Thesis (Ph.D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences and the Woods Hole Oceanographic Institution), 2000. / Vita. / Includes bibliographical references. / by Robert P. Ackert, Jr. / Ph.D.

The environmental and psychosocial adversity inherent in remote polar locales has historically been framed in pathological terms. However, a burgeoning body of evidence suggests that stressful conditions across isolated, confined, and extreme (ICE) environments may elicit positive growth outcomes as well. The purpose of this cross-sectional, retrospective study was to assess the incidence and correlates of PostExpedition Growth (PEG) in returned Antarctic expeditioners. The prevalence of five specific personal growth indicators – ‘new opportunities,’ ‘relating to others,’ ‘personal strength,’ ‘spiritual change,’ and ‘appreciation of life’ – along with individual and group variables that have been associated with growth in trauma-exposed populations (i.e., coping, mindfulness, personality traits, personal value priorities, adverse childhood experiences, and expedition/experience specific variables) were examined using a mixed methods approach. Quantitative results indicate a moderate, positive association between proactive coping and appreciation of life, as well as between universalism (i.e., a sense of harmony or oneness with humanity and the natural world), new possibilities, and appreciation of life. Qualitative findings provide a more nuanced understanding of the five dimensions of PEG and underscore the emergence of a sixth dimension, an enhanced relationship with nature. Further research is needed to illuminate knowledge gaps in ICE environment research, and to help identify potential countermeasures for individuals and groups faced with comparable adversity factors in their immediate environments (i.e., within the current context of COVID-19). A deeper understanding of PEG in ICE environments – as well as promotive factors that strengthen positive outcomes – will serve to inform the development of countermeasures to mitigate health and wellbeing risks following exposure to isolation and confinement in extreme environments. / Graduate / 2022-09-29

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Recent literature on Antarctica has suggested that China is becoming an increasingly crucial variable in defining governance structures on the continent. The thesis claims that China plays a role in restructuring relations and thus its Antarctic governance structures. It will therefore analyze the underlying causal role of China’s shifting identity, increasingly tense interactions with other treaty parties and changed interests in the Antarctic region. The analysis is based on theoretical assumptions of Conventional Constructivism which provides means to explain changes and the importance of state identities in international relations. Methodologically, the thesis employs a comparative research design to understand the cause-and-effect relationship between the independent and dependent variable. The thesis concludes that China is influencing governance structures by causing friction with other treaty parties and by exceeding the definitions of the Antarctic Treaty System based on its desire to become a ‘Polar Great Power’ and thus vast expansion.

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Studying Antarctic icebergs can provide insight into climatic changes of the Earth's frozen continent. Antarctic icebergs are regularly formed by the separations of massive sections of ice from ice shelves and glaciers. The National Ice Center (NIC) is playing a major role in sea ice analysis and forecasts. As a part of its mission the NIC is using a variety of satellite sensors to track many large Antarctic icebergs. The NIC reports iceberg positions every 15-20 days. However, there are limitations in the NIC's iceberg tracking techniques. The areas covered by the images used by the NIC are limited to specific areas of the Antarctic continent, due in part to the resources required to produce and process these high resolution images. Based on the NIC data base, the number of large Antarctic icebergs seems to be increasing in recent years. This leads to a concern of a possible climatic trend. However, our analysis of historic scatterometer and radiometer data suggests this increase is largely due to improved resources and technological advancements for iceberg tracking. Additionally sever major iceberg calving events have taken place in recent years. These calving events may represent natural variability. To evaluate the NIC's tracking and to monitor recent iceberg activity, we used current and historic scatterometer and radiometer data to track Antarctic icebergs spanning nearly 25 years. Five data sets from various instruments were used in the study. Icebergs were tracked independently with each data set for time periods between1976 to 2001. Each image provides coverage of the entire Antarctic continent allowing frequent positions to be reported for each iceberg. The results show that the number of large icebergs over the last 20-25 years has remained fairly constant with the exception of an increase in icebergs from 1994 to 2001 due to several major

Three problems at the forefront of microwave radiometry are solved using probability theory and inverse problem formulations which are heavily based in probability theory. Probability theory is able to capture information about random phenomena, while inverse problem theory processes that information. The use of these theories results in more accurate estimates and assessments of estimate error than is possible with previous, non-probabilistic approaches. The benefits of probabilistic approaches are expounded and demonstrated. The first problem to be solved is a derivation of the error that remains after using a method which corrects radiometric measurements for polarization rotation. Yueh [1] proposed a method of using the third Stokes parameter TU to correct brightness temperatures such as Tv and Th for polarization rotation. This work presents an extended error analysis of Yueh's method. In order to carry out the analysis, a forward model of polarization rotation is developed which accounts for the random nature of thermal radiation, receiver noise, and (to first order) calibration. Analytic formulas are then derived and validated for bias, variance, and root-mean-square error (RMSE) as functions of scene and radiometer parameters. Examination of the formulas reveals that: 1) natural TU from planetary surface radiation, of the magnitude expected on Earth at L-band, has a negligible effect on correction for polarization rotation; 2) RMSE is a function of rotation angle Ω, but the value of Ω which minimizes RMSE is not known prior to instrument fabrication; and 3) if residual calibration errors can be sufficiently reduced via postlaunch calibration, then Yueh's method reduces the error incurred by polarization rotation to negligibility. The second problem addressed in this dissertation is optimal estimation of calibration parameters in microwave radiometers. Algebraic methods for internal calibration of a certain class of polarimetric microwave radiometers are presented by Piepmeier [2]. This dissertation demonstrates that Bayesian estimation of the calibration parameters decreases the RMSE of the estimates by a factor of two as compared with algebraic estimation. This improvement is obtained by using knowledge of the noise structure of the measurements and by utilizing all of the information provided by the measurements. Furthermore, it is demonstrated that much significant information is contained in the covariance information between the calibration parameters. This information can be preserved and conveyed by reporting a multidimensional pdf for the parameters rather than merely the means and variances of those parameters. The proposed method is also extended to estimate several hardware parameters of interest in system calibration. The final portion of this dissertation demonstrates the advantages of a probabilistic approach in an empirical situation. A recent inverse problem formulation, sketched in [3], is founded on probability theory and is sufficiently general that it can be applied in empirical situations. This dissertation applies that formulation to the retrieval of Antarctic air temperature from satellite measurements of microwave brightness temperature. The new method is contrasted with the curve-fitting approach which is the previous state-of-the-art. The adaptibility of the new method not only results in improved estimation but is also capable of producing useful estimates of air temperature in areas where the previous method fails due to the occurence of melt events.

Multiple mechanisms control bacterial community structure but two in particular, the "legacy" of past environmental conditions, and the "priming" of bacteria to respond to seasonal or reoccurring fluctuations in resources, have the potential to determine both bacterial communities, as well as, temporal shifts in active bacterial taxa. To begin to evaluate the legacy effects of resources on microbial communities, we added four limiting resources annually (i.e., water only; C-mannitol + water; N-NH4NO3 + water; and C, N + water) and measured shifts in bacterial community composition after seven years in a cold desert ecosystem in the McMurdo Dry Valleys, Antarctica. Further, to investigate the ecological significance of priming, we conducted a series of stable isotope probing experiments (i.e., 18O-DNA SIP with 18O-labeled water, 13C-DNA SIP with 13C-labeled mannitol, 15N-DNA with 15N- NH4NO3, and a combined C and N SIP) and characterized the responding (i.e., isotopically labeled) and seed bank (i.e., unlabeled) bacterial communities. We performed each of the SIPs in soil microcosms corresponding to a single resource manipulation (e.g., 13C-labeled mannitol in C addition soils). We hypothesized that all long-term additions of nutrients and water will lead to a distinct bacterial community—a legacy effect due to the nutrient and water impoverished state of Antarctica soils. We also hypothesized that the stronger the legacy effects demonstrated by a specific community the more adapted or primed bacterial species will be to take advantage of the resource and respond. As hypothesized, resource additions created distinct bacterial legacy but to different degrees among the treatments. The extent of the resource legacy effects was greatest in the CN, intermediate in water and N, and lowest in C communities relative to the control communities, suggesting that C induced changes in communities were intensified by tandem N additions and that water alone created a more distinct legacy than water and C additions combined. Contrary to our hypothesis, the stronger the legacy effects, the less adapted or primed the community was to take advantage of resource additions. For example, the CN treatment that induced the greatest effect on bacterial communities had the lowest number of species (20.9%) in common between the responding and seed bank communities. This inverse relationship may be due to only two species (i.e., Arthrobacter, Actinobacteria and Massilia, Betaproteobacteria) really being primed to take advantage of CN and these species constituting over 75% of the seed bank community. Water, N, and C additions had similar levels of priming with 38.4%, 41.4%, and 36.3% of the responding species being present in the seed bank community, respectively. But of these three treatments, only the priming with water resulted in a unique responding community, suggesting that water, a universal bacterial resource, was enough to prime bacteria. Furthermore, water generates the most diverse responding community of all the resources with stemming from all of the fourteen dominant phyla. We did find patterns of ecological coherence among the responders, especially in the major responders (i.e., responders that increased in relative recovery by at least ten-fold). These responders were predominantly found in only three phyla (i.e., Actinobacteria, Bacteriodetes, and Gammaproteobacteria) regardless of resource addition. Alternatively minor responders (i.e., responders that increased in relative recovery at least two-fold) were contained in fourteen different phyla with specific taxa stimulated by CN (i.e., Betaproteobacteria) and N and water (i.e., Deltaproteobacteria). Further, resource additions elicited responses from 37% of bacterial species with species specializing on a specific resource (e.g., Chloroflexi) or being a generalist (e.g., Planctomycetes and Gammaproteobacteria). Our results offer the first direct links between legacy and priming effects on bacterial community composition and demonstrate that these mechanisms are not always complimentary leading to the formation of similar communities but may both be essential to maintain the high levels of bacterial diversity. Further, all resources produced elicited responders that were either specialists of generalists demonstrating that even bacteria in the extreme environment of Antarctica respond to pulses of resources.

Historical climate disturbances such as glacial cycling and fluctuating stream, lake, and sea levels strongly influence the distribution and evolutionary trajectories of Antarctic terrestrial species. Antarctic invertebrates, with limited long-range mobility, including the ubiquitous sentinel nematode species Scottnema lindsayae, are especially sensitive to climate disturbances. We tested hypotheses associated with the historical geographic and population genetic structure of this species as it occurs across the McMurdo Dry Valleys (MDVs) of Antarctica. In order to reconstruct the influence of climate disturbance and ecological conditions on this species, partial mitochondrial COI gene sequences were sequenced and analyzed from individual S. lindsayae collected from sites across the MDVs reflecting a opposing gradients of climate disturbance during the Last Glacial Maximum (LGM). We found that populations were strongly geomorphic barriers with distinct haplotypes associated with valleys except among valleys that experienced glacial advance and retreat during the LGM. One monophyletic clade corresponds with valley systems that were undisturbed during the LGM indicating putative refugia areas. A second monophyletic clade corresponds to recent dispersal and expansion of evolutionarily younger populations into valleys that were strongly reworked by glacial activity during the LGM. Our work shows that contemporary populations of these animals are strongly structured by prior climate history. Such findings can be useful for interpreting long-term monitoring of demographic shifts of soil organisms in response to changing climate trends in the McMurdo Dry Valleys.