Featured Scientist: Karen Selph

Karen in the lab-van whispering to the flow cytometer!

Hello blog, today Dr. Karen Selph from the University of Hawaii at Manoa shares some of her expert insight into the nutrient-limited world! Karen shared with the blog just a few of the multiple experiments she carried out while on board the NOAA Ship Nancy Foster during NF1704 as part of our NOAA RESTORE project. Karen’s main focus was collecting phytoplankton to analyze with a “flow cytometer” – a machine that tells us how many phytoplankton are out there and gives us a rough idea of their types.

In addition, she measured water column light levels used for photosynthesis by phytoplankton with a photosynthetically-active radiation (PAR) sensor that was attached to the CTD rosette. Karen shared with the blog: "The 6 casts that we performed will yield invaluable information on the light regime during the cruise." 

"The nutrient limiting phytoplankton growth in the Gulf of Mexico is nitrogen.  Nitrogen has many forms, and most phytoplankton can only use reduced inorganic forms (e.g., nitrate (NO₃), ammonium (NH₄)).  However, some phytoplankton can use nitrogen gas (N₂), which is in abundant supply.  This is quite a trick, as the chemistry involved is anaerobic (no or low oxygen) and phytoplankton produce oxygen! 

Karen and Lucy carry out one of the PAR casts

On this cruise, we collected many samples to figure out which of the larger nitrogen-fixing organisms that might be present – in particular, Trichodesmium (usually a bane to those who study zooplankton, as it can clog their nets!!).   Additionally, to assess the base line N-isotopic value for Trichodesmium, we collected samples for stable nitrogen isotope analyses.  We even analyzed a sample of Sargassum to figure out its isotopic signature with respect to the other nitrogen-fixing players in the GOM.  Once we get back to the lab, we will also examine our samples under the microscope looking for the presence of other nitrogen-fixers – some diatoms and other species harbor symbionts capable of this remarkable feat!"

The dynamic duo, Tom and Karen processed hundreds of samples during the survey

Shaun, Karen's travel companion, makes some new friends