Sea ice draft in the Weddell Sea, measured by upward looking sonars

Behrendt, Axel; Dierking, Wolfgang; Fahrbach, Eberhard; Witte, Hannelore

doi:10.5194/essd-5-209-2013

Cited by 65 publications

(41 citation statements)

References 29 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…We excluded two even more extreme values of 17.8 and 57.5 from the computation of the average R value. These extremes belong to medium thick sea ice (0.89 m and 1.15 m) with a very thin snow cover (0.05 m and 0.02 m) for which we obtain sea-ice thickness values of 0.72 m and 0.84 m, respectively, using Equation (9).…”

Section: Empirical Approaches From In Situ Measurements (Oc2013)mentioning

confidence: 99%

“…I " F ρ water ρ water´ρi ce (9) In order to evaluate whether Equations (8) and (9) provide reasonable estimates of the sea-ice thickness we computed R, ρi ce , and the sea-ice thickness for in situ measurements of the following Antarctic expeditions: GLOBEC in 2002 [44], ARISE in 2003 [45], ISPOL in 2004 [46], SIMBA in 2007 [47] and SIPEX-I in 2007 [48]. The majority of the in situ measurements carried out during these cruises took place in September/October.…”

Section: Empirical Approaches From In Situ Measurements (Oc2013)mentioning

confidence: 99%

See 1 more Smart Citation

Antarctic Sea-Ice Thickness Retrieval from ICESat: Inter-Comparison of Different Approaches

2016

View full text Add to dashboard Cite

Accurate circum-Antarctic sea-ice thickness is urgently required to better understand the different sea-ice cover evolution in both polar regions. Satellite radar and laser altimetry are currently the most promising tools for sea-ice thickness retrieval. We present qualitative inter-comparisons of winter and spring circum-Antarctic sea-ice thickness computed with different approaches from Ice Cloud and land Elevation Satellite (ICESat) laser altimeter total (sea ice plus snow) freeboard estimates. We find that approach A, which assumes total freeboard equals snow depth, and approach B, which uses empirical linear relationships between freeboard and thickness, provide the lowest sea-ice thickness and the smallest winter-to-spring increase in seasonal average modal and mean sea-ice thickness: A: 0.0 m and 0.04 m, B: 0.17 and 0.16 m, respectively. Approach C uses contemporary snow depth from satellite microwave radiometry, and we derive comparably large sea-ice thickness. Here we observe an unrealistically large winter-to-spring increase in seasonal average modal and mean sea-ice thickness of 0.68 m and 0.65 m, respectively, which we attribute to biases in the snow depth. We present a conceptually new approach D. It assumes that the two-layer system (sea ice, snow) can be represented by one layer. This layer has a modified density, which takes into account the influence of the snow on sea-ice buoyancy. With approach D we obtain thickness values and a winter-to-spring increase in average modal and mean sea-ice thickness of 0.17 m and 0.23 m, respectively, which lay between those of approaches B and C. We discuss retrieval uncertainty, systematic uncertainty sources, and the impact of grid resolution. We find that sea-ice thickness obtained with approaches C and D agrees best with independent sea-ice thickness information-if we take into account the potential bias of in situ and ship-based observations.

show abstract

Section: Empirical Approaches From In Situ Measurements (Oc2013)mentioning

confidence: 99%

Section: Empirical Approaches From In Situ Measurements (Oc2013)mentioning

confidence: 99%

Antarctic Sea-Ice Thickness Retrieval from ICESat: Inter-Comparison of Different Approaches

2016

View full text Add to dashboard Cite

show abstract

“…The sea ice coverage and thickness were estimated from four upward looking sonars (ULS), which were placed at about 100-150 m depth below the sea surface at the top of the oceanographic moorings. The ULS data processing technique is described by Strass (1998) with modifications introduced by Behrendt et al (2012).…”

Section: Other Environmental Parametersmentioning

confidence: 99%

Acoustic insights into the zooplankton dynamics of the eastern Weddell Sea

Cisewski

Strass

2016

Progress in Oceanography

View full text Add to dashboard Cite

The success of any efforts to determine the effects of climate change on marine ecosystems depends on understanding in the first instance the natural variations, which contemporarily occur on the interannual and shorter time scales. Here we present results on the environmental controls of zooplankton distribution patterns and behaviour in the eastern Weddell Sea, Southern Ocean. Zooplankton abundance and vertical migration are derived from the mean volume backscattering strength (MVBS) and the vertical velocity measured by moored acoustic Doppler current profilers (ADCPs), which were deployed simultaneously at 64°S, 66.5°S and 69°S along the Greenwich Meridian from February, 2005, until March, 2008 While these time series span a period of full three years they resolve hourly changes.A highly persistent behavioural pattern found at all three mooring locations is the synchronous diel vertical migration (DVM) of two distinct groups of zooplankton that migrate between a deep residence depth during daytime and a shallow depth during nighttime. The DVM was closely coupled to the astronomical daylight cycles. However, while the DVM was symmetric around local noon, the annual modulation of the DVM was clearly asymmetric around winter solstice or summer solstice, respectively, at all three mooring sites. DVM at our observation sites persisted throughout winter, even at the highest latitude exposed to the polar night. Since the magnitude as well as the relative rate of change of illumination is minimal at this time, we propose that the ultimate causes of DVM separated from the light-mediated proximal cue that coordinates it. In all three years, a marked change in the migration behaviour occurred in late spring (late October/early November), when DVM ceased. The complete suspension of DVM after early November is possibly caused by the combination of two factors: (1) increased availability of food in the surface mixed layer provided by the phytoplankton spring bloom, and (2) vanishing diurnal enhancement of the threat from visually oriented predators when the illumination is quasi-continuous during the polar and subpolar summer. 3Zooplankton abundance in the water column, estimated as the mean MVBS in the depth range 50 -300 m, was highest end of summer and lowest mid to end winter on the average annual cycle. However, zooplankton abundance varied several-fold between years and between locations. Based on satellite and in situ data of chlorophyll and sea ice as well as on hydrographic measurements, the interannual and spatial variations of zooplankton mean abundance can be explained by differences in the magnitude of the phytoplankton spring bloom, which develops during the seasonal sea ice retreat. Whereas the vernal ice melt appears necessary to stimulate the blooming of phytoplankton, it is not the determinator of the blooms magnitude, its areal extent and duration. A possible explanation for the limitation of the phytoplankton bloom in some years is top-down control. We hypothesize that the phytoplankton spring ...

show abstract

“…This is due to the lack of systematic sea-ice thickness measurements in the Southern Hemisphere. There are only few in situ data sets from upwardlooking sonars (only Weddell Sea; e.g., Harms et al, 2001;Behrendt et al, 2013), drillings (e.g., Lange and Eicken, 1991;Ozsoy-Cicek et al, 2013;Wadhams et al, 1987;Perovich et al, 2004), electromagnetic methods (Haas, 1998;Weissling et al, 2011;Haas et al, 2008) and airborne altimetry (e.g., Dierking, 1995;Leuschen et al, 2008). Those data are distributed unevenly in location, coverage and time and do not allow for the estimation of seasonal and interannual sea-ice volume changes.…”

Section: Introductionmentioning

confidence: 99%

About the consistency between Envisat and CryoSat-2 radar freeboard retrieval over Antarctic sea ice

et al. 2016

View full text Add to dashboard Cite

Abstract. Knowledge about Antarctic sea-ice volume and its changes over the past decades has been sparse due to the lack of systematic sea-ice thickness measurements in this remote area. Recently, first attempts have been made to develop a sea-ice thickness product over the Southern Ocean from space-borne radar altimetry and results look promising. Today, more than 20 years of radar altimeter data are potentially available for such products. However, the characteristics of individual radar types differ for the available altimeter missions. Hence, it is important and our goal to study the consistency between single sensors in order to develop long and consistent time series. Here, the consistency between freeboard measurements of the Radar Altimeter 2 on board Envisat and freeboard measurements from the SyntheticAperture Interferometric Radar Altimeter on board CryoSat-2 is tested for their overlap period in 2011. Results indicate that mean and modal values are in reasonable agreement over the sea-ice growth season (May-October) and partly also beyond. In general, Envisat data show higher freeboards in the first-year ice zone while CryoSat-2 freeboards are higher in the multiyear ice zone and near the coasts. This has consequences for the agreement in individual sectors of the Southern Ocean, where one or the other ice class may dominate. Nevertheless, over the growth season, mean freeboard for the entire (regionally separated) Southern Ocean differs generally by not more than 3 cm (8 cm, with few exceptions) between Envisat and CryoSat-2, and the differences between modal freeboards lie generally within ±10 cm and often even below.

show abstract

Sea ice draft in the Weddell Sea, measured by upward looking sonars

Cited by 65 publications

References 29 publications

Antarctic Sea-Ice Thickness Retrieval from ICESat: Inter-Comparison of Different Approaches

Antarctic Sea-Ice Thickness Retrieval from ICESat: Inter-Comparison of Different Approaches

Acoustic insights into the zooplankton dynamics of the eastern Weddell Sea

About the consistency between Envisat and CryoSat-2 radar freeboard retrieval over Antarctic sea ice

Contact Info

Product

Resources

About