Search for: All records

Redox-sensitive trace elements (RSTE) are well-established proxy indicators of the geochemical conditions on Earth. They have proven useful for revealing early Earth’s oxygenation and detailing past anoxic episodes in aquatic systems. Here we present evidence that large-scale Tropical Pacific climate variability associated with El Niño–Southern Oscillation (ENSO) influences the partitioning of solid, dissolved, and particulate phases of manganese, iron, and molybdenum in a meromictic, hypersaline lake of the Galápagos archipelago. The concentration of these RSTE as a geochemical proxy in this system reveals the timing of ENSO events between the years 1985–2016 CE. Additionally, these geochemical signals are associated with blooms in primary productivity, which is highly influenced by local rainfall events. Thus, we find strong evidence that climatic events influence the geochemical profile of this aquatic system and deposited sediments, such that levels of RSTE are elevated far above background levels during wet, productive El Niño years. As a result of this on/off signal behavior, RSTE offer great promise for reconstructing individual El Niño events throughout the Holocene in this lake sediment archive. Ideally, this approach could also be applied to other El Niño regions to better reconstruct past climate when combined with traditional paleoclimate proxies. 

Terrestrial proxies of wind direction spanning the last deglaciation suggest easterly winds were present near the Laurentide Ice Sheet margin in the North American midcontinent. However, the existence and spatial extent of such easterly winds have not been investigated with transient paleoclimate model simulations, which could provide improved dynamical context for interpreting the causes of these winds. Here we assess near-surface winds near the retreating southern Laurentide Ice Sheet margin using iTRACE, a transient simulation of deglacial climate from 20–11 ka. Near the south-central margin, simulated near-surface winds are northeasterly to easterly through the deglaciation, due to katabatic flow off the ice sheet and anticyclonic circulation. As the ice sheet retreats and the Laurentide High moves northeastward and weakens, near-surface northeasterly winds weaken. Meltwater fluxes also influence temperature and sea level pressure over the North Atlantic, leading to easterly wind anomalies over eastern to midwestern North America. The agreement between proxy and model wind directions is promising, although simulated easterly to northeasterly winds extend too far south in iTRACE relative to the proxy data. Agreement is also strongest in winter, spring, and fall, suggesting these may have been seasons with greater aeolian activity. 

Abstract Wind energy is a growing component of energy production in Illinois (IL). However, uncertainty remains regarding future wind speed variability and trends and their potential impact on wind energy generation. Here, we assess recent (1992–2021) trends in monthly average wind speed and direction using data from the Illinois Climate Network (ICN), which consists of 18 weather stations across IL, supplemented by five IL stations from the Global Historical Climatology Network (GHCN) hourly dataset. We find decreases in mean annual wind speed at most ICN stations, ranging from −0.46% to −17.92% decade⁻¹, and all five GHCN stations (from −1.53% to −6.53% decade⁻¹). Decreasing wind speed trends are found in all seasons. In contrast, 10-m wind speed trends for IL in reanalysis data, a primary source of data for climate model validation and wind energy projection, are positive or show no trend in most grids that approximate IL station locations [1.28%–3.10% decade⁻¹for ERA5, NASA MERRA-2, and NCEP North American Regional Reanalysis (NARR)]. Some IL stations also show a significant shift to more southerly winds, indicating a greater influence of air masses originating from the Gulf of Mexico. This trend is also not captured by reanalysis data, despite accurate wind direction climatologies. Thus, model validation of regional wind should be performed cautiously with reanalysis data, and reliance on reanalysis wind data may lead to an overestimation of future IL wind speeds and wind power generation. Significance StatementReanalysis data are used to validate climate models and for wind energy projection. The purpose of this study is to assess how well three widely used reanalysis products reproduce surface wind observations in Illinois, which ranks fifth in the country for wind power capacity. We found reanalysis data better reproduce wind direction than wind speed and tend to overestimate wind speeds. The station data show significant decreases in wind speeds and changes in wind direction, but those trends are not found in any of the reanalysis products studied here. This could lead to an overestimation of future wind energy generation and inaccuracies in wind in climate models. These results highlight the limitations of reanalysis data, which should be used cautiously. 

Abstract The hydrologic cycle is a fundamental component of the climate system with critical societal and ecological relevance. Yet gaps persist in our understanding of water fluxes and their response to increased greenhouse gas forcing. The stable isotope ratios of oxygen and hydrogen in water provide a unique opportunity to evaluate hydrological processes and investigate their role in the variability of the climate system and its sensitivity to change. Water isotopes also form the basis of many paleoclimate proxies in a variety of archives, including ice cores, lake and marine sediments, corals, and speleothems. These records hold most of the available information about past hydrologic variability prior to instrumental observations. Water isotopes thus provide a ‘common currency’ that links paleoclimate archives to modern observations, allowing us to evaluate hydrologic processes and their effects on climate variability on a wide range of time and length scales. Building on previous literature summarizing advancements in water isotopic measurements and modeling and describe water isotopic applications for understanding hydrological processes, this topical review reflects on new insights about climate variability from isotopic studies. Our intention is to highlight new work and opportunities to enhance our understanding and predictive skill, rather than be exhaustive. We offer a set of recommendations to advance observational and model-based tools for climate research, and highlight opportunities to better constrain climate sensitivity and identify anthropogenically-driven hydrologic changes within the inherently noisy background of natural climate variability. 

Oceanic islands support unique biotas but often lack ecological redundancy, so that the removal of a species can have a large effect on the ecosystem. The larger islands of the Galápagos Archipelago once had one or two species of giant tortoise that were the dominant herbivore. Using paleoecological techniques, we investigate the ecological cascade on highland ecosystems that resulted from whalers removing many thousands of tortoises from the lowlands. We hypothesize that the seasonal migration of a now-extinct tortoise species to the highlands was curtailed by decreased intraspecific competition. We find the trajectory of plant community dynamics changed within a decade of the first whaling vessels visiting the islands. Novel communities established, with a previously uncommon shrub, Miconia , replacing other shrubs of the genera Alternanthera and Acalypha . It was, however, the introduction of cattle and horses that caused the local extirpation of plant species, with the most extreme impacts being evident after c. 1930. This modified ecology is considered the natural state of the islands and has shaped subsequent conservation policy and practice. Restoration of El Junco Crater should emphasize exclusion of livestock, rewilding with tortoises, and expanding the ongoing plantings of Miconia to also include Acalypha and Alternanthera . 

Abstract ENSO and the mean zonal sea surface temperature gradient (dSST) of the tropical Pacific are important drivers of global climate and vary on decadal to centennial time scales. However, the relationship between dSST and ENSO cannot be assessed with the short instrumental record, and is uncertain in proxy data, with intervals of both stronger and weaker ENSO postulated to occur with overall strong dSST in the past. Here we assess the ENSO–dSST relationship during the last millennium using general circulation models (GCMs) participating in phase 3 of the Paleoclimate Modeling Intercomparison Project. Last millennium GCM simulations show diversity in the strength and direction of the ENSO–dSST relationship. Yet, the models that best simulate modern tropical Pacific climate frequently have a more negative ENSO–dSST correlation. Thus, last millennium tropical Pacific climate simulations support the likelihood of enhanced ENSO during decadal to centennial periods of reduced tropical Pacific dSST. However, the alternating directional ENSO–dSST relationship in all model simulations suggests that this relationship is not constant through time and is likely controlled by multiple mechanisms.