A multi-proxy palaeoenvironmental investigation of the findspot of an Iron Age bog body from Oldcroghan, Co. Offaly, Ireland

In 2003, the remains of an Early Iron Age bog body, known as ‘Oldcroghan Man’, were recovered during the cutting of a drainage ditch in a bog in the Irish Midlands. Only some fingernails and a withe fragment remained undisturbed in situ in the drain face, providing the sole evidence for the original position of the body. A detailed reconstruction of the depositional context of the body has been undertaken through multi-proxy analyses of a peat monolith collected at the findspot. The palynological record shows that the surrounding area was the focus of intensive human activity during the Later Bronze Age, but was largely abandoned during the Bronze Age–Iron transition in the mid-first millennium BC. In the mid-4th century BC, a bog pool developed at the site, evidenced in the stratigraphic, plant macrofossil, testate amoebae and coleopteran records. Plant macrofossil and pollen analysis of peat samples associated with the fingernails suggests that the body was deposited in this pool most likely during the 3rd century BC. The absence of carrion beetle fauna points to complete submergence of the body within the pool. Deposition occurred shortly before or around the time that the surrounding area again became the focus of woodland clearance, as seen in the extended pollen record from the peat monolith. This period corresponds to the Early Iron Age in Ireland, during which renewed cultural connections with Britain and continental Europe can be seen in the archaeological record and widespread forest clearance is recorded in pollen records from across Ireland. The palaeoenvironmental results indicate, therefore, that the demise of Oldcroghan Man took place at a pivotal time of socio-economic and perhaps political change.

A 4500-year proxy climate record from peatlands in the North of Ireland: the identification of widespread summer ‘drought phases’?

Mid-to-late Holocene high-resolution testate amoebae-derived water table reconstructions from two peatlands in the North of Ireland are presented. The proxy climate records are dated and correlated using a combination of AMS 14C dating, spheroidal carbonaceous particles and tephrochronology. The reconstructions start prior to the Hekla 4 tephra isochron (2395–2279 BC) and thus span the last ~4500 years. The records are compiled by the process of tuning within chronological errors, standardisation and stacking. Comparisons are made to existing palaeoclimate records from peatlands in Northern Britain and Ireland and the compiled lake-level record for mid-latitude Europe. Four coherent dry phases are identified in the records at ca 1150–800 BC, 320 BC–AD 150, AD 250–470 and AD 1850–2000. Recent research has shown that peat-derived water table reconstructions reflect summer water deficit and therefore the dry phases are interpreted as periods with a higher frequency and/or greater magnitudes of summer drought. These ‘drought phases’ occur during periods of relatively low 14C production, which may add support to the hypothesis of persistent solar forcing of climate change during the Holocene. Any relationship with the North Atlantic stacked drift ice record is less clear. © 2009 Elsevier Ltd. All rights reserved.

Peat multi-proxy data from Mannikjarve bog as indicators of late Holocene climate changes in Estonia

As part of a wider project on European climate change over the past 4500 years, a 4.5-m peat core was taken from a lawn microform on Mannikjarve bog, Estonia. Several methods were used to yield proxy-climate data: (i) a quadrat and leaf-count method for plant macrofossil data, (ii) testate amoebae analysis, and (iii) colorimetric determination of peat humification. These data are provided with an exceptionally high resolution and precise chronology. Changes in bog surface wetness were inferred using Detrended Correspondence Analysis (DCA) and zonation of macrofossil data, particularly concerning the occurrence of Sphagnum balticum, and a transfer function for water-table depth for testate amoebae data. Based on the results, periods of high bog surface wetness appear to have occurred at c. 3100, 3010-2990, 2300, 1750-1610, 1510, 14 10, 1110, 540 and 3 10 cal. yr BP, during four longer periods between c. 3170 and 2850 cal. yr BP, 2450 and 2000 cal. yr BP, 1770 and 1530 cal. yr BP and in the period from 880 cal. yr BP until the present. In the period between 1770 and 1530 cal. yr BP. the extension or initiation of a hollow microtope occurred, which corresponds with other research results from Mannikjarve bog. This and other changes towards increasing bog surface wetness may be the responses to colder temperatures and the predominance of a more continental climate in the region, which favoured the development of bog microdepressions and a complex bog microtopography. Located in the border zone of oceanic and continental climatic sectors, in an area almost without land uplift, this study site may provide valuable information about changes in palaeohydrological and palaeoclimatological conditions in the northern parts of the eastern Baltic Sea region.

Random walk simulations of fossil proxy data

A wealth of palaeoecological studies (e.g. pollen, diatoms, chironomids and macrofossils from deposits such as lakes or bogs) have revealed major as well as more subtle ecosystem changes over decadal to multimillennial timescales. Such ecosystem changes are usually assumed to have been forced by specific environmental changes. Here, we test if the observed changes in palaeoecological records may be reproduced by random simulations, and we find that simple procedures generate abrupt events, long-term trends, quasi-cyclic behaviour, extinctions and immigrations. Our results highlight the importance of replicated and multiproxy data for reliable reconstructions of past climate and environmental changes.

Globally synchronous climate change 2800 years ago: Proxy data from peat in South America

Initial findings from high-latitude ice-cores implied a relatively unvarying Holocene climate, in contrast to the major climate swings in the preceding late-Pleistocene. However, several climate archives from low latitudes imply a less than equable Holocene climate, as do recent studies on peat bogs in mainland north-west Europe, which indicate an abrupt climate cooling 2800 years ago, with parallels claimed in a range of climate archives elsewhere. A hypothesis that this claimed climate shift was global, and caused by reduced solar activity, has recently been disputed. Until now, no directly comparable data were available from the southern hemisphere to help resolve the dispute. Building on investigations of the vegetation history of an extensive mire in the Valle de Andorra, Tierra del Fuego, we took a further peat core from the bog to generate a high-resolution climate history through the use of determination of peat hurnification and quantitative leaf-count plant macrofossil analysis. Here, we present the new proxy-climate data from the bog in South America. The data are directly comparable with those in Europe, as they were produced using identical laboratory methods. They show that there was a major climate perturbation at the same time as in northwest European bogs. Its timinia, nature and apparent global synchronicity lend support to the notion of solar forcing of past climate change, amplified by oceanic circulation. This finding of a similar response simultaneously in both hemispheres may help validate and improve global climate models. That reduced solar activity might cause a global climatic change suggests that attention be paid also to consideration of any global climate response to increases in solar activity. This has implications for interpreting the relative contribution of climate drivers of recent 'global warming'. (c) 2006 Elsevier B.V. All rights reserved.

Mid- to late-Holocene climate variability and anthropogenic impacts: multi-proxy evidence from Lake Bliden, Denmark

We conducted multi-proxy geochemical analyses (including measurements of organic carbon, nitrogen and sulphur stable isotope composition, and carbonate carbon and oxygen isotope composition) on a 13.5 m sediment core from Lake Bliden, Denmark, which provide a record of shifting hydrological conditions for the past 6,700 years. The early part of the stratigraphic record (6,700-5,740 cal year BP) was wet, based on delta O-18(carb) and lithology, and corresponds to the Holocene Thermal Maximum. Shifts in primarily delta O-18(carb) indicate dry conditions prevailed from 5,740 to 2,800 cal year BP, although this was interrupted by very wet conditions from 5,300 to 5,150, 4,300 to 4,050 and 3,700 to 3,450 cal year BP. The timing of the latter two moist intervals is consistent with other Scandinavian paleoclimatic records. Dry conditions at Lake Bliden between 3,450 and 2,800 cal year BP is consistent with other paleolimnological records from southern Sweden but contrasts with records in central Sweden, possibly suggesting a more northerly trajectory of prevailing westerlies carrying moisture from the North Atlantic at this time. Overall, fluctuating moisture conditions at Lake Bliden appear to be strongly linked to changing sea surface temperatures in the Greenland, Iceland and Norwegian seas. After 2,800 cal year BP, sedimentology, magnetic susceptibility, delta C-13(ORG), delta C-13(carb) and delta O-18(carb) indicate a major reduction on water level, which caused the depositional setting at the coring site to shift from the profundal to littoral zone. The Roman Warm Period (2,200-1,500 cal year BP) appears dry based on enriched delta O-18(carb) values. Possible effects of human disturbance in the watershed after 820 cal year BP complicate attempts to interpret the stratigraphic record although tentative interpretation of the delta O-18(carb), magnetic susceptibility, delta C-13(ORG), delta C-13(carb) and delta O-18(carb) records suggest that the Medieval Warm Period was dry and the Little Ice Age was wet.

Out of tune: the dangers of aligning proxy archives

Tuning is a widespread technique to combine, date and interpret multiple fossil proxy archives through aligning supposedly synchronous events between the archives. The approach will be reviewed by discussing a number of literature examples, ranging from peat and tephra layers to orbital tuning and d¹⁸O series from marine and ice deposits. Potential problems will be highlighted such as the dangers of circular reasoning and unrecognised chronological uncertainties, and some solutions suggested. Fossil proxy research could become enhanced if tuning were approached in a more quantitative, reliable and objective way, and especially if individual proxy archives were non-tuned and kept on independent time-scales.

Pilgrimstad revisited - a multi-proxy reconstruction of Early/Middle Weichselian climate and environment at a key site in central Sweden

The site Pilgrimstad in central Sweden has often been cited as a key locality for discussions of ice-free/ice-covered intervals during the Early and Middle Weichselian. Multi-proxy investigations of a recently excavated section at Pilgrimstad now provide a revised picture of the climatic and environmental development between similar to 80 and 36 ka ago. The combination of sedimentology, geochemistry, OSL and 14C dating, and macrofossil, siliceous microfossil and chironomid analyses shows: (i) a lower succession of glaciofluvial/fluvial, lacustrine and glaciolacustrine sediments; (ii) an upper lacustrine sediment sequence; and (iii) Last Glacial Maximum till cover. Microfossils in the upper lacustrine sediments are initially characteristic for oligo- to mesotrophic lakes, and macrofossils indicate arctic/sub-arctic environments and mean July temperatures > 8 degrees C. These conditions were, however, followed by a return to a low-nutrient lake and a cold and dry climate. The sequence contains several hiatuses, as shown by the often sharp contacts between individual units, which suggests that ice-free intervals alternated with possible ice advances during certain parts of the Early and Middle Weichselian.

Evaluating periocidities in peat-based climate proxy records.

Proxy records derived from ombrotrophic peatlands provide important insights into climate change over decadal to millennial timescales. We present mid- to late- Holocene humification data and testate amoebae-derived water table records from two peatlands in Northern Ireland. We examine the repli- cation of periodicities in these proxy climate records, which have been precisely linked through teph- rochronology. Age-depth models are constructed using a Bayesian piece-wise linear accumulation model and chronological errors are calculated for each profile. A Lomb-Scargle Fourier transform-based spectral analysis is used to test for statistically significant periodicities in the data. Periodicities of c. 130, 180, 260, 540 and 1160 years are present in at least one proxy record at each site. The replication of these peri- odicities provides persuasive evidence that they are a product of allogenic climate controls, rather than internal peatland dynamics. A technique to estimate the possible level of red-noise in the data is applied and demonstrates that the observed periodicities cannot be explained by a first-order autoregressive model. We review the periodicities in the light of those reported previously from other marine and terrestrial climate proxy archives to consider climate forcing parameters. © 2012 Elsevier Ltd. All rights reserved.

Oxygen isotopes from Phorcus (Osilinus) turbinatus shells as a proxy for sea surface temperature in the central Mediterranean: a case study from Malta.

The marine topshell, Phorcus (Osilinus) turbinatus, is a common component of many archaeological sites in the Mediterranean. This species has been successfully used as a palaeoclimate proxy in Italy. To test whether d18O from P. turbinatus shells can serve as a reliable palaeoclimate archive for other regions of the Mediterranean, we collected live P. turbinatus from the northeast coast of Malta each month for a year. The d18OSHELL values of the outermost growth increments of these live-collected shells ranged between-0.4 and+2.4‰. These values correspond to growing temperatures calculated from shell edge d18O of between 15 °C and 27 °C. Calculated shell edge sea surface temperatures are highly correlated with instrumental records of sea surface temperature recorded over the period of collection. The individuals analysed for this study are smaller than P. turbinatus from populations studied elsewhere in the Mediterranean. Nonetheless, d18OSHELL provides a robust record of sea surface temperatures, suggesting that smaller/younger shells in archaeological deposits can still provide reliable palaeothermometry records. This study extends the upper growth limit P. turbinatus by 2 °C compared with the previous studies of P. turbinatus in the Mediterranean and suggests that, contrary to the previous studies, growth shutdown does not occur in all P. turbinatus when sea surface temperatures exceed 25 °C. This may reflect the higher sample resolution that can be obtained from smaller/faster growing shells, or it may reflect actual higher growth tolerances of P. turbinatus populations in Malta. By showing that P. turbinatus precipitate their shells in d18O equilibrium with surrounding sea water, this study reinforces the potential for the stable isotope chemistry of P. turbinatus shells preserved in Mediterranean archaeological sites to provide a window into the climate and seasonality regimes of the past.

Stomatal proxy record of CO2 concentrations from the last termination suggests an important role for CO2 at climate change transitions

A new stomatal proxy-based record of CO₂ concentrations ([CO₂]), based on Betula nana (dwarf birch) leaves from the Hässeldala Port sedimentary sequence in south-eastern Sweden, is presented. The record is of high chronological resolution and spans most of Greenland Interstadial 1 (GI-1a to 1c, Allerød pollen zone), Greenland Stadial 1 (GS-1, Younger Dryas pollen zone) and the very beginning of the Holocene (Preboreal pollen zone). The record clearly demonstrates that i) [CO₂] were significantly higher than usually reported for the Last Termination and ii) the overall pattern of CO₂ evolution through the studied time period is fairly dynamic, with significant abrupt fluctuations in [CO₂] when the climate moved from interstadial to stadial state and vice versa. A new loss-on-ignition chemical record (used here as a proxy for temperature) lends independent support to the Hässeldala Port [CO₂] record. The large-amplitude fluctuations around the climate change transitions may indicate unstable climates and that " tipping-point" situations were involved in Last Termination climate evolution. The scenario presented here is in contrast to [CO₂] records reconstructed from air bubbles trapped in ice, which indicate lower concentrations and a gradual, linear increase of [CO₂] through time. The prevalent explanation for the main climate forcer during the Last Termination being ocean circulation patterns needs to re-examined, and a larger role for atmospheric [CO₂] considered.