Hans Linderson

A 10,000-Year Record of Arctic Ocean Sea-Ice Variability-View from the Beach

Sea-ice coverage near northern Greenland and in the western Arctic Ocean varied in opposition over much of the Holocene. We present a sea-ice record from northern Greenland covering the past 10,000 years. Multiyear sea ice reached a minimum between ~8500 and 6000 years ago, when the limit of year-round sea ice at the coast of Greenland was located ~1000 kilometers to the north of its present position. The subsequent increase in multiyear sea ice culminated during the past 2500 years and is linked to an increase in ice export from the western Arctic and higher variability of ice-drift routes. When the ice was at its minimum in northern Greenland, it greatly increased at Ellesmere Island to the west. The lack of uniformity in past sea-ice changes, which is probably related to large-scale atmospheric anomalies such as the Arctic Oscillation, is not well reproduced in models. This needs to be further explored, as it is likely to have an impact on predictions of future sea-ice distribution.

Influence of annual weather on growth of pedunculate oak in southern Sweden

Abstract• A network of oak (Quercus robur L.) chronologies containing 49 sites and 635 single trees was analysed to identify weather variables affecting annual tree-ring increment dynamics in southern Sweden during 1860–2000.• We analysed (1) the growth response of oak to non-extreme weather, and (2) the temporal and spatial patterns of regional growth anomalies (pointer years) and associated climatic extremes resolved on a monthly scale.• Growth was controlled by precipitation in the current (June–July) and the previous growing season (August) in 48% and 22% of all sites, respectively. Temperature during July of the current year and August of the previous year was negatively correlated with growth in 29% and 43% of the sites, respectively. Growth was positively correlated with temperature in October of the previous season in 72% of the sites. The most extensive growth anomaly occurred in 1965 and was probably caused by intrusion of cold Arctic air masses into the region at the end of March that year.• During climatically non-extreme years, oak growth is driven mostly by the dynamics of summer precipitation. Many of the negative growth anomalies, however, were associated with temperature extremes. Southern Swedish oak pointer years tend not to coincide with the pan-European oak pointer years.Résumé• Une série de chronologies de chênes (Quercus robur L.) comprenant 49 stations et 635 arbres individuels a été analysée pour identifier les variables climatiques affectant la dynamique de croissance annuelle des cernes dans le Sud de la Suède, pendant la période 1860–2000.• Nous avons analysé (1) la réponse de croissance des chênes aux événements météorologiques non extrêmes et (2) les patrons temporels et spatiaux des anomalies régionales de croissance (années indices) et les extrêmes climatiques associés au pas de temps mensuel.• La croissance était contrôlée par les précipitations de la saison de végétation (juin–juillet) et les précipitations de la saison de végétation précédente (août), respectivement dans 48 % et 22 % de toutes les stations. Les températures du mois de juillet de la saison de végétation et du mois d’août de l’année précédente étaient corrélées négativement avec la croissance, respectivement dans 29 % et 43 % des stations. La croissance était corrélée positivement avec la température du mois d’octobre de l’année précédente dans 72 % des stations. L’anomalie de croissance la plus considérable est arrivée en 1965 et a été causée probablement par l’intrusion de masses d’air froid arctique dans la région, à la fin du mois de mars.• Pendant les années climatiquement non-extrêmes, la croissance du chêne est principalement commandée par la dynamique des précipitations estivales. Cependant, beaucoup d’anomalies négatives de croissance ont été associées avec des extrêmes de température. Les années indices du Sud de la Suède ont tendance a ne pas coïncider avec les années indices pan-européennes.

A dendrochronological study of the exploitation and transformation of a boreal forest stand

The history of a pine dominated (Pinus sylvestris L.) forest stand in northern Sweden was documented by applying dendrochronological crossdating technique on stumps, down logs and living trees with...

Lifespan and mortality of old oaks – combining empirical and modelling approaches to support their management in Southern Sweden

Abstract• Old oaks (Quercus robur L.) play an important role in the southern Scandinavian landscape by providing habitat for a wide range of species, a large proportion of them being currently on the National Redlists.• To provide support for the management of these trees, we review data on oak mortality and formulate a mortality-driven stochastic model analysing interactions between mortality rate, oak recruitment rate into 100–150 age class, and amount of oaks older than 200 years.• Empirical annual mortality rates varied between 0 and 13% with average 1.68%. Trees older 200 years had an average mortality rate of 1.1%. Oaks in the high density forests showed higher mortality (3.2%) as compared to the trees growing in the low density forests (1.2%). A 400-year long modelling exercises indicated that under current mortality rates (regular mortality being centred around 1% annually; and irregular mortality 7% with average return time of 13 years) the long-term maintenance of 20 trees older than 200 years per ha would require an input rate of 1 to 5 trees × year−1 × ha−1 into the 100–150 years old class.• The modelling highlighted the importance of initial oak abundance affecting amount of old trees at the end of shorter (100 years) simulation period.Résumé• Les vieux chênes (Quercus robur L.) jouent un rôle important dans le paysage du sud de la Suède en procurant un habitat pour un large éventail d’espèces, une grande proportion d’entre elles étant actuellement dans les Listes rouges nationales.• Pour appuyer la gestion de ces arbres, nous avons examiné les données relatives à la mortalité des chênes et formulons un modèle stochastique de mortalité analysant les interactions entre taux de mortalité, taux de recrutement des chênes dans les classes 100–150 ans et total des chênes plus vieux que 200 ans.• Les taux empiriques de mortalité ont varié entre 0 et 13 % avec une moyenne de 1,68 %. Les arbres de plus de 200 ans présentaient un taux de mortalité de 1,1 %. Dans les plus fortes densités forestières les chênes montraient une mortalité plus élevée (3,2 %) comparativement aux arbres poussant dans des forêts de densité plus faible (1,2 %). Des exercices de modélisation sur 400 ans ont indiqué qu’en dessous d’un taux courant de mortalité (mortalité courante annelle centrée autour de 1 % et mortalité irrégulière de 7 % avec un temps de retour de 13 ans) la maintenance à long terme de 20 vieux arbres par hectare demanderait un taux d’apport de 1 à 5 arbres par an et par hectare dans les classes d’âge de 100 à 150 ans.• Cette modélisation met l’accent sur l’importance de l’abondance initiale des chênes qui affecte la totalité des vieux arbres à la fin d’une période courte de simulation (100 ans).

The climatic significance of clastic varves in the Ångermanälven Estuary, northern Sweden, AD 1860 to 1950

Multiple regression analyses were applied to decipher the correlation between monthly discharge, precipitation and temperature records and annual varve-thickness data from river Ångermanälven north-central Sweden between 1860 and 1950. Over the whole 90-year period we found generally a strong correlation between spring/summer precipitation and annual varve thickness. However, there are clear indications that precipitation during the months of January and March–May was more important for the formation of varves in the early part of the twentieth century, while January, March, April and June seem to have been more significant during the later part of the nineteenth century. Monthly temperatures and annual varve thickness, on the other hand, did not show any significant correlations over the whole 90-year period, but, when split into 30-year periods, a dependence of varve thickness on October (1862–90) and March (1919–50) temperatures could be observed. Our results show that it is important to test each specific varve record against instrumental data sets before any conclusions can be drawn in terms of precipitation and/or temperature dependence. They also emphasize the necessity to correlate varve-thickness records against long instrumental series in order to detect any changing forcing mechanisms.

Late-Holocene expansion of a south Swedish peatland and its impact on marginal ecosystems: Evidence from dendrochronology, peat stratigraphy and palaeobotanical data

In this study, a reconstruction of the long-term development and lateral expansion of a south Swedish peat bog was performed using a multi-proxy approach, including dendrochronology, peat stratigraphy and macrofossil and pollen analyses. By combining mapping of cross-dated subfossil trees with radiocarbon-dated peat sequences, an improved approach to reconstruction of lateral peat expansion was applied. Apart from providing approximate ages of tree burial episodes, the ring-width records offer information on hydrological variations prior to the bog expansion. New bog oak, pine and alder chronologies are presented and their potential as a dating tool for peatland expansion as well as for local to regional environmental interpretations is examined. Our tree-replication records show that increased amounts of bog trees in the central parts can be linked to drier bog-surface conditions, whereas an increase in wood remains in the marginal zone is related to enhanced preservation due to lateral bog expansion. Our reconstructions of the development of the peat deposit and associated changes in the distribution of vegetation communities provide new insight into peatland responses to climate change at the end of the ‘Holocene Thermal Maximum’ (5000–4000 cal. yr BP).

Submarginal drumlin formation and late Holocene history of Fláajökull, southeast Iceland

ABSTRACT Fláajökull is a non-surging outlet glacier draining the south-eastern part of the Vatnajökull, southeast Iceland. Fláajökull was stationary or advanced slightly between 1966 and 1995 and formed a prominent end moraine. Glacial retreat since then has revealed a cluster of 15 drumlins. This study focuses on the morphology and sedimentology of the drumlins. They are 100–600 m long, 40–130 m wide, and have cores of glaciofluvial sediment or till. The drumlins are draped by ~1 m thick, massive subglacial traction till. The glacier forefield is characterized by a number of arcuate and saw-tooth, terminal and recessional moraine ridges, overridden moraines with fluted surfaces, and glaciofluvial outwash. Some of the drumlins extend towards the 1995 end moraine but terminate abruptly at the moraine and are not observed in front of it. This suggests that they were formed sub-marginally during the 1966–1995 terminal position. The sedimentary structure of the drumlins is best explained by the sticky spot model. Dating and dendrochronological analyses of birch logs found on the surface of one of the drumlins indicate that the valley was forested about 2100 calendar year BP, after which the glacier started to reform, possibly due to an abrupt change in climate.

Disrupted vegetation as a response to Jurassic volcanism in southern Sweden

Abstract Central Skåne (Scania) in southern Sweden hosts evidence of extensive Jurassic volcanism in the form of mafic volcanic plugs and associated volcaniclastic deposits that entomb well-preserved macro-plant and spore–pollen assemblages. Palynological assemblages recovered from the Höör Sandstone are of Hettangian–Pliensbachian age and those from the overlying lahar deposits are dated as Pliensbachian–early Toarcian (?). Palynomorph assemblages from these units reveal significantly different ecosystems, particularly with respect to the gymnospermous components that represented the main canopy plants. Both palynofloras are dominated by osmundacean, marattiacean and cyatheacean fern spore taxa but, whereas the Höör Sandstone hosts abundant Chasmatosporites spp. pollen produced by plants related to cycadophytes, the volcanogenic deposits are dominated by cypress family pollen (Perinopollenites) with an understorey component rich in putative Erdtmanithecales (or possibly Gnetales), and collectively representing vegetation of disturbed habitats. Permineralized conifer wood attributed to Protophyllocladoxylon sp., belonging to plants that probably produced the abundant Perinopollenites grains, is abundant in the volcanigenic strata, and shows sporadic intraseasonal and multi-year episodes of growth disruption. Together with the relatively narrow but marked annual growth rings, and the annual and mean sensitivity values that span the complacent–sensitive domains, these features suggest growth within Mediterranean-type biomes subject to episodic disturbance.

Shoreline displacement and human resource utilization in the southern Baltic Basin coastal zone during the early Holocene: New insights from a submerged Mesolithic landscape in south-eastern Sweden

Along parts of the Hanö Bay coast in south-eastern Sweden, remains of a submerged landscape can be found down to depths of almost 25 m b.s.l. The coastal landscape was formed during two periods of lowered water levels in the Baltic Basin: the Yoldia Sea and the Initial Littorina Sea stages. In order to reconstruct the local environment and shoreline displacement during the Yoldia Sea and Ancylus Lake stages, sediment sequences were obtained at 4.5, 17.5 and 18.7 m b.s.l. Detailed bathymetric mapping was based on multi-beam echo-sounding while surveillance and sampling of tree remains and archaeological findings were performed through diving. The Yoldia Sea low-stand reached its minimum level at 24–25 m b.s.l. just before 10,800 cal. BP. During the subsequent Ancylus transgression, a slow-flowing river passed through the area, accumulating thick deposits of fine-grained organic sediments in lagoonal basins. The river was surrounded by open woodland dominated by pine. Based on successive flooding of rooted tree stumps, the transgression rate was estimated at 4 cm·yr−1, until the Ancylus high-stand was reached at 5 m b.s.l. at 10,400–10,300 cal. BP. Findings of worked aurochs and beaver bones provide evidence of human presence in the landscape and show the importance of terrestrial resources for their subsistence. These integrated palaeoecological and archaeological investigations demonstrate the importance of submerged landscapes with well-preserved sediment, wood and bone material for our understanding of southern Baltic coastal landscapes and their inhabitants during the Early Mesolithic.

Early Holocene Landscape Development and Baltic Sea History Based on High-Resolution Bathymetry and Lagoonal Sediments in the Hanö Bay, Southern Sweden

The Baltic basin has experienced extensive water-level fluctuations since the last deglaciation. During two occasions of lower than present water levels, c. 11,700–10,200 and 9800–8000 cal BP, areas along the present-day coast of the Hano Bay in south-eastern Sweden were exposed and pine-dominated forests were established. Around the mouth of the Verkean River at the Havang site, remains of this landscape occur in the form of organic-rich lacustrine deposits and well-preserved stumps and trunks of pine trees, reaching depths of 21 m and distances from the present coastline of around 3 km. This study aims at refined reconstructions of the dynamic Early Holocene environment and shore-level displacement to increase the understanding of how Mesolithic people exploited the landscape. Stratigraphic analyses were performed on a sediment sequence obtained from an organic-rich deposit situated at 8.3 m water depth, aided by detailed bathymetric surveys. Radiocarbon dates obtained from the 3.6 m long sequence, supported by pollen stratigraphic correlation, indicate deposition during the period 9000–8600 cal BP with an unusually high sediment accumulation rate. As indicated by a consistently high organic matter content, stable C/N ratios and a general lack of coarse mineral matter, the sediments were deposited in a low-energy environment. Our preliminary interpretation is that the organic-rich deposit was formed in a highly productive oxbow lake, connected via a shallow threshold to the Verkean River, only allowing fine-grained, fluvially transported particles to reach the depositional environment. As indicated by numerous Mesolithic artefacts in the area, the dynamic landscape at the Havang site with its rich fishing waters and access to fresh water must have been attractive to Mesolithic hunter-gatherers. People had to adapt to the changing water levels and climatic conditions during the Early Holocene, and traces of their presence are preserved as a consequence of the accumulation of organic-rich fluvial deposits around the river mouth.