Research Interests and Current Projects:
Phytoplankton are responsible for producing half of the oxygen we breathe everyday. They also fix carbon into organic matter, which not only drives the food chain for all marine life, but it also sinks into the deep in a process called the biological pump. The biological pump helps to shape the earth's response to increasing CO2 and warming climate. In order to understand what the future holds for earth's ecosystems we need to understand what factors drive the phytoplankton productivity and the biological pump and how these factors will change in the future.
Physiology and Gene expression of a Model Diatom acclimated to elevated CO2:
I am interested in how increasing carbon dioxide levels in the atmosphere will affect the physiology and gene expression of diatoms and the biological pump. Phytoplankton, including diatoms, have evolved to cope with relatively low CO2 by developing carbon concentrating mechanisms (CCMs). Now as CO2 levels are rising rapidly, these CCMs may down regulated, changing the fluxes of energy and carbon in diatom cells. I am interested in how diatoms will acclimate to higher CO2 levels and if there will be significant physiological changes that could effect the biological pump and ocean ecology.
I just published in Nature Climate Change on culturing experiments with the diatom Thalassiosira pseudonana under low, medium and high CO2 and nitrate limitation. Using gene expression data we found co-regulated CCM and photorespiration genes that are regulated by cyclic-AMP giving us insights into how diatoms acclimate to rising CO2 (http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate2683.html).
Gradients in Microbial Ecology and the Biological pump across the Western Tropical Atlantic:
It is thought that with increasing global temperature, the oceans will become more strongly stratified, resulting in changes in phytoplankton communities. Smaller phytoplankton might out-compete larger phytoplankton resulting in a shift in the ecosystem as well as the size of organic particles and the efficiency of the biological pump.
Using the SeaFlow underway flow cytometer I collected continuous data along the DeepDOM 2013 cruise to investigate gradients in phytoplankton community composition and growth rate. In collaboration with Evan Howard and Rachel Stanley of Woods Hole Oceanographic Institution as well as Francois Ribalet, I'm preparing a manuscript to on the apparent differences in inorganic nitrogen limitation between Prochlorococcus ecotypes in different biogeochemical provinces.
Ph. D. in Oceanography, University of Washington (2015)
M. S. in Oceanography, University of Washington (2012)
B. S. in Chemistry, Massachusetts Institute of Technology (2009)
Dean A. McManus Excellence in Teaching Award (2013)
NOAA Earnest F. Hollings Scholarship (2007-2009)
Presentations and Publications:
Hennon, G. M. M. ; Howard, E.; Stanley, R.; Ribalet, F..; Armbrust, E. V. . “In situ division rates of Prochlorococcus reveal different nitrogen-utilizing ecotypes across the tropical Atlantic” (in prep)
Hennon, G. M. M. ; Ashworth J.; Groussman, R.D.; Berthiaume, C.; Morales, R. L.; Baliga, N.S.; Orellana, M.V.; Armbrust, E. V. . “Diatom acclimation to elevated CO2 via cAMP signalling and coordinated gene expression” (2015) Nature Climate Change
Hennon, G. M. M. ; Quay, P.; Morales, R. L.; Swanson, L. M.; Armbrust, E. V. . “Acclimation conditions modify physiological response of the diatom Thalassiosira pseudonana to elevated CO2 concentrations in a nitrate-limited chemostat” (2014) Journal of Phycology
Hennon, G. M. ; Armbrust, E. V.; “Acclimated Physiology and Gene Expression of the Diatom Thalassiosira pseudonana under Elevated CO2” (2013) ASLO Aquatic Sciences Meeting, New Orleans, LA, USA
Hennon, G.M.; Armbrust, E.V.; Ashworth, J.; Lee, A.; Orellana, M.V.; Baliga, N.S.; “Acclimated Physiology of the Diatom Thalassiosira pseudonana under Pre-Industrial and Future Levels of CO2: Implications for Carbon Sequestration” (2011) PSA annual meeting. Seattle, WA, USA
Bowman, J; Chan, K. Y.; Durkin, C.; Hennon, G.; Smith, D.; Sullivan, B. “Is Diversity Related to Service Provision Across an Ecosystem?” (2011) World Conference on Marine Biodiversity, Aberdeen, Scotland
Wood, M; Strutton, PG; Eberhart, B; Foley, DG; Forster, Z; Hunter, M; McKibben, SM; Miller, G; O’Higgins, L; Peterson, WT; Peterson, TD; Trainer, V; Smith, D; Tweddle, JF; White, AE. (2010) “MOCHA: Monitoring Oregon Coastal Harmful Algae”, Ocean Sciences Meeting
McKibben, SM; Strutton, PG; Wood, M; Miller, G; Eberhart, B; Trainer, V. “Development of a Predictive Model for In Situ Domoic Acid Concentrations off the Oregon Coast”. (2010) Ocean Sciences Meeting
Miller, GM. “Investigating Humpback Whale (Megaptera novaeangliae) diets using fatty acid trophic markers”, NOAA Hollings Scholar Presentation Week, Silver Spring MD, July 2008
Antos, J.M.; Miller, G.M.; Grotenbreg, G.M.; Ploegh, H.L.. Lipid Modification of Proteins through Sortase-Catalyzed Transpeptidation. JACS. 2008