skip to main content


Title: Maldives Monsoon and Sea Level
International Ocean Discovery Program (IODP) Expedition 357 successfully cored an east–west transect across the southern wall of Atlantis Massif on the western flank of the Mid-Atlantic Ridge (MAR) to study the links between serpentinization processes and microbial activity in the shallow subsurface of highly altered ultramafic and mafic sequences that have been uplifted to the seafloor along a major detachment fault zone. The primary goals of this expedition were to (1) examine the role of serpentinization in driving hydrothermal systems, sustaining microbial communities, and sequestering carbon; (2) characterize the tectonomagmatic processes that lead to lithospheric heterogeneities and detachment faulting; and (3) assess how abiotic and biotic processes change with variations in rock type and progressive exposure on the seafloor. To accomplish these objectives, we developed a coring and sampling strategy centered on the use of seabed drills—the first time that such systems have been used in the scientific ocean drilling programs. This technology was chosen in the hope of achieving high recovery of the carbonate cap sequences and intact contact and deformation relationships. The expedition plans also included several engineering developments to assess geochemical parameters during drilling; sample bottom water before, during, and after drilling; supply synthetic tracers during drilling for contamination assessment; acquire in situ electrical resistivity and magnetic susceptibility measurements for assessing fractures, fluid flow, and extent of serpentinization; and seal boreholes to provide opportunities for future experiments. Expedition 359 was designed to address changes in sea level and currents, along with monsoon evolution in the Indian Ocean. The Maldives archipelago holds a unique and mostly unread Indian Ocean archive of the evolving Cenozoic icehouse world. Cores from eight drill sites in the Inner Sea of the Maldives provide the tropical marine record that is key for better understanding the effects of this global evolution in the Indo-Pacific realm. In addition, the bank geometries of the carbonate archipelago provide a physical record of changing sea level and ocean currents. The bank growth occurs in pulses of aggradation and progradation that are controlled by sea level fluctuations during the early and middle Miocene, including the mid-Miocene Climate Optimum. A dramatic shift in development of the carbonate edifice from a sea level–controlled to a predominantly current-controlled system appears to be directly linked to the evolving Indian monsoon. This phase led to a twofold configuration of bank development: bank growth continued in some parts of the edifice, whereas in other places, banks drowned. Drowning steps seem to coincide with onset and intensification of the monsoon-related current system and subsequent deposition of contourite fans and large-scale sediment drifts. As such, the drift deposits will provide a continuous record of Indian monsoon development in the region of the Maldives. A major focus of Expedition 359 was to date precisely the onset of the current system. This goal was successfully completed during the expedition. The second important outcome of Expedition 359 was groundtruthing the hypothesis that the dramatic, pronounced change in style of the carbonate platform sequence stacking was caused by a combination of relative sea level fluctuations and ocean current system changes. These questions are directly addressed by the shipboard scientific data. In addition, Expedition 359 cores will provide a complete Neogene δ13C record of the platform and platform margin sediments and a comparison with pelagic records over the same time period. This comparison will allow assessment of the extent to which platform carbonates record changes in the global carbon cycle and whether changes in the carbon isotopic composition of organic and inorganic components covary and the implications this has on the deep-time record. This determination is important because such records are the only type that exists in deep time.  more » « less
Award ID(s):
1326927
NSF-PAR ID:
10223870
Author(s) / Creator(s):
; ;
Date Published:
Journal Name:
Proceedings of the International Ocean Discovery Program
Volume:
359
ISSN:
2377-3189
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. null (Ed.)
    International Ocean Discovery Program Expedition 359 was designed to address changes in sea level and currents, along with monsoon evolution in the Indian Ocean. Eight drill sites are located in the carbonate edifice of the Republic of Maldives, which bears a unique and mostly unread Indian Ocean archive of the evolving Cenozoic icehouse world. This tropical marine record is key for better understanding the effects of this global evolution in the Indo-Pacific realm. The bank geometries of the growing carbonate archipelago provide a physical record of changing sea level and ocean currents. The bank growth occurs in pulses of aggradation and progradation that are controlled by sea level fluctuations during the early and middle Miocene, including the mid-Miocene Climate Optimum. A dramatic shift in development of the carbonate edifice from a sea level–controlled to a predominantly current-controlled system appears to be directly linked to the evolving Indian monsoon. This phase led to a twofold configuration of bank development: bank growth continued in some parts of the edifice, whereas in other places, banks drowned. Drowning steps seem to coincide with onset and intensification of the monsoon-related current system and deposition of contourite fans and giant sediment drifts. Expedition 359 cores are intended for reconstructing the changing current system through time that is directly related to the evolution of the Indian monsoon. As such, the drift deposits will provide a continuous record of Indian monsoon development in the region of the Maldives. Expedition 359 had two main focus points. The first was to date precisely the onset of the current system that is potentially in concert with the onset or the intensification of the Indian monsoon and coincides with the onset of the modern current system in the world’s ocean. The second important outcome of Expedition 359 is groundtruthing the hypothesis that the dramatic, pronounced change in style of the sedimentary carbonate sequence stacking was caused by a combination of relative sea level fluctuations and ocean current system changes. These questions were directly addressed by the shipboard scientific data. In addition, Expedition 359 cores will provide a complete Neogene δ13C record of the platform and platform margin sediments and a comparison with pelagic records over the same time period. This comparison will allow assessment of the extent to which platform carbonates record changes in the global carbon cycle and whether changes in the carbon isotopic composition of organic and inorganic components covary and the implications this has on the deep-time record. This determination is important, as such records are the only type that exist in deep time. 
    more » « less
  2. null (Ed.)
    International Ocean Discovery Program (IODP) Expedition 359 is designed to address sea level, currents, and monsoon evolution in the Indian Ocean. Seven proposed drill sites are located in the Maldives and one site is located in the Kerala-Konkan Basin on the western Indian continental margin. The Maldives carbonate edifice bears a unique and mostly unread Indian Ocean archive of the evolving Cenozoic icehouse world. It has great potential to serve as a key area for better understanding the effects of this global evolution in the Indo-Pacific realm. Based mainly on seismic stratigraphic data, a model for the evolution of this carbonate bank has been developed, showing how changing sea level and ocean current patterns shaped the bank geometries. A dramatic shift in development of the carbonate edifice from a sea level–controlled to a predominantly current-controlled system is thought to be directly linked to the evolving Indian monsoon. Fluctuations in relative sea level control the stacking pattern of depositional sequences during the lower to middle Miocene. This phase was followed by a two-fold configuration of bank development: bank growth continued in some parts of the edifice, whereas in other places, banks drowned. Drowning steps seem to coincide with onset and intensification of the monsoon-related current system and the deposition of giant sediment drifts. The shapes of drowned banks attest to the occurrence of these strong currents. The drift sediments, characterized by off-lapping geometries, formed large-scale prograding complexes, filling the Maldives Inner Sea basin. Because the strong current swept most of the sediment around the atolls away, relict banks did not prograde, and steady subsidence was balanced by aggradation of the atolls, which are still active today. One important outcome of Expedition 359 is ground-truthing the hypothesis that the dramatic, pronounced change in the style of the sedimentary carbonate sequence stacking was caused by a combination of relative sea level fluctuations and ocean current system changes. Answering this question will directly improve our knowledge on processes shaping carbonate platforms and their stratigraphic records. Our findings would be clearly applicable to other Tertiary carbonate platforms in the Indo-Pacific region and to numerous others throughout the geological record. In addition, the targeted successions will allow calibration of the Neogene oceanic δ13C record with data from a carbonate platform to platform-margin series. This is becoming important, as such records are the only type that exist in deep time. Drilling will provide the cores required for reconstructing changing current systems through time that are directly related to the evolution of the Indian monsoon. As such, the drift deposits will provide a continuous record of Indian monsoon development in the region of the Maldives. These data will be valuable for a comparison with proposed Site KK-03B in the Kerala-Konkan Basin (see Geological setting of the Kerala-Konkan Basin, below) and other monsoon-dedicated IODP expeditions. The proposed site in the Kerala-Konkan Basin provides the opportunity to recover colocated oceanic and terrestrial records for monsoon and premonsoon Cenozoic climate in the eastern Arabian Sea and India, respectively. The site is located on a bathymetric high immediately north of the Chagos-Laccadive Ridge and is therefore not affected by strong tectonic, glacial, and nonmonsoon climatic processes that affect fan sites fed by Himalayan rivers. The cores are expected to consist of a continuous sequence of foraminifer-rich pelagic sediments with subordinate cyclical siliciclastic inputs of fluvial origin from the Indian Peninsula for the Neogene and a continuous paleoclimate record at orbital timescales into the Eocene and possibly the Paleocene. 
    more » « less
  3. null (Ed.)
    International Ocean Discovery Program (IODP) Expedition 357 successfully cored an east–west transect across the southern wall of Atlantis Massif on the western flank of the Mid-Atlantic Ridge to study the links between serpentinization processes and microbial activity in the shallow subsurface of highly altered ultramafic and mafic sequences that have been uplifted to the seafloor along a major detachment fault zone. The primary goals of this expedition were to (1) examine the role of serpentinization in driving hydrothermal systems, sustaining microbial communities, and sequestering carbon; (2) characterize the tectonomagmatic processes that lead to lithospheric heterogeneities and detachment faulting; and (3) assess how abiotic and biotic processes change with variations in rock type and progressive exposure on the seafloor. To accomplish these objectives, we developed a coring and sampling strategy based around the use of seabed rock drills—the first time that such systems have been used in the scientific ocean drilling programs. This technology was chosen in hopes of achieving high recovery of the carbonate cap sequences and intact contact and deformation relationships. The expedition plans also included several engineering developments to assess geochemical parameters during drilling; sample bottom water before and after drilling; supply synthetic tracers during drilling for contamination assessment; gather downhole electrical resistivity and magnetic susceptibility logs for assessing fractures, fluid flow, and extent of serpentinization; and seal boreholes to provide opportunities for future experiments. Seventeen holes were drilled at nine sites across Atlantis Massif, with two sites on the eastern end of the southern wall (Sites M0068 and M0075), three sites in the central section of the southern wall north of the Lost City hydrothermal field (Sites M0069, M0072, and M0076), two sites on the western end (Sites M0071 and M0073), and two sites north of the southern wall in the direction of the central dome of the massif and Integrated Ocean Drilling Program Site U1309 (Sites M0070 and M0074). Use of seabed rock drills enabled collection of more than 57 m of core, with borehole penetration ranging from 1.3 to 16.44 meters below seafloor and core recoveries as high as 75% of total penetration. This high level of recovery of shallow mantle sequences is unprecedented in the history of ocean drilling. The cores recovered along the southern wall of Atlantis Massif have highly heterogeneous lithologies, types of alteration, and degrees of deformation. The ultramafic rocks are dominated by harzburgites with intervals of dunite and minor pyroxenite veins, as well as gabbroic rocks occurring as melt impregnations and veins, all of which provide information about early magmatic processes and the magmatic evolution in the southernmost portion of Atlantis Massif. Dolerite dikes and basaltic rocks represent the latest stage of magmatic activity. Overall, the ultramafic rocks recovered during Expedition 357 revealed a high degree of serpentinization, as well as metasomatic talc-amphibole-chlorite overprinting and local rodingitization. Metasomatism postdates an early phase of serpentinization but predates late-stage intrusion and alteration of dolerite dikes and the extrusion of basalt. The intensity of alteration is generally lower in the gabbroic and doleritic rocks. Chilled margins in dolerite intruded into talc-amphibole-chlorite schists are observed at the most eastern Site M0075. Deformation in Expedition 357 cores is variable and dominated by brecciation and formation of localized shear zones; the degree of carbonate veining was lower than anticipated. All types of variably altered and deformed ultramafic and mafic rocks occur as components in sedimentary breccias and as fault scarp rubble. The sedimentary cap rocks include basaltic breccias with a carbonate sand matrix and/or fossiliferous carbonate. Fresh glass on basaltic components was observed in some of the breccias. The expedition also successfully applied new technologies, namely (1) extensively using an in situ sensor package and water sampling system on the seabed drills for evaluating real-time dissolved oxygen and methane, pH, oxidation-reduction potential, temperature, and conductivity during drilling; (2) deploying a borehole plug system for sealing seabed drill boreholes at four sites to allow access for future sampling; and (3) proving that tracers can be delivered into drilling fluids when using seabed drills. The rock drill sensor packages and water sampling enabled detection of elevated dissolved methane and hydrogen concentrations during and/or after drilling, with “hot spots” of hydrogen observed over Sites M0068–M0072 and methane over Sites M0070–M0072. Shipboard determination of contamination tracer delivery confirmed appropriate sample handling procedures for microbiological and geochemical analyses, which will aid all subsequent microbiological investigations that are part of the science party sampling plans, as well as verify this new tracer delivery technology for seabed drill rigs. Shipboard investigation of biomass density in select samples revealed relatively low and variable cell densities, and enrichment experiments set up shipboard reveal growth. Thus, we anticipate achieving many of the deep biosphere–related objectives of the expedition through continued scientific investigation in the coming years. Finally, although not an objective of the expedition, we were serendipitously able to generate a high-resolution (20 m per pixel) multibeam bathymetry map across the entire Atlantis Massif and the nearby fracture zone, Mid-Atlantic Ridge, and eastern conjugate, taking advantage of weather and operational downtime. This will assist science party members in evaluating and interpreting tectonic and mass-wasting processes at Atlantis Massif. 
    more » « less
  4. null (Ed.)
    International Ocean Discovery Program (IODP) Expedition 357 will be implemented as a Mission Specific Platform (MSP) expedition that will address two exciting discoveries in mid-ocean-ridge research: off-axis, serpentinite-hosted hydrothermal activity exemplified by the Lost City hydrothermal field (LCHF) and the significance of tectono-magmatic processes in forming and exposing heterogeneous mafic and variably serpentinized ultramafic lithosphere that are key components of slow- and ultraslow-spreading ridges. Serpentinization is a fundamental process that controls rheology and geophysical properties of the oceanic lithosphere and has major consequences for heat flux, geochemical cycles, and microbial activity in a wide variety of environments. However, we currently have no constraints on the nature and distribution of microbial communities in ultramafic subsurface environments. Our planned drilling focuses on (1) exploring the extent and activity of the subsurface biosphere in young ultramafic and mafic seafloor; (2) quantifying the role of serpentinization in driving hydrothermal systems, in sustaining microbiological communities, and in the sequestration of carbon in ultramafic rocks; (3) assessing how abiotic and biotic processes change with aging of the lithosphere and with variations in rock type; and (4) characterizing tectono-magmatic processes that lead to lithospheric heterogeneities and the evolution of hydrothermal activity associated with detachment faulting. This expedition will be the first IODP expedition to utilize seafloor drill technology (MeBo and BGS Seafloor Rockdrill 2) to core a series of shallow (50–80 m) holes across Atlantis Massif—an oceanic core complex (30°N, Mid-Atlantic Ridge), where detachment faulting exposes mafic and ultramafic lithologies on the seafloor. We aim to recover in situ sequences of sediments, hydrothermal deposits/veins, and basement rocks that comprise a broad zone of detachment faulting across (1) a spreading-parallel (east–west) profile along the southern wall and at varying distances from the LCHF and (2) a ridge-parallel (north–south) profile into the center of the massif, where the dominant rock type changes from ultramafic to mafic. Drilling the east–west profile will allow us to evaluate how microbial communities evolve with variations in hydrothermal activity and with age of emplacement on the seafloor. We aim to compare microbial activity and diversity in areas of diffuse, H2-rich fluid flow and carbonate precipitation with communities in areas away from the active hydrothermal system and with variable substrates and crustal ages. By quantifying the extent and evolution of carbonate precipitation we will evaluate the potential for natural CO2 sequestration in serpentinizing peridotites. Drilling the north–south profile will allow us to evaluate the nature of the deep biosphere in varying lithologies and to assess the role of the differing rheologies of gabbros and serpentinized ultramafic rocks in localizing detachment faults. This expedition will also include engineering developments to sample bottom waters before and after drilling and to monitor methane, dissolved oxygen, redox, conductivity, temperature, and depth while drilling. In addition, seafloor operations will include deploying borehole plugs and swellable packers to seal the holes at high-priority sites after drilling to provide opportunities for future hydrogeological and microbiological experiments. 
    more » « less
  5. null (Ed.)
    International Ocean Discovery Program (IODP) Expedition 360 was the first leg of Phase I of the SloMo (shorthand for “The nature of the lower crust and Moho at slower spreading ridges”) Project, a multiphase drilling program that proposes to drill through the outermost of the global seismic velocity discontinuities, the Mohorovičić seismic discontinuity (Moho). The Moho corresponds to a compressional wave velocity increase, typically at ~7 km beneath the oceans, and has generally been regarded as the boundary between crust and mantle. An alternative model, that the Moho is a hydration front in the mantle, has recently gained credence upon the discovery of abundant partially serpentinized peridotite on the seafloor and on the walls of fracture zones, such as at Atlantis Bank, an 11–13 My old elevated oceanic core complex massif adjacent to the Atlantis II Transform on the Southwest Indian Ridge. Hole U1473A was drilled on the summit of Atlantis Bank during Expedition 360, 1–2 km away from two previous Ocean Drilling Program (ODP) holes: Hole 735B (drilled during ODP Leg 118 in 1987 and ODP Leg 176 in 1997) and Hole 1105A (drilled during ODP Leg 179 in 1998). A mantle peridotite/gabbro contact has been traced by dredging and diving along the transform wall for 40 km. The contact is located at ~4200 m depth on the transform wall below the drill sites but shoals considerably 20 km to the south, where it was observed in outcrop at 2563 m depth. Moho reflections, however, have been found at ~5–6 km beneath Atlantis Bank and <4 km beneath the transform wall, leading to the suggestion that the seismic discontinuity may not represent the crust/mantle boundary but rather an alteration (serpentinization) front. This in turn raises the interesting possibility that methanogenesis associated with serpentinization could support a whole new planetary biosphere deep in the oceanic basement. The SloMo Project seeks to test these hypotheses at Atlantis Bank and evaluate the processes of natural carbon sequestration in the lower crust and uppermost mantle. A primary objective of SloMo Leg 1 was to explore the lateral variability of the stratigraphy established in Hole 735B. Comparison of Hole U1473A with Holes 735B and 1105A allows us to demonstrate a continuity of process and complex interplay of magmatic accretion and steady-state detachment faulting over a time period of ~128 ky. Preliminary assessment indicates that these sections of lower crust are constructed by repeated cycles of intrusion, represented in Hole U1473A by approximately three upwardly differentiated hundreds of meter–scale bodies of olivine gabbro broadly similar to those encountered in the deeper parts of Hole 735B. Specific aims of Expedition 360 focused on gaining an understanding of how magmatism and tectonism interact in accommodating seafloor spreading, how magnetic reversal boundaries are expressed in the lower crust, assessing the role of the lower crust and shallow mantle in the global carbon cycle, and constraining the extent and nature of life at deep levels within the ocean lithosphere. 
    more » « less