Controls on Millennial‐Scale Atmospheric CO2 Variability During the Last Glacial Period

• Published in: Geophysical research letters Vol. 45; no. 15; pp. 7731 - 7740
• Main Authors: Bauska, T. K., Brook, E. J., Marcott, S. A., Baggenstos, D., Shackleton, S., Severinghaus, J. P., Petrenko, V. V.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 16-08-2018
• Subjects: atmospheric CO2; Carbon; Carbon cycle; Carbon dioxide; Carbon dioxide atmospheric concentrations; Carbon dioxide flux; Carbon dioxide variations; Carbon isotopes; Carbon sequestration; Climate change; Climate variability; Cores; Deglaciation; Density stratification; Glacial periods; Heinrich events; Hydrology; Ice cores; Isotopes; Meltwater; Nitrous oxide; Northern Hemisphere; Oceans; Organic carbon; paleoclimate; Polar climates; Reservoirs; Stable isotopes; Stratification; Temperature (air-sea); Tropical environments; Variability; Northern Hemisphere
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2018GL077881

Changes in atmospheric CO2 on millennial‐to‐centennial timescales are key components of past climate variability during the last glacial and deglacial periods (70–10 ka), yet the sources and mechanisms responsible for the CO2 fluctuations remain largely obscure. Here we report the 13C/12C ratio of atmospheric CO2 during a key interval of the last glacial period at submillennial resolution, with coeval histories of atmospheric CO2, CH4, and N2O concentrations. The carbon isotope data suggest that the millennial‐scale CO2 variability in Marine Isotope Stage 3 is driven largely by changes in the organic carbon cycle, most likely by sequestration of respired carbon in the deep ocean. Centennial‐scale CO2 variations, distinguished by carbon isotope signatures, are associated with both abrupt hydrological change in the tropics (e.g., Heinrich events) and rapid increases in Northern Hemisphere temperature (Dansgaard‐Oeschger events). These events can be linked to modes of variability during the last deglaciation, thus suggesting that drivers of millennial and centennial CO2 variability during both periods are intimately linked to abrupt climate variability.
Plain Language Summary
Ice cores provide unique records of variations in atmospheric CO2 prior to the instrumental era. While it is clear that changes in atmospheric CO2 played a significant role in driving past climate change, it is unclear what in turn drove changes in atmospheric CO2. Here we investigate enigmatic changes in atmospheric CO2 levels during an interval of the last glacial period (~50,000 to 35,000 years ago) that are associated with abrupt changes in polar climate. To determine the sources and sinks for atmospheric CO2, we measured the stable isotopes of carbon in CO2 and found that the primary source of carbon to the atmosphere was an organic carbon reservoir. Most likely, this carbon was sourced from a deep ocean reservoir that waxed and waned following changes in either the productivity of the surface ocean or stratification of the deep ocean. We also found that atmospheric CO2 can change on the centennial timescale during abrupt climate transitions in the Northern Hemisphere. This observation adds to a growing body of evidence that abrupt changes in atmospheric CO2 are an important component of past carbon cycle variability.
Key Points
A new ice core record of carbon isotopes in atmospheric CO2 suggests organic carbon sources controlled CO2 during the last glacial period
The millennial‐scale CO2 variability is tentatively linked to variations in Southern Ocean carbon sources
Centennial‐scale CO2 variability during the last glacial period is associated with similarly abrupt changes during the deglaciation