Advances in Understanding the Sea Ice Floe Size Distribution

<p>Sea ice is a critical component of the polar climate system that is tightly coupled to the ocean and atmosphere. It is highly heterogeneous, composed of discrete floes which range in size across space and time. In this thesis, I use a combination of modelling and observational approaches to investigate how different physical processes determine the distribution of sea ice floe sizes. I construct the first global model that simulates floe sizes arising from the interaction of different physical processes. Floe sizes are modified by lateral melt, lateral growth, freezing together of floes and wave-ice interactions. By grounding process descriptions in underlying physics, observations of individual processes can be used to constrain model parameters. In light of the sparseness of floe size observations, I developed a novel methodology to constrain previously-unobserved floe freezing processes from in-situ observations. Results from global coupled sea ice–ocean model simulations are used to quantify the relative impacts of different processes on spatial and seasonal variability in the floe size distribution, providing hypotheses that could be tested by observational campaigns in the future. Under transient historical forcing, the model suggests that the fragmentation of Arctic sea ice has significantly increased over the satellite era. I also seek to improve understanding of feedbacks between sea ice floe size and the polar climate system. A fragmented ice cover exposes more ice area on the sides of floes to the ocean than sheet ice, promoting lateral melt, which reduces surface albedo. Conducting a statistical analysis of current climate models shows that inclusion of a lateral melt parametrization improves simulation of sea ice concentration relative to observations. However, calculation of lateral melt using the model for prognostic simulation of the sub-grid-scale floe size distribution results in little or no enhancement of lateral melt at a hemispheric scale compared to a simple parametrization, although it is likely to be important at smaller spatial and shorter temporal scales. The new model opens up the possibility of coupling sea ice and ocean surface wave models and of including floe size dependence in other processes, such as form drag, sea ice dynamics, ocean eddies and ocean–atmosphere heat transfer, which may result in significant impacts for polar climate.</p>

Advances in Understanding the Sea Ice Floe Size Distribution

<p>Sea ice is a critical component of the polar climate system that is tightly coupled to the ocean and atmosphere. It is highly heterogeneous, composed of discrete floes which range in size across space and time. In this thesis, I use a combination of modelling and observational approaches to investigate how different physical processes determine the distribution of sea ice floe sizes. I construct the first global model that simulates floe sizes arising from the interaction of different physical processes. Floe sizes are modified by lateral melt, lateral growth, freezing together of floes and wave-ice interactions. By grounding process descriptions in underlying physics, observations of individual processes can be used to constrain model parameters. In light of the sparseness of floe size observations, I developed a novel methodology to constrain previously-unobserved floe freezing processes from in-situ observations. Results from global coupled sea ice–ocean model simulations are used to quantify the relative impacts of different processes on spatial and seasonal variability in the floe size distribution, providing hypotheses that could be tested by observational campaigns in the future. Under transient historical forcing, the model suggests that the fragmentation of Arctic sea ice has significantly increased over the satellite era. I also seek to improve understanding of feedbacks between sea ice floe size and the polar climate system. A fragmented ice cover exposes more ice area on the sides of floes to the ocean than sheet ice, promoting lateral melt, which reduces surface albedo. Conducting a statistical analysis of current climate models shows that inclusion of a lateral melt parametrization improves simulation of sea ice concentration relative to observations. However, calculation of lateral melt using the model for prognostic simulation of the sub-grid-scale floe size distribution results in little or no enhancement of lateral melt at a hemispheric scale compared to a simple parametrization, although it is likely to be important at smaller spatial and shorter temporal scales. The new model opens up the possibility of coupling sea ice and ocean surface wave models and of including floe size dependence in other processes, such as form drag, sea ice dynamics, ocean eddies and ocean–atmosphere heat transfer, which may result in significant impacts for polar climate.</p>

Meteoric Beryllium-10 in Miocene permafrost and the onset of persistent polar aridity in East Antarctica

Continental scale ice sheets have occupied Antarctica since the major global cooling across the Eocene/Oligocene boundary (~33.9 Ma). However, the timing and nature of the transition to a relatively stable and persistent terrestrial East Antarctic Ice Sheet that characterizes the modern environment remains disputed. Although proxy data show global surface temperatures remained significantly warmer through the late Miocene than today, the hypothesis that the upper elevations of the McMurdo Dry Valleys remained under a hyper-arid polar climate since the mid-Miocene has persisted. Here, we constrain the onset of polar aridity in the McMurdo Dry Valleys region using meteoric Beryllium-10 as a tracer of water infiltration in mid-Miocene and late Quaternary-age soils at three sites situated >1000 m a.s.l.. Our results show that meteoric Beryllium-10 infiltrated the soils for a period after sediment emplacement ~15.0 – 14.0 Ma, terminating at ~6.0 Ma. Reconstruction of climate from paleo-active layer thickness and threshold of mobility of meteoric Beryllium-10 suggests that at 6.0 Ma, summer temperatures were 7 – 10°C with annual precipitation >10 mm. Polar aridity at high elevations has persisted since ~6.0 Ma, well after previous reconstructions (13.8 – 12.5 Ma). Together, our findings indicate that high elevations of the McMurdo Dry Valleys experienced interval(s) of warm-wet climate between ~14.0 – 6.0 Ma which reconciles observations of coastal warmth and reduced ice in the Ross Embayment.

Ciliates in different types of pools in temperate, tropical, and polar climate zones – implications for climate change

Small water bodies are typically characterized by high diversity of various groups of microorganisms. Moreover, these ecosystems react very quickly to even the slightest climate changes (e.g. a temperature increase or water level fluctuations). Thus far, studies of planktonic ciliates in small water bodies having different origins and located in various climate zones have been scarce. Our study aimed to verify the following hypotheses: planktonic ciliate assemblages exhibit higher diversity in pools with higher concentrations of biogenic compounds; pools in warmer climates have higher biodiversity of planktonic ciliates than those in the polar climate zone; individual functional groups of ciliates demonstrate considerable diversity, both between individual pool types and between climate zones. The study was conducted in 21 small pools in temperate, tropical, and polar climate zones. While the type of pool clearly influenced the makeup of microbial communities, the influence of climate was stronger. The factors with the greatest influence on the occurrence of these microorganisms were temperature, total organic carbon, and nutrients. Our results show that in warmer climates the abundance of bacterivorous ciliates is higher, while that of mixotrophs is lower. This has consequences for modelling of climate change and assessment of its influence on the carbon cycle in small water body ecosystems.

Changes of Köppen–Trewartha climate types in the Tibetan Plateau during the mid-Holocene, present day, and the future based on high-resolution datasets

&lt;p&gt;Based on the K&amp;#246;ppen&amp;#8211;Trewartha climate classification schemes, we examined the shifts in terrestrial climate regimes in the Tibetan Plateau (TP) by analyzing the WorldClim high-resolution (~25 km) downscaled climate dataset for the mid-Holocene (MH, 6,000 cal yr BP), the present day (PD, 1970-2000), and in the future (2041-2060, represented by 2050). The climate types of the PD are compared to those of the MH and the future. Our aim was to place ongoing anthropogenic climatic and environmental changes in the TP within the context of changes due to natural forcing in the three selected warm period, and to determine the differences in the spatial expression of ecosystem among these selected periods. The results indicate that the climate of the TP will continue to warm in the future. The intensity of the South Asian monsoon may increase in the future which will affect precipitation in the southern TP. There will be a significant decrease in the areas covered by polar climate, while the spatial coverage of the other climate types will increase. A tropical climate which did not exist in the MH and PD will develop in some areas and the shrinking polar climate indicates that the cryosphere of the TP will change significantly, which in turn may cause the climate system to pass a tipping point and cause irreversible consequences. The large changes in the climate regimes of the TP suggest that there will be a widespread redistribution of the surface vegetation and significant changes in plant species distributions by 2050. Compared to changes in precipitation, increasing temperature is the dominant factor that driving the change of climate types in the TP. The warming alone may cause the climate types to change in more than 20% areas by 2050.&lt;/p&gt;

InSAR monitoring of Arctic land fast sea ice deformation using L-band ALOS-2, C-band Radarsat-2 and Sentinel-1

Arctic amplification is accelerating changes in sea ice regimes in the Canadian Arctic with later freeze-up and earlier melt events, adversely affecting Arctic wildlife and communities that depend on the stability of the sea ice conditions. To monitor both the rate and impact of such change, there is a need to accurately measure sea ice deformation, an important component for understanding ice motion and polar climate. This paper presents Interferometric Synthetic Aperture Radar (InSAR) monitoring of Arctic landfast sea ice deformation as a result of thickness changes measured from ice draft and surface height using C-band Radarsat-2, Sentinel-1 and L-band ALOS-2. The small baseline subset (SBAS) approach was explored to process time series observations for retrieval of temporal deformation changes over the winter. Sea ice deformation (subsidence and uplift in the range of −32–57 cm) detected from satellite SAR data in Cambridge Bay, Nunavut, Canada during the winter of 2018–2019 was found to be in a range of values corresponding to the ice draft growth (30–62 cm) measured from an in-situ ice profiler. The trends of InSAR observations from Sentinel-1 were also consistent with ice surface height changes along two ground tracks detected from ICESat-2. SAR backscatter from Sentinel-1 also corresponded to the surface height with strong correlation coefficient (0.49–0.83). High coherence over ice from C-band was maintained over a shorter acquisition interval than L-band due to temporal decorrelation.