Map of locations for sites that were drilled during Leg 329 on the South Pacific Gyre off of the coast of New Zealand. Figure from IODP Expedition 329 Summary.
International Ocean Drilling Program (IODP) Expedition 329 took place from October to December in 2010 and drilled Sites U1365–U1371 in the South Pacific Gyre, a large system of rotating ocean currents in the South Pacific Ocean located off the coast of New Zealand. The expedition was a collaboration between scientists and staff from the United States, Japan, Germany, China, Norway, the United Kingdom, New Zealand, Korea, Australia, and India. Currently, there are no other ocean drilling sites located near Expedition 329 sites making it a massively understudied location. The sites drilled and studied during this expedition are an excellent location for exploring and researching subseafloor sedimentary habitats in what is considered to be the center of an open ocean gyre. The South Pacific Gyre is Earth’s largest gyre system out of five total gyre systems. Even though the cores recovered on Expedition 329 vary in ages, they are all extremely useful in understanding hydrothermal circulation (the circulation of hot water), and habitability (the capacity to be lived in) of oceanic crusts.
Detailed image of a calcite crystal contained within a section of basalt, the rock that makes up the ocean crust. Blue coloring is from a marker. Image from the LIMS Database.
Expedition 329 had four major objectives: 1) to document habitats; 2) research how oceanographic factors affect habitats; 3) quantify subseafloor microbial communities; and 4) determine how habitats at the sites vary with crust age. Before Expedition 329, life in the sediments beneath mid-ocean gyres was generally understudied and poorly understood, despite the South Pacific Gyre being a unique location. Within this gyre system, surface chlorophyll concentrations and primary photosynthetic productivity in the seawater are lower than in other ocean regions, contributing to some of the lowest organic burial rates in the ocean. Scientists and staff aboard the ship during this expedition found that microbial cell counts are lower than at all sites previously drilled, dissolved oxygen and nitrate are present throughout the entire sediment sequence, and dissolved hydrogen concentration is low but often above detection limits in deeper sediments. High-resolution chemical and physical measurements provided the opportunity for reconstructing glacial seawater characteristics through the South Pacific Gyre. Overall, Expedition 329’s findings and discoveries of the presence of dissolved chemicals revealed that there is microbial habitability of the entire sediment sequence, offering valuable insights into gyre habitability.
References
D’Hondt, S.L., Jørgensen, B.B., Miller, D.J., et al., 2003. Proc. ODP, Init. Repts., 201: College Station, TX (Ocean Drilling Program). doi:10.2973/odp.proc.ir.201.2003
Dubois, N., Mitchell, N. C., & Hall, I. R. (2014, April). Data report: particle size distribution for IODP Expedition 329 sites in the South Pacific Gyre. In Proc. IODP| Volume (Vol. 329, p. 2).
Expedition 329 Scientists, 2011. Methods. In D’Hondt, S., Inagaki, F., Alvarez Zarikian, C.A., and the Expedition 329 Scientists, Proc. IODP, 329: Tokyo (Integrated Ocean Drilling Program Management International, Inc.). doi:10.2204/iodp.proc.329.102.2011
Figure 1. Map of the arctic ocean showing the locations of the EXP 302 study area on the Lomonosov Ridge. The small-scale map shows the locations of EXP 302 sites. Figure from IODP Expedition 302 Summary.
In 2004, The Integrated Ocean Discovery Program (IODP), completed its three-hundred-and-second expedition located in the central Arctic Ocean at Lomonosov Ridge, about 250 km from the North Pole (Figure 1). During this expedition, the scientists and crew were able to recover sediment cores from three (M0002—M0004) out of the four holes they drilled (Figure 2F). The recovered sediment core depth was up to 428 meters below the seafloor. The main objective for this expedition was to further study the ancient ocean currents and ocean behavior (paleoceanography) of the Arctic region, specifically to better understand the past climate of the central Arctic Ocean and its impact during the Cenozoic Era (66 million years ago to today), when the Earth changed from a “Greenhouse” world (a time when there is very little to no ice on Earth) in the Eocene (~41 million years ago) to an “Icehouse” world (a time when there is extensive ice) of today.
During Expedition 302, the primary objective was to continuously recover sediment records (cores) and to sample the underlying bedrock by drilling and coring from the stationary drillship. This was not an easy task because of the prominent moving heavy sea ice at the Lomonosov Ridge. In order to prevent the ice from complicating the mission, a fleet of 3 icebreaker ships were used: The drilling vessel the Vidar Viking, a nuclear Russian icebreaker Sovetskiy Soyuz, and a diesel-electric icebreaker Oden. The primary goal of the icebreakers was to protect the drilling ship to ensure smooth drilling and coring operations.
Figure 2. Seismic reflection profile of the Lomonosov Ridge (AWI-91090) with locations of Expedition 302 coring sites. Multichannel seismic data are from Jokat et al. (1992). Cores were not retrieved from Hole M0001A because the BHA (gray on figure) was lost. Hole M0004B is located ~60 m away from Hole M0004A; Hole M0004C is located ~60 m away from Hole M0004B. SP = shotpoint. Image from IODP Expedition 302 Summary.
The scientific objectives of Expedition 302 are split between paleoceanography (reconstructing ancient ocean conditions) and tectonics.
The paleoceanographic objectives included:
Determining the history of sea ice and ice rafting in the region
Studying the differences between local and regional ice development
Determining the density structure (related to temperature and salinity) of the Arctic Ocean surface waters
Determining the timing and consequences of the opening of the Bering Strait
Studying the land-sea links and the response of the Arctic to the Pliocene (~5.3–2.58 million years ago) warming events
Investigating the development of the Fram Strait and deepwater exchange between the Arctic Ocean and Greenland/Iceland/Norwegian Sea (Figure 3)
Determine the history of biogenic sedimentation (sediments made by organisms).
The tectonic objectives included:
Investigating the nature and origin of the Lomonosov Ridge by sampling the oldest rocks below the regional unconformity (a time when there are no sediments that represent a specific time interval in the sediment and rock record) in order to establish the pre-Cenozoic environmental setting of the ridge
Studying the history of rifting and the timing of tectonic events that affected the ridge.
Figure 3. Generalized schematic of sea ice transport in the Arctic Ocean. Red contours denote average years of residence time before sea ice export through the Fram Strait. Arrows indicate average transport speeds. Figure from IODP Expedition 302 Summary.
IODP Exp. 302 was the first ever drilling project that was able to drill in this location, making the results pretty revolutionary. Not only were they able to gain information on all of their objectives, they also gained information on the Paleocene/Eocene Thermal Maximum (PETM; ~55.5 million years ago). This boundary was recovered during the drilling and it represents a time when the temperature of the Arctic Ocean waters exceeded 20°C or 68°F. The efforts put into this expedition made great advancements in science since this is the most cited IODP cruise!
The sites drilled as part of IODP Expedition 363 in the western Pacific warm pool region of the western equatorial Pacific ocean. Sites are denoted by yellow dots. Figure from IODP 363 Summary.
El-Niño is a phenomenon that occurs in the equatorial Pacific Ocean, causing a short-term shift in global weather dynamics around the world. El-Niño involves weakening of the trade winds, which usually push warm surface waters from the eastern equatorial Pacific to the western equatorial Pacific. Such weakening of the trade winds leads to warmer waters to occur in the eastern equatorial Pacific, when there is usually a ‘tongue’ of cold water at the surface ocean in this region. The rate of change in ocean temperatures, which is the driver of much of the global weather effects associated with El-Niño, have changed alongside global climate dynamics. Every few years, the wind patterns across the equatorial Pacific change, sometimes also shifting to a La Niña phase. The La Niña phase includes strengthening of the trade winds, which leads to even more warm water piling up in the western equatorial Pacific, and cooler waters to appear in the eastern equatorial Pacific. Preliminary studies show that the amount of time between La-Niña and El-Niño conditions are shifting over geologic time. A separate process affected by ocean surface water temperatures in the southeastern Asia region are the Australian Monsoons. These monsoons come off the Indian Ocean and provide rainfall to a significant portion of the northwestern Australian continent. There are two seasons in monsoon climates, a rainy season where moisture laden air moves over land, and a dry season where dry air moves over the oceans. Figuring out how both global and local processes based in the southeast Pacific are affected by warming oceanic conditions will play a large role in understanding climate change in the future.
The El-Niño Southern Oscillation pattern in the Pacific Ocean versus the Pacific Ocean in a year under normal conditions.
The best way to study how the climate system interacts with El-Niño conditions is to look at the past. A prime example is the Middle Miocene, a time period of warming occurring 15 million years ago. The warming patterns of the Middle Miocene are similar to warming trends that are seen today, and thus represent a clear example of how carbon dioxide (a greenhouse gas) changes in the atmosphere can influence global sea surface trends.
Expedition 363 took advantage of the geologic record of sediments in the western equatorial Pacific to reconstruct the La Niña and El Niño phases of the geologic past. The goal of Expedition 363 was to determine how different climate variables changed in the Western Pacific Warm Pool, the pile of warm water in the western equatorial Pacific. Of particular importance was to determine how these changes related to global climate change through the mid-Miocene to the mid-Pleistocene (~15 to 3 million years ago). More specifically, the expedition wanted to determine how shorter scale climate variability across a millennium. Particularly the study looked at the balance between El-Niño and La- Niña conditions, which can be correlated to previously obtained data on climate and greenhouse gas emissions. Additionally this expedition focused on understanding the history and variables that affect the Australian Monsoon cycle.
An illustration of La Niña Conditions over the eastern to western equatorial Pacific Ocean. During La Nina conditions, the trade winds strengthen, pushing warm surface waters from the eastern equatorial Pacific to the western equatorial Pacific. Figure from the National Oceanic and Atmospheric Administration.
Sediments recovered during Expedition 363 will allow for a better understanding of the Middle to Late Miocene Periods. Additionally it will allow for a better understanding of the Australian Monsoon system. Geochemical analyses from this site shows that mixed layer surface ocean temperatures did not cool over time, while subocean temperatures cooled significantly suggesting a change to more overall La-Niña conditions over time. Additionally, maximum greenhouse gas emissions coupled with peak insolation for the Southern Hemisphere provided the shortest Australian Monsoon season. Thus future predictions in a world with increased carbon dioxide levels and warming, would suggest that given rising global temperature a shorter monsoon season would occur.
References
Rosenthal, A.E. Holbourn, D.K. Kulhanek, I.W. Aiello, T.L. Babila, G. Bayon, L. Beaufort, S.C. Bova, J.-H. Chun, H. Dang, A.J. Drury, T. Dunkley Jones, P.P.B. Eichler, A.G. Fernando, K. Gibson, R.G. Hatfield, D.L. Johnson, Y. Kumagai, T. Li, B.K. Linsley, N. Meinicke, G.S. Mountain, B.N. Opdyke, P.N. Pearson, C.R. Poole, A.C. Ravelo, T. Sagawa, A. Schmitt, J.B. Wurtzel, J. Xu, M. Yamamoto, and Y.G. Zhang. (n.d.). Expedition 363 summary. https://doi.org/10.14379/iodp.proc.363.101.2018
Pei, R., Kuhnt, W., Holbourn, A., Hingst, J., Koppe, M., Schultz, J., Kopetz, P., Zhang, P., & Andersen, N. (2021). Monitoring Australian Monsoon variability over the past four glacial cycles. Palaeogeography, Palaeoclimatology, Palaeoecology, 568, 110280. https://doi.org/10.1016/j.palaeo.2021.110280
Steinthorsdottir, M., Coxall, H. K., De Boer, A. M., Huber, M., Barbolini, N., Bradshaw, C. D., Burls, N. J., Feakins, S. J., Gasson, E., Henderiks, J., Holbourn, A. E., Kiel, S., Kohn, M. J., Knorr, G., Kürschner, W. M., Lear, C. H., Liebrand, D., Lunt, D. J., Mörs, T., … Strömberg, C. A. E. (2021). The miocene: The future of the past. Paleoceanography and Paleoclimatology, 36(4). https://doi.org/10.1029/2020PA004037
Microfossils that were contained within the sediments retrieved during Expedition 363. The chemistry of these fossils’ shells, or tests, can be used to reconstruct ancient ocean conditions. Image from the LIMS database.
Figure 1: A schematics of proposed slip style and stability around different parts of a megathrust system (Yao et al., 2017).
The great Tohoku earthquake that struck northeastern Japan in 2011 was one of the largest earthquakes ever recorded on the Earth. The 9.1 magnitude earthquake resulted in a devastatingly shaking tsunami that not only produced large death tolls and structural damages but also revealed that our understanding of how the large subduction zone faults behave needs to improve in order to better predict and mitigate future earthquakes. Integrated Ocean Drilling Program Expedition 343 drilled down to the slip interface near the earthquake epicenter in offshore Japan subduction zone with the aim of recovering both geophysical data and material samples around the fault surface (Figure 2). Geoscientists used these data to form a detailed understanding of what is happening to the earth material around the fault when large ruptures occur, incorporating many parameters like states of temperature and stress, sediment type, pre-existing fault structure, and fluid flow (Chester et al., 2013)
Figure 2: Drill sites around the Tohoku-oki earthquake epicenter in offshore eastern Japan. Core samples were collected from ~5 km inland from the trench, sampling the toe of the sedimentary accretionary prisms closest to the subduction zone down to the depth of ~840 m (Chester et al., 2013).
Megathrusts along subduction zones produce the largest earthquakes on the Earth due to the long fault length and relatively wide slip surfaces. The fault rupture associated with the 2011 earthquake reached over 62 m in slip along a 40 km long segment of the Japan Trench (Sun et al., 2017). The slip was considered unusually large for an event that took place at shallow depths in the Earth near the subduction trench, where the fault surface was generally believed to be stable (Figure 1, Yao et al., 2013). While the occurrence is less frequent, shallow rupture events of this magnitude need to be monitored because the slip can breach and significantly displace the seafloor, which will cause tsunamis.
The deepest points in the Earth’s ocean are subduction trenches, where the downgoing oceanic plate bends and sinks beneath the overriding continental plate (Figure 1). The JFAST project reached one of the deepest water depths amongst all of the expeditions in the International Ocean Discovery Program (IODP Expedition Statistics) in order to tap into the shallowest portion of the subduction megathrust. In total, five boreholes were attempted at Site C0019 (Figure 2), three of which successfully reached the target fault surface (Chester et al., 2013). Multiple types of data were carefully collected over the course of a month. In addition to successfully recovering the cores, the expedition also performed real time well logging while drilling (LWD) to retrieve in situ conditions of the sediment and materials surrounding the fault surface. High-resolution electrical images also illuminated the structures and lithological properties in the borehole and enabled the identification of plate boundary fault zones (Figure 3, top). In particular, the patterns of the beddings and fractures inferred from the borehole images showed multiple faults that comprise the fault zone and drastic change in sediment structures as they are sheared by plate motion (Figure 3, bottom). Finally, temperature sensors were directly deployed along the fault interface in Hole C0019D during expedition 343T to measure the remaining frictional heat produced from the slip event 16 months prior (Figure 4).
Figure 3: The fault zone was reached at ~720 m below the sea surface (Chester et al., 2013). (top) borehole images and well logs taken along the fault zone and (bottom) combined interpretation of bedding structures near the fault zone (Chester et al., 2013).
References
Expedition 343/343T Scientists (2013). Site C0019. In Chester, F.M., Mori, J., Eguchi, N., Toczko, S., and the Expedition 343/343T Scientists, Proc. IODP, 343/343T: Tokyo (Integrated Ocean Drilling Program Management International, Inc.). doi:10.2204/iodp.proc.343343T.103.2013
Sun, T., Wang, K., Fujiwara, T., Kodaira, S., & He, J. (2017). Large fault slip peaking at trench in the 2011 Tohoku-oki earthquake. Nature communications, 8(1), 14044.
Yao, H., Shearer, P. M., & Gerstoft, P. (2013). Compressive sensing of frequency-dependent seismic radiation from subduction zone megathrust ruptures. Proceedings of the National Academy of Sciences, 110(12), 4512-4517.
Figure 4: Borehole opening at the seabed (6897.5 m deep!), where the tubing pipe of the temperature observatory is being lowered down and installed along the fault zone to measure frictional heat released from the Tohoku earthquake (Photo galleries, JAMSTEC).
Figure 1. The location of New Zealand with respect to the complex tectonic boundaries between the the Pacific plate and the Australian plate (Barnes et al., 2019). Cooler, darker colors represent deeper areas of the ocean, whereas warmer colors represent shallower regions around New Zealand.
New Zealand is tectonically complex, hosting both subduction and strike-slip fault zones associated with the plate boundary between the Pacific plate and the Australian plate. The country is thus geologically active, with many potential natural hazards that require investigation and close monitoring (Figure 1, Barnes et al., 2019). The need for improved mitigation also presents an opportunity to better understand the Earth processes prevalent in active tectonic settings. Between 2017–2018, International Ocean Discovery Program Expeditions 372 and 375 set out to collect data (cores, well logs, and in-situ geophysical measurements) at the Hikurangi Margin in northern New Zealand, with primary goals of better understanding the mechanisms and behaviors of gas hydrate-bearing landslide (Barnes et al., 2019) and slow slip events on subduction faults (Saffer et al., 2019). A combined total of six sites were sampled between the two expeditions, with two in the Tuaheni Landslide Complex (TLC) and four in a transect across the Kermadec Trench near the Hikurangi Margin.
Submarine landslides are often the byproduct of catastrophic destabilization events like earthquakes. If severe, the resulting slope failure can sometimes significantly displace the seafloor, even causing tsunamis (Harbitz et al., 2014). However, the submarine Tuaheni Landslide Complex in the offshore Hikurangi margin is unusual, showing evidence of slow, continuous downslope movement of sediment rather than discrete events. Furthermore, the onset of landslides seem to correlate with the edge of gas-hydrate, with a general shift in the styles of seafloor deformation above and below the depths where the gas hydrates are stable (Figure 2, Mountjoy et al., 2014). The cores and well logs collected from Expedition 372 were used to test several hypotheses on how exactly the gas hydrates are related to the observed gradual landslides.
Figure 2. A seismic subsurface image (Mountjoy et al., 2014) showing the cross section of submarine landslides at the Tuaheni Landslide Complex. The lateral change in deformation style across the locations of gas hydrates (strong amplitude in the seismic section) can be inferred from the different faulting style.
Hikurangi Margin is also well documented for another tectonic phenomenon that is observed along the subduction zones, called slow slip events (SSEs). Unlike the devastating megathrust ruptures that release strong seismic energy from sudden movements along the fault surface, SSEs release energy gradually, over a course of weeks or even months (Saffer et al., 2019). While not necessarily an immediate natural hazard, the phenomenon is a relatively recent finding and garnered increased attention from the research community in the last two decades as the observational techniques improved and densified. Hikurangi margin hosts a region of well-studied SSEs with regular occurrences, where the fault (Pāpaku fault) is at shallow depths, accessible by drilling (Saffer et al., 2019). The goal of Expedition 375 was to reach and sample the fault zone, through coring, wireline logging, and installment of geophysical observatories (Figure 3).
Figure 3. An interpreted seismic subsurface image (Barker et al., 2019) of the drill location relative to the Papaku fault.
Recent studies have begun to shed light on the mechanisms behind the above phenomena using the core and geophysical data retrieved by Expeditions 372 and 375. For example, the cores from Expedition 375 reveal highly variable lithologies near the slow slip fault surface, ranging from marine clay and carbonates to volcaniclastic and conglomerate rocks (Figure 4). The large variety of material with different compositions and grain-sizes also means different deformational responses to the stress as they are carried into the Earth on the subducting plate, and by extension, the different slip behavior (Barnes et al., 2020). Computer numerical modeling has also previously shown that fault surfaces with variable materials might favor transient slow slips over large, sudden ruptures (Saffer et al., 2015), compatible with the observations made from the borehole data.
References
Barnes, P. M., Pecher, I. A., LeVay, L. J., Bourlange, S. M., Brunet, M. M. Y., Cardona, S., … & Wu, H. Y. (2019). Expedition 372A summary. Texas A&M Univ. https://doi.org/10.14379/iodp.proc.372A.101.2019
Saffer, D. M., Wallace, L. M., Barnes, P. M., Pecher, I. A., Petronotis, K. E., LeVay, L. J., … & Wu, H. Y. (2019). Expedition 372B/375 summary. Proceedings of the International Ocean Discovery Program, 372, 1-35. https://doi.org/10.14379/iodp.proc.372B375.101.2019
Harbitz, C. B., Løvholt, F., & Bungum, H. (2014). Submarine landslide tsunamis: how extreme and how likely?. Natural Hazards, 72, 1341-1374.
Mountjoy, J.J., Pecher, I., Henrys, S., Crutchley, G., Barnes, P.M., and PlazaFaverola, A. (2014b). Shallow methane hydrate system controls ongoing,downslope sediment transport in a low-velocity active submarine landslide complex, Hikurangi Margin, New Zealand. Geochemistry, Geophysics, Geosystems, 15(11):4137–4156.https://doi.org/10.1002/2014GC005379
Barker, D.H.N., Henrys, S., Caratori Tontini, F., Barnes, P. M., Bassett, D., Todd, E., and Wallace, L. (2018). Geophysical constraints on the relationship between seamount subduction, slow slip and tremor at the north Hikurangi subduction zone, New Zealand. Geophysical Research Letters, 45(23):12804–12813. https://doi.org/10.1029/2018GL080259
Barnes, P. M., Wallace, L. M., Saffer, D. M., Bell, R. E., Underwood, M. B., Fagereng, A., … & IODP Expedition 372 Scientists (2020). Slow slip source characterized by lithological and geometric heterogeneity. Science Advances, 6(13), eaay3314.
Saffer, D. M., & Wallace, L. M. (2015). The frictional, hydrologic, metamorphic and thermal habitat of shallow slow earthquakes. Nature Geoscience, 8(8), 594-600.
Figure 4. Core and borehole data from site U1520, showing variable lithology of the material being transported into the plate boundary fault zone (Barnes et al., 2020). On the right panels, numbered 1–8, are images of the cores that were drilled during IODP Expeditions 372/375.
Reconstruction of the position of Shatsky Rise (in light blue) through time (from 140 to 0 million years ago) across the Pacific Ocean. Shatsky Rise moved due to movement of plate tectonics. Image from ODP Leg 198 Summary.
Shatsky Rise is an oceanic plateau that is located in the Northwest Pacific Ocean off of the coast of Japan. The main goals and objectives of Ocean Drilling Program (ODP) Leg 198 at the Shatsky Rise was to gain a better understanding of abrupt climatic event transitions, “greenhouse” climactic events, and climactic events in general. Shatsky Rise is an excellent location to study such events because it contains sediments of Cretaceous (145.5–65.5 million years ago) and Paleogene (66–23.03 million years ago) ages at relatively shallow burial depths on three distinct highs. Understanding past climatic events such as warming or cooling can play a key role in understanding and predicting similar climatic events in the future.
ODP Leg 198 took place from August 27th, 2001 to October 23rd, 2001. The expedition began at a port located in Yokohama, Japan and ended at a port in Honolulu, Hawaii. The large quantity of sediment cores that were collected on this expedition were helpful in meeting the goals of Leg 198, partially due to the fact that many of the cores contained a clear record of nanno- and microfossils, which are tiny microscopic fossils such as diatoms and foraminifera, that can be an incredibly useful tools to better understand geologic climatic events. Foraminifera, for example, create their shells from ions in the surrounding seawater in which they live, and as such the chemistry of their shells largely reflects the chemistry of the ocean at the time they built their shells. From these fossils and their chemistry, scientists and researchers are able to measure and reconstruct past ocean conditions such as temperature, salinity, and water productivity.
Relief map of Shatsky Rise, with the drilled locations indicated by the red and yellow circles and site numbers. Cooler colors indicate deeper areas, whereas warmer colors indicate shallower areas or areas of higher topography. Image from ODP Leg 198 Summary.
There were three main findings that researchers discovered on Leg 198 that were related to paleomagnetism, climatic transitions, and a cooling event. Paleomagnetism, which is a branch of geophysics, is a field of study that uses rocks or sediment to study the direction and intensity of Earth’s magnetic field at the time of sediment or rock formation. At Site 1208, Leg 198 recovered many mixed siliceous-calcareous Neogene aged (23.03–2.58 million years ago) sediments that were identified to have strong paleomagnetic cycles making them useful for paleoceanographic and paleomagnetic records in the Pacific Ocean during the Neogene (~23-2.58 million yeasr ago). Leg 198 also found climactic transitions related to dysoxic (low-oxygen) or anoxic (no oxygen) environments at the bottom of the seafloor, clear records of nannofossil and planktonic foraminiferal assemblage transformations at the time of major environmental upheavals and transitions, and transitions from paleodepths at the shallower sites that were less sensitive to chemical changes in the deep ocean to those that were at depth ranges highly sensitive to changes. They also found an important deep water cooling event that is related to glaciation in the Antarctic during the Eocene–Oligocene transition (33.9 million years ago), which is important for better understanding the deepening of the calcite compensation depth (CCD), which is the point at which calcium carbonate (CaCO3) is not preserved due to the bottom ocean waters being too acidic. Below the CCD organisms that secrete shells, such as corals, foraminifera, and nannoplankton are not preserved in the sediment.
References
Bains, S., Corfield, R.M., and Norris, R.D., 1999. Mechanisms of climate warming at the end of the Paleocene. Science, 285:724-727.
Bralower, T.J., Premoli Silva, I., Malone, M.J., et al., 2002 Proceedings of the Ocean Drilling Program, Initial Reports Volume 198
————, 1995. Carbon-isotope stratigraphy and paleoceanographic significance of the Lower Cretaceous shallow-water carbonates of Resolution Guyot, Mid-Pacific Mountains. In Winterer, E.L., Sager, W.W., Firth, J.V., and Sinton, J.M. (Eds.), Proc. ODP, Sci. Results, 143: College Station, TX (Ocean Drilling Program), 99-104.
ODP Leg 198 also recovered sediments that span the end-Cretaceous mass extinction, the event that wiped out all non-avian dinosaurs! The darker colored sediments indicate the mass extinction event recorded in the sediments. Image from ODP Leg 198 Summary.
Location map of the six sites drilled during IODP Expedition 353. This map is colored according to topography, with negative numbers and cooler colors indicating depths below sea level. Image from IODP Expedition 353 Summary.
International Ocean Discovery Program (IODP) Expedition 353 was intended to further the understanding of Indian Monsoon circulation changes. Expedition 353 drilled six sites into key regions around the Bay of Bengal, located off the east coast of India. As low atmospheric pressure over the Indo-Asian continent, and high atmospheric pressure over the southern subtropical Indian Ocean changes, this can lead to different weather patterns that affect precipitation over South Asia, the Bay of Bengal, and southeast China. The drillship R/V JOIDES Resolution had previously undergone many drilling voyages to this region to acquire sediments from areas of monsoon impact, however Expedition 353 was the first expedition to drill sediments from the key region of the northern Bay of Bengal.
The eastern margin of India was a result of the separation of India and the Australia/Antarctica portion of the ancient supercontinent Gondwanaland during the Early Cretaceous at ~130 million years ago (Powell et al., 1988; Scotese et al., 1988). Six key drill sites were identified to target that would allow scientists to reconstruct changes in Indian monsoon circulation since the Miocene (~23 million years ago) to the present. During the 33 days of operation at sea, over 4,280 meters of sediment cores were recovered from the six sites.
Images of sediment cores drilled during Expedition 353. A and B are both from Site U1443. The tephra layers, which appear as darker sediments, are from explosive volcanic activity on the island of Sumatra. Image from IODP Expedition 353 Summary.
Some of the main objectives of this expedition were to establish the sensitivity of changes in monsoon circulation relative to the Sun’s location and angle, heat transfer from the Southern Hemisphere, global ice volume, and greenhouse gas effects. Other objectives included determining how long Indian and East Asian monsoon winds and precipitation affected areas based on the geologic history of the area, understanding the effects of climate change and tectonics on erosion and runoff, and to provide targets for paleoclimate models.
On the northeast Indian margin, Sites U1445 and U1446 records water and salt ratios from precipitation and runoff originating from the Ganges-Brahmaputra river complex and many river basins of peninsular India (Cawthern et al., 2014; Flores et al., 2014). Site U1443 recorded salinity and temperature near the global mean. Sites U1447 and U1448 are located within the Andaman Sea, and as such these sites reveal the precipitation and runoff history from the Irrawaddy and Salween river basins. Future studies of these sediments and oceanic properties can lead to a greater understanding of how this area is affected by the Indian summer monsoon season.
In conclusion, IODP Expedition 353 helped develop an understanding of the Indian monsoon circulation changes through time. It is important to understand how these monsoonal changes have affected the area through paleo reconstructions of geologic history. This study of the subtropical Indian Ocean helped scientists understand how precipitation changes over South Asia, the Bay of Bengal, and southeast China will change in the future. Understanding what these areas have experienced throughout time during warming and cooling periods can lead us to predictions as to how the area will be affected during increased warming scenarios in the future.
References
Cawthern, T., Johnson, J.E., Giosan, L., Flores, J.A., Rose, K., and Solomon, E., 2014. A late Miocene–early Pliocene biogenic silica crash in the Andaman Sea and Bay of Bengal. Marine and Petroleum Geology, 58(Part A):490– 501. http://dx.doi.org/10.1016/j.marpetgeo.2014.07.026
Monthly mean salinity for the time period 1955-2006, in which salinity for each month of those years was averaged and plotted (Antonov et al., 2016). Notice how the surface ocean salinity changes seasonally due to the monsoonal rains bringing freshwaters to the ocean. Image from IODP Expedition 353 Summary.
Clemens, S.C., Kuhnt, W., and LeVay, L.J., 2014. iMonsoon: Indian monsoon rainfall in the core convective region. International Ocean Discovery Program Scientific Prospectus, 353. http://dx.doi.org/10.14379/iodp.sp.353.2014
Flores, J.A., Johnson, J.E., Mejía-Molina, A.E., Álverez, M.C., Sierro, F.J., Singh, S.D., Mahanti, S., and Giosan, L., 2014. Sedimentation rates from calcareous nannofossil and planktonic foraminifera biostratigraphy in the Andaman Sea, northern Bay of Bengal, and eastern Arabian Sea. Marine and Petroleum Geology, 58(Part A):425–437. http://dx.doi.org/10.1016/j.marpetgeo.2014.08.011
Johnson, J.E., Phillips, S.C., Torres, M.E., Piñero, E., Rose, K.K., and Giosan, L., 2014. Influence of total organic carbon deposition on the inventory of gas hydrate in the Indian continental margins. Marine and Petroleum Geology, 58(Part A):406–424. http://dx.doi.org/10.1016/j.marpetgeo.2014.08.021
Ponton, C., Giosan, L., Eglinton, T.I., Fuller, D.Q., Johnson, J.E., Kumar, P., and Collett, T.S., 2012. Holocene aridification of India. Geophysical Research Letters, 39(3):L3407. http://dx.doi.org/10.1029/2011GL050722
Powell, C.McA., Roots, S.R., and Veevers, J.J., 1988. Pre-breakup continental extension in East Gondwanaland and the early opening of the eastern Indian Ocean. Tectonophysics, 155(1–4):261–283. http://dx.doi.org/10.1016/0040-1951(88)90269-7
Scotese, C.R., Gahagan, L.M., and Larson, R.L., 1988. Plate tectonic reconstructions of the Cretaceous and Cenozoic ocean basins. Tectonophysics, 155(1–4):27–48. http://dx.doi.org/10.1016/0040-1951(88)90259-4
While the South Pole is covered by a glacier today, the South Pole was not always a frozen wasteland. Glaciation only started about 34 million years ago. As global temperatures changed throughout geologic history, the amount of ice covering Antarctica changed with it. As carbon dioxide (a greenhouse gas) amounts have increased and decreased in the atmosphere throughout history, the amount of ice has also fluctuated, so understanding ice flow through geologic time provides a picture of the impact of changing temperatures. It is particularly important to understand how anthropogenic warming has affected rapid ice melting in polar regions. Global carbon dioxide levels are increasing today in amounts not seen in the geologic past . The most recent time interval that had comparable atmospheric carbon dioxide levels occurred 17–15 million years ago, when the earth last warmed. Thus to best understand the future, it is imperative to understand the past and how Earth systems behaved or responded to increased greenhouse gasses in the atmosphere.
Integrated Ocean Drilling Program Expedition 318 focused on the Wilkes Land Ice Shelf, located on the eastern half of the Antarctic continent. The purpose of the expedition was to drill into the ice sheet to understand how much ice melt occurred, and the rate at which it occurred throughout the past 34 million years. In understanding the rate of ice melt it becomes possible to correlate carbon dioxide levels and accompanying temperature increases in the recent past with ice melt and growth. Additionally, another objective of the mission was to understand how phytoplankton (marine photosynthesizers) have changed through the Holocene (~117 thousand years ago to today). Understanding these changes can provide some insight into how biologic life has changed throughout recent geologic history, particularly in response to changes in the glacial ice.
The change in global temperature in the past 80 million years in relation to ice sheet activity. Time in millions of years is on the left side, and change in global temperatures (in degrees Celsius) is on the bottom axis. The left panel indicates the amount of temperature change through time with major biotic (e.g., extinction of the dinosaurs) and abiotic (e.g., first Antarctic ice sheet) denoted. Right panel indicates how warm the Earth was. Greenhouse world indicates an Earth that had very little to no ice sheets at either of the poles; Transitional world indicates a time when the Earth began to cool down and ice sheets began to appear; Icehouse world was a time when persistent ice sheets were at the South and then the North poles. Obtained fromIntegrated Ocean Drilling Program Expedition 318 Summary
Results from this expedition were found to be quite alarming. Scientists found that global ice amounts increase and decrease with global carbon dioxide concentrations respectively. This conclusion supported the hypothesis made by scientists that the amount of carbon dioxide in the atmosphere is tightly correlated with the amount of ice melt that is occurring into ocean waters. However, most alarmingly the rate of ice melt exceeded predictions, showing that global sea level rise may occur faster than previously expected.
References
Gulick, S., Shevenell, A., Montelli, A. et al. Initiation and long-term instability of the East Antarctic Ice Sheet. Nature 552, 225–229 (2017). https://doi.org/10.1038/nature25026
Expedition 318 Scientists, 2011. Expedition 318 summary. In Escutia, C., Brinkhuis, H., Klaus, A., and the Expedition 318 Scientists, Proc. IODP, 318: Tokyo (Integrated Ocean Drilling Program Management International, Inc.). doi:10.2204/iodp.proc.318.101.2011
The location of the Chicxulub Crater, where the meteor struck 66 million years ago, that led to the K-Pg mass extinction. The red circle in the top panel denotes the diameter of the crater on the Yucatan Peninsula and into the Gulf of Mexico. The bottom image indicates the trough created by the impactor, with locations of sinkholes surrounding the impact structure. NASA/JPL-Caltech, modified b – Modified NASA image, with scale and labels to increase clarity by David Fuchs. Original: http://photojournal.jpl.nasa.gov/catalog/PIA03379
The Chicxulub impact crater, located on the Yucatán Peninsula of México, is best known for being the location of a massive meteor impact causing the Cretaceous/Paleocene (K-Pg) mass extinction event. This is a major mass extinction that led to the extinction of 75% of species on Earth (Gulick et al., 2017). The site has been the subject of debate for many years surrounding the extent of the impact and the environmental fallout of the area since.
Such debates led to a need for further studies and additional information. The main goal of the International Ocean Discovery Program (IODP) and International Continental Scientific Drilling Program (ICDP) Leg 364 was to drill sediments within the impact site to study the peak rings that formed during impact, and how the meteor impact affected the surrounding area. Other expedition objectives included the nature and extent of post-impact hydrothermal circulation, the recovery of life in a sterile zone, and recovery of sediments through the Paleocene/Eocene Thermal Maximum (PETM; Gulick et al., 2017), an event that took place approximately 55 million years ago and was characterized by the Earth heating up by 5–8°C.
In 2016 the Vessel L/B Myrtle began its voyage for the Yucatán continental shelf. A single borehole (Hole M0077A) was drilled into the Chicxulub impact crater and 828.99 meters of cored sediments and rock was recovered from below the seafloor. The recovered sediments and rocks allowed scientists to achieve many of the scientific goals that were established for this expedition.
Figure 2. Image of different impact structures showing the crater rims, peak rings, basins, and troughs. These images are from Venus (upper left and right) and the Moon (bottom). Photo credit: NASA
One of the main goals of the expedition, to core sediments from the peak ring, was successful. Peak rings were formed during the large impact on the Earth’s surface causing the underlying rocks to fracture and overturn onto the impact site. The recovered rocks and sediments allowed scientists to determine that the peak ring is formed from uplifted, shocked, and fractured granitic rocks that overlie older sedimentary rocks. This supported the hypothesis made by Morgan et al. (2016), stating that the dynamic collapse model for peak-ring formation is accurate, and also supported the hypothesis that the rocks are highly porous and fractured from the impact (Gulick et al., 2013). Shipboard studies of microfossils recovered from the sediments indicated that the PETM interval is present in the core sediments, which will allow for the sediments to be studied in greater detail.
Another objective of the expedition was to understand the hydrothermal system surrounding impacts on Earth. Many scientists hypothesize that microbial life starts on Earth at impact sites. Scientists wanted to study this area for signs of early microbial life. Directly after impact Chicxulub was considered to be a sterile zone, as the impact was so sudden, the area around the impact became super heated and all life in the region was instantly wiped out. Scientists have recently found evidence that cyanobacteria may have bloomed a few months after impact (Schaefer et al., 2020). Small trace fossils and other forms of microbes are believed to have come back within a year after the impact.
In conclusion, this drilling expedition is considered to be a great success. Many of the predetermined objectives for the expedition were completed, and lots of other promising data was collected for future studies. Drilling into the impact point of the meteor that caused the Cretaceous/Paleocene (K-Pg) mass extinction was a monumental finding for scientists all over the world. This expedition gave scientists evidence for the formation of peak rings, and allowed for the unique study of how life recovers from such an event.
Figure 3. A frame from a simulation of what the Earth’s mantle to upper crust to atmosphere may have looked like at 35 seconds after impact. Dark blue represents the Earth’s mantle; green represents the basement rocks; gray indicates the seafloor sediments and projectiles; light blue represents the atmosphere. The right side of the image is distance, in kilometers, and the bottom axis is distance, in kilometers. Image modified from Artemieva and Morgan (2009). This model indicates that ejecta (sediments from the seafloor) were flung over 200 km (124 miles) into Earth’s atmosphere! In fact, the impact hit Earth so hard, there was very likely dust and sediments shot out into space. The impactor hit Earth so hard, it nearly instantaneously created a 20 mile deep hole in the Earth!
Collins, G.S., Melosh, H.J., Morgan, J.V., and Warner, M.R., 2002. Hydrocode simulations of Chicxulub crater collapse and peak-ring formation. Icarus, 157(1):24–33. https://doi.org/10.1006/icar.2002.6822
Gulick, S. P., Morgan, J. V., Mellett, C. L., Green, S. L., & Kring, D. A. (2017). Expedition 364 summary. International Ocean Discovery Program.
Gulick, S. P. S., Christeson, G. L., Barton, P. J., Grieve, R. A. F., Morgan, J. V., & Urrutia‐Fucugauchi, J. (2013). Geophysical characterization of the Chicxulub impact crater. Reviews of Geophysics, 51(1), 31-52.
Ivanov, B.A., 2005. Numerical modeling of the largest terrestrial meteorite craters. Solar System Research, 39(5):381–409. https://doi.org/10.1007/s11208-005-0051-0
Kring, D.A., Hörz, F., Zurcher, L., and Urrutia Fucugauchi, J., 2004. Impact lithologies and their emplacement in the Chicxulub impact crater: initial results from the Chicxulub Scientific Drilling Project, Yaxcopoil, Mexico. Meteoritics & Planetary Science, 39(6):879–897. https://doi.org/10.1111/j.1945-5100.2004.tb00936.x
Morgan, J. V., Gulick, S. P., Bralower, T., Chenot, E., Christeson, G., Claeys, P., … & Zylberman, W. (2016). The formation of peak rings in large impact craters. Science, 354(6314), 878-882.
Senft, L.E., and Stewart, S.T., 2009. Dynamic fault weakening and the formation of large impact craters. Earth and Planetary Science Letters, 287(3– 4):471–482. https://doi.org/10.1016/j.epsl.2009.08.033
Figure 1: Expedition 339 sites that were drilled (yellow dots) in the Gulf of Cádiz and West Iberian margin. Note that the drilled sites are located around the margins of the continents, in shallower water depths. Deeper water is denoted by darker blue colors, whereas lighter blue to light green colors indicate shallower water depths. Land is denoted by the light to dark brown colors. Figure from Expedition 339 Preliminary Report
The Strait of Gibraltar is a significant gateway that currently connects the Atlantic Ocean to the Mediterranean Sea. From November 2011 to January 2012, the Integrated Ocean Drilling Program (IODP) Expedition 339 science team drilled a total of seven sites, consisting of five sites in the Gulf of Cadiz (GC) and two sites off the West Iberian margin (Table 1 & Figure 1). The major objective of this drilling expedition was to study what happened when the Strait of Gibraltar opened about 5 million years ago, causing warm and salty water to flow into the North Atlantic Ocean. Scientists chose to drill in this region because it is an important spot to study the movement of Mediterranean Outflow Water (MOW) through the Strait of Gibraltar and how it affects the world’s ocean currents and weather patterns. It is also an area of interest for understanding the effects of tectonic activity on the evolution of the Strait of Gibraltar and how sediments collect around the continents. Climate plays a huge role in influencing the changes in the MOW and ocean currents over time. From about 6 million years ago, when the connections between the Atlantic Ocean and the Mediterranean Sea in Spain and Morocco closed off, to 5.3 million years ago when the Strait of Gibraltar opened back up, the way the Earth’s tectonic plates moved had an even bigger impact on how sediment built up and how the ocean currents changed.
Some of the Expedition 339 crew members had the opportunity to watch the International Space Station (ISS) pass overhead on the night of Dec 4th, 2011, even though it appeared as a tiny moving dot in the sky. As reported by Helder Pereira, while drilling at Site U1386, the Joides Resolution (JR) research vessel was spotted by the ISS as it was orbiting the Earth! Interestingly, while they were watching, the ISS was also observing them and took a beautiful picture of the Iberian Peninsula. Can you spot the JR inside the orange circle located a few miles southeast of Faro (Algarve, Portugal) in the lower bottom right of Figure 3?
Figure 2: Smaller inset figure of the Earth with an arrow that is pointing to the general location where Expedition 339 drilled. Larger location sketch with the main water-masses, deep ocean currents, and surface currents along the continental margin (modified from Hernández-Molina et al., 2006). Figure from Expedition 339 Preliminary Report
Expedition 339 had five broad scientific objectives, which are summarized below:
Understand the opening of the Strait of Gibraltar gateway and when the Mediterranean Outflow Water (MOW) began. Many scientists have different hypotheses on how the Strait of Gibraltar opened around 5 million years ago. Some believe it was due to tectonic changes, while others think it was caused by erosion of the land. The reopening ended the isolation of the Mediterranean Sea and the global effects of the Messinian Salinity Crisis (this was a time in which the Mediterranean Sea was isolated from the Atlantic Ocean, and drying up of the sea left behind major salt deposits and highly saline waters). It took some time for the deep MOW to flow out, and the exact timing of such outflow is relatively unknown. The first objective of Expedition 339 was to drill through sediment layers on the seafloor to determine the age of those sediments in the Gulf of Cádiz. Scientists also wanted to examine changes in contourite deposits, or sediment deposits that happen offshore, and MOW bottom water changes (temperature, salinity) during the geologic period from the end of the Miocene Period (~5 million years ago) to the early to middle Pliocene Period (~3 million years ago).
Determine the ancient circulation pattern of MOW and how such different circulation changes might affect global climate: Today, warm and salty (more than 300,000 tons of excess salt) water flows into the North Atlantic from the Mediterranean Sea through the Strait of Gibraltar gateway every second! A density increase in North Atlantic Deep Water could affect the ocean’s thermohaline circulation (circulation of deep waters driven by density differences in those waters) and could have implications for climate change. To better understand these processes, researchers are actively studying the millennial to long-term changes of Mediterranean outflow and its effects on thermohaline circulation. The second objective was to date the unconformities (where there is missing time in the sedimentary record) and discontinuities identified on seismic records. Such identification can help to assess the sedimentary record’s link to past circulation variation and events and understand the forces driving bottom water circulation changes over different timescales.
Establish a marine reference section of Pleistocene (2.58–0.017 million years ago) climate (rapid climate change): This objective intersects with the principal objective of Site U1385 [APL-763] which was to drill into the Iberian margin, offshore Portugal to recover a sediment record that could be studied to infer Pleistocene climate changes. In turn, this sediment record can be correlated with polar ice cores and terrestrial sediments and other climate records to better understand climate change during the past ~2.58 million years.
Identify external controls on the sediments from the Gulf of Cádiz contourites and West Iberian margin: The fourth objective of this expedition was to study how sea level change and the size of the Strait of Gibraltar impacted sediment deposits in the Gulf of Cádiz and the West Iberian margin. This will help to distinguish between regional changes caused by climate and sea level, and to develop a better understanding of the sediments and under what conditions they were deposited in the area. The researchers plan to drill and analyze sediment cores, date them, and correlate them to create a pattern of the sediments and the hiatuses, or times of no sediment deposition, between them. They also want to evaluate how the Mediterranean Outflow Water flux and how global sea level changes affected the Gibraltar sill, as well as the circulation of the North Atlantic. By analyzing the composition of sediments and how fast they accumulated through time, scientists hope to better understand the sediment supply and flux for the sediment deposits in the gulf.
Investigate the tectonic activity in the region, and how it controlled the deposition of sediments in the region: This objective relates to using the sediments that were drilled to infer the age of tectonic events and the changes that resulted from this events in the Gulf of Cadiz and Iberian margin. The scientists also wanted to investigate diapirs, or the movement of low-density rocks such as salts, into older, more dense rocks.
Figure 3: The Iberian Peninsula at night. This photo was taken on Dec 4th, 2011 at 00:13:44 GMT. Spacecraft nadir point: 36.6° N, 13.9° W; Photo center point: 40.5° N, 5.0° W; Spacecraft Altitude: 206 nautical miles (382 km). Figure from The JR seen from space!
The expedition successfully met all five of the scientific objectives, and recovered about 5447 meters (3.38 miles!) of cores. The region was drilled for the first time for scientific purposes and the results confirmed some pre-expedition hypotheses and also provided new information and ideas not initially anticipated. For instance, the scientists discovered a larger-than-anticipated petroleum system with huge hydrocarbon potential, presenting a new and significant opportunity to explore oil and gas reserves in the region!
Figure 4: General circulation pattern of the Mediterranean Outflow Water (MOW) pathway in the North Atlantic (modified from Iorga and Lozier, 1999). Red circles filled with yellow indicate the relative location of the sites. AB = Agadir Basin, BAP = Biscay Abyssal Plain, BB = Bay of Biscay, EP = Ex- tremadura Promontory, GaB = Galicia Bank, GoB = Gorringe Bank, HAP = Horseshoe Abyssal Plain, MAP = Madeira Abyssal Plain, MI = Madeira Island, PAP = Porcupine Abyssal Plain, RC = Rockall Channel, SAP = Seine Abyssal Plain, St.V = Cape São Vicente, TAP = Tagus Abyssal Plain. Figure from Expedition 339 Preliminary Report
Results from Expedition 339 opened the door for even more post-expedition research. Some studies focused on the reconstruction of the Mediterranean-Atlantic water exchange after the opening of the Gibraltar Strait 5.3 million years ago to understand the behavior of the Mediterranean Outflow Water during this period (Bahr et al., 2014) and to study the past ocean conditions (García-Gallardo et al., 2017). Studies published using the recovered sediments observed that MOW varied in strength and location during different historical periods, and that MOW resembles water from the Levantine Basin in the Eastern Mediterranean (Kaboth et al., 2016). A new detailed record from 416,000 years ago reveals that changes in MOW strength and depth during the Late Pleistocene age (~0.12–0.017 million years ago) were caused by the climate; the main factor controlling these changes being the rainfall pattern around the Mediterranean region (Nichols et al., 2020). Also, pollen and biomarker data from Site U1385 (Figure 1) was used to study the unique climate during Marine Isotope Stage (MIS) 13, a period around 533,000 to 478,000 years ago, when the climate was cool and humid, resulting in forest expansion in the Iberian Peninsula (Oliveira et al., 2022).
References
Bahr, A., Jiménez-Espejo, F.J., Kolasinac, N., Grunert, P., Hernández-Molina, F.J., Röhl, U., Voelker, A.H.L., Escutia, C., Stow, D.A.V., Hodell, D., and Alvarez-Zarikian, C.A., 2014. Deciphering bottom current velocity and paleoclimate signals from contourite deposits in the Gulf of Cádiz during the last 140 kyr: an inorganic geochemical approach. Geochemistry, Geophysics, Geosystems, 15(8):3145–3160. https://doi.org/10.1002/2014GC005356
García-Gallardo, Á., Grunert, P., Van der Schee, M., Sierro, F.J., Jiménez-Espejo, F.J., Alvarez Zarikian, C.A., and Piller, W.E., 2017. Benthic foraminifera-based reconstruction of the first Mediterranean-Atlantic exchange in the early Pliocene Gulf of Cadiz. Palaeogeography, Palaeoclimatology, Palaeoecology, 472:93–107. https://doi.org/10.1016/j.palaeo.2017.02.009
Kaboth, S., Bahr, A., Reichart, G.-J., Jacobs, B., and Lourens, L.J., 2016. New insights into upper MOW variability over the last 150 kyr from IODP 339 Site U1386 in the Gulf of Cadiz. Marine Geology, 377:136–145. https://doi.org/10.1016/j.margeo.2015.08.014
Nichols, M.D., Xuan, C., Crowhurst, S., Hodell, D.A., Richter, C., Acton, G.D., and Wilson, P.A., 2020. Climate-induced variability in Mediterranean Outflow to the North Atlantic Ocean during the late Pleistocene. Paleoceanography and Paleoclimatology, 35(9):e2020PA003947. https://doi.org/10.1029/2020PA003947
Oliveira, D., Desprat, S., Yin, Q., Rodrigues, T., Naughton, F., Trigo, R.M., Su, Q., Grimalt, J.O., Alonso-Garcia, M., Voelker, A.H.L., Abrantes, F., and Sánchez Goñi, M.F., 2020. Combination of insolation and ice-sheet forcing drive enhanced humidity in northern subtropical regions during MIS 13. Quaternary Science Reviews, 247:106573. https://doi.org/10.1016/j.quascirev.2020.106573
