Harriet Alexander and Sonya T. Dyhrman
Molecular Metabolic Fingerprinting to Identify Drivers of Phytoplankton Bloom Dynamics in the Southern Ocean
Marine phytoplankton are responsible for the net primary production of nearly 50 Pg (1015) of carbon per year, which is approximately 50% of the total primary production on earth. Marine primary production drives the global biogeochemical cycles of carbon as well as key nutrients (e.g. nitrogen (N) and phosphorus (P)). Overarching changes in the global climate stand to greatly alter both the biogeochemistry of the world’s oceans as well as the distribution and nature of primary production. The Southern Ocean is one of the largest High Nutrient-Low Chlorophyll (HNLC) regions in the ocean, representing the greatest reservoir of free macronutrients (e.g. N and P) in surface waters. Seasonal, massive phytoplankton blooms, dominated by Phaeocystis antarctica and pennate diatoms such as Fragilariopsis spp. and Pseudonitzschia spp. drive the production in the system. As the Southern Ocean is a crucial source of deep and intermediate water formation, it is a region of potentially great importance for carbon sequestration and the global carbon cycle. The forecasted large-scale climate alterations highlight the importance of a thorough comprehension of the global carbon cycle, which is tightly linked to biogeochemical cycling in the Southern Ocean. A more thorough understanding of the controls of phytoplankton bloom dynamics is crucial in the light of the changing ocean environment, yet there remain many fundamental questions surrounding phytoplankton growth dynamics in the Southern Ocean.
We have been offered berth space to participate in an upcoming series of cruises from the coast of Chile to Margeurite Bay on the west Antarctica peninsula currently scheduled for Fall (2012) and Spring (2013), providing us with a unique opportunity to apply molecular techniques that we have been developing in culture-based experiments to better understand the biogeochemical drivers of phytoplankton blooms in this critically important and difficult to access system. Using eukaryotic metatranscriptomic approaches, we will measure global gene expression in situ to derive metabolic fingerprints of the phytoplankton community along the cruise track. Coupling these samples with shipboard incubation experiments, we will quantitatively bound the differential gene expression signals observed in the field to address the following questions: 1) How do the blooming species P. antarctica, Fragilariopsis spp., and Pseudonitzschia spp. partition their biogeochemical niche space? and 2) What are the biogeochemical drivers of eukaryotic phytoplankton bloom formation in the Southern Ocean?
Our application of novel genome-enabled approaches, will identify biogeochemical drivers of bloom formation not discernable through traditional methods (e.g. incubation experiments and environmental chemical assays). Cutting-edge metatranscriptomic studies on eukaryotic phytoplankton have only been successfully done once before, and we anticipate that the access to the sea funding requested here will provide fundamental new insight, high-profile proof of concept papers, and lead to future federal funding. The high risk nature of this project combined with its short time-frame on these special cruises of opportunity make it difficult to fund the proposed work through traditional sources. Additionally, this funding will provide JP Student Harriet Alexander with her first at-sea experience, and the data gathered will form a significant portion of her graduate thesis work.
Donglai Gong, Robert S. Pickart and Lee E. Frietag
Glider Observation of the Western Arctic Boundary Current
The Alaska Coastal Current (ACC) in the Chukchi Sea and the Beaufort Shelfbreak Jet (BSJ) in the Beaufort Sea are two segments of an extended coastal boundary current that transports a large fraction of the heat and freshwater from the Pacific ocean into the Arctic ocean. The ACC and BSJ join at the mouth of Barrow Canyon. Previous observations have revealed large along-shelf hydrographic and flow variability on distance scales of over 100 km inside Barrow Canyon and along the Alaskan Beaufort shelfbreak. Some of this variability can be attributed to the exchange of heat and salt between the boundary current and the deep basin. Eddy formation in the boundary current due to barotropic and baroclinic instabilities, as well as shelfbreak upwelling driven by easterly winds, are two of the physical processes that can efficiently facilitate exchange at the shelfbreak and affect the ventilation of the upper halocline. Characterizing the along-shelf variability with sub-mesoscale resolution (~1 km) greatly would aid our understanding of how eddies and winds affect cross-shelfbreak exchange of heat and salt. To date, there has been no high resolution along-shelf hydrographic measurements of the ACC/BSJ boundary current with submesoscale resolution (~1 km).
With Access to the Sea’s support, we plan to use a Slocum glider, equipped with CTD and bio- optical sensors, to study the along-flow hydrographic structure of the ACC/BSJ boundary current system in the transition region immediately upstream and downstream of the mouth of Barrow Canyon. High resolution profiling data from the glider in the upper water column would enable us to measure the differing along-shelf evolution of the winter and summer Pacific water masses and characterize the effect of eddies and winds on the boundary current. The study will leverage logistics support already in place for a funded mooring cruise (Chief Sci.: Robert Pickart) for the Arctic Observing Network in the Beaufort Sea in October 2012.
This study also has a technology development/engineering component. The boundary current in the western Arctic is active year round and plays an important role in the ventilation of the Arctic halocline during the partially ice covered spring and autumn. The present generation of autonomous sampling platforms, such as the Slocum glider, can only be deployed during the ice-free summer season mainly due to the need to obtain regular surface GPS fixes for navigation. The project’s engineering goal is to test a prototype long distance acoustic communication technology to be used for future under-ice glider/AUV navigation in the Arctic shelfbreak environment. A hydrophone will be installed on the Glider glider to record acoustic signals transmitted by a shipboard transducer at distance of 10-100 km away. The research and engineering effort from this study will aid the development of future external proposals to undertake more extensive longer-term studies of the Arctic boundary current system using autonomous mobile platforms.
Andone Claire Lavery and W. Rockwell Geyer
Measuring the Three-Dimensional Structure of Statified Turbulence
Mixing in stratified flows is fundamentally important for understanding and quantifying the transport processes in the ocean. Recent field experiments conducted by the PIs in the Connecticut River estuary outflow, a highly-stratified, strongly-sheared estuarine environment, have challenged the long-standing paradigm that mixing occurs in the cores of shear instabilities. These provocative results were obtained by the unique combination of high- frequency, high-resolution broadband acoustic backscattering methods combined with a novel approach for in-situ measurements of turbulence. However, these measurements did not resolve the three-dimensional structure or temporal evolution of shear instabilities. Yet these are critical components to the complete understanding of the transition to turbulence within shear instabilities in stratified flows at very high Reynolds number.
We propose to develop and use a combination of advanced acoustic techniques and ship- mounted, in situ turbulence measurements to quantify the three-dimensional structure of stratified turbulence in an estuarine outflow. Specifically, we would like to use Access-to-the- Sea funding to develop and deploy two acoustic backscattering systems, involving a broadband acoustic backscattering array and a multibeam system, which resolve the three-dimensional structure of shear instabilities and stratified turbulence. In addition to addressing this important fluid dynamics problem, the methods have application to the quantification of a variety of physical and biological processes in the ocean.
Robert Todd and W. Brechner Owens
Advancing Glider-based Doppler Current Estimates; Ground Truthing and Improving Data Processing
Autonomous underwater gliders allow long-duration, high-resolution observations in the upper ocean and have proven to be useful observing platforms over the past decade. Doppler current profilers, which use sound to measure water velocity relative to the glider, are seeing increased use on gliders. To estimate upper ocean velocity profiles from glider-based Doppler current measurements, one must combine many individual measurements of water velocity relative to the moving glider to estimate both the unknown velocity of the glider over the ground and the ocean currents. A previously-developed inverse method provides an effective, flexible means of processing the measurements and estimating ocean currents. However, a lack of coincident, independent current measurements has precluded analysis of the accuracy of the glider-based Doppler current estimates. Accurate, depth-dependent estimates of ocean currents are essential to estimating fluxes of tracers, such as heat, salt, and nutrients, in the ocean.
Access to the Sea funds will be used to deploy both a glider equipped with a Doppler current profiler and an independent moored current profiler for two weeks. Deployment and recovery will be performed from R/V Knorr during an NSF-funded cruise along the Line W array south of Cape Cod in August 2012. The two-week deployment will provide more than 100 glider-based current profiles that will be compared to the moored current profiles. Improvements to the existing data processing technique will be explored with the goal of improving the accuracy of glider-based Doppler current estimates. The results will be applicable to past and future current estimates from various combinations of gliders and Doppler current profilers. The project will also allow a Postdoctoral Scholar to participate in deployment and recovery of oceanographic moorings for the first time.