A simulation of small to giant Antarctic iceberg evolution: Differential impact on climatology estimates

Abstract

We present a simulation of Antarctic iceberg drift and melting that includes small, medium‐sized, and giant tabular icebergs with a realistic size distribution. For the first time, an iceberg model is initialized with a set of nearly 7000 observed iceberg positions and sizes around Antarctica. The study highlights the necessity to account for larger and giant icebergs in order to obtain accurate melt climatologies. We simulate drift and lateral melt using iceberg‐draft averaged ocean currents, temperature, and salinity. A new basal melting scheme, originally applied in ice shelf melting studies, uses in situ temperature, salinity, and relative velocities at an iceberg's bottom. Climatology estimates of Antarctic iceberg melting based on simulations of small (≤2.2 km), “small‐to‐medium‐sized" (≤10 km), and small‐to‐giant icebergs (including icebergs >10 km) exhibit differential characteristics: successive inclusion of larger icebergs leads to a reduced seasonality of the iceberg meltwater flux and a shift of the mass input to the area north of 58°S, while less meltwater is released into the coastal areas. This suggests that estimates of meltwater input solely based on the simulation of small icebergs introduce a systematic meridional bias; they underestimate the northward mass transport and are, thus, closer to the rather crude treatment of iceberg melting as coastal runoff in models without an interactive iceberg model. Future ocean simulations will benefit from the improved meridional distribution of iceberg melt, especially in climate change scenarios where the impact of iceberg melt is likely to increase due to increased calving from the Antarctic ice sheet.

Modeling tabular icebergs submerged in the ocean

“…This layer could be hundreds of meters below mean-global sea level if a large iceberg was positioned above it. This means that there is no need to manually embed icebergs into the ocean by integrating ocean fields over the icebergs' thickness, as suggested in Merino et al [2016], or to integrate ocean fields over an implied iceberg surface area, as suggested in Rackow et al [2017]. Within the iceberg model, the ocean model fields are interpolated onto the Lagrangian grid using a bilinear interpolation scheme.…”

“…For an element in the interior of a large structure, the distance from the edge of the structure is large, and so using M b for the basal melt is not appropriate. Instead, the basal melt M s is determined using the three equation model for basal melt, which is a typical melting parametrization used beneath ice shelves [Holland and Jenkins, 1999], and has been used to parametrize melt rates beneath large icebergs in previous studies [Silva et al, 2006;Rackow et al, 2017].…”

“…Because of their large size, the tabular icebergs have long lifetimes during which they drift over long distances injecting meltwater along the way and impacting the Southern Ocean state (e.g., hydrography, sea-ice conditions, etc.) far away from their calving origins [Stern et al, 2016;Rackow et al, 2017]. Meltwater injection (and the accompanying upwelling) from icebergs can also influence biological productivity by bringing In recent years, there has been an increased interest in iceberg drift and decay.…”

“…Some efforts have been made to modify levitating point-particle icebergs models so that they can be used to represent tabular icebergs [Lichey and Hellmer, 2001;Hunke et al, 2011;Rackow et al, 2017]. A promising approach involves integrating ocean properties over the implied iceberg surface area [Rackow et al, 2017] or implied iceberg depth [Hunke et al, 2011;Merino et al, 2016] when calculating the iceberg forcing (or applying iceberg melt fluxes), to account for the horizontal and vertical extent of the tabular iceberg.…”

“…A promising approach involves integrating ocean properties over the implied iceberg surface area [Rackow et al, 2017] or implied iceberg depth [Hunke et al, 2011;Merino et al, 2016] when calculating the iceberg forcing (or applying iceberg melt fluxes), to account for the horizontal and vertical extent of the tabular iceberg. However, this approach does not account for influence that a submerged iceberg can have on the surrounding ocean due to its physical presence in the water column.…”