A recent study using data from the European Space Agency’s (ESA) Swarm mission has revealed new insights into faint magnetic signals generated by Earth’s tides, providing information about the ocean floor and the deeper Earth’s mantle. The findings, published in Philosophical Transactions of the Royal Society A, show the potential of satellite magnetometry to investigate underwater magma distribution and evaluate global ocean characteristics.
Researchers from the University of Cologne and the Technical University of Denmark conducted the study using magnetic field data from the Swarm and CHAMP satellite missions.
By examining the magnetic signals produced as seawater moves through Earth’s magnetic field, the study characterizes the electrical properties of oceans and the underlying solid Earth. This technique provides a new perspective on seabed conductivity, global ocean climatology, and mantle structure.
The role of tidal magnetic signals
Salty seawater, acting as a moderate electrical conductor, generates weak electric currents as it moves through Earth’s geomagnetic field.
These currents create faint magnetic signals detectable by satellites. The Swarm satellite constellation, operating at altitudes of 462 – 511 km (287 – 317 miles), delivers the precision required to identify and distinguish these subtle tidal magnetic signals from other geomagnetic sources, such as those originating in Earth’s core and crust.
The study introduces improved models of tidal magnetic fields for key tidal constituents, including M2, N2, O1, and Q1. Advanced data analysis methods and magnetic field gradiometry using Swarm allowed for higher spatial resolution and greater accuracy compared to earlier studies.
High-resolution, three-dimensional electromagnetic simulations were also used to validate these findings.
These refined models enabled researchers to examine the conductivity of the sub-oceanic mantle, identifying distinct layers: a resistive lithosphere and a more conducive asthenosphere.
This stratification corresponds to the physical characteristics of these regions, with the lithosphere as a colder, brittle layer and the asthenosphere as a hotter, more ductile one.
Swarm detects tidal magnetic signatures. Image credit: ESA
Challenges and observations
Although the study successfully detected magnetic signals for several tidal constituents, others, such as K1 and S2, proved challenging due to interference from ionospheric magnetic fields. These constituents, which align with solar daily harmonics, are overshadowed by external geomagnetic noise, complicating their detection.
The researchers said that the Sun’s less active phase during the 2017 solar minimum improved the accuracy of detected signals.
Solar activity affects space weather and introduces electromagnetic interference, hindering the detection of faint geomagnetic signals. However, reduced solar emissions during solar minimum create quieter conditions, enabling more accurate measurements.
Swarm constellation. Image credit: ESA
Implications for future research
The study demonstrated the use of tidal magnetic signals as proxies for analyzing the physical and electrical properties of Earth’s oceans and mantle. Beyond mantle induction studies, these signals may provide critical data for monitoring long-term variations in ocean temperature and salinity.
Launched in 2013 with a four-year mission plan, Swarm has continued to deliver high-quality scientific data for over a decade. As the satellites gradually descend to lower altitudes due to atmospheric drag, they provide even more precise geomagnetic measurements. Future missions, such as NanoMagSat and MSS-1, are anticipated to improve the resolution and accuracy of tidal magnetic studies, unlocking new research opportunities.
The next solar minimum, expected after 2030, presents another opportunity to advance these studies. Researchers aim to continue gathering critical data through Swarm or similar missions, enabling further investigations into oceanic and subsurface characteristics.
References:
1 Swarm detects tidal signatures of our oceans – ESA – January 22, 2025
2 Magnetic signals from oceanic tides: new satellite observations and applications – Grayver Alexander, Finlay Christopher C., and Olsen Nils – Philosophical Transactions of the Royal Society A – December 2, 2024 – http://doi.org/10.1098/rsta.2024.0078 – Open access