Current oceanographic interest in the interaction of relatively warm water of the Southern Ocean Circumpolar Deep Water (CDW) as it moves southward to the frigid waters of the Antarctic continental shelves is based on the potential importance of heat transport from the global ocean to the base of continental ice shelves. This is needed to understand the longer term mass balance of the continent, the stability of the vast Antarctic ice sheets and the rate at which sea-level will rise in a warming world. Improved observational knowledge of the mechanisms of how warming CDW moves across the Antarctic Circumpolar Current (ACC) is needed. Understanding this dynamical transport, believed to take place through the eddy flux of time-varying mesoscale circulation features, will improve coupled ocean-atmospheric climate models. The development of the next generation of coupled ocean-ice-climate models help us understand future changes in atmospheric heat fluxes, glacial and sea-ice balance, and changes in the Antarctic ecosystems. A recurring obstacle to our understanding is the lack of data in this distant region. In this project, a total of 10 subsurface profiling EM-APEX floats adapted to operate under sea ice were launched in 12 missions (and 2 recoveries) from 4 cruises of opportunity to the Amundsen Sea sector of the Antarctic continental margin during Austral summer. The floats were launched south of the Polar Front and measured shear, turbulence, temperature, and salinity to 2000m depth for 1-2 year missions while drifting with the CDW layer between profiles.
The one place on Earth consistently showing increases in sea ice area, duration, and concentration is the Ross Sea in Antarctica. Satellite imagery shows about half of the Ross Sea increases are associated with changes in the austral fall, when the new sea ice is forming. The most pronounced changes are also located near polynyas, which are areas of open ocean surrounded by sea ice. To understand the processes driving the sea ice increase, and to determine if the increase in sea ice area is also accompanied by a change in ice thickness, this project will conduct an oceanographic cruise to the polynyas of the Ross Sea in April and May, 2017, which is the austral fall. The team will deploy state of the art research tools including unmanned airborne systems (UASs, commonly called drones), autonomous underwater vehicles (AUVs), and remotely operated underwater vehicles (ROVs). Using these tools and others, the team will study atmospheric, oceanic, and sea ice properties and processes concurrently. A change in sea ice production will necessarily change the ocean water below, which may have significant consequences for global ocean circulation patterns, a topic of international importance. All the involved institutions will be training students, and all share the goal of expanding climate literacy in the US, emphasizing the role high latitudes play in the Earth's dynamic climate.<br/><br/>The main goal of the project is to improve estimates of sea ice production and water mass transformation in the Ross Sea. The team will fully capture the spatial and temporal changes in air-ice-ocean interactions when they are initiated in the austral fall, and then track the changes into the winter and spring using ice buoys, and airborne mapping with the newly commissioned IcePod instrument system, which is deployed on the US Antarctic Program's LC-130 fleet. The oceanographic cruise will include stations in and outside of both the Terra Nova Bay and Ross Ice Shelf polynyas. Measurements to be made include air-sea boundary layer fluxes of heat, freshwater, and trace gases, radiation, and meteorology in the air; ice formation processes, ice thickness, snow depth, mass balance, and ice drift within the sea ice zone; and temperature, salinity, and momentum in the ocean below. Following collection of the field data, the team will improve both model parameterizations of air-sea-ice interactions and remote sensing algorithms. Model parameterizations are needed to determine if sea-ice production has increased in crucial areas, and if so, why (e.g., stronger winds or fresher oceans). The remote sensing validation will facilitate change detection over wider areas and verify model predictions over time. Accordingly this project will contribute to the international Southern Ocean Observing System (SOOS) goal of measuring essential climate variables continuously to monitor the state of the ocean and ice cover into the future.
Intellectual Merit: The Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES) is a study of ocean mixing in the Antarctic Circumpolar Current (ACC) which runs west to east all around the continent of Antarctica, south of the other continents. This current system is somewhat of a barrier to transport of heat, carbon dioxide and other important ocean constituents between the far south and the rest of the ocean, and mixing processes play an important role in those transports. DIMES is a multi-investigator cooperative project, led by physical oceanographers in the U.S. and in the U.K. A passive tracer and an array of sub-surface floats were deployed early in 2009 more than 2000 km west of Drake Passage on a surface of constant density about 1500 m deep between the Sub Antarctic Front and the Polar Front of the ACC. In early 2010 a U.S. led research cruise sampled the tracer, turbulence levels, and the velocity and density profiles that govern the generation of that turbulence, and additional U.K. led research cruises in 2011 and 2012 continue this sampling as the tracer has made its way through Drake Passage, into the Scotia Sea, and over the North Scotia Ridge, a track of more than 3000 km. The initial results show that diapycnal, i.e., vertical, mixing west of Drake Passage where the bottom is relatively smooth is no larger than in most other regions of the open ocean. In contrast, there are strong velocity shears and intense turbulence levels over the rough topography in Drake Passage and diapycnal diffusivity of the tracer more than 10 times larger in Drake Passage and to the east than west of Drake Passage.<br/><br/>The DIMES field program continues with the U.S. team collecting new velocity and turbulence data in the Scotia Sea. It is anticipated that the tracer will continue passing through the Scotia Sea until at least early 2014. The U.K. partners have scheduled sampling of the tracer on cruises at the North Scotia Ridge and in the eastern and central Scotia Sea in early 2013 and early 2014. The current project will continue the time series of the tracer at Drake Passage on two more U.S. led cruises, in late 2012 and late 2013. Trajectories through the Scotia Sea estimated from the tracer observations, from neutrally buoyant floats, and from numerical models will be used to accurately estimate mixing rates of the tracer and to locate where the mixing is concentrated. During the 2013 cruise the velocity and turbulence fields along high-resolution transects along the ACC and across the ridges of Drake Passage will be measured to see how far downstream of the ridges the mixing is enhanced, and to test the hypothesis that mixing is enhanced by breaking lee waves generated by flow over the rough topography.<br/><br/>Broader Impacts: DIMES (see web site at http://dimes.ucsd.edu) involves many graduate students and post-doctoral researchers. Two graduate students, who would become expert in ocean turbulence and the processes generating it, will continue be trained on this project. The work in DIMES is ultimately motivated by the need to understand the overturning circulation of the global ocean. This circulation governs the transport and storage of heat and carbon dioxide within the huge oceanic reservoir, and thus plays a major role in regulating the earth?s climate. Understanding the circulation and how it changes in reaction to external forces is necessary to the understanding of past climate change and of how climate might change in the future, and is therefore of great importance to human well-being. The data collected and analyzed by the DIMES project will be assembled and made publicly available at the end of the project.<br/><br/>The DIMES project is a process experiment sponsored by the U.S. CLIVAR (Climate variability and predictability) program.
The goal of this investigation is to understand the role of snow in sea ice development processes and air-ice-ocean heat exchange interactions in the seasonal and perennial sea ice zones of the Ross Sea, the Amundsen Sea, and the Bellingshausen Sea. Observations and measurements of the characteristics of sea ice and snow will be combined with numerical models of sea-ice flooding and the entrainment of snow into the ice cover in order to gain an understanding of the sea-ice heat and mass balance, and to quantify the energy exchange within the antarctic sea-ice cover. The snow measurement program, using the RVIB Nathaniel B. Palmer, will include depth, grain size and morphology, density, temperature, thermal conductivity, water content, and stable isotope ratio. The ice measurement program will include thickness, salinity, temperature, density, brine content, and included gas volume, as well as such structural properties as the fraction of frazil, platelet, and congelation ice in the seasonal antarctic pack ice. Differences in ice types are the result of differences in the environment in which the ice forms: frazil ice is formed in supercooled sea water, normally through wind or wave-induced turbulence, while platelet and congelation ice is formed under quiescent conditions. The fraction of frazil ice is an important variable in the energy budget of the upper ocean, and contributes significantly to the stabilization of the surface layers. The numerical models will involve the thermodynamics of phase changes from liquid water to ice, along with the resulting energy transfer, brine expulsion, and the modulating effect of a snow cover. The results are expected to have broad relevance and application to understanding the effects of sea-ice processes in global change, and atmospheric, oceanographic, and remote sensing investigations of the Southern Ocean.
This project is an examination of the physical and structural properties of the antarctic ice pack in the Amundsen, Bellingshausen, and Ross Seas, with the goal of defining the geographical variability of various ice types, the deformation processes that are active in the antarctic ice pack, and the large-scale thermodynamics and heat exchange processes of the ice- covered Southern Ocean. An additional goal is to relate specific characteristics of antarctic sea ice to its synthetic aperture radar (SAR) signature as observed from satellites. Physical properties include the salinity, temperature, and brine volumes, while structural properties include the fraction of frazil, platelet, and congelation ice of the seasonal antarctic pack ice. Differences in ice types are the result of differences in the environment in which the ice forms: frazil ice is formed in supercooled sea water, normally through wind or wave-induced turbulence, while platelet and congelation ice is formed under quiescent conditions. The fraction of frazil ice (which has been observed to be generally in excess of 50% in Weddell Sea ice floes) is an important variable in the energy budget of the upper ocean, and contributes significantly to the stabilization of the surface layers. The integration of sea ice field observations and synthetic aperture radar data analysis and modeling studies will contribute to a better understanding of sea ice parameters and their geophysical controls, and will be useful in defining the kind of air-ice-ocean interactions that can be studied using SAR data, as well as having broader relevance and application to atmospheric, biological, and oceanographic investigations of the Southern Ocean.
Ultraviolet radiation influences the dynamics of plankton processes in the near-surface waters of most aquatic ecosystems. In particular, the Southern Ocean is affected in the austral spring period when biologically damaging ultraviolet radiation is enhanced by ozone depletion. While progress has been made in estimating the quantitative impact of ultraviolet radiation on bacteria and phytoplankton in the Southern Ocean, some important issues remain to be resolved. Little is known about responses in systems dominated by the colonial haptophyte Phaeocystis antarctica, which dominates spring blooms in a polyna that develops in the southern Ross Sea. The Ross Sea is also of interest because of the occurrence of open water at a far southerly location in the spring, well within the ozone hole, and continuous daylight, with implications for the regulation of DNA repair. A number of studies suggest that vertical mixing can significant modify the impact of ultraviolet radiation in the Southern Ocean and elsewhere. However, there are limited measurements of turbulence intensity in the surface layer and measurements have not been integrated with parallel studies of ultraviolet radiation effects on phytoplankton and bacterioplankton. To address these issues, this collaborative study will focus on vertical mixing and the impact of ultraviolet radiation in the Ross Sea. The spectral and temporal responses of phytoplankton and bacterioplankton to ultraviolet radiation will be characterized in both laboratory and solar incubations. These will lead to the definition of biological weighting functions and response models capable of predicting the depth and time distribution of ultraviolet radiation impacts on photosynthesis, bacterial incorporation and DNA damage in the surface layer. Diel sampling will measure depth-dependent profiles of DNA damage, bacterial incorporation, photosynthesis and fluorescence parameters over a 24 h cycle. Sampling will include stations with contrasting wind-driven mixing and stratification as the polyna develops. The program of vertical mixing measurements is optimized for the typical springtime Ross Sea situation in which turbulence of intermediate intensity is insufficient to mix the upper layer thoroughly in the presence of stabilizing influences like solar heating and/or surface freshwater input from melting ice. Fine-scale vertical density profiles will be measured with a free-fall CTD unit and the profiles will be used to directly estimate large-eddy scales by determining Thorpe scales. Eddy scales and estimated turbulent diffusivities will be directly related to surface layer effects, and used to generate lagrangian depth-time trajectories in models of ultraviolet radiation responses in the surface mixed layer. The proposed research will be the first in-depth study of ultraviolet radiation effects in the Ross Sea and provide a valuable comparison with previous work in the Weddell-Scotia Confluence and Palmer Station regions. It will also enhance the understanding of vertical mixing processes, trophic interactions and biogeochemical cycling in the Ross Sea.
This project is a contribution to a coordinated attempt to understand the interactions of biological and physical dynamics by developing relationships among the evolution of the antarctic winter ice and snow cover, biological habitat variability, and the seasonal progression of marine ecological processes. The work will be carried out in the context of the Southern Ocean Experiment of the Global Ocean Ecosystem Dynamics Study (Globec), a large, multi-investigator study of the winter survival strategy of krill under the antarctic sea ice in the vicinity of Marguerite Bay on the western side of the Antarctic Peninsula.<br/><br/>The objective of this project is to make a quantitative assessment of the small scale temperature and salinity structure of the oceanic surface layer in order to study the effect of stratification and turbulence on the biochemical and biological processes under the winter sea ice.<br/><br/>The water masses on the continental shelf off Marguerite Bay consist of inflowing Upper Circumpolar Deep Water, which is relatively warm, salty, oxygen-poor, and nutrient-rich. In winter atmospheric processes cool and freshen this water, and recharge it with oxygen to produce Antarctic Surface Water which is diffused seaward, and supports both a sea ice cover and a productive krill-based food web. The modification processes work through mixing associated with shear instabilities of the internal wave field, double diffusion of salt and heat, and mixing driven by surface stress and convection. These processes will be quantified with two microstructure profilers, capable of resolving the small but crucial vertical variations that drive these processes.<br/>***
Ultraviolet radiation influences the dynamics of plankton processes in the near-surface waters of most aquatic ecosystems. In particular, the Southern Ocean is affected in the austral spring period when biologically damaging ultraviolet radiation is enhanced by ozone depletion. While progress has been made in estimating the quantitative impact of ultraviolet radiation on bacteria and phytoplankton in the Southern Ocean, some important issues remain to be resolved. Little is known about responses in systems dominated by the colonial haptophyte Phaeocystis antarctica, which dominates spring blooms in a polyna that develops in the southern Ross Sea. The Ross Sea is also of interest because of the occurrence of open water at a far southerly location in the spring, well within the ozone hole, and continuous daylight, with implications for the regulation of DNA repair. A number of studies suggest that vertical mixing can significant modify the impact of ultraviolet radiation in the Southern Ocean and elsewhere. However, there are limited measurements of turbulence intensity in the surface layer and measurements have not been integrated with parallel studies of ultraviolet radiation effects on phytoplankton and bacterioplankton. To address these issues, this collaborative study will focus on vertical mixing and the impact of ultraviolet radiation in the Ross Sea. The spectral and temporal responses of phytoplankton and bacterioplankton to ultraviolet radiation will be characterized in both laboratory and solar incubations. These will lead to the definition of biological weighting functions and response models capable of predicting the depth and time distribution of ultraviolet radiation impacts on photosynthesis, bacterial incorporation and DNA damage in the surface layer. Diel sampling will measure depth-dependent profiles of DNA damage, bacterial incorporation, photosynthesis and fluorescence parameters over a 24 h cycle. Sampling will include stations with contrasting wind-driven mixing and stratification as the polyna develops. The program of vertical mixing measurements is optimized for the typical springtime Ross Sea situation in which turbulence of intermediate intensity is insufficient to mix the upper layer thoroughly in the presence of stabilizing influences like solar heating and/or surface freshwater input from melting ice. Fine-scale vertical density profiles will be measured with a free-fall CTD unit and the profiles will be used to directly estimate large-eddy scales by determining Thorpe scales. Eddy scales and estimated turbulent diffusivities will be directly related to surface layer effects, and used to generate lagrangian depth-time trajectories in models of ultraviolet radiation responses in the surface mixed layer. The proposed research will be the first in-depth study of ultraviolet radiation effects in the Ross Sea and provide a valuable comparison with previous work in the Weddell-Scotia Confluence and Palmer Station regions. It will also enhance the understanding of vertical mixing processes, trophic interactions and biogeochemical cycling in the Ross Sea.
