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Influence of ice thickness and surface properties on light transmission through A rctic sea ice

View Article: PubMed Central - PubMed

ABSTRACT

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.

No MeSH data available.


Related in: MedlinePlus

Physical measurements taken from the ROV during the colocated pole survey: (a) Light transmittance along the survey track. Red circles show positions of numbered marker poles. (b) Ice draft as measured along track with upward looking multibeam sonar. (c) Surface albedo extracted from the image. Blue dots indicate spot data, while lines depict data averaged over circles with different diameters. (d) Ice Draft as derived from the DVL (blue dashed line) and measured by the center beam of the multibeam sonar (red line). (e) Light transmittance measured by the radiance (red line) and irradiance (blue dashed line) sensors along the survey.
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jgrc21358-fig-0003: Physical measurements taken from the ROV during the colocated pole survey: (a) Light transmittance along the survey track. Red circles show positions of numbered marker poles. (b) Ice draft as measured along track with upward looking multibeam sonar. (c) Surface albedo extracted from the image. Blue dots indicate spot data, while lines depict data averaged over circles with different diameters. (d) Ice Draft as derived from the DVL (blue dashed line) and measured by the center beam of the multibeam sonar (red line). (e) Light transmittance measured by the radiance (red line) and irradiance (blue dashed line) sensors along the survey.

Mentions: Results from the pole survey transect are shown in Figure 3. Light transmittance was between 0.02 and 0.10 along the transect: In the vicinity of the first pole, light transmittance was high due to a melt pond, but it dropped quickly under the influence of a ridge visible on the surface. After crossing the ridge, light levels increased due to a reduction in ice draft from 2 to 1.2m before dropping again due to the thickest ice observed in the transect, between poles 2 and 3 with a draft of up to 2.5 m. The two clear peaks of light‐transmittance near poles 4 and 5, respectively can be attributed to the crossing beneath two melt ponds at the surface (Figure 3a). The final increase at the end of the survey is caused by the approach to a third, larger melt pond.


Influence of ice thickness and surface properties on light transmission through A rctic sea ice
Physical measurements taken from the ROV during the colocated pole survey: (a) Light transmittance along the survey track. Red circles show positions of numbered marker poles. (b) Ice draft as measured along track with upward looking multibeam sonar. (c) Surface albedo extracted from the image. Blue dots indicate spot data, while lines depict data averaged over circles with different diameters. (d) Ice Draft as derived from the DVL (blue dashed line) and measured by the center beam of the multibeam sonar (red line). (e) Light transmittance measured by the radiance (red line) and irradiance (blue dashed line) sensors along the survey.
© Copyright Policy - creativeCommonsBy-nc-nd
Related In: Results  -  Collection

License
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getmorefigures.php?uid=PMC5016760&req=5

jgrc21358-fig-0003: Physical measurements taken from the ROV during the colocated pole survey: (a) Light transmittance along the survey track. Red circles show positions of numbered marker poles. (b) Ice draft as measured along track with upward looking multibeam sonar. (c) Surface albedo extracted from the image. Blue dots indicate spot data, while lines depict data averaged over circles with different diameters. (d) Ice Draft as derived from the DVL (blue dashed line) and measured by the center beam of the multibeam sonar (red line). (e) Light transmittance measured by the radiance (red line) and irradiance (blue dashed line) sensors along the survey.
Mentions: Results from the pole survey transect are shown in Figure 3. Light transmittance was between 0.02 and 0.10 along the transect: In the vicinity of the first pole, light transmittance was high due to a melt pond, but it dropped quickly under the influence of a ridge visible on the surface. After crossing the ridge, light levels increased due to a reduction in ice draft from 2 to 1.2m before dropping again due to the thickest ice observed in the transect, between poles 2 and 3 with a draft of up to 2.5 m. The two clear peaks of light‐transmittance near poles 4 and 5, respectively can be attributed to the crossing beneath two melt ponds at the surface (Figure 3a). The final increase at the end of the survey is caused by the approach to a third, larger melt pond.

View Article: PubMed Central - PubMed

ABSTRACT

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.

No MeSH data available.


Related in: MedlinePlus