The mid-Cretaceous thermal maximum (KTM) during Cenomanian to Santonian times from ca. 100 to 83 Ma is considered among Earth’s warmest sustained intervals of the Phanerozoic. The time interval is also characterized by major paleoceanographic changes in the form of an oceanic anoxic event and the flooding of epicontinental seaways, such as the Western Interior Seaway in North America. We report carbonate clumped isotope (Δ47) paleotemperatures (TΔ47) of the KTM measured from Cenomanian oyster fossils of the Western Interior Seaway. Following screening of specimens for carbonate diagenesis and exclusion of geographic zones with evidence consistent with solid-state Δ47 reordering, a mean TΔ47 of 28–34 °C (95% confidence interval for the standard error of mean) for primary oyster calcite quantifies extreme mid-latitude warmth in North America. When combined with existing Campanian and Maastrichtian marine TΔ47 records, the new data constrain Late Cretaceous temperature trends underlying the evolution of North American faunal and stratigraphic records. These TΔ47 data from the peak KTM highlight the potential of this proxy to quantitatively resolve the upper thermal limits of Phanerozoic greenhouse climates.

In this study, we use aerial photographs, satellite imagery and field observations to quantify changes in the area, terminus length, snowline elevation and surface elevation of eight glaciers in the Alexandra Fiord region, eastern Ellesmere Island, between 1959 and 2019. Comparisons to written and pictorial descriptions from the British Arctic Expedition extend the record of change in terminus position and surface elevation to 1875 for Twin Glacier. Glacier area at Alexandra Fiord decreased by a total of 15.77 ± 0.65 km2 (11.77 ± 0.49%) between 1959 and 2019, the mean end of summer snowline increased in elevation by 360 ± 84 m (8 ± 2 m a−1) between 1974 and 2019, and the glaciers thinned at an average rate of 0.60 ± 0.06 m a−1 between 2001 and 2018. Annual rates of terminus retreat were ~3–5 times higher over the period 1974–2019 compared to 1875–1974, and rates of thinning were ~2–3 times higher over 2001–18 compared to 1875–2001. Our results are consistent with rates of change determined for other glaciers of similar size on Ellesmere Island, and with accelerated rates of ice loss coincident with regional increases in air temperature of ~1.5°C since the early 1980s.

The δ18O of carbonate minerals that formed at Earth’s surface is widely used to investigate paleoclimates and paleo-elevations. However, a multitude of hydrologic processes can affect δ18O values, including mixing, evaporation, distillation of parent waters, and carbonate growth temperatures. We combined traditional carbon and oxygen isotope analyses with clumped (Δ47) and triple oxygen isotopes (Δ′17O) analyses in oyster shells (Acutostrea idriaensis) of the Goler Formation in southern California (USA) to obtain insights into surface temperatures and δ18O values of meteoric waters during the early Eocene hothouse climate. The Δ47-derived temperatures ranged from 9 °C to 20 °C. We found a correlation between the δ18O of growth water (δ18Ogw) (calculated using Δ47 temperatures and δ18O of carbonate) and the δ13C values of shells. The Δ′17O values of shell growth waters (0.006‰–0.013‰ relative to Vienna standard mean ocean water–standard light Antarctic precipitation [VSMOW-SLAP]) calculated from Δ′17O of carbonate (–0.087‰ to –0.078‰ VSMOW-SLAP) were lower than typical meteoric waters. These isotopic compositions are consistent with oyster habitation in an estuary. We present a new triple oxygen isotope mixing model to estimate the δ18O value of freshwater supplying the estuary (δ18Ofw). The reconstructed δ18Ofw of –11.3‰ to –14.7‰ (VSMOW) is significantly lower than the δ18Ogw of –4.4‰ to –9.9‰ that would have been calculated using “only” Δ47 and δ18O values of carbonate. This δ18Ofw estimate supports paleogeographic reconstructions of a Paleogene river fed by high-elevation catchments of the paleo–southern Sierra Nevada. Our study highlights the potential for paired Δ47 and Δ′17O analyses to improve reconstructions of meteoric water δ18O, with implications for understanding ancient climates and elevations.

For millennia, qeros have been a primary component of ceremonially and politically important toasting rituals in the Andes and retain their cultural significance to this day. These wooden drinking vessels underwent a stylistic and technical revolution in the colonial period (1532–1821 AD). Among an array of features that distinguish colonial qeros from their Inka predecessors is the presence of lead white, a pigment that was introduced to the Andes by the Spanish. Here, we present lead (Pb) isotope measurements of lead white pigments from 20 colonial qeros from the collections of the National Museum of the American Indian, the American Museum of Natural History, the Brooklyn Museum of Art, the Metropolitan Museum of Art, and in a private collection. Although most of the vessels are not known to be associated with one another, their lead white pigments fall into three distinct and internally consistent groupings in Pb isotope space. We interpret the isotopic signatures of two of the groups to indicate that the lead white was imported from Europe. We suggest that the largest grouping (comprising pigments sampled from 12 qeros) is decorated with lead white of Andean origin. These isotopic signatures may have a chronological component, and strongly suggest some form of centralization in pigment acquisition, manufacture, and/or distribution in the colonial period.