Investigations of both short-term natural climate variability, and long-term, large-scale changes in climate state are advanced by scientific ocean drilling at globally-distributed locations. Despite its global importance as both a contributor to climate change and a region that is most affected by global warming, the Arctic Ocean is the last major region on Earth where the long-term climate history remains poorly known. While many major advances in understanding were achieved in 2004 with the successful completion of IODP Expedition 302: Arctic Coring Expedition (ACEX), the record was hampered by generally poor recovery and by a 26-myr hiatus (or condensed interval depending on the age model) spanning the global transition from the Greenhouse to Icehouse climate states. In August-September 2022, IODP Expedition 377: Arctic Ocean Paleoceanography (ArcOP) will enable another step in reconstructing the detailed history of climate change in the Arctic over the last 50+ million years. The overall goal of the ArcOP drilling campaign is the recovery of a complete stratigraphic sedimentary record on the southern Lomonosov Ridge to meet the highest priority paleoceanographic objective: the continuous long-term Cenozoic climate history of the central Arctic Ocean. Key scientific themes to be addressed by ArcOP are represented in Figure 1. The expedition goals can be achieved through 1) careful site selection, 2) the use of appropriate drilling technology and ice management supported by two ice breakers, and 3) applying multi-proxy approaches to paleoceanographic, paleoclimatic, and age-model reconstructions. The expedition will complete one primary deep drill hole (LR-11B) to 900 meters below seafloor (mbsf; twice as deep as the ACEX core depth). This will be supplemented by a short drill site (LR-10B) to 50 mbsf, to recover an undisturbed Quaternary sedimentary section to ensure complete recovery for construction of a composite section spanning the full age range through the Cenozoic. Expected sedimentation rates two to four times higher than those of ACEX will permit higher-resolution studies of Arctic climate change. More information on ArcOP can be found at the expedition website: https://www.ecord.org/expedition377/.

Proglacial aquifers are an important water store in glacierised mountain catchments that supplement meltwater-fed river flows and support freshwater ecosystems. Climate change and glacier retreat will perturb water storage in these aquifers, yet the climate-glacier-groundwater response cascade has rarely been studied and remains poorly understood. This study implements an integrated modelling approach that combines distributed glacio-hydrological and groundwater models with climate change projections to evaluate the evolution of groundwater storage dynamics and surface-groundwater exchanges in a temperate, glacierised catchment in Iceland. Focussed infiltration along the meltwater-fed Virkisà River channel is found to be an important source of groundwater recharge and is projected to provide 14-20% of total groundwater recharge by the 2080s. The simulations highlight a mechanism by which glacier retreat could inhibit river recharge in the future due to the loss of diurnal melt cycling in the runoff hydrograph. However, the evolution of proglacial groundwater level dynamics show considerable resilience to changes in river recharge and, instead, are driven by changes in the magnitude and seasonal timing of diffuse recharge from year-round rainfall. The majority of scenarios simulate an overall reduction in groundwater levels with a maximum 30-day average groundwater level reduction of 1 m. The simulations replicate observational studies of baseflow to the river, where up to 15% of the 30-day average river flow comes from groundwater outside of the melt season. This is forecast to reduce to 3-8% by the 2080s due to increased contributions from rainfall and meltwater runoff. During the melt season, groundwater will continue to contribute 1-3% of river flow despite significant reductions in meltwater runoff inputs. Therefore it is concluded that, in the proglacial region, groundwater will continue to provide only limited buffering of river flows as the glacier retreats.