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Precursors to the South Atlantic Anomaly - Magnetic field variations in Lake Eilandvlei, South Africa

Eng, Simon LU (2024) In Dissertations in Geology at Lund University GEOR02 20232
Department of Geology
Abstract
After more than a century of direct observations of the magnetic field, it’s evident that our current field does not completely follow a dipole model and is in fact slightly asymmetrical, with one region of the south Atlantic Ocean standing out in particular. The South Atlantic Anomaly (SAA) is an expansive area of lower magnetic intensity and is known to cause significant problems for satellites and space stations passing over the area as they are exposed to an elevated amount of high energy particles causing disruption to their electrical systems. This thesis aims to use a high-resolution Holocene lacustrine sediment core from Lake Eilandvlei, South Africa, to search the palaeomagnetic archive for previous magnetic anomalies similar to... (More)
After more than a century of direct observations of the magnetic field, it’s evident that our current field does not completely follow a dipole model and is in fact slightly asymmetrical, with one region of the south Atlantic Ocean standing out in particular. The South Atlantic Anomaly (SAA) is an expansive area of lower magnetic intensity and is known to cause significant problems for satellites and space stations passing over the area as they are exposed to an elevated amount of high energy particles causing disruption to their electrical systems. This thesis aims to use a high-resolution Holocene lacustrine sediment core from Lake Eilandvlei, South Africa, to search the palaeomagnetic archive for previous magnetic anomalies similar to the one we see today. The top 10 meters of the core were previously measured for magnetic inclination and declination in Oregon, and to supplement this data the bottom 20 meters were measured at Lund University. However, due to poor preservation the highly calcareous bottom 20 meters proved unreliable for further palaeomagnetic analysis. The data from the top 10 meters was of much higher quality and was processed and modeled to visualize the past 5000 years of magnetic field changes in the south Atlantic. The inclusion of the Eilandvlei data in these models suggested a strong pattern of continuous western drift with a rate of 0,09°/year and revealed that 4000 years ago, the magnetic field had characteristics very similar to our current day with a suggested magnetic anomaly in the same position as the SAA. This result hints at the possibility of another anomaly 8000 years ago, but with the bottom 20 meters being unusable the existence of any repeating patterns requires further study to be determined. (Less)
Abstract (Swedish)
Tack vare mer än 100 år av direkta mätningar av jordens magnetfält vet vi med god säkerhet att det inte kan beskrivas till fullo med en dipol, utan visar tydliga asymmetriska egenskaper. Ett av de tydligaste exemplen på magnetfältets asymmetri hittar vi i södra Atlanten, där ett expansivt område uppvisar lägre magnetisk intensitet än någon annan region. Denna Sydatlantiska anomali (SAA) är inte enbart intressant för studier om processerna i jordens yttre kärna, utan utgör även ett verkligt problem för satelliter och rymdstationer i jordens omloppsbana då det försvagade magnetfältet gör att dessa utsätts för förhöjda halter av strålning. Med hjälp av en högupplöst lakustrin kärna från Lake Eilandvlei i Sydafrikas spets syftar den här... (More)
Tack vare mer än 100 år av direkta mätningar av jordens magnetfält vet vi med god säkerhet att det inte kan beskrivas till fullo med en dipol, utan visar tydliga asymmetriska egenskaper. Ett av de tydligaste exemplen på magnetfältets asymmetri hittar vi i södra Atlanten, där ett expansivt område uppvisar lägre magnetisk intensitet än någon annan region. Denna Sydatlantiska anomali (SAA) är inte enbart intressant för studier om processerna i jordens yttre kärna, utan utgör även ett verkligt problem för satelliter och rymdstationer i jordens omloppsbana då det försvagade magnetfältet gör att dessa utsätts för förhöjda halter av strålning. Med hjälp av en högupplöst lakustrin kärna från Lake Eilandvlei i Sydafrikas spets syftar den här avhandlingen att leta efter magnetiska anomalier under Holocen som liknar SAA för att öka förståelsen för hur dessa magnetiska anomalier skapas och hur de kan utvecklas. De översta 10 meterna av kärnan har tidigare haft inklinationen och deklinationen uppmätt, och för att förstärka denna data mäts de undre 20 meterna med Lunds Universitets magnetometer. Efter mätningar och analys uppvisar de undre 20 meterna mycket höga osäkerheter på grund av en relativt hög kalkhalt, och som följd kan inte denna data använder för paleomagnetisk rekonstruktion. Resultatet från de övre 10 meterna var mer lovande, och med hjälp av modeller kunde påverkan av det nya datasetet bedömas. De nya modellerna tyder på en kontinuerlig västerlig drift med en hastighet på 0,09°/år och visar även att för 4000 år sedan verkar det ha funnits en anomali på samma plats som SAA med liknande karaktär. Om detta är ett upprepande mönster kan inte urskiljas i denna studie men med fler kompletterande studier av det södra halvklotet skulle resultatet kunna hjälpa oss förutspå den framtida utvecklingen av SAA. (Less)
Popular Abstract
The Earth’s magnetic field has been the subject of countless studies, with centuries of direct measurements giving us a pretty good idea of how it works. Almost all aspects of the field can be described as a standard dipolar field, with a few notable exceptions. One of these exceptions is the phenomena known as the South Atlantic Anomaly (SAA), a gigantic region covering most of the Atlantic that has a much weaker field than the rest of the planet. This anomaly isn’t just a fun quirk however, as the weakened field presents a real threat to low-orbit satellites passing through the area, damaging their electrical equipment. This thesis aims to search the geological archives for evidence of previous anomalies in the area during the Holocene,... (More)
The Earth’s magnetic field has been the subject of countless studies, with centuries of direct measurements giving us a pretty good idea of how it works. Almost all aspects of the field can be described as a standard dipolar field, with a few notable exceptions. One of these exceptions is the phenomena known as the South Atlantic Anomaly (SAA), a gigantic region covering most of the Atlantic that has a much weaker field than the rest of the planet. This anomaly isn’t just a fun quirk however, as the weakened field presents a real threat to low-orbit satellites passing through the area, damaging their electrical equipment. This thesis aims to search the geological archives for evidence of previous anomalies in the area during the Holocene, using a sediment core retrieved from Lake Eilandvlei in South Africa.

The top 12 m of the core have been measured previously but the data has remained unused, and to supplement it the bottom 20 m was retrieved from their storage in Germany and measured in the magnetic lab of Lunds University. Unfortunately, the bottom 20 m was of insufficient quality, being mostly calcareous with little magnetic material to carry a signal that could be used for reconstruction. However, the top 12 m showed great promise and was analyzed further using the software UPMAG and MATLAB. The results showed reasonable data when compared to other numerical models and could be inserted into the pgm9k.2 model to see if the newly added data revealed any previously unknown anomalies.

As luck would have it, a magnetic anomaly similar to the SAA was identified, sprouting out of the Indian Ocean into the Atlantic 4000 years ago. Furthermore, a western drift of 0,09°/year was identified when the data was projected as an eccentric dipole. With a drift rate of 0,09°/year, it would take 4000 years for the anomaly to complete a full rotation, which suggests that both the SAA and the older anomaly are part of the same 4000-year cycle. Further study would be needed to prove this theory, as two instances of similar anomalies does not prove a correlation, but based on the premise of this thesis, these exciting results could improve our understanding of the magnetic field and shed some light on the South Atlantic Anomaly and its ancestors. (Less)
Please use this url to cite or link to this publication:
author
Eng, Simon LU
supervisor
organization
course
GEOR02 20232
year
type
H2 - Master's Degree (Two Years)
subject
keywords
South Atlantic Anomaly, Magnetic Variations, Palaeomagnetism, Holocene
publication/series
Dissertations in Geology at Lund University
report number
676
language
English
id
9209452
date added to LUP
2025-08-06 14:13:24
date last changed
2025-08-06 14:13:24
@misc{9209452,
  abstract     = {{After more than a century of direct observations of the magnetic field, it’s evident that our current field does not completely follow a dipole model and is in fact slightly asymmetrical, with one region of the south Atlantic Ocean standing out in particular. The South Atlantic Anomaly (SAA) is an expansive area of lower magnetic intensity and is known to cause significant problems for satellites and space stations passing over the area as they are exposed to an elevated amount of high energy particles causing disruption to their electrical systems. This thesis aims to use a high-resolution Holocene lacustrine sediment core from Lake Eilandvlei, South Africa, to search the palaeomagnetic archive for previous magnetic anomalies similar to the one we see today. The top 10 meters of the core were previously measured for magnetic inclination and declination in Oregon, and to supplement this data the bottom 20 meters were measured at Lund University. However, due to poor preservation the highly calcareous bottom 20 meters proved unreliable for further palaeomagnetic analysis. The data from the top 10 meters was of much higher quality and was processed and modeled to visualize the past 5000 years of magnetic field changes in the south Atlantic. The inclusion of the Eilandvlei data in these models suggested a strong pattern of continuous western drift with a rate of 0,09°/year and revealed that 4000 years ago, the magnetic field had characteristics very similar to our current day with a suggested magnetic anomaly in the same position as the SAA. This result hints at the possibility of another anomaly 8000 years ago, but with the bottom 20 meters being unusable the existence of any repeating patterns requires further study to be determined.}},
  author       = {{Eng, Simon}},
  language     = {{eng}},
  note         = {{Student Paper}},
  series       = {{Dissertations in Geology at Lund University}},
  title        = {{Precursors to the South Atlantic Anomaly - Magnetic field variations in Lake Eilandvlei, South Africa}},
  year         = {{2024}},
}