Extreme solar particle storms and links to solar activity inferred from cosmogenic radionuclides in ice cores

Abstract: During solar storms, large amounts of solar energetic particles (SEP) are accelerated into the interplanetary medium and sometimes hit Earth. These events, known as SEP events, can have harmful impacts on our modern society by affecting spacecrafts and potentially astronauts in space. The first directly observed solar storm was the Carrington event in 1859 which is linked to disruptions of the telegraph system and an aurora oval at unusually low latitudes. The most extreme form of SEP events can be detected in cosmogenic radionuclide records from ice cores and tree rings. Cosmogenic radionuclides are produced by the interaction between high-energy galactic cosmic rays (GCRs), the dominant source of production, and SEPs with atmospheric atoms. The flux of GCRs is modulated by the strength of the Sun’s and the Earth’s magnetic fields, which vary through time. Measuring cosmogenic radionuclides in ice cores (10Be and 36Cl) and tree rings (14C) thus allows us to reconstruct the history of the Sun’s and the Earth’s magnetic fields, and of SEP events. This thesis aims to detect new SEP events over the Holocene and to discuss their timing within the 11-year solar cycle, and to test the use of excess meltwater from continuous flow analysis (CFA) to measure cosmogenic radionuclides. The 10Be record from CFA excess meltwater from the EGRIP S6 core is presented. By comparing the data to another 10Be record from discrete samples from the same core we show that the CFA excess meltwater samples are a valuable alternative to discrete samples for the measurement of cosmogenic radionuclides and, thus, solar activity reconstructions. This result opens the possibility of obtaining continuous 10Be records with a more time-efficient sample preparation.10Be and 36Cl data from Greenland and Antarctica support the occurrence of three extreme SEP events 9125 years BP, 7350 years BP and 7208 years BP. Furthermore,we show that the Carrington event cannot be detected in high-resolution 10Be and 36Cl data from Greenland, in agreement with previous studies.Finally, two proposed solar storms in 1052 CE and 1279 CE are also investigated with 10Be and 36Cl data from Greenland, which do not support the occurrenceof SEP events.