >2.0 m sea-level highstand, and (iii) a two-step melting phase for the Greenland and Antarctic Ice Sheets reduces the differences between observations and predictions. Our results show that assumptions of tectonic stability on the basis of the MIS 5e records carry intrinsically large uncertainties, stemming either from uncertainties in field data and GIA models. The latter are propagated to either Holocene or Pleistocene sea-level reconstructions if tectonic rates are considered linear through time
Surface mass balance along the K-transect in West Greenland
No full textA 21-year record is presented of surface mass balance measurements along the K-transect. The series covers the period 1990-2011. Data are available at 8 sites along a transect over an altitude range of 390 - 1850 m at approximately 67° N in West Greenland. The surface mass balance gradient is on average 3.8 x 10**-3 m w.e./m, and the mean equilibrium line altitude is 1553 m a.s.l. Only the lower 3 sites within 10 km of the margin experience a significant increasing trend in the ablation over the entire period
Cenozoic global ice volume and temperature simulations over the past 40 million years
No full textVariations in global ice volume and temperature over the Cenozoic era have been investigated with a set of one-dimensional (1-D) ice-sheet models. Simulations include three ice sheets representing glaciation in the Northern Hemisphere, i.e. in Eurasia, North America and Greenland, and two separate ice sheets for Antarctic glaciation. The continental mean Northern Hemisphere surface-air temperature has been derived through an inverse procedure from observed benthic d18O records. These data have yielded a mutually consistent and continuous record of temperature, global ice volume and benthic d18O over the past 35 Ma. The simple 1-D model shows good agreement with a comprehensive 3-D ice-sheet model for the past 3 Ma. On average, differences are only 1.0°C for temperature and 6.2 m for sea level. Most notably, over the 35 Ma period, the reconstructed ice volume–temperature sensitivity shows a transition from a climate controlled by Southern Hemisphere ice sheets to one controlled by Northern Hemisphere ice sheets. Although the transient behaviour is important, equilibrium experiments show that the relationship between temperature and sea level is linear and symmetric, providing limited evidence for hysteresis. Furthermore, the results show a good comparison with other simulations of Antarctic ice volume and observed sea level
Results of the second experiment of the Glacier Model Intercomparison Project
No full textThe data file contains projections for area and mass change of glaciers on the global scale, from 11 different glacier models, forced by 10 different climate models, under 4 different scenarios. The values are specified by regions, following the region definition of the Randolph Glacier Inventory (https://www.glims.org/RGI/). Values are given annually for the years 2000 to 2100. The data were produced in the second experiment of the Glacier Model Intercomparison Project, based on standardized boundary and initial conditions (http://www.climate-cryosphere.org/mips/glaciermip/activities-experiments)
Response to commentary by J. L. Bamber, W. P. Aspinall and R. M. Cooke (2016)
Full text linkIn a commentary paper, Bamber et al. (Nat Clim Change 3:424–427, 2016) respond to our recent assessment (De Vries and Van de Wal Clim Change 1–14, 2015) of their expert judgment based study on projections of future sea level rise due to the melting of the large ice sheets (Bamber and Aspinall Nat Clim Chang 3:424–427, 2013). In this response we comment on their remarks
Automatic weather station data collected from 2003 to 2021 at the Greenland ice sheet along the K-transect, West-Greenland
No full textWe present 18 years (2003-2021) of automatic weather station (AWS) data, collected along the K-transect near Kangerlussuaq in west Greenland. The transect runs from east to west, roughly perpendicular to the ice sheet edge at about 67° N. The K-transect originated from the Greenland Ice Margin Experiments (GIMEX), held in the summers of 1990 and 1991. Until recently, surface mass balance and ice velocity measurements were performed at nine locations along the K-transect, of which four are equipped with AWS: two in the ablation zone at approximately 500 m and 1,000 m asl, one at the approximate equilibrium-line altitude (~1,500 m asl), and one in the lower accumulation zone (~1,850 m asl) at distances of 5, 38, 88, and 140 km from the ice edge, respectively. Here, we present (mostly) half hourly UTC based AWS measurements from these four sites containing temperature/humidity, windspeed/direction, all four radiation components and atmospheric pressure. All data are corrected and quality controlled, for details about this procedure please consult doi:10.1080/15230430.2017.1420954
(Table 1) Depth characteristics and mean ion concentrations of ice cores from Belukha, the Everest and 3 Svalbard sites
No full textDate/Time is drilling date. Nitrate, chloride, ammonium and calcium concentrations since 1800 are indicative of anthropogenic, marine, biogenic, and terrestrial sulphate sources, respectively. An independent reference horizon comes from the radioactivity associated with the 1963 bomb fallout
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