An atmospheric perspective on land and ocean ecosystems in a time of global change

Wednesday, 17 December 2014: 9:00 AM
Ralph F Keeling, University of California San Diego, La Jolla, CA, United States
We are now century or more into the "great geophysical experiment" of rising levels of greenhouse gases in the atmosphere. As this "experiment" slowly plays out, a major need is to track changes in land and ocean ecosystems which are impacted both changes in physical climate and chemical climate (e.g. changing CO2 levels.). Measurements of CO2 concentration and related variables (such as O2 and the isotopes of CO2) in background air continue to provide key insights into how these systems are changing.

One surprise coming from these observations is evidence that land ecosystems are serving as a sink for a significant fraction the excess carbon dioxide from fossil-fuel burning. Ecosystems remote from direct human influences have evidently been thrown out of steady state by a range of processes and are accumulating carbon unusually. Evidence for this sink is compelling found from a variety of methods, including from measurements of atmospheric O2 abundance. Additional compelling evidence for large changes in land ecosystem comes from measurements of the seasonal cycle in atmospheric CO2.

In contrast, there is little evidence that marine ecosystems - at least those remote from coastal influences - have undergone such large changes. While the oceans are absorbing excess CO2, this is mostly a physical, not a biological, process. But just as the absence of evidence is not evidence for absence, it could just be that we lack strong long-term atmospheric constraints on marine ecosystems. Whereas atmospheric CO2 data provides a wealth of information on land processes, they do a poor job of resolving ocean biological processes because the buffering chemistry of CO2 in seawater slows the response of atmospheric CO2 to processes originating from within the ocean.

This talk will highlight evidence for changes in land ecosystems from measurements and CO2 and its isotopes, and will illustrate a path forward to resolving changes in marine ecosystems and related impacts on the ocean carbon sink via measurements in atmospheric O2 concentration, particularly via the tracer "atmospheric potential oxygen" APO, which is effectively the sum of the O2 and CO2 concentrations, which shows rich variability of marine origin.