Time series analysis of long term palaeoecological records for the understanding climate change impacts on vegetal ecosystems

Manejo de datos paleoplinológicos a escala europea para generación de modelos climáticos continentale

Multi-decadal temperature changes off Iberia over the last two deglaciations and interglacials and their connection with the polar climate

The Iberian margin provides climatic and environmental sediment records with multi-decadal resolution over the last two deglaciations and interglacials. These records allow us to identify climatic structures and discuss interhemispherical connections.Peer reviewe

The MIS 13 interglacial at Ceprano, Italy, in the context of Middle Pleistocene vegetation changes in southern Europe

PCT and VM gratefully acknowledge support from The Leverhulme Trust through a research project grant (F/00 122/AH) towards the palynological investigation of the Ceprano cores. Excavations 2001–2006 at Campogrande were directed by Itallo Biddittu and GM, authorized by the Soprintendenza Archeologica del Lazio and co-financed by research grants from the SAPIENZA, University of Rome. Drillings at Campogrande were jointly financed and supervised by the Istituto per la Dinamica dei Processi Ambientali (CNR, Venice) and by the Istituto Italiano di Paleontologia Umana (Rome).Climatic and environmental changes of the Middle Pleistocene in Europe provide the context for an important phase in the evolution and dispersal of early hominins. Pollen records from terrestrial and marine sediment sequences reveal patterns not usually visible in palaeoenvironmental reconstructions from archaeological sites alone and show that hominin evolution took place against a background of marked environmental change as forests expanded and contracted in concert with global and regional climatic shifts. It is rare to find archaeological material in stratigraphically long and continuous palaeoenvironmental sequences, yet this is what is needed to enable particular phases of hominin evolution to be securely associated with climatic and environmental changes. At the well-known Middle Pleistocene archaeological site of Ceprano in Italy we have been able to produce a pollen record from the sedimentary unit directly below the stratum of the hominin remains. The new pollen data from Ceprano are presented here in full for the first time and provide a detailed picture of interglacial vegetation development during Marine Isotope Stage (MIS) 13. This evidence contributes significantly to our knowledge of the spatial heterogeneity of ecosystem responses to climatic change during this period and helps to further constrain the age of the hominin remains. New sites combining both archaeology and long, continuous high quality palaeoecological records would help clarify the relationship between hominin presence and palaeoclimatic and palaeoenvironmental conditions. In the meantime, better communication between the research communities can also go a long way to improving our understanding of the links between the two.PostprintPeer reviewe

Vegetation responses to abrupt climatic changes during the Last Interglacial Complex (Marine Isotope Stage 5) at Tenaghi Philippon, NE Greece

The discovery that climate variability during the Last Glacial shifted rapidly between climate states has intensified efforts to understand the distribution, timing and impact of abrupt climate change under a wide range of boundary conditions. In contribution to this, we investigate the nature of abrupt environmental changes in terrestrial settings of the Mediterranean region during the Last Interglacial Complex (Marine Isotope Stage [MIS] 5) and explore the relationships of these changes to high-latitude climate events. We present a new, temporally highly resolved (mean: 170 years) pollen record for the Last Interglacial Complex from Tenaghi Philippon, north-east Greece. The new pollen record, which spans the interval from 130,000 to 65,000 years ago, forms part of an exceptionally long polleniferous sediment archive covering the last 1.35 million years. The pollen data reveal an interglacial followed by alternating forest and steppe phases representing the interstadials and stadials of the Early Glacial. Superimposed on these millennial-scale changes is evidence of persistent sub-millennial-scale variability. We identify ten high-amplitude abrupt events in the pollen record, characterised by rapid contractions of closed forest to open steppe environment and interpreted to indicate major changes in moisture availability and temperature. The contractions in forest cover on millennial timescales appear associated with cooling events in the Mediterranean Sea, North Atlantic and Greenland regions, linked to the Dansgaard-Oeschger (DO) cycles of the Early Glacial. On sub-millennial timescales, the pattern of changes in forest cover at Tenaghi Philippon display a structure similar to the pattern of short-lived precursor and rebound-type events detected in the Greenland ice-core record. Our findings indicate that persistent, high-amplitude environmental variability occurred throughout the Early Glacial, on both millennial and submillennial timescales. Furthermore, the similarity of the pattern of change between Tenaghi Philippon and Greenland on sub-millennial timescales suggests that teleconnections between the high-latitudes and the Mediterranean region operate on sub-millennial timescales and that some terrestrial archives, such as Tenaghi Philippon, are particularly sensitive recorders of these abrupt climate changes

A reference time scale for Site U1385 (Shackleton Site) on the SW Iberian Margin

We produced a composite depth scale and chronology for Site U1385 on the SW Iberian Margin. Using log(Ca/Ti) measured by core scanning XRF at 1-cm resolution in all holes, a composite section was constructed to 166.5 meters composite depth (mcd) that corrects for stretching and squeezing in each core. Oxygen isotopes of benthic foraminifera were correlated to a stacked δ^18O reference signal (LR04) to produce an oxygen isotope stratigraphy and age model. Variations in sediment color contain very strong precession signals at Site U1385, and the amplitude modulation of these cycles provides a powerful tool for developing an orbitally-tuned age model. We tuned the U1385 record by correlating peaks in L* to the local summer insolation maxima at 37^oN. The benthic δ^18O record of Site U1385, when placed on the tuned age model, generally agrees with other time scales within their respective chronologic uncertainties. The age model is transferred to down-core data to produce a continuous time series of log(Ca/Ti) that reflect relative changes of biogenic carbonate and detrital sediment. Biogenic carbonate increases during interglacial and interstadial climate states and decreases during glacial and stadial periods. Much of the variance in the log(Ca/Ti) is explained by a linear combination of orbital frequencies (precession, tilt and eccentricity), whereas the residual signal reflects suborbital climate variability. The strong correlation between suborbital log(Ca/Ti) variability and Greenland temperature over the last glacial cycle at Site U1385 suggests that this signal can be used as a proxy for millennial-scale climate variability over the past 1.5 Ma. Millennial climate variability, as expressed by log(Ca/Ti) at Site U1385, was a persistent feature of glacial climates over the past 1.5 Ma, including glacial periods of the early Pleistocene (‘41-kyr world’) when boundary conditions differed significantly from those of the late Pleistocene (‘100-kyr world’). Suborbital variability was suppressed during interglacial stages and enhanced during glacial periods, especially when benthic δ^18O surpassed ~ 3.3-3.5‰. Each glacial inception was marked by appearance of strong millennial variability and each deglaciation was preceded by a terminal stadial event. Suborbital variability may be a symptomatic feature of glacial climate or, alternatively, may play a more active role in the inception and/or termination of glacial cycles.This research was supported by the Natural Environmental Research Council Grant NE/K005804/1 to DH and LS and NE/J017922/1 to DH.This is the final version of the article. It first appeared from Elsevier via http://dx.doi.org/10.1016/j.gloplacha.2015.07.00

Can we predict the duration of an interglacial?

Differences in the duration of interglacials have long been apparent in palaeoclimate records of the Late and Middle Pleistocene. However, a systematic evaluation of such differences has been hampered by the lack of a metric that can be applied consistently through time and by difficulties in separating the local from the global component in various proxies. This, in turn, means that a theoretical framework with predictive power for interglacial duration has remained elusive. Here we propose that the interval between the terminal oscillation of the bipolar seesaw and three thousand years (kyr) before its first major reactivation provides an estimate that approximates the length of the sea-level highstand, a measure of interglacial duration. We apply this concept to interglacials of the last 800 kyr by using a recently-constructed record of interhemispheric variability. The onset of interglacials occurs within 2 kyr of the boreal summer insolation maximum/precession minimum and is consistent with the canonical view of Milankovitch forcing pacing the broad timing of interglacials. Glacial inception always takes place when obliquity is decreasing and never after the obliquity minimum. The phasing of precession and obliquity appears to influence the persistence of interglacial conditions over one or two insolation peaks, leading to shorter (~ 13 kyr) and longer (~ 28 kyr) interglacials. Glacial inception occurs approximately 10 kyr after peak interglacial conditions in temperature and CO2, representing a characteristic timescale of interglacial decline. Second-order differences in duration may be a function of stochasticity in the climate system, or small variations in background climate state and the magnitude of feedbacks and mechanisms contributing to glacial inception, and as such, difficult to predict. On the other hand, the broad duration of an interglacial may be determined by the phasing of astronomical parameters and the history of insolation, rather than the instantaneous forcing strength at inception

The last 1.35 million years at Tenaghi Philippon: revised chronostratigraphy and long-term vegetation trends

In addition to being of interest to ancient Greek and Roman historians, the site of Philippi, NE Greece, has long been noted in Quaternary circles for providing the longest continuous European pollen record, spanning the last one million years. Here the original age model is re-evaluated and a new marine-terrestrial correlation is proposed. An astronomical calibration procedure, based on a correspondence between changes in certain vegetation elements and March and June perihelion configurations, suggests that the base of the sequence extends back to 1.35 million years ago. The revised chronological framework for the Tenaghi Philippon sequence provides an opportunity to examine the long-term behaviour of individual taxa and vegetation trends within the context of global climate changes. Comparisons reveal a close correspondence between the terrestrial and marine records, in terms of orbital and suborbital variability. However, joint time-frequency analysis of the arboreal pollen record shows that the obliquity and eccentricity/precession signals persist into the ‘100-kyr’ and ‘41-kyr’ worlds, respectively, suggesting the operation of additional climate mechanisms that are independent of high-latitude glacial–interglacial effects. Unlike ice core and marine sequences, no change in the magnitude of interglacial tree population expansions is observed after the Mid-Brunhes Event. Instead, the Tenaghi Philippon record suggests a major shift in the vegetational composition of interglacials after MIS 16, with the establishment of forests of reduced diversity and a ‘modern’ appearance