The Carpathian-Balkans during the Holocene: reconstructing human influences and climatic changes

The Carpathian-Balkan region in south-eastern Europe is one of the longest inhabited regions in Europe, with evidence of some of the earliest examples of European agriculture, farming and metallurgy. Despite its importance for understanding past human activity and climate change, high-resolution reconstructions of Holocene hydroclimate variability and human impact are rare. This thesis provides a series of new high-resolution Holocene (the past 11,700 years) palaeoenvironmental records derived from peat bogs in the Carpathian Mountains of Romania, and the Dinaric Alps of Serbia, to investigate climate variation and human impact. Two peat-derived archives of environmental change in Romania are presented. First, a 7500-year record of minerogenic deposition from the Southern Carpathians linked to heavy rainfall events provides the first record of extreme precipitation for the Carpathians. Such minerogenic depositional events began 4000 calibrated years before present (yr BP, where present is 1950 CE), with increased depositional rates during the Medieval Warm Period (1150 – 850yr BP), the Little Ice Age (350 – 100 yr BP) and during periods of societal upheaval (e.g. the Roman conquest of Dacia). The timing of minerogenic events appears to indicate a teleconnection between the North Atlantic Oscillation (NAO) and hydroclimate variability in south-eastern Europe, which persists throughout the mid-to-late Holocene. Secondly, a 10,800-year record of geochemically-derived dust deposition and testate amoeba-derived local wetness from the Eastern Romanian Carpathians highlights several discrepancies between eastern and western European dust depositional records and the impact of highly complex hydrological regimes in the Carpathian region. Specifically, the record outlines the increased impact of Saharan dust after 6100 yr BP which is associated with the end of the African Humid Period. A lead (Pb) record from a peat bog in Western Serbia provides an unprecedented view on past pollution related to metal exploitation in the Balkans. Environmental Pb pollution is first observed in the very earliest Bronze Age, the oldest environmental Pb pollution in Europe. After 600 CE an almost linearly increasing Pb trend until the Medieval period is observed. Comparison with western European records suggests an alternative history of European metallurgy, one in which metal-related pollution does not cease with the fall of the Roman Empire, and which displays major Medieval pollution. Pb isotopes provide a valuable insight into the sources of Pb observed within a sample, allowing for the fingerprinting of their metal’s geological source, or production site. Presented here is the application of a state of the art Bayesian mixing model to such a purpose, outlining a ‘best practice’ and testing of the approach via a number of real-world examples

Exceptionally high levels of lead pollution in the Balkans from the Early Bronze Age to the Industrial Revolution

The Balkans are considered the birthplace of mineral resource exploitation and metalworking in Europe. However, since knowledge of the timing and extent of metallurgy in southeastern Europe is largely constrained by discontinuous archaeological findings, the long-term environmental impact of past mineral resource exploitation is not fully understood. Here we present a high resolution and continuous geochemical record from a peat bog in western Serbia, providing for the first time a clear indication of extent and magnitude of environmental pollution in this region, and a context in which to place archaeological findings. We observe initial evidence of anthropogenic lead (Pb) pollution during the earliest part of the Bronze Age (c.3600 yr before Common Era (BCE)), the earliest such evidence documented in European environmental records. A steady, almost linear increase in Pb concentration after 600 BCE, until circa 1600 CE is observed, documenting the development in both sophistication and extent of southeastern European metallurgical activity throughout Antiquity and the Medieval Period. This provides a new view on the history of mineral exploitation in Europe, with metal-related pollution not ceasing at the fall of the western Roman Empire, as was the case in western Europe. Further comparison with other Pb pollution records indicates the the amount of Pb deposited in the Balkans during the Medieval Period was if not greater, at least similar to records located close to western European mining regions, suggestive of the key role the Balkans have played in mineral resource exploitation in Europe over the last 5600 years

Detrital events and hydroclimate variability in the Romanian Carpathians during the Mid-to-Late Holocene

The Romanian Carpathians are located at the confluence of three major atmospheric pressure fields: the North Atlantic, the Mediterranean and the Siberian. Despite its importance for understanding past human impact and climate change, high-resolution palaeoenvironmental reconstructions of Holocene hydroclimate variability, and in particular records of extreme precipitation events in the area, are rare. Here we present a 7500-year-long high-resolution record of past climatic change and human impact recorded in a peatbog from the Southern Carpathians, integrating palynological, geochemical and sedimentological proxies. Natural climate fluctuations appear to be dominant until 4500 years before present (yr BP), followed by increasing importance of human impact. Sedimentological and geochemical analyses document regular minerogenic deposition within the bog, linked to periods of high precipitation. Such minerogenic depositional events began 4000 yr BP, with increased depositional rates during the Medieval Warm Period (MWP), the Little Ice Age (LIA) and during periods of societal upheaval (e.g. the Roman conquest of Dacia). The timing of minerogenic events appears to indicate a teleconnection between major shifts in North Atlantic Oscillation (NAO) and hydroclimate variability in southeastern Europe, with increased minerogenic deposition correlating to low NAO index values. By linking the minerogenic deposition to precipitation variability, we state that this link persists throughout the mid-to-late Holocene

Differential response of chlorophyll-a concentrations to explosive volcanism in the western South Pacific

When it is deposited in the ocean, volcanic ash has the potential to release iron and other nutrients into surface water to stimulate ocean productivity. In the western South Pacific Ocean (SPO), one of the most important volcanic ash deposition regions, occasional widespread transport of volcanic ash may supply the nutrients not only locally around source islands but also within the wider the western SPO, accompanied by phytoplankton response. Through a comparative analysis of satellite and reanalysis data for the past 19 years (2004–2022), this study reveals that four explosive volcanic eruptions, Rabaul volcano, Papua New Guinea (October, 2006), Ambae volcano, Vanuatu (July, 2018), Ulawun volcano, Papua New Guinea (June, 2019), and Hunga volcano, Tonga (January, 2022), had the most strong stratospheric injection (>15 km) and mass loading of volcanic materials over the wider the western SPO (covering an area of >765,000 km2). The transport of 2006, 2018, 2019 volcanic emissions, was not likely associated with significant ash deposition over the western SPO. However, the Hunga eruption led to the deposition of ash-laden volcanic plumes over a wide area (~2,000 km from source), and was followed by the increase in chlorophyll-a concentrations (Chl-a) in the region (~70% increase). Minor changes related to other nutrient sources (e.g., hydrothermal input) suggest a link between the increase in Chl-a and 2022 Hunga ash falls over the western SPO. Our results indicate that volcanic ash deposition has implications for phytoplankton productivity in the western SPO, and highlights the need for further research into understanding how nutrient supply alleviated limitations of phytoplankton at the community level

Spatial and Temporal Trends in Mineral Dust Provenance in the South Pacific—Evidence From Mixing Models

Mineral dust is an important component of the Earth system due to its role in oceanic nutrient supply, cloud formation and its radiative properties. Changes in transport pathways and fluxes of mineral dust have attracted increased attention using radiogenic isotope analysis for detailed investigation of changing dust sources through time. However, multi-isotope studies provide complex datasets of dust provenance, often without exact quantification of source contributions. Here we use Bayesian mixing models and existing radiogenic isotope data to quantify changes in South Pacific dust provenance for the Holocene and the Last Glacial Maximum (LGM; ∼18–24 ka BP). Testing different model configurations showed grouping small source regions to single continental scale end members prior to modeling can lead to biased results, and so we group model outputs post-modeling. During the LGM, a higher proportion (mean 53%) of dust entering the South Pacific was South American in origin, compared to a Holocene mean of 31%. In contrast, Australian dust contributions were lower during the LGM (mean 38%) than Holocene (mean 55%), with significant spatial gradients for both time slices. In the subpolar South Pacific, the high representation of South American dust during the LGM (up to ∼75%) coincides with larger dust particles; together indicating that far-traveled dust transport was facilitated by long atmospheric residence times and an accelerated westerly wind circulation during this time. Our study shows how Bayesian mixing models provide valuable constraints for dust source contributions, an approach which may help in the calibration of atmospheric models, using complex isotopic datasets

High variability between regional histories of long-term atmospheric Pb pollution

The advent of metal processing was one of the key technological evolutions presaging the development of modern society. However, the interplay between metal use and the long-term changes it induced in the development and functioning of past societies remains unclear. We present a compilation of global records of anthropogenic atmospheric lead (Pb) spanning the last 4000 years, an effective indirect proxy for reliably assessing Pb emissions directly linked to human activities. Separating this global Pb pollution signal into regionally representative clusters allows identification of regional differences in pollution output that reflect technological innovations, market demands, or demise of various human cultures for last 4000 years. Our European reconstruction traces well periods of intensive metal production such as the Roman and Medieval periods, in contrast to clusters from the Americas, which show low levels of atmospheric Pb until the Industrial Revolution. Further investigation of the European synthesis results displays clear regional variation in the timing and extent of past development of polluting activities. This indicates the challenges of using individual reconstructions to infer regional or global development in Pb output and related pollution

Base metal pollution as a result of historical ore smelting in the Romanian Carpathians throughout the Holocene

In Europe the characteristics, distribution and effects of recent pollution are well known, with monitoring observations existing at a continental scale. However, estimates of long-term pollution are restricted to central-western Europe, the British Isles and Scandinavia. In Eastern Europe in particular, the lack of such estimates has led to incomplete understanding of regional differences. When coupled to the insufficient knowledge of past emission sources and isotopic signatures of various ores, it is clear there are gaps in our knowledge of the history of pollution in this area. As a result, the causal relationships between humans and the environment are insufficiently explored, particularly within the Carpathian region - one with significant mineral wealth and a long history of human presenc

Mid-Norwegian Margin Magmatism and Paleoclimate Implications: Expedition 396 Preliminary Report

The opening of the North Atlantic about 56 My ago was associated with the emplacement of the North Atlantic Igneous Province, including the deposition of voluminous extrusive basaltic successions and intrusion of magma into the surrounding sedimentary basins. The mid-Norwegian Margin is a global type example of such volcanic rifted margins and is well suited for scientific drilling with its thin sediment cover and good data coverage. During International Ocean Discovery Program Expedition 396, 21 boreholes were drilled at 10 sites in five different geological settings on this volcanic margin. The boreholes sampled a multitude of igneous and sedimentary settings ranging from lava flow fields to hydrothermal vent complexes, along with thick successions of upper Paleocene and lower Eocene strata. A comprehensive suite of wireline logs was collected in eight boreholes. The main goals of the expedition were to provide constraints for geodynamic models to test different hypotheses that can explain the rapid emplacement of large igneous provinces and the hypothesis that the associated Paleocene/Eocene Thermal Maximum was caused by hydrothermal release of carbon in response to magmatic intrusions. Successful drilling, combined with high core recovery of target intervals of all nine primary sites and one additional alternate site, should allow us to achieve these goals during postcruise work

Periodic input of dust over the Eastern Carpathians during the Holocene linked with Saharan desertification and human impact

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Stone-built heritage as a proxy archive for long-term historical air quality: A study of weathering crusts on three generations of stone sculptures on Broad Street, Oxford

Black crusts on historic buildings are mainly known for their aesthetic and deteriorative impacts, yet they also can advance air pollution research. Past air pollutants accumulate in distinct layers of weathering crusts. Recent studies have used these crusts to reconstruct pollution to improve our understanding of its effects on stone-built heritage. However, the majority of the studies provide only coarse resolution reconstruction of pollution, able to distinguish between ‘inner = old’ and ‘outer = modern’ crust layers. In contrast, very few studies have linked distinct periods of exposure to pollution variations in the composition of these crusts. Here we address this research gap by developing a finer-scale resolution pollution record. Our study explored the unique configuration of limestone sculptures in central Oxford, which have been exposed over the last 350 years to three different periods of atmospheric pollution; the early Industrial Revolution, the Victorian period and the 20th century. When the first two generations of sculptures were moved to less polluted areas, their ‘pollution clocks’ were stopped. Here we discuss the potential of investigating the ‘pollution clock’ recorded in the geochemical makeup of each sculpture generation's weathering crust layers. We found the analysed crusts record clear changes related to the evolution of modes of transport and industrial and technological development in Oxford. Higher levels of Arsenic (As), Selenium (Se) are linked to pollution from coal burning during Victorian times and Lead (Pb) indicated leaded petrol use in modern times. Our work shows that stone-built heritage with a known history of air pollution exposure allows improving the pollution reconstruction resolution of these weathering crusts. The results provide the basis for calibrating long-term geochemical archives. This approach may be used to reconstruct past air quality and has the potential to inform stone weathering research and conservation, in addition to improving the reconstruction of historical pollution