scholarly journals Sea-ice habitat minimizes grazing impact and predation risk for larval Antarctic krill

Polar Biology ◽  
2021 ◽  
Author(s):  
Carmen L. David ◽  
Fokje L. Schaafsma ◽  
Jan A. van Franeker ◽  
Evgeny A. Pakhomov ◽  
Brian P. V. Hunt ◽  
...  
Keyword(s):  
Sea Ice ◽  
Predation Risk ◽  
Water Column ◽  
Antarctic Krill ◽  
Standing Stock ◽  
Euphausia Superba ◽  
Grazing Impact ◽  
Water Interface ◽  
Winter Habitat ◽  
Ice Water

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.

scholarly journals Size and stage composition of age class 0 Antarctic krill (Euphausia superba) in the ice–water interface layer during winter/early spring

Polar Biology ◽  
2016 ◽  
Vol 39 (9) ◽  
pp. 1515-1526 ◽  
Author(s):  
F. L. Schaafsma ◽  
C. David ◽  
E. A. Pakhomov ◽  
B. P. V. Hunt ◽  
B. A. Lange ◽  
...  
Keyword(s):  
Antarctic Krill ◽  
Euphausia Superba ◽  
Interface Layer ◽  
Early Spring ◽  
Water Interface ◽  
Age Class ◽  
Ice Water ◽  
Stage Composition ◽  
Antarctic Krill Euphausia Superba

scholarly journals Flexibility in Antarctic krill Euphausia superba decouples diet and recruitment from overwinter sea-ice conditions in the northern Antarctic Peninsula

2020 ◽  
Vol 642 ◽  
pp. 1-19 ◽  
Author(s):  
J Walsh ◽  
CS Reiss ◽  
GM Watters
Keyword(s):  
Sea Ice ◽  
Water Column ◽  
Antarctic Peninsula ◽  
Lipid Content ◽  
Environmental Variables ◽  
Antarctic Krill ◽  
Euphausia Superba ◽  
Ice Cover ◽  
Ice Conditions ◽  
Ice Resources

Winter sea-ice conditions are considered important for Antarctic krill Euphausia superba survival and recruitment, yet few broad-scale longitudinal studies have examined the underlying relationships between winter conditions and krill recruitment. We used data from a 4 yr winter study of krill condition (lipid content), diet (stable isotopes and fatty acids), and length distributions around the northern Antarctic Peninsula to examine relationships among environmental variables (annual sea-ice cover, water column chlorophyll a [chl a], and upper mixed-layer water temperature), the condition and diet of krill, and recruitment success the following year. Diet indicators (lipid content, δ15N, δ13C, and the fatty acid ratios 16:1n-7/18:4n-3 and 18:1n-9/18:1n-7) in post-larvae were consistent among years regardless of sea-ice cover, suggesting that post-larval krill do not rely on sea-ice resources for overwinter survival. Diet indicators in larvae were more variable and suggest that larvae may feed on sea-ice resources when they are available but can still persist in the water column when they are not. Principal component analysis between environmental variables and diet indicators showed that water-column chl a was the only variable that significantly affected diet, regardless of annual changes in sea-ice cover. Extensive winter ice in one year did not translate into successful recruitment the following year. Krill demonstrate a high degree of flexibility with respect to overwinter habitat and diet, and the degree to which sea ice is important during different times of year and at different life stages may be more complex than previously thought.

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

2002 ◽  
Vol 48 (161) ◽  
pp. 177-191 ◽  
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.

scholarly journals Visualizing brine channel development and convective processes during artificial sea-ice growth using Schlieren optical methods

2016 ◽  
Vol 62 (231) ◽  
pp. 1-17 ◽  
Author(s):  
C. A. MIDDLETON ◽  
C. THOMAS ◽  
A. DE WIT ◽  
J.-L. TISON
Keyword(s):  
Sea Ice ◽  
Growth Period ◽  
Transport Processes ◽  
Optical Methods ◽  
Water Interface ◽  
Ice Growth ◽  
Convective Processes ◽  
Ice Water ◽  
Brine Channel ◽  
Channel Development

ABSTRACTTwo non-invasive optical Schlieren methods have been adapted to visualize brine channel development and convective processes in experimentally grown sea ice obtained when a NaCl aqueous solution is cooled from above in a quasi-two-dimensional Hele–Shaw cell. The two different visualization methods, i.e. traditional and synthetic Schlieren optical imaging, produce high spatial resolution images of transport processes during ice growth, without any external perturbation. These images allow observations of the flow dynamics simultaneously within the ice layer, around the ice/water interface, and in the liquid water layer, revealing connections between the processes occurring within the two phases. Results from these methods show that desalination of the growing ice layer occurs by two concurrent, yet independent, mechanisms: (1) boundary layer convection persisting throughout the ice growth period, with short fingers present just below the ice/water interface, and (2) gravity-driven drainage from the brine channels producing deep penetrating convective streamers, which appear after a given time from the beginning of ice growth. The improved visualization and qualitative characterization of these processes show that Schlieren optical methods have exciting potential applications for future study of convective processes during sea-ice growth.

scholarly journals Oxygen exchange and ice melt measured at the ice-water interface by eddy correlation

2011 ◽  
Vol 8 (6) ◽  
pp. 11255-11284 ◽  
Author(s):  
M. H. Long ◽  
D. Koopmans ◽  
P. Berg ◽  
S. Rysgaard ◽  
R. N. Glud ◽  
...  
Keyword(s):  
Sea Ice ◽  
Primary Production ◽  
Eddy Correlation ◽  
Correlation Technique ◽  
Water Interface ◽  
Algal Communities ◽  
Ice Melt ◽  
Eddy Correlation Technique ◽  
Time Periods ◽  
Ice Water

Abstract. This study uses the eddy correlation technique to examine fluxes across the ice-water interface. Temperature eddy correlation systems were used to determine rates of ice melting and freezing, and O2 eddy correlation systems were used to examine O2 exchange rates as driven by biological and physical processes. The research was conducted below 0.7 m thick sea ice in mid March 2010 in a southwest Greenland fjord and revealed low average rates of ice melt amounting to a maximum of 0.80 ± 0.09 mm d−1 (SE, n=31). The corresponding calculated O2 flux associated with release of O2 depleted melt water was less than 13 % of the average daily O2 respiration rate. Ice melt and insufficient vertical turbulent mixing due to low current velocities caused periodic stratification immediately below the ice. This prevented the determination of fluxes during certain time periods, amounting to 66 % of total deployment time. The identification of these conditions was evaluated by examining the velocity and the linearity and stability of the cumulative flux. The examination of unstratified conditions through velocity and O2 spectra and their cospectra revealed characteristic fingerprints of well-developed turbulence. From the observed O2 fluxes, a photosynthesis/irradiance curve was established by least-squares fitting. This relation showed that light limitation of net photosynthesis began at 4.2 μmol photons m−2 s−1, and that the algal communities were well-adapted to low-light conditions as they were light saturated for 75 % of the day during this early spring period. However, the sea ice associated microbial and algal community was net heterotrophic with a daily gross primary production of 0.69 ± 0.02 mmol O2 m−2 d−1 (SE, n=4) and a respiration rate of −2.13 mmol O2 m−2 d−1 (no SE, see text for details) leading to a net primary production of −1.45 ± 0.02 mmol O2 m−2 d−1 (SE, n=4). Modeling the observed fluxes allowed for the calculation of fluxes during time periods when no O2 fluxes were extracted. This application of the eddy correlation technique produced high temporal resolution O2 fluxes and ice melt rates that were measured without disturbing the environmental conditions while integrating over a large area of approximately 50 m2 which encompassed the highly variable activity and spatial distributions of sea ice algal communities.

scholarly journals Comparison of the microalgal community within fast ice at two sites along the Ross Sea coast, Antarctica

2006 ◽  
Vol 18 (4) ◽  
pp. 583-594 ◽  
Author(s):  
K.G. Ryan ◽  
E.N. Hegseth ◽  
A. Martin ◽  
S.K. Davy ◽  
R. O'Toole ◽  
...  
Keyword(s):  
Sea Ice ◽  
Water Column ◽  
Dominant Species ◽  
Ross Sea ◽  
Standing Stock ◽  
Cylindrotheca Closterium ◽  
Strong Current ◽  
Ice Conditions ◽  
Fast Ice ◽  
And Function

Diverse microbial communities survive within the sea ice matrix and are integral to the energy base of the Southern Ocean. Here we describe initial findings of a four season survey (between 1999–2004) of community structure and biomass of microalgae within the sea ice and in the underlying water column at Cape Evans and Cape Hallett, in the Ross Sea, Antarctica as part of the Latitudinal Gradient Project. At Cape Evans, bottom-ice chlorophyll a levels ranged from 4.4 to 173 mg Chl a m−2. Dominant species were Nitzschia stellata, N. lecointei, and Entomoneis kjellmanii, while the proportion of Berkeleya adeliensis increased steadily during spring. Despite being obtained later in the season, the Cape Hallett data show considerably lower standing stocks of chlorophyll ranging from 0.11 to 36.8 mg Chl a m−2. This difference was attributed to a strong current, which may have ablated much of the bottom ice biomass and provided biomass to the water below. This loss of algae from the bottom of the ice may explain why the ice community contributed only 2% of the standing stock in the total water column. Dominant species at Cape Hallett were Nitzschia stellata, Fragilariopsis curta and Cylindrotheca closterium. The low biomass at Cape Hallett and the prevalence of smaller-celled diatoms in the bottom ice community indicate that the ice here is more typical of pack ice than fast ice. Further data will allow us to quantify and model the extent to which ice-driven dynamics control the structure and function of the sea ice ecosystem and to assess its resilience to changing sea ice conditions.

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

1998 ◽  
Vol 10 (2) ◽  
pp. 124-133 ◽  
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.

scholarly journals Towards improved estimates of sea-ice algal biomass: experimental assessment of hyperspectral imaging cameras for under-ice studies

2017 ◽  
Vol 58 (75pt1) ◽  
pp. 68-77 ◽  
Author(s):  
Emiliano Cimoli ◽  
Arko Lucieer ◽  
Klaus M. Meiners ◽  
Lars Chresten Lund-Hansen ◽  
Fraser Kennedy ◽  
...  
Keyword(s):  
Sea Ice ◽  
Hyperspectral Imaging ◽  
Algal Biomass ◽  
Large Scale ◽  
Polar Regions ◽  
Ice Algae ◽  
Water Interface ◽  
Algae Biomass ◽  
Distribution Matching ◽  
Ice Water

ABSTRACTIce algae are a key component in polar marine food webs and have an active role in large-scale biogeochemical cycles. They remain extremely under-sampled due to the coarse nature of traditional point sampling methods compounded by the general logistical limitations of surveying in polar regions. This study provides a first assessment of hyperspectral imaging as an under-ice remote-sensing method to capture sea-ice algae biomass spatial variability at the ice/water interface. Ice-algal cultures were inoculated in a unique inverted sea-ice simulation tank at increasing concentrations over designated cylinder enclosures and sparsely across the ice/water interface. Hyperspectral images of the sea ice were acquired with a pushbroom sensor attaining 0.9 mm square pixel spatial resolution for three different spectral resolutions (1.7, 3.4, 6.7 nm). Image analysis revealed biomass distribution matching the inoculated chlorophyll a concentrations within each cylinder. While spectral resolutions >6 nm hindered biomass differentiation, 1.7 and 3.4 nm were able to resolve spatial variation in ice algal biomass implying a coherent sensor selection. The inverted ice tank provided a suitable sea-ice analogue platform for testing key parameters of the methodology. The results highlight the potential of hyperspectral imaging to capture sea-ice algal biomass variability at unprecedented scales in a non-invasive way.

scholarly journals Platelet ice and the land-fast sea ice of McMurdo Sound, Antarctica

2001 ◽  
Vol 33 ◽  
pp. 21-27 ◽  
Author(s):  
Inga J. Smith ◽  
Patricia J. Langhorne ◽  
Timothy G. Haskell ◽  
H. Joe Trodahl ◽  
Russell Frew ◽  
...  
Keyword(s):  
Sea Ice ◽  
Isotopic Analysis ◽  
Field Work ◽  
Weddell Sea ◽  
Water Interface ◽  
Ice Shelf ◽  
Columnar Growth ◽  
Mcmurdo Sound ◽  
Ice Water ◽  
Platelet Ice

AbstractDendritic crystals of platelet ice appear beneath the columnar land-fast sea ice of McMurdo Sound, Antarctica. These leaf-like crystals are frozen into place by the advancing columnar growth. The platelets most probably begin to appear during July although in some parts of the Sound they may not appear at all. In addition, the amount and extent of platelet ice within the Sound varies from year to year. Previous authors have suggested that the formation of platelet ice is linked to the presence of the nearby ice shelf. It is a matter of debate whether these platelets form at depth and then float upwards or whether they grow in slightly supercooled water at the ice/water interface. The phenomenon is similar to that observed in the Weddell Sea region, but previous authors have suggested the two regions may experience different processes. This paper presents the results of field-work conducted in McMurdo Sound in 1999. Ice-structure analysis, isotopic analysis and salinity and temperature measurements near the ice/water interface are presented. Freezing points are calculated, and the possible existence of supercooling is discussed in relation to existing conjectures about the origin of platelets.

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