Cooperative Research Centre

About: Cooperative Research Centre is a based out in . It is known for research contribution in the topics: Population & Sea ice. The organization has 7633 authors who have published 8607 publications receiving 429721 citations.

Freshening by glacial meltwater enhances melting of ice shelves and reduces formation of Antarctic Bottom Water

Abstract: Strong heat loss and brine release during sea ice formation in coastal polynyas act to cool and salinify waters on the Antarctic continental shelf. Polynya activity thus both limits the ocean heat flux to the Antarctic Ice Sheet and promotes formation of Dense Shelf Water (DSW), the precursor to Antarctic Bottom Water. However, despite the presence of strong polynyas, DSW is not formed on the Sabrina Coast in East Antarctica and in the Amundsen Sea in West Antarctica. Using a simple ocean model driven by observed forcing, we show that freshwater input from basal melt of ice shelves partially offsets the salt flux by sea ice formation in polynyas found in both regions, preventing full-depth convection and formation of DSW. In the absence of deep convection, warm water that reaches the continental shelf in the bottom layer does not lose much heat to the atmosphere and is thus available to drive the rapid basal melt observed at the Totten Ice Shelf on the Sabrina Coast and at the Dotson and Getz ice shelves in the Amundsen Sea. Our results suggest that increased glacial meltwater input in a warming climate will both reduce Antarctic Bottom Water formation and trigger increased mass loss from the Antarctic Ice Sheet, with consequences for the global overturning circulation and sea level rise.

Thick and deformed Antarctic sea ice mapped with autonomous underwater vehicles

Abstract: Satellites have documented trends in Antarctic sea-ice extent and its variability for decades, but estimating sea-ice thickness in the Antarctic from remote sensing data remains challenging. In situ observations needed for validation of remote sensing data and sea-ice models are limited; most have been restricted to a few point measurements on selected ice floes, or to visual shipboard estimates. Here we present three-dimensional (3D) floe-scale maps of sea-ice draft for ten floes, compiled from two springtime expeditions by an autonomous underwater vehicle to the near-coastal regions of the Weddell, Bellingshausen, and Wilkes Land sectors of Antarctica. Mean drafts range from 1.4 to 5.5 m, with maxima up to 16 m. We also find that, on average, 76% of the ice volume is deformed ice. Our surveys indicate that the floes are much thicker and more deformed than reported by most drilling and ship-based measurements of Antarctic sea ice. We suggest that thick ice in the near-coastal and interior pack may be under-represented in existing in situ assessments of Antarctic sea ice and hence, on average, Antarctic sea ice may be thicker than previously thought.

Insights into Southern Ocean carbon export from the δ13C of particles and dissolved inorganic carbon during the SOIREE iron release experiment

Abstract: 13 C contents of total dissolved inorganic carbon ( δ 13 C-DIC) and particulate organic matter ( δ 13 C org ) were determined to examine the factors influencing phytoplankton 13 C contents and carbon export from the SOIREE iron-induced algal bloom. Suspended particles sieved into 200, 70, 20, 5, and 1 micrometer (μm) size classes displayed an extremely large range in δ 13 C org of 8‰. δ 13 C org values increased from −28‰ for the 1–5 μm class to a maximum of −20‰ for the 20–70 μm class, which was dominated by the large pennate diatom Fragilariopsis kerguelensis . Larger particles (70–200 and >200 μm) had similar δ 13 C org to the smaller (1–5 and 5–20 μm) particles, reflecting both the presence of long narrow Thalassiothrix antarctica diatoms and zooplankton that grazed on small phytoplankton. Comparison of results inside and outside the bloom identified cell surface/volume ratio (mainly reflecting cell size) as the dominant control of phytoplankton δ 13 C org , with subsidiary roles for growth rate and seawater [CO 2 ] aq . The SOIREE iron fertilization provoked an increase in the proportion of large (>20 μm) diatoms. This increased the δ 13 C org of the bulk suspended particles within the mixed layer, but there was minimal increase in the δ 13 C org of sub-surface suspended particles and negligible change in the δ 13 C org of particles obtained with sediment traps suspended below the bloom. This suggests that there was no increase in carbon export over the ∼13 day observation period. However, comparison to δ 13 C org results from previous voyages, and to vertical changes in δ 13 C-DIC, suggests that large diatoms control carbon export from the Antarctic Zone over the summer growth season. This result must be viewed with great caution as it is based on very sparse data and involves several assumptions.