NASA satellites detect a vast Atlantic gravity anomaly as Earth’s magnetic field jolts

A vast 7,000-kilometre gravity anomaly has been detected over the Atlantic Ocean by NASA’s GRACE satellites — coinciding with a sudden “geomagnetic jerk” observed worldwide. The discovery, made by a Franco-German research team, points to rapid, deep processes within Earth’s mantle and raises new questions about how the planet’s core and magnetic field interact.

The anomaly was spotted by NASA and the German Aerospace Centre’s Gravity Recovery and Climate Experiment (GRACE), a twin-satellite mission designed to measure variations in Earth’s gravity. Between 2006 and 2008, scientists noticed an unusually steep gravity gradient over the eastern Atlantic, where areas of stronger-than-expected gravity lay adjacent to weaker zones.

At first, researchers considered whether shifting water or groundwater flows could explain the anomaly. But these models fell short. “We identified an anomalously large-scale gravity gradient signal in the eastern Atlantic Ocean, maximum at the beginning of 2007, which cannot be fully explained by surface water sources nor core fluid flows,” the team wrote.

Instead, the evidence pointed deeper — to the core-mantle boundary (CMB), some 2,900 kilometres beneath Earth’s surface. Here, under crushing pressures and intense heat, the mineral bridgmanite dominates. The scientists suggest that during the anomaly, bridgmanite underwent a sudden phase transition, changing into a denser crystalline form called post-perovskite. That structural shift may have triggered rapid mass redistributions in the mantle, producing the gravity signal observed by GRACE.

“Because the depth of the Pv–pPv transition is thermally dependent, it may vary temporally as thermal heterogeneities are entrained in the upwelling and downwelling limbs of the convecting mantle,” the paper explains. In simpler terms: mantle plumes moving through different temperature zones may hit a tipping point, causing minerals to snap into new phases — and altering mass balance on a planetary scale.

The timing of the anomaly is striking. Around the same period, Earth-based magnetic observatories registered a geomagnetic jerk — a sudden shift in the planet’s magnetic field. These jerks, first recorded in the 20th century, represent abrupt changes in the long-term trends of the geomagnetic field, and their causes remain mysterious. Notable events were logged in 1991, 1999, 2003, and 2007.

The team proposes a possible link between the gravity anomaly and the magnetic jolt. If mass redistribution occurred deep in the mantle, it may have influenced flows in the liquid outer core, which generate Earth’s magnetic field. However, this connection remains hypothetical. “How the obtained changes in CMB topography may influence core flow dynamics and the geomagnetic field is now to be investigated,” the researchers caution.

While gravitational anomalies are not rare, the scale and depth of this one stand out. The Puerto Rico Trench, for example, has long been known for its intense negative anomaly of –380 milliGal, the largest on Earth. But the Atlantic signal, stretching thousands of kilometres, represents something different — a vast, transient shift linked not to surface features but to deep, unseen dynamics.

For now, the anomaly underscores how much remains unknown about Earth’s interior. The combination of satellite data, seismic modelling, and magnetic field observations is providing tantalising glimpses into processes once thought unreachable. If mantle mineral transformations can trigger both gravity shifts and geomagnetic jerks, they may offer a missing piece of the puzzle of how Earth’s deep layers shape the environment we live in.

The GRACE findings will now be cross-analysed with data from its successor mission, GRACE-FO, to see whether other rapid deep-mantle events have occurred since. The mystery of how Earth’s deepest structures ripple out to affect its magnetic shield is only beginning to unfold.