The amount of CO₂ taken up by plants (gross primary production) is the largest flux in the terrestrial carbon cycle. However, the uncertainty in how much CO₂ plants absorb is larger than annual anthropogenic CO₂ emissions. This means that small changes in plant uptake could drastically alter the carbon balance, making climate predictions more challenging. A better understanding of the terrestrial carbon cycle is essential for predicting future climate conditions and atmospheric CO₂ mole fractions. Stable isotope measurements of CO₂ (δ13C and δ18O) provide valuable insights into the magnitude of CO₂ fluxes between the atmosphere and biosphere.
Recent advancements in measurement techniques have made it possible to measure ∆′17O in atmospheric CO₂ with high precision. These high-precision measurements provide valuable constraints on terrestrial carbon fluxes that δ13C and δ18O alone could not achieve. This is because ∆′17O(CO₂) has a known stratospheric source, its variations are much smaller than those of δ18O, and conventional biogeochemical processes follow a well-defined three-isotope fractionation slope. Additionally, the triple oxygen isotope fractionation slopes for specific processes are independent of source water isotope composition, insensitive to temperature, and process specific.
In this talk, I will discuss the broader applications of ∆′17O in atmospheric CO₂ research, the challenges associated with high precision ∆′17O measurements, the latest advancements in measurement techniques, and future implications for studying the terrestrial carbon cycle.
How to cite: Adnew, G. A.: ∆′17O of Atmospheric CO2 as a tracer for gross fluxes of terrestrial carbon cycle, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3819, https://doi.org/10.5194/egusphere-egu25-3819, 2025.
The ocean carbon cycle is a critical component of the climate system. Each year, the ocean absorbs approximately a quarter of the CO2 emitted to the atmosphere from human activities, playing a vital role in mitigating climate change. The ocean will ultimately sequester the majority of these emissions over centuries and beyond, thus regulating atmospheric CO2 concentration and climate stabilisation in the long term. Understanding the mechanisms and drivers of the observed trends and variability in ocean carbon storage is therefore essential for reducing uncertainty in long-term climate projections.
Trends and variability in ocean carbon storage arise from a complex interplay of factors, including atmospheric CO2 growth, warming, ocean acidification, physical ocean dynamics, and marine ecosystem changes. While the physico-chemical effects of warming and ocean acidification on the ocean carbon cycle are well-known, the impacts of large-scale changes in ocean circulation remain less well understood. Notably, shifts in surface winds over the Southern Ocean and a weakening Atlantic Meridional Ocean Circulation could induce important changes in carbon storage that are poorly quantified. Changes in marine ecosystems under multiple stressors and their effect on the marine carbon cycle remain poorly constrained and were categorized as a “known-unknown” in the last four assessment reports of the Intergovernmental Panel on Climate Change (IPCC).
In this lecture, I will synthesise recent understanding of the drivers of trends and variability in ocean carbon storage, focusing on timescales ranging from years to centuries. I will present new insights into how marine ecosystem shape carbon dynamics and discuss how changes in ecosystems could influence the ocean carbon storage well beyond 2100. These insights underscore the need to develop new and better integrated “Ocean Systems Models” that include more detailed representations of marine ecosystems and their interactions with biogeochemical cycles.
How to cite: Le Quéré, C.: Carbon storage by the ocean in a changing climate, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9776, https://doi.org/10.5194/egusphere-egu25-9776, 2025.
