The Monday seminars are usually held in the GFI East Wing Auditorium at 11.15-12.00
Monday, 19th of December, Harald Sodemann (GFI) will give the seminar with the title: "Constraining the sources and transport history of atmospheric water vapour in models". The seminar will take place in the east wing auditorium, 11:15-12:00am. Please find the abstract below.
How long water vapour resides in the atmosphere between evaporation and precipitation is a piece of information that is relevant for the conception and design of studies and experiments targeting the atmospheric water cycle. We have recently demonstrated that the residence time of water vapour could be substantially shorter than previously assumed. We explore here the results derived from our Lagrangian diagnostic with a idealised, conceptional approach, to show that long residence times are derived for homogeneous and non-homogeneous systems, while non-stationarity may the key property that makes a system obtain short residence times. From several examples using reanalysis data it is illustrated that the atmosphere is essentially non-stationary and non-homogeneous, rendering the short residence times obtained from a Lagrangian approach in principle consistent with the real atmosphere. This is confirmed by an Eulerian approach to simulate the atmospheric residence time of water vapour over the Indian subcontinent. Field observations are essential to validate any model derived estimates of the residence time.
Wednesday 14th December 13:15-14:00, James H. Churchill (WHOI) will give a talk entitled "The Importance and Dynamics of Sea Level Variations in the Red Sea". The seminar takes place as usual in the East-wing auditorium at GFI. James H. Churchill is a guest of Abdir and Ingunn.
Sea level variations in the central Red Sea coastal zone span a range of roughly 1.2 m. Though relatively small, these water level changes can significantly impact the environment over the shallow reef tops prevalent in the central Red Sea, altering the water depth by a factor or two or more. While considerable scientific work has been directed at tidal and seasonal variations of Red Sea water level, very little attention has been given to elevation changes in an ‘intermediate’frequency band, with periods between 2 days and 1 month, even though motions in this band account for roughly half of the sea level variance in central Red Sea. We examined the sea level signal in this band using AVISO sea level anomaly (SLA) data, COARDAS wind data and measurements from pressure sensors maintained for more than five years at a number of locations in Saudi Arabian coastal waters. Empirical orthogonal function analysis of the SLA data indicates that longer-period (10-30 d) sea level variations in the intermediate band are dominated by coherent motions in a single mode that extends over most of the Red Sea axis. Idealized model results indicate that this large-scale mode of sea level motion is principally due to variations in the large-scale gradient of the along-axis wind. Our analysis indicates that coastal sea level motions at shorter periods (2-10 d) are principally generated by a combination of direct forcing by the local wind stress and forcing associated with large-scale wind stress gradients. However, also contributing to coastal sea level variations in the intermediate frequency band are mesoscale eddies, which are prevalent throughout the Red Sea base, have a sea level signal of 10’s of cm and produce relatively small-scale (order 50 km) changes in coastal sea Level.
Monday 5th December, Ralf Hand(MPI) will give a talk entitled "North Atlantic decadal climate variability in a very large ensemble of CGCM runs". The seminar takes place as usual in the East-wing auditorium at GFI and will start at 11.15.
Very large ensembles of simulations with the MPI Earth System Model were analyzed with focus on the North Atlantic sector. The set of runs consists of a 2000-year climatologically forced control run, a 100-member ensemble with historical (observed) radiative forcings and a 68-member ensemble with 1%/yr CO2 increase.
Our main objectives were to understand and quantify the influence of external forcing on different ocean indices, and to achieve a better understanding of the link between large-scale Sea Surface Temperature in the North Atlantic and the ocean circulation to determine possible implications for the predictability of multi-annual to decadal climate variability in this region.
The high number of ensemble members allows us to perform Statistical analysis and thereby to make robust estimates of what influences the different indices of ocean variability and possible links between them:
Comparison of the ensemble mean and the intra-ensemble spread of the indices allows us to distinguish externally-forced or physically generated internal modes from randomly-generated differences between the individual ensemble members. Comparing the historical ensemble and the 2000-year long climatologically forced control simulation allows us to separate externally forced features of variability from internally generated modes of the system. As one example, a noticeable part of the AMV shows common features in the individual members of the historical ensemble and therefore can be interpreted as being externally forced.
With respect to the historical simulations, the 1% simulations show strong changes to the ocean mean state. Beyond this, the ensemble spread of the AMOC is highly reduced towards the end of the simulations With strongly increased radiative forcing, indicating a weakened internal variability related to the forcing.
A lead-lag cross-correlation analysis shows a qualitatively robust link between AMV, AMOC and subpolar gyre variability. However, the strength of the correlation between AMOC and AMV is varying between different periods in the control run and has some spread within the historical ensemble. Probably related to the reduced AMOC variability under strong radiative forcing, the cross-correlation between AMOC and AMV is decreased in the 1% simulations.
Volkmar Wirth (Johannes Gutenberg University, Mainz), will talk about "The Dynamics of Orographic Banner Clouds: Previous Insight and Outstanding Questions." The seminar will take place in the eastwing auditorium, Monday, 28th of November, 10:15-11:30am. AFTER the seminar, from 11:30-12:00, Volkmar Wirth will give some insights into the Bachelor and Master programme in Mainz and the possibilities of ERASMUS following a short discussion. All Bachelor and Master students are very much welcome!
"The Dynamics of Orographic Banner Clouds: Previous Insight and Outstanding Questions"
Banner clouds are clouds which appear to be attached to the leeward slope of a steep mountain. They are frequently observed e.g. at the Matterhorn in the Swiss Alps or at Mount Zugspitze in the Bavarian Alps. Systematic observations at mount Zugspitze some ten years ago yielded information about the diurnal and the seasonal dependence of banner cloud occurrence, about the distribution of the duration, as well as the dependence on wind speed and wind direction. Investigations using numerical simulations with idealized orography have shown that the occurrence of banner clouds is mostly due to a windward-leeward flow asymmetry producing a plume of strong uplift on the leeward side of the mountain. Parcels primarily go around the mountain before they are lifted in upwelling flow on the leeward side. The leeside upwelling, in turn, is associated with a bow-shaped vortex. It follows that banner clouds require truly three-dimensional orography. Also, it has been shown that the flow of weakly stratified air past a steep mountain is most conducive to banner cloud formation. It appears that occurrence of banner clouds does not depend on the magnitude of the wind. On the other hand, the leeside vortex depends sensitively on the vertical shear of the oncoming flow. Details of these sensitivities are not well understood. Currently we perform simulations with realistic Zugspitz orography in order to better understand the results from the measurement campaign ten years ago. These simulations turn out to be rather difficult, most probably owing to the multiscale nature of the orography in the neighborhood of Mount Zugspitze. We hypothesize that the asymmetry of Mount Zusgpitze gives rise to a dependence on wind direction.It is suggested to focus future investigations on Mount Matterhorn. Ideas will be discussed indicating that measurements would help to answer some of the outstanding questions.
Tuesday, 22nd of November, 14-15-15:30 in the east-wing auditorium, Hui Tang (University of Oslo) will give a seminar about "Dynamic vegetation–atmosphere modelling of the boreal zone using NorESM". Frode Stordal, Hui Tang, and Terje Berntsen from Oslo will visit the Bjerknes Centre on 22-23 Nov. If you would like to join the discussion sessions or to meet with the guests, please contact Hanna Lee or Christoph Heinze. This could in particular be of interest also for persons working in the climate services area and also for coastal ocean researchers.
Vegetation-atmosphere interaction plays an important role in the boreal climate changes. Modeling studies on the boreal climate, however, seldomly use coupled atmosphere - dynamic vegetation model, owing to the large uncertainties of the dynamic vegetation model in depicting the Arctic vegetation and its feedbacks. In this study, we evaluate the performance of the dynamic vegetation model in the land surface model (CLM4.5) of NorESM in simulating the boreal vegetation and its climate feedbacks. A lack of Arctic shrub and a strong positive vegetation – temperature feedback are found in our experiments, which lead to a ”run-away” of the Arctic climate towards a cold-biased steady state in the coupled model. The improvement of several key vegetation parameters are proposed to reduce the model biases in the Arctic vegetation and its climate feedbacks.
Monday, 21st of November, 11:15-12:00 in the east-wing auditorium, Birgitte Furevik (met.no) will give a talk with the title: "Large measurement program (Ferjefri E39) in two Norwegian fjords opens new research possibilites".
The Norwegian Public Roads Administration is planning a ferry-free road connection (E39) between Kristiansand and Trondheim is planned and this implies the crossing of a number of large and deep fjords. In Sulafjord and Halsafjord in Mid-Norway a large measurement campaign has started to support the development of the bridge designs. The measurements from several tall meteorological masts and a number of metocean buoys will be received by the Meteorological Institute and made publicly available. The masts will be deployed by Kjeller Vindteknikk who is also doing 10 years of simulations with the atmosphere model WRF. Fugro Ocean will carry out the buoy measurements. The Institute of Marine Research (IMR) performs ocean modelling (ROMS) and MET performs wave modelling (SWAN). I will present the first measurements and preliminary results of the modelling. The measurement program is probably the largest ever carried out in Norwegian fjords and can be the foundation for other projects, additional measurements and MSc topics
Monday 7th of November already at 10:15-11:00 (!) in the east-wing auditorium, Dorothee Bakker (University of East Anglia, Norwich and SAC member) will give a talk entitled "The Surface Ocean CO2 Atlas enables quantification of the ocean carbon sink and ocean acidification". See abstract below.
The Surface Ocean CO2 Atlas (SOCAT, www.socat.info) is a synthesis activity by the international marine carbon community (>100 contributors) with support from SOLAS, IMBER, IOCCP, IOC and (jnter-)national agencies. SOCAT brings together quality-controlled fCO2 (fugacity of carbon dioxide) values for the global surface oceans and coastal seas with regular updates. Version 4 of SOCAT has 18.5 million surface water fCO2 values for the years 1957 to 2015. SOCAT now accepts well-calibrated, good quality fCO2 measurements from alternative sensors and platforms. Data set flags reflect the accuracy of surface water fCO2 values, ranging from better than 2 micro-atm (for the highest quality data) to better than 10 micro-atm (for alternative sensors). Automation of data upload will enable annual SOCAT releases from version 4 onwards. The interactive Data Set Viewer allows effective interrogation of the SOCAT data collection and rapid creation of high-quality figures for scientific presentations. Users of SOCAT data products are urged to acknowledge the contribution of data providers, as stated in the SOCAT Fair Data Use Statement. High-profile scientific applications of SOCAT include quantification of the ocean carbon sink and its long-term variation, detection of ocean acidification, as well as evaluation of coupled-climate and ocean-only biogeochemical models. SOCAT represents a milestone in coordinating international researchers, for the delivery of publically accessible and uniformly quality-controlled datasets, for marine and global carbon research and for informing government climate policy.
9 november, 10:15-12:00. Speaker: Barbara Scarnato, guest of Christoph. Title: Aerosols and their role on climate.
The importance of atmospheric gases such as carbon dioxide for climate is well known, however small particles that are present in the atmosphere, so called aerosols, also play crucial roles in weather, climate and air quality. Aerosols are minute particles suspended in the atmosphere, either solid or liquid, with diameters of a few nanometers to tens of microns. The bulk of the aerosols, about 90 percent by mass, have natural origins, and examples are volcanoes, forest fires, sea sprays and deserts. The remaining 10 percent by mass, is human-made aerosols which can come from a variety of sources, including vehicles, biomass burning, incinerators, alteration of natural surface cover due to land use changes, cooking stoves, fireplaces etc. Aerosols particles can be referred depending on their chemical compositions, and key aerosol groups include sulfate, black carbon, organic carbon, mineral dust and sea salt. In practice, many of those terms are ‘imperfect’ as aerosols often clump together while suspended in the atmosphere to form complex inhomogeneous mixtures. Different aerosols types scatter and/or absorb sunlight to varying degrees, depending on their physical properties, directly affecting the Earth’s radiation field. However, since aerosols comprise such a broad collection of particles with different properties, the overall effect is anything but simple. Aerosols can also act as cloud ‘seeds’, and produce brighter clouds that are less efficient at forming precipitation. These in turn lead to large reductions in the amount of solar irradiance reaching Earth's surface, a corresponding increase in solar heating of the atmosphere, changes in the atmospheric temperature structure, suppression of rainfall, and less efficient removal of pollutants affecting also air quality. During the lecture, Dr. Scarnato will speak about aerosols and their relevance in the climate system, air quality and current challenges with particular regard on absorbing aerosols particles.
Monday 31st October, Meike Becker (GFI) will give a talk entitled Using autonomous 13C measurements in the North Atlantic to identify patterns and driving factors of the upper ocean carbon cycle. The seminar takes place as usual in the East-wing auditorium at GFI and will start at 11.15.
Understanding the variability within the seasonal cycle of the carbon system in the North Atlantic is often limited by properly distinguishing the influences from air-sea gas exchange, primary production, respiration and mixing processes. We need to improve our quantitative description of these processes, but we also need to improve our understanding of what actually happens in the surface ocean at which time of the year. Combining continuous measurements of stable carbon isotope ratios of CO2 with a discrete sampling program (nutrients, DIC/TA, POM, DOC, Chl a, 13C(POC)) on a Voluntary Observing Ship can be a good tool for this.
Monday 24th October, Celine Heuze (University of Gothenburg) will give a talk entitled Polar Deep Waters. The seminar takes place as usual in the Auditorium and will start at 11.15.
At both poles, extremely dense waters sink to the bottom of the ocean before travelling around the world. This sinking transports oxygen, ventilating the deep ocean. It also transports heat, more and more with climate change. Since deep and bottom waters represent nearly half of the world ocean in volume, even a slight and slow warming of these waters can cause steric sea level rise that should be quantified urgently. But these deep waters remain undersampled, for they cannot be observed by satellites or even Argo floats. Hence scientists rely on models to understand the variability and drivers of the deep water circulation, and make realistic projections for adaptation and mitigation policies. But how accurate are these models?
Monday 17th October, Hiroyasu Hasumi (AORI, University of Tokyo) will give a talk entitled: Arctic physical oceanography in Japan. The seminar takes place as usual in the Auditorium and will start at 11:15. Hiroyasu is a guest of Tomas S.
An overview is given for the Arctic research in Japan by focusing on the physical oceanographic aspect. R/V Mirai of JAMSTEC has repeatedly conducted summertime cruises into the Pacific side of the Arctic Ocean over the past two decades and monitored rapid changes therein. Satellite data are widely utilized to describe the basin-wide state of the Arctic Ocean and to make a prediction of the sea ice cover. Eddy-resolving modeling is actively performed to synthesize observed features. Influence of the Arctic Ocean on the climate is also pursued using climate models with some focus on the behavior of freshwater.
Wednesday 12th of October, Per Pemberton (SMHI Gøteborg, Sweden), will give a talk entitled: Freshwater processes and water mass transformation in the Arctic Ocean.
The seminar will start at 11:15 in the foredragssal. Per is a guest of Erwin and Aleksi.
This presentation will focus on freshwater-related processes and water mass transformation in the Arctic Ocean. Knowledge of these processes is important from both a local and a global perspective. Globally, because the export of cold and low saline water and sea ice might influence the North Atlantic and global meridional overturning circulation. Locally, because freshwater processes affect the vertical stratification and permit favorable conditions for the ice cover. Based on results from experiments with a regional ocean–sea ice model (MITgcm) as well as a more simple conceptual model I will discuss how the different sources of freshwater spread and contribute to the Arctic Ocean freshwater distribution and how sensitive the system is to changes in input of freshwater.
Monday 10th of October, Brian Dushaw (NERSC) will give a talk entitled: An Empirical Model for Mode-1 Internal Tides Derived from Satellite Altimetry: Computing Accurate Tidal Predictions at Arbitrary Points Over the World Oceans. This seminar will start at 11:15 in the east wing auditorium.
A global estimate for harmonic constants of mode-1 internal tides is described, enabling accurate predictions of internal tide amplitude and phase in most regions of the world’s oceans. The estimates are derived from TOPEX/POSEIDON altimetry, building on a frequency-wave number tidal analysis technique described by Dushaw et al. (2011) [B. D. Dushaw, P. F. Worcester, and M. A. Dzieciuch, 2011. On the predictability of mode-1 internal tides, Deep-Sea Res. I, 58, 677−698]. This technique obtains tidal harmonic constants for the six largest tidal constituents (M2, S2, N2, K2, O1, K1) and the first two internal wave modes simultaneously.The global solution requires reasonably accurate intrinsic properties of low-mode internal waves, which depend on local inertial frequency, stratification and depth. These properties are derived using the 2009 World Ocean Atlas and Smith–Sandwell global seafloor topography. To account for regional variations in internal wave properties, the global solution for internal tides is obtained by knitting together solutions obtained in 11°×11° overlapping regions. In any area of the ocean, the internal tide field generally consists of the interference pattern formed by the superposition of several or many wavetrains. Inasmuch as accurate tidal estimates are derived from the satellite altimetry, a remarkably marginal observational approach for determining properties of these waves, it is evident that the phases of the interference patterns are stable, indicating extraordinary temporal coherence. The timescales of the interference patterns are faster than the internal tide waves themselves. Over ocean basins, wavetrains traveling in particular directions can be determined, which show spatially coherent wavetrains extending across these basins and suffering little loss in amplitude. The global solution is tested against point-wise, along-track estimates for the internal tide, with satisfactory comparisons obtained between the two results. Along-track estimates are error prone and provide for only a weak test. From the harmonic constants derived in the global solution, time series are predicted for several existing observations of mode-1 internal tides in the Atlantic and Pacific oceans. The clearest in situ measurements are provided by ocean acoustic tomography, but point measurements provided by moored thermistor arrays or mooring crawlers provide a complementary, if error prone, observation of mode-1 tides. Good predictability for both amplitude and phase, or as good as could be expected given the vagaries of ocean observation, is obtained in all cases. Some of these predictions are obtained for time series recorded about a decade before or after the altimetry data used to derive the global solution, consistent with extraordinary temporal coherence.
David Battisti (University of Washington) will give a talk entitled: Why is there an ocean overturning circulation in the North Atlantic and not in the North Pacific?
OBS! Please note that this seminar will take place at Nygårdsporten auditorium (Nygårdsgaten 112, Uni Research), starting at 14:00. Please find an abstract below.
A remarkable asymmetry in the climate system is the deep meridional overturning circulation in the North Atlantic Ocean (AMOC) that is not found in the North Pacific Ocean. In this talk, I will briefly discuss the myriad hypotheses that have been put forward for why there is an overturning circulation in the North Atlantic. I will then show results from experiments that test three of the most widely discussed hypotheses for why there is an AMOC: (i) the impact of the Rockies on the atmospheric circulation; (ii) the impact of the Rockies on the on the hydrologic cycle, and (iii) the net export of water from the Atlantic to the Pacific via atmospheric transports. These experiments also help to illuminate why there is no meridional overturning circulation in the North Pacific.
Monday 3d of October, Steve Barker (Cardiff University, UK) will give a talk entitled: Emergence and Development of the ‘100kyr World’.
Seminar will start at 11:15 and will take place in the east wing auditorium. Please find an abstract below.
The varying influence of Earth’s orbital geometry on climate is well documented, yet uncertainty over the precise interplay between orbital variations and the waxing and waning of continental ice sheets over tens of thousands of years continues to hinder our understanding of Earth’s climate system. In particular, the emergence of approximately 100kyr glacial cyclicity across the Mid Pleistocene Transition (MPT, ~0.7 - 1Ma) gives rise to the so-called ‘100kyr problem’; why do such large changes in climate display dominant power ~100kyr while orbital forcing at this period (changes in the eccentricity of Earth’s orbit around the Sun) is so weak? Over recent decades it has become clear that the duration of Late Pleistocene glacial cycles is not precisely 100kyr but most likely multiples of 23 and 41kyr (the periods of precession and obliquity). For example glacial periods tend to terminate every 4 or 5 precession cycles, giving an average period of around 100kyr. Furthermore it is becoming apparent that millennial-scale changes in the ocean/atmosphere system (involving the so-called bipolar seesaw) may play an active role in the non-linear amplification of insolation forcing that has been required for terminating glacial periods since the MPT. Here I will show the latest results from an ongoing project to produce a 1.7Myr record of sub-millennial-scale variability from the surface NE Atlantic Ocean. I will argue that the emergence of ‘100kyr periodicity’ was paralleled by the appearance of ‘seesaw-driven terminations’ and relate this to the increase in northward heat and moisture transport associated with a strengthening of the Nordic heat pump across the MPT.
Monday 19th of September, Ed Gasson (Sheffield University, UK) will give a talk entitled: The Antarctic ice sheet during the Miocene and Pliocene. Seminar will start at 11:15 and will take place in the east wing auditorium. Ed is a guest of Petra and he will be here on Monday, Tuesday and Wednesday. If you would like to meet him, please contact email@example.com. Please find an abstract below.
Geological data indicate that there were major variations in the volume and extent of the Antarctic ice sheet during past warm intervals of the Pliocene (~3 Ma) and the
mid-Miocene (~15 Ma). Simulating this retreat with coupled climate and ice sheet models has long been problematic due to strong stabilising mechanisms. Here we discuss how new mechanisms have enabled the simulation of retreat that is more consistent with the geological evidence. We also discuss the difficulty of constraining sea level high stands during the mid-Pliocene. This may have implications for simulations of sea level rise in a future warming world.
Monday 12th of September, Satoshi Kimora (NERSC) will give a talk entitled: Oceanographic controls on the variability of ice-shelf melting and meltwater pathways in the Amundsen Sea, Antarctica. Seminar will start at 11:15 and will take place in the east wing auditorium. Please find an abstract below.
Ice shelves are in the forefront of the ice sheet-ocean interactions in Antarctica. Nearly all the ice sheets in Antarctica terminate on the ice shelves (the floating extensions of the ice sheets), mediating the release of ice from the land to the ocean. Many of the rapidly thinning ice shelves in Antarctica are located in the Amundsen Sea Embayment. Pine Island Glacier and its neighbour Thwaites Glacier in this region, have been highlighted as major drainage pathways for the West Antarctic Ice Sheet. The origin of the imbalance in the ice shelves is almost certainly due to unsteady ocean-driven melting. We will discuss the variability of ice-shelf melting and oceanic conditions between 1991 and 2014 using a general
circulation model forced by two different atmospheric forcing scenarios, ERA-Interim and RACMO2.3. We show that the ice-shelf melting is fuelled by the meridional heat transport from the shelf break, which is weakly correlated to the offshore zonal wind stress. We showed that differences in the magnitude of melting change the circulation at the calving front of the ice shelves. The change in the circulation leads to a different spatial distribution of glacial meltwater, which has an implication to a design of the glacial-meltwater parameterisations in climate models.
September 5th, we have our next seminar - as always in the east wing auditorium from 11:15-12:00. Yiming Luo (new postdoc at GFI) will give a talk: “Disparate acidification of deep and shallow waters of the Arctic Ocean“. Please find the abstract below.
The Arctic Ocean is acidifying from absorption of man-made CO2. Current predictive models of that acidification focus on surface waters, and their results argue that deep waters will acidify by downward penetration from the surface. Here we show, with an alternative model, the rapid, near simultaneous, acidification of both surface and deep waters, a prediction supported by current, but limited, saturation data. Whereas Arctic surface water responds directly by atmospheric CO2 uptake, deeper waters will be influenced strongly by intrusion of mid-depth, pre-acidified, Atlantic Ocean water. With unabated CO2 emissions, surface waters will become undersaturated with respect to aragonite by 2105 AD and could remain so for ~600 years. In deep waters, the aragonite saturation horizon will rise, reaching the base of the surface mixed-layer by 2140 AD and likely remaining there for over a millennium. The survival of aragonite-secreting organisms is consequently threatened on long time scales.
Monday 29th of August, Michael Reeder (Monash University) will give a talk entitled: Tropical - Midlatitude Interactions and Significant Summertime Weather in the Australian Region.Seminar will start at 11:15 and take place in the east wing auditorium. Michael is a guest of Thomas S. Please find an abstract below.
In the Australian region during summer, Rossby waves preferentially break anticyclonically around the latitudes of eastern Australia, and in the process, cyclonic potential vorticity is transported equatorward and anticyclonic potential vorticity is transported poleward. Much of the significant weather in the region can be attributed to this kind of stirring of the potential vorticity field and the potential vorticity anomalies so produced. This talk will examine the main ingredients for such processes in the region.
August 22nd, we have our next seminar - as always in the east wing auditorium from 11:15-12:00. Nili Harnik (Tel Aviv University) will give the talk: “The Circumglobal North American wave pattern and its relation to North American cold events“. Nili is a guest of Thomas S. Please find the abstract below!
Extreme large scale North American cold events are associated with strong undulations in the tropospheric jet stream which bring cold polar air southward over the continent. We propose that these jet undulations are associated with the North American part of the Circumglobal Teleconnection Pattern - a pair of zonally oriented waves of zonal wavenumber 5 which are in zonal quadrature with each other. While the PNA is associated with the first circumglobal wave pattern, North American extreme cold events are associated with the second pattern. The circulation and temperature anomalies associated with Circumglobal North American wave packet and with the strongest Eastern US cold events will be compared. We will also discuss the Asian wavepacket precursor of these events, and the possible relation to SST anomalies.
Wednesday, 17th August: Markus Jochum (Niels Bohr Institute, University of Copenhagen) is a guest of Noel. The title of his talk is: “Interhemispheric Teleconnections in the Ocean“.
Motivated by the observed anti-correlation between Greenland and Antarctic temperatures, ocean mechanisms are investigated by which Southern Ocean winds influence North Atlantic circulation. The original Toggweiler and Samuels experiments are revisited to account for the effects of, firstly, an energy based representation of diapycnal mixing; secondly, resolved mesoscale eddies; and lastly, resolved coastally trapped waves. Comparisons with current non-eddy- resolving models then highlight where current eddy parameterizations fall short and where simulated remote connections should not be trusted.
Monday, 15th August: Hyungjun Kim is an assistant professor at the University of Tokyo and will talk about: „Land Surface, Snow and Soil Moisture in Land-Climate Feedback and Model Diagnosis“. Hyungjun is a guest of Hanna.
The Land Surface, Snow and Soil Moisture Model Intercomparison Project (LS3MIP) is designed to provide a comprehensive assessment of land surface, snow, and soil moisture feedbacks on climate variability and climate change, and to diagnose systematic biases in the land modules of current Earth System Models (ESMs). The solid and liquid water stored at the land surface has a large influence on the regional climate, its variability and predictability, including effects on the energy, water and carbon cycles. Notably, snow and soil moisture affect surface radiation and flux partitioning properties, moisture storage and land surface memory. They both strongly affect atmospheric conditions, in particular surface air temperature and precipitation, but also large-scale circulation patterns. However, models show divergent responses and representations of these feedbacks as well as systematic biases in the underlying processes. LS3MIP will provide the means to quantify the associated uncertainties and better constrain climate change projections, which is of particular interest for highly vulnerable regions (densely populated areas, agricultural regions, the Arctic, semi-arid and other sensitive terrestrial ecosystems).
The experiments are subdivided in two components, the first addressing systematic land biases in offline mode ("LMIP", building upon the 3rd phase of Global Soil Wetness Project; GSWP3) and the second addressing land feedbacks attributed to soil moisture and snow in an integrated framework ("LFMIP", building upon the GLACE-CMIP blueprint).
Friday 12th August, Joel Pedro (Niels Bohr Institute, University of Copenhagen) will give a talk entitled: „A Southern Hemisphere perspective on abrupt climate change (Dansgaard–Oeschger variability)“. Joel is a guest of Eystein.
The bipolar ocean seesaw hypothesis contends that past collapses of the Atlantic Meridional Overturning Circulation caused abrupt cooling in the North Atlantic and gradual warming in the South Atlantic, Southern Ocean and adjoining land-masses. I use a compilation of 84 high-resolution climate records along with model simulations to test the extent to which this hypothesis can explain the Southern Hemisphere expression of the Dansgaard–Oeschger events.
August 8 we have a seminar by Jeroen Groeneveld (University of Bremen). The title of his talk is: "Exploring recent trends in paleoceanography with new foram-based proxies". Jeroen is a guest of Ling and he is here all of next week - if you want to meet him, send a mail to Ling.Ho@uib.no! The seminar will take place in the east-wing auditorium, as usual 11:15-12. Please find the abstract below!
Paleo-climate reconstructions are increasingly focusing on the impact of future global change. Increasing temperatures and decreasing global ice volume are well-known factors, and commonly reconstructed. But there are other changes, which may even be more directly impacting human society including extending oceanic “dead-zones” where no marine life is possible anymore due to the lack of oxygen. Also, climate becomes more extreme, inter-annual phenomena like NAO or ENSO will intensify. Proxies to address these issues are recently receiving a lot of attention in paleo-reconstructions. In this presentation I will, therefore, present and discuss recent developments in the use of foraminifer-based geochemistry to reconstruct paleo-oxygen conditions and inter annual variability based on individual foraminifera.
We start the new semester with a seminar by Stacy Carolin (University of Oxford) this Thursday, 4th of August at 13:15-14:00 in the east-wing auditorium. Stacy is a guest of Nele and Harald and will talk about: "Iranian speleothems: Investigating Quaternary climate variability in semi-arid Western Asia". Please find the abstract below.
Currently, very few terrestrial paleoclimate records with a robust absolute age model are able to extend climate records beyond the limits of the instrumental period in semi-arid Western Asia, a significant region of rapid population growth and limited water supply. I present here a synthesis of new speleothem climate records spanning across northern Iran, from the dry northeast to the wetter climate of the Alborz and Zagros mountain ranges. I focus on two periods in the past: the mid-Holocene and the penultimate deglaciation. The mid-Holocene stalagmite’s growth spans 1700-3200 BC, an important archeological period in the Near East which includes the alleged ~2200 BC mega-drought event purported to have had a substantial impact on the world’s first agricultural civilizations. The second stalagmite shows variable rates of vertical growth from 180-69 kyBP. Particularly slow growth is found in the interval from ~155-128 kyBP, however there is no visual or trace element evidence of a growth hiatus during this period. Notably, the stalagmite’s stable isotope record reveals a significantly large (4‰) abrupt oxygen isotope shift toward more depleted values near 135kyBP, suggesting an association of a rainwater isotopic shift over the Iranian plateau with the glacial termination.
Monday 27th of June at 11.15, Raúl Tapia (GEOMAR) will give a talk on "Variable glacial signature of Southern Ocean intermediate waters in the central South Pacific: Implications for the subsurface transfer of southern climatic signals". Raul is a guest of Bjørg. Please find the abstract below.
Southern Ocean Intermediate Waters (SOIWs), such as Antarctic Intermediate Water and Subantarctic Mode Water, play a key role in modulating the global climate on glacial-interglacial time scales. They link high and low latitudes by transporting climatic signals (e.g. heat, salt and nutrients) across latitudes, via mechanisms such as “oceanic tunneling”.
The South Pacific hosts the major area of intermediate water formation, rendering it a key region for studies of intermediate water masses. But the few paleoceanographic records at the southernmost Pacific have limited our capability to infer changes on intermediate waters at times scales longer that one Glacial-Interglacial cycle.
To evaluate changes in the SOIWs in the South Pacific during full glacial conditions (Last Glacial and Penultimate Glacial), we compared Mg/Ca, stable carbon and oxygen isotope records from surface-dwelling and deep-dwelling planktic foraminifera at the central Pacific (45°S) and northern boundary of the Antarctic Circumpolar Current region (54°S), were the Antarctic Intermediate Water and Subantarctic Mode Water are formed.
Our temperature and salinity reconstructions suggest latitudinal differences in presence of the SOIWs during glacial periods. This is unlikely to be due to a cease in the production of SOIWs, since subsurface temperature and salinity suggest presence of Antarctic Intermediate Water at our southern study site (54°S) during both glacial time windows. Latitudinal differences of the water column in terms of thermal gradient and mixed layer depth resemble the effects that changes intensity of the South Westerly Winds have on the ocean. These findings underlined the spatio-temporal complexities in the formation and transport of the SOIWs in the Pacific Ocean.
Tuesday, 21st of June, 11:15-12:00 in the east-wing auditorium. Aleksi Nummelin (GFI) will give a talk "On the meridional structure of the northward ocean heat transport". Please find the abstract below.
As the climate system adjust to greenhouse gas warming the poleward heat transport is expected to change, both in the ocean and in the atmosphere. While the atmospheric heat transport is expected to increase due to enhanced moisture transport, the large scale poleward oceanic heat transport is expected to decrease. However, a more detailed examination of the Atlantic-Arctic sector reveals that the oceanic response to greenhouse gas warming shows a rich meridional structure. The reduced ocean heat transport drives reduced warming ('the warming hole') in the subpolar North Atlantic, while further north in the Arctic the enhanced northward ocean heat transport explains the ocean warming. Interestingly, the heat transport trends in the Arctic seem disconnected from their lower latitude counterparts. The meridional dependence of the ocean heat transport trends has also lead to discrepancies in the reported ocean contributions to the Arctic Amplification - studies focusing on mid-latitudes have found no, or negative, connection between the ocean heat transport trends and the Arctic Amplification, while studies focusing on high latitudes have suggested that ocean heat transport contributes to Arctic Amplification. Here we aim to clarify the role of the ocean heat transport in Arctic climate change, by examining a set of future climate change projections under the Coupled Model Intercomparison Project (CMIP5). Our results suggest that atmospheric driven changes in subpolar heat fluxes enhance the ocean heat transport to the Arctic Ocean, which drives the Arctic Ocean heat content increase and contributes to the intermodel spread in the Arctic Amplification.
Monday June 6 Thomas Spengler (GFI) will talk about "Maintenance of Baroclinicity in the Atlantic Storm Track (and its Relation to the Sea Surface Temperature Gradient along the Gulf Stream)". Please find the abstract below.
The maintenance of baroclinicity along mid- and high-latitude storm tracks is a matter of ongoing debate. We devise a diagnostic based on the tendency equation for the slope of isentropic surfaces – a measure of the baroclinicity. The tendency comprises contributions from dynamic processes, latent heat release, radiation and subgrid-scale turbulence, which incorporates the effect of sensible heat fluxes. We present a climatology (for winter 2009 and 2010) of these tendencies over the North Atlantic and discuss the relevance of the SST gradient associated with the Gulf Stream.
We find that adiabatic tilting flattens the isentropic surfaces, reflecting the action of growing baroclinic cyclones. This tendency is balanced climatologically by the generation of isentropic slope by diabatic processes. In the lower troposphere, the most intense diabatic increase of slope is found along the oceanic frontal zone associated with the Gulf Stream and at higher latitudes in the Labrador Sea, the Nordic Seas and the Barents Sea. Latent heat release and sensible heat fluxes both contribute substantially in these regions. A quantitative analysis of cold-air outbreaks emphasizes their important role in restoring the slope in the lower troposphere over the Gulf Stream region and off the sea-ice edge at high latitudes. We also present composites of strong events of slope tendency and latent heating as well as surface fluxes, pinpointing the relative contribution of the cold or warm sector of a cyclone to the slope tendency in the Gulf Stream region. In the upper troposphere, latent heat release due to cloud microphysical processes is the dominant mechanism maintaining the slope.
Thursday June 2 Mingfang Ting (Lamont Doherty Earth Observatory, Columbia University) will talk about "The Role of Aerosol and Greenhouse Gas Forcing in CMIP5 Models: Impacts on Asian Monsoon and Atlantic Hurricane Intensity". Mingfang is a guest of Noel and member of Lea's defense committee.
In this talk, I will discuss our recent work on the regional climate changes in the historical period due to both the aerosol and greenhouse gas forcing, in particular how these anthropogenic forcing may have impacted the Asian monsoon and the Atlantic hurricane intensity. While aerosols and greenhouse gases tend to produce opposite sign changes in terms of surface temperature and precipitation as previously discussed, the mechanisms by which these changes occur are not entirely symmetric between the two forcing cases. For example, aerosols tend to produce largely dynamical responses in Asian monsoon circulation changes, while greenhouse gas forcing tends to be dominated by the thermodynamic impact through changes in atmospheric moisture content. For their impact on the Atlantic hurricane intensity, aerosols are more effective in causing changes in hurricane intensity than greenhouse gases, due to differences in surface energy balances. Future changes in Asian monsoon and hurricane intensity as simulated by the CMIP5 models will also be discussed as a comparison to that during the historical period.
Thursday, 25 May, 11:15-12:00 Yuanchao Fan (University of Göttingen) will talk about "Modeling oil palm monoculture and its associated impacts on land-atmosphere carbon, water and energy fluxes in Indonesia". Yuanchao is a guest of Hanna Lee.
In Southeast Asia, the rapid expansion of oil palm monocultures and the concurrent destruction of rainforests and peatlands have been in the spotlight for their prominent roles in greenhouse gas emission. A thorough quantification of the carbon balance of oil palm plantations and the long-term and large-scale forest – oil palm replacement effects is necessary for understanding the climatic impacts of tropical land use change. This study presents a comprehensive analysis of the carbon dynamics and water and energy exchanges of oil palm plantations throughout developmental stages (from planting to rotation) with a land surface modeling approach. A new modeling scheme for palm species has been developed within the Community Land Model framework (named CLM-Palm). CLM-Palm incorporates the agricultural model capacity for simulating growth and yield of palms with unique phenology and allocation functions and a suit of new parameterizations on biogeophysics (e.g. radiative transfer and evapotranspiration (ET)) and on biogeochemistry (e.g. carbon and nitrogen dynamics, fertilization effects).Validated with available field data, the simulation shows clear distinctions between young and mature oil palm plantations and old-growth rainforest in carbon fluxes (e.g. GPP, NEE) and biophysical properties (e.g. ET, surface albedo and temperature). A transient simulation spanning two rotation periods (each 25 years) showed that long-term oil palm cultivation is only able to restore about a half of the original total carbon storage capacity of the forested site before clear-cut. More than 50% of the net primary production by the oil palm plantation is not retained on the site but instead exported as oil products which are soon reverted to CO2. Soil carbon stocks decline slowly and gradually due to the limited litter return in the managed plantation. Conversion of rainforest to oil palm plantation also has potential warming effects on the land surface at the site scale.
When: Friday, 13th, 13:15-14:00. Who: Roger Samelson (College of Earth, Ocean, and Atmospheric Sciences at Oregon State University). Title: A Linear Stochastic Field Model of Mid-Latitude Mesoscale Variability
A semi-empirical model of mid-latitude sea-surface height (SSH) variability is formulated and tested against two decades of weekly global fields of merged altimeter data. The model is constrained to match approximately the observed SSH wavenumber power spectrum, but predicts the spatio-temporal SSH field structure as a propagating, damped, linear response to a stochastic forcing field. An objective, coherent-eddy identification and tracking procedure is applied to the model and altimeter SSH fields. The model eddy dataset reproduces the basic global-mean characteristics of the altimeter eddy dataset, including the structure of mean amplitude and scale life cycles, the number distributions vs.~lifetime, the increases of mean amplitude and scale with lifetime, and the distributions of week-to-week amplitude and scale increments, and, approximately, of all amplitude and scale realizations for eddies with lifetimes of 16 weeks or more. The model also shows some discrepancies relative to the observed eddy statistics. The stochastic forcing evidently represents nonlinear dynamical interactions, implying that eddy splitting and merging events are equally likely, that mesoscale nonlinearity is weaker than long-wave linearity but as strong as short-wave dispersion, and that mesoscale eddy potential vorticity fluxes are, to leading order, independent of the mean field. These theoretical inferences have potential implications for eddy flux parameterizations. (Joint work with M. Schlax and D. Chelton, Oregon St Univ.)
When: Wednesday 11th, 14:30-15:30,Who: Samar Khatiwala (University of Oxford), Guest of Jerry. Title: Constraining ocean ventilation pathways and time scales with observations and models
The ocean's key role in regulating Earth's climate is in large part due to its thermohaline circulation that transports water and climatically important trace gases such as carbon dioxide from the surface into the ocean interior and back to the surface. This so-called "conveyor belt" circulation allows the ocean to absorb and sequester CO2 and heat on centennial to millennial time scales, thus potentially mitigating the impact of anthropogenic climate change. Quantitatively characterizing this complex circulation is an important problem in oceanography and climate science but remains highly challenging because of the eddy-diffusive nature flow of the flow and the scarcity of observations. In this talk I will present a mathematically rigorous approach to characterizing ocean circulation based on Green's functions that accounts for the multiplicity of transport pathways and transit times characteristic of the ocean's turbulent flow. I will use observations and simulations from global ocean general circulation models to illustrate these ideas and describe their implications for our understanding of the ocean's large scale circulation and CO2 uptake.
When: Monday , 9th, 11:15-12:00, Who: Jeremie Mouginot (UCI), Guest of Basile, Title: Remote sensing of the changing ice sheets
Under the current changing climate, the ice sheets in Antarctica and Greenland responded with an increase in mass loss resulting in a significant contribution to sea level rise. In order to quantify these changes and understand the underlying processes, it is essential to monitor the glacier dynamic and geometry. Using remote sensing techniques, I will highlight ongoing (significant) changes of two regions far apart from each other: North-Eastern Greenland and the Amundsen Sea Embayment in Antarctica. Both regions have encountered ice shelf weakening, retreat of the grounding line, acceleration of the ice streams, and finally sustained increase in mass loss than can be attributed to either the direct or indirect effects of the surrounding warm oceans. In light of the existing observations, it seems unlikely that the current changes will stop, or even attenuate, in a near future. I conclude on the needs for continuous dense monitoring of the ice sheets with the current and future remote sensing missions.
Please be invited to the BCCR seminar next Monday, May 2nd, 11:15-12:00 in the east-wing auditorium! Davide Zanchettini (University of Venice), who is the leader of VoIMP will give a talk about: "Volcanically-forced decadal climate variability: a retrospective based on ensemble climate simulations". Davide is a guest of Thomas T.
Numerical climate simulations suggest that strong tropical volcanic eruptions have the potential to induce dynamical responses in the coupled ocean-atmosphere system on decadal and even longer time scales. In this talk I will illustrate different aspects of post-eruption decadal climate evolution in several historical, paleo and idealized climate simulations. In particular, I will show how background climate conditions can modulate the strength of the feedbacks initiated by the imposed volcanic forcing and activate different decadal response mechanisms. I will discuss how uncertainties on both forcing and background conditions complicate the assessment of simulated decadal climate responses to strong tropical volcanic eruptions and, consequently, the predictability of decadal climate evolutions after major volcanic events. I will conclude with a brief overview on ongoing and planned modeling activities within the Model Intercomparison Project on the climatic response to Volcanic forcing, showing how they will help to identify the causes that limit robust post-eruption simulated behavior across state-of-the-art coupled climate models.
On Thursday, March 17th, Sally Close from LOCEAN-IPSL will give a talk: "Regional dependence in Arctic sea ice variability". Sally is a Bjerknes fellow visiting Ingrid, Lars Henrik and Tor. This seminar will start at 14:15 in the east wing auditorium.
Analyses of Arctic sea ice tendencies often employ either large-scale metrics (e.g. total sea ice area) or fixed regional definitions to describe sea ice variability. Such an approach will inherently mask any smaller-scale regional variation occurring within these pre-defined regions; this issue motivates the work that will be presented, in which we explore the spatial structure associated with the long-term evolution of sea ice loss season-by-season. An objective method is applied to the satellite passive microwave record to detect the timing of onset of rapid decline on a pointwise basis. The analysis reveals a strongly regional picture of sea ice decline, with differences in the timing of onset of up to 20 years across the Arctic in summer. Co-variability is noted amongst the seasons, both at the interannual and longer time scales. Potential mechanisms for the onset time transition are briefly analysed for two case regions. In a second step, the large-scale variability of the winter sea ice cover is analysed, based on EOF analysis. Whilst previous analyses have demonstrated the existence of a quadrupole, or double-dipole, phase structure in the first EOF mode, interpreted to describe correlated variability amongst the marginal seas, we suggest that this structure does not represent a significant relationship amongst all four poles. The hypothesized driving mechanism will be discussed.
On Monday March 14th, Mike Spall will give a talk: "Coupled ocean/atmosphere offshore decay scale of cold SST signals along upwelling eastern boundaries". Mike is a Senior Scientist at WHOI and a guest of Tor. The seminar will start at 11:15am in the east wing auditorium.
A simple analytic model is developed to represent the offshore decay of cold sea surface temperature (SST) signals that originate from wind-driven upwelling at a coastal boundary. The model couples an oceanic mixed layer to an atmospheric boundary layer through wind stress and air-sea heat exchange. The primary mechanism that controls SST is a balance between Ekman advection and air-sea exchange. The offshore penetration of the cold SST signal decays exponentially with a length scale that is the product of the ocean
Ekman velocity and a time scale derived from the air-sea heat flux and the radiative balance in the atmospheric boundary layer. This cold SST signal imprints strongly on the atmosphere in terms of both the boundary layer temperature and surface wind. Weakly nonlinear theory shows that the feedback between SST and atmospheric wind, baroclinic instability, and thermal wind in the atmospheric boundary layer all slightly modify this linear theory. The decay scale diagnosed from two-dimensional and three-dimensional eddy resolving numerical ocean models are in close agreement with the theory. Analysis of climatological SST off the west coast of the US also shows a decay of the cold SST anomaly with scale roughly in agreement with the theory.
On March 7 at 11.15, Trine Dahl (NHH) will give a talk with the title "Tech-fix, plan B or messing with nature? A linguistic framing analysis of a geoengineering experiment".
In this presentation, Trine Dahl will talk about how the discipline of linguistics can contribute to our understanding of how complex and contested scientific issues are presented and talked about in the public sphere.. Climate change (and by implication geoengineering) is one such issue. It no longer belongs only in sphere of the natural sciences. Rather, it has become relevant within and across a number of different academic disciplines, as well as in politics and civil society in general. The presentation takes its point of departure in a paper (2015) where she analyses how six news reports (from US and UK sources) involving the same geoengineering experiment (ocean iron fertilization) have chosen to frame the experiment.
On March 2d (Wednesday) at 13:15 we will have an additional BCCR seminar given by Augustin Kessler. The title of the talk is "Southern Ocean as a constrain to reduce uncertainty in future ocean carbon sinks". Please note that this talk will take place in the Foredragssal.
Earth System Model (ESM) simulations exhibit large biases compares to observations of the present ocean CO2 sink. The inter-model spread in projections increases by nearly two-fold by the end of the 21st century, and therefore contributes significantly to the uncertainty of future climate projections. In this study, the Southern Ocean (SO) is shown to be one of the hot-spot regions for future uptake of anthropogenic CO2, characterized by both the solubility pump and biological-mediated carbon drawdown in the Spring and Summer. We show, by analyzing a suite of fully-interactive ESMs simulations from the Coupled Model Intercomparison Project phase 5 (CMIP5) over the 21st century under the high CO2 RCP8.5 scenario, that the SO is the only region where the atmospheric CO2 uptake rate continues to increase toward the end of the 21st century. Furthermore, our study discovers a strong inter-model link between the contemporary CO2 uptake in the Southern Ocean and the projected global cumulated uptake over the 21st century. The inter-model spread for the contemporary CO2 uptake in the Southern Ocean is attributed to the variations in the simulated seasonal cycle of surface pCO2. Two groups of model behaviour have been identified. The first one simulates anomalously strong SO carbon uptake, generally due to both too-strong net primary production and too-low surface pCO2 in December–January. The second group simulates an opposite CO2 flux seasonal phase, which is driven mainly by the bias in the sea surface temperature variability. We show that these biases are persistent throughout the 21st century, which highlight the urgent need for a sustained and comprehensive biogeochemical monitoring system in the Southern Ocean to better constrain key processes represented in current model systems.
On Feb 29th (Monday) at 11:15 we will have a talk by Sze Ling Ho (Deartment of Earth Science). The title of the talk is "Going subsurface: Reconciling proxy and model estimates of early Eocene marine temperatures". This talk will take place in the East Wing Auditorium.
The early Eocene (49-55 million years ago) is a time interval characterized by elevated surface temperatures and atmospheric CO2, and a flatter-than-present latitudinal surface temperature gradient. The multi-proxy derived flat temperature gradient has been a challenging feature to reproduce in model simulations, especially the subtropical warmth at the high-latitude surface oceans inferred from the archaeal lipid-based palaeothermometry, namely TEX86H. Although widely applied on marine and lacustrine sediments, archaeal lipid paleothermometry is not without uncertainties, especially in the water depth origin of the lipids. Here we take an alternative approach to constrain this uncertainty, by comparing the temperature variability inferred from multiple proxies over a broad range of time-scales (millennial to multi-million years). Our analysis shows that the widely used TEX86H overestimates both past temperatures and their amplitude of change, and suggests that the archaeal temperature signals originate from depths considerably greater than previously thought. A recalibration of the TEX86H thermometry, using the independent estimates of past temperature variability as a constraint, strongly improves the model-proxy comparison of Eocene temperature at water depths corresponding to the calibration. This finding implies that the apparent, extremely high polar surface temperatures inferred from TEX86H, which are not reproducible in climate models, are likely an artefact due to the fundamental bias in the applied calibration. This study emphasizes that learning from model-data comparisons needs an in depth understanding of the proxy as well as the model uncertainty.
Thursday February 18 at 14:15 we will have a talk by Thomas Schuler (University of Oslo). The title of his talk will be announced next week. Thomas is a guest of Kerim and Atle. This talk will also take place in the East Wing Auditorium.
Glacier surges are commonly explained by either thermal or hydraulic mechanisms. In the first case, changes in the subglacial temperature conditions inhibit or enable basal motion of cold or poly-thermal glaciers. Alternatively, surge-behavior of temperate glaciers has been attributed to hydraulic lubrication, where predominance of inefficient subglacial drainage involves high basal water pressure and thus causes enhanced basal motion. The poly-thermal glaciers on Svalbard are believed to belong to the first group and a-posteriori observations from winter satellite images suggest a gradually increasing acceleration over several years, attributed to an increasing proportion of the glacier bed that becomes temperate. Since 2004, a wealth of ground data has been collected on the Austfonna ice cap, Svalbard. Basin-3 is a marine-terminating drainage basin that has surged in the past. We present 5-year, continuous GPS records (2008-2013) from Basin-3 which display hitherto unknown detail of the surge initiation. Winter velocities largely follow the known pattern of increasing acceleration, but the timeseries reveal a step-wise rather than a continuous acceleration. The bulk of the acceleration takes place in a short period during summer and is highly correlated to the surface melt-water production. These observations are difficult to explain using common surge theory and hence suggest the existence of a so far overlooked process. The close relation between glacier acceleration and surface melt rates suggests a hydraulic control on basal thermal conditions. Here we propose an extension to the cryo-hydrologic warming mechanism where we focus on the role of melt-water in warming the glacier bed, in addition to the significance of melt-water for ice rheology. The still ongoing (February 2016) surge of Basin-3 caused drastically enhanced ice discharge from Austfonna and estimated frontal ablation rates from this surge alone are comparable to those of entire Svalbard.
Monday February 15 at 11:15 Laurence Padman (Earth & Space Research, USA) will give a talk "Oceanic controls on ice shelf mass balance". Laurence is a guest of Ilker. The talk will take place in the East Wing Auditorium.
This talk will combine studies of satellite altimetry of ice-shelf height changes with numerical modeling to identify key processes by which ice shelves transfer changes in ocean temperature and circulation to mass loss from the grounded ice sheet. Overall, over the last two decades the loss of mass from Antarctic ice shelves has accelerated, indicating weakening of buttressing of grounded ice streams and glaciers. Most of this ice shelf mass loss is caused by accelerated basal melting, which changes in response to changes in oceanic forcing on time scales from tidal to interannual. Individual ice shelves respond very differently depending on the properties of water that flow under them, polynyas as a control on dense water production, strength of tidal currents, and geological constraints. When the ice dynamics of the adjacent grounded ice is also taken into account, changes in land-ice loss can vary dramatically from one Antarctic sector to another.
Monday February 8 at 11:15 Phil Sexton will give a talk "Using the foraminifer fossil record to reveal the links between ocean circulation, plankton population dynamics and the extinction process". Phil is a guest of Nele. The talk will take place in the East Wing Auditorium.
Plankton form the base of oceanic food chains and thus limit the growth of all other marine creatures. Yet we have little idea of the rates, nature and causes of nearly all species disappearances (i.e. those occurring from ‘background’ extinctions, as opposed to mass extinctions). The controls on plankton species’ biogeographic distributions are similarly poorly understood, with two competing classes of explanations having arisen – those that invoke ‘barriers to dispersal’ versus those that instead invoke ‘high dispersal’. Here I tackle these gaps in our understanding using the marine fossil record of foraminifera, which is unparalleled in its temporal resolution, continuity, chronological precision and spatial coverage. I show that species extinction can be abrupt, and species may disappear from different regions sequentially, with these regional disappearances paced by Earth's orbital cycles. I also show that a change in population dynamics towards globally synchronized biogeographic behaviour may provide an early warning signal of extinction risk. Finally, I show that the equator-to-Pole partitioning of surface ocean macro-nutrient distributions exerts a major (indirect) control on ocean-wide disappearances of zooplankton species via their dependency (for food) on phytoplankton.
On Monday, February 1 at 11.15, Yanchun He from the NERSC here in Bergen will present "A model-based evaluation of the TTD method for inferring anthropogenic carbon in the ocean". As usual, the talk will take place in the East Wing Auditorium.
The world ocean has taken up about half of the anthropogenic carbon since pre-industrial era. However, the anthropogenic carbon in the ocean is not directly measurable so far, and the challenge is to separate the small perturbation of anthropogenic carbon from the large and variable background of natural carbon (DIC). The so-called Transit-time Distribution method (TTD method) is one of the indirect inferring techniques developed to estimate the anthropogenic carbon in the ocean. As other methods, several assumptions are made for the TTD methods, e.g., steady-state ocean circulation and constant air-sea carbon disequilibrium assumptions. In our work, we apply the TTD method to output from NorESM-HAMOCC in which the simulated anthropogenic carbon is taken as the “true” value. The uncertainties of the inferred water mass age and anthropogenic carbon due to the underlying assumptions are evaluated, and some preliminary results will be presented in my talk.
Tuesday February 2 at 11.15, Markus Jochum from NBI/CU will present "The connection between Southern Ocean winds, Atlantic Meridional Overturning Circulation and Indo-Pacific upwelling. ". Markus is a guest of Kerim. This talk will also take place in the East Wing Auditorium.
Coupled GCM simulations are analyzed to quantify the dynamic effect of Southern Ocean (SO) winds on transports in the ocean. It is found that the closure for skew diffusivity in the non-eddy-resolving ocean model does not allow for a realistic eddy saturation of the zonal transports in the SO in response to the wind changes, and that eddy compensation of the meridional transports in the SO is underestimated too. Despite this underestimated eddy compensation in the SO, and in contrast to previous suggestions, the Atlantic Meridional Overturning Circulation (AMOC) strength is almost insensitive to SO winds. In the limit of weak SO winds the AMOC waters do not upwell in the SO but in the tropical Indo-Pacific. Through their effect on sea-ice, weaker SO winds also lead to less production of Antarctic Bottom Water and therefore a deeper and stronger AMOC.
Thursday February 4 at 14.15, Erlend Moster Knudsen will have a talk titled "Climate scientists: Pencil pushers or activists?". This talk will also take place in the East Wing Auditorium.
What makes two young climate scientists leave their offices to run and cycle across the globe? In this talk, I will talk about what made the climate outreach project Pole to Paris (poletoparis.com) so unique. This was one example of how climate scientists made climate information more accessible to the general public. However, there are not only positives associated with an unusual choice like this. 'Credibility' is a key word. I will thus put the task of climate scientists as providers of climate information in a bigger perspective, touching upon challenges met in connection with politics, media and opposing industries. My aim is to create a discussion on what role climate scientists should have in our ever-changing society. I do not have the answer and welcome all opinions. Personal info Erlend Moster Knudsen earned his PhD in Arctic climate dynamics from the University of Bergen and the Bjerknes Centre for Climate Research in March 2015. Since then, he has been co-leading the NGO Pole to Paris. Their aim was to raise awareness about climate change in general and the importance of COP21 in particular, using traditional and social media, giving talks in schools, university and in the open spheres, and connecting with people outside academia. As part of this, Knudsen ran 2459 km from Tromsø to Paris last fall.
Monday January 25 at 11.15, Johannes Röhrs from the MET office here in Bergen will present "Drift in the uppermost part of the ocean"
ABSTRACT Johannes Röhrs
Lagrangian drift velocities within the uppermost meter of the ocean mostly depend on the local wind forcing, turbulent mixing, and waves. While the interior part of the Ekman layer has been extensively studied using drogued drifters, the drift at—or very close to—the surface is less investigated. The wind response of surface currents on time scales from 1 h to 10 days is analyzed using two types of satellite-tracked drifters: (i) spherical floats on the surface and (ii) drifters with a drogue centered at 70 cm depth. The response of drifting objects to wind and wave forcing is highly dependent on the vertical position, even within the upper meter of the ocean. The surface drifters are wind
coherent for both cyclonic and anticyclonic subinertial frequencies. In contrast, the subsurface drift responds primarily to anticyclonic forcing that resonates with the intrinsic ocean dynamics.
In this talk, I will start out explaining how rotary cross spectra of wind and drifter velocities are calculated and interpreted.Afterwards, I'll present my data and and draw some new conclusions about wind-induced drift in the upper meter of the ocean. Both wind- and wave induced drift will be discussed, but I don't fully understand my results on the wave-induced drift and hope to get some ideas or comments from the audience.
On Tuesday January 26 at 11.15, Pina Kingman will present "Scientific animation as a communication tool: how animated film can help researchers disseminate their work". Pina is an award-winning animator and filmmaker, and a guest of Nadine.
ABSTRACT Pina Kingman
Communicating the nuances of climate research to the general public poses many challenges. Climate change is a hot topic in the media, but the message is not always consistent. This can create a dangerous platform for misinformation. Images and graphs describing climate change
can be misconstrued to support alternate agendas or misguided opinions. It is therefore very important to clearly and effectively communicate the scientific research behind climate change, so that the public can make well informed decisions.
Several groups have already created effective animations to explain the general concepts of climate change, but few have tackled detailed descriptions of in-depth research questions. Animated film is the perfect tool for communicating these elaborated issues as it brings stories to life and makes information accessible, thus increasing our ability to understand complex ideas. Amongst the many effective communication tools at our disposal, animated film is at the forefront. Whether used to inform the general public, to teach university students, or to disseminate advances in research, animated film is a tool worth exploring.
But what are scientific animations and what goes into making them? I will explain the step-by-step process of creating scientific animations and show some inspiring examples. I will also discuss how animation can help researchers disseminate their projects to other groups of people
outside their immediate communities. Funding bodies require creative outreach initiatives and clear strategies regarding research dissemination. It is my believe that animated film can help attract more funding and result in a better informed society.
On Monday 18.1.2016 at 11.15, Kristian Vasskog (GEO) on Monday will be presenting "Past glacier variability in western Himalaya – Fieldwork report and preliminary results from the GLACINDIA project".
The GLACINDIA project is an interdisciplinary project under the Agreement of Cooperation in Science & Technology between the governments of India and Norway. The project combines geology, geophysics and meteorology in order to look into past, present, and potential future effects of changes in glacier mass-balance and river runoff in western Himalaya. A field campaign was organized in October 2015, with the aim of collecting data on past glacier length changes and related climate, potentially all the way back to the last glacial period. Two main methods are utilised for this purpose: field mapping and dating of glacial landforms (moraines) using cosmogenic exposure dating, and lake sediment coring and analysis. In addition to a report on the field campaign itself, some preliminary results will be presented, together with plans on how the collected material will be analysed in order to shed light on long-term glacier and climate variability in western Himalaya.
Then, on Tuesday 19.1.2016 at 14.15, David Ferreira will present "Two-timescale response of the Antarctic ocean and sea ice to ozone depletion".
In recent modelling work, we showed that the response of Antarctic sea surface temperature and sea ice cover to abrupt ozone depletion has two phases: a fast inter-annual (~1-5y) adjustment in which the surface ocean cools and sea ice cover increases, followed by a slower decadal trend leading to a warming of the surface ocean and a reduction of sea ice cover. This result reconciles diverging views, found in the literature, on the relationship between ozone depletion and Antarctic sea ice changes. I will describe the dynamics behind the two-timescale response, the sources of uncertainties in the modeled response, and observational constraints. I will then discuss implications of the two-timescale response for evaluating the contribution of ozone depletion (and recovery) to observed decadal trends and future trends of the Antarctic sea ice.
We start the new semester with a seminar on January 4 at 11.15 in *Foredragssalen* (NOTE the place!). Basile de Fleurian (Post Doc, UiB) will present "Modelling Subglacial Hydrology for Ice Dynamics Purpose, Why, What and How"
Field observations show that surface melt and ice velocities are tightly linked but that the relation between the two is not straightforward. These observations are showing a need for efficient subglacial hydrological models which would be able to relate the amount of melt water produced to the water pressure at the base of glacier. Coupling of these model will then allow a more precise modelling of the dynamics of glaciers and ultimately increase the precision of the sea level rise prediction. This presentation will provide some background information on ice dynamics and subglacial hydrological modelling before presenting some new results obtained on a land terminating Greenland glacier.