Highly accuracy classification and mapping of seafloor hydrothermal fields provides an important addition to research into the geological background and exploration of seafloor massive sulphides ...(SMS). Currently, acoustic remote sensing using multibeam sounding systems (MBES) is the primary means of achieving large-scale seafloor classification. However, the characteristics of complex topography, complex seafloor distribution and deep water depth of the hydrothermal fields make it difficult to obtain accurate high-resolution seafloor classification maps using shipboard MBES surveys. Here a seafloor classification strategy combining shipboard MBES and autonomous underwater vehicle (AUV) sidescan sonar data is proposed. First, a downscaling model is established, which downscales the MBES backscatter mosaic (12 kHz, 10 m resolution) to a resolution of 2 m. The second step performs feature extraction of the downscaled MBES backscatter mosaic (12 kHz, 2 m resolution), the AUV sidescan sonar backscatter mosaic (150 kHz, 2 m resolution), and a seafloor digital elevation model (2 m resolution). Finally, a deep neural network model was built for training and classification. To evaluate the classification performance of the model, the method was applied to the survey of the Duanqiao hydrothermal field. Results were verified using field data (deep-tow video). The overall root mean square error and coefficient of determination (R2) for the classification were 0.032 and 0.840, respectively. The experimental results show that the method can effectively meet the challenges to seafloor classification presented by complex seafloor distribution, and can obtain an accurate high-resolution seafloor classification map.
We present astronomically tuned high resolution (∼3–4 Kyr) 15.8-Myr long benthic foraminiferal δ18O and δ13C records from IODP Site U1337 in the east equatorial Pacific, which provide a reference ...standard for stratigraphic correlation of deep sea sediments. A long-term glaciation history over the past 15.8 Myr has been recorded in the δ18O. Two of the most significant glaciation events include the East Antarctic Ice Sheet expansion (EAIE) at 13.8 Ma and the final onset of the Northern Hemisphere Glaciation (NHG) in 3.3–2.5 Ma. A series of Miocene and Pliocene glaciation events exist between the EAIE and NHG, which are important glaciation attempts before the Earth finally entered the full “icehouse” world in the late Pleistocene. A long-term ocean carbon isotope decrease over the past 15.8 Myr has been recorded in the δ13C. Ocean circulation change was the major cause of the ocean carbon isotope decrease in 9.4–8.1 Ma and 4–0 Ma, whereas strengthened continental chemical weathering controlled the long-term ocean carbon isotope decrease in most of the time of the past 15.8 Myr. The divergence in benthic foraminiferal δ13C and εNd provides strong evidence of significant ocean circulation change between 12.1 and 9.2 Ma which was probably related to the formation of the Isthmus of Panama. The internal feedbacks such as continental weathering and sea surface temperature change have great potential for modulating the weak 100 and 400 Kyr signals in astronomical forcing into strong 100 and 400 Kyr signals in global ice volume and carbon cycle.
•First continuous 16-Myr benthic δ18O and δ13C records and astrochronology.•Stepwise glaciation and secular ocean carbon isotope decrease in 16–0 Ma.•Formation of the Isthmus of Panama in 12.1–9.2 Ma.
The Middle Miocene East Antarctic ice sheet expansion (EAIE), which is indicated by an abrupt ~1‰ increase in global benthic foraminiferal δ18O at ~13.8 Ma, marks the Middle Miocene climate ...transition (MMCT) and has been related to astronomically modulated changes in the global carbon cycle. Here, we present high resolution (3–4 kyr) benthic foraminiferal δ18O and δ13C records from IODP Site U1337 in the central equatorial Pacific, which spans the period 12.2–15.8 Ma. The isotopic records clearly demonstrate significant imprints from periodic variations in the Earth's orbital parameters, particularly the obliquity (40 kyr) and the long eccentricity (400 kyr) cycles. While the benthic δ18O and δ13C exhibit nearly identical amplitudes for glacial‐interglacial cycles from 15.8 to 12.2 Ma, the long‐term trends in the benthic δ18O and δ13C had started to reverse after the beginning of the EAIE. Within the 400‐kyr band, the benthic −δ18O and δ13C displays a constant phase relationship between 15.8 and 12.2 Ma. At the 41‐kyr band, however, a phase reversal reaching >180° between −δ18O and δ13C occurs from 13.8 Ma to 14.0 Ma during the period of the EAIE. A similar phase relationship of benthic foraminiferal −δ18O and δ13C at the 400‐kyr band and the 41‐kyr band is also observed at ODP Site 1146 from the northern South China Sea. This phase jump occurs when the long‐term trends in δ18O and δ13C split, suggesting a decoupling of the global ice volume and ocean carbon reservoir changes during the Middle Miocene.
Key PointsEast Antarctic Ice Sheet Expansion in the middle MioceneObliquity and long eccentricity paced the middle miocene climate changesThe global ice volume and carbon cycle decoupled durint the middle Miocene
We analyzed the data consist of core digital images and X-rays, core-logs, LWD (logging-while-drilling), and sediment grain-size from the second Ulleung Basin Gas Hydrate Expedition (UBGH2) in the ...East Sea. Core digital images and X-rays were spliced as a complete composite core in meters below seafloor (mbsf) for five sites; UBGH2-1_1 (Hole D), 2_1 (B), 2_2 (B), 2-6 (B) and 2-10 (C–D), and were correlated with the core-log and LWD measurements showing that possible gas hydrate bearing layers are between the depths of about 60–180 mbsf at these sites. Bulk densities generally increase with depth from 1.3 to 2.0 g/cm3 in LWD data, and from 1.1 to 1.8 g/cm3 onboard which measured lower than in-situ. Gas hydrate bearing sediments respond with an increase of LWD densities (1.4–1.6 g/cm3) and a decrease in core-logs (1.1–1.4 g/cm3). P-wave velocity values of LWD increase (1400 to 1700 m/s) with depth for non-reservoirs, and are high (1500 and 2000 m/s) within the gas hydrate bearing intervals depending on the hydrate saturations.Resistivity values logged onboard range from less than 1.0 to over 10.0 Ω-m, while LWD records are around 1.0 Ω-m and between 5.0 and 30.0 Ω-m in background sediments and possible gas hydrate reservoirs, respectively. High resistivity values were observed (5.0–30.0 Ω-m) within coarse-grained turbidites (mean grain-size between 2.9 and 5.1 ϕ; laminated sandy mud or muddy sands). Medium resistivities were observed (5.0 Ω-m) within the silt-dominant hemi-pelagic and turbiditic sediments (5.1–7.4 ϕ; crudely laminated, bioturbated, homogeneous sand, and disintegrated sand and sandy mud facies) bearing pore-filling gas hydrates, or disseminated gas hydrates either formed in pores or small fractures of fine-grained sediments. Core-log measurements are highly fluctuating and sensitive but mostly lower (e.g., density and resistivity) than LWD records.
•UBGH2 (the Ulleung Basin Gas Hydrate Expedition 2) was performed.•Digital images and X-rays of gas hydrate bearing-sediments were examined.•Core image data and LWD log data were compared and studied.•We suggest the relationships between gas hydrate occurrences and lithological conditions and physical properties.
Manganese nodule coverage is estimated based on multi-beam and deep-towed video nodule survey profiles of about 1,700 km in the China Pioneer Area of Eastern Pacific. Two statistical equations for ...estimating nodule coverage are derived separately from the multi-beam normal incidence amplitude data and angular amplitude data based on theoretical analysis of influence factors on multi-beam amplitude data. Predictions generated by the normal incidence amplitude model fall within 5% of real nodule coverage, and theoretically calculated angular amplitude data fits well with the original multi-beam amplitudes at incident angles larger than 20° according to nodule coverage estimated from the deep-towed video data.
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