Meng Zhou, Ph.D. - US grants

9523748 Huntley Patchiness of zooplankton and micronekton is a feature of central importance in marine ecosystems. In the Southern Ocean, aggregations of krill (Euphausia superba) are of particular interest. The distribution and dynamics of such aggregations are critical to determining the transformation of organic matter (e.g. carbon flux) and the fate of populations in the sea. These phenomena are especially important in the mesoscale and sub- mesoscale domains, where patchiness is most strongly expressed. If the means to predict patch dynamics is lacking, then so is the means to adequately predict carbon flux and population dynamics at these scales. Traditional models of zooplankton patch dynamics generally treat animals as Lagrangian particles whose aggregations are determined solely by processes of advection and diffusion. This approach ignores behavior induced by biotic and abiotic forces and manifested as purposeful motion - motion that clearly is not governed by advection and diffusion. Attempts to acknowledge behavior in models of plankton motility have been successful at the level of the individual animal, but even the most powerful computers cannot run individual-based models to predict aggregation dynamics of n individuals. This proposal takes a new approach to modeling aggregation dynamics, based on "bio-continuum" theory, and provides for model verification against benchmark field data. Rather than relying on traditional advection-diffusion equations, which ignore behavior, the bio-continuum theory recognizes behavioral forces in the context of statistical mechanics. Model output provides information on animal behaviors, manifest as swimming velocities, that are absent from other models of patch dynamics. All key model variables are measurable using common sampling techniques, such as acoustic Doppler and multiple net systems. The proposed research consists of studying both the internal and external forces that act on aggregations of Euphausia superba. First, the internal forces of autocoherence (that act between animals to maintain patch integrity) will be measured in krill aggregations observed in the Gerlache Strait region in 1992. Our database consists of more than 20 such aggregations observed by ADCP and MOCNESS. Second, the effect of external physical forcing on krill aggregations will be studied by embedding krill swarms of typical scales in numerically modeled flow regimes that are typical of the Gerlache Strait region (Zhou and Niiler 1995), by combining the Princeton circulation model (e.g. Blumberg and Mellor 1987) with our aggregation model. This research provides a novel, dynamic theory of animal aggregations in the sea. A study of the fundamental theory, coupled with model realizations that can be compared to observed aggregations of Euphausia superba, may lead to more realistic predictions of krill patch dynamics in the Southern Ocean. Such predictions are critical to more accurate measurements of carbon flux and the population dynamics of krill.

Project Summary: We propose to construct a practical zooplankton population dynamics model based on novel advances in the biomass spectrum theory (Platt and Dernman 1977; Zhou and Huntley submitted). Testing and application of the theory will use eddy resolving CTD OPC (Optical Plankton Counter: Focal Instruments Inc.) data collected in the California Current region during June July 1993 and September October 1993. The novel advances in the biomass spectrum theory explicitly include population dynamics parameters such as rates of individual growth, birth, and mortality. We first developed a general biomass spectrum theory of size structured zooplankton population dynamics based on Platt and Denman's model (1977), and then demonstrated that this theory can be practically applied to estimate zooplankton population dynamics rates and productivity from observations of the biomass spectrum. In this theory, zooplankton, including all species and stages, are classified by weight. For estimating population dynamics rates from field observations and verifying modeling results, we further developed an objective interpolation method which removes the effects of advection from observations and calculates statistical properties of the spatiotemporal interpolation. This objective interpolation method will be applied to zooplankton data obtained in the California Current region. The results, together with the biomass spectrum theory and individual population growth models. will be used to estimate rates of population dynamics. These rates and zooplankton spatiotemporal distributions allow us realistically to construct and verify a population model. Then we will develop a numerical model based on the biomass spectrum theory and analyzed population dynamics rates, which takes the phytoplankton and physical fields from observations or modeling, and outputs zooplankton spatiotemporal distribution and productivity. This model provides the trophic link between models of phytoplankton and fish, and can be directly embedded into an existing hydrodynamic ecosystem model for ecosystem study and prediction of secondary production. This approach assertively addresses the central GLOBEC paradigm First, it directly addresses population dynamics at the mesoscale. Second, it couples modeling with observations derived from new sampling technology (OPC). Third, this research involves a conscious effort to provide a model that can assimilate field data and therefore can be used to both guide and interpret GLOBEC observations in Northeast North Pacific Ocean.

9908079/9906757
Ashijan/Zhou

The Barents Sea contains a fishery rich in commercially important species such as capelin, polar cod, and herring. The southern Barents Sea functions as a critical nursery area for the herring, which depend on zooplankton stocks during early life stages, and also supports populations of the planktivorous polar cod and capelin. It has been suggested that Calanus finmarchicus, as an expatriate in Arctic waters, may not reproduce successfully or be capable of sustaining its populations. The transport of zooplankton into the southern Barents Sea by the Norwegian Atlantic Current (NAC) and the Norwegian Coastal Current is an important mechanism to the Barents Sea ecosystem.
To understand the spatiotemporal distribution and fate of zooplankton in the ocean, it is necessary to understand the interaction between advection, migration behavior, and population dynamics, especially at the mesoscale. This interaction is most profound in polar regions because the internal Rossby Radius is on the order of 101 km. Obtaining quantitative measurements of 3-dimensional advection and in situ population dynamics rates of plankton in a mesoscale eddy are daunting tasks. Traditional sampling and experimental methods cannot resolve processes at mesoscales. Acoustic instruments can resolve these scales, but cannot provide information necessary for traditional models to estimate population dynamics rates. Optical instruments, such as the Optical Plankton Counter (OPC) or Video Plankton Recorder (VPR), can provide information on the size-distribution of zooplankton at high vertical and temporal resolution but have not been used for the study of zooplankton rate processes. Theories and models describing rate processes in zooplankton based on size structure exist but have not been applied extensively.
The PI's of this project have synthesized survey strategies using new high-resolution sampling methods with new mathematical theories of population dynamics and objective analysis, yielding a quantitative approach to the study of advection, vertical migration, and population dynamics of zooplankton on unprecedented scales. This project will undertake a critical test of this synthesis of theories and survey strategies in Tromsoflaket, northern Norway.
Tromsoflaket is an important ecosystem located where the Norwegian Atlantic Current (NAC) bifurcates. A permanent eddy is formed in Tromsoflaket between these two branches. The northeast-flowing branch of the NAC appears to be an important mechanism for transporting zooplankton productive shelf water farther northwards into the Barents Sea during the productive season. In the vicinity of Tromsoflaket, a single species (Calanus finmarchicus) accounts for 95% of the copepod biomass in May and June. A composition of mixed species is found in August and September. This provides opportunities to test our new approach first in a simple case of a single dominant species, and then in a more complicated general case of mixed species.
The successful outcome of this research could lead to an understanding of how zooplankton population dynamics in mesoscale eddy systems support high trophic levels in Arctic regions, and represent an important advance in biological oceanography, opening up the possibility of high-resolution measurements of zooplankton dynamics in mesoscale eddies, not just distributions.

9988098
Ricketts
This award to University of Minnesota at Duluth will provide instrumentation for lake research for use on R/V Blue Heron, a research vessel operated by the University's Large Lakes Observatory as part of the University-National Oceanographic Laboratory System research fleet. Specific instrumentation to be acquired includes a portable winch and two computers. The shared-use instrumentation supported here will assist marine scientists conduct studies in the Great Lakes during 2000 and future years.
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The Shackleton Fracture Zone (SFZ) in the Drake Passage defines a boundary between low and high phytoplankton waters. West of Drake Passage, Southern Ocean waters south of the Polar Front and north of the Antarctic continent shelf have very low satellite-derived surface chlorophyll concentrations. Chlorophyll and mesoscale eddy kinetic energy are higher east of SFZ compared to values west of the ridge. In situ data from a 10-year survey of the region as part of the National Marine Fisheries Service's Antarctic Marine Living Resources program confirm the existence of a strong hydrographic and chlorophyll gradient in the region. An interdisciplinary team of scientists hypothesizes that bathymetry, including the 2000 m deep SFZ, influences mesoscale circulation and transport of iron leading to the observed phytoplankton patterns. To address this
hypothesis, the team proposes to examine phytoplankton and bacterial physiological states (including responses to iron enrichment) and structure of the plankton communities from virus to zooplankton, the concentration and distribution of Fe, Mn, and Al, and mesoscale flow patterns near the SFZ. Relationships between iron concentrations and phytoplankton characteristics will be examined in the context of the mesoscale transport of trace nutrients to determine how much of the observed variability in phytoplankton biomass can be attributed to iron supply, and to determine the most important sources of iron to pelagic waters east of the Drake Passage. The goal is to better understand how plankton productivity and community structure in the Southern Ocean are affected by the coupling between bathymetry, mesoscale circulation, and limiting nutrient distributions.
The research program includes rapid surface surveys of chemical, plankton, and hydrographic properties complemented by a mesoscale station grid for vertical profiles, water sampling, and bottle incubation enrichment experiments. Distributions of manganese and aluminum will be determined to help distinguish aeolian, continental shelf and upwelling sources of iron. The physiological state of the phytoplankton will be monitored by active fluorescence methods sensitive to the effects of iron limitation. Mass concentrations of pigment, carbon and nitrogen will be obtained by analysis of filtered samples, cell size distributions by flow cytometry, and species identification by microscopy. Primary production and photosynthesis parameters (absorption, quantum yields, variable fluorescence) will be measured on depth profiles, during surface surveys and on bulk samples from enrichment experiments. Viruses and bacteria will be examined for abundances, and bacterial production will be assessed in terms of whether it is limited by either iron or organic carbon sources. The proposed work will improve our understanding of processes controlling distributions of iron and the response of plankton communities in the Southern Ocean. This proposal also includes an outreach component comprised of Research Experiences for Undergraduates (REU), Teachers Experiencing the Antarctic and Arctic (TEA), and the creation of an educational website and K-12 curricular modules based on the project.

P.I. Chant, Robert (Rutgers) Proposal #: 0238957

Proposal Title: COLLABORATIVE RESEARCH: Lagrangian studies of the transport, transformation, and biological impact of nutrients and contaminant metals in a buoyant plume

Project Summary
The PIs propose a coordinated program of field and numerical experiments to examine processes that control the fate and transport of nutrients and chemical contaminants in the Hudson River plume. Urban estuarine plumes such as this one represent a major pathway for the transport of nutrients and chemical contaminants to the coastal ocean. The fates and transports of this material are controlled not only by the plume dynamics but also by biological and chemical processes coupled to the dynamics of the plume. To investigate these processes, the PIs propose to conduct a series of dye experiments along with continuous underway chemical and biological sampling using a towed vehicle. These experiments will occur within the framework of the LEO-15 Observatory to enable interpretation of the dye study by placing the Lagrangian surveys in context with shelf-wide observations from satellite imagery, surface currents and far-field subsurface hydrography. LEO-15 will be augmented by a cross shelf array of moored instruments to provide detailed estimates of subtidal circulation, stratification and Reynold stresses. In addition, data-assimilative numerical simulations will provide high resolution and realistic hindcasts of the coastal ocean during the field experiments. The modeling will assimilate the dye-tracer data into a 3-D coastal circulation model and guide future efforts to assimilate other tracers into circulation models with complex sources and sinks.
The major aims of this work are to distinguish between physical processes that transport/mix material in a buoyant plume from biological and chemical transformation processes as well as the quantification of biological and chemical interactions in a Lagrangian perspective to provide a means to assess their importance in determining the fate and transport of nutrients and chemical contaminants in a buoyant plume. The proposed experimental plan will contrast the response of physical, biological, and chemical processes in the Hudson plume during upwelling and downwelling conditions. A major outcome of this work will be the determination of the extent and biological impact of contaminants in the plume along the New Jersey coast and Middle Atlantic Bight and will improve the ability to predict the fate and transport of contaminants and the rate that they enter the base of the food chain in the coastal ocean.

Ecological responses to mesoscale physical dynamics are not limited to a mesoscale spatial domain. Consequently, an understanding of the linkage to ecological dynamics over larger spatial scales and longer time scales is critically dependent upon a characterization of the mesoscale physical/biological interactions. The investigators propose to evaluate the link between mesoscale physical dynamics, as driven by local and remote forcing, and the variability in phytoplankton and zooplankton abundance and spatial pattern observed across the GLOBEC Northeast Pacific region. The two primary objectives are to (1) determine the contribution of variability in mesoscale physical forcing and ocean dynamics to the variability in ecosystem dynamics, as expressed by phytoplankton and zooplankton abundance, spatial pattern, size distribution and indices of production and (2) extend this mesoscale understanding across a larger spatial domain and across longer time scales through the use of coupled models and other GLOBEC datasets. The investigators will examine the consequences of variability in forcing on the ecosystem and develop indices of mesoscale variability in both the physical and biological properties of the northern California Current. The indices will be related to changes in energy input into the system, e.g. interannual changes in wind forcing. Within the GLOBEC synthesis effort, this work will contribute to a causal understanding of the link between local physical and biological mesoscale activity to large spatial-scale, long time-scale regional forcing, and will establish a basis for developing a predictive capability for estimating mesoscale ecosystem response to forcing. The results will be disseminated through multi-authored papers, linked websites, and through LiveAccess servers. The investigators also propose to collaborate with the Oregon Office of Adult Education.

The Shackleton Fracture Zone (SFZ) in Drake Passage of the Southern Ocean defines a boundary between low and high phytoplankton waters. Low chlorophyll water flowing through the southern Drake Passage emerges as high chlorophyll water to the east, and recent evidence indicates that the Southern Antarctic Circumpolar Current Front (SACCF) is steered south of the SFZ onto the Antarctic Peninsula shelf where mixing between the water types occurs. The mixed water is then advected off-shelf with elevated iron and phytoplankton biomass. The SFZ is therefore an ideal natural laboratory to improve the understanding of plankton community responses to natural iron fertilization, and how these processes influence export of organic carbon to the ocean interior. The bathymetry of the region is hypothesized to influence mesoscale circulation and transport of iron, leading to the observed patterns in phytoplankton biomass. The position of the Antarctic Circumpolar Current (ACC) is further hypothesized to influence the magnitude of the flow of ACC water onto the peninsula shelf, mediating the amount of iron transported into the Scotia Sea. To address these hypotheses, a research cruise will be conducted near the SFZ and to the east in the southern Scotia Sea. A mesoscale station grid for vertical profiles, water sampling, and bottle incubation enrichment experiments will complement rapid surface surveys of chemical, plankton, and hydrographic properties. Distributions of manganese, aluminum and radium isotopes will be determined to trace iron sources and estimate mixing rates. Phytoplankton and bacterial physiological states (including responses to iron enrichment) and the structure of the plankton communities will be studied. The primary goal is to better understand how plankton productivity, community structure and export production in the Southern Ocean are affected by the coupling between bathymetry, mesoscale circulation, and distributions of limiting nutrients. The proposed work represents an interdisciplinary approach to address the fundamental physical, chemical and biological processes that contribute to the abrupt transition in chl-a which occurs near the SFZ. Given recent indications that the Southern Ocean is warming, it is important to advance the understanding of conditions that regulate the present ecosystem structure in order to predict the effects of climate variability. This project will promote training and learning across a broad spectrum of groups. Funds are included to support postdocs, graduate students, and undergraduates. In addition, this project will contribute to the development of content for the Polar Science Station website, which has been a resource since 2001 for instructors and students in adult education, home schooling, tribal schools, corrections education, family literacy programs, and the general public.

The PIs propose to develop a Lagrangian Bio-acoustic Drifter system to remotely sense zooplankton in the upper ocean (100 m) and to provide real-time data via satellite telemetry. The PIs hope to integrate this technology into the Global Drifter Program - a global array of approximately 1000 drifters now operated jointly by NOAA and Scripps Institution of Oceanography. This system represents the novel convergence of three mature technologies: high-frequency bioacoustics; Lagrangian drifters; and wireless telemetry together comprise a cost-effective instrument for zooplankton remote sensing. The advance in technology proposed is a wide-band probe that sequentially samples multiple frequencies. Such a probe has been successfully developed for very high frequencies, but is costly and has limited range (<5m). The probe proposed here uses precisely the same acoustic principles, has a much greater range (100 m), and lower cost. Funding of this SGER proposal will provide the proof-of-concept demonstration needed before integrating them into the drifter package.

Broader Impacts

This project will collaborate with the .Hawaii Kumu Ola: Source of Knowledge Program at UH, an NSF-funded project (J Vergun, PI) aimed at increasing the number of underrepresented undergraduates (e.g. Native Hawaiians, Pacific Islanders) who earn degrees in science, technology, engineering and mathematics. This project will provide one internship to a qualified student who will participate fully in all aspects of the project. On a national and international level, the collaboration with the Global Drifter Center establishes a clear path for integrating new data products into an existing network and facility that serves oceanographic research on a global scale.

Abstract

Intellectual Merit: The krill surplus hypothesis argues that the near-extirpation of baleen whales from Antarctic waters during much the twentieth century led to significant changes in the availability of krill for other predators. Over the past decade, however, overall krill abundance has decreased by over an order of magnitude around the Antarctic Peninsula, in part due to physical forces, including the duration and extent of winter sea ice cover. Krill predators are vulnerable to variability in prey and have been shown to alter their demography in response to changes in prey availability This research will use novel tagging technology combined with traditional fisheries acoustics methods to quantify the prey consumed by a poorly understood yet ecologically integral and recovering krill predator in the Antarctic, the humpback whale (Megaptera novaeangliae). It also will use a combination of advanced non-invasive tag technology to study whale behavior concurrent with hydro-acoustic techniques to map krill aggregations. The project will (1) provide direct and quantitative estimates of krill consumption rates by humpback whales and incorporate these into models for the management of krill stocks and the conservation of the Antarctic marine ecosystem; (2) provide information integral to understanding predator-prey ecology and trophic dynamics, i.e., if/how baleen whales affect the distribution and behavior of krill and/or other krill predators; (3) add significantly to the knowledge of the diving behavior and foraging ecology of baleen whales in the Antarctic; and (4) develop new geospatial tools for the construction of multi-trophic level models that account for physical as well as biological data.

Broader Impacts: Whales are assumed to be a major predator on Antarctic krill, yet there is little understanding of how whales utilize this resource. This knowledge is critical to addressing both bottom-up and top-down questions, e.g., how climate change may affect whales or how whales may affect falling krill abundances. This program will integrate research and education by providing opportunities for undergraduate and graduate students as well as postdoctoral researchers at Duke University, the Florida State University and the University of Massachusetts at Boston. This project will also seek to integrate interactive learning through real time, seasonal and curriculum development in collaboration with the National Geographic Society as well as at the participating universities and local schools in those communities.

The ocean plays a critical role in sequestering CO2 by exporting fixed carbon to the deep ocean through the biological pump. There is a pressing need to understand the systematics of carbon export in the Southern Ocean in the context of global warming because of the sensitivity of this region to climate change, already manifested as significant temperature increases. Numerous studies have indicated that Fe supply is a primary control on phytoplankton biomass and productivity in the Southern Ocean. The results from previous cruises in Feb-Mar 2004 and Jul-Aug 2006 have revealed the major natural Fe fertilization from Fe-rich shelf waters to the Fe-limited high nutrient low chlorophyll (HNLC) Antarctic Circumpolar Current Surface Water (ASW) in the southern Drake Passage, producing a series of phytoplankton blooms. Remaining questions include: How is natural Fe transported to the euphotic zone through small-meso-large scale horizontal-vertical transport and mixing in different HNLC ACC areas? How does plankton community structure evolve in response to a natural Fe addition, how does Fe speciation respond to biogeochemical processes, and how is Fe recycled to determine the longevity of phytoplankton blooms? How does the export of POC evolve as a function of upwelling-mixing, Fe addition-recycling and bacteria-plankton structure? This synthesis proposal will address these fundamental questions using a unique dataset combining multiyear physical, Fe and biogeochemical data collected between 2004 and 2006 from 2 NSF-funded Fe fertilization experiment cruises and 3 Antarctic Marine Living Resource (AMLR) cruises in the southern Drake Passage and southwestern Scotia Sea through collaboration with scientists in the AMLR program and US Southern Ocean GLOBEC projects. All investigators involved in this study are engaged in graduate and undergraduate instruction, and mentoring of postdoctoral researchers. Each P.I. will incorporate key elements of the proposed syntheses in our lectures, problem sets and group projects. The project includes support to convene a 4-5 day international workshop on natural Fe fertilization at Woods Hole Oceanographic Institution. The workshop will include scientists from United Kingdom, France and Germany who have conducted natural Fe fertilization experiments, and Korea and China who are planning to conduct natural Fe fertilization experiments. The participation of graduate students and postdoctoral scholars will be especially encouraged. The results will be published in a Deep-Sea Research II special issue.

Krill, Euphausia superba, is a keystone species in the Antarctic ecosystem and provides the trophic link between microscopic plankton and charismatic megafauna such as penguins and whales. Recent evidence suggests krill may not be exclusively planktonivorous, which introduces the potential of new pathways of carbon flux through krill based ecosystems. A change in our view of krill from one of being herbivores to omnivores opens up several questions.

Climate induced change in the extent, thickness and duration of overlying sea ice coverage is expected to change the prey fields available to krill, and to have subsequent effects on the suite of predators supported by krill. The nature of this benthic prey?krill link, which may be crucial in those parts of the seasonal cycle other than the well studied spring bloom, is yet to be determined. DNA techniques will be used to identify and quantify the prey organisms.

This project will measure the in situ feeding ecology and behavior of krill and, ultimately, the success of this key species. An overall goal is
to investigate seasonal changes in Euphausia superba in-situ feeding and swimming behavior in the Wilhelmina Bay region of the Western Antarctic Peninsula (WAP) area, known to be a region of changing climate. Understanding the biological impacts of climate change is important to societal and economic goals. The project scientists will additionally team with a marine and environmental reporting group to design presentations for an annual journalist meeting.