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1. Shark teeth zinc isotope values document intrapopulation foraging differences related to ontogeny and sex

   https://doi.org/10.1038/s42003-023-05085-6  

   McCormack, Jeremy; Karnes, Molly; Haulsee, Danielle; Fox, Dewayne; Kim, Sora L. (December 2023, Communications Biology)

   Abstract Trophic ecology and resource use are challenging to discern in migratory marine species, including sharks. However, effective management and conservation strategies depend on understanding these life history details. Here we investigate whether dental enameloid zinc isotope (δ⁶⁶Zn_en) values can be used to infer intrapopulation differences in foraging ecology by comparing δ⁶⁶Zn_enwith same-tooth collagen carbon and nitrogen (δ¹³C_coll, δ¹⁵N_coll) values from critically endangered sand tiger sharks (Carcharias taurus) from Delaware Bay (USA). We document ontogeny and sex-related isotopic differences indicating distinct diet and habitat use at the time of tooth formation. Adult females have the most distinct isotopic niche, likely feeding on higher trophic level prey in a distinct habitat. This multi-proxy approach characterises an animal’s isotopic niche in greater detail than traditional isotope analysis alone and shows that δ⁶⁶Zn_enanalysis can highlight intrapopulation dietary variability thereby informing conservation management and, due to good δ⁶⁶Zn_enfossil tooth preservation, palaeoecological reconstructions. 

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2. Antarctic Peninsula moss and water isotopes influenced by high evaporative conditions and topography

   https://doi.org/10.1017/S0954102025100485  

   Groff, Dulcinea V; Beilman, David W (January 2026, Antarctic Science)

   Abstract There is clear evidence that rapid warming has been fuelling significant changes in the ocean and cryosphere in the Antarctic Peninsula region. Less is known about how terrestrial biological ecosystems, particularly plants, are responding to warming and hydroclimatic change. We show that high evaporative environmental conditions and microclimate associated with topography lead to humidity-dependent evaporative effects on the oxygen isotope ratios (δ¹⁸O) of moss waters and α-cellulose in the northern Antarctic Peninsula, based on a spatial (> 400 km) isotopic survey at 14 sites over 24 days during summer 2020. The δ¹⁸O of moss waters define a water line of δ²H = 4 × δ¹⁸O + 37 forPolytrichum strictumand δ²H = 3.8 × δ¹⁸O + 38.9 forChorisodontium aciphyllum, indicating enrichment compared to line slopes ranging from 6.7 to 8.5 for snow, standing water, previous published snapshots of moss waters and the long-term local meteoric water lines along the Antarctic Peninsula. The δ¹⁸O of moss waters negatively correlated with relative humidity (which ranged from ~50% to 100%) and not with temperature or latitude, where a higher δ¹⁸O indicates increased evaporative enrichment or dry conditions. A positive correlation between the δ¹⁸O of moss waters and α-cellulose (ρ = 0.397,P= 0.011) forP. strictum(ρ = 0.533,P= 0.007) but notC. aciphyllumsuggests that the high evaporative conditions from the season imprinted on the cellulose. Lastly, we found significant positive correlations between topographic aspect (north-exposedness) and the δ¹⁸O of moss waters (ρ = 0.569,P< 0.001) and α-cellulose (ρ = 0.579,P< 0.001), indicating that irradiance on north-facing slopes promotes drier conditions and evaporative enrichment. Topographic aspect (and resulting microclimate) is an important and predictable determinant of the δ¹⁸O of moss waters and α-cellulose. This study highlights that mosses are sensitive recorders of climatic and non-climatic conditions in polar terrestrial ecosystems. 

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3. Shelf Ecosystems Along the U.S. Atlantic Coastal Plain Prior to and During the Paleocene‐Eocene Thermal Maximum: Insights Into the Stratigraphic Architecture

   https://doi.org/10.1029/2022PA004475  

   Doubrawa, Monika; Stassen, Peter; Robinson, Marci M.; Babila, Tali L.; Zachos, James C.; Speijer, Robert P. (October 2022, Paleoceanography and Paleoclimatology)

   Abstract The Paleocene‐Eocene Thermal Maximum (PETM) is the most pronounced global warming event of the early Paleogene related to atmospheric CO₂increases. It is characterized by negative δ¹⁸O and δ¹³C excursions recorded in sedimentary archives and a transient disruption of the marine biosphere. Sites from the U.S. Atlantic Coastal Plain show an additional small, but distinct δ¹³C excursion below the onset of the PETM, coined the “pre‐onset excursion” (POE), mimicking the PETM‐forced environmental perturbations. This study focuses on the South Dover Bridge core in Maryland, where the Paleocene‐Eocene transition is stratigraphically constrained by calcareous nannoplankton and stable isotope data, and in which the POE is well‐expressed. The site was situated in a middle neritic marine shelf setting near a major outflow of the paleo‐Potomac River system. We generated high‐resolution benthic foraminiferal assemblage, stable isotope, trace‐metal, grain‐size and clay mineralogy data. The resulting stratigraphic subdivision of this Paleocene‐Eocene transition is placed within a depth transect across the paleoshelf, highlighting that the PETM sequence is relatively expanded. The geochemical records provide detailed insights into the paleoenvironment, developing from a well‐oxygenated water column in latest Paleocene to a PETM‐ecosystem under severe biotic stress‐conditions, with shifts in food supply and temperature, and under dysoxic bottom waters in a more river‐dominated setting. Environmental changes started in the latest Paleocene and culminated atthe onset of the PETM, hinting to an intensifying trigger rather than to an instantaneous event at the Paleocene‐Eocene boundary toppling the global system. 

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4. Seasonal SIMS δ18O record in Astarte borealis from the Baltic Sea tracks a modern regime shift in the NAO

   https://doi.org/10.3389/fmars.2023.1293823  

   Hughes, Hunter P; Surge, Donna; Orland, Ian J; Zettler, Michael L; Moss, David K (December 2023, Frontiers in Marine Science)

   IntroductionAstarte borealisholds great potential as an archive of seasonal paleoclimate, especially due to its long lifespan (several decades to more than a century) and ubiquitous distribution across high northern latitudes. Furthermore, recent work demonstrates that the isotope geochemistry of the aragonite shell is a faithful proxy of environmental conditions. However, the exceedingly slow growth rates ofA. borealisin some locations (<0.2mm/year) make it difficult to achieve seasonal resolution using standard micromilling techniques for conventional stable isotope analysis. Moreover, oxygen isotope (δ¹⁸O) records from species inhabiting brackish environments are notoriously difficult to use as paleoclimate archives because of the simultaneous variation in temperature and δ¹⁸O_watervalues. MethodsHere we use secondary ion mass spectrometry (SIMS) to microsample anA. borealisspecimen from the southern Baltic Sea, yielding 451 SIMS δ¹⁸O_shellvalues at sub-monthly resolution. ResultsSIMS δ¹⁸O_shellvalues exhibit a quasi-sinusoidal pattern with 24 local maxima and minima coinciding with 24 annual growth increments between March 1977 and the month before specimen collection in May 2001. DiscussionAge-modeled SIMS δ¹⁸O_shellvalues correlate significantly with bothin situtemperature measured from shipborne CTD casts (r² = 0.52, p<0.001) and sea surface temperature from the ORAS5-SST global reanalysis product for the Baltic Sea region (r² = 0.42, p<0.001). We observe the strongest correlation between SIMS δ¹⁸O_shellvalues and salinity when both datasets are run through a 36-month LOWESS function (r² = 0.71, p < 0.001). Similarly, we find that LOWESS-smoothed SIMS δ¹⁸O_shellvalues exhibit a moderate correlation with the LOWESS-smoothed North Atlantic Oscillation (NAO) Index (r² = 0.46, p<0.001). Change point analysis supports that SIMS δ¹⁸O_shellvalues capture a well-documented regime shift in the NAO circa 1989. We hypothesize that the correlation between the SIMS δ¹⁸O_shelltime series and the NAO is enhanced by the latter’s influence on the regional covariance of water temperature and δ¹⁸O_watervalues on interannual and longer timescales in the Baltic Sea. These results showcase the potential for SIMS δ¹⁸O_shellvalues inA. borealisshells to provide robust paleoclimate information regarding hydroclimate variability from seasonal to decadal timescales. 

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5. Diets and environments of late pleistocene pygmy and Columbian mammoths: Isotopic evidence from Southern California

   https://doi.org/10.1371/journal.pone.0338674  

   Hannold, Chance D; Wang, Yang; Wang, Xiaoming; Dunn, Regan; Hoffman, Jonathan (January 2026, PLOS One)

   Drucker, Dorothée (Ed.)

   Pygmy mammoths (Mammuthus exilis) and Columbian mammoths (Mammuthus columbi) coexisted on the island of Santarosae (now the Northern Channel Islands of California) until the Late Pleistocene megafaunal extinctions, but the ecology of these mammoths is not yet well explored. In this study, we reconstructed the diets and environments of Late Pleistocene pygmy and Columbian mammoths using stable isotopes in tooth enamel samples from the Northern Channel Islands and Rancho La Brea. The enamel δ¹³C values indicate that these mammoths primarily consumed C₃vegetation. However, a few individuals consumed significant amounts of C₄plants, CAM plants, or water-stressed woody C₃plants. The mean diet-δ¹³C value for mainland mammoths (−24.2 ± 1.4‰) is about 2‰ higher than that of island mammoths (−26.4 ± 1.9‰), suggesting that most mainland mammoths consumed either water-stressed C₃vegetation, or some C₄and/or CAM plants. Reconstructed δ¹⁸O values of paleo-water from the mainland are generally lower than the mean δ¹⁸O values of modern precipitation in Southern California, suggesting conditions were wetter and/or cooler than today. Reconstructed δ¹⁸O values of paleo-water from the islands are more similar to modern precipitation. δ¹³C-based estimates of mean annual precipitation range from 159 to 1407 mm/yr on the islands and from 28 to 387 mm/yr on the mainland. However, consumption of small amounts of C₄and/or CAM plants may have resulted in an underestimation of precipitation for the mainland. Radiometric dating of additional fossils from both localities will help clarify the links between climate change and mammoth evolution and extinction in the region. 

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