Jonas H Akerman | Lund University (original) (raw)

Uploads

Papers by Jonas H Akerman

Ecosystems along the 0 degree C mean annual isotherm are arguably among the most sensitive to cha... more Ecosystems along the 0 degree C mean annual isotherm are arguably among the most sensitive to changing climate. When the temperature goes from below to above 0 degree C for more than two subsequent years permafrost moves out of equilibrium with the climate and starts thawing. This in itself provide an early warning of a warming climate while the permafrost

Monitoring of permafrost has been ongoing since 1978 in the Abisko area, northernmost Sweden, whe... more Monitoring of permafrost has been ongoing since 1978 in the Abisko area, northernmost Sweden, when measurements of active layer thickness started. In 1980, boreholes were drilled in three mires in the area to record permafrost temperatures. Recordings were made twice per year, and the last data were obtained in 2002. During the International Polar Year (2007-2008), new boreholes were drilled within the 'Back to the Future' (BTF) and 'Thermal State of Permafrost' (TSP) projects that enabled year-round temperature monitoring. Mean annual ground temperatures (MAGT) in the mires are close to 0°C, ranging from -0.16 to -0.47°C at 5 m depth. Data from the boreholes show increasing ground temperatures in the upper and lower part by 0.4 to 1°C between 1980 and 2002. At one mire, permafrost thickness has decreased from 15 m in 1980 to ca. 9 m in 2009, with an accelerating thawing trend during the last decade.

Permafrost and Periglacial Processes, 2020

Active layer probing in northern Sweden, northeast Greenland, and central Svalbard indicates acti... more Active layer probing in northern Sweden, northeast Greenland, and central Svalbard indicates active layer thickening has occurred at Circumpolar Active Layer Monitoring (CALM) sites with long‐term, continuous observations, since the sites were established at these locations in 1978, 1996, and 2000, respectively. The study areas exhibit a reverse latitudinal gradient in average active layer thickness (ALT), which is explained by site geomorphology and climate. Specifically, Svalbard has a more maritime climate and thus the thickest active layer of the study areas (average ALT = 99 cm, 2000–2018). The active layer is thinnest at the northern Sweden sites because it is primarily confined to superficial peat. Interannual variability in ALT is not synchronous across this Nordic Arctic region, but study sites in the same area respond similarly to local meteorology. ALT correlates positively with thawing degree days in Sweden and Greenland, as has been observed in other Arctic regions. How...

Permafrost and Periglacial Processes, 2016

The thermal regime of permafrost is sensitive to changes in the climate system. A common, researc... more The thermal regime of permafrost is sensitive to changes in the climate system. A common, research-based understanding of the permafrost distribution at a sufficient spatial resolution is important to meet scientific, educational and societal demands. We present a new permafrost map for Norway, Sweden and Finland providing a more detailed and updated description of the permafrost distribution in this area. The CryoGRID1 model is implemented at 1 km 2 resolution, forced by a new operationally gridded dataset of daily air temperature and snow cover for Finland, Norway and Sweden. 100 model realizations are run for each grid cell, based on statistical snow distributions, allowing for the representation of sub-grid variability of ground temperatures. The new map indicates a total permafrost area (palsas excluded) of 23 400 km 2 in equilibrium with the average 1981-2010 climate, corresponding to 2.2 % of the total land area. About 56 % of the area is within Norway, 35 % in Sweden, and 9 % in Finland. The model results are thoroughly evaluated, both quantitatively and qualitatively, as a collaboration project including permafrost experts in the three countries. Observed ground temperatures from 25 boreholes are within ±2 °C from the average modelled grid cell ground 2 temperature, and all are within the range of the modelled ground temperature for the corresponding grid cell. The model results are also evaluated qualitatively by the representatives conducting field investigations on permafrost at several sites within the three countries, and are shown to reproduce observed lower altitudinal limits of permafrost and permafrost distributions mapped by the corresponding detailed field investigations.

Global Change Biology, Sep 28, 2006

Thawing permafrost in the sub-Arctic has implications for the physical stability and biological d... more Thawing permafrost in the sub-Arctic has implications for the physical stability and biological dynamics of peatland ecosystems. This study provides an analysis of how permafrost thawing and subsequent vegetation changes in a sub-Arctic Swedish mire have changed the net exchange of greenhouse gases, carbon dioxide (CO 2) and CH 4 over the past three decades. Images of the mire (ca. 17 ha) and surroundings taken with film sensitive in the visible and the near infrared portion of the spectrum, [i.e. colour infrared (CIR) aerial photographs from 1970 and 2000] were used. The results show that during this period the area covered by hummock vegetation decreased by more than 11% and became replaced by wet-growing plant communities. The overall net uptake of C in the vegetation and the release of C by heterotrophic respiration might have increased resulting in increases in both the growing season atmospheric CO 2 sink function with about 16% and the CH 4 emissions with 22%. Calculating the flux as CO 2 equivalents show that the mire in 2000 has a 47% greater radiative forcing on the atmosphere using a 100-year time horizon. Northern peatlands in areas with thawing sporadic or discontinuous permafrost are likely to act as larger greenhouse gas sources over the growing season today than a few decades ago because of increased CH 4 emissions.

Nomadic pastoralism is the way of life and basically the only income for around a third part of t... more Nomadic pastoralism is the way of life and basically the only income for around a third part of the Mongolian population. Pastoral lands are state property in Mongolia whereas the livestock is owned by the herding households who received it after the dismantling of the herding collectives in the beginning of the 1990s. The last fifteen years have been characterised by changes in the herders grazing practice, and changes in the pastoral land management policy as a result of the new land legislation. The problems most often related to the new grazing patterns are: reduced mobility of the herders, high concentration of livestock in some places, out-of-season grazing and trespassing. These factors are all said to lead to overgrazing and pasture degradation. The Mongolian Land Law promotes allocation of the pasture land to groups of herders’ for possession and management thus trying to facilitate more sustainable grazing practises. Sustainable Grassland Management projects implemented by...

Geografisk Tidsskrift-Danish Journal of Geography, 1982

... mounds. >> download as pdf. Geografisk Tidsskrift-Danish Journal of Geography | Oester ... more ... mounds. >> download as pdf. Geografisk Tidsskrift-Danish Journal of Geography | Oester Voldgade 10 | DK-1350 Copenhagen K | tel. +45 3532 2500 | djg-editor@ geo.ku.dk. developed by Olander Consulting | © 2007-2009.

Permafrost and Periglacial Processes, 2010

This paper provides a snapshot of the permafrost thermal state in the Nordic area obtained during... more This paper provides a snapshot of the permafrost thermal state in the Nordic area obtained during the International Polar Year (IPY) 2007-2009. Several intensive research campaigns were undertaken within a variety of projects in the Nordic countries to obtain this snapshot. We demonstrate for Scandinavia that both lowland permafrost in palsas and peat plateaus, and large areas of permafrost in the mountains are at temperatures close to 08C, which makes them sensitive to climatic changes. In Svalbard and northeast Greenland, and also in the highest parts of the mountains in the rest of the Nordic area, the permafrost is somewhat colder, but still only a few degrees below the freezing point. The observations presented from the network of boreholes, more than half of which were established during the IPY, provide an important baseline to assess how future predicted climatic changes may affect the permafrost thermal state in the Nordic area. Time series of active-layer thickness and permafrost temperature conditions in the Nordic area, which are generally only 10 years in length, show generally increasing active-layer depths and rising permafrost temperatures.

Global Change Biology, 2006