Stephen R. Meyers and Mark Pagani
The North Atlantic Oscillation (NAO) is the leading mode of atmospheric variability in the North Atlantic region, influencing storm tracks and creating a dipole pattern of precipitation from north to south across Western Europe. This distinct spatial distribution of precipitation provides a framework that can be potentially used to identify and reconstruct patterns of past NAO-forced climate variability. In this study we use tree-ring width series from Western Europe, in conjunction with principal components analysis and advanced spectral methods, to prospect for quasi-periodic climate signals that are forced by the NAO. We identify a robust 25 year anti-phased synchronization in climate variability between Scandinavia and the Mediterranean during the 17th-20th centuries. The amplitude of the 25 year beat displays a long-term modulation in northern and southern Europe, with minimum amplitude during the late Maunder Minimum. This amplitude minimum coincides with a maximum in Delta14C, suggesting a potential solar or oceanic influence on the intensity of the 25 year band of quasi-periodic variability.
Mark Pagani, Nikolai Pedentchouk, Matthew Huber, Appy Sluijs, Stefan Schouten, Henk Brinkhuis, Jaap S. Sinninghe Damste, Gerald R. Dickens, and the IODP Expedition 302 Expedition Scientists
Sediments were recovered from the central Arctic Ocean, providing the first opportunity to evaluate the environmental response at the North Pole during the PETM. Here we present stable hydrogen and carbon isotope measurements of terrestrial-plant and aquatic-derived n-alkanes that record changes in hydrology, including surface water salinity and precipitation. Records are interpreted as documenting decreased rainout during hemispheric moisture transport and increased moisture delivery to the Arctic at the onset of the PETM, consistent with predictions of poleward storm track migrations during global warming. The terrestrial-plant carbon isotope excursion is substantially larger than those of marine carbonates. Previously, this offset was explained by a plant’s physiological response to increases in surface humidity. However, this mechanism is not an effective explanation in this wet Arctic setting, leading us to hypothesize that the true magnitude of the carbon isotope excursion and associated carbon input was greater than originally surmised. Greater carbon release and strong hydrological cycle feedbacks help explain the maintenance of this unprecedented PETM warmth.
Carlos Jaramillo, Diana Ochoa, Lineth Contreras, Mark Pagani, Humberto Carvajal-Ortiz, Lisa M. Pratt, Srinath Krishnan, and others
|Temperatures in tropical regions are estimated to have increased by 3 to 5 degrees C, compared with Late Paleocene values, during the Paleocene-Eocene Thermal Maximum (PETM, 56.3 million years ago) event. We investigated the tropical forest response to this rapid warming by evaluating the palynological record of three stratigraphic sections in eastern Colombia and western Venezuela. We observed a rapid and distinct increase in plant diversity and origination rates, with a set of new taxa, mostly angiosperms, added to the existing stock of low-diversity Paleocene flora. There is no evidence for enhanced aridity in the northern Neotropics. The tropical rainforest was able to persist under elevated temperatures and high levels of atmospheric carbon dioxide, in contrast to speculations that tropical ecosystems were severely compromised by heat stress.|
Sara K. Enders, Mark Pagani, Silvio Pantoja, Jill S. Baron, Alexander P. Wolfe, Nikolai Pedentchouk, Lilian Nunez
Compound-specific nitrogen, carbon, and hydrogen isotope records from sediments of Sky Pond, an alpine lake in Rocky Mountain National Park (Colorado, United States of America), were used to evaluate factors contributing to changes in diatom assemblages and bulk organic nitrogen isotope records identified in lake sediments across Colorado, Wyoming, and southern Montana. Nitrogen isotopic records of purified algal chlorins indicate a substantial shift in nitrogen cycling in the region over the past 60 years. Temporal changes in the growth characteristics of algae, captured in carbon isotope records in and around Sky Pond, as well as a 60 permil excursion in the hydrogen isotope composition of algal-derived palmitic acid, are coincident with changes in nitrogen cycling. The confluence of these trends is attributed to an increase in biologically available nitrogenous compounds caused by an expansion of anthropogenic influences and temporal changes in catchment hydrology and nutrient delivery associated with meltwater dynamics.
Brett J. Tipple and Mark Pagani
Hydrology, source region, and timing of precipitation are important controls on the climate of the Great Plains of North America and the composition of terrestrial ecosystems. Moisture delivered to the Great Plains varies seasonally and predominately derives from the Gulf of Mexico/Atlantic Ocean with minor contributions from the Pacific Ocean and Arctic region. For this work, we evaluate long-term relationships for the past ~35 million years between North American hydrology, climate, and floral change, using isotopic records and average carbon chain lengths of higher plant n-alkanes from Gulf of Mexico sediments. We posit that hydrological changes were linked to tectonic and oceanographic processes including the shoaling and closure of the Panamanian Seaway, amplification of North Atlantic Deep Water Production and an associated increase of meridional winds. The southerly movement of the Intertropical Convergence Zone near 4 Ma allowed for the development of a near-modern pressure/storm track system, driving increased aridity and changes in seasonality within the North American interior.