Jón Eiríksson

The Barmur Group (Tjörnes beds) sedimentary sequence onshore Iceland records the first opening of the Bering Strait oceanic gateway, and late Miocene–early Pliocene cooling that preceded intensification of the Northern Hemisphere glaciation. The stratigraphy of the Barmur Group is not known in detail because of difficulties in correlating coastal and inland exposures. To address this issue, we carried out remotely piloted vehicle (drone-based) mapping of the entire 11 km outcrop. We correlated the processed ‘virtual outcrop’ image with previously logged sections and constructed a 3D structural model. The composite thickness of the Barmur Group in the model is 442 m, which is 16% thinner than previously estimated. This discrepancy reflects earlier difficulties in correlating coastal and inland exposures and the recognition of faulting at the base of the succession. We recently showed that the bioevent signalling the first Pacific-to-Atlantic faunal migration through the Bering Strait occurred during magnetic chrons C3n.4n–C3n.3r (5.235–4.896 Ma); the new model suggests that it occurred near the chron boundary ( c. 5.0 Ma). Thus, we show that a 3D virtual outcrop is a useful tool to quantify uncertainty when assembling a composite section. We also provide the complete workflow used to plan, acquire and process the virtual outcrop.

In this study, we use IP₂₅ and alkenone biomarker proxies to document the subdecadal variations of sea ice and sea surface temperature in the subpolar North Atlantic induced by the decadally paced explosive tropical volcanic eruptions of the second half of the thirteenth century. The short‐ and long‐term evolutions of both variables were investigated by cross analysis with a simulation of the IPSL‐CM5A LR model. Our results show short‐term ocean cooling and sea ice expansion in response to each volcanic eruption. They also highlight that the long response time of the ocean leads to cumulative surface cooling and subsurface heat buildup due to sea ice capping. As volcanic forcing relaxes, the surface ocean rapidly warms, likely amplified by subsurface heat, and remains almost ice free for several decades.