New ice2ice publication- A generalized approach to estimating diffusion length of stable water isotopes from ice‐core data

Our new publication led by Emma Kahle (University of Washington) deals with the technical challenges the new continuous melting techniques for water isotope analysis have introduced to the study of the firn isotope diffusion. Improvements in precision and resolution have resulted in sizeable effects that hinder our ability to accurately infer diffusion lengths from high resolution water isotope records. In this paper we consider various new approaches for describing the power spectral densities of high resolution data sets and  discuss their implications for temperature reconstructions based on firn isotope diffusion.

Kahle, E. C., Holme, C., Jones, T. R., Gkinis, V., & Steig, E. J. (2018). A generalized approach to estimating diffusion length of stable water isotopes from ice‐core data. Journal of Geophysical Research: Earth Surface, 123.

Diffusion of water vapor in the porous firn layer of ice sheets damps high‐frequency variations in water‐isotope profiles. Through spectral analysis, the amount of diffusion can be quantified as the“diffusion length,” the mean cumulative diffusive displacement of water molecules relative to their original location at time of deposition. In this study, we use two types of ice‐core data, obtained from either continuous‐flow analysis or discrete sampling, to separate diffusional effects occurring in the ice sheet from those arising through analytical processes in the laboratory. In both Greenlandic and Antarctic ice cores, some characteristics of the power spectral density of a data set depend on the water‐isotope measurement process. Due to these spectral characteristics, currently established approaches for diffusion estimation do not work equally well for newer, continuously measured data sets with lower instrument noise levels. We show how smoothing within the continuous‐flow analysis system can explain these spectral differences. We propose two new diffusion‐estimation techniques, which can be applied to either continuously or discretely measured data sets. We evaluate these techniques and demonstrate their viability for future use. The results of this study have the potential to improve climate interpretation of ice‐core records as well as models of firn densification and diffusion.

What’s wrong with the bipolar ocean seesaw hypothesis?

Fig. 1
Temperature reconstructions from Greenland and Antarctic ice cores spanning Marine Isotope Stage 3

The thermal bipolar ocean seesaw hypothesis was proposed by Stocker and Johnsen (2003) as the ‘simplest possible thermodynamic model’ to explain the time relationship between Dansgaard-Oeschger (DO) and Antarctic Isotope Maxima (AIM) events. Following the Bergen ice2ice MIS3/Southern Ocean and Bipolar Seesaw Workshop a group of ice2ice researchers and some international collaborators were invited by Quaternary Science Reviews to write a review on the thermal seesaw. The resulting paper, “Beyond the bipolar seesaw: towards a process-understanding of inter-hemispheric coupling” by J. Pedro, M. Jochum, C. Buizert, F. He, S. Barker and S. Rasmussen, is now live and open access at QSR.

In the review we use theory, coupled model simulations and paleoclimate data to test the thermal seesaw. Our results lead to four main challenges to the hypothesis:

  • Compensating heat transports: Changes in Atlantic heat transport invoked by the thermal seesaw are compensated by opposing changes in heat transport by the global atmosphere and the Pacific ocean. This compensation (which would come as no surprise to Vilhelm Bjerknes) has a decisive influence on the spatial pattern of climate anomalies. Changed ocean heat transport strongly affects sea ice, triggering ice-albedo feedbacks that dominate the high-latitude climate response. Changed atmospheric heat transport alters the position and intensity of the Hadley circulation and of atmospheric jets and eddies, dominating the response at low to mid-latitudes.
  • A global ocean—not Southern Ocean—heat reservoir: According to the thermal seesaw hypothesis, the Southern Ocean acts as a heat reservoir during the DO/AIM events, integrating changes in South Atlantic temperature. We dispute this because South Atlantic temperature anomalies spread much more efficiently into the Indian and Pacific Ocean, by Kelvin and Rossby wave processes and by advection, than they do into the Southern Ocean. This is because the Southern Ocean has no zonal boundary to support waves and because the Antarctic Circumpolar Current (ACC) prohibits advection, since by definition the flow is along the current’s axis. In coupled model simulations the heat content of the Southern Ocean shows very little change during the DO/AIM events; instead, the global ocean north of the ACC better fits the description of heat reservoir.
  • Wind-driven thermocline deepening: In the conventional thermal seesaw, a collapse of the AMOC causes heat that would otherwise be advected north to accumulate in the South Atlantic. In our coupled model experiments, a southward shift of the ITCZ accompanies northern high latitude cooling (as commonly seen in previous studies). The ITCZ shift and associated changes in wind stress over the South Atlantic gyre deepen the thermocline there, such that abrupt South Atlantic warming results from reduced northward advection coupled to the wind-driven deepening of the thermocline. The thermocline deepening is essential in enabling heat to be stored at depth rather than released to the atmosphere through the Ekman layer.
  • Atmospheric heat transport warms Antarctica: Antarctica warms during AIM events due to an increase in poleward atmospheric heat and moisture transport following sea ice retreat and surface warming over the Southern Ocean. The sea-ice retreat is itself driven by gradual eddy-heat fluxes across the ACC that initiate sea ice melt and are amplified by sea-ice albedo feedbacks. The centennial lag of Antarctic warming after AMOC collapse (WAIS Divide Project Members, 2015) reflects the time required for heat to accumulate in the global ocean interior before it can be mixed across the ACC by eddies and trigger the sea-ice feedback. For the nitty gritty, including our full assessment of the Antarctic and Southern Ocean energy balance during AIM events, please do refer to the paper.

In the spirit of ice2ice the review was a collaboration between ice-core (Buizert, Rasmussen, Pedro), sediment core (Barker) and modelling (Jochum, He) specialists. I’m grateful to all these coauthors for their excellent (and diverse!) inputs and to ice2ice for the support throughout, including for the MIS3/Southern Ocean and Bipolar Seesaw Workshop that kicked this effort off.

Joel Pedro
Hobart, 26 June 2018

Stocker, T.F., Johnsen, S.J., 2003. A minimum thermodynamic model for the bipolar seesaw. Paleoceanography 18, 11-1.
Pedro, J. B., Jochum, M., Buizert, C., He, F., Barker, S., Rasmussen S.O., Beyond the bipolar seesaw: Toward a process understanding of inter-hemispheric coupling. Quaternary Science Reviews (in press),, 2018.
WAIS Divide Project Members, 2015. Precise interpolar phasing of abrupt climate change during the last ice age. Nature 520, 661-665.

Team Bergen is getting ready for Greenland, are you?

by ice2ice PhD Sunniva Rutledal

Over the course of three days (9-11 May), seven BCCR and Ice2Ice researchers participated in a glacier safety course on the Folgefonna glacier

Anais, Andreas, Alexios and Tobias. Photo credit: Tobias Zolles

If you drive about 1.5 hour east of Bergen, you reach Jondal, a small village in the Hardangerfjord with the scenic Folgefonna glacier in the background. Folgefonna glacier is the third largest glacier in Norway and was going to be our office for the next three days.

The course started down in warm and sunny Jondal where we practiced on different pulley systems and knots. Afterwards we hiked up to the glacier for a small taste of what was to come.

Practicing on pulley systems down in Jondal. Photo credit: Petra Langebroek

Most of the second day was spent on the glacier and we practiced walking in rope teams and on the pulley systems we had learned down in Jondal the day before. However, now we faced harsher weather conditions, perfect for testing our skills under pressure. On the top of a small hill we divided in teams and practiced on using the pulley systems to pull a team member up a steep slope, imitating a crevasse. In the evening, back in Jondal, we went through some techniques on rescuing injured people down from a glacier.


Alexios, Petra and Sunniva working on their pulley system. Photo credit: Tobias Zolles

The last day the sun was shining (let’s be honest, I think all of us got a sunburn) and up on the glacier we practiced on our navigational skills using maps and GPS. The afternoon was spent at the shooting range down in Jondal.

Petra, Margit and Sunniva on the top of the Folgefonna glacier.

Thank you to our guides Snorre and Lars Petter (Folgefonni Breførerlag) and to the Ice2Ice project for arranging the course.


By Ice2Ice PhD Sunniva Rutledal

Paleoclimate states as future climate analogues

Ice2ice workshop summary

Written by Rasmus Pedersen

Can our combined knowledge of past abrupt changes provide lessons for the future?

20 ice2ice researchers with varying backgrounds and ‘seniority’ met in Copenhagen to discuss to what extent the combined ice2ice knowledge of past climate change is relevant for future climate scenarios.

With input from modellers and proxy data experts, the very interactive workshop featured presentations and discussions of proxy data reconstructions, paleoclimate modelling efforts, and future model projections focusing on sea ice related warming near Greenland.

The program was split into three sessions – leading to a step-by-step assessment of similarities and differences between the past and potential future conditions. Below are some headlines from the sessions, along with the summary with notes and plans for future work (if you are part of ice2ice you can find these in the dropbox).

Topic 1: Rate of warming and sea ice loss

  • Magnitude of past Greenland warming in proxy data and paleo modelling efforts are similar (10 K), but rate of change is higher in models compared to proxy records.
  • Rate of future warming in model projections does not appear abrupt (but are the models able to simulate abrupt change?). Rate of future ice loss does appear abrupt in selected models

Topic 2: Nordic Seas [paleo] vs Arctic Ocean [future]

  • The dynamics and properties of the present/future Arctic Ocean and past Nordic Seas have similar features, but there might smaller differences that are of key importance.
  • Greenland is sensitive to ice loss in “the vicinity”, but the atmospheric response to sea ice loss is highly sensitive to the location (and magnitude) of ice loss.

Topic 3: Drivers of (abrupt) sea ice loss

  • The paleo mechanism(s) could in principle apply in a future, Arctic Ocean setting. This does, however, require further investigation. The potential for future abrupt sea ice loss can be assessed by testing concrete ice2ice hypotheses explaining the past abrupt (D-O) sea ice loss.


Modelling Greenland to determine future sea level

Ice2ice researcher Christian Rodehacke is co-author on a new article in The cryosphere investigating different models of Greenland ice sheet and how they compare.

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.

The full study can be found here.

Common ice mask of the ensemble of models in the in-
tercomparison. The colour code indicates the number of models
(out of 35 in total) that simulate ice at a given location. Outlines
of the observed ice sheet proper (Rastner et al., 2012) and all ice-
covered regions (i.e. main ice sheet plus small ice caps and glaciers;
Morlighem et al., 2014) are given as black and grey contour lines,

Goelzer, H., Nowicki, S., Edwards, T., Beckley, M., Abe-Ouchi, A., Aschwanden, A., Calov, R., Gagliardini, O., Gillet-Chaulet, F., Golledge, N. R., Gregory, J., Greve, R., Humbert, A., Huybrechts, P., Kennedy, J. H., Larour, E., Lipscomb, W. H., Le clec’h, S., Lee, V., Morlighem, M., Pattyn, F., Payne, A. J., Rodehacke, C., Rückamp, M., Saito, F., Schlegel, N., Seroussi, H., Shepherd, A., Sun, S., van de Wal, R., and Ziemen, F. A.: Design and results of the ice sheet model initialisation initMIP-Greenland: an ISMIP6 intercomparison, The Cryosphere, 12, 1433-1460,, 2018.

ice2ice is again very well represented at EGU

Again this year ice2ice is very will be very well represented at European Geophysical Union meeting running from 8-14th of April in Vienna. Below some of the sessions, presentations and posters that will be presented or is co-authored by ice2ice. But please do keep updated at


Mon, 09 Apr

 CR1.6The Antarctic Ice Sheet: past, present and future contributions towards global sea level PICO08:30–10:00PICO spot 4
EGU2018-1964 Antarctic snow accumulation over the past 200 years by Elizabeth Thomas, Brooke Medley, Melchior van Wessem, Elisabeth Isaksson, Elisabeth Schlosser, Paul Vallelonga, Jan Lenaerts, Nancy Bertler, and Michiel van den Broeke

Mon, 09 Apr

You have selected presentations in the following Sessions:

  • CL5.02/AS5.7/BG1.38/GD10.9/GI0.5/GM2.10/GMPV10.9/HS11.25/NH11.1/NP9.4/OS4.14/PS6.4/SM7.04/SSP1.12/SSS13.12/ST4.8/TS11.9, PICO, PICO spot 5a
  • CR5.3, Orals, Room N1
CL5.02/AS5.7/BG1.38/GD10.9/GI0.5/GM2.10/GMPV10.9/HS11.25/NH11.1/NP9.4/OS4.14/PS6.4/SM7.04/SSP1.12/SSS13.12/ST4.8/TS11.9,The development of geoscientific modelling (co-organized) PICO15:30–17:00PICO spot 5a
EGU2018-7122 A Fast Versatile Ocean Simulator (Veros) in Pure Python by Dion Häfner, René Løwe Jacobsen, Carsten Eden, Mads R.B. Kristensen, Markus Jochum, Roman Nuterman, and Brian Vinter
 CR5.3Subglacial Environments of Ice Sheets and Glaciers Orals15:30–17:00Room N1
16:15–16:30 EGU2018-7498 The effect of subglacial hydrology when assessing the impact of geothermal heat flux on sliding and ice dynamics by Silje Smith-Johnsen, Basile de Fleurian, and Kerim Nisancioglu

Mon, 09 Apr

 CL0.00Open Session on Climate: Past, Present and Future Posters17:30–19:00Hall X5
X5.240 EGU2018-9787 Early Holocene establishment of the Barents Sea Arctic front by Bjørg Risebrobakken and Sarah M. Berben
 CL1.02Studying the climate of the last two millennia Posters17:30–19:00Hall X5
X5.264 EGU2018-6586 Sclerochronologic and oxygen isotope analysis of growth increments in the bivalve Arctica islandica from the Southwest Icelandic Shelf by Carin Andersson, Vilde Melvik, Fabian Bonitz, and Tamara Trofimova
X5.267 EGU2018-12415 Temperature reconstructions for the Faroese region based on the analysis of the d18O signal in Arctica islandica shells by Fabian Bonitz, Carin Andersson, and Tamara Trofimova
 CL4.10Arctic climate change: governing mechanisms and global implications Posters17:30–19:00Hall X5
X5.346 EGU2018-10916 The fate of the NAO in a very long climate change simulation by Martin Stendel, Shuting Yang, Peter Langen, Christian Rodehacke, Ruth Mottram, and Jens Hesselbjerg Christensen
 CR1.1State of the Cryosphere: Observations and Modelling Posters17:30–19:00Hall X4
X4.13 EGU2018-15488 Polar Portal – See changes in the Arctic as they occur by Martin Stendel, Peter Langen, Jason Box, Louise Sandberg Sørensen, and Thomas Ingeman-Nielsen
 CR1.4Glaciers and ice caps under climate change Posters17:30–19:00Hall X4
X4.30 EGU2018-14812 Sensitivity of runoff from Vatnajökull, Iceland, to spring snow cover by Louise Steffensen Schmidt, Guðfinna Aðalgeirsdóttir, Peter Langen, Finnur Palsson, Sverrir Guðmundsson, and Andri Gunnarsson

Tue, 10 Apr

 OS1.1Open Session on General Circulation, Ocean Climate Variability and Air-Sea Interactions (including Fridtjof Nansen Medal Lecture) Orals08:30–10:00Room N1
08:45–09:00 EGU2018-12068 A geometric interpretation of vertical structure and eddy-mean flow interaction in the Southern Ocean by Mads Bruun Poulsen, Markus Jochum, James R. Maddison, David P. Marshall, and Roman Nuterman

Tue, 10 Apr

 CR1.8/CL1.16The Quest for Oldest Ice (co-organized) PICO15:30–17:00PICO spot 3
EGU2018-12782 Coupling water isotope firn diffusion to a fork of the Community Firn Modelby Vasileios Gkinis, Christian Holme, Bo Vinther, Emma Kahle, and Eric Steig

Tue, 10 Apr

You have selected presentations in the following Sessions:

  • AS1.35, Posters, Hall X5
  • CR1.3/CL1.26/GM9.5, Posters, Hall X4
 AS1.35Dynamical coupling between the stratosphere and the troposphere Posters17:30–19:00Hall X5
X5.89 EGU2018-6474 The QBO/ENSO connection in climate models by Bo Christiansen, Federico Serva, Shuting Yang, and Chiara Cagnazzo
 CR1.3/CL1.26/GM9.5Reconstructing paleo ice dynamics: Comparing and combining field-based evidence and numerical modeling (co-organized) Posters17:30–19:00Hall X4
X4.16 EGU2018-4323 Fast retreat of a marine outlet glacier in western Norway at the last glacial termination by Henning Åkesson, Richard Gyllencreutz, Jan Mangerud, John Inge Svendsen, Faezeh M. Nick, and Kerim H. Nisancioglu

Tue, 10 Apr

 TM6Scientific integrity in a politically challenged world 19:00–20:00Room L4/5


Wed, 11 Apr
 CL1.18Proxy system modelling and data assimilation in paleoclimatology Orals08:30–10:00Room 0.94
09:15–09:30 EGU2018-12472 How informative are SST proxy data in paleoceanographic inverse modeling? – Insights from comprehensive uncertainty quantification by Nora Loose, Patrick Heimbach, and Kerim H. Nisancioglu
Wed, 11 Apr

You have selected presentations in the following Sessions:

  • CL1.21, Orals, Room F2
  • CR1.2/CL4.19, Orals, Room L3
  • GD8.1/CR6.4/SM4.12/SSP2.18/TS1.6, Orals, Room -2.47
 CL1.21On the dynamics of Dansgaard-Oeschger events; perspectives from paleoclimate data and modeling (including Hans Oeschger Medal Lecture and CL Division Outstanding ECS Lecture) Orals13:30–15:00Room F2
13:30–13:45 EGU2018-1989 Climatic teleconnections during the last ice age: postcards and text messages from the North Atlantic by Christo Buizert, Michael Sigl, Mirko Severi, Bradley Markle, Joseph McConnell, Joel Pedro, Justin Wettstein, Harald Sodemann, Kumiko Goto-Azuma, Kenji Kawamura, Shuji Fujita, Hideaki Motoyama, Motohiro Hirabayashi, Ryu Uemura, Barbara Stenni, Frédéric Parrenin, Feng He, Tyler Fudge, and Eric Steig
13:45–14:00 EGU2018-10494 Relative timing of precipitation and ocean circulation changes in the western equatorial Atlantic over the last 45 ky by Claire Waelbroeck, Sylvain Pichat, Bryan C. Lougheed, Evelyn Böhm, Lise Missiaen, Mathieu Vrac, Natalia Vazquez Riveiros, Pierre Burckel, Jörg Lippold, Helge Arz, Trond Dokken, François Thil, and Arnaud Dapoigny
14:00–14:15 EGU2018-14136 Testing the assumption of synchronous Dansgaard Oeschger events in ice cores and speleothems: Linking GICC05 to the U/Th timescale via cosmogenic radionuclide records by Florian Adolphi, Tobias Erhardt, Christopher Bronk-Ramsey, and Raimund Muscheler
14:15–14:30 EGU2018-16354 Glacial Climate Stability: Pathway to understand abrupt glacial climate shiftsby Xu Zhang, Gregor Knorr, Steve Barker, and Gerrit Lohmann
14:30–14:45 EGU2018-11230 Dansgaard-Oeschger cycles as a mode of internal climate variability by Heather Andres and Lev Tarasov
14:45–15:00 EGU2018-18793 DO-like oscillation under limited range of CO2 and freshwater forcing by Ayako Abe-Ouchi, Wing-Le Chan, Sam Tadano-Sherriff, Takashi Obase, Akira Oka, Masa Yoshimori, Kenji Kawamura, and Takahito Mitsui
 CR1.2/CL4.19Modelling ice sheets and glaciers and ice-climate interactions (co-organized) Orals13:30–15:00Room L3
13:30–13:45 EGU2018-14615 Modeling Greenland ice sheet evolution during the Plio-Pleistocene transition: new constraints for pCO2 pathway by Ning Tan, Jean-Baptiste Ladant, Gilles Ramstein, Christophe Dumas, Paul Bachem, and Eystein Jansen
13:45–14:00 EGU2018-8693 Simulated Eemian Greenland Surface Mass Balance shows strong sensitivity to SMB model choice by Andreas Plach, Kerim Hestnes Nisancioglu, and Sebastien Le clec’h
 GD8.1/CR6.4/SM4.12/SSP2.18/TS1.6The Arctic connection – geodynamic, geologic and oceanographic development of the Arctic (co-organized) Orals13:30–15:00Room -2.47
13:30–13:45 EGU2018-17845 Impact of basaltic sills on sedimentary host rocks in the High Arctic Large Igneous Province by Frances M. Deegan, Jean H. Bédard, Valentin R. Troll, Keith Dewing, Steve E. Grasby, Hamed Sanei, Chris Harris, Chris Yakymchuck, Sean R. Sheih, Carmela Freda, Valeria Misiti, Silvio Mollo, Harri Geiger, and Carol A. Evenchick
13:45–14:00 EGU2018-5122 Fault activity and diapirism in the Mississippian to Late Cretaceous Sverdrup Basin: New insights into the tectonic evolution of the Canadian Arctic by Berta Lopez Mir, Peter Hulse, and Simon Schneider
14:00–14:15 EGU2018-3865 An overview of the Greenland cross-shelf glaciations by Lara F. Pérez, Tove Nielsen, Paul C. Knutz, Julia C. Hofmann, and Katrien Heirman
14:15–14:30 EGU2018-19462 Oblique opening and mantle exhumation in the western Eurasia Basin, Arctic Ocean by Kai Berglar, Rüdiger Lutz, Dieter Franke, Ingo Heyde, Bernd Schreckenberger, Peter Klitzke, Wolfram Geissler, and Volkmar Damm
14:30–14:45 EGU2018-12480 Improved location estimates for seismicity along the northern North Atlantic Ridge by Steven J. Gibbons, Valérie Maupin, Christian Grude Kolstad, Tormod Kværna, and Asbjørn Johan Breivik
14:45–15:00 EGU2018-6083 Weakened lithosphere beneath Greenland inferred from effective elastic thickness: A hotspot effect? by Rebekka Steffen, Pascal Audet, and Björn Lund
Wed, 11 Apr
 CL1.21On the dynamics of Dansgaard-Oeschger events; perspectives from paleoclimate data and modeling (including Hans Oeschger Medal Lecture and CL Division Outstanding ECS Lecture) Orals15:30–17:00Room F2
15:30–15:45 EGU2018-12467 Improving the simulation of the Northern Hemisphere ice-sheet response to millennial-scale climate variability by Marisa Montoya, Rubén Banderas, Jorge Álvarez-Solas, and Alexander Robinson
15:45–16:00 EGU2018-16393 Evidence for dynamic changes in the subpolar gyre during Dansgaard-Oeschger cycles by Andreas Born and Camille Li
16:00–17:00 EGU2018-1891 Dansgaard-Oeschger events: rapid, rare and unexpected!? by Hubertus Fischer
Wed, 11 Apr

You have selected presentations in the following Sessions:

  • CL1.21, Posters, Hall X5
  • CL4.09, Posters, Hall X5
  • CR5.4/OS1.16, Posters, Hall X5
  • GD8.1/CR6.4/SM4.12/SSP2.18/TS1.6, Posters, Hall X2
 CL1.21On the dynamics of Dansgaard-Oeschger events; perspectives from paleoclimate data and modeling (including Hans Oeschger Medal Lecture and CL Division Outstanding ECS Lecture) Posters17:30–19:00Hall X5
X5.257 EGU2018-958 Changes in wetland exposure during Dansgaard-Oeschger events 19-21 suggested by atmospheric methane and temperature records from the Eastern Greenland RECAP ice core by Diana Vladimirova, Bo Vinther, Paul Vallelonga, Vasileios Gkinis, Todd Sowers, Helle Kjaer, Remi Dallmayr, Emilie Capron, Sune Rasmussen, Alexey Ekaykin, and Thomas Blunier
X5.258 EGU2018-2551 Beyond the bipolar seesaw: toward a process understanding of interhemispheric coupling by Joel Pedro, Markus Jochum, Christo Buizert, Feng He, Stephen Barker, and Sune Rasmussen
X5.259 EGU2018-9221 The role of glacial sea ice variability in the Norwegian Sea during abrupt Dansgaard-Oeschger climate changes by Henrik Sadatzki, Trond M. Dokken, Sarah M. P. Berben, Francesco Muschitiello, Ruediger Stein, Kirsten Fahl, Laurie Menviel, Axel Timmermann, and Eystein Jansen
X5.260 EGU2018-16904 Deep-water temperature change across ‘Heinrich-events’ and its implications for inter-hemispheric coupling via the thermal bipolar seesaw by Luke Skinner, Lauren Broadfield, Salima Souanef-Ureta, and Mervyn Greaves
X5.261 EGU2018-10827 Paleo Arctic sea ice evolution during DO events 7 to 10: a multidisciplinary approach. by Federico Scoto, Carlo Barbante, Alfonso Saiz-Lopez, Paul Vallelonga, Dorthe Dahl-Jensen, and Andrea Spolaor
X5.262 EGU2018-14808 Investigating ice sheet instabilities and abrupt climate change with a fully coupled ice sheet – climate model by Aurélien Quiquet, Didier M. Roche, and Christophe Dumas
X5.263 EGU2018-15543 Interaction between ocean circulation and sea ice explains Dansgaard-Oeschger events by Niklas Boers, Michael Ghil, and Denis-Didier Rousseau
X5.264 EGU2018-13449 Large changes in sea ice and climate triggered by small changes in Atlantic water temperature by Mari F. Jensen and Kerim H. Nisancioglu
X5.265 EGU2018-9298 External control or pure randomness of Dansgaard-Oeschger events? by Johannes Lohmann and Peter Ditlevsen
X5.266 EGU2018-7741 Oceanic control on the existence and stability of a Nordic Seas sea ice cover by Jonathan Rheinlaender and David Ferreira
X5.267 EGU2018-18685 Mapping Greenland glacial climate using ice cores and models by Anne-Katrine Faber, Bo Møllesøe Vinther, Sindhu Vudayagiri, and Chuncheng Guo
X5.268 EGU2018-4730 Dynamical sequence of ocean, atmosphere, and sea ice changes during an abrupt stadial-to-interstadial climate transition by Chuncheng Guo and Kerim Nisancioglu
X5.269 EGU2018-18789 Key roles of sea ice-atmosphere feedback in inducing contrasting modes of glacial AMOC and climate by Sam Sherriff-Tadano and Ayako Abe-Ouchi
X5.270 EGU2018-3294 Simulated DO-like AMOC transitions driven by salt-oscillations and interactions with the North Atlantic subpolar gyre by Marlene Klockmann, Uwe Mikolajewicz, and Jochem Marotzke
 CL4.09Processes and impacts of climate and ocean changes in the Arctic-subartic and the North Atlantic – from past to future: Posters17:30–19:00Hall X5
X5.350 EGU2018-11937 Millennial-scale changes in oceanic influence on the northern Barents Sea deglaciation and environments over the last termination by Elena Ivanova, Ivar Murdmaa, Anne de Vernal, Bjørg Risebrobakken, Sergey Pisarev, Camille Brice, and Alexander Peyve
 CR5.4/OS1.16Ice shelves and tidewater glaciers – dynamics, interactions, observations, modelling (co-organized) Posters17:30–19:00Hall X5
X5.406 EGU2018-10732 Highly temporally resolved response to seasonal surface melt of the Zachariae and 79N outlet glaciers in northeast Greenland by Nicholas Rathmann, Christine Hvidberg, Anne Solgaard, Anders Grinsted, Hilmar Gudmundsson, Peter Langen, Kristian Nielsen, and Anders Kusk
 GD8.1/CR6.4/SM4.12/SSP2.18/TS1.6The Arctic connection – geodynamic, geologic and oceanographic development of the Arctic (co-organized) Posters17:30–19:00Hall X2


Thu, 12 Apr

You have selected presentations in the following Sessions:

  • IE2.1/NP3.4/AS1.8/CL2.08/CR1.9/OS1.20/ST4.7, Orals, Room N2
  • AS3.21, Orals, Room 0.11
  • CL1.15, Orals, Room E2
 IE2.1/NP3.4/AS1.8/CL2.08/CR1.9/OS1.20/ST4.7Climate Variability Across Scales and Climate States (co-organized) Orals08:30–10:00Room N2
08:30–08:45 EGU2018-10339 On scale break in the climate spectrum at glacial time scales by Peter Ditlevsen, Michel Crucifix, and Takahito Mitsu
08:45–09:00 EGU2018-18392 At which spatiotemporal scales, and in which climate states, can the linear temperature response hypothesis be rejected by data? by Hege-Beate Fredriksen, Martin Rypdal, and Kristoffer Rypdal
09:00–09:15 EGU2018-7391 Low-frequency variability of wintertime Euro-Atlantic planetary wave-breakingby Gabriele Messori, Paolo Davini, M. Carmen Alvarez-Castro, Francesco S. R. Pausata, Pascal Yiou, and Rodrigo Caballero
09:15–09:30 EGU2018-8085 Observational constrains reduce the increases of summertime temperature variance in CMIP5 projections by Duo Chan, Alison Cobb, and David Battisti
Statistical Methods
09:30–09:45 EGU2018-17995 Time-scale dependent estimation of spatial degrees of freedom by Torben Kunz and Thomas Laepple
09:45–10:00 EGU2018-12977 A statistical significance test for sea-level variability by Daniele Castellana, Henk A. Dijkstra, and Fred W. Wubs
 AS3.21Halogens in the Troposphere Orals08:30–10:00Room 0.11
08:30–08:45 EGU2018-6262 Iodine levels in the North Atlantic since the mid-20th century by Carlos Alberto Cuevas, Niccolò Maffezzoli, Juan Pablo Corella, Andrea Spolaor, Paul Vallelonga, Helle Astrid Kjær, Marius Simonsen, Mai Winstrup, Bo Vinther, Christopher Horvat, Rafael Pedro Fernandez, Douglas Kinnison, Jean-François Lamarque, Carlo Barbante, and Alfonso Saiz-Lopez
 CL1.15Diagnosing past climate mechanisms through the Integration of Ice core, MArine and TErrestrial records Orals08:30–10:00Room E2
09:15–09:30 EGU2018-165 Northern origin of western tropical Atlantic deep waters during Heinrich Stadials by Natalia Vazquez Riveiros, Claire Waelbroeck, Didier Roche, Santiago Moreira, Pierre Burckel, Fabien Dewilde, Luke Skinner, Helge Arz, Evelyn Boehm, and Trond Dokken
Thu, 12 Apr
 IE2.1/NP3.4/AS1.8/CL2.08/CR1.9/OS1.20/ST4.7Climate Variability Across Scales and Climate States (co-organized) Orals10:30–12:00Room N2
10:30–10:45 EGU2018-500 Inferring Variability from Paleoclimate Time Series by Raphael Hébert and Kira Rehfeld
10:45–11:00 EGU2018-1079 How wrong are climate field reconstruction techniques in reconstructing a climate with long-range memory? by Tine Nilsen, Johannes P. Werner, and Dmitry V. Divine
Impact of Seasonality
11:00–11:15 EGU2018-2501 Seasonal cycle effects on tropical climate variability by Axel Timmermann and Malte Stuecker
11:15–11:30 EGU2018-1299 How predictable are human-induced changes in the seasonal cycle of surface temperature? by Vineel Yettella and Mark England
11:30–11:45 EGU2018-5785 Northern Hemisphere summer season lengthening at 1.5 and 2.0 degree global warming by Bo-Joung Park and Seung-Ki Min
11:45–12:00 EGU2018-9712 Robust changes in tropical rainy season length at 1.5°C by Fahad Saeed, Ingo Bethke, Hideo Shiogama, Erich Fischer, and Carl-Friedrich Schleussner
Thu, 12 Apr

You have selected presentations in the following Sessions:

  • IE2.1/NP3.4/AS1.8/CL2.08/CR1.9/OS1.20/ST4.7, Posters, Hall X4
  • CL1.15, Posters, Hall X5
  • CR1.5/AS4.6, Posters, Hall X5
 IE2.1/NP3.4/AS1.8/CL2.08/CR1.9/OS1.20/ST4.7Climate Variability Across Scales and Climate States (co-organized) Posters17:30–19:00Hall X4
CL1.15Diagnosing past climate mechanisms through the Integration of Ice core, MArine and TErrestrial records Posters17:30–19:00Hall X5
X4.353 EGU2018-4584 The seasonal signal of the East Greenland area – a perspective through the water stable isotopes of ice cores from Renland by Christian Holme, Bo Møllesøe Vinther, and Vasileios Gkinis

X5.265EGU2018-1116 Inferences from the total air content measurements of RECAP ice core by Sindhu Vudayagiri, Thomas Blunier, Bo Møllesøe Vinther, Johannes Freitag, and Tetsuro Taranczewski

 CR1.5/AS4.6Atmosphere – Cryosphere interaction (co-organized) Posters17:30–19:00Hall X5

X5.437EGU2018-16120 Changes in Surface Energy Budget and Firn Structure on the Accumulation Area of the Greenland Ice Sheet Revealed by Weather Station Observations and Modelling by Baptiste Vandecrux, Robert Fausto, Peter Langen, Dirk van As, Michael MacFerrin, William Colgan, Thomas Ingeman-Nielsen, Konrad Steffen, Nina Jensen, Mette Møller, and Jason Box


Fri, 13 Apr
 GMPV6.1/AS3.32/CL5.22/NH2.7Volcanic Ash – Generation, Transport, Impacts and Applications (co-organized) Orals10:30–12:00Room G1
11:00–11:15 EGU2018-6808 Linking Greenland to the Pacific northwest with the Khangar Tephra. First identification of cryptotephra from the Kamchatka Peninsula in a Greenland ice core. by Eliza Cook, Maxim Portnyagin, Vera Ponomareva, Lilia Bazanova, Anders Svensson, and Dieter Garbe-Schönberg
Fri, 13 Apr
 CL5.06Regional climate modeling, including CORDEX Orals15:30–17:00Room F2
15:30–15:45 EGU2018-17581 Regional Climate Change for Europe; From PRUDENCE and ENSEMBLES to CORDEX – a consistent story by Jens H. Christensen, Morten A. D. Larsen, Ole B. Christensen, Martin Stendel, and Martin Drews | Highlight





Making statistics fun again

“But is that significant?” You have probably heard that question many times. Perhaps you can confidently say “Yes it is”. Perhaps you don’t know. Perhaps you are not enitrely sure how to test if it is significant or not. Perhaps you just used a build-in tool in your favourite program, got a p-value that looks reasonably and say “sure, that looks significant enough”. Regardless of you being a statistical master or apprentice, you just missed out on a great opportunity to learn even more statistics.

by ice2ice PhD Ida Ringaard

To brighten up cold and weary February in Copenhagen, Ice2ice hosted a climate statistics workshop. Over three days, the three instructors Martin Miles (UniResearch), Francesco Muschitiello (University of Cambridge) and Peter Thejll (Danish Meterological Institute) guided the 12 participants (6 PhD students, 3 masters students, 2 senior researchers and 1 postdoc) through the jungle of statistics.

First things first, you have to be able to crawl before you can walk. Therefore, Martin spend the first day making sure everyone could crawl i.e. getting everyone up to speed with the basic descriptive and inferential statistics (looking at the distribution of the data, computing probabilities and confidence levels). Having mastered the theory, it was now time for the practical part. Francecso steered us through practical hands-on exercises of what we just learned using the statistical program R.

Next day was all about correlation, regression and handling errors. Martin started the day by going through correlation theory and potential pitfalls, as well as the basics of regression analysis. Peter followed with more advanced regression analysis, which assumptions are made, how to handle errors in x or y-direction, or the combination of both etc. After a well deserved (and needed) lunch break, Francesco ended the day by lecturing about Monte Carlo simulations, live-coding examples on how to do it in-practical at the same time.

The last day with planned lectures started off with Martin talking about time- and time-frequency analysis. Francesco was once again in charge of transforming the theory into practical use. After spending 2.5 days on learning time series analysis, the afternoon lecture lead by Martin switched gear and briefly touced upon spatial analysis, spatial autocorrelation and regression and EOF’s.

Too not end this statistics workshop too abruptly, there was no official program on Friday. Instead, Martin hung around, ready to help the participants with questions regarding their own data.

This rounded up a very rewarding, intense and actually fun statistics workshop, worth repeating. For me at least, is was very helpful to see the theory used on time series and data that I actually use in my research and can relate to.

And know I can honestly answer “Yes, that is significant!”.


How well is the Southern Ocean represented in climate models?

by ice2ice Phd Mads Bruun Poulsen

Markus, Roman and I recently published a paper in Ocean Modelling (which can be found here: about the representation of the Southern Ocean in climate models. Here is a short summary of our study as well as our take on how this piece fits into the ice2ice puzzle.

The schematic shown in Figure 1 places the Southern Ocean at the center stage in the modern view of the large-scale ocean circulation. Not only does it allow for an exchange of properties between the three major ocean basins via the Antarctic Circumpolar Current (ACC), it is also a key region of wind-driven upwelling due to persistent overlying westerlies and hence provides closure for the meridional overturning circulation. From a present-day perspective, these properties of the Southern Ocean are important to oceanic uptake of anthropogenic heat and carbon dioxide, as well as the oceanic poleward heat transport.

FIG1: Schematic from Talley (2013)

The issue with the representation of the Southern Ocean in ocean general circulation models (OGCMs) is that mesoscale eddies (Figure 2), a vital component to the dynamical balance that prevails in the Southern Ocean, evolve on a spatial length scale which is smaller than the typical ‘coarse’ horizontal grid resolution in commonly-used climate models (about 1 deg. X 1 deg.). That is, the effect of eddies on the large-scale ocean circulation is not present unless we parameterize it in the model. This problem has a long history in the oceanographic literature, and how to parameterize the effects in practice is still hotly debated. The vastness and remoteness of the Southern Ocean means that we do not have a reliable observational constraint on what it is that we attempt to parameterize, but a considerable amount of theoretical and modelling studies have given us a reasonable idea about what properties such parameterization needs to fulfill.

FIG2: A random snapshot of Southern Ocean surface ocean velocity magnitude from an eddy-resolving ocean model. Adopted from Poulsen, Mads B., Markus Jochum, and Roman Nuterman. “Parameterized and resolved Southern Ocean eddy compensation.” Ocean Modelling (2018).

In our study we decided to compare a commonly used climate model, with an implemented eddy parameterization, to a high-resolution version of the same model, with explicitly resolved eddies, to examine how well the coarse resolution model mimics the physics. A forward integration of a global eddy-resolving OGCM is a demanding computational task why this study was only made possible through granted computer time at the supercomputer in Jülich, Germany, and support from the NBI e-science section. Using 4096 cores of the IBM BlueGene, the experiments generated about one Petabyte model output, required a continuous data transfer of about one Terabyte pr. day and took three years to complete.

Perhaps the most important eddy effect in the Southern Ocean is that eddies drive an overturning circulation of opposite sign to the one set by the winds alone i.e. it compensates the wind-driven upwelling of water. To keep it short, we found that the coarse resolution model distributes the eddy-circulation differently across water masses compared to the high-resolution model, which imply that  the eddy compensation is different between the models (Figure 3). We also found that the total southward heat transport in the Southern Ocean compares well between the models, but that the heat transported by the eddy field alone is different. These two results indicate that there is room for improvement in the formulated eddy parameterization.

Fig3: Southern Ocean overturning streamfunctions in latitude-density space. The left and right column of panels is from the coarse and high resolution model, respectively. The upper panels show the total flow, the middle panels the mean-flow and the lower row the eddy-induced circulation. The sum of the mean-flow and the eddy-induced circulation equals the total flow. Units are in Sverdrups (1 Sverdrup = 1 million m3 / s). Adopted from Poulsen, Mads B., Markus Jochum, and Roman Nuterman. “Parameterized and resolved Southern Ocean eddy compensation.” Ocean Modelling (2018).

This is all fine, you may say, but why is this relevant to the ice2ice community? A satisfactory theory for global-scale abrupt climate change, such as D-O events, has to explain how the northern and southern hemisphere exchange information in order to arrive at the d18O signals that we find in the ice cores from Greenland and Antarctica. If the information of climate change between the hemispheres is transmitted through the ocean, the climate signal has to cross the ACC. Here models often struggle, which either tell us that the signal does not transmit through the ocean or that it does but the relevant physical processes are not well represented in the models. A substantial amount of heat is fluxed poleward across the ACC by mesoscale eddies, which our study indicates is distributed wrongly in the coarse resolution model. If eddies do play a role in transmitting the climate signal, a better mesoscale eddy parameterization might be needed to obtain the correct response in OGCMs.

ice2ice all staff 2018- Synergies!

The annual all staff meeting was held in Sweden in start of February. 55 internal ice2ice researchers attended the meeting and had intense focus on synergies within ice2ice.

The annual all ice2ice staff meeting was held in Mölle, Sweden.

The scope for this year’s all-staff meeting was synergies in Ice2ice. We are at the state in the ice2ice project where several great publications has allrady been publishedfrom the individual ice2ice researchers, expanding the knowledge on how sea ice and land ice influence each other (the full list of ice2ice publications so far can be seen here). However to fully benefit from the versatile group of people we are within ice2ice this years all staff meeting was set up with a focus on collaboration and synergy between the individual institutions.

ice2ice PI Bo Vinther kicking off the 1 min/1 slide presentations with an update on water isotopes in ice cores and what they can teach us about past temperature and accumulation.

To get everyone up to date on the new and exiting research that has happened within ice2ice since last year, each staff member quickly introduced their science with a 1 minute slide. Further a poster session was used to update on ongoing research.

Happy ice2ice researchers during the poster session

The remaining workshop was used to identify and start the process of writing synergy papers. We split into 6  working groups, each with a theme covering part of the overall work packages of ice2ice:

  • Sea ice reconstruction combining marine and ice core records
  • Surface Mass Balance
  • Ocean state estimation
  • Evolution of Greenland ice sheet elevation, accumulation and water isotopic composition
  • Sea ice vs Greenland Climate
  • Dynamics of stadial and interstadial transitions

Each working group discussion was initiated by a few scientific talks and from there continued discussions over two days led to the concrete identification of at least 2 synergy paper per group. In several groups more than 2 ideas for ice2ice synergy papers came out of the fruitful discussions. Making for a busy, but exciting period until the end of the ice2ice project by September 2019.

Also time for a few walks and talks during the meeting.

Such a close collaboration on papers can only be facilitated when researchers know each other well, thus we also found time for social excursion to Kullaberg led by a geologic expert.