Abstract The arctic environment is changing: air temperatures, major river discharges and open water season length have increased, and storm intensities and tracks are changing. Thirteen quantitative studies of the rates of coastline position change throughout the Arctic show that recently observed environmental changes have not led to ubiquitously or continuously increasing coastal erosion rates, which currently range between 0 and 2 m/yr when averaged for the arctic shelf seas. Current data is probably insufficient, both spatially and temporally, however, to capture change at decadal to sub-decadal time scales. In this context, we describe the current understanding of arctic coastal geomorphodynamics with an emphasis on erosional regimes of coasts with ice-rich sedimentary deposits in the Laptev, East Siberian and Beaufort seas, where local coastal erosion can exceed 20 m/yr. We also examine coasts with lithified (rocky) substrates where geomorphodynamics are intensified by rapid glacial retreat. Coastlines of Svalbard, Greenland and the Canadian Archipelago are less frequently studied than ice-rich continental coasts of North America and Siberia, and studies often focus on coastal sections composed of unlithified material. As air temperature and sea ice duration and extent change, longer thaw and wave seasons will intensify coastal dynamics in the Arctic.

ABSTRACT New zircon U-Pb dates from the Mount Fitton, Mount Sedgwick, Mount Schaeffer, Old Crow, and Dave Lord plutons indicate that granitoids of the Old Crow plutonic suite in northern Yukon were emplaced in the North Slope subterrane of the Arctic Alaska composite terrane between 375 ± 2 Ma and 368 ± 3 Ma. Whole-rock major and trace element and Nd-Sr isotope geochemistry, combined with zircon trace element and Hf isotope geochemistry, indicate magma genesis involved significant contribution from older continental crust. Samples from the five plutons yield whole-rock εNd (t) values from -3.9 to -11.6 and 87 Sr/ 86 Sr (i) ratios of 0.7085–0.7444 and 0.8055. Zircon εHf (t) values range from -6.2 to -13.3. These North Slope subterrane granitoids are generally younger and isotopically more evolved than felsic rocks in the Coldfoot and Hammond subterranes of the southern Brooks Range (Arctic Alaska terrane), but in part are coeval with felsic rocks on the Seward and Chukotka peninsulas. The North Slope granitoids are also coeval and geochemically similar to arc magmatism in the Yukon-Tanana terrane in Yukon and on Axel Heiberg and northern Ellesmere islands, Nunavut. The Old Crow plutonic suite is interpreted as part of a Late Devonian arc system developed along the Arctic and Cordilleran margins. Late Devonian plutons were most likely emplaced after initial translation of the North Slope subterrane along the northern Laurentian margin. The plutons lie within or north of the Porcupine shear zone and thus do not limit post-Late Devonian displacement on the boundary between the North Slope subterrane and northwestern Laurentia.