Small Icebergs Research Articles

A simulation of small to giant Antarctic iceberg evolution: Differential impact on climatology estimates

AbstractWe present a simulation of Antarctic iceberg drift and melting that includes small, medium‐sized, and giant tabular icebergs with a realistic size distribution. For the first time, an iceberg model is initialized with a set of nearly 7000 observed iceberg positions and sizes around Antarctica. The study highlights the necessity to account for larger and giant icebergs in order to obtain accurate melt climatologies. We simulate drift and lateral melt using iceberg‐draft averaged ocean currents, temperature, and salinity. A new basal melting scheme, originally applied in ice shelf melting studies, uses in situ temperature, salinity, and relative velocities at an iceberg's bottom. Climatology estimates of Antarctic iceberg melting based on simulations of small (≤2.2 km), “small‐to‐medium‐sized" (≤10 km), and small‐to‐giant icebergs (including icebergs >10 km) exhibit differential characteristics: successive inclusion of larger icebergs leads to a reduced seasonality of the iceberg meltwater flux and a shift of the mass input to the area north of 58°S, while less meltwater is released into the coastal areas. This suggests that estimates of meltwater input solely based on the simulation of small icebergs introduce a systematic meridional bias; they underestimate the northward mass transport and are, thus, closer to the rather crude treatment of iceberg melting as coastal runoff in models without an interactive iceberg model. Future ocean simulations will benefit from the improved meridional distribution of iceberg melt, especially in climate change scenarios where the impact of iceberg melt is likely to increase due to increased calving from the Antarctic ice sheet.

Impact of icebergs on net primary productivity in the Southern Ocean

Abstract. Productivity in the Southern Ocean (SO) is iron-limited, and supply of iron dissolved from aeolian dust is believed to be the main source from outside the marine environment. However, recent studies show that icebergs could provide a comparable amount of bioavailable iron to the SO as aeolian dust. In addition, small-scale areal studies suggest increased concentrations of chlorophyll, krill, and seabirds surrounding icebergs. Based on previous research, this study aims to examine whether iceberg occurrence has a significant impact on marine productivity at the scale of the SO, using remote sensing data of iceberg occurrences and ocean net primary productivity (NPP) covering the period 2002–2014. The impacts of both large and small icebergs are examined in four major ecological zones of the SO: the continental shelf zone (CSZ), the seasonal ice zone (SIZ), the permanent open ocean zone (POOZ), and the polar front zone (PFZ). We found that the presence of icebergs is associated with elevated levels of NPP, but the differences vary in different zones. Grid cells with small icebergs on average have higher NPP than other cells in most iron-deficient zones: 21 % higher for the SIZ, 16 % for the POOZ, and 12 % for the PFZ. The difference is relatively small in the CSZ where iron is supplied from meltwater and sediment input from the continent. In addition, NPP of grid cells adjacent to large icebergs on average is 10 % higher than that of control cells in the vicinity. The difference is larger at higher latitudes, where most large icebergs are concentrated. From 1992 to 2014, there is a significant increasing trend for both small and large icebergs. The increase was most rapid in the early 2000s and has leveled off since then. As the climate continues to warm, the Antarctic Ice Sheet is expected to experience increased mass loss as a whole, which could lead to more icebergs in the region. Based on our study, this could result in a higher level of NPP in the SO as a whole, providing a possible negative feedback for global warming in near future.

A review of iceberg and bergy bit hydrodynamic interaction with offshore structures

This paper establishes the current state of the art in the subject of iceberg and bergy bit motion during interaction and impact with offshore structures. Our particular interest in the present case is the influence of hydrodynamic interaction on change in velocity as small ice masses approach a larger structure in open water. Iceberg impacts are a design driver for structures located in offshore regions subject to drifting glacial ice. It is found that although many studies note that near-field effects influence the velocity and trajectory of drifting bergs prior to impact, the understanding of near-field hydrodynamic effects such as negative wave drift force, fluid cushioning, shadowing, reduction in impact velocity, and hydrodynamic damping, is incomplete. These effects are more obvious for small ice masses and bergy bits and although they have been identified qualitatively, there is very little quantitative information available. The inability to properly account for these phenomena generally leads to overestimation in impact velocity and consequently input impact energy. Better understanding of hydrodynamic interaction between small icebergs and offshore structures in very close proximity could improve load predictions by improving the estimation of input energy.

A Depolarization Ratio Anomaly Detector to Identify Icebergs in Sea Ice Using Dual-Polarization SAR Images

Icebergs represent hazards to maritime traffic and offshore operations. Satellite synthetic aperture radar (SAR) is very valuable for the observation of polar regions, and extensive work was already carried out on detection and tracking of large icebergs. However, the identification of small icebergs is still challenging especially when these are embedded in sea ice. In this paper, a new detector is proposed based on incoherent dual-polarization SAR images. The algorithm considers the limited extension of small icebergs, which are supposed to have a stronger cross-polarization and higher cross- over copolarization ratio compared to the surrounding sea or sea ice background. The new detector is tested with two satellite systems. First, RADARSAT-2 quad-polarimetric images are analyzed to evaluate the effects of high-resolution data. Subsequently, a more exhaustive analysis is carried out using dual-polarization ground-detected Sentinel-1a extra wide swath images acquired over the time span of two months. The test areas are in the east coast of Greenland, where several icebergs have been observed. A quantitative analysis and a comparison with a detector using only the cross-polarization channel are carried out, exploiting grounded icebergs as test targets. The proposed methodology improves the contrast between icebergs and sea ice clutter by up to 75 times. This returns an improved probability of detection.

Antarctic icebergs distributions 1992–2014

AbstractBasal melting of floating ice shelves and iceberg calving constitute the two almost equal paths of freshwater flux between the Antarctic ice cap and the Southern Ocean. The largest icebergs (>100 km2) transport most of the ice volume but their basal melting is small compared to their breaking into smaller icebergs that constitute thus the major vector of freshwater. The archives of nine altimeters have been processed to create a database of small icebergs (<8 km2) within open water containing the positions, sizes, and volumes spanning the 1992–2014 period. The intercalibrated monthly ice volumes from the different altimeters have been merged in a homogeneous 23 year climatology. The iceberg size distribution, covering the 0.1–10,000 km2 range, estimated by combining small and large icebergs size measurements follows well a power law of slope −1.52 ± 0.32 close to the −3/2 laws observed and modeled for brittle fragmentation. The global volume of ice and its distribution between the ocean basins present a very strong interannual variability only partially explained by the number of large icebergs. Indeed, vast zones of the Southern Ocean free of large icebergs are largely populated by small iceberg drifting over thousands of kilometers. The correlation between the global small and large icebergs volumes shows that small icebergs are mainly generated by large ones breaking. Drifting and trapping by sea ice can transport small icebergs for long period and distances. Small icebergs act as an ice diffuse process along large icebergs trajectories while sea ice trapping acts as a buffer delaying melting.

Large icebergs characteristics from altimeter waveforms analysis

AbstractLarge uncertainties exist on the volume of ice transported by the Southern Ocean large icebergs, a key parameter for climate studies, because of the paucity of information, especially on iceberg thickness. Using icebergs tracks from the National Ice Center (NIC) and Brigham Young University (BYU) databases to select altimeter data over icebergs and a method of analysis of altimeter waveforms, a database of 5366 icebergs freeboard elevation, length, and backscatter covering the 2002–2012 period has been created. The database is analyzed in terms of distributions of freeboard, length, and backscatter showing differences as a function of the iceberg's quadrant of origin. The database allows to analyze the temporal evolution of icebergs and to estimate a melt rate of 35–39 m·yr−1 (neglecting the firn compaction). The total daily volume of ice, estimated by combining the NIC and altimeter sizes and the altimeter freeboards, regularly decreases from 2.2 104km3 in 2002 to 0.9 104km3 in 2012. During this decade, the total loss of ice ( km3·yr−1) is twice as large as than the input ( km3·yr−1) showing that the system is out of equilibrium after a very large input of ice between 1997 and 2002. Breaking into small icebergs represents 80% ( km3·yr−1) of the total ice loss while basal melting is only 18% ( km3·yr−1). Small icebergs are thus the major vector of freshwater input in the Southern Ocean.

Characteristics of the meltwater field from a large Antarctic iceberg using

AbstractLarge tabular icebergs represent a disruptive influence on a stable water column when drifting in the open ocean. This is a study of one iceberg, C18A, encountered in the Powell Basin in the Weddell Sea in March 2009, formed from iceberg C18 ( ) originating from the Ross Ice Shelf in May 2002. C18A was lunate in shape with longest dimensions of . The meltwater field from C18A was characterized using from water samples collected near C18A (Near‐field, 0.4–2 km) and contrasted with a Far‐field comprised of samples from an Away site (19 km from C18A), a Control site (70 km away), and a region populated with small icebergs (Iceberg Alley, 175 km away). The in‐sample fractions of meteoric water were calculated relative in iceberg ice and Weddell Deep Water and converted to meteoric water height (m) and a percentage within 100 m depth bins. The Near‐field and Far‐field difference from surface to 200 m was %. The concentration of meteoric water dropped to approximately half that value below 200 m, approximate keel depth of the iceberg, although detectable to 600 m. From surface to 600 m, the overall difference was statistically significant ( ). From this, we estimate the Near‐field volume astern of the iceberg ( ) as a continuous source of meteoric water.

External influences on the Mertz Glacier Tongue (East Antarctica) in the decade leading up to its calving in 2010

AbstractThe Mertz Glacier Tongue (MGT) in East Antarctica lost ~55% of its floating length in February 2010, when it calved large tabular iceberg C28 (78 × 35 km). We analyze the behavior of the MGT over the preceding 12 years using a variety of satellite data (synthetic aperture radar and Landsat imagery and Ice, Cloud, and land Elevation Satellite laser altimetry). Contact of its northwestern tip with the eastern flank of shoals from 2002/2003 caused eastward deflection of the ice flow by up to ~47°. This change contributed to opening of a major rift system ~80 km to the south, along which iceberg C28 eventually calved. Paradoxically, the seabed contact may have also held the glacier tongue in place to delay calving by ~8 years. Our study also reveals the effects of other, more localized external influences on the MGT prior to calving. These include an abrupt sideways displacement of the glacier tongue front by at least ~145 m following an apparent collision with iceberg C08 in early 2002 and calving of numerous small icebergs from the advancing northwestern front due to the “chiseling” action of small grounded icebergs and seabed contact, resulting in the loss of ~36 km2 of ice from 2001 to 2006. The example of the MGT confirms the need for accurate bathymetry in the vicinity of ice shelves and glacier tongues and suggests that the cumulative effect of external factors might be critical to understanding and modeling calving events and ice shelf stability, necessarily on a case‐specific basis.

Small Target Detection and Noise Reduction in Marine Radar Systems

The most fundamental problem in radar signal is detection of an object or physical phenomenon. This problem became more challenging to the signal processing and radar communities to detect small targets (like small icebergs) in an oceanic environment. These small targets are difficult to detect for a marine radar system since they protrude only about a meter or so above the sea surface level. Unfortunately these small targets can cause severe damage to ships traveling in ice-ridden waters. In this paper, we make detection decision for small targets such as small fragments of icebergs using cross- correlation instead of statistical decision theory. Then we recover a transmitted signal using matched filter. Our simulation results give the exact result even when the received signal is attenuated more than 90%.

Marine radar observations of iceberg distribution in the summer Southern Ocean

AbstractDuring the 19th Chinese National Antarctic Research Expedition from December 2002 to January 2003, 1085 icebergs were observed along the cruise track within the range 58–68° S in the Southern Ocean using the marine radar on the R/V Xuelong. These icebergs were located mainly in the Ross Sea, Weddell Sea and Prydz Bay with lengths ranging from 68 to 8169 m. Both power-law and Weibull functions are applied to the curve fitting of cumulative probability distribution of iceberg length in each region. The results reveal that the power-law function underestimates the measured data in the middle of the data, but overestimates them for both the smallest and largest iceberg sizes, whereas the Weibull function underestimates the measured data when iceberg length is large enough. To reduce the relative error increasing with iceberg length, the Weibull function is used only in fitting to iceberg lengths less than a threshold value of iceberg size (Lt) and the power-law function is used in fitting to iceberg lengths >Lt. The improved curve fits show a good correlation over the full range of the data. This clearly reveals that an upper limit of iceberg length exists in the good agreement between the Weibull function and the measured data, which is attributed to different thermodynamic effects on calving processes and subsequent modification of large and small icebergs. In addition, iceberg size in Prydz Bay increases and then decreases when approaching the Amery Ice Shelf as a result of bergy bits and growlers calved from large icebergs in front of the ice shelf.

Antarctic icebergs distributions, 2002–2010

Interest for icebergs and their possible impact on southern ocean circulation and biology has increased during the recent years. While large tabular icebergs are routinely tracked and monitored using scatterometer data, the distribution of smaller icebergs (less than some km) is still largely unknown as they are difficult to detect operationally using conventional satellite data. In a recent study, Tournadre et al. (2008) showed that small icebergs can be detected, at least in open water, using high resolution (20 Hz) altimeter waveforms. In the present paper, we present an improvement of their method that allows, assuming a constant iceberg freeboard elevation and constant ice backscatter coefficient, to estimate the top‐down iceberg surface area and therefore the distribution of the volume of ice on a monthly basis. The complete Jason‐1 reprocessed (version C) archive covering the 2002–2010 period has been processed using this method. The small iceberg data base for the southern ocean gives an unprecedented description of the small iceberg (100 m–2800 m) distribution at unprecedented time and space resolutions. The iceberg size, which follows a lognormal distribution with an overall mean length of 630 m, has a strong seasonal cycle reflecting the melting of icebergs during the austral summer estimated at 1.5 m/day. The total volume of ice in the southern ocean has an annual mean value of about 400 Gt, i.e., about 35% of the mean yearly volume of large tabular icebergs estimated from the National Ice Center database of 1979–2003 iceberg tracks and a model of iceberg thermodynamics. They can thus play a significant role in the injection of meltwater in the ocean. The distribution of ice volume which has strong seasonal cycle presents a very high spatial and temporal variability which is much contrasted in the three ocean basins (South Atlantic, Indian and Pacific oceans). The analysis of the relationship between small and large (>5 km) icebergs shows that a majority of small icebergs are directly associated with the large ones but that there are vast regions, such as the eastern branch of the Wedell Gyre, where the transport of ice is made only through the smaller ones.

Iceberg signatures and detection in SAR images in two test regions of the Weddell Sea, Antarctica

AbstractA pixel-based methodology has been established for automatic identification of icebergs in satellite synthetic aperture radar (SAR) images acquired during different seasons and for different sea- ice conditions. This includes, in particular, smaller icebergs (longitudinal axis 100 m to 18.5 km). Investigations were carried out for two test regions located in the Weddell Sea, Antarctica, using images of the Envisat Advanced SAR (ASAR) at HH polarization and of the European Remote-sensing Satellite-2 (ERS-2) SAR (VV-polarized). From the former, a sequence of Image Mode and Wide Swath Mode data are available for the whole of 2006. The ERS data were acquired around the tip of the Antarctic Peninsula in spring and summer months of the years 2000-03. The minimum size of icebergs that could be identified in the IM images was <0.02 km2. Radar backscattering coefficients of icebergs, sea ice and open water were determined separately. We demonstrate that the error in separating icebergs from their surroundings (sea ice or open water) depends on meteorological, oceanographic and sea-ice conditions. Also the pre-processing of the SAR images (e.g. speckle reduction) influences iceberg recognition. Differences in detection accuracy as a function of season could not be substantiated for our test sites, but have in general to be taken into account, as results of other investigations indicate.

A brief study of the force balance between a small iceberg, the ocean, sea ice, and atmosphere in the Weddell Sea

Abstract Icebergs are an important source of freshwater to the Weddell Sea. A unique set of oceanographic and other observations made during the Maud Rise Nonlinear Equation of State Study around one of the small icebergs, ubiquitous in the winter Weddell Sea, give us the opportunity to examine the dynamics of the interaction between an iceberg and the ocean. The iceberg was mapped using radar ranges and bearings from our ship, the research icebreaker Nathaniel Palmer, and found to be about 200 m wide above the water with a draft estimated to be 219 m. For this size, form drag dominates skin friction in both the atmosphere and ocean. Sea ice was ridged against the upwind side of the iceberg and thin sea ice and open water were on the downwind side. The iceberg was drifting 0.14 m s− 1, or about 3% of the wind speed and 23° to the left. An automated CTD operating through the ship's moon-pool was used to measure temperature and salinity profiles upstream, downstream, and to the side of the iceberg. These profiles show a mixed upper layer 150 m deep upstream and 60 m deep downstream of the iceberg. The difference in density across the pycnocline was 0.05 kg m− 3, which for the average pycnocline depth of 105 m and size of the iceberg corresponds to an interfacial internal wave speed equal to 0.166 m s− 1. This and the upstream–downstream difference in pycnocline depth are consistent with a ± 45 m internal wave wake being generated by the motion of the iceberg. We estimate the contributions to total water drag from form drag and generation of the internal wake to be about equal. Consistent with theory, a qualitative argument using the observed pycnocline displacements suggests that internal wake drag should be a maximum when iceberg drafts are near the pycnocline depth. The drift rate of the iceberg (and sea ice) relative to wind speed was near the relative drift rate for the Weddell Sea ice we encountered during MaudNESS, but three times greater than what would result from a pure balance of atmospheric form drag against ocean form drag on the iceberg. Therefore, the force of sea ice on the iceberg, evidenced by ridging on the upwind side was dominant in moving the iceberg with the sea ice drift speed. The force transmitted through the sea ice required to drive the ice at the observed rate would be equivalent to the wind stress acting on an area of sea ice of 7.5 km2. Maximum ridging forces in the 0.5 m thick sea ice should be adequate to drive the iceberg with this 219-m draft at 0.56 m s− 1, much more than the observed drift rate but similar to the sea ice velocities during Weddell Sea storms.

Isolated ice floe impacts

Abstract This paper summarizes all available data related to ice floe impacts on structures. These data include laboratory tests, forces on several bridge piers (Hondo, Pembina, Rideau), forces from small icebergs impacting dedicated test structures (Grappling Island, Newmans Cove), first-year and multi-year ice impacts on the offshore structure Molikpaq, and the Hans Island experiments. The data represent ice masses covering ten orders of magnitude and impact forces covering seven orders of magnitude. The impacts were analyzed using various simple approaches and it was found that the impact force was best related to the kinetic energy of the floe at impact. This energy ranged over thirteen orders of magnitude in value. There was a good correlation of the impact force (F) with the energy (E) at impact with a function form F = A E0.532 where F is in MN and E is in GJ. The coefficient A was determined to be 61.7 for the “likely” impact force and 388 for the upper-limit impact force. The reason for this wide range is discussed and related to the wide range of ice strength and failure modes of the ice. The equation is applied to provide guidance on the forces for four different scenarios: (1) river ice impacts on bridge piers, (2) multi-year ice floe impacts on offshore drilling platforms, (3) isolated impact on the leg of a jack-up structure, and (4) impact forces on a Dynamically Positioned drillship with optimization of ice management. The analysis shows that as a rule-of-thumb, the likely impact force in kN is approximately the product of the square root of the mass (in kg) multiplied by the ice floe speed at impact (in m/s).

Observation and parameterization of small icebergs: Drifting breakwaters in the southern ocean

The variability of small-size iceberg distributions is revealed from a novel analysis of satellite altimeter data. A strong annual cycle is modulated by pulse-like events confined to single ocean basins, with dense iceberg populations in the South Atlantic in 2004–2005, and in the South Pacific in 2008. Anomalies in sea surface temperatures of the order of 1 °C may be related to the iceberg distribution. Icebergs also appear very strongly associated with anomalies in the heights of ocean waves. A preliminary parameterization of wave blocking by icebergs significantly reduces wave model errors in the region south of 45° South, and has a perceptible influence on all the west coasts of the Southern hemisphere.

Free-drifting icebergs as sources of iron to the Weddell Sea

In recent years glaciers on the Antarctic Peninsula have retreated, resulting in loss of mass from ice shelves and increased supply of icebergs to the Southern Ocean. Free-drifting icebergs may serve as an important source of Fe to surrounding waters. We measured concentrations of dissolved Fe and Fe content of suspended particulate material (via flow injection-chemiluminescence and ICP-MS, respectively) in the waters surrounding several icebergs during cruises to the Scotia and Weddell Seas in June 2008 and March 2009. Surface dissolved Fe (DFe) concentrations varied from 0.58 to 2.92 nM and were elevated up to 60% at some stations <1 km from the nearest iceberg. The highest surface DFe concentrations were associated with low salinity waters, regardless of distance to the iceberg. Depth profiles revealed surface enrichment at most stations >10 km from the icebergs, indicating general Fe enrichment in the lower-salinity surface layer. However surface DFe within 1 km of the iceberg was similar to that measured at depths below the draft of the iceberg, a feature that may result from upwelling of circumpolar deep water caused by basal melting at the face of the iceberg. Iron concentrations in ice collected following calving events were highly variable (4-600 nM) but were elevated above concentrations in seawater. Particulate Fe (normalized to particulate P) in suspended particulate material was up to 20-fold higher within 0.6 km of two large tabular icebergs, but no enrichment was observed at two smaller icebergs. Iron:phosphorus ratios of suspended particulate material were also higher in deeper (40 m) waters compared to shallow (ca. 15 m) waters at the iceberg face. Iron release appeared to be episodic, producing a spatially heterogeneous environment around icebergs. This source term may increase in coming years as Antarctic ice shelves degrade further, potentially impacting the ecology and biogeochemistry of low-Fe waters of the Southern Ocean.

Phytoplankton composition and abundance in relation to free-floating Antarctic icebergs

Free-drifting icebergs in the Weddell Sea are expected to affect the surrounding marine ecosystem. Sampling associated with iceberg C-18a, a large tabular, free-drifting iceberg in the NW Weddell Sea, carried out from 10 March to 7 April 2009, was designed to test the hypothesis that the iceberg's presence modified phytoplankton composition and abundance. Areas that define a gradient of possible iceberg influence were sampled for phytoplankton: stations close (<1 km) and far (18 km) from iceberg C-18a, an area with numerous small icebergs, Iceberg Alley, and a control site 74 km away. Quantitative samples were obtained from Niskin bottles and counted with an inverted microscope for species abundance. Qualitative samples were collected with nets from the ship's seawater intake. Taxonomic determinations were performed with light and electron microscopy. Overall, diatoms dominated in the mixed layer (surface-∼40 m) and unidentified small flagellated and coccid cells at depth (∼100 m). Fragilariopsis nana, a diatom 2.4–15.5 μm in length, dominated numerically the phytoplankton and was most abundant at the control area. The iceberg's effect on phytoplankton composition was consistent with the hypothesis that they facilitate phytoplankton communities enriched in diatoms, as found in other productive areas of Antarctica. Near the iceberg, diatoms were most abundant, principally at depth, while small flagellate concentration diminished. However, total phytoplankton abundance was lowest at Iceberg Alley in the area of highest meltwater contribution, as indicated by low mean temperature in the mixed layer, and highest at the control site. These results suggest that during austral fall, low growth or high zooplankton grazing could be counteracting the positive effect by icebergs on phytoplankton biomass, otherwise observed in summer months.

Deformation and failure of the ice bridge on the Wilkins Ice Shelf, Antarctica

AbstractA narrow bridge of floating ice that connected the Wilkins Ice Shelf, Antarctica, to two confining islands eventually collapsed in early April 2009. In the month preceding the collapse, we observed deformation of the ice bridge by means of satellite imagery and from an in situ GPS station. TerraSAR-X images (acquired in stripmap mode) were used to compile a time series. The ice bridge bent most strongly in its narrowest part (westerly), while the northern end (near Charcot Island) shifted in a northeasterly direction. In the south, the ice bridge experienced compressive strain parallel to its long axis. GPS position data were acquired a little south of the narrowest part of the ice bridge from 19 January 2009. Analysis of these data showed both cyclic and monotonic components of motion. Meteorological data and re-analysis of the output of weather-prediction models indicated that easterly winds were responsible for the cyclic motion component. In particular, wind stress on the rough ice melange that occupied the area to the east exerted significant pressure on the ice bridge. The collapse of the ice bridge began with crack formation in the southern section parallel to the long axis of the ice bridge and led to shattering of the southern part. Ultimately, the narrowest part, only 900 m wide, ruptured. The formation of many small icebergs released energy of &gt;125 ×106 J.

Iceberg detection in open water by altimeter waveform analysis

Small icebergs (edge lengths &lt;1 km) are difficult to detect and track. In a recently published study, it was demonstrated that small targets (ships, islets,…) emerging from the sea can be detected by the analysis of high‐rate altimeter waveforms. The analysis of Jason altimeter data revealed that small icebergs also have a detectable signature in the thermal noise part of the altimeter waveforms for open water. These signatures are very similar to that of transponders and are almost deterministic. An automated method based on the detection of parabolic shapes in the thermal part of the waveforms by analysis of the convolution product with a filter has been developed and applied to 1 year of Jason high‐rate waveform data. In addition, the minimum height and backscatter of the iceberg can also be estimated by this method. More than 8000 icebergs were identified between December 2004 and November 2005 in the open water around Antarctica. The annual distribution of icebergs presents a well‐defined tripole structure, with maxima near the Antarctic Peninsula, the West Ice Shelf, and the Ross Sea. This distribution is in good agreement with the main trends in Antarctic iceberg motion presented in the scientific literature. The high concentration of icebergs propagating from the Antarctic Peninsula seems to confirm the importance of this region in the discharge of Antarctic ice into the ocean. The results clearly show that altimeter data are a powerful tool in the study of the distribution of small icebergs largely inaccessible by other satellite means. The principle of detection of icebergs by altimeter is quite simple and could be easily applied to the existing archive of all the past and present altimeters (ERS, Topex/Poseidon, Jason, and Envisat) to create a database covering more than 13 years that could improve our knowledge of climate change in Antarctica.

On the Current Location of the Byrd “Snow Cruiser” and Other Artifacts from Little America I, II, III and Framheim

Analysis of maps, sightings, satellite images, and aerial photos indicates that a ∼105 km2 section of the eastern side of the Bay of Whales, containing the buried remains of several bases from the “heroic era” of Antarctic exploration, calved away around late 1961. A small iceberg from this event (or closely spaced events), with the remains of Little America III exposed in the ice face, was sighted in February 1963 near the western Ross Ice Shelf front. Satellite observations of more recent calving events show that most small icebergs from the Bay of Whales area drift westward and repeatedly impact the shelf, fragmenting as they move. This implies that a number of artifacts from the bases, such as the 1939–1941 Snow Cruiser, are likely strewn along the seabed near the 1962 ice-front position. Major Ross Ice Shelf calvings of 2000 and 2002 have removed the ice cover from parts of the 1962 front area for the first time since that period. Thus a search for the artifacts is technically more feasible for the next few years until shelf ice flow re‐covers the area.