Greenland Geothermal Heat Flow Database and Map (Version 1)

We compile and analyze all available geothermal heat flow measurements collected in and around Greenland into a new database of 419 sites and generate an accompanying spatial map. This database includes 290 sites previously reported by the International Heat Flow Commission (IHFC), for which we now standardize measurement and metadata quality. This database also includes 129 new sites, which have not been previously reported by the IHFC. These new sites consist of 88 offshore measurements and 41 onshore measurements, of which 24 are subglacial. We employ machine learning to synthesize these in situ measurements into a gridded geothermal heat flow model that is consistent across both continental and marine areas in and around Greenland. This model has a native horizontal resolution of 55ĝ€¯km. In comparison to five existing Greenland geothermal heat flow models, our model has the lowest mean geothermal heat flow for Greenland onshore areas. Our modeled heat flow in central North Greenland is highly sensitive to whether the NGRIP (North GReenland Ice core Project) elevated heat flow anomaly is included in the training dataset. Our model's most distinctive spatial feature is pronounced low geothermal heat flow (<ĝ€¯40ĝ€¯mWĝ€¯m-2) across the North Atlantic Craton of southern Greenland. Crucially, our model does not show an area of elevated heat flow that might be interpreted as remnant from the Icelandic plume track. Finally, we discuss the substantial influence of paleoclimatic and other corrections on geothermal heat flow measurements in Greenland. The in situ measurement database and gridded heat flow model, as well as other supporting materials, are freely available from the GEUS Dataverse (10.22008/FK2/F9P03L; Colgan and Wansing, 2021).publishedVersionPeer reviewe

Greenland’s lithospheric structure and its implications for geothermal heat flow

In light of the contribution of the Greenland ice sheet to sea-level rise, the geothermal heat flow (GHF) and lithospheric structure of Earth’s largest island are of great interest. While extensively studied, both are ill-constrained. Therefore, I evaluated the lithospheric structure and GHF in Greenland by focusing on data integration and model consistency. First, a new GHF map is predicted in a machine-learning framework, trained on global GHF measurements and a multitude of globally available geophysical datasets. No evidence for plume-lithosphere interaction in the form of elevated GHF can be found along the Iceland hotspot track. In the next step, a full lithospheric model based on the integration of multiple data sets, is constructed. The model’s lithospheric mantle and its boundaries are adjusted to fit satellite gravity gradient and seismic tomography data. The crustal density and susceptibility structure is determined by a joint inversion of gravity and magnetic data. The model self-consistently reproduces gravity, topographic, and magnetic data and seismic velocities from a tomography model. To compare the modelled crustal parameters with in-situ data, a Greenland-specific petrophysical database was established and evaluated statistically. Finally, a regional model for the upper crust in South Greenland is derived from joint inversion of potential field data. The employment of a new, high-resolution magnetic data set allows the compilation of a simplified geological map. By sampling radiogenic heat production (RHP) data onto the geology polygons, a model for sub-ice RHP and the resulting GHF is proposed. The presented results demonstrate the importance of lithospheric modelling and GHF estimation coupling. It is necessary to consider the two main contributions to GHF, the thermal field of the mantle lithosphere and heat production in the crust on their respective length scales

Evaluating different geothermal heat-flow maps as basal boundary conditions during spin-up of the Greenland ice sheet

&lt;jats:p&gt;Abstract. There is currently poor scientific agreement on whether the ice–bed interface is frozen or thawed beneath approximately one third of the Greenland ice sheet. This disagreement in basal thermal state results, at least partly, from differences in the subglacial geothermal heat-flow basal boundary condition used in different ice-flow models. Here, we employ seven widely used Greenland geothermal heat-flow maps in 10 000-year spin-ups of the Community Ice Sheet Model (CISM). We perform two spin-ups: one nudged toward thickness observations and the other unconstrained. Across the seven heat-flow maps, and regardless of unconstrained or nudged spin-up, the spread in basal ice temperatures exceeds 10 ∘C over large areas of the ice–bed interface. For a given heat-flow map, the thawed-bed ice-sheet area is consistently larger under unconstrained spin-ups than nudged spin-ups. Under the unconstrained spin-up, thawed-bed area ranges from 33.5 % to 60.0 % across the seven heat-flow maps. Perhaps counterintuitively, the highest iceberg calving fluxes are associated with the lowest heat flows (and vice versa) for both unconstrained and nudged spin-ups. These results highlight the direct, and non-trivial, influence of the heat-flow boundary condition on the simulated equilibrium thermal state of the ice sheet. We suggest that future ice-flow model intercomparisons should employ a range of basal heat-flow maps, and limit direct intercomparisons with simulations using a common heat-flow map. &lt;/jats:p&gt