Articles | Volume 7, issue 3
Research article 12 Aug 2011
Research article | 12 Aug 2011
Antarctic ice sheet and oceanographic response to eccentricity forcing during the early Miocene
D. Liebrand et al.
No articles found.
Constantijn J. Berends, Heiko Goelzer, and Roderik S. W. van de Wal
Geosci. Model Dev., 14, 2443–2470,Short summary
The largest uncertainty in projections of sea-level rise comes from ice-sheet retreat. To better understand how these ice sheets respond to the changing climate, ice-sheet models are used, which must be able to reproduce both their present and past evolution. We have created a model that is fast enough to simulate an ice sheet at a high resolution over the course of an entire 120 000-year glacial cycle. This allows us to study processes that cannot be captured by lower-resolution models.
Constantijn J. Berends, Bas de Boer, and Roderik S. W. van de Wal
Clim. Past, 17, 361–377,Short summary
For the past 2.6 million years, the Earth has experienced glacial cycles, where vast ice sheets periodically grew to cover large parts of North America and Eurasia. In the earlier part of this period, this happened every 40 000 years. This value changed 1.2 million years ago to 100 000 years: the Mid-Pleistocene Transition. We investigate this interesting period using an ice-sheet model, studying the interactions between ice sheets and the global climate.
Bas de Boer, Marit Peters, and Lucas J. Lourens
Clim. Past, 17, 331–344,
Xavier Fettweis, Stefan Hofer, Uta Krebs-Kanzow, Charles Amory, Teruo Aoki, Constantijn J. Berends, Andreas Born, Jason E. Box, Alison Delhasse, Koji Fujita, Paul Gierz, Heiko Goelzer, Edward Hanna, Akihiro Hashimoto, Philippe Huybrechts, Marie-Luise Kapsch, Michalea D. King, Christoph Kittel, Charlotte Lang, Peter L. Langen, Jan T. M. Lenaerts, Glen E. Liston, Gerrit Lohmann, Sebastian H. Mernild, Uwe Mikolajewicz, Kameswarrao Modali, Ruth H. Mottram, Masashi Niwano, Brice Noël, Jonathan C. Ryan, Amy Smith, Jan Streffing, Marco Tedesco, Willem Jan van de Berg, Michiel van den Broeke, Roderik S. W. van de Wal, Leo van Kampenhout, David Wilton, Bert Wouters, Florian Ziemen, and Tobias Zolles
The Cryosphere, 14, 3935–3958,Short summary
We evaluated simulated Greenland Ice Sheet surface mass balance from 5 kinds of models. While the most complex (but expensive to compute) models remain the best, the faster/simpler models also compare reliably with observations and have biases of the same order as the regional models. Discrepancies in the trend over 2000–2012, however, suggest that large uncertainties remain in the modelled future SMB changes as they are highly impacted by the meltwater runoff biases over the current climate.
Heiko Goelzer, Sophie Nowicki, Anthony Payne, Eric Larour, Helene Seroussi, William H. Lipscomb, Jonathan Gregory, Ayako Abe-Ouchi, Andrew Shepherd, Erika Simon, Cécile Agosta, Patrick Alexander, Andy Aschwanden, Alice Barthel, Reinhard Calov, Christopher Chambers, Youngmin Choi, Joshua Cuzzone, Christophe Dumas, Tamsin Edwards, Denis Felikson, Xavier Fettweis, Nicholas R. Golledge, Ralf Greve, Angelika Humbert, Philippe Huybrechts, Sebastien Le clec'h, Victoria Lee, Gunter Leguy, Chris Little, Daniel P. Lowry, Mathieu Morlighem, Isabel Nias, Aurelien Quiquet, Martin Rückamp, Nicole-Jeanne Schlegel, Donald A. Slater, Robin S. Smith, Fiamma Straneo, Lev Tarasov, Roderik van de Wal, and Michiel van den Broeke
The Cryosphere, 14, 3071–3096,Short summary
In this paper we use a large ensemble of Greenland ice sheet models forced by six different global climate models to project ice sheet changes and sea-level rise contributions over the 21st century. The results for two different greenhouse gas concentration scenarios indicate that the Greenland ice sheet will continue to lose mass until 2100, with contributions to sea-level rise of 90 ± 50 mm and 32 ± 17 mm for the high (RCP8.5) and low (RCP2.6) scenario, respectively.
Hélène Seroussi, Sophie Nowicki, Antony J. Payne, Heiko Goelzer, William H. Lipscomb, Ayako Abe-Ouchi, Cécile Agosta, Torsten Albrecht, Xylar Asay-Davis, Alice Barthel, Reinhard Calov, Richard Cullather, Christophe Dumas, Benjamin K. Galton-Fenzi, Rupert Gladstone, Nicholas R. Golledge, Jonathan M. Gregory, Ralf Greve, Tore Hattermann, Matthew J. Hoffman, Angelika Humbert, Philippe Huybrechts, Nicolas C. Jourdain, Thomas Kleiner, Eric Larour, Gunter R. Leguy, Daniel P. Lowry, Chistopher M. Little, Mathieu Morlighem, Frank Pattyn, Tyler Pelle, Stephen F. Price, Aurélien Quiquet, Ronja Reese, Nicole-Jeanne Schlegel, Andrew Shepherd, Erika Simon, Robin S. Smith, Fiammetta Straneo, Sainan Sun, Luke D. Trusel, Jonas Van Breedam, Roderik S. W. van de Wal, Ricarda Winkelmann, Chen Zhao, Tong Zhang, and Thomas Zwinger
The Cryosphere, 14, 3033–3070,Short summary
The Antarctic ice sheet has been losing mass over at least the past 3 decades in response to changes in atmospheric and oceanic conditions. This study presents an ensemble of model simulations of the Antarctic evolution over the 2015–2100 period based on various ice sheet models, climate forcings and emission scenarios. Results suggest that the West Antarctic ice sheet will continue losing a large amount of ice, while the East Antarctic ice sheet could experience increased snow accumulation.
Anna Joy Drury, Diederik Liebrand, Thomas Westerhold, Helen M. Beddow, David A. Hodell, Nina Rohlfs, Roy H. Wilkens, Mitch Lyle, David B. Bell, Dick Kroon, Heiko Pälike, and Lucas L. Lourens
Clim. Past Discuss.,
Revised manuscript accepted for CPShort summary
We use the first high-resolution southeast Atlantic carbonate record to see how climate dynamics evolved since 30 million years ago (Ma). During Oligocene-mid Miocene warmth (~30–13 Ma), eccentricity (orbital circularity) paced carbonate deposition. After the mid Miocene Climate Transition (~14 Ma), precession (Earth’s tilt direction) increasingly drove carbonate variability. In the latest Miocene (~8 Ma), obliquity (Earth’s tilt) pacing appeared, signalling increasing high latitude influence.
Sophie Nowicki, Heiko Goelzer, Hélène Seroussi, Anthony J. Payne, William H. Lipscomb, Ayako Abe-Ouchi, Cécile Agosta, Patrick Alexander, Xylar S. Asay-Davis, Alice Barthel, Thomas J. Bracegirdle, Richard Cullather, Denis Felikson, Xavier Fettweis, Jonathan M. Gregory, Tore Hattermann, Nicolas C. Jourdain, Peter Kuipers Munneke, Eric Larour, Christopher M. Little, Mathieu Morlighem, Isabel Nias, Andrew Shepherd, Erika Simon, Donald Slater, Robin S. Smith, Fiammetta Straneo, Luke D. Trusel, Michiel R. van den Broeke, and Roderik van de Wal
The Cryosphere, 14, 2331–2368,Short summary
This paper describes the experimental protocol for ice sheet models taking part in the Ice Sheet Model Intercomparion Project for CMIP6 (ISMIP6) and presents an overview of the atmospheric and oceanic datasets to be used for the simulations. The ISMIP6 framework allows for exploring the uncertainty in 21st century sea level change from the Greenland and Antarctic ice sheets.
Cinthya Nava-Fernandez, Adam Hartland, Fernando Gázquez, Ola Kwiecien, Norbert Marwan, Bethany Fox, John Hellstrom, Andrew Pearson, Brittany Ward, Amanda French, David A. Hodell, Adrian Immenhauser, and Sebastian F. M. Breitenbach
Hydrol. Earth Syst. Sci., 24, 3361–3380,Short summary
Speleothems are powerful archives of past climate for understanding modern local hydrology and its relation to regional circulation patterns. We use a 3-year monitoring dataset to test the sensitivity of Waipuna Cave to seasonal changes and El Niño–Southern Oscillation (ENSO) dynamics. Drip water data suggest a fast response to rainfall events; its elemental composition reflects a seasonal cycle and ENSO variability. Waipuna Cave speleothems have a high potential for past ENSO reconstructions.
Heiko Goelzer, Brice P. Y. Noël, Tamsin L. Edwards, Xavier Fettweis, Jonathan M. Gregory, William H. Lipscomb, Roderik S. W. van de Wal, and Michiel R. van den Broeke
The Cryosphere, 14, 1747–1762,Short summary
Future sea-level change projections with process-based ice sheet models are typically driven with surface mass balance forcing derived from climate models. In this work we address the problems arising from a mismatch of the modelled ice sheet geometry with the one used by the climate model. The proposed remapping method reproduces the original forcing data closely when applied to the original geometry and produces a physically meaningful forcing when applied to different modelled geometries.
Emily Dearing Crampton-Flood, Lars J. Noorbergen, Damian Smits, R. Christine Boschman, Timme H. Donders, Dirk K. Munsterman, Johan ten Veen, Francien Peterse, Lucas Lourens, and Jaap S. Sinninghe Damsté
Clim. Past, 16, 523–541,Short summary
The mid-Pliocene warm period (mPWP; 3.3–3.0 million years ago) is thought to be the last geological interval with similar atmospheric carbon dioxide concentrations as the present day. Further, the mPWP was 2–3 °C warmer than present, making it a good analogue for estimating the effects of future climate change. Here, we construct a new precise age model for the North Sea during the mPWP, and provide a detailed reconstruction of terrestrial and marine climate using a multi-proxy approach.
Heiko Goelzer, Violaine Coulon, Frank Pattyn, Bas de Boer, and Roderik van de Wal
The Cryosphere, 14, 833–840,Short summary
In our ice-sheet modelling experience and from exchange with colleagues in different groups, we found that it is not always clear how to calculate the sea-level contribution from a marine ice-sheet model. This goes hand in hand with a lack of documentation and transparency in the published literature on how the sea-level contribution is estimated in different models. With this brief communication, we hope to stimulate awareness and discussion in the community to improve on this situation.
Anders Levermann, Ricarda Winkelmann, Torsten Albrecht, Heiko Goelzer, Nicholas R. Golledge, Ralf Greve, Philippe Huybrechts, Jim Jordan, Gunter Leguy, Daniel Martin, Mathieu Morlighem, Frank Pattyn, David Pollard, Aurelien Quiquet, Christian Rodehacke, Helene Seroussi, Johannes Sutter, Tong Zhang, Jonas Van Breedam, Reinhard Calov, Robert DeConto, Christophe Dumas, Julius Garbe, G. Hilmar Gudmundsson, Matthew J. Hoffman, Angelika Humbert, Thomas Kleiner, William H. Lipscomb, Malte Meinshausen, Esmond Ng, Sophie M. J. Nowicki, Mauro Perego, Stephen F. Price, Fuyuki Saito, Nicole-Jeanne Schlegel, Sainan Sun, and Roderik S. W. van de Wal
Earth Syst. Dynam., 11, 35–76,Short summary
We provide an estimate of the future sea level contribution of Antarctica from basal ice shelf melting up to the year 2100. The full uncertainty range in the warming-related forcing of basal melt is estimated and applied to 16 state-of-the-art ice sheet models using a linear response theory approach. The sea level contribution we obtain is very likely below 61 cm under unmitigated climate change until 2100 (RCP8.5) and very likely below 40 cm if the Paris Climate Agreement is kept.
Constantijn J. Berends, Bas de Boer, Aisling M. Dolan, Daniel J. Hill, and Roderik S. W. van de Wal
Clim. Past, 15, 1603–1619,Short summary
The Late Pliocene, 3.65–2.75 million years ago, is the most recent period in Earth's history that was warmer than the present. This makes it interesting for climatological research, because it provides a possible analogue for the near future. We used a coupled ice-sheet–climate model to simulate the behaviour of these systems during this period. We show that the warmest moment saw a sea-level rise of 8–14 m, with a CO2 concentration of 320–400 ppmv.
Christopher J. Hollis, Tom Dunkley Jones, Eleni Anagnostou, Peter K. Bijl, Margot J. Cramwinckel, Ying Cui, Gerald R. Dickens, Kirsty M. Edgar, Yvette Eley, David Evans, Gavin L. Foster, Joost Frieling, Gordon N. Inglis, Elizabeth M. Kennedy, Reinhard Kozdon, Vittoria Lauretano, Caroline H. Lear, Kate Littler, Lucas Lourens, A. Nele Meckler, B. David A. Naafs, Heiko Pälike, Richard D. Pancost, Paul N. Pearson, Ursula Röhl, Dana L. Royer, Ulrich Salzmann, Brian A. Schubert, Hannu Seebeck, Appy Sluijs, Robert P. Speijer, Peter Stassen, Jessica Tierney, Aradhna Tripati, Bridget Wade, Thomas Westerhold, Caitlyn Witkowski, James C. Zachos, Yi Ge Zhang, Matthew Huber, and Daniel J. Lunt
Geosci. Model Dev., 12, 3149–3206,Short summary
The Deep-Time Model Intercomparison Project (DeepMIP) is a model–data intercomparison of the early Eocene (around 55 million years ago), the last time that Earth's atmospheric CO2 concentrations exceeded 1000 ppm. Previously, we outlined the experimental design for climate model simulations. Here, we outline the methods used for compilation and analysis of climate proxy data. The resulting climate
atlaswill provide insights into the mechanisms that control past warm climate states.
Hélène Seroussi, Sophie Nowicki, Erika Simon, Ayako Abe-Ouchi, Torsten Albrecht, Julien Brondex, Stephen Cornford, Christophe Dumas, Fabien Gillet-Chaulet, Heiko Goelzer, Nicholas R. Golledge, Jonathan M. Gregory, Ralf Greve, Matthew J. Hoffman, Angelika Humbert, Philippe Huybrechts, Thomas Kleiner, Eric Larour, Gunter Leguy, William H. Lipscomb, Daniel Lowry, Matthias Mengel, Mathieu Morlighem, Frank Pattyn, Anthony J. Payne, David Pollard, Stephen F. Price, Aurélien Quiquet, Thomas J. Reerink, Ronja Reese, Christian B. Rodehacke, Nicole-Jeanne Schlegel, Andrew Shepherd, Sainan Sun, Johannes Sutter, Jonas Van Breedam, Roderik S. W. van de Wal, Ricarda Winkelmann, and Tong Zhang
The Cryosphere, 13, 1441–1471,Short summary
We compare a wide range of Antarctic ice sheet simulations with varying initialization techniques and model parameters to understand the role they play on the projected evolution of this ice sheet under simple scenarios. Results are improved compared to previous assessments and show that continued improvements in the representation of the floating ice around Antarctica are critical to reduce the uncertainty in the future ice sheet contribution to sea level rise.
Marcus P. S. Badger, Thomas B. Chalk, Gavin L. Foster, Paul R. Bown, Samantha J. Gibbs, Philip F. Sexton, Daniela N. Schmidt, Heiko Pälike, Andreas Mackensen, and Richard D. Pancost
Clim. Past, 15, 539–554,Short summary
Understanding how atmospheric CO2 has affected the climate of the past is an important way of furthering our understanding of how CO2 may affect our climate in the future. There are several ways of determining CO2 in the past; in this paper, we ground-truth one method (based on preserved organic matter from alga) against the record of CO2 preserved as bubbles in ice cores over a glacial–interglacial cycle. We find that there is a discrepancy between the two.
Alena Giesche, Michael Staubwasser, Cameron A. Petrie, and David A. Hodell
Clim. Past, 15, 73–90,Short summary
A foraminifer oxygen isotope record from the northeastern Arabian Sea was used to reconstruct winter and summer monsoon strength from 5.4 to 3.0 ka. We found a 200-year period of strengthened winter monsoon (4.5–4.3 ka) that coincides with the earliest phase of the Mature Harappan period of the Indus Civilization, followed by weakened winter and summer monsoons by 4.1 ka. Aridity spanning both rainfall seasons at 4.1 ka may help to explain some of the observed archaeological shifts.
Constantijn J. Berends, Bas de Boer, and Roderik S. W. van de Wal
Geosci. Model Dev., 11, 4657–4675,Short summary
We have devised a novel way to couple a climate model to an ice-sheet model. Usually, climate models are too slow to simulate more than a few centuries, whereas our new model set-up can simulate a full 120 000-year ice age in about 12 h. This makes it possible to look at the interactions between global climate and ice sheets on long timescales, something which is relevant for both research into past climate and future projections.
Eef C. H. van Dongen, Nina Kirchner, Martin B. van Gijzen, Roderik S. W. van de Wal, Thomas Zwinger, Gong Cheng, Per Lötstedt, and Lina von Sydow
Geosci. Model Dev., 11, 4563–4576,Short summary
Ice flow forced by gravity is governed by the full Stokes (FS) equations, which are computationally expensive to solve. Therefore, approximations to the FS equations are used, especially when modeling an ice sheet on long time spans. Here, we report a combination of an approximation with the FS equations that allows simulating the dynamics of ice sheets over long time spans without introducing artifacts caused by application of approximations in parts of the domain where they are not valid.
Sarah L. Bradley, Thomas J. Reerink, Roderik S. W. van de Wal, and Michiel M. Helsen
Clim. Past, 14, 619–635,
Heiko Goelzer, Sophie Nowicki, Tamsin Edwards, Matthew Beckley, Ayako Abe-Ouchi, Andy Aschwanden, Reinhard Calov, Olivier Gagliardini, Fabien Gillet-Chaulet, Nicholas R. Golledge, Jonathan Gregory, Ralf Greve, Angelika Humbert, Philippe Huybrechts, Joseph H. Kennedy, Eric Larour, William H. Lipscomb, Sébastien Le clec'h, Victoria Lee, Mathieu Morlighem, Frank Pattyn, Antony J. Payne, Christian Rodehacke, Martin Rückamp, Fuyuki Saito, Nicole Schlegel, Helene Seroussi, Andrew Shepherd, Sainan Sun, Roderik van de Wal, and Florian A. Ziemen
The Cryosphere, 12, 1433–1460,Short summary
We have compared a wide spectrum of different initialisation techniques used in the ice sheet modelling community to define the modelled present-day Greenland ice sheet state as a starting point for physically based future-sea-level-change projections. Compared to earlier community-wide comparisons, we find better agreement across different models, which implies overall improvement of our understanding of what is needed to produce such initial states.
Timme H. Donders, Niels A. G. M. van Helmond, Roel Verreussel, Dirk Munsterman, Johan ten Veen, Robert P. Speijer, Johan W. H. Weijers, Francesca Sangiorgi, Francien Peterse, Gert-Jan Reichart, Jaap S. Sinninghe Damsté, Lucas Lourens, Gesa Kuhlmann, and Henk Brinkhuis
Clim. Past, 14, 397–411,Short summary
The buildup and melting of ice during the early glaciations in the Northern Hemisphere, around 2.5 million years ago, were far shorter in duration than during the last million years. Based on molecular compounds and microfossils from sediments dating back to the early glaciations we show that the temperature on land and in the sea changed simultaneously and was a major factor in the ice buildup in the Northern Hemisphere. These data provide key insights into the dynamics of early glaciations.
Anna Joy Drury, Thomas Westerhold, David Hodell, and Ursula Röhl
Clim. Past, 14, 321–338,Short summary
North Atlantic Site 982 is key to our understanding of climate evolution over the past 12 million years. However, the stratigraphy and age model are unverified. We verify the composite splice using XRF core scanning data and establish a revised benthic foraminiferal stable isotope astrochronology from 8.0–4.5 million years ago. Our new stratigraphy accurately correlates the Atlantic and the Mediterranean and suggests a connection between late Miocene cooling and dynamic ice sheet expansion.
Brice Noël, Willem Jan van de Berg, J. Melchior van Wessem, Erik van Meijgaard, Dirk van As, Jan T. M. Lenaerts, Stef Lhermitte, Peter Kuipers Munneke, C. J. P. Paul Smeets, Lambertus H. van Ulft, Roderik S. W. van de Wal, and Michiel R. van den Broeke
The Cryosphere, 12, 811–831,Short summary
We present a detailed evaluation of the latest version of the regional climate model RACMO2.3p2 at 11 km resolution (1958–2016) over the Greenland ice sheet (GrIS). The model successfully reproduces the present-day climate and surface mass balance, i.e. snowfall minus meltwater run-off, of the GrIS compared to in situ observations. Since run-off from marginal narrow glaciers is poorly resolved at 11 km, further statistical downscaling to 1 km resolution is required for mass balance studies.
Helen M. Beddow, Diederik Liebrand, Douglas S. Wilson, Frits J. Hilgen, Appy Sluijs, Bridget S. Wade, and Lucas J. Lourens
Clim. Past, 14, 255–270,Short summary
We present two astronomy-based timescales for climate records from the Pacific Ocean. These records range from 24 to 22 million years ago, a time period when Earth was warmer than today and the only land ice was located on Antarctica. We use tectonic plate-pair spreading rates to test the two timescales, which shows that the carbonate record yields the best timescale. In turn, this implies that Earth’s climate system and carbon cycle responded slowly to changes in incoming solar radiation.
Werner M. J. Lazeroms, Adrian Jenkins, G. Hilmar Gudmundsson, and Roderik S. W. van de Wal
The Cryosphere, 12, 49–70,Short summary
Basal melting of ice shelves is a major factor in the decline of the Antarctic Ice Sheet, which can contribute significantly to sea-level rise. Here, we investigate a new basal melt model based on the dynamics of meltwater plumes. For the first time, this model is applied to all Antarctic ice shelves. The model results in a realistic melt-rate pattern given suitable data for the topography and ocean temperature, making it a promising tool for future simulations of the Antarctic Ice Sheet.
Renske C. de Winter, Thomas J. Reerink, Aimée B. A. Slangen, Hylke de Vries, Tamsin Edwards, and Roderik S. W. van de Wal
Nat. Hazards Earth Syst. Sci., 17, 2125–2141,Short summary
This paper provides a full range of possible future sea levels on a regional scale, since it includes extreme, but possible, contributions to sea level change from dynamical mass loss from the Greenland and Antarctica ice sheets. In contrast to the symmetric distribution used in the IPCC report, it is found that an asymmetric distribution toward high sea level change values locally can increase the mean sea level by 1.8 m this century.
Lennert B. Stap, Roderik S. W. van de Wal, Bas de Boer, Richard Bintanja, and Lucas J. Lourens
Clim. Past, 13, 1243–1257,Short summary
We show the results of transient simulations with a coupled climate–ice sheet model over the past 38 million years. The CO2 forcing of the model is inversely obtained from a benthic δ18O stack. These simulations enable us to study the influence of ice sheet variability on climate change on long timescales. We find that ice sheet–climate interaction strongly enhances Earth system sensitivity and polar amplification.
Michiel M. Helsen, Roderik S. W. van de Wal, Thomas J. Reerink, Richard Bintanja, Marianne S. Madsen, Shuting Yang, Qiang Li, and Qiong Zhang
The Cryosphere, 11, 1949–1965,Short summary
Ice sheets reflect most incoming solar radiation back into space due to their high reflectivity (albedo). The albedo of ice sheets changes as a function of, for example, liquid water content and ageing of snow. In this study we have improved the description of albedo over the Greenland ice sheet in a global climate model. This is an important step, which also improves estimates of the annual ice mass gain or loss over the ice sheet using this global climate model.
Stefanie Kaboth, Patrick Grunert, and Lucas Lourens
Clim. Past, 13, 1023–1035,Short summary
This study is devoted to reconstructing Mediterranean Outflow Water (MOW) variability and the interplay between the Mediterranean and North Atlantic climate systems during the Early Pleistocene. We find indication that the increasing production of MOW aligns with the intensification of the North Atlantic overturning circulation, highlighting the potential of MOW to modulate the North Atlantic salt budget. Our results are based on new stable isotope and grain-size data from IODP 339 Site U1389.
Markella Prokopiou, Patricia Martinerie, Célia J. Sapart, Emmanuel Witrant, Guillaume Monteil, Kentaro Ishijima, Sophie Bernard, Jan Kaiser, Ingeborg Levin, Thomas Blunier, David Etheridge, Ed Dlugokencky, Roderik S. W. van de Wal, and Thomas Röckmann
Atmos. Chem. Phys., 17, 4539–4564,Short summary
Nitrous oxide is the third most important anthropogenic greenhouse gas with an increasing mole fraction. To understand its natural and anthropogenic sources we employ isotope measurements. Results show that while the N2O mole fraction increases, its heavy isotope content decreases. The isotopic changes observed underline the dominance of agricultural emissions especially at the early part of the record, whereas in the later decades the contribution from other anthropogenic sources increases.
Constantijn J. Berends and Roderik S. W. van de Wal
Geosci. Model Dev., 9, 4451–4460,Short summary
This paper describes several improvements to the so-called "flood-fill algorithm" – a computer program widely known for its use in the "paint bucket" tool in several drawing programs such as MS Paint. However, it can also be used to determine the extent and depth of lakes in a topography map, which is useful in hydrology and climatology. In such cases, the default algorithm can be too slow to be of much use. Our improvements can make it up to 100 times faster, making it much more feasible.
Thomas J. Reerink, Willem Jan van de Berg, and Roderik S. W. van de Wal
Geosci. Model Dev., 9, 4111–4132,Short summary
Ice sheets are part of the climate system and interact with the atmosphere and the ocean. OBLIMAP is a powerful tool to map climate fields between GCMs and ISMs (ice sheet models), which run on grids that differ in curvature, resolution and extent. OBLIMAP uses optimal aligned oblique projections, which minimize area distortions. OBLIMAP 2.0 allows for high-frequency embedded coupling and masked mapping. A fast search strategy realizes a huge performance gain and enables high-resolution mapping.
David A. Hodell and James E. T. Channell
Clim. Past, 12, 1805–1828,Short summary
For the past 2.7 million years the Earth's climate has switched more than 50 times between a cold glacial and warm interglacial state. We found the trend towards larger ice sheets over the past 2.7 million years was accompanied by changes in the style, frequency, and intensity of shorter-term (millennial) variability. We suggest the interaction between millennial climate change and longer-term variations in the Earth's orbit may be important for explaining the patterns of Quaternary climate.
Mathieu Martinez, Sergey Kotov, David De Vleeschouwer, Damien Pas, and Heiko Pälike
Clim. Past, 12, 1765–1783,Short summary
Identification of Milankovitch cycles within the sedimentary record depends on spectral analyses, but these can be biased because there are always slight uncertainties in the sample position within a sedimentary column. Here, we simulate uncertainties in the sample position and show that a tight control on the inter-sample distance together with a density of 6–12 samples per precession cycle are needed to accurately reconstruct the contribution of the orbital forcing on past climate changes.
Hemmo A. Abels, Vittoria Lauretano, Anna E. van Yperen, Tarek Hopman, James C. Zachos, Lucas J. Lourens, Philip D. Gingerich, and Gabriel J. Bowen
Clim. Past, 12, 1151–1163,Short summary
Ancient greenhouse warming episodes are studied in river floodplain sediments in the western interior of the USA. Paleohydrological changes of four smaller warming episodes are revealed to be the opposite of those of the largest, most-studied event. Carbon cycle tracers are used to ascertain whether the largest event was a similar event but proportional to the smaller ones or whether this event was distinct in size as well as in carbon sourcing, a question the current work cannot answer.
Claudia Agnini, David J. A. Spofforth, Gerald R. Dickens, Domenico Rio, Heiko Pälike, Jan Backman, Giovanni Muttoni, and Edoardo Dallanave
Clim. Past, 12, 883–909,Short summary
In this paper we present records of stable C and O isotopes, CaCO3 content, and changes in calcareous nannofossil assemblages in a upper Paleocene-lower Eocene rocks now exposed in northeast Italy. Modifications of nannoplankton assemblages and carbon isotopes are strictly linked one to each other and always display the same ranking and spacing. The integration of this two data sets represents a significative improvement in our capacity to correlate different sections at a very high resolution.
Peter Köhler, Lennert B. Stap, Anna S. von der Heydt, Bas de Boer, and Roderik S. W. van de Wal
Clim. Past Discuss.,
Revised manuscript not acceptedShort summary
Evidence indicate that specific equilibrium climate sensitivity, the global annual mean surface temperature change as a response to a change in radiative forcing, is state dependent. We here show that the interpretation of data in the state-dependent case is not straightforward. We analyse the differences of a point-wise approach and one based on a piece-wise linear analysis, combine both, compare with potential model results and apply the theoretical concepts to data of the last 800 kyr.
P. Köhler, B. de Boer, A. S. von der Heydt, L. B. Stap, and R. S. W. van de Wal
Clim. Past, 11, 1801–1823,Short summary
We find that the specific equilibrium climate sensitivity due to radiative forcing of CO2 and land ice albedo has been state-dependent for the last 2.1Myr (most of the Pleistocene). Its value is ~45% larger during intermediate glaciated climates and interglacial periods than during Pleistocene full glacial conditions. The state dependency is mainly caused by a latitudinal dependency in ice sheet area changes. Due to uncertainties in CO2, firm conclusions for the Pliocene are not yet possible.
J. H. C. Bosmans, F. J. Hilgen, E. Tuenter, and L. J. Lourens
Clim. Past, 11, 1335–1346,Short summary
Our study shows that the influence of obliquity (the tilt of Earth's rotational axis) can be explained through changes in the insolation gradient across the tropics. This explanation is fundamentally different from high-latitude mechanisms that were previously often inferred to explain obliquity signals in low-latitude paleoclimate records, for instance glacial fluctuations. Our study is based on state-of-the-art climate model experiments.
V. Lauretano, K. Littler, M. Polling, J. C. Zachos, and L. J. Lourens
Clim. Past, 11, 1313–1324,Short summary
Several episodes of global warming took place during greenhouse conditions in the early Eocene and are recorded in deep-sea sediments. The stable carbon and oxygen isotope records are used to investigate the magnitude of six of these events describing their effects on the global carbon cycle and the associated temperature response. Findings indicate that these events share a common nature and hint to the presence of multiple sources of carbon release.
B. Noël, W. J. van de Berg, E. van Meijgaard, P. Kuipers Munneke, R. S. W. van de Wal, and M. R. van den Broeke
The Cryosphere, 9, 1831–1844,Short summary
We compare Greenland Ice Sheet surface mass balance (SMB) from the updated polar version of the regional climate model RACMO2.3 and the previous version 2.1. RACMO2.3 has an adjusted rainfall-to-snowfall conversion favouring summer snowfall over rainfall. Enhanced summer snowfall reduce melt rates in the ablation zone by covering dark ice with highly reflective fresh snow. This improves the modelled SMB-elevation gradient and surface energy balance compared to observations in west Greenland.
L. G. van der Wel, H. A. Been, R. S. W. van de Wal, C. J. P. P. Smeets, and H. A. J. Meijer
The Cryosphere, 9, 1089–1103,Short summary
We performed 2H isotope diffusion measurements in the upper 3 metres of firn at Summit, Greenland, by following over a 4-year period isotope-enriched snow that we deposited. We found that the diffusion process was much less rapid than in the most commonly used model. We discuss several aspects of the diffusion process that are still poorly constrained and might lead to this discrepancy. Quantitative knowledge of diffusion is necessary for use of the diffusion process itself as a climate proxy.
B. de Boer, A. M. Dolan, J. Bernales, E. Gasson, H. Goelzer, N. R. Golledge, J. Sutter, P. Huybrechts, G. Lohmann, I. Rogozhina, A. Abe-Ouchi, F. Saito, and R. S. W. van de Wal
The Cryosphere, 9, 881–903,Short summary
We present results from simulations of the Antarctic ice sheet by means of an intercomparison project with six ice-sheet models. Our results demonstrate the difficulty of all models used here to simulate a significant retreat or re-advance of the East Antarctic ice grounding line. Improved grounding-line physics could be essential for a correct representation of the migration of the grounding line of the Antarctic ice sheet during the Pliocene.
R. S. W. van de Wal, C. J. P. P. Smeets, W. Boot, M. Stoffelen, R. van Kampen, S. H. Doyle, F. Wilhelms, M. R. van den Broeke, C. H. Reijmer, J. Oerlemans, and A. Hubbard
The Cryosphere, 9, 603–611,Short summary
This paper addresses the feedback between ice flow and melt rates. Using 20 years of data covering the whole ablation area, we show that there is not a strong positive correlation between annual ice velocities and melt rates. Rapid variations around the equilibrium line indicate the possibility of rapid variations high on the ice sheet.
B. S. Slotnick, V. Lauretano, J. Backman, G. R. Dickens, A. Sluijs, and L. Lourens
Clim. Past, 11, 473–493,
S. J. Koenig, A. M. Dolan, B. de Boer, E. J. Stone, D. J. Hill, R. M. DeConto, A. Abe-Ouchi, D. J. Lunt, D. Pollard, A. Quiquet, F. Saito, J. Savage, and R. van de Wal
Clim. Past, 11, 369–381,Short summary
The paper assess the Greenland Ice Sheet’s sensitivity to a warm period in the past, a time when atmospheric CO2 concentrations were comparable to current levels. We quantify ice sheet volume and locations in Greenland and find that the ice sheets are less sensitive to differences in ice sheet model configurations than to changes in imposed climate forcing. We conclude that Pliocene ice was most likely to be limited to highest elevations in eastern and southern Greenland.
P. M. Alexander, M. Tedesco, X. Fettweis, R. S. W. van de Wal, C. J. P. P. Smeets, and M. R. van den Broeke
The Cryosphere, 8, 2293–2312,
L. B. Stap, R. S. W. van de Wal, B. de Boer, R. Bintanja, and L. J. Lourens
Clim. Past, 10, 2135–2152,
B. de Boer, P. Stocchi, and R. S. W. van de Wal
Geosci. Model Dev., 7, 2141–2156,
M. N. A. Maris, B. de Boer, S. R. M. Ligtenberg, M. Crucifix, W. J. van de Berg, and J. Oerlemans
The Cryosphere, 8, 1347–1360,
A. B. A. Slangen, R. S. W. van de Wal, Y. Wada, and L. L. A. Vermeersen
Earth Syst. Dynam., 5, 243–255,
T. Westerhold, U. Röhl, H. Pälike, R. Wilkens, P. A. Wilson, and G. Acton
Clim. Past, 10, 955–973,
D. A. Hodell, L. Lourens, D. A. V. Stow, J. Hernández-Molina, C. A. Alvarez Zarikian, and the Shackleton Site Project Members
Sci. Dril., 16, 13–19,
M. M. Helsen, W. J. van de Berg, R. S. W. van de Wal, M. R. van den Broeke, and J. Oerlemans
Clim. Past, 9, 1773–1788,
M. N. A. Maris, B. de Boer, and J. Oerlemans
Clim. Past, 8, 803–814,
M. M. Helsen, R. S. W. van de Wal, M. R. van den Broeke, W. J. van de Berg, and J. Oerlemans
The Cryosphere, 6, 255–272,
R. S. W. van de Wal, B. de Boer, L. J. Lourens, P. Köhler, and R. Bintanja
Clim. Past, 7, 1459–1469,
A. B. A. Slangen and R. S. W. van de Wal
The Cryosphere, 5, 673–686,
I. G. M. Wientjes, R. S. W. Van de Wal, G. J. Reichart, A. Sluijs, and J. Oerlemans
The Cryosphere, 5, 589–601,
M. R. van den Broeke, C. J. P. P. Smeets, and R. S. W. van de Wal
The Cryosphere, 5, 377–390,
M. A. G. den Ouden, C. H. Reijmer, V. Pohjola, R. S. W. van de Wal, J. Oerlemans, and W. Boot
The Cryosphere, 4, 593–604,
T. J. Reerink, M. A. Kliphuis, and R. S. W. van de Wal
Geosci. Model Dev., 3, 13–41,
M. van den Broeke, P. Smeets, J. Ettema, C. van der Veen, R. van de Wal, and J. Oerlemans
The Cryosphere, 2, 179–189,
J. Oerlemans, M. Dyurgerov, and R. S. W. van de Wal
The Cryosphere, 1, 59–65,
J. O. Sewall, R. S. W. van de Wal, K. van der Zwan, C. van Oosterhout, H. A. Dijkstra, and C. R. Scotese
Clim. Past, 3, 647–657,
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