Papers by Dr Jens Holtvoeth
Climate of The Past, Jan 11, 2019
Our study aims to reconstruct climate changes that occurred at Lake Ohrid (south-western Balkan P... more Our study aims to reconstruct climate changes that occurred at Lake Ohrid (south-western Balkan Peninsula), the oldest extant lake in Europe, between 160 and 70 ka (covering part of marine isotope stage 6, MIS 6; all of MIS 5; and the beginning of MIS 4). A multi-method approach, including the "Modern Analog Technique" and the "Weighted Averaging Partial Least-Squares Regression", is applied to the high-resolution pollen sequence of the DEEP site, collected from the central part of Lake Ohrid, to provide quantitative estimates of climate and bioclimate parameters. This allows us to document climatic change during the key periods of MIS 6 and MIS 5 in southern Europe, a region where accurate climate reconstructions are still lacking for this time interval. Our results for the penultimate glacial show cold and dry conditions, while the onset of the "last interglacial" is characterized by wet and warm conditions, with temperatures higher than today (by ca. 2 • C). The Eemian also shows the well-known climatic tri-partition in the Balkans, with an initial pre-temperate phase of abrupt warming (128-121 ka), a central temperate phase with decreasing temperatures associated with wet conditions (121-118 ka), followed by a posttemperate phase of progressive change towards cold and dry conditions (118-112 ka). After the Eemian, an alternation of four warm/wet periods with cold/dry ones, likely related to the succession of Greenland stadials and cold events known from the North Atlantic, occurred. The observed pattern is also consistent with hydrological and isotopic data from the central Mediterranean. The Lake Ohrid climate reconstruction shows greater similarity with climate patterns inferred from northern European pollen records than with southern European ones, which is probably due to its intermediate position and the mountainous setting. However, this hypothesis needs further testing as very few climate reconstructions are available for southern Europe for this key time period.
We present elemental, lipid biomarker and compound-specific isotope (δ 13 C, δ 2 H) data for soil... more We present elemental, lipid biomarker and compound-specific isotope (δ 13 C, δ 2 H) data for soils and leaf litter collected in the catchment of Lake Ohrid (Albania, Macedonia), as well as macrophytes, particulate organic matter and sediments from the lake itself. Lake Ohrid provides an outstanding archive of continental environmental change of at least 1.2 M years and the purpose of our study is to ground truth organic geochemical proxies that we developed in order to study past changes in the terrestrial biome. We show that soils dominate the lipid signal of the lake sediments rather than the vegetation or aquatic biomass, while compound-specific isotopes (δ 13 C, δ 2 H) determined for n-alkanoic acids confirm a dominant terrestrial source of organic matter to the lake. There is a strong imprint of suberin monomers on the composition of total lipid extracts and chain-length distributions of n-alkanoic acids, n-alcohols, ω-hydroxy acids and α,ω-dicarboxylic acids. Our end-member survey identifies that ratios of mid-chain length suberin-derived to long-chain length cuticular-derived alkyl compounds as well as their average chain length distributions can be used as new molecular proxies of organic matter sources to the lake. We tested these for the 8.2 ka event, a pronounced and widespread Holocene climate fluctuation. In SE Europe climate became drier and cooler in response to the event, as is clearly recognizable in the carbonate and organic carbon records of Lake Ohrid sediments. Our new proxies indicate biome modification in response to hydrological changes, identifying two phases of increased soil OM supply, first from topsoils and then from mineral soils. Our study demonstrates that geochemical fingerprinting of terrestrial OM should focus on the main lipid sources, rather than the living biomass. Both can exhibit climate-controlled variability, but are generally not identical.
Sustainability, Jul 11, 2023
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Total lipid analysis concentration in percentages and Principal Component Analysis Figure.
Palaeogeography, Palaeoclimatology, Palaeoecology, Dec 1, 2019
Evolution of ecosystems in the northeastern Mexico since the Last Glacial Maximum (LGM) and throu... more Evolution of ecosystems in the northeastern Mexico since the Last Glacial Maximum (LGM) and through the Holocene are yet to be fully characterised, creating a gap in our understanding of the ecological response to climate change in this water scarce region. Here we explore the response of lacustrine and surrounding terrestrial habitats of this region to hydrological changes of the late Pleistocene and especially the Holocene. Biomarker-based proxy data from the El Potosi Basin indicates dynamic and variable input of organic matter (OM) into the basin, with sources being the surrounding vegetation, bacterial biomass and aquatic microfauna. Changes in these inputs reveal distinct stages of ecosystem development over the last 20,000 years. Overall low lipid abundances (as a proportion of TOC) from 20-19 cal kyr BP, mainly from aquatic/in-situ microbial biomass and degraded terrestrial OM, are attributed to relatively low runoff. Increasing lipid proportions during the deglaciation, from 19 to 15 cal kyr BP, were mostly derived from terrestrial sources like woodland vegetation, soil and wetland vegetation, and we attribute them to more rainfall and runoff. Subsequently, the wetland biomarkers disappeared, and woodland input began to dominate the OM assemblage from 15 to 11.7 cal kyr BP. During the early-and mid-Holocene, after about 11.7 cal kyr BP, putative woodland and grass inputs decreased and the dominant vegetation appeared to shift to subtropical desert shrub, which could have been due to increasing regional aridity. The onset of the dry late Holocene was characterized by gradual environmental transition and ecosystem adaption, especially from 4.2 to 2.8 cal kyr BP. The terrestrial vegetation comprised increasing proportions of C4 grasses, documented by changes in leaf wax carbon isotopic compositions, and potentially more open-vegetation, while the in-lake bacterial production increased. With increasing desertification from 2.8 cal kyr BP, the terrestrial productivity decreased substantially, the lake became shallower/ephemeral, and the surrounding soils became more alkaline. Changes of the limnic habitat from algal towards microbial communities occurred ~300 years after the onset of terrestrial habitat changes. During the last millennium, the C3 components of the vegetation again dominated. This implies an enhanced moisture supply, possibly from agricultural activities. Overall, this work reveals the marked sensitivity of northeastern Mexico ecosystems to the climatic shifts that occurred since the LGM, and this perhaps indicates their vulnerability to future global warming.
Quaternary Science Reviews, Jul 1, 2018
Hydroclimate variation of the northwest Mexico during the late Pleistocene and Holocene is an act... more Hydroclimate variation of the northwest Mexico during the late Pleistocene and Holocene is an active area of debate, with uncertainty in the nature and sources of precipitation. Previous research has inferred the influences of winter storms, summer monsoonal rain and autumn tropical cyclones. The impacts on regional and local ecosystems, however, are not well constrained. Here, we investigate the response of lacustrine and terrestrial habitats of the Santiaguillo Basin in the Chihuahua Desert (Mexico) to hydrological changes occurring since the late last glacial. Biomarkers from the sediments reflect variable input of organic matter (OM) from algal and bacterial biomass, aquatic microfauna and surrounding vegetation, revealing distinct stages of ecosystem adaption over the last 27 cal ka. Based on previously published and new data, we show that a perennial productive lake was present during the late glacial and it persisted until 17.5 cal ka BP. Coinciding with Heinrich event 1, OM supply from deteriorating wetland soils may have been caused by early dry conditions. Further phases of increasing aridity and a shrinking water body drove changing OM quality and biomarker composition during the early and mid-Holocene. A pronounced shift in biomarker distributions at 4 cal ka BP suggests that the supply of plant litter from resinous trees and grasses increased, likely reflecting the establishment of modern vegetation. Our results illustrate the potential of biomarker applications in the area, adding to the evidence of hydroclimate variability and enabling reconstructions of local ecosystem dynamics.
Earth-Science Reviews, Aug 1, 2020
Understanding and quantifying the processes and geochemical cycles associated with catchment eros... more Understanding and quantifying the processes and geochemical cycles associated with catchment erosion, the development of soils and weathering horizons, and terrestrial habitat change beyond the scales of modern observations remain challenging. Such research, however, has become increasingly important to help predict future landscape change in light of increasing land use and rapid global warming. We herein review organic and inorganic geochemical tools applied to depositional archives to better understand various aspects of landscape evolution on geological time scales. We highlight the potentials and limitations of inorganic geochemical analytical methods, such as major element geochemistry, metal and radiogenic isotopes, and in-situ cosmogenic nuclides, as qualitative, semi-quantitative, and quantitative proxies for the transformation of bedrock material via regolith and soils to sediments. We also show how stable isotope geochemistry applied to lacustrine endogenic carbonates can be used to infer rock-water interactions, vegetation change, and soil development in limestonerich catchments. Proxies focusing on the silicilastic element of sediment formation, transport and deposition are also ideally combined with organic geochemical proxies for vegetation change and soil organic matter evolution in a catchment to gain a comprehensive picture of the Critical Zone's evolution over time. Multi-proxy and multidisciplinary research combining organic and inorganic geochemical techniques from several sedimentary archives in the same catchment have high potential to provide comprehensive information on Quaternary landscape evolution and thus improve the robustness of associated forecasting models.
Highlights: Soil lipids encompass substances of mainly plant or microbial origin, which encompass... more Highlights: Soil lipids encompass substances of mainly plant or microbial origin, which encompasses biomarkers associated to soil microbial communities and soil organic matter (SOM) dynamics. According to their structure, biomarkers from total lipid extracts (TLE) would exhibit different degrees of susceptibility to degradation, affecting thus their preservation in soils. In this study, we assessed SOC contributions from aboveground and developed a wider approach based on the allocation of C to quantitatively assess the sources of organic matter in low SOM content, highly weathered Mediterranean soils.
AGUFM, Dec 1, 2005
The North Atlantic plays an important role as the source region for northern component waters of ... more The North Atlantic plays an important role as the source region for northern component waters of thermohaline circulation. The hydrological system is highly sensitive to climatic changes. Underlying drift sediments record both changes in the hydrological system (lateral advection) and in `direct' material input from surface waters (primary production and eolian supply), and therefore represent excellent archives for past ocean
Springer eBooks, 2003
The established view of a marine-dominated organic signature of modern and late Quarternay deep o... more The established view of a marine-dominated organic signature of modern and late Quarternay deep ocean sediments is challenged by recently performed organic geochemical, petrolocical, and palynological investigations. This study reviews multidisciplinary concepts that were developed over the last decade in Bremen and have been successfully applied to modern and late Quarternary sediments from the low latitude Atlantic. Relative proportions and compositional variations of terrigenous OM are deduced from macerals (organic particles), freshwater diatoms, phytoliths, pollen grains, lignin signatures, and carbon isotopic compositions of bulk organic matter as well as from higher plant-derived long-chain n-alkanes. For their variety of depositional settings and their close location next to each other the dust-influenced central Equatorial Atlantic and the West-African continental margin are examined. To assess environmental variations during the late Quarternary, terrigenous organic records from the central Atlantic to the low latitude West-African continental margin and the Congo deep-sea fan are discussed with regard to the paleoclimatic evolution of central African dust source areas, continental run off and vegetational changes in the Congo catchment area. Additionally, the influence of degradation processes and/or selective preservation, both on short and long time scales, of non-reactive (mostly terrigenous) organic matter is investigated.
Scientific Reports, Aug 14, 2017
Geochemistry Geophysics Geosystems, Dec 1, 2003
Late Quaternary sections (1.2 Ma) of ODP-Site 1075 from the Congo deep-sea fan are investigated t... more Late Quaternary sections (1.2 Ma) of ODP-Site 1075 from the Congo deep-sea fan are investigated to reconstruct variations of terrigenous organic matter supply to the eastern equatorial Atlantic. To characterize the organic matter (OM) with regard to marine and terrigenous amounts we used elemental analysis (C, N, S), stable carbon isotopes (bulk d 13 C org), Rock-Eval pyrolysis, and terrigenous biomarkers (lignin phenols from CuO oxidation). The records of total organic carbon (TOC) contents, C org /N tot ratios, bulk OM degradation rates (C org /C org *), and the ratios of hydrocarbons (HC) from low-mature versus HC from high-mature OM (lm/hm) reveal pronounced cyclic changes in OM abundance, preservation, and reactivity that are closely related to the precessional controlled record of insolation, and thus, to variations in upwelling intensity and fluvial runoff. Primary productivity off the Congo is stimulated by both, enhanced nutrient supply in response to trade-induced upwelling during arid African climates (insolation minima) and fluvial nutrient delivery during humid stages (following insolation maxima), especially due to the contribution of dissolved silica that is taken up preferably by diatoms. However, results stemming from a multiparameter approach reveal that the fluvial supply of degraded OM and black carbon (BC) associated with fine-grained sediments from soil erosion is a decisive factor for the preservation of marine OM and, in addition, significantly influences the geochemical signature of bulk and terrigenous OM. Riverine and eolian supply of C 4 plant matter, as well as enhanced concentrations of BC, during arid and arid-to-humid transitional climate stages, may lead to a severe underestimation of terrigenous organic carbon, if its amount is calculated from bulk isotopic ratios using binary end-member models. During the humid stages, it is the massive supply of 13 C-enriched soil OM with low C org /N tot ratios that may suggest a mainly marine composition of bulk OM. In fact, terrigenous OM governs bulk OM geochemical signatures in the sediments of the Congo deep-sea fan, a result that is contradictory to earlier studies, especially to the conventional interpretation of the bulk d 13 C org signal.
Biogeosciences, Nov 8, 2010
Organic matter preserved in Lake Ohrid sediments originates from aquatic and terrestrial sources.... more Organic matter preserved in Lake Ohrid sediments originates from aquatic and terrestrial sources. Its variable composition reflects climate-controlled changes in the lake basin's hydrology and related organic matter export, i.e. changes in primary productivity, terrestrial plant matter input and soil erosion. Here, we present first results from lipid biomarker investigations of Lake Ohrid sediments from two near-shore settings: site Lz1120 near the southern shore, with low-lying lands nearby and probably influenced by river discharge, and site Co1202 which is close to the steep eastern slopes. Variable proportions of terrestrial n-alkanoic acids and n-alkanols as well as compositional changes of ωhydroxy acids document differences in soil organic matter supply between the sites and during different climate stages (glacial, Holocene, 8.2 ka cooling event). Changes in the vegetation cover are suggested by changes in the dominant chain length of terrestrial n-alkanols. Effective microbial degradation of labile organic matter and in situ contribution of organic matter derived from the microbes themselves are both evident in the sediments. We found evidence for anoxic conditions within the photic zone by detecting epicholestanol and tetrahymanol from sulphur-oxidising phototrophic bacteria and bacterivorous ciliates and for the influence of a settled human community from the occurrence of coprostanol, a biomarker for human and animal faeces (pigs, sheep, goats), in an early Holocene sample. This study illustrates the potential of lipid biomarkers for future environmental reconstructions using one of Europe's oldest continental climate archives, Lake Ohrid.
International Journal of Sustainable Development and World Ecology, Jul 14, 2019
Measuring sustainability is an integral part of decision-making processes in order to promote sus... more Measuring sustainability is an integral part of decision-making processes in order to promote sustainable development. The present paper focuses on sustainability indicators as these are measured on local level and explores two main issues: firstly, the subjective measurement of indicators focusing especially on social dimensions of sustainability, secondly, the incorporation of local perceptions in sustainability assessments. These two issues are explored in the Asopos River basin in Greece, an area where significant environmental degradation has been observed in the past decades and is also under financial pressure due to the ongoing national recession. A large-scale research study was conducted measuring environmental, economic and social indicators while, at a second stage, a model was developed, estimating new indicators that incorporate local communities' perceptions on what they considered as important for their area. The results of the study reveal that the most important indicators for the sustainable development of the area, according to locals' perceptions, are environmental quality as well as quality of life. By contrast, trust in local and central institutions and also local enterprises were not considered as important by locals. These results illustrate the importance of combining global and national scale assessment with locally focused social measurements of sustainability in order to better understand what is important for local communities prior to embarking on public policy planning.
Geochimica et Cosmochimica Acta, Aug 1, 2006
Biogeosciences, Apr 20, 2017
This study reviews and synthesises existing information generated within the SCOPSCO (Scientific ... more This study reviews and synthesises existing information generated within the SCOPSCO (Scientific Collaboration on Past Speciation Conditions in Lake Ohrid) deep drilling project. The four main aims of the project are to infer (i) the age and origin of Lake Ohrid (Former Yugoslav Republic of Macedonia/Republic of Albania), (ii) its regional seismotectonic history, (iii) volcanic activity and climate change in the central northern Mediterranean region, and (iv) the influence of major geological events on the evolution of its endemic species. The Ohrid basin formed by transtension during the Miocene, opened during the Pliocene and Pleistocene, and the lake established de novo in the still relatively narrow valley between 1.9 and 1.3 Ma. The lake history is recorded in a 584 m long sediment sequence, which was recovered within the framework of the International Continental Scientific Drilling Program (ICDP) from the central part (DEEP site) of the lake in spring 2013. To date, 54 tephra and cryptotephra horizons have been found in the upper 460 m of this sequence. Tephrochronology and tuning biogeochemical proxy data to orbital parameters revealed that the upper 247.8 m represent the last 637 kyr. The multi-proxy data set covering these 637 kyr indicates longterm variability. Some proxies show a change from generally cooler and wetter to drier and warmer glacial and interglacial periods around 300 ka. Short-term environmental change caused, for example, by tephra deposition or the climatic impact of millennial-scale Dansgaard-Oeschger and Heinrich events are superimposed on the long-term trends. Evolutionary studies on the extant fauna indicate that Lake Ohrid was not a refugial area for regional freshwater animals. This differs from the surrounding catchment, where the mountainous setting with relatively high water availability provided a refuge for temperate and montane trees during the relatively cold and dry glacial periods. Although Lake Ohrid experienced significant environmental change over the last 637 kyr, preliminary molecular data from extant microgastropod species do not indicate significant changes in diversification rate during this period. The reasons for this constant rate remain largely unknown, but a possible lack of environmentally induced extinction events in Lake Ohrid and/or the high resilience of the ecosystems may have played a role.
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Papers by Dr Jens Holtvoeth