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Highlights • Upstream flow properties are not representative of iceberg basal flow properties. • A Taylor column of reduced flow forms under large icebergs. • Two conflicting representations of the heat transfer coefficient exist in ice melt parameterizations. • A new parameterization of tabular iceberg basal melt is proposed, accounting for these factors. Abstract In this study, we consider the influence of icebergs on the ocean when they are modeled as occupying physical space, to answer the question of how the melting of icebergs and subsequent distribution of meltwater in the water column might be accurately parameterized in climate models. Iceberg melt is analyzed by comparing in-situ melt rates calculated via the three-equation parameterization, which was developed for application under ice shelves, with the commonly used bulk parameterization of iceberg basal melt. Our results suggest an updated velocity-independent version of the basal melt parameterization for tabular icebergs for use in calculating the basal melt rate of icebergs that are large (relative to the deformation radius), to account for the changes in ocean properties caused by the physical presence of a large iceberg in the ocean. [ABSTRACT FROM AUTHOR]

Although iceberg models have been used for decades, they have received far more widespread attention in recent years, due in part to efforts to explicitly represent icebergs in climate models. This calls for increased scrutiny of all aspects of typical iceberg models. An important component of iceberg models is the representation of iceberg capsizing, or rolling. Rolling occurs spontaneously when the ratio of iceberg width to height falls below a critical threshold. Here we examine previously proposed representations of this threshold, and we find that there have been crucial flaws in the representation of rolling in many modeling studies to date. We correct these errors and identify an accurate model representation of iceberg rolling. Next, we assess how iceberg rolling influences simulation results in a hierarchy of models. Rolling is found to substantially prolong the lifespan of individual icebergs and allow them to drift farther offshore. However, rolling occurs only after large icebergs have lost most of their initial volume, and it thus has a relatively small impact on the large-scale freshwater distribution in comprehensive model simulations. The results suggest that accurate representations of iceberg rolling may be of particular importance for operational forecast models of iceberg drift, as well as for regional changes in high-resolution climate model simulations. [ABSTRACT FROM AUTHOR]

The interaction between an Antarctic Circumpolar Current-like channel flow and a continental shelf break is considered using eddy-permitting simulations of a quasigeostrophic and a primitive equation model. The experimental setup is motivated by the continental shelf of the West Antarctic Peninsula. Numerical experiments are performed to study how the width and slope of an idealized continental shelf topography affect the characteristics of the flow. The main focus is on the regime where the shelfbreak width is slightly greater than the eddy scale. In this regime, a strong baroclinic jet develops on the shelf break because of the locally stabilizing effect of the topographic slope. The velocity of this jet is set at first order by the gradient of the background barotropic geostrophic contours, which is dominated by the slope of the topography. At statistical equilibrium, an aperiodic cycle is observed. Initially, over a long stable period, an upper-layer jet develops over the shelf break. Once the vertical shear reaches the critical condition for baroclinic instability, the jet becomes unstable and drifts away from the shelf break. The cross-shelf mixing is intrinsically linked with the jet drifting, as most of the meridional flux occurs during this instability period. Investigation of the zonal momentum budget reveals that a strong Reynolds stress divergence inversion across the jet is associated with a drifting event, accelerating one flank of the jet and decelerating the other. The hypothesis that jet drifting may be due to one flank of the jet being more baroclinically unstable than the other is tested using topographic profiles with variable curvatures. [ABSTRACT FROM AUTHOR]

Icebergs and glacial meltwater have been observed to significantly affect chlorophyll concentrations, primary production, and particle export locally, yet the quantitative influence of glacial iron on the carbon cycle of the Southern Ocean remains unknown. We analyze the impact of icebergs and glacial meltwater on the Southern Ocean carbon cycle in a global Earth System Model. We consider several simulations spanning low and high bounds of current estimates of glacial iron concentration. We find that a high glacial iron input produces the best agreement with observed iron and chlorophyll distributions. These high glacial iron input results indicate that about 30% of the Southern Ocean particle export production, that is, the flux of particulate organic matter through the 100 m depth level, is driven by glacial iron sources. This export production is associated with an uptake of 0.14 Pg carbon per year, which reduces carbon outgassing in the Southern Ocean by 30%. Plain Language Summary: Icebergs and glacial meltwater from Antarctica contain significant amounts of iron, which is important for phytoplankton growth and marine production in the iron‐limited Southern Ocean. Since phytoplankton growth is connected to the carbon cycle, glacial iron sources are assumed to influence the Southern Ocean carbon cycle. However, this influence has not been quantified yet. We use a global Earth System Model to analyze the impacts of icebergs and glacial meltwater on the Southern Ocean carbon cycle. We calculate several simulations using low and high bounds of current estimates of glacial iron concentration. In our model, a high glacial iron input produces the best agreement with observed iron and chlorophyll distributions. These high glacial iron input results indicate that about 30% of the carbon export to depth is driven by glacial iron sources in the Southern Ocean, associated with a 30% reduction in carbon outgassing. Our results indicate that glacial iron plays a significant role in Southern Ocean carbon cycling and oceanic carbon uptake. Key Points: In a preindustrial scenario, iron from icebergs and glacial melt water drive 30% of the marine particle export production south of 50°SThis increased particle export production is associated with a reduction of carbon outgassing of about 30% (0.14 Pg C per year) [ABSTRACT FROM AUTHOR]

In August 2010, a 253 km² ice island calved from the floating glacial tongue of Petermann Glacier in Northwest Greenland. Petermann Ice Island (PII)-B, a large fragment of this original ice island, is the most intensively observed ice island in recent decades. We chronicle PII-B's deterioration over four years while it drifted more than 2,400 km south along Canada's eastern Arctic coast, investigate the ice island's interactions with surrounding ocean waters, and report on its substantial seafloor scour. Three-dimensional sidewall scans of PII-B taken while it was grounded 130 km southeast of Clyde River, Nunavut, show that prolonged wave erosion at the waterline during sea ice-free conditions created a large underwater protrusion. The resulting buoyancy forces caused a 100 m × 1 km calving event, which was recorded by two GPS units. A field team observed surface waters to be warmer and fresher on the side of PII-B where the calving occurred, which perhaps led to the accelerated growth of the protrusion. PII-B produced up to 3.8 gigatonnes (3.8 × 1012 kg) of ice fragments, known hazards to the shipping and resource extraction industries, monitored over 22 months. Ice island seafloor scour, such as a 850 m long, 3 m deep trench at PII-B's grounding location, also puts subseafloor installations (e.g., pipelines) at risk. This long-term and interdisciplinary assessment of PII-B is the first such study in the eastern Canadian Arctic and captures the multiple implications and risks that ice islands impose on the natural environment and offshore industries. [ABSTRACT FROM AUTHOR]