An International Ocean Discovery Program (IODP) workshop
was held at Sydney University, Australia, from 13 to 16 June 2017 and was
attended by 97 scientists from 12 countries. The aim of the workshop was to
investigate future drilling opportunities in the eastern Indian Ocean,
southwestern Pacific Ocean, and the Indian and Pacific sectors of the Southern
Ocean. The overlying regional sedimentary strata are underexplored relative
to their Northern Hemisphere counterparts, and thus the role of the Southern
Hemisphere in past global environmental change is poorly constrained. A
total of 23 proposal ideas were discussed, with
The importance of the Southern Hemisphere in the narratives of global plate tectonics and oceanography is well established, but understudied. This is in large part due to the vastness of the eastern Indian Ocean, southwestern Pacific Ocean, and the Indian and Pacific sectors of the Southern Ocean. This is an ideal region to address many of the 14 science challenges in the 2013–2023 IODP science plan. The Australian and Indian continents have undergone the largest and most rapid paleo-latitudinal shifts of any continents globally since 150 Ma. The region boasts the following: (i) arguably the greatest diversity of subduction zones from fully seismically coupled to uncoupled; (ii) extensive shallow marine seas and submerged continents (e.g., Zealandia) with extraordinary and unstudied stratigraphic records; and (iii) the largest suite of plume-related products and the largest mantle cold spot. Sampling of plateaus, ridges, and their associated sedimentary strata will provide an enormous wealth of information about their origin and address fundamental paleoceanographic and paleoclimate questions. Drilling of the Antarctic margin in the Indian Ocean and South Pacific sectors will increase our understanding of the Antarctic cryosphere and global climate evolution and past land and sea ice extent from the Cretaceous through the Cenozoic. Geomicrobiological questions can be addressed on a number of expeditions, including targeted expeditions to study the deep biosphere in a variety of tectonic settings. Petrological and geochemical studies of oceanic, back-arc and arc crust, as well as uplifted mantle remain a high priority, as do those of geological hazards.
To facilitate and nurture cross-disciplinary proposals, workshop breakout sessions focused on distinct tectonic settings and their associated paleo-environmental evolution. These included (1) large igneous provinces and associated paleoceanography, (2) subduction zones and associated paleoceanography, (3) a separate focus group on the Hikurangi subduction zone, (4) conjugate margin/Zealandia studies and associated paleoceanography, and (5) a biosphere frontiers subgroup meeting not related to the above tectonic settings. The potential proposals discussed in the breakout sessions are listed in Table 1, and locations shown in Fig. 1.
Location map of potential proposals discussed in the workshop, with color-coded dots denoting the main theme for each proposal. Small colored circles indicate previous (and planned) drilling by the Deep Sea Drilling Project (DSDP), Ocean Drilling Program (ODP), and IODP. Larger circles and diamonds are projects discussed in the meeting and are colored by theme, and numbered according to sections discussed in text. Large circles indicate proposals that appear mature enough to develop pre-proposals. Large diamonds require site survey proposals to be developed, or are awaiting the results of upcoming drilling in the region (e.g., Hikurangi subduction zone and Lord Howe Rise regions) and may require a focus workshop to further refine hypotheses.
List of proposals discussed in the workshop, lead contacts and current status for each proposal. Number relates to section number in main text.
Earth's evolution includes multiple, geologically brief episodes when
extraordinary volcanism occurred across some surface regions. Documentation
for this comes from large igneous provinces (LIPs), extensive areas covered
by thick layers of mostly mafic material that was emplaced on million-year
timescales. While LIPs have been widely acknowledged and discussed by the
geoscience community for more than two decades, major first-order questions
regarding their origin and environmental impact remain. Profound and rapid
changes in biota and chemical cycling have also punctuated Earth's history
and many of these ”events” have been linked to the formation of LIPs. For
example, massive volcanic outpouring may have been coupled to large
increases in atmospheric
Manihiki Plateau, in the southwestern Pacific, is a large (770 000 km
Drilling on the Hikurangi Plateau will yield insights into the mantle source and LIP emplacement rates, and help to constrain geodynamic models and environmental impacts of LIP emplacement. It will also enable testing of the hypothesis that Ontong Java, Manihiki, and Hikurangi were once part of a single super-LIP, and will allow controls on subduction megathrust slip behavior to be studied. Upcoming drilling on IODP expeditions 372 and 375 will provide critical information to underpin the development of such a proposal, as will multichannel seismic reflection and refraction lines to be acquired in November/December of this year. It was suggested that the proponent group aim to develop a pre-proposal by October 2018, once all of the information is available and hypotheses could be fully formulated.
A multidisciplinary drilling expedition on the Kerguelen Plateau will investigate LIP formation and Southern Ocean paleoceanography over the past 120 Ma. The Kerguelen Plateau incorporates multiple microcontinents, and has as unknown relationship to dipping reflection sequences on the nearby Antarctic margin. Tectonomagmatic questions include why the most voluminous magmatism appears to have post-dated continental breakup (unlike other flood basalts associated temporally with breakup), and how continental fragments were isolated in the plateau. Cretaceous and Cenozoic paleoceanographic records are well preserved in regional carbonates, and the complex topography of the Kerguelen Plateau exerts a strong influence on the pathways of water masses within the Antarctic Circumpolar Current (ACC) and the Antarctic Bottom Water (AABW). In the Cenozoic era, the pathways and intensities of Southern Ocean circulation were developed and significantly modified by emplacement of the Kerguelen Plateau and opening of regional tectonic gateways.
A preliminary proposal (918-Pre) to drill in the Conrad Rise and Del
Caño Rise regions (Indian Ocean sector) of the Southern Ocean (SO) was
submitted to IODP in April 2017. Five high sediment accumulation sites are
proposed, with the aim to document Southern Ocean variability and
atmosphere, ocean, and cryosphere interactions in the southwestern Indian Ocean
sector. The targeted drill sites will fill important gaps in our knowledge
covering the middle Miocene cooling (
It is proposed to drill Mesozoic sedimentary sequences on the northeastern
Wombat Plateau, on the northernmost continental margin of Australia.
Drilling during Ocean Drilling Program (ODP) Leg 122 in 1988 obtained a
thick succession of Late Triassic deltaic and shallow marine sediments
unconformably overlain by Late Cretaceous pelagic sediments, including
records of Oceanic Anoxic Event (OAE) 2 and the Cretaceous–Paleogene
boundary. However, recovery was poor in part and new core from the Wombat
Plateau will provide a better understanding of early Mesozoic paleoclimate,
paleoceanography, and paleoenvironments in the Southern Hemisphere. These
sites should provide key Southern Hemisphere data for Late Triassic climate
events, including the hypothesized late Norian–Rhaetian increase in
atmospheric
The Andaman back-arc basin was formed by subduction of the Indian plate under
the Burmese plate. Linear magnetic anomalies indicate that seafloor
spreading in the Andaman basin commenced at
The geodynamic evolution of the southwestern Pacific, from Gondwana break-up during the Cretaceous to subduction-dominated tectonism in the Cenozoic, resulted in the obduction of a string of peridotite ophiolites/massifs from the Anita ophiolite in Southern New Zealand to the Papuan Ultramafic Belt ophiolite. The New Caledonian ophiolite is one of the largest obducted peridotitic masses in the world. An amphibious drilling proposal (ADP) will provide a more complete understanding of an obducted deep geological system from a terrestrial setting to its marine extension, which is as close as possible to its unobducted mantle lithosphere counterpart. Drilling onshore and offshore along the New Caledonia ophiolite will allow emplacement mechanisms of mantle-dominated allochthons to be assessed, as well as constraining high- and low-temperature alteration processes. Other objectives could relate to studying archaeal and eubacterial communities that are known to develop in these alkaline systems, while the formation of the world's second largest rimmed carbonate reefs during the Miocene to Quaternary will be investigated. Developing an ADP will require engagement of the scientific communities associated with IODP and the International Continental Scientific Drilling Program (ICDP).
The Puysegur incipient subduction zone south of New Zealand is an ideal
location to constrain key geodynamic unknowns. Precise plate tectonic
constraints along with a high level of seismicity reveal the transition of
strike-slip motion along the Macquarie Ridge in the south to a clear Benioff
zone and active subduction beneath southwestern South Island of New Zealand,
in the north. It is likely that the Puysegur subduction zone is currently
transitioning from a forced to a self-sustaining state. IODP drilling around
Puysegur will allow testing and refinement of three topics fundamental to
the IODP science plan 2013–2023: (1) the forces associated with subduction
initiation, (2) the origin of subseafloor communities in the deep biosphere,
and (3) the development of fault properties in a mega-thrust environment.
Site survey data at Puysegur will be acquired with the R/V
The world's largest known intraplate earthquakes have occurred in the subducting Indian Plate offshore Sumatra, and have raised many questions about the genesis of such events. IODP Expedition 362 had two prospective sites approved for drilling (SUMA-22A and SUMA-23A) located 10–20 km to the north and south of the epicenter of one of these major intraplate earthquakes. Although approved for drilling, the sites were not drilled during Expedition 362 due to time constraints. However, these sites provide a unique opportunity to investigate the stress state in the region of these great intraplate earthquakes, and also to advance understanding of the sedimentary sequence entering the Sumatra subduction zone farther north, thereby building on the goals of Expedition 362. Depending on the scope, either an APL or a full proposal is planned to follow up on Expedition 362 objectives, and to investigate the state of stress state in upper oceanic crust near these highly seismogenic fracture zones.
The Hikurangi margin of New Zealand is arguably one of the best locales on the planet to resolve controls on subduction megathrust slip behavior due to the strong along-strike variations in subduction interface slip behavior. The nature of the material entering the subduction zone on the subducting Pacific Plate likely exerts a strong control on these along-strike variations in slip behavior. This proposal will acquire cores and logs sampling the incoming sedimentary section and underlying Hikurangi Plateau at several sites along the Hikurangi Plateau (from north to south). These sites will illuminate along-strike variations in the sedimentary section and underlying Hikurangi Plateau, and how these variations in lithology and fluid content may influence locked versus creeping behavior at subduction megathrusts. It will target portions of the plateau where the sedimentary cover is less than several hundred meters, well east of the deformation front, to avoid thick trench-fill sections near the Hikurangi Trough. We will also target expanded sections of the portions of incoming stratigraphy that correlate with where the plate boundary décollement is forming.
Bottom simulating reflectors (BSRs) observed at the Hikurangi subduction margin and their relationship to geothermal heat flow changes suggest that regional gas hydrate systems may be strongly influenced by episodic fluid flow processes. These processes may be driven by large strain transients that occur during episodic slow slip events. This proposal seeks to install subseafloor observatories to monitor pore pressure and temperature changes throughout the slow slip cycle. Genius plugs with osmotic samplers could undertake time-series sampling of fluids to evaluate changes in geochemistry with time. These observatories will enable evaluation of the impact of fluid pulsing on gas hydrate systems, and also quantify the degree of overpressure that builds up beneath hydrate systems during and between fluid pulsing, potentially driven by slow slip events. The latter could also play a role in submarine slope stability processes. Installation of a denser network of simple observatories will also enable more detailed spatiotemporal investigation of the distribution of offshore slow slip events, allowing many questions about shallow slow slip distribution and its impact on hydrogeology in the upper plate to be addressed.
Results from IODP Expedition 317 in the Canterbury Basin showed a freshening
signature at
Marine volcanic eruptive processes and underwater transport/deposition of volcanic material are poorly understood. In particular, the transport and depositional processes during submarine eruptions, and the behavior of pyroclastic flows as they transition from onshore to offshore environments is understudied. In some historical cases (such as the Krakatoa eruption), large tsunami have resulted from these processes, so understanding the underlying mechanisms of eruption-fed volcaniclastic transport into and under water also has important geohazard implications. Recent drilling in the Izu–Bonin–Mariana arc system uncovered 20–100 m thick eruption-fed units, but drilling on the flanks of submarine volcanoes is more suited to fully investigate these processes. The Kermadec Arc is an attractive location for such an effort, because (a) a number of submarine volcanoes have always been submarine and also have produced eruptions with significant volume, and (b) Macauley Island is an excellent locale to investigate pyroclastic transport and depositional processes into the sea, where arcuate sediment waves are observed on the order of 100 m high and 1 km long. Key questions include (1) what are the physics and processes behind submarine and coastal volcanic eruptions and subsequent deposition of their products, and (2) are the eruption products emplaced all at once, or do they occur in multiple episodes?
After three decades of scientific effort there is no definitive answer to
the question ”What Earth system processes were responsible for the
systematic variations in atmospheric CO
The southeastern continental margin of Chatham Rise is conjugate to the Amundsen Sea margin of West Antarctica. Deep crustal seismic, gravity, and magnetic data coupled with dredged samples from seamounts reveal a complex transition from continental to oceanic crust on both conjugate margin segments. In particular, the southeastern Chatham Terrace is underlain by a broad zone of thinned and fragmented transitional crust, presumably containing continental blocks separated by zones of oceanic crust. The nature of this type of transitional crust and the processes of its generation during Cretaceous rifting and breakup is poorly understood. The southern Chatham Rise is an ideal location to investigate crustal fragmentation during continental breakup by drilling into the different crustal zones, and could be combined with drilling into well-imaged sediment drifts to address hypotheses related to the development and evolution of southwestern Pacific Ocean circulation (e.g., Deep Western Boundary Current (DWBC) and ACC) during the Cenozoic.
Vulnerability of the East Antarctic Ice Sheet (EAIS) to climate change is
uncertain. The low-lying, glacially sculpted Aurora Subglacial Basin (ASB;
This project aims to obtain high-latitude paleoclimate records from the
Miocene to Pleistocene of ice sheet and ocean interactions at the East
Antarctic margin to understand the history of Totten Glacier mobility and
melting. It will obtain more continuous records of the oceanic drivers and
responses to East Antarctic Ice Sheet variability than drilling on the
continental shelf. It will also seek to obtain pre-Miocene records during
past greenhouse climates, and correlation to continental shelf records in
the Totten Glacier region in the proposal above (Sect. 5.3). Extensive
seismic lines exist across the area with more than 28 crossing lines for
selection of many potential drill sites. Turbidite overbank deposits are
proposed as targets, as these were demonstrated during IODP Expedition 318
(Wilkes Land margin of East Antarctica) to provide high-resolution
continuous archives of glacially-influenced sedimentation. Critically, such
archives have proven valuable in identifying ice-sheet retreat events and
characterizing these in the context of associated oceanographic change.
Experience from an R/V
The Southern Ocean encircles a highly dynamic glaciated Antarctic margin,
and accommodates the amalgamation of several major water masses. Changes in
the vigor of this top-to-bottom current would have significant implications
for the exchange of heat between the Pacific, Indian, and Atlantic ocean
basins, and may have consequences for the ventilation and primary
productivity of the Southern Ocean. Contourite drifts are rapidly-deposited
signatures of bottom current activity, and provide high-resolution records
of paleoceanographic change. There are several lines of evidence suggesting
that the Southeast Indian Ridge (SEIR) is covered extensively by a
succession of Pleistocene to Pliocene-aged drifts. Long-term sedimentation
rates exceed 5.5 cm kyr
The recovery of a sequence of Miocene to recent sediments from the eastern
equatorial Indian Ocean will help resolve the history of the Indian Ocean
dipole (IOD) on annual to tectonic timescales. The objectives of the
drilling are to understand the following: (1) the evolution of sea surface temperatures
(SSTs) in the eastern Indian Ocean since the Miocene, (2) the long-term
relationship between eastern Indian Ocean SSTs and strengthening/weakening
of the Indian monsoon, (3) the response of eastern Indian Ocean SSTs/IOD to
atmospheric CO
Northern Zealandia and the Lord Howe Rise were drilled during IODP
Expedition 371 using
New site survey data obtained in support of these recent and planned expeditions provide modern seismic coverage of the entire width of northern Zealandia from the Norfolk Ridge to the Tasman Sea oceanic basin. These data undoubtedly reveal a large number of additional drill sites, many of which have not yet been considered in detail. Another possible long-term objective in the region is to target seamounts and submerged plateaus within and to the north of northern Zealandia where drilling could address important geodynamic questions surrounding changes in Pacific Plate motion, and the connections among deep mantle plumes and large igneous provinces. It was agreed at the workshop that future plans for IODP drilling in northern Zealandia should be revisited in mid-2018 after results from Expedition 371 begin to emerge and the status of funding and logistics for Proposal 871-CPP is clearer.
The Australo–Antarctic rift system affords an opportunity to document lithosphere thinning history during continental breakup, and to understand the transition between rift and oceanic crust formation. The peridotite ridge in this region, representing the boundary between continental and oceanic crust, has risen high enough to be reached with riserless drilling. A second aim is to understand the timing, nature, and consequences of post-rift subsidence of the outer continental shelf of both the Australian and Antarctic margins. It is expected that post-rift subsidence was minimal, because continental migration was compensated for by formation of oceanic crust. Both margins should be completely independent in terms of subsidence history as soon as oceanic crust formation commences, but evidence from IODP Expedition 318 (Wilkes Land) suggests that the outer continental shelf of the Antarctic margin collapsed long after oceanic crust started forming in the rift system. Moreover, and surprisingly, seismic profiles along the conjugate Australian and Antarctic margins show considerable symmetry. However, on the Australian side, we lack recovered sedimentary records that allow dating of the sediments from the seaward limit of the continental margin. The region also has fundamental climate questions to address, including the deep-sea expression of Eocene–Oligocene glaciation and circum-Antarctic erosion, and the history of the development of the ACC and spatial migration of Southern Ocean frontal systems. It was proposed to develop a plan to drill a transect which connects the Otway–Ceduna basins (Australian margin) and the Antarctic margin.
The role of mass transport in continental margin environments has historically been underappreciated. Recent oceanographic tracer studies indicate that discharge of saline groundwater from passive continental margins occurs at rates equal to, or exceeding, river discharge. This implies large-scale migration of saline groundwater through continental shelf sediments and is consistent with decades of research in carbonate diagenesis, where the importance of groundwater mass transport has long been recognized. Sea-level pumped reflux brines, formed by evaporation of seawater on the exposed shelf during sea-level minima, should be common in subtropical passive margin sequences, and may provide the missing mechanism to explain the large-scale dolomitization and mineralization processes observed throughout Earth's history. These shelf-scale hydrological systems may also support abundant deep microbial life on the upper shelf slope.
Results from ODP Leg 182 show that Great Australian Bight (GAB) likely contains an actively discharging reflux brine system. Two transects across the outer GAB margin were proposed to assess coupled groundwater flow, geochemical reactions and microbial metabolic processes. Results from ODP Leg 182 suggest that the brine-supported microbial ecosystem in the GAB thrives under hyper-alkaline and hyper-sulfidic conditions, which are profoundly distinct from most other known deep biosphere environments. The tantalizing possibility is that we will gain an unprecedented glimpse into the microbial and organic geochemical processes that are responsible for the formation of a large portion of the world's hydrocarbon resources, as well as determining the role of saline groundwater flow in carbonate diagenesis in continental margin environments.
A transect of sites from the South Pacific Gyre into the Southern Ocean will
record a north–south gradient of different biogeochemical and oceanographic
regimes within oxic and suboxic sediments through the Cenozoic.
Microbiological research will help to address questions honed from the
results of IODP Expedition 329 to the South Pacific Gyre. One of its most
southern sites (Site U1371) included a shift from pelagic clay sedimentation
to siliceous accumulation at
The 97 scientists from 12 different countries gathered at the 2017 Australasian IODP Workshop in Sydney, tasked with planning scientific ocean drilling expeditions in the eastern Indian, southern, and southwestern Pacific oceans, emphasize the critical importance of geoscientific site characterization to the future success of IODP and its successors. Site characterization data, most importantly seismic reflection data, are essential for the identification of suitable primary and alternate drill sites in every full drilling proposal submitted to the IODP science support office, and are subsequently carefully considered by the program's science evaluation panel (SEP) and the three facility boards.
Without this type of information, the scientific exploration of the deep subseafloor and our understanding of its role in tectonic, climatic, oceanographic, biological, and geochemical processes in the Earth system cannot advance. Providing suitably capable vessels for that purpose is essential for the advancement of scientific ocean drilling as it addresses ever-evolving global scientific questions, particularly in underexplored parts of the world ocean like the Australasian region.
Accordingly, we emphasize that blue water research vessels with the necessary seismic reflection systems should continue to be available to researchers in all IODP member countries under reasonable fiscal conditions, and with suitable advance (national and international) planning mechanisms.
No data sets were used in this article.
The authors declare that they have no conflict of interest.
The organizers gratefully acknowledge generous and critically important funding for participants' travel to the workshop. Funding came from the Australian and New Zealand IODP Consortium (ANZIC), the US Science Support Program (USSSP), the Magellan-Plus Workshop Program of the European Consortium for Ocean Research Drilling (ECORD), the Japan Drilling Earth Consortium (J-DESC), the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), IODP-India, and the home institutions of numerous scientists. The University of Sydney assisted us in providing facilities for the workshop. Edited by: Jan Behrmann Reviewed by: Antony Morris and one anonymous referee