Researchers from ice2ice Physics of Ice, Climate and Earth (PICE) at the Niels Bohr Institute, University of Copenhagen, have succeeded in making a method to enlighten an otherwise dark period in climate history. Working with the ice core ReCap, drilled close to the coast in East Greenland, postdoc Marius Simonsen wondered why the dust particles from the interglacial period – the warmer period of time between the ice ages – were several times bigger than the dust particles from the ice age. His research led to the invention of a method able to map the advancement of the glaciers in cold periods and the melting in warmer periods. This data is important for the climate models we use to predict sea level rise. The result is now published in Nature Communications.

 

The larger particles of dust don’t travel far – they come from East Greenland

Based on the hypothesis that the bigger dust particles in the ice couldn’t have come from afar, the then PhD student, Marius Simonsen, examined the dust at select locations on the coast of East Greenland close to the drill site. The chemical composition turned out to be similar to the larger particles in the ice. The smaller particles of dust caught in the ice, on the other hand, travel from Asia, blown to Greenland by dust storms. In other words, the bigger particles of dust in the ice must mean presence of bare land close to the drill site. The ice is composed of annual layers, like the growth rings in a tree, so the distribution of large and small dust particles can be linked to the advancement and melting of the ice. Large particles mean bare land in the vicinity, small particles mean the land is covered in ice. The end of the ice age, where the ice cap is receding, is well explained scientifically, Marius Simonsen explains. “But it is very difficult to retrieve data on the period before the ice age. The ice is an extremely strong natural force, so it grinds away everything when advancing. But with the new method, we have data on the advancement of the ice. All of a sudden, we have a link to information on how quickly we enter an ice age, in a way we never used to have”.

Gaining knowledge on Glacier reaction to atmospheric content of CO2 is crucial

It is important to know more about how glaciers react to changes in the atmosphere, and rather a lot is known on the composition of the atmosphere during the ice age. The results from the new method can now be used to compare the reaction in the masses of ice to changes in the atmospheric content of greenhouse gasses like CO2. Marius Simonsen says: “The glaciers receded at the beginning of the present interglacial, just like they do today because of climate change. The two scenarios are not entirely comparable, because there was much more inland ice then than now by the coast in East Greenland where the ice core is drilled. Never the less, the results are very interesting indeed when making climate models, because the models must be tested by comparison to reality. And in the new method we’ve acquired an anchor point in a period about which not much scientific knowledge existed”. The method helps putting constraints on our knowledge on the influence of greenhouse gasses on ice melting and, consequently, sea level.

The method can provide us with new information on how fast the glaciers recede

Helle Astrid Kjær, Assistant professor in PICE, says the objective of PICE now is to utilize the new method at other locations so we can gather more data on the changes of glaciers in the past. The researchers are already planning new drill sites in North East Greenland and Canada. It is very likely that advancement and melting of the ice there is different from East Greenland. “Perhaps, with the new method, we are able to see how fast the ice age came in from the north and moved south”, Helle Astrid Kjær says.

It is a precondition for the feasibility of the method that bare land exists in the vicinity of the drill site, so dust particles can be found. This was the case during the last interglacial as the temperature then, app. 115,000 years ago, was up to 8 degrees C. warmer than today, according to a former study from the Niels Bohr Institute. Hence, the method will most likely be usable in North East Greenland and Canada. The researchers at the Niels Bohr Institute are already establishing new collaborations with Canadian researchers based on the new method.

Drilling of the ice core ReCap was supported by The Danish National Research Foundation, the American National Science Foundation, the German Alfred Wegener Institute and the European Union Horizon 2020 Research and Innovation Programme. The measurements of dust were supported by the EU funding ice2ice and Horizon 2020 – TIPES

A new ice2ice paper co-authored by ice2ice researchers Ruth Mottram and Peter Langen from DMI documents how solid ice lenses formed as a result of melt have increased the runoff area in Greenland  by 26% since 2001. The study is published in Nature.

Although runoff from ice slabs has added less than a millimeter to global sea levels so far, this contribution will grow substantially as ice slabs continue to expand in a warming climate.

Such melt episodes are becoming increasingly common in Greenland: In July of 2012, snow and ice melted from 97 percent of Greenland’s ice sheet surface, an event not seen in the 33-year satellite record.

ice2ice researcher and expert in ice dynamics, Ruth Mottram states that “So far the increased melt water from the ice sheet has contributed just 1 cm to the global sea level in the last 15 years. However from the new study we observe that surface melt, which contributes to the sea level, will increase significantly. And that is really unfortunate for the icecaps ability to contain mass”

The process of refreezing melt water has so far not been well implemented in climate models, but with research from ice2ice and DMI the process is now better constrained also in the models allowing for more correct estimates of future sea level changes.

The study was a collaboration between ice2ice partner the Danish Meteorological Institute (DMI) and partners from the danish geological surveys, university of Colorado, the national snow and data centre (NSIDC) and University of Freiburg. You can read the full paper here

 

 

The 29th of June ice2ice PhD Ida Magrethe Ringgaard succesfully defendend her PhD on “Sensitivity of Arctic sea ice change on climate in the coupled climate model EC-Earth”.

In the PhD she investigated the sensitivity of the climate to changes in the Arctic sea ice using an atmosphere-ocean coupled climate model. Ida has found that Barents-Kara sea ice loss might be linked to a weak cooling over parts of Europe in winter only present for the temporal mean winter temperatures. However the coldest winters did not show a statistically significant cooling over Europe for any amount of sea ice loss in the Barents-Kara Seas.

She also used the warm RCP8.5 scenario to look at sea ice loss in the period 1850-3200 and found that the Arctic transitioned from having a perennial sea ice cover to an ice-free Arctic Ocean. The loss of the Arctic sea ice appeared to lead to a shift in trends for some key parameters such as the precipitation variability which increased and the Atlantic Meriodional Ocean Circulation which stabilized after an initial reduction as well as a change in the Arctic Ocean stratification which strengthened.

Ida was supervised by:

• Professor Eigil Kaas, Physics of Ice, Climate and Earth, Niels Bohr Institute, University of Copenhagen
• Professor Jens Hesselbjerg Christensen, Physics of Ice, Climate and Earth, Niels Bohr Institute, University of Copenhagen

and in the assesment committee was:

• Associate Professor Anders Svensson, Physics of Ice, Climate and Earth, Niels Bohr Institute, University of Copenhagen
• Professor Gunilla Svensson, Meteorologiska Institutionen, Stockholm University 
• Professor Timo Vihma, Finnish Meteorological Institute   

Today 3 ice2ice Msc students successfully defended their MSc thesis at the Niels Bohr Institute.

The three students have all been working with chemical ice core proxies, but on very different timescales.

Mirjam Läderach has worked on “Continuous flow analysis on EastGRIP ice core: Optimization of optical dye method and results from acidity measurements on the EastGRIP ice core” where she successfully optimized an acid method for the determination of volcanoes in ice cores.

Michelle Shu-Ting Lee worked on “Climate proxies based on the NEEM ice core for the Holocene period 4000-7000 years B2K: An integrated CFA and IEC method for NEEM brittle zone”. The brittle zone is a zone in deep ice cores where continuous chemical sampling by CFA is not possible and thus time consuming discrete sampling combined with Ion Chromatography is required to obtain the chemical proxies for forest fire, volcanoes, wind and aridity.

And Nicholas Robles worked on “Spatial and Temporal Analysis of Greenland Shallow Snow Cores and HIRHAM5 Data”. He analysed the variability in several shallow snow cores covering only the past 5 years and compared the chemical results with weather data from climate modelling to generate a better understanding of the chemical proxies we use for the deep ice cores.

Congratulations to all 3.

by Anne-Katrine Faber & Kerim Nisancioglu

The Olav Thon Foundation recently announced the recipients of awards and financial support for research and teaching. Two ice2ice scientists from Bergen, Kerim Nisancioglu and Anne-Katrine Faber were awarded 1.5 mio NOK to their project “IceFinse – a field course on Arctic climate with focus on engaging students in research”. 

The project aims to give Master level students first hand experience with Arctic research and fieldwork.  This course offer opportunities for learning that is not achieved in classical curriculum-based classes.  By giving students insight into  all steps of the research process, from formulation of a research question, to data collection and analysis and interpretation the course aims to engage students in research and prepare them to start working on their master thesis. This research-based field course on glaciology, ice cores and climate will be designed around the lecturers existing research. The studentdriven fieldwork and research projects will therefore contribute to ongoing research.

During the coming years they will develop and organize fieldwork courses at the research station at Finse in Norway  (https://www.finse.uio.no/) and the research station “Arktisk station”  (https://arktiskstation.ku.dk/).  at Disko Island in Greenland.

 The scientists officially received the financial support for their project at a  ceremony in Oslo on March 7^th. 

Ice2ice Phd Mads Bruun Poulsen the 16/01-2019 successfully defended his PhD thesis on Parameterizing Southern Ocean eddy-induced circulation in coarse resolution ocean models. He was evaluated by an impressed committee consisting of Professor, Brian Vinter, eScience, Niels Bohr Institute, University of Copenhagen, Associate Professor, David Ferreira, Department of Meteorology, University of Reading, and Professor Joe LaCasce, Department of Geosciences, University of Oslo. He has been supervised by Markus Jochum from the Niels Bohr Institute.

Abstract: Baroclinic mesoscale eddies in the Southern Ocean induce a circulation which modulates wind-driven ventilation of the interior ocean, with implication for exchanges of heat and carbon dioxide with the atmosphere. In coarse resolution ocean general circulation models which do not explicitly resolve mesoscale eddies, eddy-induced circulation is typically parameterized with a skew-diffusive tracer flux that depends on an eddy transfer coefficient, κ. Several plausible closures for κ exist, yet consensus on a specific expression for κ remains largely absent in the ocean modeling community and results in uncertain Southern Ocean ventilation rate estimates. With the use of two ocean general circulation models of coarse and eddy-resolving horizontal resolution, this thesis assesses the properties of two recently proposed expressions for κ with the aim to provide guidance towards the optimal closure.

First an expression for κ which solely depends on local stratification is examined in a suite of model simulations with varying intensity of the zonal wind stress in the Southern Ocean. The simulations suggest that implementation of a dynamic κ alleviates coarse models from an overly sensitive overturning circulation although the parameterized eddy-induced circulation does not completely match that found in the eddy-resolving model. The latter shortcoming is associated with an overly strong poleward eddy heat transport in the coarse model, which is largely compensated by mean-flow heat transports. In addition, the coarse model demonstrates a centennial equilibration time scale to wind stress change that, if representative of the dynamics, has implication for evaluation of eddy compensation in eddying models.

Second, an expression for κ which additionally depends on eddy geometry and energy is investigated. It is shown that this closure derives from a correspondence between horizontal eddy buoyancy fluxes and variance ellipses, which offers a concise geometric interpretation of baroclinic mean-flow stability and vertical momentum transfers. The eddy geometry is examined in the eddy-resolving model to assess its potential to form basis for parameterization. The geometry obeys simple probability distributions and is insensitive to external forcing change, but also possesses vertical structure which relates to the orientation of horizontal eddy buoyancy fluxes with respect to the large-scale buoyancy gradient. This structure is not explained by rotational fluxes and hence represents a possible parameterization challenge.

The thesis also presents estimates of κ extracted directly from the eddy-resolving model and provides a discussion on the assumption of horizontally down-gradient eddy fluxes upon which the skew-diffusive tracer flux relies. In particular, this discussion reiterates a previous finding that a dynamically important component of the horizontal eddy buoyancy flux appears unaccounted for in coarse models.

Last week a new ice2ice article was published-below the ice2ice authors have written a short version covering the main findings. The full paper can be found here: Geng, Marilena Sophie, Jens Hesselbjerg Hesselbjerg Christensen, and Torben Christensen. “Potential future methane emission hot spots in Greenland.” Environmental Research Letters (2018).

by Marilena Sophie Geng, Jens Christensen Hesselbjerg, and Torben Røjle Christensen

Permafrost is defined as ground at a soil temperature below freezing for at least two consecutive years.  It is an important part of the cryosphere as 25 % of the northern hemisphere is underlain by permafrost and it stores a large amount of carbon in the frozen ground.

In a changing climate and warming Arctic, permafrost is starting to thaw more and more. The frozen organic matter in the ground can therefore reach temperatures above freezing and become available to decay. Decomposition of organic matter produces greenhouse gases. A feedback loop is triggered, higher temperatures lead to thawing permafrost lead to greenhouse gas emission lead to higher temperatures. Depending on the oxygen available to decay either carbon dioxide (CO2) or methane (CH4, which we concentrated our work on) is released.

Permafrost can be found in all cold regions like Alaska, northern Canada, Siberia and Greenland. As we had high spatial resolution model simulations of Greenland (figure 1) for present and future scenarios at hand, we used those for a permafrost analysis.

The issue with permafrost analysis is that most climate models don’t have permafrost and methane emissions included in their formulation. A high resolution of the soil and complicated processes within it (that are partially still not fully understood) would be needed which is often computationally to expensive at the moment. So our idea was to find a way to derive permafrost conditions and methane emissions from parameters that are in all climate models.

In a first step we use an established frost index that uses a ratio of degree days of freezing and thawing to derive permafrost conditions from our HIRHAM5 regional climate simulations. We can compare the permafrost conditions predicted by the frost index with observations from Greenland. As we are satisfied with the performance of the frost index and the model, we use the index for simulations of future climate scenarios and find spots on Greenland that showed significant thawing of permafrost (figure 2).

In a second step, we need to find a correlation between methane emissions from permafrost and some other variable included in the climate model. We can use methane flux data from the GEM (Greenland ecosystem monitoring) project in Nuuk and Zackenberg. We test correlations of methane emissions with air temperature, sensible and latent heat flux. Finally, we find that an exponential relationship between methane emissions and air temperature describe the observations best. As the air temperature rises, methane CH4 emissions increase exponentially.

We can use the found correlation all over Greenland with our present day and future simulated temperatures. When we now compare our maps of future potential methane emissions and permafrost thaw we find spots that show both, potential high emissions and thawing permafrost (figure 2 and 3). These spots, like Kangerlussuaq and Scoresby land, are likely to show high emission in the future and need some additional monitoring.

Congratulations to ice2ice PhD Nicholas Rathmann at Centre for Ice and Climate who successfully defended his PhD thesis Monday 26 November 2018, and obtained the degree of Doctor of Philosophy. Nicholas will continue to work as Postdoc at the Centre for Ice and Climate.

Title and abstract of the PhD thesis:

Title: “Nonlinear fluid dynamics – Studies on the dynamics of ice sheet deformation and the turbulent energy cascade”

Abstract: Nonlinear fluid motion occurs naturally in central components of the climate system. Studying such motion is instrumental for improving the accuracy and realism of models of climate components, which has important implications for future climate projections. This thesis presents four studies on the topic of nonlinear fluid dynamics addressing two subjects: the dynamics of ice sheet deformation and the dynamics of the turbulent energy cascade.

The first study investigates the controlling mechanisms of the observed 2016 seasonal speed-up of Zachariae and Nioghalvfjerdsfjorden outlet glaciers in northeast Greenland, which drain a significant part of the Greenland ice sheet. From surface imagery made available by the newest generation of satellites, state-of-theart velocity maps are derived, and the timings of processes potentially impacting the speed-up are estimated. By combining observations with numerical modelling, it is shown that the subglacial environment exerts an important control over the ice discharge rate of the region, which has implications for estimating the region’s contribution to near-term sea level rise.

The second study investigates the influence of strong single-maximum fabrics on the transient deformation of internal layers within ice sheets. By using a new Lagrangian numerical ice flow model, it is shown that discrete, strong single maximum layers — which may account for suppressed shearing along nonbasal crystallographic planes — are a plausible candidate for explaining the disturbed flow observed from ice-penetrating radar transects. The results have potential implications for interpreting ice-core stratigraphies and chronologies, as well as understanding of how internal disturbances might influence surrounding flow fields.

The third and fourth study address the origin of the transfer direction of kinetic energy between scales of motion (upscale/downscale) in fully developed turbulence using the spectral-helical decomposition of the velocity field. In this decomposition, the nonlinear term in the Navier–Stokes equation becomes to a sum over eight distinct types of three-wave interactions. In the third study, a simple model (a shell model) is introduced to investigate the behaviour of the eight types of nonlinear interactions, which is compared to a linear stability analysis, finding a fair agreement. In the fourth study, a subset of the three-wave interactions are shown to conserve a new positive-definite quadratic quantity in addition to kinetic energy, which cause the interactions to contribute to a reverse transfer of energy in three dimensions (small to large scales) in analogy to two-dimensional turbulence. Understanding the energy transfer directionality, and possible ties between two- and three-dimensional turbulence, has implications for geophysical flows such as the free atmosphere and oceans where vertical motion in many places is suppressed, thereby affecting predictability time scales and the transport of energy and momentum in climate.

by ice2ice PhD Andreas Plach

Many people are interested in how much the melting of the Greenland ice sheet will contribute to rising sea levels in the future. In my PhD I therefore investigate how the Greenland ice sheet looked like during the last period with much warmer summers on Greenland than today, a period called the Eemian interglacial period approximately 125,000 years ago. Ice from this period has been found in several Greenland ice cores and we therefore know that Eemian ice is preserved at the bottom of the Greenland ice sheet. Unfortunately, it is impossible to get an exact picture of the Eemian ice sheet from these few ice core data points and we therefore need to use computer models to simulate the Eemian ice sheet and get a more complete picture of its extent and the sea level rise it caused. If we know how much smaller the Eemian Greenland ice sheet was, this will help us to know how the Greenland ice sheet behaves in a warmer climate and to estimate how much smaller it will become in the warming future.

However, it is challenging to simulate the Eemian Greenland ice sheet. Many previous studies which did simulate the Eemian ice sheet, got very different results (Fig. 1). In our recent paper, we try to understand what caused the large differences in between these previous studies and we focus on how different surface mass balance (SMB) models (which are used to simulate the melting of the ice sheet) behave in the warm Eemian climate. A comparison of various SMB (melt) models shows large differences in melt between these models. Since the previous studies (Fig. 1) partly used different SMB models, the variation in simulated melt in these SMB models is likely a cause for the differences between the previous studies. Our results show the high importance of SMB model selection for Eemian ice sheet simulations which will help scientists to improve future attempts to simulate the Eemian Greenland ice sheet.

Want to know more?

Read the full paper where we compare different surface mass balance (SMB) models for the Eemian interglacial period: https://www.clim-past.net/14/1463/2018/cp-14-1463-2018.pdf

You might also be interested in our recent discussion paper where we simulate the Eemian Greenland ice sheet with a selection of SMBs derived in the paper above: https://www.the-cryosphere-discuss.net/tc-2018-225/tc-2018-225.pdf

 

 

 

The following ice2ice article was recently published: Sessford, E. G., et al. “High resolution benthic Mg/Ca temperature record of the intermediate water in the Denmark Strait across D‐O stadial‐interstadial cycles.” Paleoceanography and Paleoclimatology (2018). Below ice2ice Evangeline Sessford has written about the findings. This blogpost also appears on http://www.scisnack.com/

 

We set sail from Iceland on Research Vessel G.O. Sars, in July 2015, to extract sediment cores from the ocean floor in the Denmark Strait. The aim was to find sediment containing fossilized shells of zooplankton called foraminifera, to aid our understanding of what the past ocean was like. Over time, mud and foraminifera shells accumulate layer by layer, year after year building the ocean floor. These separate layers contain valuable information about how the ocean climate system changed over time in the past because the oldest layers are at the bottom. We cannot measure the past directly therefore we need proxies.

Proxies are substitute measurements that reflect ocean properties in the past. For example, to get a record of past ocean temperatures we measure the amounts of magnesium and calcium in foraminifera shells. These amounts depend on ocean water temperature. The higher the magnesium to calcium ratio; the higher the temperature. One of the cores, GS15-198-36CC -or Caprice, as I like to call her- was exceptionally full of our required proxy.

We measured the magnesium to calcium ratio in the shells of a type of foraminifera that lives on the ocean floor. Caprice was extracted from 770m below the surface so the measurements reflect intermediate depth water masses and how they changed over time.

Different water masses in the ocean have different characteristics. For example, the modern Gulf Stream flowing into the Nordic Seas at the surface in the east is warm and saline Atlantic Water. However, as it circulates in the Nordic Seas it loses heat to the atmosphere, cools and sinks and returns to the North Atlantic through the Denmark Strait in the west as intermediate water.

Some warm Atlantic Water makes it up to the Arctic Ocean. The Arctic Ocean is covered with sea ice and a cool, fresh layer of water. This water is lighter than the warmer Atlantic Water. Despite being warmer, the Atlantic Water is forced below the fresh layer because of its higher salt content and therefore density. This warm intermediate water then circulates in the Arctic Ocean while retaining most of its heat content and exits as intermediate water with a similar temperature as it entered.

The measurements from Caprice indicate that both these processes happened at our core location in the Denmark Strait during the last ice age, 30-40 thousand years ago. Basically, our core indicates that the Nordic Seas were sometimes covered by sea-ice and were sometimes open.

Results from Caprice record an intermediate water mass in the Denmark Strait that alternated between periods of cold (-1 to 1 °C), fluctuating and warm (1 to 3 °C), stable temperatures. These large shifts in the intermediate water temperature record are coherent with substantial, well-known climate fluctuations, Dansgaard-Oeschger events. These events are clearly visible in Greenland ice core records that show air temperatures rapidly warming by up to 15 °C in less than 30 years. The abrupt warmings and following warm periods are known as Greenland Interstadials. They were followed by drops back into cold periods known as Greenland Stadials. Research suggests that these shifts between interstadials and stadials are governed by a fluctuating sea ice cover retreating and then expanding over most of the Nordic Seas.

Our magnesium-calcium proxy measurements support this timeline of events. When the intermediate water was warm and stable -similar to the modern-day Arctic Ocean- there was sea ice cover over the Nordic Seas and it was a Greenland Stadial. When the intermediate water was cold and fluctuating -similar to modern Nordic Seas- there was no sea ice cover over the Nordic Seas, and it was a Greenland Interstadial.

Our measurements of intermediate water from Caprice help us understand what happened with sea ice at the surface of the Nordic Seas thousands of years ago. But we are still left wondering how the ocean actually circulated during these events.  The stories from cores like Caprice become truly spellbinding when you combine them with other scientific methods, like modelling. Only then can we get a complete picture of how the oceans behaved. We need to extend the study area from where we were on board G.O. Sars to the inflow region in the eastern Nordic Seas. We will incorporate a model to test if the ocean was physically capable of these proposed fluctuations.

 

References:

• Dansgaard, W., et al. (1993), Evidence for general instability of past climate from a 250-kyr ice-core record, Nature, 364, 218-220.
• Rahmstorf, S. (2002), Ocean circulation and climate during the past 120,000 years, Nature, 419, 207-214.
• Rosenthal, Y., and B. K. Linsley (2007), Mg/Ca and Sr/Ca paleothermometry, in Paleoceanography, Physcial and Chemical Proxies, pp. 1723-1731.
• Rudels, B., G. Björk, J. Nilsson, P. Winsor, I. Lake, and C. Nohr (2005), The interaction between waters from the Arctic Ocean and the Nordic Seas north of Fram Strait and along the East Greenland Current: results from the Arctic Ocean-02 Oden expedition, Journal of Marine Systems, 55(1–2), 1-30.
• Voelker, A. (2002), Global distribution of centennial-scale records for Marine Isotope Stag (MIS) 3: a database, Quaternary Science Reviews, 21, 1185-1212.

Check out the links below if you’re craving to learn more about the ocean:

Movies:

More about proxies – https://vimeo.com/154733972

More about Dansgaard-Oeschger events – https://vimeo.com/156830900

 

For kids and teaching:

https://climatekids.nasa.gov/ocean/

https://iglo.w.uib.no/