Description: William’s Ridge, a ~300-km-long salient extending southeast from the Central Kerguelen Plateau, and Broken Ridge are conjugate divergent margins in the southern Indian Ocean that separated at ~43 Ma. In early 2020, scientists aboard Australia’s Marine National Facility, RV Investigator, acquired multichannel seismic reflection (MCS), sub-bottom profiling, multibeam bathymetry, and gravity data on these margins, as well as dredged rock samples, on a 57-day voyage. The research project constitutes the first-ever case study of conjugate oceanic plateau end-member tectonic plates, with the goal of advancing knowledge of lithospheric rifting, breakup, and initial plate separation processes. The first-ever dedicated multibeam mapping of William’s and Broken ridges encompassed ~52,000 km2 and ~43,000 km2, respectively. Four new RV Investigator MCS profiles (500 line-km) across William’s Ridge complement one legacy RV Rig Seismic and three new RV Sonne MCS profiles; five new RV Investigator MCS profiles (603 line-km) across the conjugate portion of Broken Ridge are the first to be acquired on that feature. Multibeam bathymetry and MCS transects of William’s Ridge show multiple linear ridges and troughs interpreted as horst and graben. In contrast, multibeam bathymetry and MCS transects of Broken Ridge show a prominent E-W scarp (Diamantina Escarpment) with a complex morphology of emanating en echelon crustal blocks and depressions at the base of the scarp. Prominent angular unconformities (middle Eocene hiatus?) characterize the sedimentary section on some ridges, and dipping reflection sequences within interpreted igneous basement suggest subaerial basalt flows. Rock dredges on the facing conjugate margin fault scarps targeted all stratigraphic levels exposing basement rocks. Nine on William’s Ridge yielded both oceanic and (in situ?) continental rocks; eight on Broken Ridge yielded solely oceanic rocks. The new geophysical data and geological samples may justify a new or revised submission to the United Nations Commission on the Limits of the Continental Shelf to extend Australia’s marine jurisdiction on and around William’s Ridge under the United Nations Convention on the Law of the Sea.

Description: This paper is not subject to U.S. copyright. The definitive version was published in Global and Planetary Change 167 (2018): 1-23, doi:10.1016/j.gloplacha.2018.04.004.

Description: A compilation of foraminiferal stable isotope measurements from southern high latitude (SHL) deep-sea sites provides a novel perspective important for understanding Earth's paleotemperature and paleoceanographic changes across the rise and fall of the Cretaceous Hot Greenhouse climate and the subsequent Paleogene climatic optimum. Both new and previously published results are placed within an improved chronostratigraphic framework for southern South Atlantic and southern Indian Ocean sites. Sites studied were located between 58° and 65°S paleolatitude and were deposited at middle to upper bathyal paleodepths. Oxygen isotope records suggest similar trends in both bottom and surface water temperatures in the southern sectors of the South Atlantic and in the Indian Ocean basins. Warm conditions were present throughout the Albian, extreme warmth existed during the Cretaceous Thermal Maximum (early-mid-Turonian) through late Santonian, and long-term cooling began in the Campanian and culminated in Cretaceous temperature minima during the Maastrichtian. Gradients between surface and seafloor δ18O and δ13C values were unusually high throughout the 11.5 m.y. of extreme warmth during the Turonian-early Campanian, but these vertical gradients nearly disappeared by the early Maastrichtian. In absolute terms, paleotemperature estimates that use standard assumptions for pre-glacial seawater suggest sub-Antarctic bottom waters were ≥21 °C and sub-Antarctic surface waters were ≥27 °C during the Turonian, values warmer than published climate models support. Alternatively, estimated temperatures can be reduced to the upper limits of model results through freshening of high latitude waters but only if there were enhanced precipitation of water with quite low δ18O values. Regardless, Turonian planktonic δ18O values are ~1.5‰ lower than minimum values reported for the Paleocene-Eocene Thermal Maximum (PETM) from the same region, a difference which corresponds to Turonian surface temperatures ~6 °C warmer than peak PETM temperatures if Turonian and Paleocene temperatures are estimated using the same assumptions. It is likely that warm oceans surrounding and penetrating interior Antarctica (given higher relative sea level) prevented growth of Antarctic ice sheets at all but the highest elevations from the late Aptian through late Campanian; however, Maastrichtian temperatures may have been cool enough to allow growth of small, ephemeral ice sheets. The standard explanation for the sustained warmth during Cretaceous Hot Greenhouse climate invokes higher atmospheric CO2 levels from volcanic outgassing, but correlation among temperature estimates, proxy estimates of pCO2, and intervals of high fluxes of both mafic and silicic volcanism are mostly poor. This comparison demonstrates that the relative timing between events and their putative consequences need to be better constrained to test and more fully understand relationships among volcanism, pCO2, temperature ocean circulation, Earth's biota and the carbon cycle.

Description: Funding from the Smithsonian National Museum of Natural History and the National Science Foundation (NSF-OCE 1261586) helped support this research.

Description: © The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Marine Geology 395 (2018): 301-319, doi:10.1016/j.margeo.2017.10.014.

Description: A high-resolution multibeam echosounder (MBES) dataset covering over 279,000 km2 was acquired in the southeastern Indian Ocean to assist the search for Malaysia Airlines Flight 370 (MH370) that disappeared on 8 March 2014. The data provided an essential geospatial framework for the search and is the first large-scale coverage of MBES data in this region. Here we report on geomorphic analyses of the new MBES data, including a comparison with the Global Seafloor Geomorphic Features Map (GSFM) that is based on coarser resolution satellite altimetry data, and the insights the new data provide into geological processes that have formed and are currently shaping this remote deepsea area. Our comparison between the new MBES bathymetric model and the latest global topographic/bathymetric model (SRTM15_plus) reveals that 62% of the satellite-derived data points for the study area are comparable with MBES measurements within the estimated vertical uncertainty of the SRTM15_plus model (± 100 m). However, 〉 38% of the SRTM15_plus depth estimates disagree with the MBES data by 〉 100 m, in places by up to 1900 m. The new MBES data show that abyssal plains and basins in the study area are significantly more rugged than their representation in the GSFM, with a 20% increase in the extent of hills and mountains. The new model also reveals four times more seamounts than presented in the GSFM, suggesting more of these features than previously estimated for the broader region. This is important considering the ecological significance of high-relief structures on the seabed, such as hosting high levels of biodiversity. Analyses of the new data also enabled sea knolls, fans, valleys, canyons, troughs, and holes to be identified, doubling the number of discrete features mapped. Importantly, mapping the study area using MBES data improves our understanding of the geological evolution of the region and reveals a range of modern sedimentary processes. For example, a large series of ridges extending over approximately 20% of the mapped area, in places capped by sea knolls, highlight the preserved seafloor spreading fabric and provide valuable insights into Southeast Indian Ridge seafloor spreading processes, especially volcanism. Rifting is also recorded along the Broken Ridge – Diamantina Escarpment, with rift blocks and well-bedded sedimentary bedrock outcrops discernible down to 2400 m water depth. Modern ocean floor sedimentary processes are documented by sediment mass transport features, especially along the northern margin of Broken Ridge, and in pockmarks (the finest-scale features mapped), which are numerous south of Diamantina Trench and appear to record gas and/or fluid discharge from underlying marine sediments. The new MBES data highlight the complexity of the search area and serve to demonstrate how little we know about the vast areas of the ocean that have not been mapped with MBES. The availability of high-resolution and accurate maps of the ocean floor can clearly provide new insights into the Earth's geological evolution, modern ocean floor processes, and the location of sites that are likely to have relatively high biodiversity.

Description: Author Posting. © Oceanography Society, 2019. This article is posted here by permission of Oceanography Society for personal use, not for redistribution. The definitive version was published in Neal, C.R., M.F. Coffin, and W.W. Sager. Contributions of scientific ocean drilling to understanding the emplacement of submarine large igneous provinces and their effects on the environment. Oceanography 32(1), (2019):176–192, doi:10.5670/oceanog.2019.142.

Description: The Ontong Java Plateau (OJP), Shatsky Rise (SR), and Kerguelen Plateau/Broken Ridge (KP/BR) represent three large igneous provinces (LIPs) located in oceanic settings. The basement lavas have been investigated through scientific ocean drilling and, in the case of the OJP, fieldwork on the emergent obducted portions of the plateau in the Solomon Islands. Such studies show that these three LIPs have very different characteristics. For example, the KP/BR still has an active hotspot, whereas the OJP and the SR do not. The OJP is remarkable in its compositional monotony across the plateau (the Kwaimbaita geochemical type), with minor compositional variation found at the margins (the Kroenke, Singgalo, and Wairahito types). Shatsky Rise shows more compositional variation and, like the OJP, has a dominant lava type (termed the “normal” type) in the early stages (Tamu Massif), but subsequent eruptions at the Ori and Shirshov massifs comprise isotopically and trace element enriched lavas, likely reflecting a change in mantle source over time. The KP/BR has highly variable basement lava compositions, ranging from lavas slightly enriched above that of normal mid-ocean ridge basalt in the northern portion (close to the South East Indian Ridge) to more enriched varieties to the south and on Broken Ridge, with a continental crust signature present in lavas from the southern and central KP/BR. The OJP and the KP/BR appear to have formed through punctuated magmatic events, whereas the SR was formed by one relatively long, drawn out event. The formation of oceanic LIPs has in many (but not all) cases been synchronous with oceanic anoxic events. This paper focuses on three oceanic plateaus to emphasize the debate surrounding the environmental impact such LIPs may have had, and also highlights the contributions of scientific ocean drilling to our knowledge of oceanic LIP formation and evolution. This new knowledge allows planning for future oceanic LIP drilling.

Description: Many thanks to the crew and operators of the scientific ocean drilling vessel JOIDES Resolution without whom the understanding of oceanic flood basalts would be severely limited. We also thank the US National Science Foundation for continued support of scientific ocean drilling. We are indebted to Jörg Geldmacher, Paul Wallace, Carlotta Escutia, and Anthony Koppers for reviews of this paper that were insightful and extremely helpful in making it much better than the initial submission.

Description: Author Posting. © The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Australian Journal of Earth Sciences 64 (2017): 851-869, doi:10.1080/08120099.2017.1367326.

Description: Volcanism associated with the Kerguelen Large Igneous Province is found scattered in southwestern Australia (the ca 136 to ca 130 Ma Bunbury Basalts, and ca 124 Ma Wallaby Plateau), India (ca 118 Ma Rajmahal Traps and Cona Basalts), and Tibet (the ca 132 Ma Comei Basalts), but apart from the ∼70 000 km2 Wallaby Plateau, these examples are spatially and volumetrically minor. Here, we report dredge, geochronological and geochemical results from the ∼90 000 km2 Naturaliste Plateau, located ∼170 to ∼500 km southwest of Australia. Dredged lavas and intrusive rocks range from mafic to felsic compositions, and prior geophysical analyses indicate these units comprise much of the plateau substrate. 40Ar/39Ar plagioclase ages from mafic units and U–Pb zircon ages from silicic rocks indicate magmatic emplacement from 130.6 ± 1.2 to 129.4 ± 1.3 Ma for mafic rocks and 131.8 ± 3.9 to 128.2 ± 2.3 Ma for silicic rocks (2σ). These Cretaceous Naturaliste magmas incorporated a significant component of continental crust, with relatively high 87Sr/86Sr (up to 0.78), high 207Pb/204 Pb ratios (15.5–15.6), low 143Nd/144Nd (0.511–0.512) and primitive-mantle normalised Th/Nb of 11.3 and La/Nb of 3.97. These geochemical results are consistent with the plateau being underlain by continental basement, as indicated by prior interpretations of seismic and gravity data, corroborated by dredging of Mesoproterozoic granites and gneisses on the southern plateau flank. The Cretaceous Naturaliste Plateau igneous rocks have signatures indicative of extraction from a depleted mantle, with trace-element and isotopic values that overlap with Kerguelen Plateau lavas reflect crustal contamination. Our chemical and geochronological results therefore show the Naturaliste Plateau contains evidence of an extensive igneous event representing some of the earliest voluminous Kerguelen hotspot magmas. Prior work reports that contemporaneous correlative volcanic sequences underlie the nearby Mentelle Basin, and the Enderby Basin and Princess Elizabeth Trough in the Antarctic. When combined, the igneous rocks in the Naturaliste, Mentelle, Wallaby, Enderby, Princess Elizabeth, Bunbury and Comei-Cona areas form a 136–124 Ma Large Igneous Province covering 〉244 000 km2.

Description: Major National Research Facility [grant number Southern Surveyor Voyage SS09/2005] Frogtech Pty Ltd, Geoscience Australia, Australian Research Council [grant number DE150130, DP0666062]

Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Spain, E. A., Johnson, S. C., Hutton, B., Whittaker, J. M., Lucieer, V., Watson, S. J., Fox, J. M., Lupton, J., Arculus, R., Bradney, A., & Coffin, M. F. Shallow seafloor gas emissions near Heard and McDonald Islands on the Kerguelen Plateau, Southern Indian Ocean. Earth and Space Science, 7(3), (2020): e2019EA000695, doi:10.1029/2019EA000695.

Description: Bubble emission mechanisms from submerged large igneous provinces remains enigmatic. The Kerguelen Plateau, a large igneous province in the southern Indian Ocean, has a long sustained history of active volcanism and glacial/interglacial cycles of sedimentation, both of which may cause seafloor bubble production. We present the results of hydroacoustic flare observations around the underexplored volcanically active Heard Island and McDonald Islands on the Central Kerguelen Plateau. Flares were observed with a split‐beam echosounder and characterized using multifrequency decibel differencing. Deep‐tow camera footage, water properties, water column δ3He, subbottom profile, and sediment δ13C and δ34S data were analyzed to consider flare mechanisms. Excess δ3He near McDonald Islands seeps, indicating mantle‐derived input, suggests proximal hydrothermal activity; McDonald Islands flares may thus indicate CO2, methane, and other minor gas bubbles associated with shallow diffuse hydrothermal venting. The Heard Island seep environment, with subbottom acoustic blanking in thick sediment, muted 3He signal, and δ13C and δ34S fractionation factors, suggest that Heard Island seeps may either be methane gas (possibly both shallow biogenic methane and deeper‐sourced thermogenic methane related to geothermal heat from onshore volcanism) or a combination of methane and CO2, such as seen in sediment‐hosted geothermal systems. These data provide the first evidence of submarine gas escape on the Central Kerguelen Plateau and expand our understanding of seafloor processes and carbon cycling in the data‐poor southern Indian Ocean. Extensive sedimentation of the Kerguelen Plateau and additional zones of submarine volcanic activity mean additional seeps or vents may lie outside the small survey area proximal to the islands.

Description: We thank the Australian Marine National Facility (MNF) for its support in the form of sea time on RV Investigator , support personnel, scientific equipment, and data management. We also thank the captain, crew, and fellow scientists of RV Investigator voyage IN2016_V01. We also thank specifically the following: T. Martin, F. Cooke, S. L. Sow, N. Bax, J. Ford, and F. Althaus, CSIRO (Commonwealth Scientific and Industrial Research Organisation); Echoview Software Pty. Ltd. (Hobart, Australia); C. Dietz and C. Cook, Central Science Laboratory, University of Tasmania; C. Wilkinson and T. Baumberger, National Oceanic and Atmospheric Administration; R. Carey, University of Tasmania; T. Holmes, Institute for Marine and Antarctic Studies, University of Tasmania; N. Polmear; and A. Post, Geoscience Australia. The overall science of the project is supported by Australian Antarctic Science Program (AASP) grant 4338. E.S.' PhD research is supported by the Australian Research Council's Special Research Initiative Antarctic Gateway Partnership (Project ID SR140300001) and by an Australian Government Research Training Program Scholarship. S.C.J. is supported by iCRAG under SFI, European Regional Development Fund, and industry partners, as well as ANZIC‐IODP. J.M.W. is supported by ARC grant DE140100376 and DP180102280. This is PMEL publication number 4910. All IN2016_V01 data and samples acquired on IN2016_V01 are made publicly available in accordance with MNF policy.

Description: Numerous large igneous provinces formed in the Pacific Ocean during Early Cretaceous time, but their origins and relations are poorly understood. We present new geochronological and geochemical data on rocks from the Manihiki Plateau and compare these results to those for other Cretaceous Pacific plateaus. A dredged Manihiki basalt gives an 40Ar-39Ar age of 117.9+/-3.5 Ma (2 sigma), essentially contemporaneous with the Ontong Java Plateau ~2500 km to the west, and the possibly related Hikurangi Plateau ~3000 km to the south. Drilled Manihiki lavas are tholeiitic with incompatible trace element abundances similar to those of Ontong Java basalts. These lavas may result from high degrees of partial melting during the main eruptive phase of plateau formation. There are two categories of dredged lavas from the Danger Islands Troughs, which bisect the plateau. The first is alkalic lavas having strong enrichments in light rare earth and large-ion lithophile elements; these lavas may represent late-stage activity, as one sample yields an 40Ar-39Ar age of 99.5+/-0.7 Ma. The second category consists of tholeiitic basalts with U-shaped incompatible element patterns and unusually low abundances of several elements; these basalts record a mantle component not previously observed in Manihiki, Ontong Java, or Hikurangi lavas. Their trace element characteristics may result from extensive melting of depleted mantle wedge material mixed with small amounts of volcaniclastic sediment. We are unaware of comparable basalts elsewhere.