A simulation of small to giant Antarctic iceberg evolution: Differential impact on climatology estimates. Issue 4 (13th April 2017)

• Record Type: Journal Article
• Authors: Rackow, Thomas; Wesche, Christine; Timmermann, Ralph; Hellmer, Hartmut H.; Juricke, Stephan; Jung, Thomas
• Is Part Of: Journal of geophysical research. Volume 122:Issue 4(2017)
• Page Start: 3170
• Page End: 3190
• Publication Date: 2017-04-13
• Subjects: iceberg drift -- iceberg melting -- giant icebergs -- melt climatology -- Southern Ocean -- FESOM‐IB; Oceanography -- Periodicals; 551.4605
• DOI: 10.1002/2016JC012513
• Languages: English
• ISSNs: 2169-9275

Abstract

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. Plain Language Summary: Antarctic icebergs are large blocks of frozen fresh water that melt around the Antarctic continent while moving under the influence of winds, sea ice, and ocean currents. Small icebergs (≤2.2km) are mainly driven by winds and ocean currents, whereas giant icebergs (> 10 km) tend to 'surf' the tilted sea surface and are less sensitive to changes in the wind. The relative importance between melting at the iceberg's base and mass loss at the side walls is also different for small and large icebergs.We present a computer simulation of Antarctic iceberg movement and melting that includes not only small icebergs, but at the same time also larger icebergs with side lengths of 10 km or more. The study highlights the necessity to account for larger icebergs in order to obtain an accurate depiction of the spatial distribution of iceberg meltwater, which, e.g., stabilizes and fertilizes the upper water column and thus supports phytoplankton growth. Future climate change simulations will benefit from the improved distribution, where the impact of iceberg melting is likely to increase due to increased calving from the Antarctic ice sheet. Key Points: Initialization with observed iceberg positions and a realistic size distribution Drift and melt of small (≤2.2 km length) to giant icebergs (≳10 km) is simulated Including larger icebergs leads to a northward shift of the freshwater input with reduced seasonality