Matthew Gerard Jackson

Constraining the origin of Earth’s carbon requires knowing the isotopic composition of the core—a geochemical signature long presumed to be beyond observation for the planet’s largest carbon reservoir. Here, we report high-precision δ ¹³ C measurements from Hawaiian plume melt inclusions entrapped before significant degassing and sampling distinct mantle sources. Melt inclusions from shield-stage lavas, interpreted to sample the plume’s central axis, inferred to be rooted in the core–mantle boundary thermal boundary layer, converge toward a primary δ ¹³ C signature of –1 ± 2‰. In contrast, melt inclusions from rejuvenated-stage lavas, derived from entrained mantle at the plume’s periphery, record a normal mantle source signature of –7 ± 2‰. We interpret the uniquely ¹³ C-rich shield-stage signature as the isotopic fingerprint of carbon exchanged from the core into the mantle. Our results point to ¹³ C-rich carbonaceous chondrites as the primary source of Earth’s carbon.

We demonstrate a remarkable change in the chemical bonding of iron under pressure that underlies the distribution of elements in the Earth’s mantle and core. Using a massive-scale, first-principles study, we show that while reacting with p -block elements under increasing pressure from ambient to Earth core conditions, iron tends to reverse its redox nature, changing from an electron donor (reductant) to an electron acceptor (oxidant), and oxidizes many p -block elements. Such reverse redox propensity significantly impacts the stoichiometries, bond types and strengths, structures, and properties of iron compounds under deep planetary conditions. This change transforms many p- block elements (conventionally labeled lithophile or chalcophile) into highly siderophile species. The chemical binding strengths with iron show an inverse correlation with the depletion of p -block elements in the silicate Earth. Furthermore, silicon shows a distinct anomaly in its bonding to iron, which suggests silicon may readily be incorporated into Earth’s core.

Recent changes in US oceanographic assets are impacting scientists' ability to access seafloor and sub‐seafloor materials and thus constraining progress on science critical for societal needs. Here we identify national infrastructure needs to address critical science questions. This commentary reports on community‐driven discussions that took place during the 3‐day FUTURE of US Seafloor Sampling Capabilities 2024 Workshop , which used an “all‐hands‐on‐deck” approach to assess seafloor and sub‐seafloor sampling requirements of a broad range of scientific objectives, focusing on capabilities that could be supported through the US Academic Research Fleet (US‐ARF) now or in the near future. Cross‐cutting issues identified included weight and size limitations in the over‐boarding capabilities of the US‐ARF, a need to access material at depths greater than ∼20 m below the seafloor, sampling capabilities at the full range of ocean depths, technologies required for precise navigation‐guided sampling and drilling, resources to capitalize on the research potential of returned materials, and workforce development.

Volcanic hotspots are thought to form by melting in an upwelling mantle plume head followed by melting of the plume tail. Plate motion then generates an age-progressive volcanic track originating from a large igneous province to a currently active hotspot. The most voluminous large igneous province, the approximately 120-million-year-old Ontong Java Nui Plateau (OJP-Nui) in the mid-Pacific, however, lacks an obvious volcanic track. Although the Louisville hotspot track was originally proposed as a candidate, limited constraints for Pacific absolute plate and plume motion before 80 million years ago (Ma) suggest a mismatch¹. Existing Pacific models rely on age–distance data from the continuous Hawai‘i–Emperor and Louisville tracks, but their tracks older than approximately 80 Ma are subducted. Elsewhere on the Pacific Plate, only discontinuous seamount tracks that formed before 80 Ma are documented^2,3,4,5,6,7. Currently, models require approximately 1,200 kilometres of latitudinal motion to link the Louisville plume to the OJP-Nui¹, but palaeolatitude estimates from about 70 Ma to today remain within error of its present location^8,9, suggesting that any substantial Louisville plume motion occurred earlier. Here, through a combination of geochemistry and geochronology^{9,10,11,12,13,14}, we demonstrate that Samoa and Rurutu–Arago are the longest-lived Pacific hotspots, traceable to more than 100 Ma before subducting into the Mariana Trench. These tracks better constrain plate rotation between 80 Ma and 100 Ma, allowing us to update Pacific absolute plate motion models and link the Louisville volcanic track to OJP-Nui without requiring major plume motion.

Oceanic island basalts are the products of mantle plume melting and their chemistry provides insights into the Earth's deep interior. We report a statistical and machine learning study of 8 radiogenic isotopes and 19 incompatible trace element ratios in basalts from 27 oceanic island volcanic chains associated with mantle plumes compiled from the GEOROC and EARTHCHEM‐PetDB databases. Machine‐learning hierarchical analysis and agglomerative clustering results based on t‐distributed stochastic neighbor embedding (t‐SNE) reveal distinct clusters of isotopic compositions corresponding to canonical ones of HIMU, EM I, EM II, PREMA. and DM as well as a LOND cluster, which however do not reflect the existence of discrete components. The HIMU clan is restricted to only a couple of plumes and is characterized by low K/U, Pb/Ce, Ba/Nb and strong REE fractionation. EM I has higher K/U, Ce/Rb, Ba/Nb and lower U/Pb, Rb/Ba, Rb/Sr than EM II reflecting a difference in prevalent recycled components. Stepwise multiple regression reveals that fractionations of incompatible element ratios can be explained by variations in partial melting controlled by lithospheric thickness and plume buoyancy flux; the latter indicates that buoyancy flux primarily reflects plume temperature. ³He/⁴He also correlates with plume buoyancy flux, suggesting that the hottest plumes carry the least radiogenic He. The hottest plumes may be those rising from the core‐mantle boundary. This, and the absence of evidence of a primordial mantle reservoir suggest that unradiogenic He may be derived from the core.

The Samoan hotspot generated an age‐progressive volcanic track that can be traced back to 24 Ma at Alexa Bank, but the trace of the older portion (>24 Ma) of the hotspot track is unclear. We show that six seamounts located in and around the Magellan Seamount chain—north of the Ontong‐Java Plateau (OJP)—have ages (87–106 Ma), geochemistry, and locations consistent with absolute plate motion model reconstructions of the Samoan hotspot track in the late Cretaceous, and three additional seamounts have geochemistry and locations consistent with a Samoan origin. However, a large segment of the Samoan hotspot (24–87 Ma) remains unidentified. Absolute plate motion models show that, from ∼60 to 30 Ma, the OJP passed over the Samoan plume. The exceptional thickness of the OJP lithosphere may have largely suppressed Samoan plume melting because the inferred volcanic trace of the Samoan hotspot wanes, and then disappears, on the OJP. Fortunately, 44 Ma volcanism at Malaita Island, located on the southern margin of the OJP, has a location, age, and geochemistry consistent with a Samoan plume origin, and provides a “missing link” bridging the younger and older segments of the Samoan hotspot. Our synthesis of geochemical, geochronological, and plate motion model evidence reveals that Samoa exhibits a clear hotspot age progression for over 100 Myr. Passage of ancient plateaus over young plumes—here called “plume‐plateau” interaction—may be relatively common: the OJP also passed over the putative Rarotonga hotspot, and the Society and Pitcairn hotspots were overtopped by the Manihiki Plateau.

Mantle plumes contain heterogenous chemical components and sample variable depths of the mantle, enabling glimpses into the compositional structure of Earth's interior. In this study, we evaluated ocean island basalts (OIB) from nine plume locations to provide a global and systematic assessment of the relationship between fO₂ and He‐Sr‐Nd‐Pb‐W‐Os isotopic compositions. Ocean island basalts from the Pacific (Austral Islands, Hawaii, Mangaia, Samoa, Pitcairn), Atlantic (Azores, Canary Islands, St. Helena), and Indian Oceans (La Réunion) reveal that fO₂ in OIB is heterogeneous both within and among hotspots. Taken together with previous studies, global OIB have elevated and heterogenous fO₂ (average = +0.5 ∆FMQ; 2SD = 1.5) relative to prior estimates of global mid‐ocean ridge basalts (MORB; average = −0.1 ∆FMQ; 2SD = 0.6), though many individual OIB overlap MORB. Specific mantle components, such as HIMU and enriched mantle 2 (EM2), defined by radiogenic Pb and Sr isotopic compositions compared to other OIB, respectively, have distinctly high fO₂ based on statistical analysis. Elevated fO₂ in OIB samples of these components is associated with higher whole‐rock CaO/Al₂O₃ and olivine CaO content, which may be linked to recycled carbonated oceanic crust. EM1‐type and geochemically depleted OIB are generally not as oxidized, possibly due to limited oxidizing potential of the recycled material in the enriched mantle 1 (EM1) component (e.g., sediment) or lack of recycled materials in geochemically depleted OIB. Despite systematic offset of the fO₂ among EM1‐, EM2‐, and HIMU‐type OIB, geochemical indices of lithospheric recycling, such as Sr‐Nd‐Pb‐Os isotopic systems, generally do not correlate with fO₂.