Deep water cycling and sea level over supercontinental cycles
Krister Karlsen, Clinton P. Conrad, and Valentina Magni
Earth’s mantle is thought to contain hydrated minerals that can store up to several oceans of water. This water is released to the surface environment by volcanism at mid-ocean ridges and hotspots, and returned to the mantle at subduction zones. This project looks at how the H2O flux rates for these “degassing” and “regassing” processes have changed during the past several hundred million years, as the configuration of ridges and subduction zones has changed. We have found that these rates likely became imbalanced for extended periods since the breakup of Pangea, resulting in sea level change.
Magnetotelluric Analysis for Greenland and Postglacial Isostatic Evolution (MAGPIE)
Clinton P. Conrad, Kate Selway, and Maaike Weerdesteyn
Rising sea levels due to melting of the Greenland ice sheet threaten to drastically impact global environments. It is therefore vital to measure ice sheet melting, but this has proved challenging because measurements of the ice sheet’s mass and elevation, which both decrease as the ice melts, are also sensitive to movements of Earth's ground surface. The ground surface in Greenland, and across most of the Arctic, is still deforming in a viscous response to deglaciation since the last ice age. How much does this glacial isostatic adjustment (GIA) affect ice loss calculations? At present we do not know because both GIA and mantle viscosity are poorly constrained for Greenland. Furthermore, Greenland’s complex geologic history, with a recent passage over the Iceland Plume, probably created large lateral viscosity variations beneath Greenland that complicate the GIA response. The MAGPIE project, which is funded by the Research Council of Norway, aims to improve GIA models for Greenland. First, we will collect the first ever magnetotelluric data on the Greenland ice cap. We will use the resulting electrical conductivity models, together with other geological and geophysical data, to constrain mantle temperatures and compositions beneath Greenland. From these we will infer lateral viscosity variations and test for a hot, low-viscosity channel beneath the Iceland Plume track. Second, we will build a new set of GIA models for Greenland by repurposing a mantle flow code with adaptive mesh refinement to solve the GIA problem with 3D viscosity variations. This open-source code will be available to the geophysical community for solving similar problems, which are also vitally important in Antarctica. Using this code, we will generate the first GIA models for Greenland that include constrained 3D viscosity variations. These predictions of GIA uplift will enable us to greatly improve estimates for modern-day ice loss in Greenland.