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  • 1
    Publication Date: 2016-01-08
    Description: The perennially ice-covered Central Arctic is changing rapidly due to extensive sea-ice retreat and the loss of multiyear ice. The thinning of the ice allows more light to reach the water column enhancing productivity. These changes in the under ice ecosystem can lead to under-ice phytoplankton blooms which may increase grazing and carbon export. However, our knowledge of the interactions between sea ice, sub-ice and under-ice communities is still poor, especially in high latitudes. A key limitation is observations of the undisturbed under-ice flora and fauna. To address this gap in observations, the Nereid Under Ice remotely operated vehicle (NUI) was developed, equipped with thin optical fibre and acoustic navigation to explore under-ice environments at distances up to 20 km away from research vessels from which it is deployed. This vehicle can accommodate various interdisciplinary payloads including HD video cameras, CTD and biological sensor packages including chlorophyll fluorometers, CDOM optical sensors and optical nitrate sensors. Research capabilities of NUI were tested during the RV Polarstern PS86 expedition to the Aurora Vent field, at 83ºN 6°W north-east of Greenland. From 12 to 30 July 2014 the evolution of a phytoplankton bloom below 2m thick multiyear ice was followed. Video footage obtained with NUI directly below the ice showed the development of algal mats at the bottom of the ice floe and a succession of zooplankton blooms presumably causing a decline of the phytoplankton bloom. Polar copepods, ctenophores and appendicularia could be identified forming dense biomasses underneath the ice. From NUI’s chlorophyll, CDOM and nitrate profiles, steep gradients of high biogeochemical activity were detected in the mixed layer (upper 6-15 m), which could not be observed by the ship-deployed CTD. These structures were identified as layers of sinking particles with different optical characteristics. This poster summarizes the advantages of robotic observations over classical ship-based sampling for the study of under ice communities. In vivo observations of phyto- and zooplankton communities are needed to better assess the impacts of changing sea-ice conditions on under ice organisms.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 2
    Publication Date: 2015-09-15
    Description: The observed changes in physical properties of sea ice such as decreased thickness and increased melt pond cover severely impact the energy budget of Arctic sea ice. Increased light transmission leads to increased deposition of solar energy in the upper ocean and thus plays a crucial role for amount and timing of sea-ice-melt and under-ice primary production. Recent developments in underwater technology provide new opportunities to study light transmission below the largely inaccessible underside of sea ice. We measured spectral under-ice radiance and irradiance using the new Nereid Under-Ice (NUI) underwater robotic vehicle, during a cruise of the R/V Polarstern to 838N 68W in the Arctic Ocean in July 2014. NUI is a next generation hybrid remotely operated vehicle (H-ROV) designed for both remotely piloted and autonomous surveys underneath land-fast and moving sea ice. Here we present results from one of the first comprehensive scientific dives of NUI employing its interdisciplinary sensor suite. We combine under-ice optical measurements with three dimensional under-ice topography (multibeam sonar) and aerial images of the surface conditions. We investigate the influence of spatially varying ice-thickness and surface properties on the spatial variability of light transmittance during summer. Our results show that surface properties such as melt ponds dominate the spatial distribution of the under-ice light field on small scales (〈1000 m2), while sea ice-thickness is the most important predictor for light transmission on larger scales. In addition, we propose the use of an algorithm to obtain histograms of light transmission from distributions of sea ice thickness and surface albedo.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev , info:eu-repo/semantics/article
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  • 3
    Publication Date: 2015-04-20
    Description: The observed changes in physical properties of sea ice such as decreased thickness and increased melt pond cover severely impact the energy balance of Arctic sea ice. Increased light transmission leads to increased deposition of solar energy and thus plays a crucial role for sea-ice-melt as well as for the amount and timing of under-ice primary production. Recent developments in underwater technology provide new opportunities to undertake challenging research at the largely inaccessible underside of sea ice. We measured spectral under-ice radiance and irradiance onboard the new Nereid Under-Ice (Nereid-UI) under- water robotic vehicle, during a cruise of the R/V Polarstern to 83°N 6°W in the Arctic Ocean in July 2014. Nereid-UI is a next generation hybrid remotely operated vehicle (H-ROV) designed for both remotely-piloted and autonomous surveys underneath fixed and moving sea ice. Here we present results from the first comprehensive scientific dive of Nereid-UI employing its interdisci- plinary sensor suite. We combine under-ice optical measurements with three dimensional under-ice topography (multibeam sonar) and aerial images of the surface conditions. We investigate the influence of spatially varying ice-thickness and surface properties on the spatial variability of light transmittance on floe scale. Our results indicate that surface properties dominate the spatial distribution of the under-ice light field, while sea ice-thickness and snow-depth are most important for mean light levels.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev , info:eu-repo/semantics/conferenceObject
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  • 4
    Publication Date: 2016-01-08
    Description: The changes in physical properties of sea ice such as decreased thickness and increased melt pond cover observed over the last decades severely impact the energy budget of Arctic sea ice. Increased light transmission leads to increased deposition of solar energy in the upper ocean and thus plays a crucial role in the amount and timing of sea-ice-melt and under-ice primary production. Recent developments in underwater technology provide new opportunities to undertake challenging research at the largely inaccessible underside of sea ice. We measured spectral under-ice radiance and irradiance onboard the new Nereid Under-Ice (NUI) underwater robotic vehicle, during a cruise of the R/V Polarstern to 83°N 6°W in the Arctic Ocean in July 2014. NUI is a next generation hybrid remotely operated vehicle (H-ROV) designed for both remotely-piloted and autonomous surveys underneath land-fast and moving sea ice. Here we present results from one of the first comprehensive scientific dives of NUI employing its interdisciplinary sensor suite. We combine under-ice optical measurements with three-dimensional under-ice topography and aerial images of the surface conditions. We investigate the influence of spatially varying ice-thickness and surface properties during summer on the spatial variability of light transmittance. Results show that surface properties dominate the spatial distribution of the under-ice light field on small scales (〈1000m²), while sea ice-thickness is the most important predictor for light transmission on larger scales. In addition, we suggest an algorithm to obtain histograms of light transmission from distributions of sea ice thickness and surface albedo.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 5
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    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Publication Date: 2022-05-25
    Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2015
    Description: The copepod Calanus glacialis is one of the most important zooplankton taxa in the Arctic shelf seas where it serves as a key grazer, predator, and food source. Its summer distribution and abundance have direct effects on much of the food web, from blooming phytoplankton to migrating bowhead whales. The Chukchi Sea represents a highly advective regime dominated by a barotropicly driven northward flow modulated by wind driven currents that reach the bottom boundary layer of this shallow environment. In addition, a general northward gradient of decreasing temperature and food concentration leads to geographically divergent copepod growth and development rates. The physics of this system establish the connection potential between specific regions. Unless biological factors are uniform and ideal the true connections will be an uneven subset of this physically derived connection potential. In August 2012 and 2013, C. glacialis distributions were observed over Hanna Shoal in the northeast Chukchi Sea. Here we used the Finite Volume Community Ocean Model i-State Configuration Model to advect these distributions forward and back in time to determine the source and sink regions of the transient Hanna Shoal C. glacialis population. We found that Hanna Shoal supplies diapause competent C. glacialis to both the Beaufort Slope and the Chukchi Cap, mainly receives juveniles from the broad slope between Hanna Shoal and Herald Canyon and receives second year adults from as far as the Anadyr Gulf and as close as the broad slope between Hanna Shoal and Herald Canyon. These connection potentials were not sensitive to precise times and locations of release, but were quite sensitive to depth of release. Deeper particles often traveled further than shallow particles due to strong vertical shear in the shallow Chukchi. The 2013 sink region was shifted west relative to the 2012 region and the 2013 adult source region was shifted north relative to the 2012 region.
    Description: The U.S. Department of Interior, Bureau of Ocean Energy and Management (BOEM), Alaska Outer Continental Shelf Region, Anchorage, Alaska provided funding for the fieldwork and plankton sample enumeration as part of the Chukchi Sea Offshore Monitoring in Drilling Area (COMIDA) Project and the BOEM Alaska Environmental Studies Program under contract Number M11AC00007 to the University of Texas and a subcontract to the Woods Hole Oceanographic Institution.
    Repository Name: Woods Hole Open Access Server
    Type: Thesis
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  • 6
    Publication Date: 2022-05-25
    Description: © The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Journal of Geophysical Research: Oceans 120 (2015): 5932–5944, doi:10.1002/2015JC010914.
    Description: The observed changes in physical properties of sea ice such as decreased thickness and increased melt pond cover severely impact the energy budget of Arctic sea ice. Increased light transmission leads to increased deposition of solar energy in the upper ocean and thus plays a crucial role for amount and timing of sea-ice-melt and under-ice primary production. Recent developments in underwater technology provide new opportunities to study light transmission below the largely inaccessible underside of sea ice. We measured spectral under-ice radiance and irradiance using the new Nereid Under-Ice (NUI) underwater robotic vehicle, during a cruise of the R/V Polarstern to 83°N 6°W in the Arctic Ocean in July 2014. NUI is a next generation hybrid remotely operated vehicle (H-ROV) designed for both remotely piloted and autonomous surveys underneath land-fast and moving sea ice. Here we present results from one of the first comprehensive scientific dives of NUI employing its interdisciplinary sensor suite. We combine under-ice optical measurements with three dimensional under-ice topography (multibeam sonar) and aerial images of the surface conditions. We investigate the influence of spatially varying ice-thickness and surface properties on the spatial variability of light transmittance during summer. Our results show that surface properties such as melt ponds dominate the spatial distribution of the under-ice light field on small scales (〈1000 m2), while sea ice-thickness is the most important predictor for light transmission on larger scales. In addition, we propose the use of an algorithm to obtain histograms of light transmission from distributions of sea ice thickness and surface albedo.
    Description: U.S. National Science Foundation Office of Polar Programs NSF OPP ANT-1126311, National Oceanic and Atmospheric Administration Office of Exploration and Research NOAA OER NA14OAR4320158, European Research Council Advanced Investigator Grant Number: 294757
    Keywords: Melt ponds ; Light transmittance ; Albedo ; ROV ; Spatial variability ; Shortwave radiation
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 7
    Publication Date: 2022-05-25
    Description: © The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Elliott JA, Patterson MR, Staub CG, Koonjul M, Elliott SM. 2018. Decline in coral cover and flattening of the reefs around Mauritius (1998–2010) PeerJ 6:e6014, doi: 10.7717/peerj.6014 .
    Description: Coral reefs are degrading through the impacts of multiple anthropogenic stressors. How are coral reef communities going to change and how to protect them for future generations are important conservation questions. Using coral reef data from Mauritius, we examined changes in cover in 23 benthic groups for a 13-yr period and at 15 sites. Moreover, we determined which land-based stressor out of four (human population, agriculture, tourism, rainfall) correlated the most with the observed changes in coral reef cover. Among the stony corals, Acropora corals appeared to be the most impacted, decreasing in cover at many sites. However, the non-Acropora encrusting group increased in cover at several sites. The increase in abundance of dead corals and rubble at some sites also supported the observations of stony coral decline during the study period. Additionally, the decline in stony corals appeared to be more pronounced in second half of the study period for all sites suggesting that a global factor rather than a local factor was responsible for this decline. There was little change in cover for the other benthic groups, some of which were quite rare. Human population was significantly correlated with changes in coral reef cover for 11 sites, followed by tourism and agriculture. Rainfall, a proxy for runoff, did not appear to affect coral reef cover. Overall, our results showed that there has been a decline of stony coral cover especially the ones with complex morphologies, which in turn suggest that coral reefs around Mauritius have experienced a decline in habitat complexity during the study period. Our study also suggests that humans are an important factor contributing to the demise of coral reefs around the island.
    Description: We would like to thank the Albion Fisheries Research Centre, Ministry of Fisheries, Government of Mauritius for providing the long-term benthic community dataset without which this work would not have been possible. Jennifer Elliott expresses her deepest gratitude to the members of her advisory committee, Peter Edmunds, Tarik Gouhier, Brian Helmuth and Steve Vollmer for their thoughtful inputs during the execution of this work. This is contribution number 384 from the Marine Science Center at Northeastern University.
    Keywords: Coral morphology ; Coral bleaching ; Coral reef monitoring ; nMDS ; Human impacts
    Repository Name: Woods Hole Open Access Server
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 5625-5632 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Bulk glasses in the (As0.4S0.6)100−xAux system have been prepared by melt-quenching in air. Homogeneous glasses were limited in composition up to 0.5 at. % Au and precipitation of pure Au particles was observed above 0.5 at. %. The physical properties have been studied and compared with those of Ag-doped bulk glasses. The compositional trends of the density, Vickers hardness, and glass-transition temperature were found to be significantly different between the Au and Ag systems. The optical gap and activation energy of the Au-doped glasses were less than those of the Ag-doped glasses with the same dopant concentration. The Au atoms incorporated into As2S3 glass are suggested to be located in and/or between the As–S network and behave as neutral atoms or form some weak bond with surrounding S atoms, in contrast to Ag atoms that break up the network through the formation of Ag—S ionic bonds. An increase in the randomness of the As–S network structure with the addition of Au may mainly affect the electronic band structure of the Au-doped glasses. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: To understand the nature of Ag-rich chalcogenide glasses, the optical, electrical, and structural properties of evaporated amorphous (Ge0.3S0.7)100−xAgx and (Ge0.3Se0.7)100−yAgy films have been examined and compared with each other over a wide compositional range in Ag content. The maximum Ag content for the amorphous films was 67 at. % for the S-based system and 40 at. % for the Se-based system. The physical properties of both systems depended significantly on the Ag content but the compositional trends resembled each other. All the photoinduced and thermally induced phenomena observed for the S-based system were also observed for the Se-based system but with the compositional ranges shifted to lower Ag concentration: the photo- and thermal bleachings (0≤y〈22 for the Se-based system, 0≤x〈40 for the S-based system), the photoinduced surface deposition (PSD) of metallic Ag phenomenon, and the phase separation on annealing (25〈y≤40, 50〈x≤67). The Se-based system was found to exhibit the PSD phenomenon at low Ag concentrations where the S-based system never exhibits this effect. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 270-273 (Aug. 2004), p. 2158-2163 
    ISSN: 1013-9826
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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