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  • 1.
    Boyd, Meighan
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Hoffmann, Dirk
    Max Planck Institute for Evolutionary Anthropology, Germany.
    Jochum, Klaus Peter
    Max Planck Institute for Chemistry, Germany.
    Karkanas, Panagiotis
    American School of Classical Studies at Athens, Greece.
    Krusic, Paul J.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Papathanasiou, Anastasia
    Greek Ministry of Culture, Greece.
    Scholz, Denis
    Johannes Gutenberg-University Mainz, Germany.
    Stoll, Brigitte
    Max Planck Institute for Chemistry, Germany.
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Trace elements as recorders of human activity and environmental indicators at Alepotrypa Cave, GreeceManuscript (preprint) (Other academic)
  • 2.
    Boyd, Meighan
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Speleothems from Alepotrypa Cave: Towards climate reconstruction2015In: Alepotrypa Cave in the Mani, Greece: A festschrift to honor Dr. G. Papathanasopoulos on the occasion of his 90th birthday / [ed] Α. Papathanasiou, M. Galaty, P. Karkanas, W. Parkinson, D. Pullen, Oxford: Oxbow Books, 2015Chapter in book (Other academic)
  • 3.
    Boyd, Meighan
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Finné, Martin
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Hoffmann, Dirk
    Max Planck Institute for Evolutionary Anthropology, Germany.
    Jochum, Klaus Peter
    Max Planck Institute for Chemistry, Germany.
    Karkanas, Panagiotis
    American School of Classical Studies at Athens, Greece.
    Papathanasiou, Anastasia
    Greek Ministry of Culture, Greece.
    Stoll, Brigitte
    Max Planck Institute for Chemistry, Germany.
    Scholz, Denis
    Johannes Gutenberg-Universität Mainz, Germany.
    Spötl, Christoph
    University of Innsbruck, Austria.
    Stable isotopes and phosphorus patterns in calcite stalagmites from Alepotrypa Cave, Peloponnese, Greece as indicators of Holocene changes in rainfall and vegetationManuscript (preprint) (Other academic)
  • 4.
    Boyd, Meighan
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Shaw, Paul
    University of the West Indies, Jamaica.
    Hoffmann, Dirk
    Max Planck Institute for Evolutionary Anthropology, Germany.
    Mangini, Augusto
    University of Heidelberg, Germany.
    Mudelsee, Manfred
    Alfred Wegener Institute for Polar and Marine Research, Germany.
    Spötl, Christoph
    University of Innsbruck, Austria.
    Early Holocene patterns of rainfall, vegetation and soil conditions, inferred from a southern Caribbean stalagmiteManuscript (preprint) (Other academic)
  • 5.
    Boyd, Meighan
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Karkanas, Panagiotis
    American School of Classical Studies at Athens, Greece.
    Papathanasiou, Anastasia
    Greek Ministry of Culture, Greece.
    Hoffmann, Dirk
    Max Planck Institute for Evolutionary Anthropology, Germany.
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography.
    U-Th dating of calcite on human bones from Alepotrypa Cave, GreeceManuscript (preprint) (Other academic)
  • 6. Ekblom, Anneli
    et al.
    Gillson, Lindsey
    Risberg, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Chidoub, Zara
    Rainfall variability and vegetation dynamics of the lower Limpopo Valley, Southern Africa, 500 AD to present2012In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 363, p. 69-78Article in journal (Refereed)
    Abstract [en]

    The long-term responses of vegetation to climate variability are of relevance for predicting present and future vegetation change, and have implications for the management of savanna and riparian ecosystems. This paper explores the links between regional rainfall, hydrology and vegetation dynamics in the savannas and riverine forests of the lower Limpopo Valley, southern Africa, from 800 AD to the present, reviewing palaeoecological data (fossil pollen, spores, diatoms and lithology) from several hydrological systems in Kruger National Park (KNP), South Africa and Limpopo National Park (PNL), Mozambique. The PNL-KNP records show that riverine arboreal taxa expanded during wetter periods, including 800-1400 AD and after 1800 AD. Between 1400 and 1800 AD, grasses, savanna taxa and generalist taxa were favored over riparian taxa, a change that is linked with the onset of dry spells in the region (corresponding to the so-called Little Ice Age). The most extreme drought events around 1700 AD resulted in a marked decline of riparian forest taxa near Lake Mapimbi, KNP. In contrast, many water-scarce sequences away from the riverine environment, such as Radio Pan, Mafayeni Pan, Malahlapanga Pan and Lake Makwadzi show stable grassland vegetation throughout the last 1200 years. The results demonstrate the resilience of the grassland-savanna ecosystems to projected climate change with warmer and overall drier climate. The riverine forests are predicted to be more vulnerable especially as more extreme weather events are projected.

  • 7. Ekblom, Anneli
    et al.
    Risberg, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Coastal forest and Miombo woodland history of the Vilankulo region, Mozambique2014In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 24, no 3, p. 284-294Article in journal (Refereed)
    Abstract [en]

    The present day distribution of Miombo savanna-woodland in Mozambique has been attributed to an expansion due to the clearing of original coastal forests through agriculture and use of fire. Here, we test this hypothesis using palaeoecological data from Lake Nhauhache, situated in the Vilankulo region. Our analysis shows that Brachystegia, one of the main constituents of the Miombo, has varied over time, and its variability seems to be driven by hydrological changes related to climatic variability rather than by land-use changes. The analyses show that Brachystegia was most common during ad 200-700 when a marshy forest/shrub community was dominant. After ad 700, this community changes to a dominance of Syzygium and Fagara linked to gradually rising water levels. Brachystegia remains in low abundance and fluctuating over time. From ad 1000, a general decline in trees/shrubs in favour of grasses concurs with an increase in grass pollen (possibly cereal) and charcoal, most probably as a result of farming activities. The decline in tree taxa was probably exacerbated by periodic droughts after c. ad 1200 as indicated by the diatom assemblage. In the period ad 1700 to late 1800, arboreal pollen is well represented, and this is concurrent with the diatom record suggesting high lake levels.

  • 8.
    Finné, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Bar-Matthews, Miryam
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Sundqvist, Hanna S.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Liakopoulos, Ilias
    Zhang, Qiong
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Speleothem evidence for late Holocene climate variability and floods in Southern Greece2014In: Quaternary Research, ISSN 0033-5894, E-ISSN 1096-0287, Vol. 81, no 2, p. 213-227Article in journal (Refereed)
    Abstract [en]

    We present stable isotope data (delta O-18, delta C-13) from a detrital rich stalagmite from Kapsia Cave, the Peloponnese, Greece. The cave is rich in archeological remains and there are reasons to believe that flooding of the cave has directly affected humans using the cave. Using a combination of U-Th and C-14 dating to constrain a site-specific correction factor for (Th-232/U-238) detrital molar ratio, a linear age model was constructed. The age model shows that the stalagmite grew during the period from ca. 950 BC to ca. AD 830. The stable oxygen record from Kapsia indicates cyclical changes of close to 500 yr in precipitation amount, with rapid shifts towards wetter conditions followed by slowly developing aridity. Superimposed on this signal, wetter conditions are inferred around 850, 700, 500 and 400-100 BC, and around AD 160-300 and AD 770; and driest conditions are inferred to have occurred around 450 BC, AD 100-150 and AD 650. Detrital horizons in the stalagmite indicate that three major floods took place in the cave at 500 BC, 70 BC and AD 450. The stable carbon isotope record reflects changes in biological activity being a result of both climate and human activities. (c) 2014 University of Washington.

  • 9.
    Finné, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Bar-Matthews, Miryam
    Geological Survey of Israel.
    Rapid climatic shifts in southern Greece during Marine Isotope Stages 5a-3In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616XArticle in journal (Refereed)
    Abstract [en]

    We present a speleothem based stable isotope (δ13C, δ18O) record from southern Greece covering a period from 79±5.8 ka to 37±3 ka, i.e. the end of Marine Isotope Stage (MIS) 5a and large parts of MIS 4 and MIS 3. The record from Glyfada Cave provides a U-Th dated proxy paleoclimate record from Greece, covering this time period, and shows that the climate over the Peloponnese rapidly responded to interstadial and stadial conditions over Greenland. During stadial (interstadial) conditions colder (warmer) and drier (wetter) conditions are reflected by depleted (enriched) δ13C-values in the speleothems from Glyfada Cave. Depositional hiatuses in Glyfada Cave correspond to periods of severe cold conditions in the northern Hemisphere and reduced precipitation over the Peloponnese most likely due to a southward displacement of Mediterranean cyclone tracks due to expanding northern ice sheets and increased snow cover over the European continent. By comparing our independently dated record with previously published pollen studies from Greece a time lag between the records from Ioannina and Megali Limni and Glyfada is evident. The match in time between the Glyfada speleothem record and the Tenaghi Philippon pollen record, when tuned to NGRIP, is rather precise.

  • 10.
    Finné, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Sundqvist, Hanna S.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Weiberg, Erika
    Lindblom, Michael
    Climate in the eastern Mediterranean, and adjacent regions, during the past 6000 years - A review2011In: Journal of Archaeological Science, ISSN 0305-4403, E-ISSN 1095-9238, Vol. 38, no 12, p. 3153-3173Article, review/survey (Refereed)
    Abstract [en]

    The eastern Mediterranean, with its long archaeological and historical records, provides a unique opportunity to study human responses to climate variability. We review paleoclimate data and reconstructions from the region with a focus on the last 6000 years. We aim to provide an up-to-date source of information on climate variability and to outline present limitations and future opportunities. The review work is threefold: (1) literature review, (2) spatial and temporal analysis of proxy records, and (3) statistical estimation of uncertainties in present paleoclimate reconstructions (temperature, C). On a regional scale the review reveals a wetter situation from 6000 to 5400 yrs BP (note: all ages in this paper are in calibrated years before present (i.e. before 1950), abbreviated yrs BP, unless otherwise stated). This is followed by a less wet period leading up to one of fully-developed aridity from c. 4600 yrs BP. There is a need for more high-resolution paleoclimate records, in order to (i) better understand regional patterns and trends versus local climate variability and to (ii) fill the gap of data from some regions, such as the Near East, Greece and Egypt. Further, we evaluate the regional occurrence of a proposed widespread climate event at 4200 yrs BP. This proposed climate anomaly has been used to explain profound changes in human societies at different locations in the region around this time. We suggest that although aridity was widespread around 4200 yrs BP in the eastern Mediterranean region, there is not enough evidence to support the notion of a climate event with rapidly drying conditions in this region.

  • 11. Harrison, S. P.
    et al.
    Bartlein, P. J.
    Brewer, S.
    Prentice, I. C.
    Boyd, Meighan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Hessler, I.
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Izumi, K.
    Willis, K.
    Climate model benchmarking with glacial and mid-Holocene climates2014In: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 43, no 3-4, p. 671-688Article in journal (Refereed)
    Abstract [en]

    Past climates provide a test of models' ability to predict climate change. We present a comprehensive evaluation of state-of-the-art models against Last Glacial Maximum and mid-Holocene climates, using reconstructions of land and ocean climates and simulations from the Palaeoclimate Modelling and Coupled Modelling Intercomparison Projects. Newer models do not perform better than earlier versions despite higher resolution and complexity. Differences in climate sensitivity only weakly account for differences in model performance. In the glacial, models consistently underestimate land cooling (especially in winter) and overestimate ocean surface cooling (especially in the tropics). In the mid-Holocene, models generally underestimate the precipitation increase in the northern monsoon regions, and overestimate summer warming in central Eurasia. Models generally capture large-scale gradients of climate change but have more limited ability to reproduce spatial patterns. Despite these common biases, some models perform better than others.

  • 12.
    Holmgren, Karin
    Stockholm University.
    Den sårbara kontinenten: Afrikas klimat och samhällets anpassning.2007In: Framtider, no 3, p. 4-10Article in journal (Other (popular science, discussion, etc.))
  • 13.
    Holmgren, Karin
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Gogou, Alexandra
    Izdebski, Adam
    Luterbacher, Juerg
    Sicre, Marie-Alexandrine
    Xoplaki, Elena
    Mediterranean Holocene climate, environment and human societies2016In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 136, p. 1-4Article in journal (Refereed)
    Abstract [en]

    This paper introduces the reader to a special issue of articles that explores links and processes behind societal change, climate change and environmental change in a Holocene perspective in the Mediterranean region. All papers are, by purpose, co-authored by scientists representing different disciplines. The cross-cutting theme has been to reach beyond simple explanations of potential climate-society relationships and advance our understanding on how to improve research methods and theories in the field. The thirteen papers in this issue address these questions in three different ways, by i) conceptual/methodological approaches; ii) review papers; and iii) case studies.

  • 14.
    Holmgren, Karin
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kuylenstierna, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Bredda perspektiven för klimatsäkrat bistånd2007In: GöteborgspostenArticle in journal (Other (popular science, discussion, etc.))
  • 15.
    Holmgren, Karin
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Risberg, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Freudendahl, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Achimo, Mussa
    Ekblom, Anneli
    Mugabe, Joao
    Norström, Elin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Sitoe, Sandra
    University of Eduardo Mondlane, Mozambique.
    Water-level variations in Lake Nhauhache, Mozambique, during the last 2,300 years2012In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 48, no 2, p. 311-322Article in journal (Refereed)
    Abstract [en]

    Stratigraphic variations in diatom composition and phytolith abundance in a sediment core from a small, hydrologically isolated waterbody, Lake Nhauhache, Mozambique, provide evidence of water-level fluctuations over the past 2,300 years. Ten AMS radiocarbon dates on bulk sediment samples show that the lake came into existence about 2,300 years ago and that it has dried out since then, but only for brief time periods. Changes in the diatom assemblage composition indicate that lake level fluctuated in response to shifting humidity conditions. The changes reflect wetter conditions ca. 300 BC-AD 800, more variable conditions between AD 800 and 1150, a distinct dry phase within the time span AD 1150-1700 and a return thereafter to more humid conditions until present. There is general agreement between the Lake Nhauhache record and other records from the Southern Hemisphere summer rainfall region. This suggests that sediments from small interdunal lakes, which are abundant along the coast of southern Africa, provide reliable, regional paleoenvironmental information about an area from which more such data are needed.

  • 16.
    Holmgren, Karin
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Sicre, Marie-Alexandrine
    Gogou, Alexandra
    Xoplaki, Elena
    Luterbacher, Juerg
    Mediterranean Holocene climate and human societies2014In: Past Global Changes Magazine, ISSN 1811-1602, Vol. 22, no 2, p. 110-110Article in journal (Other academic)
  • 17.
    Holmgren, Karin
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Öberg, Helena
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Climate Change in Southern and East Africa during the Past Millennium and its Implications for Societal Development.2007In: The World System and the Earth System: global socioenvironmental change and sustainability since the Neolithic / [ed] Alf Hornborg & Carole Crumley, Walnut Creek, Calif: Left Coast Press Inc., 2007, p. 121-131Chapter in book (Refereed)
  • 18. Izdebski, Adam
    et al.
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Weiberg, Erika
    Stocker, Sharon R.
    Büntgen, Ulf
    Florenzano, Assunta
    Gogou, Alexandra
    Leroy, Suzanne A. G.
    Luterbacher, Jürg
    Martrat, Belen
    Masi, Alessia
    Mercuri, Anna Maria
    Montagna, Paolo
    Sadori, Laura
    Schneider, Adam
    Sicre, Marie-Alexandrine
    Triantaphyllou, Maria
    Xoplaki, Elena
    Realising consilience: How better communication between archaeologists, historians and natural scientists can transform the study of past climate change in the Mediterranean2016In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 136, p. 5-22Article in journal (Refereed)
    Abstract [en]

    This paper reviews the methodological and practical issues relevant to the ways in which natural scientists, historians and archaeologists may collaborate in the study of past climatic changes in the Mediterranean basin. We begin by discussing the methodologies of these three disciplines in the context of the consilience debate, that is, attempts to unify different research methodologies that address similar problems. We demonstrate that there are a number of similarities in the fundamental methodology between history, archaeology, and the natural sciences that deal with the past (palaeoenvironmental sciences), due to their common interest in studying societal and environmental phenomena that no longer exist. The three research traditions, for instance, employ specific narrative structures as a means of communicating research results. We thus present and compare the narratives characteristic of each discipline; in order to engage in fruitful interdisciplinary exchange, we must first understand how each deals with the societal impacts of climatic change. In the second part of the paper, we focus our discussion on the four major practical issues that hinder communication between the three disciplines. These include terminological misunderstandings, problems relevant to project design, divergences in publication cultures, and differing views on the impact of research. Among other recommendations, we suggest that scholars from the three disciplines should aim to create a joint publication culture, which should also appeal to a wider public, both inside and outside of academia.

  • 19.
    Katrantsiotis, Christos
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Norström, Elin
    Stockholm University, Faculty of Science, Department of Physical Geography. Stockholm University, Faculty of Science, Department of Geological Sciences.
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Risberg, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Skelton, Alasdair
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    High-resolution environmental reconstruction in SW Peloponnese, Greece, covering the last c. 6000years: Evidence from Agios Floros fen, Messenian plain2016In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 26, no 2, p. 188-204Article in journal (Refereed)
    Abstract [en]

    A paleolimnological record from the central Messenian plain (southwestern Peloponnese, southern Greece) indicates rapid changes in the water level and chemistry of a transient lake on the flanks of the Taygetos Mountains during the last c. 6000years. The analyses are based on diatoms as well as carbon and nitrogen isotopes from bulk sediments in a 7.5-m-long sediment core retrieved from the drained fen of Agios Floros, at the northern banks of the ancient River Pamisos. The sequence consists of fen peat in the uppermost section underlain by lacustrine sediments, which are punctuated by two layers of clay with diatomaceous silt bands. High accumulation rate is recorded in the oldest part of the section (up to 23mm/yr), particularly during two decadal-long periods centered at c. 5700 and c. 5300 cal. BP. The diatom record reveals pronounced peaks in the planktonic taxon Cyclotella distinguenda, which correspond to the laminated sequences, reflecting the rapid development of a deep lake with an open water environment during these two time periods. Another two events with intermediate water levels are inferred at c. 5200 and c. 4600 cal. BP. These short-lived phases were probably, to a large extent, caused by local tectonic processes and the consequent hydrological anomalies of the nearby karst springs, although abrupt climatic changes with enhanced precipitation might have also played a role. At c. 4500 cal. BP, our data suggest the development of terrestrial conditions in this area, which can be attributed to the decreasing activity/dry up of springs, probably associated with more arid climate. After c. 2500 cal. BP, the diatom record infers a return to wetter conditions, probably as a response to more humid climate with marked seasonality and human activities, developing the present-day environment with cultivated and seasonally semi-flooded fields.

  • 20.
    Katrantsiotis, Christos
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Risberg, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Norström, Elin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Morphological study of Cyclotella distinguenda with a description of a new fossil species Cyclotella paradistinguenda sp nov from the Agios Floros fen, SW Peloponnese, Greece in relation to other Cyclotella species2016In: Diatom Research, ISSN 0269-249X, E-ISSN 2159-8347, Vol. 31, no 3, p. 243-267Article in journal (Refereed)
    Abstract [en]

    In a previous palaeoenvironmental study based on a high-resolution diatom record from a core sampled at the Agios Floros fen, SW Peloponnese, Greece, Cyclotella distinguenda was reported as exhibiting two morphs with distinct central area and stria arrangement, as well as a specific distribution throughout the sequence. In the present paper, we examine this morphological variability through detailed observations using light and scanning electron microscope combined with a simple statistical approach. Our new data suggest that the two morphs present substantial and constant differences in the structure and size of their central areas, the structure and number of their striae, the arrangement of their marginal fultoportulae/density of costae between fultoportulae, the shape of their rimoportulae and their alveolar chambers. On the basis of these morphological and stratigraphic variations one morph is described as a new species, Cyclotella paradistinguenda sp. nov., while the other is assigned to C. distinguenda and is also consistent with the original description of this taxon. The two species share well-defined central areas without fultoportulae, almost equal length striae and one rimoportula situated on a costa within the ring of marginal fultoportulae. Cyclotella paradistinguenda sp. nov. can be distinguished by a combination of the following characteristics: (1) large central area (1/3 of valve diameter), smooth or decorated with puncta and depressions, flat or concentrically undulated, (2) distinct, narrow striae (12-15/10 mu m) consisting of one or two short rows of areolae of the same size expanding into three rows at the mantle, (3) marginal fultoportulae on each first to third costae (4) poorly developed alveolar chambers and rimoportula. Based on the stratigraphic distribution and the associated flora in the Agios Floros sequence, it can be inferred that C. paradistinguenda sp. nov. is tolerant of shallower water conditions with lower nutrient availability and/or higher pH than C. distinguenda.

  • 21.
    Kleman, J.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Destouni, G.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Gustafsson, Ö.
    Holmgren, K.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Svensson, G.
    Presentation of the Bert Bolin Centre for Climate Research for the Environmental Committee of Swedish Parliament, Stockholm, May 3, 2011.2011Other (Other (popular science, discussion, etc.))
  • 22.
    Kleman, Johan
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Rodhe, Henning
    Stockholm University, Faculty of Science, Department of Meteorology .
    Destouni, Georgia
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Gustafsson, Örjan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Nilsson, Johan
    Stockholm University, Faculty of Science, Department of Meteorology .
    Svensson, Gunilla
    Stockholm University, Faculty of Science, Department of Meteorology .
    Tjernström, Michael
    Stockholm University, Faculty of Science, Department of Meteorology .
    Rubbat förtroende för forskarna2010In: Svenska Dagbladet, ISSN 1101-2412, no 25 majArticle in journal (Other (popular science, discussion, etc.))
  • 23. Luterbacher, J.
    et al.
    Werner, J. P.
    Smerdon, J. E.
    Fernandez-Donado, L.
    Gonzalez-Rouco, F. J.
    Barriopedro, D.
    Charpentier Ljungqvist, Fredrik
    Stockholm University, Faculty of Humanities, Department of History.
    Buentgen, U.
    Zorita, E.
    Wagner, S.
    Esper, J.
    McCarroll, D.
    Toreti, A.
    Frank, D.
    Jungclaus, J. H.
    Barriendos, M.
    Bertolin, C.
    Bothe, O.
    Brazdil, R.
    Camuffo, D.
    Dobrovolny, P.
    Gagen, M.
    Garica-Bustamante, E.
    Ge, Q.
    Gomez-Navarro, J. J.
    Guiot, J.
    Hao, Z.
    Hegerl, G. C.
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Klimenko, V. V.
    Martin-Chivelet, J.
    Pfister, C.
    Roberts, N.
    Schindler, A.
    Schurer, A.
    Solomina, O.
    von Gunten, L.
    Wahl, E.
    Wanner, H.
    Wetter, O.
    Xoplaki, E.
    Yuan, N.
    Zanchettin, D.
    Zhang, H.
    Zerefos, C.
    European summer temperatures since Roman times2016In: Environmental Research Letters, ISSN 1748-9326, E-ISSN 1748-9326, Vol. 11, no 2, article id 024001Article in journal (Refereed)
    Abstract [en]

    The spatial context is criticalwhen assessing present-day climate anomalies, attributing them to potential forcings and making statements regarding their frequency and severity in a long-term perspective. Recent international initiatives have expanded the number of high-quality proxy-records and developed new statistical reconstruction methods. These advances allow more rigorous regional past temperature reconstructions and, in turn, the possibility of evaluating climate models on policy-relevant, spatiotemporal scales. Here we provide a new proxy-based, annually-resolved, spatial reconstruction of the European summer (June-August) temperature fields back to 755 CE based on Bayesian hierarchical modelling (BHM), together with estimates of the European mean temperature variation since 138 BCE based on BHM and composite-plus-scaling (CPS). Our reconstructions compare well with independent instrumental and proxy-based temperature estimates, but suggest a larger amplitude in summer temperature variability than previously reported. Both CPS and BHM reconstructions indicate that the mean 20th century European summer temperature was not significantly different from some earlier centuries, including the 1st, 2nd, 8th and 10th centuries CE. The 1st century (in BHM also the 10th century) may even have been slightly warmer than the 20th century, but the difference is not statistically significant. Comparing each 50 yr period with the 1951-2000 period reveals a similar pattern. Recent summers, however, have been unusually warm in the context of the last two millennia and there are no 30 yr periods in either reconstruction that exceed the mean average European summer temperature of the last 3 decades (1986-2015 CE). A comparison with an ensemble of climate model simulations suggests that the reconstructed European summer temperature variability over the period 850-2000 CE reflects changes in both internal variability and external forcing on multi-decadal time-scales. For pan-European temperatures we find slightly better agreement between the reconstruction and the model simulations with high-end estimates for total solar irradiance. Temperature differences between the medieval period, the recent period and the Little Ice Age are larger in the reconstructions than the simulations. This may indicate inflated variability of the reconstructions, a lack of sensitivity and processes to changes in external forcing on the simulated European climate and/or an underestimation of internal variability on centennial and longer time scales.

  • 24.
    Moberg, Anders
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Renssen, Hans
    Sundqvist, Hanna S.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Zhang, Qiong
    Stockholm University, Faculty of Science, Department of Meteorology .
    Preface "Holocene climate variability over Scandinavia – A special issue originating from a workshop organized by the Bert Bolin Centre for Climate Research"2010In: Climate of the Past, ISSN 1814-9324, E-ISSN 1814-9332, Vol. 6, p. 719-721Article in journal (Other academic)
  • 25.
    Norström, Elin
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Ämnesöverskridande forskarskola för lärare verksamma inom geografi, naturkunskap, fysik och kemi2008In: Gegrafiska notiser, no 4, p. 211-214Article in journal (Other (popular science, discussion, etc.))
  • 26.
    Norström, Elin
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Rainfall driven variations in δ13C and wood anatomy of Breonadia salicina trees from South Africa between AD1375 and 19952005In: South African Journal of Science, ISSN 0038-2353, E-ISSN 1996-7489, Vol. 101, no 3/4, p. 162-168Article in journal (Refereed)
    Abstract [en]

    This study demonstrates the potential of deriving palaeoenvironmental information from carbon isotope composition (δ<sup>13</sup>C) and wood anatomy properties along the growth radii of two Breonadia salicina trees from Limpopo province, South Africa. An age model, based on AMS dating and 'wiggle-match' dating of the wood, shows that the data series from the two trees span AD 1375-1995 and 1447-1994, respectively. Shifts in the trees' δ<sup>13</sup>C composition and wood anatomy resemble the indications of climate change observed in regional palaeoclimatic studies, and the parts of the B. salicina record from the last century show similarities with the observed variations in annual rainfall in the region. We propose that changes in carbon isotope composition and wood anatomy indicate variations in regional rainfall during the period of tree growth. Both the δ<sup>13</sup>C and the wood anatomy records of B. salicina signify dry conditions in the early 1400s, mid-1500s, 1700s and early 1900s. The wettest conditions were during the late 1400s and in the 1600s.

  • 27.
    Norström, Elin
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Risberg, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Gröndahl, Helena
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Snowball, Ian
    Mugabe, João Alberto
    Raúl Sitoe, Sandra
    University of Eduardo Mondlane, Mozambique.
    Coastal paleo-environment and sea-level change at Macassa Bay, southern Mozambique, since c. 6600 cal BP2012In: Quaternary International, ISSN 1040-6182, E-ISSN 1873-4553, Vol. 260, p. 153-163Article in journal (Refereed)
    Abstract [en]

    Changes in Holocene coastal paleo-environment and sea-level variations have been recorded in estuary sediments from Macassa Bay, southern Mozambique. Methods include analysis of fossil diatoms, sediment stratigraphy, mineral magnetic properties, stable carbon and nitrogen isotope composition and carbon and nitrogen content. The chronology, based on six AMS 14C dates, suggests a basal age of the sediment core of c 6600 cal BP (calibrated years Before Present). The multi-proxy dataset implies two phases when the site was experiencing marine conditions and tentative sea-level high-stands: 1) between c 6600–6300 cal BP which is contemporary with the last phase of the global transgression and the Holocene climatic optimum, and 2) between c 4700–1000 cal BP, a period when sea level curves from the region suggest occasional minor sea level high-stands. Between these phases (c 6300–4700 cal BP), the environment within the Macassa Bay estuary was less influenced by marine processes, and studied proxies indicate a freshwater phase associated with relatively low sea levels. After c 1000 cal BP, a terrestrial environment prevailed at the site, probably as a result of a combined effect of sea level lowering and high accumulation of organic peat within the estuary.

  • 28. Persoiu, Aurel
    et al.
    Onac, Bogdan P.
    Wynn, Jonathan G.
    Bojar, Ana-Voica
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Stable isotope behavior during cave ice formation by water freezing in Scarisoara Ice Cave, Romania2011In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 116, p. D02111-Article in journal (Refereed)
    Abstract [en]

    Recently, a series of studies have targeted the stable isotopic composition of cave ice as a possible source of paleoclimatic information, but none presented an explanation for the way in which the external climatic signal is transferred to cave ice. While the relation between the stable isotopic composition of precipitation and drip water can be relatively easily determined, a more complex problem arises, i.e., the possible alteration of the primary climatic signal recorded by the oxygen and hydrogen stable isotopes during the freezing of water to form cave ice. Here we report the results of the first detailed investigations of the oxygen and hydrogen stable isotope behavior during the formation of ice in Scarisoara Ice Cave. Samples of ice align on a straight line with a slope lower than 8 in a delta(18)O-delta(2)H plot, characteristic for ice formed by the freezing of water. A model is presented for the reconstruction of the initial isotopic composition of water, despite the complexity induced by kinetic effects during early stages of freezing. These results are consistent with ice that forms by the downward freezing of a stagnant pool of water, under kinetic conditions in the initial stages of the process, and isotopic equilibrium thereafter. As ice caves are described in many parts of the world, otherwise poorly represented in ice-based paleoclimatology, the results of this study could open a new direction in paleoclimatic research so that an array of significant paleoclimate data can be developed on the basis of their study.

  • 29.
    Ryner, Maria
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Bonnefille, Raymonde
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Muzuka, Alfred
    Vegetation changes in Empakaai Crater, northern Tanzania, at 14,800–9300 cal yr BP2006In: Review of Palaeobotany and Palynology, ISSN 0034-6667, Vol. 140, p. 163-174Article in journal (Refereed)
    Abstract [en]

    Vegetation changes are documented from a well-dated pollen record from Lake Emakat, Empakaai Crater, northern Tanzania.

    This pollen record includes the time interval covering the Pleistocene/Holocene transition, analysed at a resolution interval

    averaging 200 yr. Around the crater lake, an Hagenia-forest development starting at 14,500 cal yr BP lasted until 13,000 cal yr BP.

    A change in vegetation, indicated by an increased proportion of Nuxia congesta in the forest and Artemisia in the afro alpine

    grassland after 13,000 cal yr BP, corresponds in time to the Northern Hemisphere's Younger Dryas cooling. Grasses and sedges

    increased at ∼10,100 cal yr BP, indicating a significant increase in local pollen possibly attributed to lowered lake level, related to

    drier conditions. Although the Empakaai pollen record documents continuous forest conditions, from 14,500 to 10,100 cal yr BP,

    the variation in the proportion of forest components seem to respond to environmental changes at the millennium scale

  • 30.
    Ryner, Maria
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Taylor, David
    A record of vegetation dynamics and lake level changes from Lake Emakat, northern Tanzania, during the last c. 1200 years2007In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 40, no 2, p. 583-601Article in journal (Refereed)
    Abstract [en]

    Analyses of down-core variations in pollen and charcoal in two short cores of lake sediment and wood samples taken from the in situ remains of Nuxia congesta from Lake Emakat, a hydrologically-closed volcanic crater lake occupying the Empakaai Crater in northern Tanzania, have generated evidence of past vegetation change and lake level fluctuations. Eight AMS radiocarbon (14C) dates on bulk samples of lake sediment provide a chronological framework for the two cores and indicate that the sediment record analysed incorporates the last c. 1200 years. The in situ remains of a Nuxia congesta tree, now standing in deep water, were dated with three additional AMS 14C dates, suggesting tree growth within the interval ∼1500–1670 AD. Down-core variations in pollen from terrestrial taxa, particularly the montane forest trees Hagenia abyssinica and Nuxia congesta, indicate a broad period of generally more arid conditions in the catchment to c. 1200 AD and at a prolonged period between c. 1420 and 1680 AD. Variations in pollen from plants in lake margin vegetation indicate low lake levels, presumably as a result of reduced effective precipitation, contemporary with indications of relatively dry conditions mentioned above, but also during the late 18th and the late 19th centuries. The presence of charcoal throughout both cores indicates the frequent occurrence of vegetation fires. An increase in burning, evident in the charcoal data and dated to the early to mid second millennium AD, could relate to an expansion of human population levels and agricultural activity in the region.

  • 31.
    Ryner, Maria
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Taylor, David
    A record of vegetation dynamics and lake level changesfrom Lake Emakat, northern Tanzania, during the last c 1200 years2008In: Journal of Paleolimnology, ISSN 0921-2728, Vol. 40, no 2, p. 583-601Article in journal (Refereed)
    Abstract [en]

    Analyses of down-core variations in pollen and charcoal in two short cores of lake sediment and wood samples taken from the in situ remains of Nuxia congesta from Lake Emakat, a hydrologically-closed volcanic crater lake occupying the Empakaai Crater in northern Tanzania, have generated evidence of past vegetation change and lake level fluctuations. Eight AMS radiocarbon (C-14) dates on bulk samples of lake sediment provide a chronological framework for the two cores and indicate that the sediment record analysed incorporates the last c. 1200 years. The in situ remains of a Nuxia congesta tree, now standing in deep water, were dated with three additional AMS C-14 dates, suggesting tree growth within the interval similar to 1500-1670 AD. Down-core variations in pollen from terrestrial taxa, particularly the montane forest trees Hagenia abyssinica and Nuxia congesta, indicate a broad period of generally more arid conditions in the catchment to c. 1200 AD and at a prolonged period between c. 1420 and 1680 AD. Variations in pollen from plants in lake margin vegetation indicate low lake levels, presumably as a result of reduced effective precipitation, contemporary with indications of relatively dry conditions mentioned above, but also during the late 18th and the late 19th centuries. The presence of charcoal throughout both cores indicates the frequent occurrence of vegetation fires. An increase in burning, evident in the charcoal data and dated to the early to mid second millennium AD, could relate to an expansion of human population levels and agricultural activity in the region.

  • 32. Scott, L.
    et al.
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Partridge, T.C.
    Reconciliation of vegetation and climatic interpretations of pollen profiles and other regional records from the last 60 thousand years in the Savanna Biome of Southern Africa2008In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, Vol. 257, no 1-2, p. 198-206Article in journal (Refereed)
    Abstract [en]

    Long environmental proxy records are very scarce in semi-dry continental areas and often those available present conflicting

    interpretations. However, more in-depth investigation of apparent contradictions, can address these problems. For example,

    comparison of the upper parts of pollen and sediment sequences from the Tswaing Crater and Wonderkrater spring (South Africa)

    and isotopes in a speleothem at Lobatse Cave (Botswana) from the Savanna Biome establishes a basis for understanding of longterm

    regional environmental processes in central Southern Africa over the last 60 ka. The different proxies for the vegetation can

    hypothetically be reconciled on condition that the chronologies on which they are based and environmental controls are firm. We

    discuss the ratio of woody elements, under-storey herb-cover and the vegetation's general C4/C3 status in the central savanna

    region, in relation to seasonal rainfall and temperature variations and long-term climate forcing.

  • 33.
    Sundqvist, Hanna S.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Baker, A
    Holmgren, Karin
    Luminescence in fast growing stalagmites from Uppsala, Sweden2005In: Geografiska Annaler. Series A, Physical Geography, ISSN 0435-3676, E-ISSN 1468-0459, Vol. 87, no 4, p. 539-548Article in journal (Refereed)
    Abstract [en]

    Two fast-growing stalagmites from a cellar vault in Uppsala, southeast Sweden, are ana-lysed for their luminescent properties. The results

    indicate that variations in luminescence intensity in the stalagmites are annual. Due to problems in find-ing a suitable absolute dating method this assump-tion cannot yet be firmly tested; however, results from radiocarbon dating of one of the stalagmites do not contradict the proposal that the laminae are annual. If so, the speleothems have been growing for 10-15 years with a growth rate of 3-8 mm per year, which is a similar rate to other fast-growing speleothems in Great Britain that have formed from the reaction of lime mortar and carbon dioxide. It is likely that the assumed annual laminae of the lumi-nescence record represent a flush of organic mate-rial.

  • 34.
    Sundqvist, Hanna S.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Fohlmeister, J.
    Zhang, Qiong
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Bar Matthews, M.
    Spoetl, C.
    Kornich, H.
    Evidence of a large cooling between 1690 and 1740 AD in southern Africa2013In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 3, p. 1767-Article in journal (Refereed)
    Abstract [en]

    A 350-year-long, well-dated delta O-18 stalagmite record from the summer rainfall region in South Africa is positively correlated with regional air surface temperatures at interannual time scales. The coldest period documented in this record occurred between 1690 and 1740, slightly lagging the Maunder Minimum (1645-1710). A temperature reconstruction, based on the correlation between regional surface temperatures and the stalagmite delta O-18 variations, indicates that parts of this period could have been as much as 1.4 degrees C colder than today. Significant cycles of 22, 11 and 4.8 years demonstrate that the solar magnetic and the El Nino-Southern Oscillation cycle could be important drivers of multidecadal to interannual climate variability in this region. The observation that the most important driver of stalagmite delta O-18 on interannual time scales from this subtropical region is regional surface temperature cautions against deterministic interpretations of delta O-18 variations in low-latitude stalagmites as mainly driven by the amount of precipitation.

  • 35.
    Sundqvist, Hanna S
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Lauritzen, Stein-Erik
    Stable isotope variations in stalagmites from northwestern Sweden document changes in temperature and vegetation, during early Holocen.2007In: the Holocene, Vol. 17, no 2, p. 259-267Article in journal (Refereed)
  • 36.
    Sundqvist, Hanna S.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Moberg, Anders
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Spötl, Christoph
    Mangini, Augusto
    Stable oxygen isotopes in a stalagmite from Jämtland, NW Sweden, record large temperature variations over the last 4000 years2010In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 39, no 1, p. 77-86Article in journal (Refereed)
    Abstract [en]

     

     

     

    This study of a 4000-year-old stalagmite from Korallgrottan in northwestern Sweden highlights the potentials and challenges when using stable isotopes in stalagmites as climate proxies, as well as the fact that the relationship between climate and proxy may change through time. Both the oxygen and the carbon isotopes display an overall trend of enrichment together with decreasing growth rates over the time period covered by the stalagmite, which is considered a generally cooling period according to current palaeoclimate understanding. The stable isotope records show enriched isotopic values during the, for Scandinavia, comparatively cold period AD 1300–1700 and depleted values during the warmer period AD 800–1000. The indication of a negative relationship between measured

    d18O and surface temperature concurs with earlier reported stalagmite records from regions with a seasonal snow cover and is further supported by the fact that the stalagmite d18

    O record shows general similarities with both regional and hemispheric temperature reconstructions available for the past 500 and 2000 years, respectively.

    Compared with a stable isotope record of lacustrine carbonates from northern Sweden, however, shifting correlations over time between the two records indicate that a local hydrological change may have taken place at Korallgrottan, or at the lake, compared with around 1000 years ago. The earlier part of the stalagmite

    d18O might thus be influenced, to some extent, by another process than the later part, which means that a negative relationship between d18O and surface temperature might not hold for the entire 4000-year-old record.

  • 37.
    Sundqvist, Hanna S.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Seibert, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Understanding conditions behind speleothem formation in Korallgrottan, northwestern Sweden2007In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 347, no 1-2, p. 13-22Article in journal (Refereed)
    Abstract [en]

    In this study we investigate and characterise the environmental factors that control active speleothem growth in Korallgrottan, northwestern Sweden, in order to get a better understanding of seepage processes in karst areas and to determine whether the fossil speleothems from this site are suitable as palaeoclimatic archives. The drip rates from fast-dripping stalactites (>100 ml/day) vary substantially with the season and the snow regime. Comparisons with measurements of river discharge and simulated ground water recharge show that the drip rate from fast-dripping stalactites can be used as an estimation of the weekly to monthly ground water recharge. Slow-dripping stalactites however, have a steadier drip rate, with almost no seasonal variations. The δ18O composition of the drip water from both fast- and slow-dripping stalactites show some seasonal variation (±1.2‰), but is fairly stable compared to outside precipitation (±11.1‰). The δ18O signal from fast-dripping stalactites is biased towards summer conditions, while the signal is dampened at slow-dripping sites and an annual or even longer signal is evident. This holds true even though calcite precipitation may not occur continuously throughout the year. Similarly, the trace elemental composition of drip water is more stable in the slow-dripping stalactites, reflecting mean annual values or longer. Generally the drip water reaches the highest saturation level during the summer and autumn when biological activity in the soil zone is most intense, and the partial pressure of carbon dioxide, which controls limestone dissolution, is high.

  • 38.
    Sundqvist, Hanna S.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Zhang, Qiong
    Stockholm University, Faculty of Science, Department of Meteorology .
    Moberg, Anders
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Körnich, Heiner
    Stockholm University, Faculty of Science, Department of Meteorology .
    Nilsson, Johan
    Stockholm University, Faculty of Science, Department of Meteorology .
    Northern high-latitude climate change between the mid and late Holocene: Part 1: Proxy data evidence2009In: Climate of the Past Discussions, ISSN 1814-9340, Vol. 5, no 4, p. 1819-1852Article in journal (Other academic)
  • 39.
    Sundqvist, Hanna S.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Zhang, Qiong
    Stockholm University, Faculty of Science, Department of Meteorology .
    Moberg, Anders
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Körnich, Heiner
    Stockholm University, Faculty of Science, Department of Meteorology .
    Nilsson, Johan
    Stockholm University, Faculty of Science, Department of Meteorology .
    Brattström, Gudrun
    Stockholm University, Faculty of Science, Department of Mathematics.
    Climate change between the mid and late Holocene in the northern high latitudes: Part I: Survey of temperature and precipitation proxy data2010In: Climate of the Past, ISSN 1814-9324, E-ISSN 1814-9332, Vol. 6, p. 591-608Article in journal (Refereed)
    Abstract [en]

    We undertake a study in two parts, where theoverall aim is to quantitatively compare results from climateproxy data with results from several climate model simulationsfrom the Paleoclimate Modelling IntercomparisonProject for the mid-Holocene period and the pre-industrial,conditions for the pan-arctic region, north of 60 N. In thisfirst paper, we survey the available published local temperatureand precipitation proxy records. We also discuss andquantifiy some uncertainties in the estimated difference inclimate between the two periods as recorded in the availabledata. The spatial distribution of available published localproxies has a marked geographical bias towards land areassurrounding the North Atlantic sector, especially Fennoscandia.The majority of the reconstructions are terrestrial, andthere is a large over-representation towards summer temperaturerecords. The available reconstructions indicate that thenorthern high latitudes were warmer in both summer, winterand the in annual mean temperature at the mid-Holocene(6000 BP±500 yrs) compared to the pre-industrial period(1500AD±500 yrs). For usage in the model-data comparisons(in Part 1), we estimate the calibration uncertainty andalso the internal variability in the proxy records, to derive acombined minimum uncertainty in the reconstructed temperaturechange between the two periods. Often, the calibrationuncertainty alone, at a certain site, exceeds the actual reconstructedclimate change at the site level. In high-density regions,however, neighbouring records can be merged into aCorrespondence to: H. S. Sundqvist(hanna.sundqvist@natgeo.su.se)composite record to increase the signal-to-noise ratio. Thechallenge of producing reliable inferred climate reconstructionsfor the Holocene cannot be underestimated, consideringthe fact that the estimated temperature and precipitationfluctuations during this period are in magnitude similar to, orlower than, the uncertainties the reconstructions. We advocatea more widespread practice of archiving proxy recordsas most of the potentially available reconstructions are notpublished in digital form.

  • 40. Weiberg, Erika
    et al.
    Unkel, Ingmar
    Kouli, Katerina
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Avramidis, Pavlos
    Bonnier, Anton
    Dibble, Flint
    Finné, Martin
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Izdebski, Adam
    Katrantsiotis, Christos
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Stocker, Sharon R.
    Andwinge, Maria
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Baika, Kalliopi
    Boyd, Meighan
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Heymann, Christian
    The socio-environmental history of the Peloponnese during the Holocene: Towards an integrated understanding of the past2016In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 136, p. 40-65Article in journal (Refereed)
    Abstract [en]

    Published archaeological, palaeoenvironmental, and palaeoclimatic data from the Peloponnese in Greece are compiled, discussed and evaluated in order to analyse the interactions between humans and the environment over the last 9000 years. Our study indicates that the number of human settlements found scattered over the peninsula have quadrupled from the prehistoric to historical periods and that this evolution occurred over periods of climate change and seismo-tectonic activity. We show that societal development occurs both during periods of harsh as well as favourable climatic conditions. At some times, some settlements develop while others decline. Well-known climate events such as the 4.2 ka and 3.2 ka events are recognizable in some of the palaeoclimatic records and a regional decline in the number and sizes of settlements occurs roughly at the same time, but their precise chronological fit with the archaeological record remains uncertain. Local socio-political processes were probably always the key drivers behind the diverse strategies that human societies took in times of changing climate. The study thus reveals considerable chronological parallels between societal development and palaeoenvironmental records, but also demonstrates the ambiguities in these correspondences and, in doing so, highlights some of the challenges that will face future interdisciplinary projects. We suggest that there can be no general association made between societal expansion phases and periods of advantageous climate. We also propose that the relevance of climatic and environmental regionality, as well as any potential impacts of seismo-tectonics on societal development, need to be part of the interpretative frameworks.

  • 41.
    Westerberg, Lars-Ove
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Börjeson, Lowe
    Stockholm University, Faculty of Social Sciences, Department of Human Geography.
    Håkansson, Thomas
    Laulumaa, Vesa
    Ryner, Maria
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Öberg, Helena
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    The development of the ancient irrigation system at Engaruka, northern Tanzania: Physical and societal factors2010In: Geographical Journal, ISSN 0016-7398, E-ISSN 1475-4959, Vol. 176, no 4, p. 304-318Article in journal (Refereed)
    Abstract [en]

    Climate data from Empakaai Crater in northern Tanzania, covering the last 1200 years, are related to the establishment, development and decline of the ancient irrigation system at Engaruka. New dates for the system are linked to reconstructed climatic variations and historical data on long-distance and regional trade and migration patterns. A shift from a comparatively humid climate to drier conditions in the 1400s prompted the establishment of irrigated agriculture at Engaruka, and a flourishing long-distance trade increased its value as a water and food source for passing caravans. Once established, the land-use system at Engaruka was sufficiently resilient to survive and even intensify during much drier climate from c. 1500 to 1670 CE (Common Era) and during the decline of caravan trade between c. 1550 and 1750. The ancient land-use system probably reached its maximum extension during the humid conditions between 1670 and 1740, and was deserted in the early to mid 1800s, presumably as a result of the added effects of climate deterioration, the Maasai expansion, and change of livelihood strategies as agriculturalists became pastoralists. Towards the end of the 1800s irrigated agriculture was again established at Engaruka, in part driven by the transfer from pastoral to agricultural livelihoods caused by the Rinderpest.

  • 42.
    Zhang, Qiong
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Sundqvist, Hanna
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Decadal Rainfall Dipole Oscillation over Southern Africa Modulated by Variation of Austral Summer Land-Sea Contrast along the East Coast of Africa2015In: Journal of Atmospheric Sciences, ISSN 0022-4928, E-ISSN 1520-0469, Vol. 72, no 5, p. 1827-1836Article in journal (Refereed)
    Abstract [en]

    A rainfall dipole mode characterized by negative correlation between subtropical southern Africa and equatorial eastern Africa is identified in instrumental observation data in the recent 100 years. The dipole mode shows a pronounced oscillation signal at a time scale of about 18 years. This study investigates the underlying dynamical mechanisms responsible for this dipole pattern. It is found that the southern African rainfall dipole index is highly correlated to the land-sea contrast along the east coast of Africa. When the land-sea thermal contrast strengthens, the easterly flow toward the continent becomes stronger. The stronger easterly flow, via its response to east coast topography and surface heating, leads to a low pressure circulation anomaly over land south of the maximum easterly flow anomalies and thus causes more rainfall in the south. On a decadal time scale, an ENSO-like SST pattern acts to modulate this land-sea contrast and the consequent rainfall dipole. During a wet in the south and dry in the north dipole, there are warm SSTs over the central Indian Ocean and cold SSTs over the western Indian Ocean. The cold SSTs over the western Indian Ocean further enhance the land-sea contrast during austral summer. Moreover, these cold western Indian Ocean SSTs also play an important role in regulating land temperature, thereby suppressing clouds and warming the land via increased shortwave radiation over the less-cloudy land. This cloud-SST coupling acts to further strengthen the land-sea contrast.

  • 43.
    Zhang, Qiong
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Körnich, Heiner
    Stockholm University, Faculty of Science, Department of Meteorology .
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    How well do reanalyses represent the southern African precipitation?2013In: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 40, no 3-4, p. 951-962Article in journal (Refereed)
    Abstract [en]

    Monthly-mean precipitation observations over southern Africa are used to evaluate the performance of eight global reanalyses: ERA-40, ERA-interim, JRA-25, MERRA, CFSR, NCEP-R1, NCEP-R2 and 20CRv2. All eight reanalyses reproduce the regionally averaged seasonal cycle fairly well; a few spatial mismatches with the observations are found in the climate mean for the rainy season. Principal component analyses show a dipole in the leading modes of all reanalyses, however with crucial differences in its spatial position. Possible reasons for the differences between the reanalyses are discussed on the basis of the ERA-interim and 20CRv2 results. A comparison between the moisture transports shows that ERA-interim manifests a very strong moisture convergence over the eastern equatorial Atlantic, resulting in the strong precipitation here. This excessive convergence may be due to the water-vapor assimilation and convection parameterization. Over the Indian Ocean, the ITCZ is shifted northward in ERA-interim compared to its position in 20CRv2. This discrepancy is most likely attributable to the meridional SST gradients in the Indian Ocean which are significantly larger in the ERA-interim than those in the 20CRv2, and the resulting atmospheric response prevents a southward shift of the ITCZ. Overall, the consistent description of the dynamical circulation of the atmosphere and the hydrological cycle appears as a crucial benchmark for reanalysis data. Based on our evaluation, the preferential reanalysis for investigating the climate variability over southern Africa is 20CRv2 that furthermore spans the longest time period, hence permitting the most precise investigations of interannual to decadal variability.

  • 44.
    Zhang, Qiong
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Sundqvist, Hanna
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Moberg, Anders
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Körnich, Heiner
    Stockholm University, Faculty of Science, Department of Meteorology .
    Nilsson, Johan
    Stockholm University, Faculty of Science, Department of Meteorology .
    Northern high-latitude climate change between the mid and late Holocene: Part 2: Model-data comparisons2009In: Climate of the Past Discussions, ISSN 1814-9340, Vol. 5, no 3, p. 1659-1696Article in journal (Other academic)
  • 45.
    Zhang, Qiong
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Sundqvist, Hanna
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Moberg, Anders
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Körnich, Heiner
    Stockholm University, Faculty of Science, Department of Meteorology .
    Nilsson, Johan
    Stockholm University, Faculty of Science, Department of Meteorology .
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Climate change between the mid and late Holocene in northern high latitudes: Part 2: Model-data comparisons2010In: Climate of the Past, ISSN 1814-9324, E-ISSN 1814-9332, Vol. 6, p. 609-626Article in journal (Refereed)
    Abstract [en]

    The climate response over northern high latitudesto the mid-Holocene orbital forcing has been investigated inthree types of PMIP (Paleoclimate Modelling IntercomparisonProject) simulations with different complexity of themodelled climate system. By first undertaking model-datacomparison, an objective selection method has been appliedto evaluate the capability of the climate models to reproducethe spatial response pattern seen in proxy data. The possiblefeedback mechanisms behind the climate response havebeen explored based on the selected model simulations. Subsequentmodel-model comparisons indicate the importanceof including the different physical feedbacks in the climatemodels. The comparisons between the proxy-based reconstructionsand the best fit selected simulations show that overthe northern high latitudes, summer temperature change followsclosely the insolation change and shows a commonfeature with strong warming over land and relatively weakwarming over ocean at 6 ka compared to 0 ka. Furthermore,the sea-ice-albedo positive feedback enhances this response.The reconstructions of temperature show a strongerresponse to enhanced insolation in the annual mean temperaturethan winter and summer temperature. This is verified inthe model simulations and the behaviour is attributed to thelarger contribution from the large response in autumn. Despitea smaller insolation during winter at 6 ka, a pronouncedwarming centre is found over Barents Sea in winter in thesimulations, which is also supported by the nearby northernEurasian continental and Fennoscandian reconstructions.This indicates that in the Arctic region, the response of theocean and the sea ice to the enhanced summer insolationis more important for the winter temperature than the synchronousdecrease of the insolation.

  • 46.
    Öberg, Helena
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Andersen, Thorbjørn J.
    Westerberg, Lars-Ove
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Risberg, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    A diatom record of recent environmental change in Lake Duluti, northern Tanzania2012In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 48, no 2, p. 401-416Article in journal (Refereed)
    Abstract [en]

    Lake Duluti is a small, topographically closed crater lake located on the flanks of Mt Meru, northern Tanzania. Analyses of diatoms in three short sediment cores and four modern samples from Lake Duluti were used to infer past environmental changes. 210Pb and 137Cs activity profiles combined with AMS 14C dates provide the chronological framework. Weak agreement between the 210Pb and 14C records, together with dating uncertainty, precludes construction of precise age models. The modern diatom flora, from plankton and three periphytic habitats, is dominated by Aulacoseira ambigua (Grunow) Simonsen, Gomphonema parvulum (Kützing) Grunow and Nitzschia amphibia Grunow. All three cores display similar stratigraphic succession, but the relative ratio of habitats represented by the diatoms varies substantially between cores. Diatoms indicate that the oldest part of the record is characterized by relatively low lake level and swampy vegetation. In the late nineteenth or early twentieth century there was a rapid lake level rise and the swamp turned into an open-water lake. High lake levels have prevailed since that time.

  • 47.
    Öberg, Helena
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Norström, Elin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Ryner, Maria
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Westerberg, Lars-Ove
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Risberg, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Dögg Eddudóttir, Sigrún
    Muzuka, Alfred
    Institute of Marine Science, University of Dar es Salaam.
    Environmental variability in northern Tanzania from c. AD 1000 to 1800, as inferred from diatoms and pollen in Lake DulutiManuscript (preprint) (Other academic)
    Abstract [en]

    Fossil pollen and diatoms have been analysed in a sediment sequence from a topographically closed crater lake in northern Tanzania(Lake Duluti), with the aim to reconstruct past changes in lake level and vegetation dynamics. The results contribute with a new paleoenvironmental record from equatorial Africacovering the period c. AD 1000 to AD 1800. Overall, the pollen and diatom records generate comparative stories of dry and wet periods. Dry conditions are inferred at c. AD 1040–1470, c. AD 1510–1640 and c. AD 1650–1670 with the lowest lake levels at c. AD 1260–1290 and AD 1600–1640. Wetter conditions occurred c. AD 1640–1650 and c. AD 1670–1790. The chronology is based on combined analyses of 210Pb activity and AMS 14C on bulk sediment, and a Bayesian model was applied to establish the age-depth relationship. The hydroclimatic record fromLakeDuluti shows good correlation with several East African lakes although precise comparison is hampered by dating uncertainties.

  • 48.
    Öberg, Helena
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Norström, Elin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Ryner, Maria Malmström
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Westerberg, Lars-Ove
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Risberg, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Eddudottir, Sigrun Dogg
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Andersen, Thorbjörn J.
    Muzuka, Alfred
    Environmental variability in northern Tanzania from AD 1000 to 1800, as inferred from diatoms and pollen in Lake Duluti2013In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 374, p. 230-241Article in journal (Refereed)
    Abstract [en]

    Fossil pollen and diatoms have been analyzed in a sediment sequence from a topographically closed crater lake in northern Tanzania (Lake Duluti), with the aim to reconstruct past changes in lake level and vegetation dynamics. The results provide a new paleoenvironmental record from equatorial Africa covering the period c. AD 1000 to AD 1800. Overall, the pollen and diatom records generate comparable stories of dry and wet periods. Dry conditions are inferred at c. AD 1040-1470, c. AD 1510-1640 and C. AD 1650-1670 with the lowest lake levels at c. AD 1260-1290 and AD 1600-1640. Wetter conditions occurred c. AD 1640-1650 and c. AD 1670-1790. The chronology is based on combined analyses of Pb-210 activity and AMS C-14 on bulk sediment, and a Bayesian model was applied to establish the age-depth relationship. The hydroclimatic record from Lake Duluti shows good correlation with several East African lakes in a centennial time perspective, although comparison of high frequency variability in the region is hampered by dating uncertainties.

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