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1. Paleogene Paleohydrology of Ellesmere and Axel Heiberg Islands (Arctic Canada) From Palustrine Carbonates

   https://doi.org/10.1029/2023PA004609  

   Padgett, Ashly B; Hyland, Ethan G; West, Christopher K; Burgener, Landon K; Greenwood, David R; Basinger, James F (October 2023, Paleoceanography and Paleoclimatology)

   Abstract Ancient greenhouse periods are useful analogs for predicting effects of anthropogenic climate change on regional and global temperature and precipitation patterns. A paucity of terrestrial data from polar regions during warm episodes challenges our understanding of polar climate responses to natural/anthropogenic change and therefore our ability to predict future changes in precipitation. Ellesmere and Axel Heiberg Islands in the Canadian Arctic preserve terrestrial deposits spanning the late Paleocene to middle Eocene (59–45 Ma). Here we expand on existing regional sedimentology and paleontology through the addition of stable (δ¹³C, δ¹⁸O) and clumped (Δ₄₇) isotope analyses on palustrine carbonates. δ¹³C isotope values range from −4.6 to +12.3‰ (VPDB), and δ¹⁸O isotope values range from −23.1 to −15.2‰ (VPDB). Both carbon and oxygen isotope averages decrease with increasing diagenetic alteration. Unusually enriched carbon isotope (δ¹³C) values suggest that analyzed carbonates experienced repeated dissolution‐precipitation enrichment cycles, potentially caused by seasonal fluctuations in water availability resulting in summer carbonate dissolution followed by winter carbonate re‐precipitation. Stable isotopes suggest some degree of precipitation seasonality or reduction in winter water availability in the Canadian Arctic during the Paleogene. Clumped (Δ₄₇) temperature estimates range from 52 to 121°C and indicate low temperature solid‐state reordering of micritic samples and diagenetic recrystallization in sparry samples. Average temperatures agree with vitrinite reflectance data for Eureka Sound Group and underlying sediments, highlighting structural complexity across the region. Broadly, combined stable and clumped isotope data from carbonates in complex systems are effective for describing both paleoclimatic and post‐burial conditions. 

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2. Carbon and carbon-13 in the preindustrial and glacial ocean

   https://doi.org/10.1371/journal.pclm.0000434  

   Schmittner, Andreas; Fillman, Nathaniel J (July 2024, PLOS Climate)

   Carré, Matthieu (Ed.)

   Despite their importance for Earth’s climate and paleoceanography, the cycles of carbon (C) and its isotope¹³C in the ocean are not well understood. Models typically do not decompose C and¹³C storage caused by different physical, biological, and chemical processes, which makes interpreting results difficult. Consequently, basic observed features, such as the decreased carbon isotopic signature (δ¹³C_DIC) of the glacial ocean remain unexplained. Here, we review recent progress in decomposing Dissolved Inorganic Carbon (DIC) into preformed and regenerated components, extend a precise and complete decomposition to δ¹³C_DIC, and apply it to data-constrained model simulations of the Preindustrial (PI) and Last Glacial Maximum (LGM) oceans. Regenerated components, from respired soft-tissue organic matter and dissolved biogenic calcium carbonate, are reduced in the LGM, indicating a decrease in the active part of the biological pump. Preformed components increase carbon storage and decrease δ¹³C_DICby 0.55 ‰ in the LGM. We separate preformed into saturation and disequilibrium components, each of which have biological and physical contributions. Whereas the physical disequilibrium in the PI is negative for both DIC and δ¹³C_DIC, and changes little between climate states, the biological disequilibrium is positive for DIC but negative for δ¹³C_DIC, a pattern that is magnified in the LGM. The biological disequilibrium is the dominant driver of the increase in glacial ocean C and the decrease in δ¹³C_DIC, indicating a reduced sink of biological carbon. Overall, in the LGM, biological processes increase the ocean’s DIC inventory by 355 Pg more than in the PI, reduce its mean δ¹³C_DICby an additional 0.52 ‰, and contribute 60 ppm to the lowering of atmospheric CO₂. Spatial distributions of the δ¹³C_DICcomponents are presented. Commonly used approximations based on apparent oxygen utilization and phosphate are evaluated and shown to have large errors. 

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3. Plio‐Pleistocene Southwest African Hydroclimate Modulated by Benguela and Indian Ocean Temperatures

   https://doi.org/10.1029/2023GL103003  

   Rubbelke, Claire B.; Bhattacharya, Tripti; Feng, Ran; Burls, Natalie J.; Knapp, Scott; McClymont, Erin L. (October 2023, Geophysical Research Letters)

   Abstract Future projections of southwestern African hydroclimate are highly uncertain. However, insights from past warm climates, like the Pliocene, can reveal mechanisms of future change and help benchmark models. Using leaf wax hydrogen isotopes to reconstruct precipitation (δD_p) from Namibia over the past 5 million years, we find a long‐term depletion trend (−50‰). Empirical mode decomposition indicates this trend is linked to sea surface temperatures (SSTs) within the Benguela Upwelling System, but modulated by Indian Ocean SSTs on shorter timescales. The influence of SSTs on reconstructed regional hydroclimate is similar to that observed during modern Benguela Nio events, which bring extreme flooding to the region. Isotope‐enabled simulations and PlioMIP2 results suggest that capturing a Benguela Nio‐like state is key to accurately simulating Pliocene, and future, regional hydroclimate. This has implications for future regional climate, since an increased frequency of Benguela Nios poses risk to the ecosystems and industries in the region. 

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4. Relatively warm deep-water formation persisted in the Last Glacial Maximum

   https://doi.org/10.1038/s41586-025-10012-2  

   Wharton, Jack H; Kozikowska, Emilia; Keigwin, Lloyd D; Marchitto, Thomas M; Maslin, Mark A; Ziegler, Martin; Thornalley, David_J R (February 2026, Nature)

   Abstract The Last Glacial Maximum (19–23 thousand years ago) was characterized by low greenhouse gas concentrations and continental ice sheets that covered large parts of North America and Europe¹. Glacial climate was therefore very different, with colder global mean temperatures and an increased Equator-to-pole temperature gradient, probably resulting in stronger westerlies². However, the state of the deep North Atlantic Ocean under these glacial climate forcings remains uncertain^3–6, particularly owing to the rarity of deep-ocean temperature and salinity constraints. Here we show that the temperature of the glacial deep (>1.5 km) Northwest Atlantic was approximately 0–2 °C (only 1.8 ± 0.5 °C (2 s.e.) colder than today), and, after accounting for the whole-ocean change, seawater δ¹⁸O was 0.3 ± 0.1‰ (2 s.e.) higher and can be traced back to the surface subtropics via the subpolar Northeast Atlantic and Nordic Seas. Together, our hydrographic data reveal the thermal and isotopic structure of the deep Northwest Atlantic and suggest sustained production of relatively warm and probably salty North Atlantic Deep Water during the Last Glacial Maximum. Furthermore, our results provide updated constraints for benchmarking Earth system models used to project future climate change. 

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5. Alpine permafrost could account for a quarter of thawed carbon based on Plio-Pleistocene paleoclimate analogue

   https://doi.org/10.1038/s41467-022-29011-2  

   Cheng, Feng; Garzione, Carmala; Li, Xiangzhong; Salzmann, Ulrich; Schwarz, Florian; Haywood, Alan M.; Tindall, Julia; Nie, Junsheng; Li, Lin; Wang, Lin; et al (December 2022, Nature Communications)

   Abstract Estimates of the permafrost-climate feedback vary in magnitude and sign, partly because permafrost carbon stability in warmer-than-present conditions is not well constrained. Here we use a Plio-Pleistocene lacustrine reconstruction of mean annual air temperature (MAAT) from the Tibetan Plateau, the largest alpine permafrost region on the Earth, to constrain past and future changes in permafrost carbon storage. Clumped isotope-temperatures (Δ 47 -T) indicate warmer MAAT (~1.2 °C) prior to 2.7 Ma, and support a permafrost-free environment on the northern Tibetan Plateau in a warmer-than-present climate. Δ 47 -T indicate ~8.1 °C cooling from 2.7 Ma, coincident with Northern Hemisphere glacial intensification. Combined with climate models and global permafrost distribution, these results indicate, under conditions similar to mid-Pliocene Warm period (3.3–3.0 Ma), ~60% of alpine permafrost containing ~85 petagrams of carbon may be vulnerable to thawing compared to ~20% of circumarctic permafrost. This estimate highlights ~25% of permafrost carbon and the permafrost-climate feedback could originate in alpine areas. 

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