Collaborative Proposal: Quantifying the effects of variable light and iron on the nitrate assimilation isotope effect of phytoplankton
This project will test the hypothesis that light and/or iron stress on phytoplankton change the isotopic ratios (15N/14N) of water column nitrate due to a change in nitrate uptake to nitrate leakage. A combination of laboratory culture and field experiments in the Southern Ocean are conducted.
PI's on the project: Sven Kranz (FSU), Angie Knapp (FSU), Dreux Chappell (ODU) and our unfunded collaborator in CapeTown (South Africa) Sarah Fawcett
Students involved: Jared Rose (FSU), Margaret Baker (FSU), Rachel Thomas (FSU), Sveinn Einnarson (ODU), Heather Forrer (FSU/Cape Town) and many undergraduate helpers!
Award Abstract #1850925; https://www.nsf.gov/awardsearch/showAward?AWD_ID=1850925
Phytoplankton are microscopic, single-celled organisms that play an important role in the Earth's ecosystems, elemental cycles, and climate. These organisms, which live in surface ocean waters, require sunlight and nutrients to grow and reproduce. In the oceans around Antarctica, nitrate (NO3-) as a nutrient source of nitrogen (N) is usually abundant while the nutrient iron is often sparse. Light availability also changes from complete darkness to 24 hours of constant sunlight, as well as from low light deeper in the water column to high, stressful light at the ocean surface. As a consequence, the phytoplankton in the Southern Ocean often live in a suboptimal environment in which conditions for growth are frequently changing. Scientists understand that nutrient supply and light availability affect these organisms and that these organisms, in turn, can alter the chemical composition of the seawater. For example, nitrate can occur in different forms, including a lighter (14N) and heavier (15N) form of NO3-, depending on which stable isotope of N is present in the molecule. Phytoplankton prefer to use the lighter isotope during uptake and incorporation into biomass, though the ratio of 15N/14N used by phytoplankton has been shown to vary depending on environmental conditions. Notably, the isotope ratio used by phytoplankton is recorded in sediments and can be used to determine both the historic composition of ocean waters and the productivity of phytoplankton. This project will test the hypothesis that enhanced light and/or iron stress change the isotopic ratios of water column nitrate- in specific ways. A combination of laboratory culture and field experiments will be conducted. Cultures of important Southern Ocean phytoplankton species will be grown under environmentally-relevant light and iron conditions where ratio of 15N/14N used by phytoplankton, physiological changes, and molecular markers of iron and light stress and nitrate assimilation will be measured. Similar measurements will be done in shipboard experiments on a cruise in the Southern Ocean with South African colleagues (SCALE'19). These data will increase our understanding of past and present productivity in the Southern Ocean, and how phytoplankton changed the chemical composition of the seawater. Undergraduates from underrepresented groups in the STEM field and graduate students from Florida State University and Old Dominion University as well as students from South Africa will collaborate on this project. The improved process understanding of the N isotope effect will be presented not only at scientific national and international conferences but also during local outreach events at local K-12 schools. Interpretation of both modern water column nitrate (NO3-) isotopic ratio (d15N) measurements generated by GEOTRACES and other cruises, as well as metrics of paleo-nutrient utilization, depend upon a mechanistic understanding of the degree to which NO3- assimilation by phytoplankton discriminates against the heavier isotope, 15NO3- (NO3- assimilation epsilon). We currently lack the ability to predict how iron and light stress impacts the NO3- assimilation epsilon. The proposed work will test the hypothesis that enhanced light and/or iron stress elevates the epsilon for NO3- assimilation. This hypothesis will be tested by a combination of laboratory culture work and field work on a cruise of opportunity in the Southern Ocean. Mesocosm experiments will include both, increasing and alleviating light and/or iron stress on monoclonal phytoplankton cultures and in natural phytoplankton communities while measuring the response of the NO3--assimilation epsilon. Water column samples will be collected on the cruise for analysis of dissolved and size-fractionated particulate N concentration and d15N, as well as phytoplankton community composition, photophysiology and gene expression markers of iron and light stress and NO3- assimilation. In particular, the expression of iron and light stress markers will be used to evaluate the relative contribution of iron and light stress to field-based estimates of the NO3--assimilation epsilon. The results from these field measurements, together with lab-based culture studies, will be used to constrain the range of the epsilon for NO3--assimilation under environmentally-relevant light and iron conditions, including the potential alleviation of iron stress as has been hypothesized to have occurred during the last glacial maximum (a.k.a. the Martin hypothesis).
Multi-Scale Exploration of Nutrient Cycles and its Socio-Economic Impacts in Coastal Areas
This project will explore the Energy Exascale Earth System Model (E3SM) for simulating nutrient fluxes from a terrestrial system to an ocean system and for linking E3SM-simulated nutrient fluxes to red tide occurrence in support of socio-economic impact assessment.
PI's on the project: Ming Ye (FSU), Sven Kranz (FSU), Julie Harrington (FSU)
Post-Doc on the project: Ahmed Elshall, X. Yang,Y. Wang, M. Maltrud
Students on the project:A. Boesel, A. Hodapp, Sally Gorrie, Brooke Gilbert
Award Abstract #1939994: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1939994
Excessive nutrients in surface and ocean waters cause nutrient pollution, which is responsible for water quality degradation in more than 60% of coastal rivers, bays, and seas in the U.S. With a continuous nutrient supply, certain phytoplankton species can become disproportionately abundant under distinctive environmental conditions, forming what is commonly known as "red tides". The economic impacts of red tides in the U.S. are estimated to be at least tens of million dollars per year. It is imperative to reduce the risk of red tides and to increase the associated resilience of coastal communities. Research results of this project will be disseminated to a broad audience in multiple communities through outreach to the public and by collaborating with researchers, practitioners, and decision-makers in county, state and federal agencies. This project will support two undergraduate students and one postdoctoral researcher who will be recruited from underrepresented groups in science. The PIs will incorporate the research results into their classroom teaching and curriculum development. This project will conduct innovative interdisciplinary research across the coastline boundary between terrestrial and ocean systems and across the disciplinary boundaries between geosciences, natural, and social sciences. This project will explore the Energy Exascale Earth System Model (E3SM) for simulating nutrient fluxes from a terrestrial system to an ocean system and for linking E3SM-simulated nutrient fluxes to red tide occurrence in support of socio-economic impact assessment. The goal of this project is to explore whether E3SM can be used as a new software to simulate nutrient fluxes at multiple scales for estimating red tide development and persistence and for assessing socio-economic impacts of red tides under various environmental and management scenarios. Additionally, the research team will evaluate whether E3SM can be used as a community tool to facilitate coastal management. The State of Florida has been chosen as the primary study site for this project, yet the model can be used along the US coastline. E3SM and its uses for nutrient pollution study and socio-economic impact assessment can be an emerging software infrastructure for coastal researchers, decision-makers, practitioners, and stakeholders to address coastal nutrient pollution problems.
Collaborative Research: Mesoscale variability in nitrogen sources and food-web dynamics supporting larval southern bluefin tuna in the eastern Indian Ocean
This project investigates how mesoscale variability in new production, food-web structure and trophic fluxes affects feeding and growth conditions for Southern Bluefin Tuna larvae in the Indian Ocean.
PI's on the project: Sven Kranz (FSU), Michael Stukel (FSU), Karen Selph (U. o Hawaii), David Die (RSMS) and Michael Landry (Scripps)
Students on the project:A. Boesel (FSU), Jared Rose (FSU), Natalie Yingling (FSU), Opeyemi Kehinde (FSU), Christian Fender (FSU) and many others participated on the cruise
Award Abstract #1851347: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1851347
The small area between NW Australia and Indonesia in the eastern Indian Ocean (IO) is the only known spawning ground of Southern Bluefin Tuna (SBT), a critically endangered top marine predator. Adult SBT migrate thousands of miles each year from high latitude feeding areas to lay their eggs in these tropical waters, where food concentrations on average are below levels that can support optimal feeding and growth of their larvae. Many critical aspects of this habitat are poorly known, such as the main source of nitrogen nutrient that sustains system productivity, how the planktonic food web operates to produce the unusual types of zooplankton prey that tuna larvae prefer, and how environmental differences in habitat quality associated with ocean fronts and eddies might be utilized by adult spawning tuna to give their larvae a greater chance for rapid growth and survival success. This project investigates these questions on a 38-day expedition in early 2021, during the peak time of SBT spawning. This project is a US contribution to the 2nd International Indian Ocean Expedition (IIOE-2) that advances understanding of biogeochemical and ecological dynamics in the poorly studied eastern IO. This is the first detailed study of nitrogen and carbon cycling in the region linking Pacific and IO waters. The shared dietary preferences of SBT larvae with those of other large tuna and billfish species may also make the insights gained broadly applicable to understanding larval recruitment issues for top consumers in other marine ecosystems. New information from the study will enhance international management efforts for SBT. The shared larval dietary preferences of large tuna and billfish species may also extend the insights gained broadly to many other marine top consumers, including Atlantic bluefin tuna that spawn in US waters of the Gulf of Mexico. The end-to-end study approach, highlights connections among physical environmental variability, biogeochemistry, and plankton food webs leading to charismatic and economically valuable fish production, is the theme for developing educational tools and modules through the ?scientists-in-the-schools? program of the Center for Ocean-Atmospheric Prediction Studies at Florida State University, through a program for enhancing STEM learning pathways for underrepresented students in Hawaii, and through public outreach products for display at the Birch Aquarium in San Diego. The study also aims to support an immersive field experience to introduce talented high school students to marine research, with the goal of developing a sustainable marine-related educational program for underrepresented students in rural northwestern Florida. Southern Bluefin Tuna (SBT) migrate long distances from high-latitude feeding grounds to spawn exclusively in a small oligotrophic area of the tropical eastern Indian Ocean (IO) that is rich in mesoscale structures, driven by complex currents and seasonally reversing monsoonal winds. To survive, SBT larvae must feed and grow rapidly under environmental conditions that challenge conventional understanding of food-web structure and functional relationships in poor open-ocean systems. The preferred prey of SBT larvae, cladocerans and Corycaeidae copepods, are poorly studied and have widely different implications for trophic transfer efficiencies to larvae. Differences in nitrogen sources - N fixation vs deep nitrate of Pacific origin - to sustain new production in the region also has implications for conditions that may select for prey types (notably cladocerans) that enhance transfer efficiency and growth rates of SBT larvae. The relative importance of these N sources for the IO ecosystem may affect SBT resiliency to projected increased ocean stratification. This research expedition investigates how mesoscale variability in new production, food-web structure and trophic fluxes affects feeding and growth conditions for SBT larvae. Sampling across mesoscale features tests hypothesized relationships linking variability in SBT larval feeding and prey preferences (gut contents), growth rates (otolith analyses) and trophic positions (TP) to the environmental conditions of waters selected by adult spawners. Trophic Positions of larvae and their prey are determined using Compound-Specific Isotope Analyses of Amino Acids (CSIA-AA). Lagrangian experiments investigate underlying process rates and relationships through measurements of water-column 14C productivity, N2 fixation, 15NO3- uptake and nitrification; community biomass and composition (flow cytometry, pigments, microscopy, in situ imaging, genetic analyses); and trophic fluxes through micro- and mesozooplankton grazing, remineralization and export. Biogeochemical and food web elements of the study are linked by CSIA-AA (N source, TP), 15N-constrained budgets and modeling. The project elements comprise an end-to-end coupled biogeochemistry-trophic study as has not been done previously for any pelagic ecosystem.