Ultra-algae (<5 pm) in the ice, at the ice-water interface and in the under-ice water column (southeastern Hudson Bay, Canada)

AbstractSurvival of larval Antarctic krill (Euphausia superba) during winter is largely dependent upon the presence of sea ice as it provides an important source of food and shelter. We hypothesized that sea ice provides additional benefits because it hosts fewer competitors and provides reduced predation risk for krill larvae than the water column. To test our hypothesis, zooplankton were sampled in the Weddell-Scotia Confluence Zone at the ice-water interface (0–2 m) and in the water column (0–500 m) during August–October 2013. Grazing by mesozooplankton, expressed as a percentage of the phytoplankton standing stock, was higher in the water column (1.97 ± 1.84%) than at the ice-water interface (0.08 ± 0.09%), due to a high abundance of pelagic copepods. Predation risk by carnivorous macrozooplankton, expressed as a percentage of the mesozooplankton standing stock, was significantly lower at the ice-water interface (0.83 ± 0.57%; main predators amphipods, siphonophores and ctenophores) than in the water column (4.72 ± 5.85%; main predators chaetognaths and medusae). These results emphasize the important role of sea ice as a suitable winter habitat for larval krill with fewer competitors and lower predation risk. These benefits should be taken into account when considering the response of Antarctic krill to projected declines in sea ice. Whether reduced sea-ice algal production may be compensated for by increased water column production remains unclear, but the shelter provided by sea ice would be significantly reduced or disappear, thus increasing the predation risk on krill larvae.

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Dissolved gases in perennially ice-covered lakes of the McMurdo Dry Valleys, Antarctica

Antarctic Science ◽

10.1017/s0954102098000170 ◽

1998 ◽

Vol 10 (2) ◽

pp. 124-133 ◽

Cited By ~ 18

Author(s):

D.T. Andersen ◽

C.P. Mckay ◽

R.A. Wharton

Keyword(s):

Water Column ◽

Turbulent Mixing ◽

Bubble Formation ◽

Gas Content ◽

Main Process ◽

Water Interface ◽

Dry Valleys ◽

The Mean ◽

Ice Water ◽

Made In

Measurements of dissolved N2, O2, Ar, CO2, and CH4 were made in perennially ice-covered Lake Hoare. Results confirm previous reports that O2 concentrations in the upper water column exceed atmospheric equilibrium and that N2 and Ar are supersaturated throughout the water column. The mean supersaturation of N2 was found to be 2.0 (±0.37) and Ar was 3.8 (±1.1). The ratios of N2/Ar (20.3 ±3.8), and O2/Ar (22.5 ±4.0) at the ice-water interface are consistent with those previously measured, suggesting that bubble formation is the main process for removing gas from the lake. However, the saturations of N2 and Ar greatly exceed those previously predicted for degassing by bubble formation only at the ice-water interface. The data support the hypothesis that removal of gas by bubbles occurs in the water column to a depth of 11 m in Lake Hoare. CO2 concentration increases from near zero at the ice-water interface to 80–100 times saturation at and below the chemocline at c. 28 m. There is considerable variability in the gas concentrations throughout the water column; samples separated in depth by one metre may vary by more than 50% in gas content. It is likely that this phenomenon results from the lack of turbulent mixing in the water column. Methane (c. 2 μg 1−1) was detected below the chemocline and immediately above the sediment/water interface at a depth of 30 m. Samples from lakes Vanda, Joyce, and Miers, also show supersaturations of O2, N2, and Ar at levels similar to levels found in Lake Hoare.

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Tank study of physico-chemical controls on gas content and composition during growth of young sea ice

Journal of Glaciology ◽

10.3189/172756502781831377 ◽

2002 ◽

Vol 48 (161) ◽

pp. 177-191 ◽

Cited By ~ 64

Author(s):

Jean-Louis Tison ◽

Christian Haas ◽

Marcia M. Gowing ◽

Suzanne Sleewaegen ◽

Alain Bernard

Keyword(s):

Sea Ice ◽

Sea Water ◽

Bubble Nucleation ◽

Water Dynamics ◽

Gas Content ◽

First Year ◽

Water Interface ◽

Atmospheric Gases ◽

Physico Chemical ◽

Ice Water

AbstractDuring an ice-tank experiment, samples were taken to study the processes of acquisition and alteration of the gas properties in young first-year sea ice during a complete growth–warming–cooling cycle. The goal was to obtain reference levels for total gas content and concentrations of atmospheric gases (O2, N2, CO2) in the absence of significant biological activity. The range of total gas-content values obtained (3.5–18 mL STP kg−1) was similar to previous measurements or estimates. However, major differences occurred between current and quiet basins, showing the role of the water dynamics at the ice–water interface in controlling bubble nucleation processes. Extremely high CO2concentrations were observed in all the experiments (up to 57% in volume parts). It is argued that these could have resulted from two unexpected biases in the experimental settings. Concentrations in bubbles nucleated at the interface are controlled by diffusion both from the ice–water interface towards the well-mixed reservoir and between the interface water and the bubble itself. This double kinetic effect results in a transition of the gas composition in the bubbles from values close to solubility in sea water toward values close to atmospheric, as the ice cover builds up.

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Effects of Fe addition on sediment P dynamics in a eutrophic lake

10.5194/egusphere-egu21-4941 ◽

2021 ◽

Author(s):

Melanie Münch ◽

Rianne van Kaam ◽

Karel As ◽

Stefan Peiffer ◽

Gerard ter Heerdt ◽

...

Keyword(s):

Water Quality ◽

Organic Matter ◽

Surface Water ◽

Water Column ◽

Sediment Cores ◽

Surface Water Quality ◽

Water Interface ◽

Eutrophic Lakes ◽

Fe Addition

The decline of surface water quality due to excess phosphorus (P) input is a global problem of increasing urgency. Finding sustainable measures to restore the surface water quality of eutrophic lakes with respect to P, other than by decreasing P inputs, remains a challenge. The addition of iron (Fe) salts has been shown to be effective in removing dissolved phosphate from the water column of eutrophic lakes. However, the resulting changes in biogeochemical processes in sediments as well as the long-term effects of Fe additions on P dynamics in both sediments and the water column are not well understood.In this study, we assess the impact of past Fe additions on the sediment P biogeochemistry of Lake Terra Nova, a well-mixed shallow peat lake in the Netherlands. The Fe-treatment in 2010 efficiently reduced P release from the sediments to the surface waters for 6 years. Since then, the internal sediment P source in the lake has been increasing again with a growing trend over the years.In 2020, we sampled sediments at three locations in Terra Nova, of which one received two times more Fe during treatment than the other two. Sediment cores from all sites were sectioned under oxygen-free conditions. Both the porewaters and sediments were analysed for their chemical composition, with sequential extractions providing insight into the sediment forms of P and Fe. Additional sediment cores were incubated under oxic and anoxic conditions and the respective fluxes of P and Fe across the sediment water interface were measured.The results suggest that Fe and P dynamics in the lake sediments are strongly coupled. We also find that the P dynamics are sensitive to the amount of Fe supplied, even though enhanced burial of P in the sediment was not detected. The results of the sequential extraction procedure for P, which distinguishes P associated with humic acids and Fe oxides, as well as reduced flux of Fe(II) across the sediment water interface in the anoxic incubations, suggest a major role of organic matter in the interaction of Fe and P in these sediments.Further research will include investigations of the role of organic matter and sulphur in determining the success of Fe-treatment in sequestering P in lake sediments. Based on these data in combination with reactive transport modelling we aim to constrain conditions for successful lake restoration through Fe addition.

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Sediment-water column fluxes of carbon, oxygen and nutrients in Bedford Basin, Nova Scotia, inferred from 224Ra measurements

Biogeosciences ◽

10.5194/bg-10-53-2013 ◽

2013 ◽

Vol 10 (1) ◽

pp. 53-66 ◽

Cited By ~ 13

Author(s):

W. J. Burt ◽

H. Thomas ◽

K. Fennel ◽

E. Horne

Keyword(s):

Organic Matter ◽

Nova Scotia ◽

Water Column ◽

Explicit Knowledge ◽

Dissolved Inorganic Carbon ◽

Chemical Constituents ◽

Water Interface ◽

Benthic Fluxes ◽

Pore Waters ◽

Overlying Water

Abstract. Exchanges between sediment pore waters and the overlying water column play a significant role in the chemical budgets of many important chemical constituents. Direct quantification of such benthic fluxes requires explicit knowledge of the sediment properties and biogeochemistry. Alternatively, changes in water-column properties near the sediment-water interface can be exploited to gain insight into the sediment biogeochemistry and benthic fluxes. Here, we apply a 1-D diffusive mixing model to near-bottom water-column profiles of 224Ra activity in order to yield vertical eddy diffusivities (KZ), based upon which we assess the diffusive exchange of dissolved inorganic carbon (DIC), nutrients and oxygen (O2), across the sediment-water interface in a coastal inlet, Bedford Basin, Nova Scotia, Canada. Numerical model results are consistent with the assumptions regarding a constant, single benthic source of 224Ra, the lack of mixing by advective processes, and a predominantly benthic source and sink of DIC and O2, respectively, with minimal water-column respiration in the deep waters of Bedford Basin. Near-bottom observations of DIC, O2 and nutrients provide flux ratios similar to Redfield values, suggesting that benthic respiration of primarily marine organic matter is the dominant driver. Furthermore, a relative deficit of nitrate in the observed flux ratios indicates that denitrification also plays a role in the oxidation of organic matter, although its occurrence was not strong enough to allow us to detect the corresponding AT fluxes out of the sediment. Finally, comparison with other carbon sources reveal the observed benthic DIC release as a significant contributor to the Bedford Basin carbon system.

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Isotopic fractionation during grain coarsening of wet snow

Annals of Glaciology ◽

10.3189/s0260305500011381 ◽

1993 ◽

Vol 18 ◽

pp. 129-134 ◽

Cited By ~ 1

Author(s):

Masayoshi Nakawo ◽

Shigeru Chiba ◽

Hiroshi Satake ◽

Shigeru Kinouchi

Keyword(s):

Experimental Data ◽

Simple Model ◽

Rapid Change ◽

Isotopic Fractionation ◽

Water Interface ◽

Grain Coarsening ◽

Isotope Concentration ◽

Large Particles ◽

Wet Snow ◽

Ice Water

Isotopic composition of solid and liquid portions of wet snow was investigated experimentally. The compositions changed with time, δ values of ice becoming heavier than those for water. A simple model was proposed to explain their temporal variation. It predicted, however, a more rapid change of δ values than the trend obtained in the experiments. This suggests the presence of a “diffusion layer” adjacent to growing snow particles, where isotope concentration has dropped at the ice-water interface because of the fractionation during grain coarsening. The slope in δD–δ18O diagram estimated by the model is compatible with the experimental data. It is considered, therefore, that the freezing fraction, the part of the liquid which refreezes to relatively large particles during grain coarsening, could be estimated by measuring the isotope concentration.

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Heightened Cold-Denaturation of Proteins at the Ice–Water Interface

Journal of the American Chemical Society ◽

10.1021/jacs.9b13454 ◽

2020 ◽

Vol 142 (12) ◽

pp. 5722-5730 ◽

Cited By ~ 4

Author(s):

Andrea Arsiccio ◽

James McCarty ◽

Roberto Pisano ◽

Joan-Emma Shea

Keyword(s):

Water Interface ◽

Cold Denaturation ◽

Ice Water ◽

Denaturation Of Proteins

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Observations of a rift in the Ronne Ice Shelf, Antarctica

Journal of Glaciology ◽

10.3189/s0022143000003968 ◽

1994 ◽

Vol 40 (134) ◽

pp. 187-189

Author(s):

E.C. King

Keyword(s):

Weddell Sea ◽

Surface Elevation ◽

Water Interface ◽

Ice Shelf ◽

Seismic Profiling ◽

Ice Water

AbstractDuring seismic profiling on the northwest Ronne Ice Shelf Antarctica, a rift in the ice shelf was encountered. The rift trends southeast to northwest and is located approximately 30 km inland from the present-day ice front The rift is 340 m wide and the surface elevation of the ice shelf drops by 14.65 m over the axis of the rift. The rift has an asymmetrical base with a near-vertical ice-water interface on its northeast flank and a more gently dipping ice-water interface forming its southeastern flank. The ice shelf thins from a thickness of 350 m away from the rift to a thickness of 225 m at the rift axis. The rift is the probable location of a future major calving event on this section of the Ronne Ice Shelf, an event which would release an iceberg of up to 30 km by 180 km into the Weddell Sea.

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