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Abstract Marine-terminating glaciers lose mass through melting and iceberg calving, and we find that meltwater drainage systems influence calving timing at Helheim Glacier, a tidewater glacier in East Greenland. Meltwater feeds a buoyant subglacial discharge plume at the terminus of Helheim Glacier, which rises along the glacial front and surfaces through the mélange. Here, we use high-resolution satellite and time-lapse imagery to observe the surface expression of this meltwater plume and how plume timing and location compare with that of calving and supraglacial meltwater pooling from 2011 to 2019. The plume consistently appeared at the central terminus even as the glacier advanced and retreated, fed by a well-established channelized drainage system with connections to supraglacial water. All full-thickness calving episodes, both tabular and non-tabular, were separated from the surfacing plume by either time or by space. We hypothesize that variability in subglacial hydrology and basal coupling drive this inverse relationship between subglacial discharge plumes and full-thickness calving. Surfacing plumes likely indicate a low-pressure subglacial drainage system and grounded terminus, while full-thickness calving occurrence reflects a terminus at or close to flotation. Our records of plume appearance and full-thickness calving therefore represent proxies for the grounding state of Helheim Glacier through time. 

Linear elastic fracture mechanics suggests that short‐lived flow accelerations, such as the one initiated by a flooding event beneath Byrd Glacier in 2006, can form abnormally large basal crevasses at the grounding line. Airborne radar measurements acquired in 2011 reveal hundreds of basal crevasses ranging in height from40–335 m. Particle tracking results show that formation of the largest basal crevasse occurred at the grounding line during the 2006 flooding event. Very large basal crevasses form distinctive surface depressions directly overhead, which are observed along the Byrd Glacier flowline to the terminus of the Ross Ice Shelf. By using these surface depressions as proxies for abnormally large basal crevasses, we create a timeline of past subglacial flooding events on Byrd Glacier. Understanding the frequency of flooding events and their effect on glacier dynamics will help inform models of ice sheet stability and subglacial hydrology.

 

The one‐dimensional steady state analytical solution of the energy conservation equation obtained by Robin (1955, https://doi.org/10.3189/002214355793702028) is frequently used in glaciology. This solution assumes a linear change in surface velocity from a minimum value equal to minus the mass balance at the surface to zero at the bed. Here we show that this assumption of a linear velocity profile leads to large errors in the calculated temperature profile and especially in basal temperature. By prescribing a nonlinear power function of elevation above the bed for the vertical velocity profile arising from use of the Shallow Ice Approximation, we derive a new analytical solution for temperature. We show that the solution produces temperature profiles identical to numerical temperature solutions with the Shallow Ice Approximation vertical velocity near ice divides. We quantify the importance of strain heating and demonstrate that integrating the strain heating and adding it to the geothermal heat flux at the bed is a reasonable approximation for the interior regions. Our analytical solution does not include horizontal advection components, so we compare our solution with numerical solutions of a two‐dimensional advection‐diffusion model and assess the applicability and errors of the analytical solution away from the ice divide. We show that several parameters and assumptions impact the spatial extent of applicability of the new solution including surface mass balance rate and surface temperature lapse rate. We delineate regions of Greenland and Antarctica within which the analytical solution at any depth is likely within 2 K of the actual temperatures with horizontal advection.

 

Latitudinal diversity gradients have provided many insights into species differentiation and community processes. In the well‐studied intertidal zone, however, little is known about latitudinal diversity in microbiomes associated with habitat‐forming hosts. We investigated microbiomes ofFucus vesiculosusbecause of deep understanding of this model system and its latitudinally large, cross‐Atlantic range. Given multiple effects of photoperiod, we predicted that cross‐Atlantic microbiomes of theFucusmicrobiome would be similar at similar latitudes and correlate with environmental factors. We found that community structure and individual amplicon sequencing variants (ASVs) showed distinctive latitudinal distributions, but alpha diversity did not. Latitudinal differentiation was mostly driven by ASVs that were more abundant in cold temperate to subarctic (e.g., Granulosicoccus_t3260,Burkholderia/Caballeronia/Paraburkholderia_t8371) or warm temperate (Pleurocapsa_t10392) latitudes. Their latitudinal distributions correlated with different humidity, tidal heights, and air/sea temperatures, but rarely with irradiance or photoperiod. Many ASVs in potentially symbiotic genera displayed novel phylogenetic biodiversity with differential distributions among tissues and regions, including closely related ASVs with differing north‐south distributions that correlated withFucusphylogeography. An apparent southern range contraction ofF. vesiculosusin the NW Atlantic on the North Carolina coast mimics that recently observed in the NE Atlantic. We suggest cross‐Atlantic microbial structure ofF. vesiculosusis related to a combination of past (glacial‐cycle) and contemporary environmental drivers.