Abstract
The past century has been a time of unparalleled changes in global climate and global biogeochemistry. At the forefront of the study of these changes are regular time-series observations at remote stations of atmospheric CO2, isotopes of CO2, and related species, such as O2 and carbonyl sulfide (COS). These records now span many decades and contain a wide spectrum of signals, from seasonal cycles to long-term trends. These signals are variously related to carbon sources and sinks, rates of photosynthesis and respiration of both land and oceanic ecosystems, and rates of air-sea exchange, providing unique insights into natural biogeochemical cycles and their ongoing changes. This review provides a broad overview of these records, focusing on what they have taught us about large-scale global biogeochemical change.
Highlights
CO2 concentration the sensitivity of carbon exchange to climate changes, and the detection of large-scale metabolic changes
Measurements of old air preserved in Antarctic ice cores have allowed atmospheric CO2 concentration to be determined for earlier periods, with more limited temporal resolution [17, 18]
The trend is driven by CO2 sources from fossil-fuel burning (FF) and land use (LU), which are partially offset by sinks from the ocean (O) and land biosphere (B): M · dCa/dt = F F + LU − O − B, 1
Summary
Throughout the Northern Hemisphere, atmospheric CO2 undergoes a regular seasonal cycle with a peak in late spring and a trough in late summer or early fall. Observed peak-to-trough of (a) amplitude and (b) phase based on day of year of downward zero crossing of CO2 at Barrow, Alaska (71.3°N, orange dots, right axis) and Mauna Loa, Hawaii (19.5°N, blue dots, left axis) as measured by the Scripps CO2 program and the National Oceanic and Atmospheric Administration Global Monitoring Division. A strong link to warming is suggested by the larger amplification of the CO2 cycle at higher latitudes, where warming has occurred more rapidly [32] Another significant change in the cycle is the earlier shift of the upwards zero crossing, suggesting increases in fall respiration are occurring, possibly linked to warming [37]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
