Please join me in congratulating GRG collaborator Dr Thomas Felis (based at the MARUM, University of Bremen) and the team on the publication of our new paper in the journal Geophysical Research Letters.

Felis, T., Hinestrosa, G., Köhler, P. and Webster, J.M., 2022. Role of the Deglacial Buildup of the Great Barrier Reef for the Global Carbon Cycle. Geophysical Research Letters, 49(4). https://doi.org/10.1029/2021GL096495

The paper represents another great contribution to the ongoing IODP Expedition 325 (Great Barrier Environmental Changes) project – our wider program focused on reconstructing sea level and environmental changes, and the response of the Great Barrier Reef over the past 30,000 years.

Key Points of the Paper:

• Great Barrier Reef corals indicate pronounced decrease in skeletal stable carbon isotopes between 12.8 and 11.7 ka during Younger Dryas.
• Event follows shelf flooding and barrier reef initiation at 13 ka and coincides with prominent atmospheric stable carbon isotope minimum.
• Carbon cycle modeling reveals marginal impact of changes in reef carbonate production and land carbon decomposition on atmospheric carbon.

We hope this paper will be of value to the community interested in the global carbon cycle and potential role played by coral reef systems. Bravo Thomas!!

Future work will focus on increasing the sample coverage and density of δ13C GBR coral records to better constrain any millennial to centennial variations (and drivers) in the signal.

Cheers

Jody

#MarineScienceSydneyUni

Plain Language Summary

An outstanding problem in our understanding of the global carbon cycle is unraveling the processes that were responsible for the rise of atmospheric CO2 during the last deglaciation (19,000–11,000 years ago). The carbon isotope 13C is commonly used to attribute the last deglacial atmospheric CO2 rise to various processes. The growth of tropical coral reefs has been controversially discussed in this context. To test this, well constrained reef carbonate records that span the last deglaciation are necessary, but such records are generally not available. Here we make use of a multi-proxy coral reef record obtained at the Great Barrier Reef (GRB). The δ13C signal in the carbonate skeletons of fossil corals indicates a pronounced minimum that precisely coincides with a prominent minimum in atmospheric δ13CO2 as indicated by ice core records for the Younger Dryas cold period. We show, by carbon cycle simulations, that the GBR coral δ13C signal can be explained by changes in reef carbonate production and decomposition of organic land carbon on a newly flooded wide area. However, the simulations indicate that that the world’s largest reef system in existence appears to have little effect on the last deglacial atmospheric CO2 and δ13CO2 changes.

Abstract

The carbon isotope ¹³C is commonly used to attribute the last deglacial atmospheric CO₂ rise to various processes. Here we show that the growth of the world’s largest reef system, the Great Barrier Reef (GBR), is marked by a pronounced decrease in δ¹³C in absolutely dated fossil coral skeletons between 12.8 and 11.7 ka, which coincides with a prominent minimum in atmospheric δ¹³CO₂ and the Younger Dryas. The event follows the flooding of a large shelf platform and initiation of an extensive barrier reef system at 13 ka. Carbon cycle simulations show the coral δ¹³C decrease was mainly caused by the combination of isotopic fractionation during reef carbonate production and the decomposition of organic land carbon on the newly flooded shallow-water platform. The impacts of these processes on atmospheric CO₂ and δ¹³CO₂, however, are marginal. Thus, the GBR was not contributing to the last deglacial δ¹³CO₂ minimum at ∼12.4 ka.