Opportunities and challenges with palaeomagnetic data sources

In our quest to understand the geomagnetic field of past millennia, we rely on two primary sources of data. The first source is archaeomagnetic data, which provides us with valuable information about the geomagnetic field based on ancient artefacts. However, one major challenge we encounter is the uneven distribution of this data in both space and time. It's like trying to put together a historical jigsaw puzzle without all the pieces.

But don't worry, there is another data source that helps overcome these limitations and provides a more comprehensive understanding of the past geomagnetic field. Sedimentary records, a treasure trove of information spanning vast time periods and offering improved spatial coverage. Imagine these records as growing bars, each representing a time series of the geomagnetic field at a specific location. In contrast, archaeomagnetic data appears as dots, providing snapshots of the geomagnetic field at specific locations. As we venture further back in time, sediment data becomes increasingly essential since archaeomagnetic data becomes sparser.

The spatial and temporal data coverage.

Now let's unravel the different magnetization mysteries within these sediments. Archaeomagnetic data captures the geomagnetic field through a fascinating process known as thermoremanent magnetization (TRM). Picture this: ancient artifacts, like pottery and kiln structures but also lava flows are heated and then left to cool down. But here's the magical part - during this process, they become magnetized, preserving a snapshot of the geomagnetic field at that exact moment. It's like capturing a piece of geomagnetic field's history in a magnetic time capsule.

The magnetization process in sediments is known as detrital remanent magnetization (DRM). During the sedimentation process, magnetic particles settle in such a way that their magnetic moments tend to point in the direction of the geomagnetic field. It's like they have an ancient compass within them, pointing in the direction of the geomagnetic forces. With the accumulation of additional sediment material, the magnetic particles become mechanically fixed within the sediment structure, preserving their magnetic orientations. It's as if they have been frozen in time, capturing the magnetic field's influence at the lock-in moment.

The magnetization in sediments is influenced by several factors, such as the interaction between the magnetic particles and the substrate at the sediment-water interface (depositional DRM), as well as the consolidation and dewatering process of the sediment (post-depositional DRM). Within depositional DRM, various effects come into play. For instance, there is the inclination error, which arises when non-spherical particles settle flat on the sediment-water interface. This leads to a distortion of the inclination, resulting in smaller inclination values than expected.

In our investigation, we're particularly interested in unraveling the secrets of post-depositional DRM. Initially, only the larger sediment particles become mechanically fixed shortly after deposition. Smaller particles, on the other hand, enjoy a freer journey, moving within water-filled voids and pore spaces for a longer duration. However, as the sediment consolidates and dries out, these smaller particles slowly become locked in too. It's a mesmerizing process, like witnessing magnetic particles tell stories of the ever-changing geomagnetic field.

Check out the figure below that illustrates the journey of magnetic particles during the lock-in or pDRM process.

The sedimentation process.

A The lock-in adventure begins when the particles settle on the sediment-water interface. Sediments are composed of a mix of magnetic and non-magnetic particles, creating a vibrant playground. During the early stages of the lock-in process, particles rotate freely and align with the geomagnetic field. It's like a magnetic ballroom dance conducted by the geomagnetic field forces.

B As time passes and sedimentation continues, the surrounding material consolidates. Larger magnetic particles begin to lose their mobility and get locked in. They find their forever spots, holding onto the memories of the geomagnetic field at that time. But what about the smaller particles? They're still lively and free, closely following the twists and turns of the geomagnetic field.

C After ample sedimentation and consolidation, the lock-in process reaches its grand finale. Each particle becomes a storyteller, carrying a piece of the geomagnetic field's history within it. The sediment layer becomes a mosaic of magnetic moments, depicting diverse states of the geomagnetic field throughout the entire lock-in period. It's like a magnetic symphony composed of the melodies of the geomagnetic field.

The magnetic moment of a whole sediment layer represents a weighted average of the geomagnetic field over the lock-in period. This is where the concept of a lock-in function comes into play. The lock-in function assigns weights to the different geomagnetic field values, reflecting their significance during the lock-in process.

The investigation of the lock-in process and the development of a modeling concept to estimate the lock-in functions for individual core samples is the primary goal of our studies. Our research outcomes provide in-depth details, methodologies, and findings that shed light on the fascinating world of sediment records and post-depositional DRM. Visit https://sec23.git-pages.gfz-potsdam.de/korte/pdrm/ for more information. With our results we make sediment data a more reliable data source for modeling the geomagnetic field. It's time to unlock the secrets of the geomagnetic past!

Lukas Bohsung is a second year PhD student at the University of Potsdam and the Helmholtz Centre Potsdam — GFZ German Research Centre for Geosciences in Germany. His main focus is on investigating and modeling magnetization processes in sediments to make sediment records a more reliable data source for geomagnetic field reconstructions. He can be contacted via email here.

PhD in IAGA #6

IAGA has a lot of different scientists working on various topics. In this series of blogs, we introduce some topics that were or are being worked on by PhD students. Hopefully this will give a better picture of the work being done in the field and encourage more early career researchers.

Dr. Anita Devi completed her postgrad from the Department of Geophysics, Kurukshetra University, India after which she worked for two years as a Geophysicist in TVIPL. She did her Ph.D. from Indian Institute of Technology, Roorkee in 2019. For a brief period of 3 months, she also worked as a Post-Doctoral fellow (SERB-NPDF) at Wadia Institute of Himalayan Geology, India. During her doctoral research, she worked on various electrical and electromagnetic prospecting methods to deciphered resistivity structures. She is currently working as a Scientist at CSIR-NGRI, in magnetotelluric group. 

Her Ph.D. research was focused on 3D (3-Dimensional) individual and joint inversion of magnetotelluric (MT), Radio magnetotelluric and Electrical resistivity tomography (ERT) data. She presented the first 3D resistivity model for Garhwal Himalayan region around Roorkee-Gangotri and Chamoli region. She has worked on all the aspects of Magnetotelluric (acquisition, processing, 3D modelling and inversion). She is interested in delineating the 3D resistivity subsurface structures for exploration and tectonic studies. Her earlier work focuses on the geodynamic studies of Himalayan region. Currently she is working on 3D MT studies of both the Central Indian Tectonic Zone and the Himalaya region. She has published research papers in reputed national and international journals like Journal of Applied Geophysics and Near Surface Geophysics and participated in several International workshops (EMIW, IAGA-IASPEI).

Depth slices of the inverted 3D electrical model of Roorkee-Gangotri profile from Devi et al. 2019 with the letters marking the major resistivity features.

Training experiences: IAGA 2023 School

The IUGG Assembly that took place at Berlin from 11th to 20th July 2023 was preceded by the IAGA Summer School in Niemegk from 7th to 11th July. The school was organised by IAGA's ICEO - International Commission on Education and Outreach.

The participants were Early Career Researchers who got together at the magnetic observatory of Niemegk, Germany for theoretical and practical training in magnetism. There were 6 courses on various aspects of the magnetic field such as core and crustal fields, electromagnetic induction, and numerical as well as observational modelling among others. The 25 participants hailed from 15 different countries spread over the globe. Some testimonies of their experience are below-

Manu Varghese: IAGA summer school 2023 was my first in-person summer school, and the experience was really amazing! I met fellow students and researchers from different parts of the world. We discussed our research areas and I feel like such interactions open the way for future collaborative research and friendships. I also found lectures other than my focus area understandable since the professors started from first principles and their approach was well rooted in fundamental principles. Niemegk observatory, Germany is a place of long tradition in measuring the geomagnetic field and the observatory itself possesses a valuable set of archives. The visit to the observatory enlightened the path forward for my research.

Frederik Madsen: It was such a great experience, both to get a better understanding of the different aspects of the geomagnetic field, as well as being in the place where data is recorded, but also to make friends from all over the world - friends who may very well be my future colleagues. We all study different parts of the geomagnetic field, so in a sense, we’re all becoming experts in each other’s noise. It was really valuable to get such deep insight from people who are really passionate about the different features of geomagnetism. I'm very grateful for having had this experience - the 198 mosquito bites was definitely worth meeting such wonderful people!

Miroslav Hanzelka: The IAGA summer school was a great opportunity to meet with young scientists working on topics across the whole range of IAGA disciplines, something I don't usually experience during narrowly focused conference sessions. As someone who recently finished their Ph.D., hearing from the other students and post-docs about how Ph.D. research works in different countries helped me broaden my horizons. The hosts at the Niemegk observatory gave us a tour around the facilities, letting us see the history and present of geomagnetic field measurements in Germany. Many of the school organizers and lecturers were available even outside of the scheduled program, happy to discuss their work and give research tips to the students. The overall atmosphere at the IAGA school was very friendly and laid-back, thanks to both the organizers and the relaxed ambience of German villages. Would attend again :)

Nitin Kadam: My IAGA summer school experience was very transformative and enlightening. I gained valuable insights and connected with like-minded peers. The brainstorming lectures and hands-on activities (more specifically during the paleomagnetic sessions) provided a deeper understanding of the topics. The experience has undoubtedly enriched my academic journey and broadened my perspective.

Space News

The Voyager 1 and 2 satellites were launched in 1977 to study and understand the giant planets of our
Solar System. It provided the first and only measurements yet around the two ice giants - Uranus and Neptune. However, the mission didn't end after that. The two satellites are still operating far beyond the giant planets in interstellar space.

The interstellar space starts where the Sun can no longer affect the surroundings. Voyager 1 entered this region in August 2012 while Voyager 2's entry was in November 2018. Their present distances from Earth are about 23 and 19 billion kms respectively. But a few days ago, NASA lost communication with Voyager 2 due to a shift in antenna. Hopefully, they can get it back by October when the satellite next resets itself for orientation. The mission also has a twitter account to keep us updated about news beyond the Solar System.

Lastly, we leave you with an interesting image from Voyager 1 taken at a distance of about 6 billion kms (from the Sun) called 'The Pale Blue Dot'. Try to find the Earth here. Hint: Look at the bright scattered light near the right of the image. It shows just how unimportant we are in the vast expanse of the universe. A reminder to not take ourselves and others too seriously! 

Images Credit: NASA

Early Career Researchers at IUGG '23

The International Union of Geodesy and Geophysics (IUGG) recognises the Early Career Scientists (ECS) upper limit as people who completed their PhD 10 years back. For all the ECS, there was a registered social event that took place at the IUGG General Assembly in Berlin on 15th July 2023. It was the first of its kind event with participation from all the 8 associations of IUGG working on different sciences. 

The ECS social evening was attended by more than 200 people spread across all the associations. After a long break from online conferences due to the pandemic, everybody was quite happy to interact face-to-face. Scientists early in their career got the chance to meet and interact with other scientists working on a different domain in a different country. The highlight of the event was a set of 10 questions related to their fears and academic lives that was to be discussed in a panel session the next day. Some pertinent questions were raised in hopes of the associations recognising and solving these problems. The attendees also had the opportunity to give suggestions and ask questions to IUGG.

Poll results from two of the ten questions asked to the Early Career Researchers in the social evening. Credit: Jamie Farquharson

The next day, at the Big Themes panel discussion, each of the association had a representative who tried to answer the poll results and raise the awareness and concerns of their association to IUGG. It was an hour long open discussion which was attended by both ECRs and established scientists.

The representatives and organisers of each of the 8 IUGG associations with the IUGG Secretary General at the Big Themes panel discussion on July 16th, 2023 in CityCube Berlin. Credit: Jan Pauls

This event was the starting point of a hopeful long association between IUGG and its ECR's needs, wishes and demands. Hopefully, in 4 years, in the next IUGG Assembly in Incheon, Korea, some of these problems will no longer exist or will be partially solved.

IAGA Social Media meetings in IUGG

The IUGG General Assembly is finally here! The sessions for IAGA happen between 13th and 18th July in CityCube Berlin. Specifically, the social media has a lot of sessions happening in IUGG. If you are a registered candidate, you are welcome to attend any and all of them!

14th July 2023

Business meeting of IAGA Interdivisional Commission on Education and Outreach with Social Media WG - 18:00 to 19:30 CEST in Hall M5

15th July 2023

Session JH06b (morning) - Bimbim's Team: A journey to the planets - 10:30 to 10:45 CEST in Hall A3

Session JH06b (afternoon) - Geoscience Connections - 13:45 to 14:00 CEST in Hall A3

Session JH06b (afternoon) - Content Creation from the IAGA Social Media Working Group - 14:00 to 14:15 CEST in Hall A3

See you at IUGG in our sessions!

IUGG Public Days

The 28th General Assembly of the International Union of Geodesy and Geophysics (IUGG) taking place in Berlin, Germany is right around the corner. The conference, from 11th to 20th July 2023, has 3 public days where interested people are welcome to know more about trending research and innovations in geoscience. 

On 14th, 15th and 16th July, everyone can attend the exhibition hall B for free and interact with researchers about current geoscience inventions. Special highlights include the GFZ stand as well as the NASA exhibition. The local planetarium will also be present.

You can indicate your interest by answering three questions here.

More about other exhibitions can be found here. You can also look at the list of sponsors and exhibitors that will be present at IUGG. See you in a week at the conference!