Sea Ice Mass Balance Research Articles

Sea ice mass balance observations from the North Pole Environmental Observatory

In recent years the periphery of the Arctic sea ice cover has undergone significant changes, with a reduction in summer ice extent, a thinning of the ice, and a shift from multiyear to first year ice. Here we examine sea ice conditions during nine summers between 2000 and 2013 in the interior of the ice pack, using autonomous measurements of sea ice mass balance deployed near the North Pole. Results exhibit no definitive trends. There is large interannual variability, with surface melt ranging from 0.02 m to 0.50 m and bottom melt from 0.10 m to 0.57 m. The largest amounts of bottom melt have occurred in the past few years. For all 9 years the ice at the end of the melt season was at least 1.2 m thick.

Multiyear sea ice thermal regimes and oceanic heat flux derived from an ice mass balance buoy in the Arctic Ocean

The conductive and oceanic heat fluxes and the mass balance of sea ice were investigated utilizing an ice mass balance buoy (IMB) deployed in the Arctic Ocean. After IMB deployment, the ice thinned from 1.95 m in late August to 1.46 m by mid‐October 2008. From then on, ice growth until mid‐June 2009 increased the ice thickness to 3.12 m. The ice temperature and consequently the conductive heat flux at the ice surface exhibited persistent high‐frequency variations due to diurnal and synoptic‐scale atmospheric forcing. These signals propagated downward with damped magnitude and temporal lag. The competition of oceanic and conductive heat flux dominated the low‐frequency variations of ice growth. However, high‐frequency variations in ice growth were controlled largely by the oceanic heat flux. From mid‐November 2008 to mid‐June 2009, the average oceanic heat flux along a track from 86.2°N, 115.2°W to 84.6°N, 33.9°W was 7.1 W/m2. This was in agreement with that derived from an IMB deployed in 2005, about 1.5° to the north of our buoy. We attributed the relatively high oceanic heat flux (10–15 W/m2) observed during autumn and early winter to summer warming of the surface ocean. Upward mixing of warm deep water, as observed when our buoy drifted over the shallow region of the Lomonosov Ridge (85.4°–85.9°N, 52.2°–66.4°W), demonstrated the impact of bathymetry on the oceanic heat flux under ice cover, and consequently on the basal ice mass balance.

Improved Retrieval of Sea Ice Thickness and Density from Laser Altimeter

The sensitivity of weather and climate system to sea ice thickness (SIT) in the Arctic is recognised from various studies. Decrease of SIT will affect atmospheric circulation, temperature, precipitation and wind speed in the Arctic and remotely. Ice thermodynamics and dynamic properties depend strongly on ice and snow thickness. The heat transfer through ice critically depends on ice thickness. Long term accurate SIT records with corresponding uncertainties are required for improved seasonal weather forecast and estimate of the sea ice mass balance. Satellite radar and Laser Altimeter (LA) provide long term records of sea ice freeboard. Assuming isostatic equilibrium, SIT is retrieved from the freeboard, extracted from radar altimeter (RA) or LA, where the snow depth, density, ice and water density are input variables in the equation for hydrostatic equilibrium to derive SIT from LA or RA. Different input variables (snow depth, density, ice and water density) with unknown accuracy have been applied from various authors to retrieve SIT and Sea Ice Draft (SID) from RA or LA, leading to not comparative results. Sea ice density dependence on ice type, thermodynamic properties and freeboard is confirmed with different studies. Sensitivity analyses confirm the great impact of sea ice density, snow depth and density on accuracy of the retrieved SIT and the importance of inserting variable ice density (VID) in the equation for hydrostatic equilibrium for more accurate SIT retrieval, weather and climate forecast. The impact of sea ice density and snow depth and density on retrieved SIT from the freeboard derived from LA and RA have been analyzed in this study using the equation for hydrostatic equilibrium, statistical and sensitivity analyses. An algorithm is developed to convert the freeboard, derived from LA in SIT, inserting VID in the equation for hydrostatic equilibrium. The algorithm is validated with field, laboratory studies and collocated SIT retrieved from RA on board Envisat. The accuracy of the developed algorithm is analyzed, using statistical and uncertainty analyses. It is found that the uncertainty of the retrieved SIT from LA is decreased 7.6 times (from rhi = 59 cm for fixed ice density) if variable ice density is inserted in the equation for hydrostatic equilibrium. The SIT, which has been retrieved from the freeboard derived from LA is validated with collocated SIT derived from RA2 on Envisat, using variable ice density. The bias of the mean SIT derived from LA and RA has been reduced from -1.1 m to about one millimeter when VID is applied to retrieve SIT from LA and RA. The results and algorithms, discussed in this paper are essential contribution to SIT and SID retrieval, satellite remote sensing, cryosphere, meteorology and improved weather and climate forecast.

A Novel and Low-Cost Sea Ice Mass Balance Buoy

Abstract The understanding of sea ice mass balance processes requires continuous monitoring of the seasonal evolution of the ice thickness. While autonomous ice mass balance (IMB) buoys deployed over the past two decades have contributed to scientists' understanding of ice growth and decay processes, deployment has been limited, in part, by the cost of such systems. Routine, basinwide monitoring of the ice cover is realistically achievable through a network of reliable and affordable autonomous instrumentation. This paper describes the development of a novel autonomous platform and sensor that replaces the traditional thermistor strings for monitoring temperature profiles in the ice and snow using a chain of inexpensive digital temperature chip sensors linked by a single-wire data bus. By incorporating a heating element into each sensor, the instrument is capable of resolving material interfaces (e.g., air–snow and ice–ocean boundaries) even under isothermal conditions. The instrument is small, low cost, and easy to deploy. Field and laboratory tests of the sensor chain demonstrate that the technology can reliably resolve material boundaries to within a few centimeters. The discrimination between different media based on sensor thermal response is weak in some deployments and efforts to optimize the performance continue.

Warming of the Intermediate Atlantic Water of the Arctic Ocean in the 2000s

Abstract This analysis evaluates the thermal state of the intermediate (depth range of 150–900 m) Atlantic Water (AW) of the Arctic Ocean, beginning in the 1950s and with particular focus on the transition from the 1990s to the 2000s and on changes during the 2000s. Using an extensive array of observations, the authors document AW warming trends across various time scales and demonstrate that the 2000s were exceptionally warm, with no analogy since the 1950s or probably in the history of instrumental observations in the Arctic Ocean. Warming in the recent decade was dominated by a warm AW pulse in addition to the underlying trend. Since 1997, the Canadian Basin experienced a faster warming rate compared with the Eurasian Basin. The relative role of the AW warmth in setting the net energy flux and mass balance of the Arctic sea ice is still under debate. Additional carefully orchestrated field experiments are required in order to address this question of ongoing Arctic climate change.

First Observations of Energy Budget and Bulk Fluxes at Ny Ålesund (Svalbard) during a 2010 Transition Period as Analyzed with the BEAR Station

A small-size meteorological mast, BEAR (Budget of Energy for Arctic regions) has been developed as a part of a new autonomous buoy for monitoring the sea ice mass balance. BEAR complements observations of the thickness and thermodynamic properties of the ice/snow pack determined by the so-called Ice-T (Ice-Thickness) buoy, giving access to bulk fluxes and energy budget at the surface, using meteorological measurements. The BEAR mast has been tested with success during ten days in April-May 2010 at Ny Alesund, in the Svalbard archipelago (Norway) showing that meteorological data were close to measurements at the same level of the Italian Climate Change Tower (CCT) from the ISAC-CNR. A discussion is undertaken on bulk fluxes determination and uncertainties. Particularly, the strategy to systematically use different relevant fluxes parameterizations is pointed out to explore flux range uncertainty before to analyze energy budget. Net radiation, bulk fluxes and energy budget are estimated using as average 10 minutes, 24 hours and the ten days of the experiment. The observation period was very short, but we observe a spring transition when the net radiation begins to warm the surface while the very small turbulent heat flux cools the surface.

Reflection and transmission of irradiance by snow and sea ice in the central Arctic Ocean in summer 2010

Reflection and transmission of irradiance by the combined snow and sea ice layer were measured at an ice camp (ca. 10 days) and several short-term stations (ca. 2 h) established in the western sector of the Arctic Ocean above 80°N during the 2010 summer. These measurements were made with an intention to quantify the apparent optical properties of snow and sea ice, and to evaluate their roles in the mass balance of snow-covered sea ice in the High Arctic. The integrated 350–920 nm albedo ranged from 0.54 to 0.88, and was primarily dependent on the geophysical properties of snow, but not those of sea ice. This implies that all snow cover was still optically thick, even though snow melting had commenced at all measurement sites. For sea ice about 1.66 m thick and covered by 2.5–8.5 cm of snow at the ice camp, the integrated 350–920 nm transmittance ranged from 0.017 to 0.065. Rapid snow melting resulting from an event of slight drizzle doubled the available solar irradiance under the ice (from ca. 3.6 toca. 7.2 W·m–2), which further accelerated ice-bottom decay. During the measurement at the camp, the temporally averaged incident solar irradiance at 320–950 nm was 110.6 ± 33.6 W·m–2, 29.2 ± 2.9% of which was absorbed by snow and sea ice and utilized to melt snow and sea ice. The melting of snow and sea ice had a distinctly greater effect on the spectral reflection and transmission for the near-infrared spectrum than for the ultraviolet and visible spectra.Keywords: Sea ice; snow; solar irradiance; reflection; transmission; Arctic(Published: 30 March 2012)Citation: Polar Research 2012, 31, 17325, DOI: 10.3402/polar.v31i0.17325

The Arctic Ocean halocline and its interannual variability from 1997 to 2008

As a key structure to understand the role of the ocean on the sea ice mass balance, the Arctic Ocean halocline and its spatiotemporal variability require serious attention. In this paper, we are proposing a new definition of the halocline, which is based on the salinity gradient structure, taking into account both the salinity amplitude and the thickness of the halocline. The Brunt Vaisala frequency is used as the halocline stratification index. CTD data collected from 1997 to 2008 and coming from various sources (icebreaker cruises, drifting buoys, etc.) are used to determine the halocline, and its time and space variability during three time periods, with a special focus on three main regions of the Arctic Ocean: the Canada basin, the Makarov basin and the Amundsen basin. Observations reveal that the halocline in the Amundsen basin was always present and rather stable over the three time periods. In contrast, the Canada and Makarov basins' halocline became more stratified during the IPY than before, mainly because of surface water freshening. In addition, observations also confirmed the importance of the halocline thickness for controlling the stratification variability. Observations suggest that both large scale and small scale processes affect the halocline. Changes in surface salinity observed in the Makarov basin are more likely due to atmospheric variability (AO, Dipole Anomaly), as previously observed. More locally, some observations point out that salt/heat diffusion from the Atlantic water underneath and brine rejection during sea ice formation from above could be responsible for salt content variability within the halocline and, as a consequence, being influential for the variability of the halocline. In spite of the existence of interannual variability, the Arctic Ocean main stratification, characterized by a stable and robust halocline until now, suggested that the deep ocean had a limited impact on the mixed layer and on sea ice in actual conditions. The drastic changes observed in Arctic sea ice during this period (1997–2008) cannot be attributed to a weakening of the halocline that could trigger an enhanced vertical heat flux from the deep ocean.

Investigation of the thermodynamic processes of a floe-lead system in the central Arctic during later summer

Thermodynamic processes of a system involving a floe and a small lead in the central Arctic were investigated during the ice-camp period of the third Chinese National Arctic Research Expedition from 20 to 28 August,2008. The measurements included surface air temperatures above the floe,spectral albedo of the lead,seawater temperatures in the lead and under the ice cover,and the lateral and bottom mass balance of the floe. The surface air temperature at 1.15 m remained below 0℃throughout the observation period and sea ice had commenced its annual cycle of growth in response to autumn cooling during the study.The surface of the lead was frozen by 23 August,after which the spectral albedo of the thin-ice-covered lead in the band of 320-950 nm was 0.46 ±0.03,the seawater temperatures both in the lead and under the ice cover,as well as the vertical seawater-temperature gradient in the lead decreased gradually,and the oceanic heat under the ice was maintained at a low level approaching 0 W/m 2 . By the end of the measurement,the thickness of the investigated floe had reached its annual minimum,while the lateral of the floe was still in the melting phase,with a mean melting rate of 1.0 ±0.3 cm/d during the measurement,responding to an equivalent latent heat flux of 21 ±6 W/m 2 . The lateral melting of the floe had made a more significant contribution to the sea-ice mass balance than the surface and bottom melting in the end of August.

Antarctic sea-ice altimetry: scale and resolution effects on derived ice thickness distribution

AbstractThree ice type regimes at Ice Station Belgica (ISB), during the 2007 International Polar Year SIMBA (Sea Ice Mass Balance in Antarctica) expedition, were characterized and assessed for elevation, snow depth, ice freeboard and thickness. Analyses of the probability distribution functions showed great potential for satellite-based altimetry for estimating ice thickness. In question is the required altimeter sampling density for reasonably accurate estimation of snow surface elevation given inherent spatial averaging. This study assesses an effort to determine the number of laser altimeter ‘hits’ of the ISB floe, as a representative Antarctic floe of mixed first- and multi-year ice types, for the purpose of statistically recreating the in situ-determined ice-thickness and snow depth distribution based on the fractional coverage of each ice type. Estimates of the fractional coverage and spatial distribution of the ice types, referred to as ice ‘towns’, for the 5 km2 floe were assessed by in situ mapping and photo-visual documentation. Simulated ICESat altimeter tracks, with spot size ~70m and spacing ~170 m, sampled the floe’s towns, generating a buoyancy-derived ice thickness distribution. 115 altimeter hits were required to statistically recreate the regional thickness mean and distribution for a three-town assemblage of mixed first- and multi-year ice, and 85 hits for a two-town assemblage of first-year ice only: equivalent to 19.5 and 14.5 km respectively of continuous altimeter track over a floe region of similar structure. Results have significant implications toward model development of sea-ice sampling performance of the ICESat laser altimeter record as well as maximizing sampling characteristics of satellite/airborne laser and radar altimetry missions for sea-ice thickness.

Antarctic sea-ice extents and concentrations: comparison of satellite and ship measurements from International Polar Year cruises

AbstractAntarctic Sea Ice Processes and Climate (ASPeCt) ship-based ice observations, conducted during the Sea Ice Mass Balance in the Antarctic (SIMBA) and Sea Ice Physics and Ecosystem eXperiment (SIPEX) International Polar Year (IPY) cruises (September–October 2007), are used to validate remote-sensing measurements of ice extent and concentration. Observations include varied sea-ice types at and inside the ice edge of West (~90˚ W) and East (~120˚ E) Antarctica. Time series of Advanced Microwave Scanning Radiometer–Earth Observing System (AMSR-E) ice extents and US National Ice Center (NIC) ice edges were obtained for the 2007–08 periods bracketing the period these cruises were conducted. A comparison between passive microwave satellite imagery and ASPeCt observations of sea-ice concentration during two cruises was also performed. In 90˚W regions, the concentrated pack ice indicated good correlation between ship observations and passive microwave estimates of the ice concentration (R2 = 0.80). In the marginal zone of West Antarctica and over nearly the entire sea-ice zone of East Antarctica, correlation dropped to R2 < 0.60. These findings are consistent with other studies comparing passive microwave and ship observations and further verify that the East Antarctic sea-ice zone is more marginal in character. There are significant ice-edge differences between AMSR-E and NIC between late November 2007 and early March 2008 such that the AMSR-E sea-ice extent estimate is 1–2 × 106 km2 less than the NIC estimate.

The importance of wind-blown snow redistribution to snow accumulation on Bellingshausen Sea ice

AbstractSnow distribution is a dominating factor in sea-ice mass balance in the Bellingshausen Sea, Antarctica, through its roles in insulating the ice and contributing to snow-ice production. the wind has long been qualitatively recognized to influence the distribution of snow accumulation on sea ice, but the relative importance of drifting and blowing snow has not been quantified over Antarctic sea ice prior to this study. the presence and magnitude of drifting snow were monitored continuously along with wind speeds at two sites on an ice floe in the Bellingshausen Sea during the October 2007 Sea Ice Mass Balance in the Antarctic (SIMBA) experiment. Contemporaneous precipitation measurements collected on board the RVIB Nathaniel B. Palmer and accumulation measurements by automated ice mass-balance buoys (IMBs) allow us to document the proportion of snowfall that accumulated on level ice surfaces in the presence of high winds and blowing-snow conditions. Accumulation on the sea ice during the experiment averaged <0.01 m w.e. at both IMB sites, during a period when European Centre for Medium-Range Weather Forecasts analyses predicted >0.03 m w.e. of precipitation on the ice floe. Accumulation changes on the ice floe were clearly associated with drifting snow and high winds. Drifting-snow transport during the SIMBA experiment was supply-limited. Using these results to inform a preliminary study using a blowing-snow model, we show that over the entire Southern Ocean approximately half of the precipitation over sea ice could be lost to leads.

Seasonal ice mass-balance buoys: adapting tools to the changing Arctic

AbstractMonitoring the local mass balance of Arctic sea ice provides opportunities to attribute the observed changes in a particular floe’s mass balance to specific forcing phenomena. A shift from multi-year to seasonal ice in large portions of the Arctic presents a challenge for the existing Lagrangian array of autonomous ice mass-balance buoys, which were designed with a perennial ice cover in mind. This work identifies the anticipated challenges of operation in seasonal ice and presents a new autonomous buoy designed to monitor ice mass balance in the seasonal ice zone. the new design presented incorporates features which allow the buoy to operate in thin ice and open water, and reduce its vulnerability to ice dynamics and wildlife damage, while enhancing ease of deployment. A test deployment undertaken from April to June 2009 is discussed and results are presented with analysis to illustrate both the features and limitations of the buoy’s abilities.

Assessment of radiation forcing data sets for large-scale sea ice models in the Southern Ocean

Little is known about errors in the atmospheric forcings of large-scale sea ice-ocean models around Antarctica. These forcings involve atmospheric reanalyses, typically those from the National Center for Environmental Prediction and National Center from Atmospheric Research (NCEP-NCAR), climatologies, and empirical parameterizations of atmosphere-ice heat and radiation fluxes. In the present paper, we evaluate the atmospheric forcing fields of sea ice models in the Southern Ocean using meteorological and radiation observations from two drifting station experiments over Antarctic sea ice. These are Sea Ice Mass Balance in the Antarctic (SIMBA, Bellingshausen Sea, October 2007) and ISPOL (Ice Station POLarstern, Weddell Sea, December 2004). For the comparison, it is assumed that those point measurements are representative of the whole model grid cell they were collected in. Analysis suggests that the NCEP-NCAR reanalyses have relatively low biases for variables that are assimilated by the system (temperature, winds and humidity) and are less accurate for those which are not (cloud fraction and radiation fluxes). The main deficiencies are significant day-to-day errors in air temperature (root-mean-square error 1.4–3.8 °C) and a 0.2–0.6 g/kg mean overestimation in NCEP-NCAR specific humidity. In addition, associated with an underestimation of cloud fraction, NCEP-NCAR shortwave radiation features a large positive bias (43–109 W/m 2), partly compensated by a 20–45 W/m 2 negative bias in longwave radiation. Those biases can be drastically reduced by using empirical formulae of radiation fluxes and climatologies of relative humidity and cloud cover. However, this procedure leads to a loss of day-to-day and interannual variability in the radiation fields. We provide technical recommendations on how the radiation forcing should be handled to reduce sea ice model forcing errors. The various errors in forcing fields found here should not hide the great value of atmospheric reanalyses for the simulation of the ice-ocean system.

Sea-ice thickness and mass at Ice Station Belgica, Bellingshausen Sea, Antarctica

Ice Station Belgica was commenced in late winter 2007 in the Bellingshausen Sea as part of Sea Ice Mass Balance in Antarctica (SIMBA), an IPY 2007 cruise on the research vessel N.B. Palmer. A primary objective was to build on the work of previous Antarctic drift station experiments to geophysically characterize sea ice in terms of thickness, surface and ice bottom morphology, and ultimately area-unitized mass. A 24 day drift station was established at approximately 70°S and 93°W in mixed first-year and multi-year ice with three geophysical study sites selected on a 5 km 2 floe. A comprehensive time series assessment of elevation-surveyed transects ranging from 100 m to 300 m in length included snow surface elevation, snow depth, electromagnetic (EM) profiling, and direct drilling for ice draft and ice freeboard. Additional work included a snow surface morphology characterization of a 100 m×300 m area between the primary time series EM transects. Correlation of EM ice thicknesses with collocated drilled ice thickness yielded equations for the correction of EM underestimation of thick deformed ice, particularly at pressure ridges. Mean ice thickness from corrected EM was compared to isostatic ice thickness calculated from surface elevation, snow depth, ice freeboard and respective snow, slush, ice, and sea water densities. Results were consistent, with mean ice thicknesses for multi-year ice of 2.35 m, 2.34 m, and 2.41 m, with similar variance, for corrected EM, drilling, and buoyancy methods respectively. Additionally, a mean ice thickness of 2.31 m was calculated from ASPeCt observations of the ice field associated with the floe, using the method incorporating mean sail heights and fractional coverage of surface deformities or ridging. Temporal series assessment of ice freeboard indicated a slightly negative mean ice freeboard (<0.04 m), with clear evidence of new snow-ice formation from the freezing of slush. The three distinct snow and ice regions assessed on the Belgica floe had mean corrected EM ice thickness of 0.52±0.04 m (±1 std. deviation), 0.92±0.17 m, and 2.35±1.37 m, and mean snow depths of 0.08±0.03 m, 0.36±0.09 m, and 0.68±0.31 m respectively. Each ice type represented a sizable fraction of the floe's total area (∼20%, 40%, and 40% respectively from visual estimates) reflecting a complex dynamic and thermodynamic history of formation, as well as the difficulty in characterizing even a single floe by a single class or mean value for thickness and snow depth. Implications of these results are discussed with regards to the resolution of satellite-based altimetry and snow depth products and efforts to generate and validate satellite sea ice and snow thickness products.

Intercomparisons of Antarctic sea ice types from visual ship, RADARSAT-1 SAR, Envisat ASAR, QuikSCAT, and AMSR-E satellite observations in the Bellingshausen Sea

Antarctic Sea Ice Processes and Climate (ASPeCt) visual ship-based observations were conducted in the Bellingshausen Sea during the Sea Ice Mass Balance in the Antarctic (SIMBA) cruise in austral spring 2007. A total of 59 ASPeCt observations are compared to coincident satellite active and passive microwave data. Envisat and RADARSAT-1 C-Band HH-polarization radar backscatter values (called NRCS henceforth) are derived on km-scales for six individual ice types and ice type mixtures. C-Band HH-polarized and Ku-Band VV-polarized NRCS are extracted on several 10 km-scale areas from coincident Envisat, RADARSAT-1, and QuikSCAT radar images for areas primarily covered with multiyear, deformed first-year, and undeformed young ice, as well as ice of the marginal ice zone (MIZ). The C-Band NRCS permits distinction between first-year, MIZ, and undeformed young ice. However, NRCS of the multiyear ice zone overlaps with that of the other ice zones and types. Ku-Band NRCS obtained for the same ice types permits discrimination of the first-year ice zone only. Obtained NRCS agree with those of previous studies and suggest a high degree of deformation and considerable potential for flooding for the first-year ice case. In comparison to large scale NRCS, AMSR-E snow depth values form two clearly separated clusters, one for 0.24–0.35 m depth (first-year ice zone) and one for 0.36–0.54 m depth (multiyear ice zone). However, a comparison to ASPeCt observations suggests a remarkable underestimation of the snow depth by AMSR-E in the multiyear–first-year-ice transition zone and for first-year cake ice. Nevertheless, a fusion of the coarse AMSR-E snow depth ranges for interior pack ice regions with radar imagery at large scale, appears promising for mapping the major zones (MIZ and Pack Ice) and ice types (first-year and multiyear) of Antarctic sea ice on a circumpolar basis.

Bio-optical properties of Antarctic pack ice in the early austral spring

Pack ice in the Bellingshausen Sea contained moderate to high stocks of microalgal biomass (3–10 mg Chl a m −2) spanning the range of general sea-ice microalgal microhabitats (e.g., bottom, interior and surface) during the International Polar Year (IPY) Sea Ice Mass Balance in the Antarctic (SIMBA) studies. Measurements of irradiance above and beneath the ice as well as optical properties of the microalgae therein demonstrated that absorption of photosynthetically active radiation (PAR) by particulates (microalgae and detritus) had a substantial influence on attenuation of PAR and irradiance transmission in areas with moderate snow covers (0.2–0.3 m) and more moderate effects in areas with low snow cover. Particulates contributed an estimated 25 to 90% of the attenuation coefficients for the first-year sea ice at wavelengths less than 500 nm. Strong ultraviolet radiation (UVR) absorption by particulates was prevalent in the ice habitats where solar radiation was highest—with absorption coefficients by ice algae often being as large as that of the sea ice. Strong UVR-absorption features were associated with an abundance of dinoflagellates and a general lack of diatoms—perhaps suggesting UVR may be influencing the structure of some parts of the sea-ice microbial communities in the pack ice during spring. We also evaluated the time-varying changes in the spectra of under-ice irradiances in the austral spring and showed dynamics associated with changes that could be attributed to coupled changes in the ice thickness (mass balance) and microalgal biomass. All results are indicative of radiation-induced changes in the absorption properties of the pack ice and highlight the non-linear, time-varying, bio-physical interactions operating within the Antarctic pack ice ecosystem.

The influence of winds, sea-surface temperature and precipitation anomalies on Antarctic regional sea-ice conditions during IPY 2007

The 2007 International Polar Year (IPY) in the Antarctic was distinguished by strong regional and seasonal ice-atmosphere-ocean anomalies associated with an overall weakening of the prevailing westerly circulation. Here we assess the ice-atmosphere-ocean conditions leading up to and during two IPY field campaigns that took place in early spring (September-October): the U.S.-led Sea Ice Mass Balance Antarctica (SIMBA, 68-72°S, 90-95°W) and the Australian-led Sea Ice Physics and Ecosystems eXperiment (SIPEX, 63-67°S, 115-130°E). Our regional analysis is presented within the context of circumpolar and inter-annual variability relevant to other IPY Antarctic studies. Using satellite-derived and numerically analyzed surface and atmospheric variables, we examine relationships between (i) winds and sea-ice concentration and drift, (ii) sea-surface temperature and ice-edge anomalies, and (iii) precipitation and snow accumulation. Though Antarctic-averaged sea-ice extent in September 2007 was the second highest observed for 1979-2007, the SIMBA and SIPEX studies sampled the two regions showing the largest negative sea-ice anomalies in the Southern Ocean. Maps of sea-surface temperature (SST) and sea-ice concentration (SIC) anomalies revealed distinct regional patterns, showing warm SST/low SIC in the greater SIMBA (including all of the Bellingshausen and Amundsen seas) and western SIPEX regions, versus cool SST/high SIC in the Weddell, Ross and eastern SIPEX regions. In the SIMBA and western SIPEX regions, warm northerly winds in May (overlying the warm SSTs) brought anomalously high precipitation to those regions, but due to the regional delays in sea-ice advance (by up to 2 months), most fell on open ocean, which in turn contributed to negative and near-zero September snow depth anomalies in those two regions, respectively. During autumn (March to May), warm SSTs offshore of those regions extended from mid-to-high latitudes, resulting from meridional advection of heat associated with a wave-3 atmospheric circulation pattern. In the SIMBA and SIPEX regions, the late sea-ice advance followed unusually long ice-free summer periods, which suggests that solar ocean warming was relatively high in those regions. The warm ocean conditions may help to explain why the ice edge remained well south of its mean position despite instances during winter of cold southerly winds and northward sea-ice drift. Finally, with respect to the 1978-2008 record, year 2007 was a continuation of decreasing sea ice in the SIMBA region (e.g., decreased annual sea-ice extent and ice season duration), whereas in the SIPEX region, year 2007 was a negative departure from an otherwise slightly positive trend in annual sea-ice extent and ice season duration.

Sea ice and snow cover characteristics during the winter–spring transition in the Bellingshausen Sea: An overview of SIMBA 2007

The Sea Ice Mass Balance in the Antarctic (SIMBA) experiment was conducted from the RVIB N.B. Palmer in September and October 2007 in the Bellingshausen Sea in an area recently experiencing considerable changes in both climate and sea ice cover. Snow and ice properties were observed at 3 short-term stations and a 27-day drift station (Ice Station Belgica, ISB) during the winter–spring transition. Repeat measurements were performed on sea ice and snow cover at 5 ISB sites, each having different physical characteristics, with mean ice (snow) thicknesses varying from 0.6 m (0.1 m) to 2.3 m (0.7 m). Ice cores retrieved every five days from 2 sites and measured for physical, biological, and chemical properties. Three ice mass-balance buoys (IMBs) provided continuous records of snow and ice thickness and temperature. Meteorological conditions changed from warm fronts with high winds and precipitation followed by cold and calm periods through four cycles during ISB. The snow cover regulated temperature flux and controlled the physical regime in which sea ice morphology changed. Level thin ice areas had little snow accumulation and experienced greater thermal fluctuations resulting in brine salinity and volume changes, and winter maximum thermodynamic growth of ∼0.6 m in this region. Flooding and snow–ice formation occurred during cold spells in ice and snow of intermediate thickness. In contrast, little snow–ice formed in flooded areas with thicker ice and snow cover, instead nearly isothermal, highly permeable ice persisted. In spring, short-lived cold air episodes did not effectively penetrate the sea ice nor overcome the effect of ocean heat flux, thus favoring net ice thinning from bottom melt over ice thickening from snow–ice growth, in all cases. These warm ice conditions were consistent with regional remote sensing observations of earlier ice breakup and a shorter sea ice season, more recently observed in the Bellingshausen Sea.

Preparatory Tests with an Explorer Class Autonomous Underwater Vehicle for Missions under Sea Ice

The autonomous underwater vehicle (AUV) operations described here are preparatory missions to enable operation of an AUV under sea ice in polar regions. The proposed polar projects include operations under land fast ice in the Arctic through an ice moon pool and a planned project to assess sea ice mass balance and habitat assessment in the Southern Ocean in East Antarctica. This paper focuses on the preparatory missions, done in open water, and the planned Southern Ocean project. The plan is to use an autonomous underwater vehicle (AUV) for the under ice component of measurements. The ultimate goals are to quantify the size and shape of ridge keel structures and their contribution to the sea ice mass balance over a study region; to understand the processes that link sea ice with the distribution of ice algae and krill; to provide the necessary field measurements, over sufficiently large areas, for the calibration/validation of satellite and aircraft-based measurements of the sea ice and snow cover thickness; and to provide baseline measurements of sea ice thickness for future climate monitoring.