Testing the hypothesis of a link between Earth’s magnetic field and climate change : a case study from southern Sweden focusing on the 1st millennium BC

Abstract: It is commonly believed that long-term (10 to 1000 kyr) and short-term (10 to 1000 years) climatic changes on Earth can be interpreted by periodic variations in Earth’s orbit around the Sun and variations in solar irradiance, respectively. In recent years, geomagnetic field changes have been suggested as a potential driver of climate change. However, a link between these two factors is not straightforward. A relationship between geomagnetic field changes and climate is still debatable. To test the hypothesis of a link between past changes in the geomagnetic field and climate, reliable reconstructions of paleoclimate and paleogeomagnetic field are needed. In this study, high resolution palaeomagnetic and palaeoecological records obtained from varved sediments in Lake Gyltigesjön, southern Sweden, with an emphasis on the 1st millennium BC, are directly compared to test the hypothesis. The 1st millennium BC is one of the most interesting periods of geomagnetic variation during the Holocene, which is characterized in palaeomagnetic records by high magnetic field intensity and relatively abrupt geomagnetic pole movement. Through measurements of magnetic hysteresis parameters and First Order Reversal Curves (FORCs), sediments from Gyltigesjön are believed to contain abundant single domain (SD) magnetite grains, which are an excellent source of paleomagnetic field reconstructions. In order to reconstruct paleoclimate conditions during the 1st millennium BC, pollen analysis, measurements of varve thickness, loss on ignition (LOI), total organic carbon (TOC), ration of C/N, grey scale and magnetic parameters were conducted. The main conclusion is that no evidence of a link between geomagnetic field and climate change can be found in southern Sweden during the study period. Early human activity, however, could have masked the palaeoclimatic significance of the proxies used.