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Project Progress

Our contribution to Astrobiology Roadmap Objective 6.1, is entitled, “Environmental changes and the cycling of elements by the biota, communities, and ecosystems” and is a past-ecosystem-process model. The Hindcasting Ecosystems Model (HEMO) uses proxy data to predict past net primary production (p-NPP), as follows,

p-NPP= LGS/p-NDVI * (PET/ p-NDVI) * p-NDVI * (N in soil/p-NDVI)

Climate is represented by the length of the growing season (LGS), soil by concentration of nitrogen in soils (N in soil) and Potential Evapotranspiration (PET), and vegetation by the vegetation index (NDVI). SST holds high correlation with NDVI and hence, our tree-ring based reconstruction of past SST was used to infer past NDVI. With these predictions we reconstructed past NPP at 1-year resolution (Figures 1, 2, and 3). In order to validate our assumptions on changes in NDVI related to changes in the forcings of climate during the Holocene (volcanic, orbital, and solar) we explored the history of these forcings over the last 754 year. While the orbital and solar forcing could account for changes of a few calories in the solar energy received at the surface of the Earth, the volcanic forcing produced a maximum cooling of SST starting in 1453 when the Kuwae volcano erupted explosively in the New Hebrides and elevated the concentration of non-marine sulfates to 1380 μg per liter of ice in Antarctica. The aerosols of this eruption shaded the Earth and lowered the SST of the South Atlantic and the Western Pacific for several years. This and other volcanic eruptions have affected terrestrial vegetation of South America and hence the carbon cycle in the period 1246-2000. The project produced an SST reconstruction cross referenced with the record of volcanic eruptions in Antarctica, 754 maps of past NDVI, 754 maps of NDVI deviations from the average value for the period 1246-2000, and 41 reconstructions of past NPP (as those shown in Figures 1, 2 and 3). These data will be available to users at the Earth Science Division website.

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