Department of Earth and Planetary Sciences
327 Olin Hall
Johns Hopkins University
3400 N. Charles Street
Baltimore, MD 21218
gnanades at jhu.edu
About me Teaching Research Publications Science Olympiad
Our planet is shaped by the interaction of living things with their physical environment. My interests center on understanding these interactions. Since I trained as an oceanographer, my primary expertise is in how the ocean circulates and influences marine life, climate, and atmospheric chemistry. I got my Ph.D. from the MIT/Woods Hole Joint Program in Physical Oceanography and spent over fifteen years in Princeton at Princeton University and NOAA’s Geophysical Fluid Dynamics Laboratory working to develop computer models of how the planet works. In January 2011 I joined the Department of Earth and Planetary Sciences at Johns Hopkins University.
Introduction to Global Environmental Change and Sustainability: 270.103
Oceans and Atmospheres: 270.108 (changing to 200 level, Spring 2014)
Introduction to Oceanography: 270.325
Ocean biogeochemical cycles: 270.323
Climate variability: Physics and proxies
Advanced Atmospheric Dynamics
What are the physical controls on ocean circulation?
I have a long-term interest is understanding how the large scale overturning of the ocean is driven by winds and mixing. I explore this question using numerical models of the circulation. While at GFDL, I helped lead the development of the ocean component of the global climate models CM2. I’m currently interested in the role of deep mixing in setting the overturning. With Chris Little and Dan Goldberg at GFDL I helped develop the first fully coupled ocean-ice shelf-ice stream models.
At Hopkins, research scientist Marie-Aude Pradal and I are working to understand the role of lateral mixing in setting climate within coupled climate models. Marie's work helps to explain why the poorly—constrained turbulent diffusion coefficient along density surfaces can have a significant role in setting the global temperature and circulation.
Graduate student Eshwan Ramudu is working to understand what sets the transfer velocity between ice and ocean.
Bathymetry may also play an important role in determining the ocean circulation. As part of an NSF-funded project headed by Peter Olson, I'm working with Arghya Goswami to understand how differences in the ocean bathymetry associated with mantle dynamics could affect tides and climate.
How does global climate vary on interannual to centennial scales?
The ocean plays a key role in holding and releasing heat. I work to understand how variations in the circulation are connected with climate variability. Areas of particular interest at present are the Atlantic Meridional Overturning and its connection to temperature variability, long-period variations in El Nino and precipitation in the tropics, and changes in winds forced by ozone depletion over the Southern Ocean.
Graduate student Alexi Russell and I recently submitted a paper showing that changes in ocean stratification may modulate the amplitude of El Nino over decadal scales.
How do we model ocean ecosystems and their interactions with ocean circulation?
Mixing and overturning are responsible for returning nutrients sequestered in the deep ocean to the well-lit surface layer where they can be used for biological cycling. As they are taken up by biology, they drive phytoplankton blooms which trap solar heating near the surface. As the resulting organic material sinks back into the deep it rots, consuming oxygen. I'm interested in all aspects of this cycle.
How does nutrient make it back to the surface? How will changes in Southern Ocean winds, eddies and stratification affect this resupply? Graduate student Grace Kim is starting to work on examining this question in the Southern Ocean using profiling floats.
How do we model nutrient uptake as simply as possible? With Eric Galbraith, John Dunne and Mike Hiscock, I've worked to develop simple ecosystem models that can be constrained with data.
What sets the intensity of ocean hypoxia? Recent work with Marie-Aude Pradal and Daniele Bianchi suggests that lateral stirring by ocean eddies plays a critical role.
Click here for a list of publications with links.
Click at right for my profile at Researcher ID with citations.
I’ve been very involved in Science Olympiad, the nation’s largest team science competition. Click here for more information.