Geological Survey of Denmark and Greenland

About: Geological Survey of Denmark and Greenland is a facility organization based out in Copenhagen, Denmark. It is known for research contribution in the topics: Greenland ice sheet & Ice sheet. The organization has 844 authors who have published 3152 publications receiving 104706 citations. The organization is also known as: Danmarks og Grønlands Geologiske Undersøgelse.

Evidence from the rare-earth-element record of mantle melting for cooling of the Tertiary Iceland plume

Abstract: Widespread flood basalt volcanism and continental rifting in the northeast Atlantic in the early Tertiary period (∼55 Myr ago) have been linked to the mantle plume now residing beneath Iceland1,2,3,4,5. Although much is known about the present-day Iceland plume6,7,8,9, its thermal structure, composition and position in the early Tertiary period remain unresolved. Estimates of its temperature, for example, range from >1,600 °C in some plume models3 to ∼1,500 °C based on the volume and composition of basaltic crust10,11,12. Several recent studies4 have emphasized similarities in the thermal and chemical structure of the Tertiary and present-day plumes to argue for stability of the mantle anomaly, whereas others12,13 relate variations in basalt volumes and compositions to changes in plume flux. Moreover, some authors1,2,13 have assumed that the plume was rift-centred for its entire history, whereas others argue that it became ridge-centred only after plate separation14,15. Here we report compositional data for ∼6,000 metres of flood basalts erupted in east Greenland, close to the inferred plume axis, that we use to constrain the Tertiary plume structure. Rare-earth-element systematics place limits on the pressures and extents of mantle melting and show that the mantle was initially moderately hot (∼1,500 °C), but that its temperature declined during flood volcanism. These observations are difficult to reconcile with current plume-head models, and call for important lithospheric control5,10,16,17,18 on actively upwelling mantle along the rifted margin.

Sensitivity of Greenland Ice Sheet Projections to Model Formulations

Abstract: Physically based projections of the Greenland ice sheet contribution to future sea-level change are subject to uncertainties of the atmospheric and oceanic climatic forcing and to the formulations within the ice flow model itself. Here a higher-order, three-dimensional thermomechanical ice flow model is used, initialized to the present-day geometry. The forcing comes from a high-resolution regional climate model and from a flowline model applied to four individual marine-terminated glaciers, and results are subsequently extended to the entire ice sheet. The experiments span the next 200 years and consider climate scenario SRES A1B. The surface mass-balance (SMB) scheme is taken either from a regional climate model or from a positive-degree-day (PDD) model using temperature and precipitation anomalies from the underlying climate models. Our model results show that outlet glacier dynamics only account for 6-18% of the sea-level contribution after 200 years, confirming earlier findings that stress the dominant effect of SMB changes. Furthermore, interaction between SMB and ice discharge limits the importance of outlet glacier dynamics with increasing atmospheric forcing. Forcing from the regional climate model produces a 14-31% higher sea-level contribution compared to a PDD model run with the same parameters as for IPCC AR4.

A framework for testing the ability of models to project climate change and its impacts

Abstract: Models used for climate change impact projections are typically not tested for simulation beyond current climate conditions. Since we have no data truly reflecting future conditions, a key challenge in this respect is to rigorously test models using proxies of future conditions. This paper presents a validation framework and guiding principles applicable across earth science disciplines for testing the capability of models to project future climate change and its impacts. Model test schemes comprising split-sample tests, differential split-sample tests and proxy site tests are discussed in relation to their application for projections by use of single models, ensemble modelling and space-time-substitution and in relation to use of different data from historical time series, paleo data and controlled experiments. We recommend that differential-split sample tests should be performed with best available proxy data in order to build further confidence in model projections.