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.

Impact of Ice Algae on Inorganic Nutrients in Seawater and Sea Ice in Barrow Strait, NWT, Canada, During Spring

1990 ◽  
Vol 47 (7) ◽  
pp. 1402-1415 ◽  
Author(s):  
Glenn F. Cota ◽  
Jeffrey L. Anning ◽  
Leslie R. Harris ◽  
W. Glen Harrison ◽  
Ralph E. H. Smith
Keyword(s):  
Sea Ice ◽  
Surface Waters ◽  
Algal Biomass ◽  
Ice Sheet ◽  
Inorganic Nutrients ◽  
Ice Algae ◽  
High Biomass ◽  
Dissolved Nutrients ◽  
Particulate Nitrogen ◽  
Ice Water

Except in "bottom ice" (lowest few centimetres) and surface waters impacted by autotrophs, the major inorganic nutrients behave conservatively in seawater and sea ice. From mid- to late spring, steep and persistent nutrient gradients were observed in the "well-mixed surface layer" with minima near the ice–water interface. Nitrate, ammonium, and phosphate are highly concentrated in heavily colonized bottom ice relative to seawater and the remainder of the ice sheet; concentrations in darkened, weakly colonized bottom ice are similar to the ice sheet. These nutrients also display strong vertical stratification over millimetre scales. Nitrate and phosphate in the bottom ice layer display strong positive relationships with chlorophyll. The accumulation of these nutrients in bottom ice must be biologically mediated and constitutes a significant sink. In contrast, silicic acid concentrations in bottom ice are close to those expected for sea ice formed from the source seawater, are only weakly related to algal biomass, and vary much less seasonally. Ice algae are apparently shocked osmotically and release their intracellular pools of dissolved nutrients. Intracellular pools of nitrate averaged 1.4–9.5% of total particulate nitrogen. Nitrient stresses, during periods of high biomass and sluggish supply, may be alleviated by pooling.

scholarly journals An Under-Ice Hyperspectral and RGB Imaging System to Capture Fine-Scale Biophysical Properties of Sea Ice

2019 ◽  
Vol 11 (23) ◽  
pp. 2860 ◽  
Author(s):  
Emiliano Cimoli ◽  
Klaus M. Meiners ◽  
Arko Lucieer ◽  
Vanessa Lucieer
Keyword(s):  
Sea Ice ◽  
Algal Biomass ◽  
Bottom Topography ◽  
Environmental Drivers ◽  
Future Research ◽  
Ice Algae ◽  
Digital Photogrammetry ◽  
Biophysical Properties ◽  
Algae Biomass ◽  
Non Invasive

Sea-ice biophysical properties are characterized by high spatio-temporal variability ranging from the meso- to the millimeter scale. Ice coring is a common yet coarse point sampling technique that struggles to capture such variability in a non-invasive manner. This hinders quantification and understanding of ice algae biomass patchiness and its complex interaction with some of its sea ice physical drivers. In response to these limitations, a novel under-ice sled system was designed to capture proxies of biomass together with 3D models of bottom topography of land-fast sea-ice. This system couples a pushbroom hyperspectral imaging (HI) sensor with a standard digital RGB camera and was trialed at Cape Evans, Antarctica. HI aims to quantify per-pixel chlorophyll-a content and other ice algae biological properties at the ice-water interface based on light transmitted through the ice. RGB imagery processed with digital photogrammetry aims to capture under-ice structure and topography. Results from a 20 m transect capturing a 0.61 m wide swath at sub-mm spatial resolution are presented. We outline the technical and logistical approach taken and provide recommendations for future deployments and developments of similar systems. A preliminary transect subsample was processed using both established and novel under-ice bio-optical indices (e.g., normalized difference indexes and the area normalized by the maximal band depth) and explorative analyses (e.g., principal component analyses) to establish proxies of algal biomass. This first deployment of HI and digital photogrammetry under-ice provides a proof-of-concept of a novel methodology capable of delivering non-invasive and highly resolved estimates of ice algal biomass in-situ, together with some of its environmental drivers. Nonetheless, various challenges and limitations remain before our method can be adopted across a range of sea-ice conditions. Our work concludes with suggested solutions to these challenges and proposes further method and system developments for future research.

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 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.

Recent atmospheric circulation trends: two major flaws in reanalyses and in climate models

2020 ◽  
Author(s):  
Rei Chemke ◽  
Lorenzo Polvani
Keyword(s):  
Sea Ice ◽  
Atmospheric Circulation ◽  
Large Scale ◽  
Climate Models ◽  
Heat Fluxes ◽  
Hadley Cell ◽  
Polar Regions ◽  
Large Scale Circulation ◽  
Model Simulations ◽  
Eddy Heat Flux

<p>The weakening of the Hadley cell and of the midlatitude eddy heat fluxes are two of the most robust responses of the atmospheric circulation to increasing concentrations of greenhouse gases.  These changes have important global climatic impacts, as the large-scale circulation acts to transfer heat and moisture from the tropics to polar regions.  Here, we examine Hadley cell and eddy heat flux trends in recent decades: contrasting model simulations with reanalyses, we uncover two important flaws -- one in the reanalyses and other in the model simulations -- that have, to date, gone largely unnoticed.<br><br>First, we find that while climate models simulate a weakening of the Hadley cell over the past four decades, most atmospheric reanalyses indicate a considerable strengthening.  Interestingly, that discrepancy does not stem from biases in climate models, but appears to be related to artifacts in the representation of latent heating in the reanalyses.  This suggests that when dealing with the divergent part of the large-scale circulation, reanalyses may be fundamentally unreliable for the calculation of trends, even for trends spanning several decades.<br><br>Second, we examine recent trends in eddy heat fluxes at midlatitudes, which are directly linked the equator-to-pole temperature gradient.  In the Northern Hemisphere models and reanalyses are in good agreement. In the Southern Hemisphere, however, models show a weakening while reanalyses indicate a robust strengthening.  In this case, the flaw is found to be with the climate models, which are unable to simulate the observed multidecadal cooling of the Southern Ocean at high-latitudes, and the accompanying increase in sea-ice.  While the biases in modeled Antarctic sea ice trends have been widely reported, our results demonstrates that such biases have important implications well beyond the high Southern latitudes, as they impact the equator-to-pole temperature and, as a consequence, the midlatitude atmospheric circulation.</p>

Biodiversity and ecophysiology of bacteria associated with Antarctic sea ice

1997 ◽  
Vol 9 (2) ◽  
pp. 134-142 ◽  
Author(s):  
John P. Bowman ◽  
Mark V. Brown ◽  
David S. Nichols
Keyword(s):  
Sea Ice ◽  
Halophilic Bacteria ◽  
Ice Algae ◽  
Bacterial Strains ◽  
Dna Base Composition ◽  
Algae Biomass ◽  
Antarctic Sea Ice ◽  
Dna Base ◽  
Vestfold Hills ◽  
Reference Strains

A total of 135 bacterial strains were isolated from congelation (land fast) sea ice samples and ice algae biomass samples obtained from the coastal areas of the Vestfold Hills in East Antarctica (68°S, 78°E) during the summers of 1992–95. The sea ice isolates, along with reference strains. were analysed by numerical taxonomy and for DNA base composition in order to determine the biodiversity of sea ice bacteria. From these analyses 22 clusters of strains (phena) were obtained with most phena apparently representing novel bacterial taxa. The sea ice isolates could be categorized into three groups based on their ecophysiology: 1) slightly halophilic, psychrophilic bacteria often possessing fastidious growth requirements and which were predominantly isolated from sea ice algae biomass or from algae-rich ice samples; 2) halotolerant and psychrotolerant bacteria; and 3) non-halophilic bacteria isolated primarily from upper sections of congelation ice and other ice samples with low levcls of algal biomass.

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 Do pelagic grazers benefit from sea ice? Insights from the Antarctic sea ice proxy IPSO<sub>25</sub>

2017 ◽  
Author(s):  
Katrin Schmidt ◽  
Thomas A. Brown ◽  
Simon T. Belt ◽  
Louise C. Ireland ◽  
Kyle W. R. Taylor ◽  
...  
Keyword(s):  
Sea Ice ◽  
Primary Production ◽  
Carbon Sources ◽  
Euphausia Superba ◽  
Polar Regions ◽  
Ice Algae ◽  
Calanoid Copepods ◽  
Scotia Sea ◽  
Ice Retreat ◽  
Ice Edge

Abstract. Sea ice affects primary production in polar regions in multiple ways. It can dampen water column productivity by reducing light or nutrient supply, it provides a habitat for ice algae and on its seasonal retreat can condition the marginal ice zone (MIZ) for phytoplankton blooms. The relative importance of three different carbon sources (ice-derived, ice-conditioned, non-ice associated) for the polar food web is not well understood, partly due to the lack of methods that enable their unambiguous distinction. Here we analysed two highly branched isoprenoid (HBI) biomarkers to trace ice-derived and ice-conditioned carbon in Antarctic krill (Euphausia superba), and relate their concentrations to the grazers' body reserves, growth and recruitment. During our sampling in January/February 2003, the proxy for sea ice diatoms (a di-unsaturated HBI termed IPSO25, δ13C = −12.5 ± 3.3 ‰) occurred in open waters of the western Scotia Sea, where seasonal ice retreat was slow. In suspended matter, IPSO25 was present at a few stations close to the ice edge, but in krill the marker was widespread. Even at stations that had been ice-free for several weeks, IPSO25 was found in krill stomachs, suggesting that they gathered the ice-derived algae from below the upper mixed layer. Peak abundances of the proxy for MIZ diatoms (a tri-unsaturated HBI termed HBI III, δ13C = −42.2 ± 2.4 ‰) occurred in regions of fast sea ice retreat and persistent salinity-driven stratification in the eastern Scotia Sea. Krill sampled in the area defined by the ice edge bloom likewise contained high amounts of HBI III. As indicators for the grazer's performance we used the mass-length ratio, size of digestive gland and growth rate for krill, and recruitment for the biomass-dominant calanoid copepods Calanoides acutus and Calanus propinquus. These indices consistently point to blooms in the MIZ as an important feeding ground for pelagic grazers. Even though ice-conditioned blooms are of much shorter duration than the bloom downstream of the permanently sea ice-free South Georgia, they enabled fast growth and offspring development. Our study shows two rarely considered ways that pelagic grazers may benefit from sea ice: Firstly, after their release from sea ice, suspended or sinking ice algae can supplement the grazers' diet if phytoplankton concentrations are low. Secondly, conditioning effects of seasonal sea ice can promote pelagic primary production and therefore food availability in spring and summer.

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