Tag Archives: Ryan Green

Radiocarbon anomalies in the Gulf of California, companion papers published

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Radiocarbon (14C) is produced in the atmosphere and spreads through the surface carbon cycle before, you guessed it, radioactive decay. Hence the name, radiocarbon. In contrast, carbon spit out from Earth’s interior is 14C-free and can thus produce a “negative 14C anomaly” in the region of release. Working with Pat Rafter at USF and my former PhD student Ryan Green (now at Equatic), we reconstruct and simulate a major 14C anomaly in the Gulf of California.

Dr Ryan Green

We find two main pulses of maybe 800PgC total carbon release during the end of the last ice age, but smaller 14C anomalies persist to the modern day. We also find that the carbon release did not cause ocean acidification or significantly increase CO2, because it was neutralized by a equimolar pulse of alkalinity release to the ocean. Our results lead us to conclude that this highly unusual instance of large scale neutralized-carbon release could be an important geologic analogue for Ocean Alkalinity Enhancement (OAE) as means for marine Carbon Dioxide Removal (mCDR) in the ongoing challenge to mitigate anthropogenic climate change and ocean acidification.

Our four papers on the topic (left to right): (1) detailed reconstructions of deglacial 14C anomalies in the Gulf of California, (2) global carbon cycle constraints on geologic carbon release during the deglacial period, (3) mass balance and pH constraints in simulating regional impacts of carbon release, and (4) regional assessment of 14C anomalies since the last ice age. This inferred release of neutralized carbon remains a challenge to our current paradigm of the global carbon cycle, but it does not significantly affect our understanding of the ice age carbon cycle or our ability to reconstruct ocean circulation using 14C.

Rafter_et_al_2019_GRL

Green-et-al-2024-GRL-GoC

Rafter-et-al-2026-Paleo-GoCal-14C-observations

Green-et-al-2026-Paleo-GoCal-14C-simulation-

Neutralized carbon anomaly in the Gulf of California

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Dr. Ryan Green just had a second manuscript accepted for publication, where we argue that the large-scale release of geologic carbon at the end of the last ice age is likely responsible for radiocarbon (14C) anomalies discovered in the Gulf of California region. Unlike any previous work, we argue that the carbon was released with and neutralized by alkalinity so as not to cause ocean acidification or atmospheric CO2 increase.

Green-et-al-2026-Paleo-GoCal-14C-simulation-

Figure 4. Physical and geochemical constraints on geologic carbon addition. (a) Physical constraints showing simulated carbon release across a range of mixing rates (y-axis) and Marchitto Box sizes (x-axis, in multiples of GoC volume). Contours represent the total carbon required to simulate Δ14C anomalies, with gray lines indicating global radiocarbon budget limits (Green et al., 2024). Yellow and red circles denote slow and fast flushing end-member experiments, respectively, with black dashed lines showing their respective residence times of the Marchitto box. (b) Geochemical constraints based on PyCO2SYS (Humphreys et al., 2021) solver results and observations. Unlike Figure 3f, which covers the 20–10 ka interval, Figure 4b includes the full δ¹¹B-derived pH dataset extending back to 35 ka; no interpolation was applied. We apply a scaling relationship between 14C-free carbon addition and resulting Δ14C anomalies from the CYCLOPS carbon cycle model (ΔΔ14C = -0.31 * ΔDIC) to align PyCO2SYS-derived aragonite saturation state (Ω) contours with calculated ΔpH and ΔΔ14C from observed GoC data spanning 35 kyr to 11 kyr BP (yellow squares for benthic and red triangles for planktic). 1σ error bars are shown for the pH reconstruction derived from δ11B. Ω contours are calculated from a range of DIC and pH values, assuming a baseline DIC concentration of 2150 μmol kg⁻¹ and a pH of 8.07. Dashed black lines indicate ALK:DIC ratios for different hypothetical geologic carbon sources. Collectively, the δ¹¹B and Δ¹⁴C data are consistent with an ALK:DIC ratio in the range of 1.0–1.2, similar to the constant ratio of 1 used in our simulations and the mean ratio of ~1.1 estimated by Green et al. (2024). For all ratios in this range, CaCO₃ saturation (Ω) increases with carbon addition, consistent with the observed preservation of foraminiferal tests.

Ryan Green receives ARCS fellowship

By community,
Ryan Green

Ryan’s ongoing research investigates a massive pH-neutral carbon release in the Gulf of California region at the end of the last ice age with carbon cycle model simulations. For his ARCS fellowship he proposes to leverage his skills and expertise to investigate the neutralization of anthropogenic ocean acidification by purposeful release of base in the ocean, which is meant to remove CO2 from the atmosphere and mitigate climate change. Congrats Ryan!