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COLLABORATIVE RESEARCH: Quantifying the effects of variable light and iron on the nitrate assimilation isotope effect of phytoplankton

The SCALexperiment Twitter account HERE . Amazing pictures, video and info about the cruise.

From October 11th to November 28th 2019, Dr. Kranz and graduate student Rachel Thomas, both from the department of Earth, Ocean and Atmospheric Science, will be on a research cruise in the Southern Ocean.

The collaborative project received $1.08 million from the National Science foundation (award #1851113 and # 1850925) to conduct the proposed laboratory and field research.

Dr. Kranz and student Rachel Thomas operated a successful deployment of a McLane pump to filter large quantities of water

November 7th, 2019 – Cruise updates – Dr. Kranz and student Rachel Thomas operated a successful deployment of a McLane pump to filter large quantities of water

Co-PI’s on this project are Dr. Angela Knapp also from FSU’s EOAS Dept. as well as Dr. Dreux Chappell from Old Dominion University. The team and their groups of students will leave from Cape Town (SA) towards Antarctica aboard the University of Cape Town’s research vessel Agulhas II. This work is being done in collaboration with Drs. Sarah Fawcett and Katye Altieri at the University of Cape Town, South Africa, who invited their American collaborators to participate in the cruise aboard the research vessel S.A. Agulhas II, which is owned by the South African Department of Environmental Affairs (DEA).


Ship Agulhas II


cruise track

Cruise track for the SCALE Spring 2019 cruise (Southern Hemisphere Spring)


During the cruise, the professors and their students will explore the sensitivities of phytoplankton (single celled algae) growing in the Southern Ocean to changes in physiological stress – especially from limited iron availability and changing light conditions, and measure the geochemical signatures these organisms leave behind.

Ultimately, the goal is to relate what’s happening in the modern ocean to what happened in the ocean during the last glacial maximum 20,000 years ago, when atmospheric CO2 concentrations were much lower.

Based on geochemical signatures left behind in the sediments, a leading hypothesis for why atmospheric CO2 was lower in the past is that increased iron from Patagonian dust allowed more phytoplankton to grow, and the increased phytoplankton growth reduced atmospheric CO2 concentrations. Hence, past phytoplankton communities would have been physiologically less iron stressed than modern phytoplankton.

However, it is not known yet if an alternate interpretation of the sedimentary record is that a reduced physiological stress of the phytoplankton due to higher iron availability could lead to the same signal. This is one of the motivations for their work.

The research team will be using a variety of tools to test their hypothesis. During the field campaign they will be collecting physiological and molecular data from the phytoplankton community in the Southern Ocean while simultaneously measuring geochemical data from the seawater. Using this suite of data, they can evaluate whether “stressed” phytoplankton leave behind distinct chemical signatures. To relate the geochemical data from the ocean to the phytoplankton they are also carrying out incubations at sea where they artificially “stress out” phytoplankton by changing their light and iron availability relative to what they are experiencing naturally.

In PI Kranz’s lab at FSU, graduate student Tristyn Bercel is currently growing a variety of Southern Ocean phytoplankton species under physiological “stressful” iron and light conditions to investigate if they change their geochemical signature. Co-PI Knapp (FSU) and her graduate student Rachel Thomas will be measuring the geochemistry of the phytoplankton cultures, seawater, as well as the experiments at sea.

Additionally, Co-PI Dr.Dreux Chappell at Old Dominion University has developed molecular markers of iron and light stress in Southern Ocean phytoplankton. She will use the gene expression of these molecular markers as another tool to evaluate whether and how different degrees of physiological stress experienced by the phytoplankton lead to changes in the geochemistry of the ocean water.


Dr. Drexu Chappell and Student Sveinn Einarsson

  Dr. Dreux Chappell and student Sveinn Einarsson

Prior studies on this topic have not utilized all three kinds of responses (cellular physiology, molecular markers and biogeochemical signatures) at the same time and therefore could not satisfactorily answer the working hypothesis.
Together, the tools used by the PIs and students of this project represent a novel, interdisciplinary investigation of phytoplankton physiology and how it influences seawater as well as the paleo-oceanographic record.

More info and updates on the cruise:

Photos credits : Dr.Kranz, University of Cape Town, Dr. Dreux Chappell and Svein Einarsson