High-resolution near-seafloor magnetic data processing and interpretation of hydrothermal activity on the arctic Gakkel ridge

Submarine hydrothermal eruptions can alter the lithology and physical properties of the regional oceanic crust, thereby resulting in the formation of magnetic anomaly zones. As a result, near-bottom magnetic surveys are considered an effective method for the detailed investigation of hydrothermal areas. During China's 12th Arctic Scientific Expedition, near-bottom magnetic data were acquired using the "Explorer 4500" AUV in the newly formed volcanic region at 85°E on the Gakkel Ridge in the Arctic Ocean, which is characterized by the slowest spreading rate among all mid-ocean ridges. In order to reduce magnetic interference from the AUV platform and to accommodate the unique geomagnetic characteristics of polar regions, dynamic heading corrections were subsequently applied to the raw magnetic data to eliminate platform-induced disturbances. Normal field corrections were then conducted using the International Geomagnetic Reference Field (IGRF-13), thereby producing gridded magnetic anomaly data for the study area. Three significant low magnetic anomaly zones, with diameters of approximately 150 m, 200 m, and 500 m, respectively, were delineated and found to exhibit a strong spatial correlation with multibeam bathymetric features. It is hypothesized that these low magnetic anomalies may be associated with alteration processes induced by hydrothermal activity—processes analogous to the so-called hydrothermal "burn holes" formed by the thermal demagnetization of basalt due to hightemperature hydrothermal fluids, as observed along the Juan de Fuca Ridge and the Southwest Indian Ridge. Based on water column anomaly data collected during the Arctic Gakkel Vents (AGAVE) expedition, anomalies in seawater temperature and redox potential were detected within these low magnetic anomaly zones, thereby supporting the possible presence of hydrothermal activity. In this study, high-precision processing and interpretation of near-seafloor magnetic data from the 85°E segment of the Gakkel Ridge were conducted, which led to the development of a data processing and interpretation methodology tailored to polar conditions. These results offer high-resolution geophysical evidence for the investigation of hydrothermal activity along ultraslow-spreading mid-ocean ridges.