Description: Tropical islands, including many in island arcs, are susceptible to recurring disturbances from extreme storms. To test whether such storms bias isotopic indicators of long-term erosion, we measured 10Be in samples collected before and after Hurricane Maria (2017, category five) from Dominica, an andesitic island in the Caribbean. Populations of before- and after-storm concentrations of 10Be are indistinguishable (n = 7 for in situ, n = 11 for meteoric); however, individual sample sites replicate less well with isotopic concentrations in samples taken before and after the storm varying by an average of 12%. These data suggest that processes controlling the depth and amount of near-surface erosion on Dominica during extreme storms are stochastic. Erosion rates determined from in situ 10Be are low compared to similarly steep and wet areas (median = 0.082 mm/yr, n = 12) and appear to be controlled by orographic precipitation.

Description: Climate change, including warmer winter temperatures, a shortened snowfall season, and more rain-on-snow events, threatens nordic skiing as a sport. In response, over-summer snow storage, attempted primarily using wood chips as a covering material, has been successfully employed as a climate change adaptation strategy by high-elevation and/or high-latitude ski centers in Europe and Canada. Such storage has never been attempted at a site with both a low altitude and latitude, and few studies have quantified snowmelt repeatedly through the summer. Such data, along with tests of different cover strategies, are prerequisites to optimizing snow storage strategies. Here, we assess the melt rates of two wood-chip covered snow piles (each ~200 m3) emplaced during spring 2018 in Craftsbury, Vermont (45o N and 360 m asl) to develop an optimized snow storage strategy. In 2019, we tested that strategy on a much larger, 9300 m3 pile. In 2018, we continually logged air-to-snow temperature gradients under different cover layers including rigid foam, open cell foam, and wood chips both with and without an underlying insulating blanket and an overlying reflective cover. We also measured ground temperatures to a meter depth both under and adjacent to the snow piles and used a snow tube to measure snow density. During both years, we monitored volume change over the melt season using terrestrial laser scanning. In 2018, snow volume loss ranged from -0.29 to -2.81 m3 day-1 with highest rates in mid-summer and lowest rates in the fall; mean melt rates were 1.24 and 1.50 m3 day-1, 0.6 to 0.7 % of initial pile volume per day. Snow density did increase over time but most volume loss was the result of melting. Wet wood chips underlain by an insulating blanket and covered with a reflective sheet was the most effective cover combination for minimizing melt, likely because the surface reflected incoming shortwave radiation while the wet wood chips provided significant thermal mass, allowing much of the energy absorbed during the day to be lost by long-wave emission at night. The importance of pile surface area to volume ratio is demonstrated by the melt rates of the 9300 m3 pile emplaced in 2019 which lost only 〈0.16% of its initial volume per day between April and September, retaining 75% of the initial snow volume over summer. Together, these data demonstrate the feasibility of over-summer snow storage at mid-latitudes and low altitudes and suggest efficient cover strategies.

Description: Coccolithophores are an abundant phytoplankton group that exhibit remarkable diversity in their biology, ecology and calcitic exoskeletons (coccospheres). Their extensive fossil record is a testament to their important biogeochemical role and is a valuable archive of biotic responses to environmental change stretching back over 200 million years. However, to realise the full potential of this archive for (palaeo-)biology and biogeochemistry requires an understanding of the physiological processes that underpin coccosphere architecture. Using culturing experiments on four modern coccolithophore species (Calcidiscus leptoporus, Calcidiscus quadriperforatus, Helicosphaera carteri and Coccolithus braarudii) from three long-lived families, we investigate how coccosphere architecture responds to shifts from exponential (rapid cell division) to stationary (slowed cell division) growth phases as cell physiology reacts to nutrient depletion. These experiments reveal statistical differences in coccosphere size and the number of coccoliths per cell between these two growth phases, specifically that cells in exponential-phase growth are typically smaller with fewer coccoliths, whereas cells experiencing growth-limiting nutrient depletion have larger coccosphere sizes and greater numbers of coccoliths per cell. Although the exact numbers are species-specific, these growth-phase shifts in coccosphere geometry demonstrate that the core physiological responses of cells to nutrient depletion result in increased coccosphere sizes and coccoliths per cell across four different coccolithophore families (Calcidiscaceae, Coccolithaceae, Isochrysidaceae and Helicosphaeraceae), a representative diversity of this phytoplankton group. Building on this, the direct comparison of coccosphere geometries in modern and fossil coccolithophores enables a proxy for growth phase to be developed that can be used to investigate growth responses to environmental change throughout their long evolutionary history. Our data also show that changes in growth rate and coccoliths per cell associated with growth-phase shifts can substantially alter cellular calcite production. Coccosphere geometry is therefore a valuable tool for accessing growth information in the fossil record, providing unprecedented insights into the response of species to environmental change and the potential biogeochemical consequences.

Description: Atmospheric _p_CO~2~ is a critical component of the global carbon system and is considered to be the major control of Earth's past, present and future climate. Accurate and precise reconstructions of its concentration through geological time are, therefore, crucial to our understanding of the Earth system. Ice core records document _p_CO~2~ for the past 800 kyrs, but at no point during this interval were CO~2~ levels higher than today. Interpretation of older _p_CO~2~ has been hampered by discrepancies during some time intervals between two of the main ocean-based proxy methods used to reconstruct _p_CO~2~: the carbon isotope fractionation that occurs during photosynthesis as recorded by haptophyte biomarkers (alkenones) and the boron isotope composition (δ^11^B) of foraminifer shells. Here we present alkenone and δ^11^B-based _p_CO~2~ reconstructions generated from the same samples from the Plio-Pleistocene at ODP Site 999 across a glacial-interglacial cycle. We find a muted response to _p_CO~2~ in the alkenone record compared to contemporaneous ice core and δ^11^B records, suggesting caution in the interpretation of alkenone-based records at low _p_CO~2~ levels. This is possibly caused by the physiology of CO~2~ uptake in the haptophytes. Our new understanding resolves some of the inconsistencies between the proxies and highlights that caution may be required when interpreting alkenone-based reconstructions of _p_CO~2~.

Description: Integrated Ocean Drilling Program (IODP) Expedition 342 recovered exceptional Paleogene to early Neogene sedimentary archives from clay-rich sediments in the northwest Atlantic Ocean. These archives present an opportunity to study Cenozoic climate in a highly sensitive region at often unprecedented resolution. Such studies require continuous records in the depth and time domains. Using records from multiple adjacent drilled holes, intervals within consecutive cores are typically spliced into a single composite record on board the R/V JOIDES Resolution using high-resolution physical properties data sets acquired before the cores are split. The highly dynamic nature of the sediment drifts drilled during Expedition 342 and the modest amplitude of variance in the physical property records made it possible to construct only highly tentative initial working splices, which require extensive postexpedition follow-up work. Postexpedition, high-resolution X-ray fluorescence (XRF) core scanning data enabled the construction of a preliminary composite depth scale and splice. Here, we present the revised composite depth scale and splice for IODP Site U1406, predominantly constructed using detailed hole-to-hole correlations of newly generated high-resolution XRF data and revisions of the initial XRF data set. The revised composite depth scale and splice serve as a reference framework for future research on Site U1406 sediments.

Description: The interval spanning from the Early Eocene Climatic Optimum (EECO) to the onset of long-term cooling in the middle Eocene is marked by prominent changes in calcareous nannofossil assemblages and coincides with modification of the North Atlantic deep-ocean circulation. Here we present an integrated calcareous nannoplakton and bulk stable isotope records (δ18O and δ13C) across the early-middle Eocene (~52- 43 Ma) from IODP Site U1410 (northwest Atlantic), where middle Eocene deposits occur as clay-rich drift sediments reflecting the formation of persistent deep currents. Abundance patterns of selected biostratigraphically relevant taxa encompassing Ypresian-Lutetian calcareous nannofossil Zones CNE4-CNE12 served to test the biostratigraphic reliability of the species. In addition, long- and short-term trends documented in geochemical data have been used to determine the temporal relationships between palaeoenvironmental trends and changes in calcareous nannofossil assemblages. After the EECO to the Ypresian-Lutetian boundary, calcareous nannofossils switched from an assemblage mainly composed of warm-water and oligotrophic taxa (Zygrhablithus, Discoaster, Sphenolithus, Coccolithus) to one dominated by the more temperate and eutrophic reticulofenestrids. This prominent change occurred during a phase of relatively high δ18O values likely related to the post-EECO cooling. Although the dominance of reticulofenestrids persisted unvaried throughout the study middle Eocene interval, early Lutetian stable isotope records indicate a reversal in the paleoenvironmetal trends suggesting a temporary restoration of warmer conditions associated with an increase in abundance of D. sublodoensis. These results confirm previous records of environmental instability but the comparison of our results with different dataset highlights a global enigmatic scenario in term of bio-chemo-magnetostratigraphy.