Sea ice is an important driver of climate patterns and polar marine ecosystem dynamics. In particular, primary production by microalgae in sea ice has been postulated as a sink for anthropogenic CO2, and as a critical resource in the life cycle of Antarctic krill Euphausia superba, a keystone species. Study of the sea ice ecosystem is difficult at regional and global scales, however, because of the expense and logistical difficulties in accessing such a remote and hostile environment. Consequently, models remain valuable tools for investigations of the spatial and temporal dynamics of sea ice and associated ecology and biogeochemistry. Recent advances in model representations of sea ice have called into question the accuracy of previous studies, and allow the creation of new tools to perform mechanistic simulations of sea ice physics and biogeochemistry. To address spatial and temporal variability in Antarctic sea ice algal production, and to establish the bounds and sensitivities of the sea ice ecosystem, a new, coupled sea ice ecosystem model was developed. In the vertical dimension, the model resolves incorporated saline brine, macronutrients concentrations, spectral shortwave radiation, and the sea ice algae community at high resolution. A novel method for thermodynamics, desalination, and fluid transfer in slushy, high-brine fraction sea ice was developed to simulate regions of high algal productivity. The processes of desalination, fluid transfer, snow-ice creation, and superimposed ice formation allowed the evolution of realistic vertical profiles of sea ice salinity and algal growth. The model replicated time series observations of ice temperature, salinity, algal biomass, and estimated fluid flux from the Ice Station Weddell experiment. In the horizontal dimension, sub-grid scale parameterizations of snow and ice thickness allow more realistic simulation of the ice thickness distribution, and consequently, sea ice algal habitat. The model is forced from above by atmospheric reanalysis climatologies, and from below by climatological ocean heat flux and deep-water ocean characteristics. Areal sea ice concentration and motion are specified according to SSM/I passive microwave satellite estimates of these parameters. Sensitivity testing of different snow and ice parameterizations showed that without a sub-grid scale ice thickness distribution, mean ice and snow thickness is lower and bottom sea ice algal production is elevated. Atmospheric forcing from different reanalysis data sets cause mean and regional shifts in sea ice production and associated ecology, even when sea ice extent and motion is controlled. Snow cover represents a first-order control over ice algal production by limiting the light available to bottom ice algal communities, and changes to the regional, rather than mean, snow thickness due to the use of different ice and snow representations are responsible for large differences in the magnitude and distribution of sea ice algal production. Improved convective nutrient exchange in high-brine fraction (slush) sea ice is responsible for up to 18% of total sea ice algal production. A continuous 10-year model run using climatological years 1996-2005 produced a time series of sea ice algal primary production that varied between 15.5 and 18.0 Tg C yr-1. This study represents the first interannual estimate of Antarctic sea ice algal production that dynamically considers the light, temperature, salinity, and nutrient conditions that control algal growth. On average, 64% of algal production occurred in the bottom 0.2 m of the ice pack. Production was spatially heterogeneous, with little consistency between years when examined at regional scales; however, at basin or hemispheric scales, annual production was fairly consistent in magnitude. At a mean of 0.9 g C m-2 yr-1, the magnitude of carbon uptake by sea ice algae will not significantly affect the Southern Ocean carbon cycle. Light availability was the dominant control on sea ice algae growth over the majority of the year; however, severe nutrient limitation that occurred annually during late spring and summer proved to be the largest control over sea ice algal productivity.

Sea ice is an important driver of climate patterns and polar marine ecosystem dynamics. In particular, primary production by microalgae in sea ice has been postulated as a sink for anthropogenic CO2, and as a critical resource in the life cycle of Antarctic krill Euphausia superba, a keystone species. Study of the sea ice ecosystem is difficult at regional and global scales, however, because of the expense and logistical difficulties in accessing such a remote and hostile environment. Consequently, models remain valuable tools for investigations of the spatial and temporal dynamics of sea ice and associated ecology and biogeochemistry. Recent advances in model representations of sea ice have called into question the accuracy of previous studies, and allow the creation of new tools to perform mechanistic simulations of sea ice physics and biogeochemistry. To address spatial and temporal variability in Antarctic sea ice algal production, and to establish the bounds and sensitivities of the sea ice ecosystem, a new, coupled sea ice ecosystem model was developed. In the vertical dimension, the model resolves incorporated saline brine, macronutrients concentrations, spectral shortwave radiation, and the sea ice algae community at high resolution. A novel method for thermodynamics, desalination, and fluid transfer in slushy, high-brine fraction sea ice was developed to simulate regions of high algal productivity. The processes of desalination, fluid transfer, snow-ice creation, and superimposed ice formation allowed the evolution of realistic vertical profiles of sea ice salinity and algal growth. The model replicated time series observations of ice temperature, salinity, algal biomass, and estimated fluid flux from the Ice Station Weddell experiment. In the horizontal dimension, sub-grid scale parameterizations of snow and ice thickness allow more realistic simulation of the ice thickness distribution, and consequently, sea ice algal habitat. The model is forced from above by atmospheric reanalysis climatologies, and from below by climatological ocean heat flux and deep-water ocean characteristics. Areal sea ice concentration and motion are specified according to SSM/I passive microwave satellite estimates of these parameters. Sensitivity testing of different snow and ice parameterizations showed that without a sub-grid scale ice thickness distribution, mean ice and snow thickness is lower and bottom sea ice algal production is elevated. Atmospheric forcing from different reanalysis data sets cause mean and regional shifts in sea ice production and associated ecology, even when sea ice extent and motion is controlled. Snow cover represents a first-order control over ice algal production by limiting the light available to bottom ice algal communities, and changes to the regional, rather than mean, snow thickness due to the use of different ice and snow representations are responsible for large differences in the magnitude and distribution of sea ice algal production. Improved convective nutrient exchange in high-brine fraction (slush) sea ice is responsible for up to 18% of total sea ice algal production. A continuous 10-year model run using climatological years 1996-2005 produced a time series of sea ice algal primary production that varied between 15.5 and 18.0 Tg C yr-1. This study represents the first interannual estimate of Antarctic sea ice algal production that dynamically considers the light, temperature, salinity, and nutrient conditions that control algal growth. On average, 64% of algal production occurred in the bottom 0.2 m of the ice pack. Production was spatially heterogeneous, with little consistency between years when examined at regional scales; however, at basin or hemispheric scales, annual production was fairly consistent in magnitude. At a mean of 0.9 g C m-2 yr-1, the magnitude of carbon uptake by sea ice algae will not significantly affect the Southern Ocean carbon cycle. Light availability was the dominant control on sea ice algae growth over the majority of the year; however, severe nutrient limitation that occurred annually during late spring and summer proved to be the largest control over sea ice algal productivity.

Over the past 20 years the study of the frozen Arctic and Southern Oceans and sub-arctic seas has progressed at a remarkable pace. This third edition of Sea Ice gives insight into the very latest understanding of the how sea ice is formed, how we measure (and model) its extent, the biology that lives within and associated with sea ice and the effect of climate change on its distribution. How sea ice influences the oceanography of underlying waters and the influences that sea ice has on humans living in Arctic regions are also discussed. Featuring twelve new chapters, this edition follows two previous editions (2001 and 2010), and the need for this latest update exhibits just how rapidly the science of sea ice is developing. The 27 chapters are written by a team of more than 50 of the worlds’ leading experts in their fields. These combine to make the book the most comprehensive introduction to the physics, chemistry, biology and geology of sea ice that there is. This third edition of Sea Ice will be a key resource for all policy makers, researchers and students who work with the frozen oceans and seas.

This dissertation examines several aspects of the unique physical-biological system that controls biogeochemical cycling in the Ross Sea, the largest continental shelf sea along the Antarctic margin and the most biologically productive region in the Southern Ocean. The core component of the research involves interpretation of data from two oceanographic cruises to the region, one during Summer of 2005--2006 and another in Spring of 2006--2007. Four key research questions are addressed. (1) What physical mechanisms force spatial and temporal variability in mixing depths? (2) How does the dynamic physical environment characteristic of Antarctic continental shelf seas structure distributions of biomass and chemical tracers of production? (3) What key physical and physiological mechanisms control the 13C/12C ratio of organic and inorganic carbon in waters on the Ross Sea continental shelf? and (4) How do physiological variables interact with environmental variability to control phytoplankton taxonomic zonation? Chapter 1 presents an introduction to ocean carbon biogeochemistry and the oceanography of the Southern Ocean and the Ross Sea. Chapter 2 examines the mechanisms effecting early season stratification in the Ross Sea. Lateral advection in the region of upper ocean fronts is shown to be an important mechanism setting early season stratification. Chapter 3 examines several tracer-based methods for estimating upper ocean net community production in the Ross Sea, with explicit recognition of the complexities associated with control volume assumptions and high rates of temporal change. Chapter 4 considers the environmental controls on the distribution of 13C/12C ratios in the Ross Sea. It is shown quantitatively that the two dominant phytoplankton taxa in the Ross Sea have different intrinsic fractionation factors, likely as a result of differing carbon-acquisition physiologies. Air-sea exchange is shown to occur with very noisy fractionation. Finally, Chapter 5 examines the interaction of algal physiology with environmental variability, addressing the key physiological-environmental controls on the taxonomic distribution of phytoplankton in the Ross Sea. While it is difficult to draw concrete conclusions, the most compelling line of evidence suggests that differing photoprotective capacities is the most important physiological characteristic structuring taxonomic distributions. An appendix presents a design for an infrared absorbance-based instrument for the determination of total dissolved inorganic carbon in seawater.

The sea ice surrounding Antarctica has increased in extent and concentration from the late 1970s, when satellite-based measurements began, until 2015. Although this increasing trend is modest, it is surprising given the overall warming of the global climate and the region. Indeed, climate models, which incorporate our best understanding of the processes affecting the region, generally simulate a decrease in sea ice. Moreover, sea ice in the Arctic has exhibited pronounced declines over the same period, consistent with global climate model simulations. For these reasons, the behavior of Antarctic sea ice has presented a conundrum for global climate change science. The National Academies of Sciences, Engineering, and Medicine held a workshop in January 2016, to bring together scientists with different sets of expertise and perspectives to further explore potential mechanisms driving the evolution of recent Antarctic sea ice variability and to discuss ways to advance understanding of Antarctic sea ice and its relationship to the broader ocean-climate system. This publication summarizes the presentations and discussions from the workshop.

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