Browsing by Subject "Sea ice"

Now showing 1 - 5 of 5
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    Antarctic climate change: extreme events disrupt plastic phenotypic response in Adélie penguins
    (Public Library of Science, 2014) Lescroël, Amélie; Ballard, Grant; Grémillet, David; Authier, Matthieu; Ainley, David G
    In the context of predicted alteration of sea ice cover and increased frequency of extreme events, it is especially timely to investigate plasticity within Antarctic species responding to a key environmental aspect of their ecology: sea ice variability. Using 13 years of longitudinal data, we investigated the effect of sea ice concentration (SIC) on the foraging efficiency of Adélie penguins ( Pygoscelis adeliae ) breeding in the Ross Sea. A 'natural experiment' brought by the exceptional presence of giant icebergs during 5 consecutive years provided unprecedented habitat variation for testing the effects of extreme events on the relationship between SIC and foraging efficiency in this sea-ice dependent species. Significant levels of phenotypic plasticity were evident in response to changes in SIC in normal environmental conditions. Maximum foraging efficiency occurred at relatively low SIC, peaking at 6.1% and decreasing with higher SIC. The 'natural experiment' uncoupled efficiency levels from SIC variations. Our study suggests that lower summer SIC than currently observed would benefit the foraging performance of Adélie penguins in their southernmost breeding area. Importantly, it also provides evidence that extreme climatic events can disrupt response plasticity in a wild seabird population. This questions the predictive power of relationships built on past observations, when not only the average climatic conditions are changing but the frequency of extreme climatic anomalies is also on the rise.
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    Investigating the air and liquid porosity of sea ice
    (2025) Swait, Hayley; Rampai, Tokoloho
    Micro-scale sea ice properties have cascading effects onto larger scale climate and ocean systems. Brine and air inclusions are influenced by the growth conditions, which are highly dynamic in the Antarctic Marginal Ice Zone (MIZ) compared to the calmer Arctic. There are varying depths within an Antarctic pancake floe due to these dynamic conditions, yet the spatial variability of brine and air porosity profiles has not been previously investigated. Additionally, the sea ice brine phase is greatly influenced by temperature, yet similarly there are limited studies on the impact of temperature storage and heating methods on brine inclusions. Understanding the impacts of environmental and storage conditions is essential to ensure accurate and representative analysis of sea ice's thermally responsive properties. In this study, non-destructive X-ray computer tomography (CT) analysis was used to investigate the brine and air inclusions within pancake ice from the Antarctic MIZ during winter 2019 and 2022 expeditions. Sampling protocols from the 2019 expedition were optimised during the 2022 expedition to store samples at the CT analysis temperature (-10°C) to minimise the impact of low temperature (-18°C) storage on these inclusions. Investigating the impacts of low temperature storage and heating methods on these inclusions was then conducted through uni- (UD) and multidirectional (MD) heating samples from -18°C to -10°C. This study showed on average reductions of 41% in the brine porosity of sea ice after being subjected to low temperature storage, unlike air porosity that showed no significant changes. However, there was no significant difference between the UD and MD heating methods. The number of brine inclusions increased after low temperature storage. The brine inclusions showed a decrease in sphericity in samples subjected to low temperature storage conditions. Air showed slight increases in the number of air inclusions in the sections in the upper region of the ice while the lower region showed a decrease in air number densities, potentially attributed to the gas saturation factor within the sea ice. In addition to the storage conditions influencing the inclusions, the spatial variability of coring locations within a pancake floe has also shown to have slight variation in the porosity profiles within sea ice samples. This study disqualifies the general assumption that sea ice porosity is not affected by low temperature storage conditions and therefore the storage conditions are of paramount importance in studying the microstructural properties of sea ice. Maintaining sea ice samples at higher analysis temperatures that is closer to in situ temperatures will minimize the effects of low temperature storage on the sea ice inclusions.
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    Physical and biogeochemical properties of seasonal sea ice in the Atlantic sector of the Antarctic marginal ice zone
    (2025) Audh, Riesna Reuben; Vichi, Marcello; Fawcett, Sarah
    The study of Antarctic sea ice biogeochemistry has largely focused on samples collected from pack ice during summer, with few winter data available. Measurements from the Antarctic marginal ice zone (AMIZ) have proven even more difficult to obtain. The AMIZ is a broad, circumpolar feature of the Southern Ocean where sea ice begins to form during winter. The incorporation of seawater during sea-ice growth along with chemical and biological processes operating within the ice results in a complex biogeochemical environment within the sea ice matrix. This thesis presents the first biogeochemical datasets for sea ice collected in the Atlantic AMIZ during winter and spring, including measurements from young pancake ice, consolidated first-year ice and brash ice. It also proposes a revised set of standard operating procedures for conducting interdisciplinary sampling in complex marginal ice conditions. Measurements of sea-ice temperature, salinity, crystal structure, δ O18 , chlorophyll and nutrient concentrations were combined with model simulations to decipher the conditions under which the ice formed and grew, how these conditions influenced the subsequent biogeochemical environment and how the sea-ice properties evolved from winter to spring. Our findings confirm that winter sea ice is biologically active and further suggest that the growth of sea ice in the AMIZ is not a linear progression of thickness with habitat space reduction as sea ice consolidates. Instead, sea ice consolidates and thickens as a result of multiple cycles of breaking and rafting of young ice, and the biogeochemical signatures of the young ice are conserved in the reformed, consolidated ice cover. Novel nitrate and particle δ N15 measurements enabled us to investigate the seasonal evolution of sea-ice nitrogen cycle dynamics in the AMIZ, revealing that processes such as nitrate assimilation and nitrification are ongoing during winter. A comparison of our data to previous studies suggests a temporally advanced nitrogen cycle compared to pack ice in the region. Finally, the first measurements of winter pancake ice and spring brash ice biogeochemistry are highlighted and illustrate the seasonal influence on the sea ice environment and surface ocean in the AMIZ. The work detailed in this thesis significantly advances the available data and knowledge base for the AMIZ, particularly related to the biogeochemistry of sea ice, and will help to improve and validate future modelling efforts by providing observations in a severely understudied region.
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    SHARC Buoy: Robust firmware design for a novel, low-cost autonomous platform for the Antarctic Marginal Ice Zone in the Southern Ocean
    (2021) Jacobson, Jamie Nicholas; Verrinder, Robyn; Mishra, Amit; Vichi, Marcello
    Sea ice in the Antarctic Marginal Ice Zone (MIZ) plays a pivotal role in regulating heat and energy exchange between oceanic and atmospheric systems, which drive global climate. Current understanding of Southern Ocean sea ice dynamics is poor with temporal and spatial gaps in critical seasonal data-sets. The lack of in situ environmental and wave data from the MIZ in the Antarctic region drove the development of UCT's first generation of in situ ice-tethered measurement platform as part of a larger UCT and NRF SANAP project on realistic modelling of the Marginal Ice Zone in the changing Southern Ocean (MISO). This thesis focuses on the firmware development for the device and the design process taken to obtain key measurements for understanding sea ice dynamics and increasing sensing capabilities in the Southern Ocean. The buoy was required to survive the Antarctic climate and contained a global positioning system, temperature sensor, digital barometer and inertial measurement unit to measure waves-in-ice. Power was supplied to the device by a power supply unit consisting of commercial-grade batteries in series with a temperature-resistant low dropout regulator, and a power sensor to monitor the module. A satellite modem transmitted data through the Iridium satellite network. Finally, Flash chips provided permanent data storage. Firmware and peripheral driver files were written in C for an STMicroelectronics STM32L4 Arm-based microcontroller. To optimise the firmware for low power consumption, inactive sensors were placed in power-saving mode and the processor was put to sleep during periods of no sampling activity. The first device deployment took place during the SCALE winter expedition in July 2019. Two devices were deployed on ice floes to test their performance in remote conditions. However, due to mechanical and power errors, the devices failed shortly after deployment. A third device was placed on the deck of SA Aghulas II during the expedition and successfully survived for one week while continuously transmitting GPS coordinates and ambient temperature. The second generation featured subsequent improvements to the mechanical robustness and sensing capabilities of the device. However, due to the 2020 COVID-19 pandemic, subsequent Antarctic expeditions were cancelled resulting in the final platform evaluation taking place on land. The device demonstrates a proof of concept for a low-cost, ice-tethered autonomous sensing device. However, additional improvements are required to overcome severe bandwidth and power constraints.
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    Where to forage in the absence of sea ice? Bathymetry as a key factor for an arctic seabird
    (Public Library of Science, 2016) Amélineau, Françoise; Grémillet, David; Bonnet, Delphine; Le Bot, Tangi; Fort, Jérôme
    The earth is warming at an alarming rate, especially in the Arctic, where a marked decline in sea ice cover may have far-ranging consequences for endemic species. Little auks, endemic Arctic seabirds, are key bioindicators as they forage in the marginal ice zone and feed preferentially on lipid-rich Arctic copepods and ice-associated amphipods sensitive to the consequences of global warming. We tested how little auks cope with an ice-free foraging environment during the breeding season. To this end, we took advantage of natural variation in sea ice concentration along the east coast of Greenland. We compared foraging and diving behaviour, chick diet and growth and adult body condition between two years, in the presence versus nearby absence of sea ice in the vicinity of their breeding site. Moreover, we sampled zooplankton at sea when sea ice was absent to evaluate prey location and little auk dietary preferences. Little auks foraged in the same areas both years, irrespective of sea ice presence/concentration, and targeted the shelf break and the continental shelf. We confirmed that breeding little auks showed a clear preference for larger copepod species to feed their chick, but caught smaller copepods and nearly no ice-associated amphipod when sea ice was absent. Nevertheless, these dietary changes had no impact on chick growth and adult body condition. Our findings demonstrate the importance of bathymetry for profitable little auk foraging, whatever the sea-ice conditions. Our investigations, along with recent studies, also confirm more flexibility than previously predicted for this key species in a warming Arctic.