GFDL - Geophysical Fluid Dynamics Laboratory

Anand Gnanadesikan’s Biogeochemical Cycles Page

The earth’s biosphere is profoundly affected by the physical circulation of the atmosphere and ocean. Winds in the atmosphere drive upwelling and mixing in the ocean that brings surface nutrients to the surface in some parts of the ocean (above) but not others. The convergence of moisture in the atmosphere results in rain, the timing of this rain can make the difference between having a woodland or an open savanna. I’ve been interested in these connections since I was an undergraduate. Some of the areas I’ve worked in are listed below.

Ocean nutrient cycling

I’ve looked at how the cycling of nutrients in the ocean is affected by the large scale circulation, as well as collaborating with colleagues here and at Princeton University to better characterize the cycling of nitrogen, phosphate and calcium carbonate, using remote sensing techniques. To learn more about this work, click here.

I’ve also looked at how changes in the nutrient cycle, due to changes in things like iron supply, could affect atmospheric carbon dioxide. Such changes are thought to be the major driver of glacial-interglacial changes in atmospheric carbon dioxide. This work has led to the finding of a Southern Ocean Biogeochemical Divide. It is also leading us to consider impacts of proposed geoengineering strategies, such as iron fertilization, on the earth system.

Recently, Eric Galbraith and I have been working on simplified models of the Earth System with highly parameterized biogeochemical dynamics. The first of these (BLING) is described here.

Abiotic tracers and the ocean circulation

I have long standing interests in mixing and advection of tracers determines their distribution, and whether better knowledge of these distributions can be used to put constraints on the circulation. Under the first heading, I’ve looked at the diurnal cycling of photochemical tracers such as carbon monoxide, and the impact of circulation on the uptake of anthropogenic carbon dioxide from the atmosphere and the retention of anthropogenic carbon dioxide injected into the deep ocean. Under the second, I’ve looked at the distribution of idealized ventilation tracers (which show where surface waters enter the deep ocean), radiocarbon, and helium-3.

Terrestrial ecosystems and climate

I’ve done a little work in this area, examining how changes in surface properties affect the large-scale atmospheric circulation, and how ecosystems, acting as a nonlinear filter on climate, can serve as interesting diagnostics of climate models.

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