Jørn Bjarke Torp Pedersen

Holocene changes in climate and vegetation in the Ammassalik area, East Greenland, recorded in lake sediments and soil profiles

Abstract Geografisk Tidsskrift, Danish Journal of Geography 108(1):21–50, 2008 Holocene climatic, vegetational and environmental changes on the Ammassalik Island in SE Greenland (65.5 N and 37.5 W) have been studied in lake sediments and soil profiles. Based on the stratigraphy of sediments, geobiochemical characteristics, pollen and other biological proxies, a history of the land is outlined. The overall and continued climatic cooling during the Holocene basically seems to be orbitally controlled and due to both decreasing annual and summer insulations. The very early Holocene, concurrent with and following the final postglacial melting of glaciers in the landscape, appears to have experienced the warmest Holocene summer conditions, ice-free seas and limited snow covers. The climate situation seems to have been to a considerable extent based on internal regional meteorological processes and largely without strong and regular cyclonic impacts from lower latitudes. Generally decreasing insulation, a still colder landscape and near coastal sea, potentially further cooled by the negative albedo feedback from snow and ice, generally increase a gradient driven circulation of heat and moisture northwards in the western part of the North Atlantic. Counteracting this southerly influx of heat and moisture, will be the blocking effect of a snow and ice-covered region, resulting in decreasing precipitation and probably slightly increasing net radiation in landscapes. A framework and a climatic system are created to characterize the environmental changes of the latest 4–5 millennia. There has presumably been a continuous cooling trend interrupted by both spells and somewhat longer periods of renewed and stronger southerly influxes, relatively warmer conditions, higher precipitation and less sea ice.

Total sediment budget of a transgressive barrier-spit, Skallingen, SW Denmark: A review

Abstract Average sea-level rise in the northern part of the Danish Wadden Sea has been 1.3 mm a−1 during the last 100 years but during the last 25 years a rise of 4.2 mm a−1 was observed. Concurrent with the recent sea-level rise the Skallingen barrier spit has migrated landward by 3–5 m a−1. Long term sediment budgets for each of the morphological units involved in the migration are reviewed (e.g. onshore in the shore face +90.000 m3 a−1, longshore -641.000 m3 a−1, foredunes +65,000 m3 a−1, overwash fan including shorenormal dunes +11,000 m3 a−1, spit terminus -96,000 m3 a−1, tidal flat + 10,000 m3 a−1 and backbarrier salt marsh +33,000 m3 a−1) and used to establish the relative importance of sediment transport processes involved in barrier migration. Strong interannual variations exist in the long term budget making evaluation of barrier behaviour based on short term measurements doubtful. In a cross shore sense the barrier spit is accreting in spite of the sea level rise. This is specially pronounced at an active overwash fan. However, due to substantial sediment losses to longshore transport the barrier, gets narrower and shorter during its transgressive behaviour. This may indicate that preservation of barriers in the geological record during rapid sea level rise is promoted when sediment loss to longshore transport is insignificant.

Multidecadal Shoreline Changes in Denmark

ABSTRACT Kabuth, A.K.; Kroon, A., and Pedersen, J.B.T., 2014. Multidecadal shoreline changes in Denmark. Multidecadal shoreline changes along ca. 7000 km coastline around Denmark were computed for the time interval between 1862 AD and 2005 AD and were connected with a geomorphological coastal classification. The shoreline data set was based on shoreline positions from historical and modern topographic maps. Coastal landforms were identified on a digital terrain model in combination with aerial photographs. Two shoreline-change computation methods were evaluated at a test site, aiming for optimized time efficiency and accuracy of the countrywide application: a Nearest Neighbor search and a cross-shore transect method based on the ArcGIS-based Digital Shoreline Analysis System (DSAS). The cross-shore transect method was more robust and performed better in the detection of local extremes in shoreline changes, which was crucial for the scope of the mapping. Countrywide shoreline-change distances and rates were, therefore, computed with the DSAS method. Patterns in coastline dynamics were identified through the connection of shoreline-change rates with the occurrence of coastal landforms. Short-term changes and alterations of shoreline evolution through coastal structures were not resolved in this study. Because of the long time span covered, the relative errors originating from data and method are acceptable. The scope of the mapping was to provide a coastal management tool that allows screening for critical sites with respect to coastal erosion. As the first countrywide quantification of historical shoreline changes around Denmark, the mapping can contribute to enhanced adaptation and mitigation strategies in response to increased risks of erosion and flooding under a changing climate.

The Northeast Greenland Sirius Water Polynya dynamics and variability inferred from satellite imagery

Abstract Geografisk Tidsskrift—Danish Journal of Geography 110(2):131–142, 2010 One of the most prominent polynyas in Northeast Greenland, already noted by the early expeditions in the area, is located around Shannon Ø and Pendulum Øer between 75° and 74°N in the transition zone between the fast ice and pack ice. This study names the polynya the ‘Sirius Water Polynya’, and examines its spatial and temporal dynamics by analysis of recent satellite imagery, modelled meteorological data and historical data covering the last decade. The dominating mechanisms to form and sustain the polynya are inferred and the persistence and inter-annual variability of the phenomenon are estimated. The polynya formation is predominantly governed by mechanical forcing caused by northerly gales, and it is classified as a wind-driven shelf water polynya. A marked seasonal difference in the surface wind field, together with the obvious seasonal cycle in insolation, creates distinct winter and summer regimes in the seasonal evolution of the polynya. During the winter regime, both the size of and the ice cover within the polynya varies significantly on a temporal and spatial scale. Intermittent wind-driven openings of the polynya alternate with periods of increasing ice cover. Some of the most persistent areas of open water in the polynya coincide with locations where significant concentrations of spring and summer settlements from the Thule Inuit culture (AD 1400–1850) are observed, indicating a connection between the presence of the polynya and the Thule Inuit living in the area in prehistoric times.

At the edge. High Arctic Walrus hunters during the Little Ice Age

A multi-disciplinary study of settlement in north-east Greenland found that life in this High Arctic zone was actually favoured by the climate brought in by the Little Ice Age (fifteenth–nineteenth century). Extensive ice cover meant high mobility, and the rare polynyas — small patches of permanently open coastal water — provided destinations, like oases, where huge numbers of migrating marine mammals and birds congregated. One such place was Walrus Island on Sirius Water, a veritable processing plant for walrus, where every spring Thule people stocked up meat supplies that would get the rest of the region through the winter. It was a further drop in the temperature in the mid nineteenth century that led to the region being abandoned.

Fluctuations of sediment accumulation rates in front of an Arctic delta in Greenland

An automated layer counting technique is developed to estimate the chronology of a marine sediment core and this technique is validated with Pb210 chronology. The marine sediment core was sampled in front of the delta of Mittivakkat Glacier meltwater river in the Sermilik Fjord, SE Greenland, and is a proxy of the sediment delivery from a glacial drainage basin to a fjord. The estimated time series was based on automatic lamination detection (varves) on a line scan of the core using gray scale intensities, and covered the last two centuries. The estimated time series of sediment accumulation rates was coupled to modelled runoff from the Mittivakkat Glacier and compared with local climatic parameters (air temperature and precipitation) and with the Atlantic Multidecadal Oscillation (AMO) index. Maxima in the sediment accumulation rate at the bottom of the side-fjord, about 1 km from the delta, mostly depended on glacier ablation and consequently on changes in river runoff, which were initiated by the air temperature. This was especially the case during transition from colder periods towards warmer, where short-lived maxima in sediment accumulation rates were followed by lower rates, even though the temperature remained high. This suggested a quite rapid glacial response to changes in climatic forcing, and/or a hysteresis effect, where sediment stored in the glacier/valley system was evacuated soon after a temperature dependent increase in discharge. The air temperature was in turn controlled by the AMO index.

Coastal environments around Thule settlements in Northeast Greenland

Abstract Geografisk Tidsskrift—Danish Journal of Geography 110(2):143–154, 2010 Inuit have travelled to and settled in the coastal landscapes of Northeast Greenland for several longer periods during the latest ca. 4500 years. Most recently the Thule culture Inuit lived in the region from around 1400 until 1850 AD. The access to partly and periodically ice covered near coastal waters has been crucial to the primarily marine based subsistence strategy of the Thule Inuit culture, and their settlements are therefore found immediately at the coast. Changing geological and geomorphologic settings strongly influence the coastal morphodynamics, and only specific locations offer stable and protected conditions needed for proper winter settlements. The comprehensive study of coastal environments and Thule culture winter settlements in the Young Sound region show an accumulation of winter settlements, nearly all located either in protected pocket beaches or on stable basalt capes. The Thule culture abandoned Northeast Greenland about 1850 AD, and apart from settlements on basalt capes, most of the winter settlement sites in pocket beach areas have been affected by erosion of local character and in some cases also affected by increasing wave erosion during recent periods of less ice in near coastal waters.

A late Holocene palaeoenvironmental record from Altona Bay, St. Croix, US Virgin Islands

Abstract Geografisk Tidsskrift, Danish Journal of Geography 108(2):59–70, 2008 A reconstruction of the palaeoenvironmental development of Altona Bay, St. Croix, northeastern Caribbean, has been made based on the sedimentological, geochemical and pollen analyses of a 1.83 m long vibracore. For chronological control, AMS 14C measurements were made at 5 levels downcore. The sedimentary sequence covers the last c. 4,700 years, containing both (mangrove) peat and fine-grained clastic sediment units. Comparison with regional Holocene sea level data demonstrates a gradual marine flooding of a mangrove environment around 3,500 cal BP was presumably related to a regional late Holocene sea-level rise, from a position, c. 2 m lower than present. After a c. 1,000 year period of marine sedimentation lasting until c. 2,500 cal BP, renewed formation of tropical wetland occurred at the site. This development may be attributed to the increased isolation of the shallow Altona Bay, most likely due to sea- ward formation of a well-developed spit system and possibly under the influence of enhanced storm-wave action in the period between c. 4,000 and 2,200 cal BP. Since the 1960s the repeated passage of severe hurricanes (e.g. Hugo, 1989) has had a significant impact on the sedimentation pattern of the bay and has caused a major hiatus and the recent deposition of sediments immediately overlying the c. 2,500 year old peat.

MORPHODYNAMIC EVOLUTION OF TWO DELTAS IN ARCTIC ENVIRONMENTS, EAST COAST OF GREENLAND

Changes in fluvial channel patterns on deltas have a significant impact on the coastal morphology along its fringes. Lateral channel migration can locally cause cliff erosion and introduce an extra sediment source in the local budget of an active delta plain. Stabilization of channels or even channel lobe switching reduce the fluvial impact on the delta and introduce the formation of beach ridges and spits along the (former) delta edge. These accumulative features are formed in the ice-free summer periods and fed by alongshore sediment input from adjacent shores due to wave-driven alongshore currents, and by the reworking of the sediments on the delta plain by wavedriven cross-shore processes.

Commercial hunting activities in the Greenland Sea: The impact of the European blubber industry on East Greenland Inuit societies/Optically Stimulated Luminescence dating of Inuit settlement structures in coastal landscapes of Northeast Greenland

Geografisk Tidsskrift—Danish Journal of Geography 110(2):357–363, 2010 Geografisk Tidsskrift—Danish Journal of Geography 110(2):365–371, 2010