Glacier tongue calving reduced dense water formation and enhanced carbon uptake

Dense shelf water formed in the Mertz Polynya supplies the lower limb of the global overturning circulation, ventilating the abyssal Indian and Pacific Oceans. Calving of the Mertz Glacier Tongue (MGT) in February 2010 altered the regional distribution of ice and reduced the size and activity of the...

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Published inGeophysical research letters Vol. 40; no. 5; pp. 904 - 909
Main Authors Shadwick, E. H., Rintoul, S. R., Tilbrook, B., Williams, G. D., Young, N., Fraser, A. D., Marchant, H., Smith, J., Tamura, T.
Format Journal Article
LanguageEnglish
Published Washington Blackwell Publishing Ltd 16.03.2013
John Wiley & Sons, Inc
Subjects
Algae
Carbon
carbon uptake
dense water formation
Drawdown
Geochemistry
glacier calving
Glaciers
Ice formation
Meltwater
Oceans
Sea ice
Surface water
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Summary:Dense shelf water formed in the Mertz Polynya supplies the lower limb of the global overturning circulation, ventilating the abyssal Indian and Pacific Oceans. Calving of the Mertz Glacier Tongue (MGT) in February 2010 altered the regional distribution of ice and reduced the size and activity of the polynya. The salinity and density of dense shelf water declined abruptly after calving, consistent with a reduction of sea ice formation in the polynya. Breakout and melt of thick multiyear sea ice released by the movement of iceberg B9B and the MGT freshened near‐surface waters. The input of meltwater likely enhanced the availability of light and iron, supporting a diatom bloom that doubled carbon uptake relative to precalving conditions. The enhanced biological carbon drawdown increased the carbonate saturation state, outweighing dilution by meltwater input. These observations highlight the sensitivity of dense water formation, biological productivity, and carbon export to changes in the Antarctic icescape. Key Points Glacier calving causes sharp decline in dense shelf water formation Freshwater input promotes phytoplankton growth, doubles seasonal carbon uptake Meltwater‐induced diatom bloom may provide modern analogue to deglaciation
Bibliography:ArticleID:GRL50178
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Geographic distribution of mixed-layer depth (MLD, top panels), and mixed-layer salinity (bottom panels) observed in 2011 (left), 2008 (center) and 2001 (right). The MLD was determined using the density criteria sigma> 0.1 from the 10 m value. While the upper ocean properties in 2001 were more similar to 2011 than to 2008, there was a significant freshening of the upper ocean in 2011 and shallower mixed layers were observed, particularly East of the former position of the Mertz Glacier Tongue (see Figure 1 in the main text).Histograms of mixed layer depth (MLD, top panels) and mixed-layer salinity (bottom panels) observed in 2011 (left), 2008 (center) and 2001 (right). The red line indicates the median (see Table 1 in the main text).Photographs of the seafloor were taken by Geoscience Australia at several stations at depths of 400-1000m, using a camera fitted to the CTD. This photograph was taken at a depth of 550 m beneath the surface phytoplankton bloom east of the former position of the Mertz Glacier Tongue (see the station marked with a star in Figure 1c in the main text). The distance between the two red laser dots is 50 cm. Most of the sea floor is covered with a thick mat of diatoms that have sunk from the surface layer (green-brown material). Halos around the benthic organisms (holothurians) have formed due to the organisms sweeping their surrounds of organic matter. Samples taken at selected depths in Niskin bottles were concentrated by filtration using 0.8μm pore size polycarbonate filters ay 3.5 C and examined using a Zeiss Axioskop fitted with differential interference contrast optics for species identification.Supporting Information
ISSN:0094-8276
1944-8007
DOI:10.1002/grl.50178