Stockholms universitet

Martina HättestrandLaboratorieansvarig

Om mig

Forskning: Min forskning behandlar istidshistoria och vegetations- och klimathistoria. Inom forskningen arbetar jag med studier av sediment för att se hur miljön har varit tillbaka i tiden och ibland innebär studierna samarbeten med arkeologer och historiker. Geografiska områden jag har fokuserat på är främst Sverige och Peloponnesos i södra Grekland. Forskningsmetoder jag fördjupat mig inom är pollenanalys och OSL-datering.

Undervisning: Jag undervisar på kurser som behandlar kvartärgeologi och miljökunskap.

Ansvarsområden: Föreståndare för NEO, Navarino Environmental Observatory, Peloponnesos, Grekland; Laboratoriesäkerhetssamordnare; Ansvarig för sediment- och OSL laboratorierna på NG, Miljörepresentant, Ansvarig för brandfarlig vara.

Forskning

Publikationer på Google Scholar

 

 

Publikationer

I urval från Stockholms universitets publikationsdatabas

  • Mid-late Holocene vegetation history of the Argive Plain (Peloponnese, Greece) as inferred from a pollen record from ancient Lake Lerna

    2022. Cristiano Vignola (et al.). PLOS ONE 17 (7)

    Artikel

    This study provides a high-resolution reconstruction of the vegetation of the Argive Plain (Peloponnese, Greece) covering 5000 years from the Early Bronze Age onwards. The well dated pollen record from ancient Lake Lerna has been interpreted in the light of archaeological and historical sources, climatic data from the same core and other regional proxies. Our results demonstrate a significant degree of human impact on the environments of the Argive Plain throughout the study period. During the Early Bronze Age evidence of a thermophilous vegetation is seen in the pollen record, representing the mixed deciduous oak woodland of the Peloponnesian uplands. The plain was mainly used for the cultivation of cereals, whereas local fen conditions prevailed at the coring site. Towards the end of this period an increasing water table is recorded and the fen turns into a lake, despite more arid conditions. In the Late Bronze Age, the presence of important palatial centres modified the landscape resulting in decrease of mixed deciduous oak woodland and increase in open land, partly used for grazing. Possibly, the human management produced a permanent hydrological change at Lake Lerna. From the Archaic period onwards the increasing human pressure in association with local drier conditions caused landscape instability, as attested by a dramatic alluvial event recorded in the Pinus curve at the end of the Hellenistic Age. Wet conditions coincided with Roman times and favoured a forest regeneration pattern in the area, at the same time as we see the most intensive olive cultivation in the pollen record. The establishment of an economic landscape primarily based on pastures is recorded in the Byzantine period and continues until modern times. Overgrazing and fires in combination with arid conditions likely caused degradation of the vegetation into garrigue, as seen in the area of the Argive Plain today.

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  • Age, formation and significance of loess deposits in central Sweden

    2022. Thomas Stevens (et al.). Earth Surface Processes and Landforms 47 (14), 3276-3301

    Artikel

    Loess deposits are common in the mid-latitudes and are excellent records of past climate, landscape change and dust. However, loess deposits are seldom reported from Fennoscandia. Here we investigate two former glaciofluvial areas in central Sweden, Brattforsheden and Bonäsheden, where post-glacial loess and sand dune activity have been documented previously. Based on detailed mapping, grain size, scanning electron microscopy and optically stimulated luminescence dating analyses, we confirm the presence of loess deposits at the sites and extend the known area of loess coverage. Our results suggest that loess deposits are more common than previously thought in Sweden. The results also demonstrate that basal parts of the loess are often mixed with underlying sediment, which may be a common feature of thin loess deposits close to former ice margins. Quartz luminescence is well suited for dating these deposits, but ages from the mixed basal loess layers are older than expected, while ages from undisturbed loess extend to c. 5 ka. The loess ages contrast with the timing of main dune activity in these areas, which is dominantly in the 1–3 kyr post-deglaciation (c. 10.9–10.5 cal kyr BP). We suggest that either sediment mixing during soil formation is responsible for the mid-Holocene loess ages, or that the loess deposits record periodic landscape destabilization into the mid-Holocene. Furthermore, there is a clear topographic control on aeolian sedimentary facies, with loess mantling high ground and dunes restricted to valleys. Loess deposits are also primarily found to the south and southwest of source areas, implying transport from the north and east. This pattern contrasts with evidence for NW winds inferred from associated sand dunes. At present, the reasons for this mismatch are unclear, although one possible explanation is that silts deposited at higher elevations were affected by Ekman flow deflection of NW surface winds.

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  • MIS 3 age of the Veiki moraine in N Sweden – Dating the landform record of an intermediate-sized ice sheet in Scandinavia

    2022. Helena Alexanderson (et al.). Arctic, Antarctic and Alpine research 54 (1), 239-261

    Artikel

    The Veiki moraine in northern Sweden, a geomorphologically distinct landscape of ice-walled lake plains, has been interpreted to represent the former margin of an intermediate-sized pre–Last Glacial Maximum (LGM) Fennoscandian ice sheet, but its age is debated as either marine isotope stage (MIS) 5c or MIS 3. We have applied optically stimulated luminescence (OSL) and radiocarbon dating to four sites within the northern part of the Veiki moraine to establish its chronology. The radiocarbon ages provide only minimum ages and most OSL ages have low precision due to poor luminescence characteristics and problems with incomplete bleaching, leading to two alternative ages. In either case, the OSL dating places the Veiki moraine formation in MIS 3 (best estimate 56–39 ka). Sedimentation continued in the low-lying centers of some plateaus (ice-walled lake plains) during MIS 3 and during the Holocene, with a break during the Last Glacial Maximum when the area was ice covered. We speculatively constrain the broad timing further by relating the sequence of events to other climate records. We suggest that ice margin retreat to the west of the Veiki area took place during Greenland Interstadial (GI) 16.1 (58.0–56.5 ka) and that limited ice advances, which led to debris-covered ice margins in the Veiki zone, occurred during the following stadials GS-16.1 to 15.1 (56.5–54.2 ka). The GI-14 interstadial, which began 54.2 ka and lasted ~5.9 ka, could then be the period when the ice within the dead-ice landscape melted, first leading to ice-walled lakes and later to the inversed topography characteristic of the Veiki landscape. 

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  • Age and duration of a MIS 3 interstadial in the Fennoscandian Ice Sheet core area-Implications for ice sheet dynamics

    2021. Johan Kleman (et al.). Quaternary Science Reviews 264

    Artikel

    Previous assumptions of continuous ice cover of the core area of the Fennoscandian Ice Sheet, from Marine Isotope Stage 4 (ca. 70 ka) to the end of MIS 2 (ca. 12 ka), have been challenged by the discovery of several sites in central and northern Scandinavia with interstadial sediments of assumed MIS 3 age. The sequences have often been dated by Optically Stimulated Luminescence (OSL) and dates of around 55 ka are present at most sites, indicating ice-free conditions at this time. There is less consensus about the timing of the build-up and advance of the last (Late Weichselian) ice sheet after this ice-free stage. To address the duration of MIS 3 ice-free conditions in central Scandinavia, we reviewed available dating evidence. At the few sites where multiple OSL dates are available, ages indicate around 15 ka of ice-free conditions. Two studies employing cosmogenic nuclide dating of preserved interstadial ground surfaces both indicate a 20 ka long period of ice-free conditions during the last ice-free period before the Holocene. Our interpretation is that central Scandinavia became ice-free around 55 ka and remained so until c. 35 ka, when the Scandinavian Ice Sheet started to expand once again. Expansion started from a small-sized remnant ice sheet, or from separate remnant ice caps in Norway. Available data limits the size of any Scandinavian ice sheet remnant surviving the MIS 3 interstadial to less than 1 m of global sea-level equivalent.

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  • Evaluation of anhydrosugars as a molecular proxy for paleofire activity: A case study on a Holocene sediment core from Agios Floros, Peloponnese, Greece

    2021. Elin Norström (et al.). Organic Geochemistry 153

    Artikel

    The anhydrosugars, levoglucosan, mannosan and galactosan, are regarded as suitable molecular indicators of natural biomass combustion. Here, we evaluate summed anhydrosugars (SAS) as a paleofire indicator in a 6000 year-long fossil core from Agios Floros fen, Peloponnese, Greece, by analyzing charcoal fragments in parallel, throughout the sediment sequence. Modern surface soil samples from the same region were analysed for the presence of SAS, confirming the biomarker as an indicator of recent fire activity. The highest SAS concentrations in the fossil core were found in sections representing periods of wet conditions, both on local and regional scales and regionally widespread arboreal vegetation. Low amounts, or the absence, of SAS in the fossil core were associated with periods of dryness, regional dominance of non-arboreal vegetation and the presence of a fen rather than a lake ecosystem at the site. Micro-charcoal fragments were generally more abundant under these conditions. This suggests that SAS yield and deposition may vary with fuel availability and fire behavior, which in turn is affected by climate, local moisture and vegetation type. Forest fires result in more SAS compared to grass fires. SAS yield is also favored by low-temperature fires sustained under wet climate conditions. Preservation of SAS is likely to be compromised in the only seasonally wet fen ecosystem under the dry and warm Mediterranean climate conditions. The moist and shallow conditions in the wetland during hot summer months probably promote oxidation and biodegradation of the labile SAS molecules, compared to the more robust charcoal fragments. Thus, a multiproxy approach - using several proxies, both for fire, hydroclimate and vegetation change - is preferred when aiming to reconstruct past biomass burning from wetland ecosystems in a Mediterranean environment. The micro-charcoal record from Agios Floros reveals significant fire activity between 4400 and 2800 cal yr BP. This partly overlaps the Bronze Age period, associated with intense human environmental interaction and climate change in this area of Peloponnese, Greece.

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  • Patterns in recent and Holocene pollen accumulation rates across Europe - the Pollen Monitoring Programme Database as a tool for vegetation reconstruction

    2021. Vojtech Abraham (et al.). Biogeosciences 18 (15), 4511-4534

    Artikel

    The collection of modern, spatially extensive pollen data is important for the interpretation of fossil pollen assemblages and the reconstruction of past vegetation communities in space and time. Modern datasets are readily available for percentage data but lacking for pollen accumulation rates (PARs). Filling this gap has been the motivation of the pollen monitoring network, whose contributors monitored pollen deposition in modified Tauber traps for several years or decades across Europe. Here we present this monitoring dataset consisting of 351 trap locations with a total of 2742 annual samples covering the period from 1981 to 2017. This dataset shows that total PAR is influenced by forest cover and climate parameters, which determine pollen productivity and correlate with latitude. Treeless vegetation produced PAR values of at least 140 grains cm(-2) yr(-1). Tree PAR increased by at least 400 grains cm(-2) yr(-1) with each 10% increase in forest cover. Pollen traps situated beyond 200 km of the distribution of a given tree species still collect occasional pollen grains of that species. The threshold of this long-distance transport differs for individual species and is generally below 60 grains cm(-2) yr(-1). Comparisons between modern and fossil PAR from the same regions show similar values. For temperate taxa, modern analogues for fossil PARs are generally found downslope or southward of the fossil sites. While we do not find modern situations comparable to fossil PAR values of some taxa (e.g. Corylus), CO2 fertilization and land use may cause high modern PARs that are not documented in the fossil record. The modern data are now publicly available in the Neotoma Paleoecology Database and aid interpretations of fossil PAR data.

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  • Environment and climate change during the late Holocene in Hjaltadalur, Skagafjörður, northern Iceland

    2020. Magnus Hellqvist (et al.). Geografiska Annaler. Series A, Physical Geography 102 (1), 68-82

    Artikel

    We present an overview of the local environmental development of the valley of Hjaltadalur, situated in Skagafjorour, northern Iceland. The aim of this study is to increase the knowledge about the valley region before and during human settlement in the ninth century. Four mires were investigated after which the Viovik peat bog was selected as the main site for evaluating changes in climate and landscape. The master core from Viovik (V-325) was dated and studied further through sediment analysis, loss-on-ignition (LOI), and pollen analysis. According to the age-depth model, based on three radiocarbon dates and analysis of two tephra layers, the 325 cm long Viovik core comprises approximately 5500 years. In the pollen percentage record, there is a decrease in birch (Betula) and an increase in grass (Poaceae) in the central part of the core, between Hekla 3 horizon at c. 2800 BP and the next dated level at c. 2000 BP. This change corresponds well with previously outlined environmental fluctuations, showing a transition from warm and dry climate to cool and humid climate at this time. Human activity is mainly reflected by a distinct peak in Lactucae pollen in the uppermost part of the core. This change in vegetation corresponds with earlier studies, showing that the vegetation changed dramatically after the colonization of Iceland in the ninth century (during Landnam period, 870-930 AD). The present study shows that a decline in birch started well before human settlement, although the subsequent Viking Age and later settlements continued the deforestation trend.

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  • Landscape development at Lina myr fen, Eastern Gotland, 9000-2500 cal. yr BP

    2020. Nichola Ann Strandberg (et al.). The Holocene 30 (8), 1205-1219

    Artikel

    Using diatoms, pollen, and geochemistry, we explore human habitation around Lina myr, Gotland, in relation to shore displacement. Archeological evidence has shown that Lina myr was an important area for its prehistoric human inhabitants. We investigate if and when Lina myr was connected to the sea and could therefore have been part of an inland water system useful for transport. A chronology was based on C-14 AMS dating of terrestrial macrofossils and bulk sediments with dates ranging between 9100 and 2360 cal. yr BP. The initiation of the Littorina transgression was dated to 8500 cal. yr BP. A twofold pattern for the maximum sub-phase of the Littorina Sea is suggested from 8100 to 7500 cal. yr BP and from 6500 to 6000 cal. yr BP. The onset of cultivation and grazing was indicated by the presence of Hordeum and Plantago lanceolata in the pollen record during the Late Neolithic, at about 4580 cal. yr BP. During this time sea level was relatively higher than today and the Lina myr basin was connected with the Littorina Sea, which it continued to be until isostatic uplift caused it to become isolated at about 3820 cal. yr BP. After about 3000 cal. yr BP, human-made landscape changes intensified, grasslands increased, and shrublands decreased.

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  • Climate changes in the Eastern Mediterranean over the last 5000 years and their links to the high-latitude atmospheric patterns and Asian monsoons

    2019. Christos Katrantsiotis (et al.). Global and Planetary Change 175, 36-51

    Artikel

    This research aims to improve the knowledge of the mid to late Holocene climate changes and the underlying drivers in the eastern Mediterranean. We focus on the Peloponnese peninsula, SW Greece, characterized by a W-E rainfall/temperature gradient and a strong climate-sensitivity to shifts in the large-scale atmospheric patterns. A radiocarbon-dated sediment core, taken from the ancient Lake Lerna, a former lake in NE Peloponnese, was analyzed for distribution and hydrogen isotope (δD) composition of n-alkanes and bulk organic geochemistry (δ13C, TOC). The predominantly macrophyte (submerged/floating)-derived δD23 profile exhibits the largest long-term fluctuation in the record and co-varies with δD of long-chain n-alkanes providing evidence for precipitation and temperature changes over the last 5000 years. The Lerna δD23 signal is sometimes in agreement with other n-alkane δD records from SW Peloponnese indicating wetter conditions in the peninsula at ca 5000–4600, ca 4500–4100, ca 3000–2600 (more unstable in SW) and after ca 700 cal BP with drier periods at ca 4100–3900 and ca 1000–700 cal BP. Conversely, a NE-SW climate see-saw is revealed at ca 4600–4500, ca 3200, ca 2600–1800, and ca 1200–1000 cal BP when the δD23 Lerna exhibits more positive trends (drier in NE) with a reversal at ca 3900–3300, ca 3200–3000 and ca 1800–1300 cal BP. These opposing and sometimes similar signals between NE and SW Peloponnese can be explained by the relative dominance of high-latitude atmospheric patterns over the peninsula. A similar signal would be expected when the North Atlantic Oscillation (NAO) exerts the main control with NAO (+) creating conditions of reduced moisture. The dipole pattern is likely driven by shifts in North Sea–Caspian Atmospheric pattern (NCP), which account for the present-day regional climate variability with NCP (+) leading to wetter and colder conditions in NE Peloponnese. The Asian monsoonal system likely has an additional impact on the δD variabilities through influencing the summer temperatures. There is a consistency between the Peloponnesian δD signals and monsoonal records after ca 4000 cal BP confirming the actualistic models. Strong monsoonal periods coincide with cooler summers (lower δD values) in Lerna, due to the northerly winds, the Etesians. On the contrary, SW Peloponnese is dominated by warmer conditions during the same periods as the area is located on the lee side of the mountain and highly influenced by the adiabatic warming associated with the subsidence over the Eastern Mediterranean.

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  • Widespread global peatland establishment and persistence over the last 130,000 y

    2019. Claire C. Treat (et al.). Proceedings of the National Academy of Sciences of the United States of America 116 (11), 4822-4827

    Artikel

    Glacial-interglacial variations in CO2 and methane in polar ice cores have been attributed, in part, to changes in global wetland extent, but the wetland distribution before the Last Glacial Maximum (LGM, 21 ka to 18 ka) remains virtually unknown. We present a study of global peatland extent and carbon (C) stocks through the last glacial cycle (130 ka to present) using a newly compiled database of 1,063 detailed stratigraphic records of peat deposits buried by mineral sediments, as well as a global peatland model. Quantitative agreement between modeling and observations shows extensive peat accumulation before the LGM in northern latitudes (> 40 degrees N), particularly during warmer periods including the last interglacial (130 ka to 116 ka, MIS 5e) and the interstadial (57 ka to 29 ka, MIS 3). During cooling periods of glacial advance and permafrost formation, the burial of northern peatlands by glaciers and mineral sediments decreased active peatland extent, thickness, and modeled C stocks by 70 to 90% from warmer times. Tropical peatland extent and C stocks show little temporal variation throughout the study period. While the increased burial of northern peats was correlated with cooling periods, the burial of tropical peat was predominately driven by changes in sea level and regional hydrology. Peat burial by mineral sediments represents a mechanism for long-term terrestrial C storage in the Earth system. These results show that northern peatlands accumulate significant C stocks during warmer times, indicating their potential for C sequestration during the warming Anthropocene.

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  • Eastern Mediterranean hydroclimate reconstruction over the last 3600 years based on sedimentary n-alkanes, their carbon and hydrogen isotope composition and XRF data from the Gialova Lagoon, SW Greece

    2018. Christos Katrantsiotis (et al.). Quaternary Science Reviews 194, 77-93

    Artikel

    Understanding past hydroclimate variability and related drivers is essential to improve climate forecasting capabilities especially in areas with high climatic sensitivity, such as the Mediterranean. This can be achieved by using a broad spectrum of high resolution, multiple proxy records which can also allow us to assess linkages between regional hydroclimate variability and shifts in the large-scale atmospheric patterns. Here, we present a multiproxy reconstruction of the central-eastern Mediterranean hydro climate changes over the last 3600 years based on a sediment core from the Gialova Lagoon, a shallow coastal ecosystem in SW Peloponnese, Greece. Our combined dataset consists of the distribution and compound-specific carbon and hydrogen isotope (delta C-13 and 8D) composition of n-alkanes, bulk organic matter properties and X-ray fluorescence (XRF) core scanning data. This approach was complemented with a semi-quantitative analysis of plant remains in the core. The results indicate a high contribution of local aquatic vegetation to organic matter. Large delta C-13 variations in predominantly aquatic plant-derived mid-chain alkanes (C23-23) mainly reflect changes in the aquatic plant abundance and their carbon source. Our data suggest that higher delta C-13(23-25) values (up to 19 parts per thousand) largely correspond to expansion of aquatic vegetation during wet and/or cold periods causing carbon-limiting conditions in the water and assimilation of isotopically-enriched bicarbonate by the plants. The 8D records of the individual n-alkanes (C-17 to C-31) exhibit a nearly identical pattern to each other, which implies that they all reflect changes in the source water isotope composition, driven by hydroclimate variability. In addition, the 8D profiles are consistent with the XRF data with both proxies being driven by a common hydroclimate signal. We observe two major shifts from dry and/or warm periods at ca 3600-3000 cal BP and ca 17001300 cal BP to wet and/or cold episodes at ca 3000-2700 cal BP and ca 1300-900 cal BP. The period ca 700-200 cal BP is the wettest and/or coldest in our record and coeval with the Little Ice Age. The climatic fluctuation reported in this study can be explained by the relative dominance of high-latitude (e.g. North Atlantic Oscillation during winters) and the low-latitude atmospheric patterns (Intertropical convergence zone, Subtropical High and the effects of Asian monsoons during summers) which suggests an Atlantic-Mediterranean-Monsoon climate link in this area for the late Holocene.

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  • Eight years of annual pollen monitoring in northern Sweden, from the boreal forest to above the birch forest-line

    2013. Martina Hattestrand. Grana 52 (1), 26-48

    Artikel

    Pollen deposition during 1997-2004 was monitored for seven sites in northern Sweden, ranging from the boreal forest zone to above the birch forest-line. Fifty-three taxa were recorded in the traps. Of these, 22 are observed in the vegetation surrounding the trap sites. The remaining 31 taxa are most probably long distance transported. Taxa that strongly correlate with the site above the birch forest-line are Trientalis europaea, Asteraceae, Ericales and Linnaea borealis, while pollen of Pinus, Picea, Betula, Alnus and Juniperus correlates with sites within the boreal forest zone. A positive correlation is noted between pollen accumulation rates (PARs) of Pinus and Picea and mean July temperatures of the year prior to pollen release. A comparison between pollen counts retrieved from pollen traps, lake surface sediments and moss polster samples at one site shows similar pollen composition for the pollen trap and lake surface sediments, while the moss polster samples have higher percentage of Pinus pollen, lower percentage of Betula pollen and generally a lower diversity of pollen and spores.

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  • Weichselian interstadials at Riipiharju, northern Sweden - interpretation of vegetation and climate from fossil and modern pollen records

    2010. Martina Hättestrand, Ann-Marie Robertsson. Boreas 39 (2), 296-311

    Artikel

    The most complete records of Weichselian ice-free conditions in northern Sweden have been retrieved from kettleholes in the Riipiharju esker. In an earlier study, the Riipiharju I core was described as containing two Weichselian interstadials and Riipiharju was chosen as type site for the second Weichselian interstadial in northern Sweden. Here, we present a palynological investigation of two new sediment cores (Riipiharju II and III) retrieved from Riipiharju. Together, the new cores comprise a late cold part of the first Weichselian interstadial recorded in northeastern Sweden (Tarendo I, earlier correlated with Perapohjola in Finland) as well as a long sequence of the second Weichselian interstadial (Tarendo II, earlier named Tarendo). The results indicate that the climate during deposition of the Tarendo II sequence was more variable than earlier suggested. According to the present interpretation it was relatively warm in the early part of Tarendo II; thereafter a long cold phase persisted, and finally the climate was warmer again in the late part of Tarendo II. The warm phases are characterized by Betula-dominant pollen assemblages, while the cold phase is characterized by high percentages of Artemisia and Gramineae pollen. Since there is still no firm chronology established of the interstadials in northeastern Sweden, two possible correlations are discussed; either Tarendo I and II are correlated with Brorup (MIS 5c) and Odderade (MIS 5a), or, perhaps more likely, they are correlated with Odderade and early Middle Weichselian (MIS 3) time.

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