Northwestern Indian Ocean Research Articles

Modern-like deep water circulation in Indian Ocean caused by Central American Seaway closure

Global overturning circulation underwent significant changes in the late Miocene, driven by tectonic forcing, and impacted the global climate. Prevailing hypotheses related to the late Miocene deep water circulation (DWC) changes driven by the closure of the Central American Seaways (CAS) and its widespread impact remains untested due to the paucity of suitable records away from the CAS region. Here, we test the hypothesis of the large-scale circulation changes by providing a high-resolution record of DWC since the late Miocene (11.3 to ~2 Ma) from the north-western Indian Ocean. Our investigation reveals a progressive shift from Pacific-dominated DWC before ~9.0 Ma to the onset of a modern-like DWC system in the Indian Ocean comprising of Antarctic bottom water and northern component water during the Miocene-Pliocene transition (~6 Ma) caused by progressive shoaling of the CAS and suggests its widespread impact.

Sea surface height fluctuations relevant to Indian summer monsoon over the northwestern Indian Ocean

We examined the interannual variations in sea surface height (SSH) over the northwestern Indian Ocean during 1993–2016, by using in situ observations along the east coast of the Arabian Peninsula together with satellite observations, objective analysis, and reanalysis. Focusing on the impacts of the Indian summer monsoon relative to the El Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) modes, we found that the monsoon predominantly controls the summertime SSH variations at the in situ observatories, consistent with satellite observations. The monsoon is closely related to the SSH at a specific observatory in almost all seasons, whereas the wintertime SSH is strongly influenced by ENSO and IOD at other observatories. These SSH variations with local modulations in the coastal area were accompanied by basin-scale variations. The reduced southwesterly monsoon wind, for example, is found with the reduced ocean upwelling narrowly confined near the coast and the upper ocean temperature rise implying reduced meridional heat transport over the south of the Arabian Peninsula.

A new tsunami hazard assessment for eastern Makran subduction zone by considering splay faults and applying stochastic modeling

ABSTRACT Tsunami hazard imposed by possible rupture of splay faults is important as it may significantly intensify tsunami heights locally. The Makran Subduction Zone (MSZ) in the northwestern Indian Ocean can generate large thrust earthquakes that could trigger significant tsunamis. In this paper, the effects of possible rupture of splay faults on the tsunami hazards of eastern MSZ are studied by developing a framework that uses stochastic earthquake rupture models and considers uncertainties related to rupture location, rupture geometry, seismic moment split ratio, earthquake slip asperity location within a fault plane, and earthquake slip heterogeneity. To quantify these uncertainties, 484 different parameter combinations of tsunami sources are considered systematically. The geometry of splay faults is developed using the most recent marine seismic surveys of the tectonic structure of the MSZ. A moment magnitude of 8.6 is considered as a scenario magnitude. The results of this study are generated in two parts, by considering average sources and stochastic sources. Results show significant local amplification of the maximum tsunami heights due to splay faults. For instance, the maximum wave height in Pasni, Pakistan can be amplified by a factor of four due to a single splay fault rupture scenario of average sources.

Great earthquake and tsunami potential in the eastern Makran subduction zone: New insights from geodetic and structural constraints

The Makran subduction zone ranks one of the highest potentials for seismic and tsunami hazards. However, the rupture style and tsunami-wave dynamics remain ambiguous due to incomplete historical recordings and the lack of modern seismo-geodetic measurements. In this study, we integrate geomorphological, seismic structural models based on seismic images, InSAR measurement, high-resolution multibeam bathymetry, and the Slab-2 model of the subducted oceanic lithosphere to propose a series of geodetic-structural-constrained slip deficit models for tsunami hazard assessment in the northwestern Indian Ocean with a focus on Gwadar port in Pakistan. We show that the accumulated strain on the megathrust could generate an Mw 8.1–8.4 earthquake assuming current steady-state coupling ratio and a 30 GPa rigidity. We reveal the imbricate thrusts of the outer wedge are more efficient to excite tsunamis than the sub-horizontal megathrust (reference model) by increase in wave height at least 1 m (50%) when included, and these have not been considered in tsunami hazard assessments previously. In the worst-case of Mw 9 megathrust model, can occur waves >5 m, strong currents reaching 6 m/s, and inundation distance (>1 km) in the Gwadar port when rupturing to the trench. Additionally, if the updip area of the 1945 event source region ruptured, it could amplify wave height by 0.2-1 m in the Gwadar port and generate a strong tsunami current (>2 m/s) compared with the reference model. These new findings are crucial for seismic and tsunami hazard mitigation and preparedness in the northwestern Indian Ocean. We also demonstrate that modeled maximum tsunami wave heights based on the multibeam, SRTM15+ and GEBCO_2020 bathymetry differ by 0.2-1 m in the source and by 0.1–0.3 m in the far-field. Our study provides better-constrained source models for inundation studies at coastal mega-cities for hazard preparedness and highlights that the tsunami hazard potential is notably higher than previously recognized in this region.

CORRIGENDUM: Biology and conservation of marine turtles in the northwestern Indian Ocean: a review

CORRIGENDUM: Biology and conservation of marine turtles in the northwestern Indian Ocean: a review

Dynamic hydrographic and water-quality variations in the northwestern Arabian Gulf, a sinking zone of reverse estuarine circulation

Continuous measurements of hydrographic, hydrodynamic, and water quality showed marked diurnal, tidal, and seasonal variabilities in Kuwait Bay, a stressed coastal system in the northwestern Arabian/Persian Gulf. Advection of water masses and seasonality in vertical mixing regulated the Bay's hydrographic and water quality properties. Intensive stratification in summer had substantial implications on the Bay environment. Kuwait Bay constantly exports dense bottom water laden with dissolved inorganic nutrients and organic matter to the central basin of the Gulf. The export was largest in August under strong water column stratification. These in-situ findings agreed well with earlier studies that corroborated Kuwait Bay as an important area where the phenomenon of reverse estuarine circulation originates in the Gulf. Thus, Kuwait Bay is a significant source of nutrients and organic matter to the Gulf Deep Water that flows into the core of the oxygen minimum zone in the northwestern Indian Ocean.

The opposite response of the South Asian high to increasing CO2 at different heights

AbstractBased on the multimodel ensemble of 22 models in Coupled Model Intercomparison Project Phase 6 (CMIP6), the present manuscript found that in response to increasing CO2, the South Asian high (SAH) displays the opposite response over its southern region in the upper troposphere: an anticyclonic response at 100 hPa and a weak (insignificant) cyclonic response at 200 hPa. This opposite response is a product of tropospheric warming. In response to increasing CO2, the troposphere warms, with the potential temperatures peaking at 150–200 hPa over the northern Indian Ocean (IO). With transportation by local vertical motion (ascendance over the northeastern IO and descendance over the northwestern IO), various changes in vertical temperature advection with height form at 100 and 200 hPa. Finally, the changes contribute to a decrease in the ω response with pressures at 100 hPa but an increase in the ω response with pressures at 200 hPa over the northwestern IO. Over the northwestern IO, ω change is inversely related to pressure. At 100 hPa, the sign of ω changes with pressure, which yields distinct vorticity forcing over the northeastern and northwestern IO. This causes an anticyclonic response, which may generate zonal vorticity advection and balance the vorticity forcing. At 200 hPa, the contribution is roughly opposite to that at 100 hPa. In addition, although diabatic heating contributes to the vertical profile of ω, it yields the same‐sign vorticity response at 100 and 200 hPa.

Wedge‐Shaped Southern Indian Continental Margin Without Proper Weakness Hinders Subduction Initiation

AbstractThe closure of a subduction zone with continental terrane collision and accretion is generally thought to be followed by the initiation of a new subduction zone in the neighboring oceanic plate, which is suggested to happen repeatedly during the evolution of Tethyan system. Although the Indian‐Asian continental collision has occurred for >50 Myrs, there is still no clear sign for subduction initiation (SI) of the northern Indian oceanic plate, which is a puzzling issue and requires further investigations. This problem is studied here by systematic 3‐D thermo‐mechanical numerical models with a constant stress boundary condition. The model results indicate that the lack of proper weak zones at passive continental margin plays a critical role in hindering the collapse and SI of the northern Indian oceanic plate. In addition, the wedge‐shaped southern Indian continental margin provides an additional resistance for the SI. However, the strain localization with shortening of the Tibetan Plateau does not have a significant effect on the SI of Indian oceanic plate in the current models, which requires further studies with wider Tibetan plate. The numerical results explain why no SI has occurred in the northern Indian Ocean with pushing from the high gravitational potential energy of the uplifted Tibetan Plateau and seafloor spreading in the Northern Indian Ocean, and further predict that the future SI is more likely to occur in the northwestern Indian Ocean than the northeastern region due to continuous counterclockwise rotation of the Indian Continent.

Biology and conservation of marine turtles in the northwestern Indian Ocean: a review

The northwestern Indian Ocean hosts globally crucial marine biodiversity, which is relatively understudied. There has, however, been significant research and conservation effort focused on marine turtles across the region in recent decades. We undertook an exhaustive review of 251 relevant publications to extract and collate the current information concerning marine turtles. To ensure completeness, we received input on a preliminary draft from a large group of experts who have worked extensively in the region. Data presented here are from all 13 countries with significant coastlines in the region (Bahrain, Djibouti, Egypt, Eritrea, Iran, Kuwait, Oman, Qatar, Saudi Arabia, Somalia, Sudan, United Arab Emirates, and Yemen) on occurrence, nesting biology, morphology, foraging areas, population status, threats, and relevant national legislation and international conservation strategies. The experts independently provided details on what they felt were the (1) most significant threats to marine turtles, (2) most critical knowledge gaps for marine turtle ecology, (3) impediments to practical conservation, and (4) essential strengths and opportunities in the region.

New Constraints for the On‐Shore Makran Subduction Zone Crustal Structure

AbstractThe Makran Subduction Zone is the primary seismic/tsunami hazard of the northwestern Indian Ocean, but little is known of its on‐shore seismic structure. We derived a shear wave velocity model extending to 100 km depth beneath a ∼400 km‐long seismic profile oriented parallel to the convergence vector of the Arabian Sea Plate. Receiver function/surface wave analysis shows that the average structure in the coastal region comprises a ∼22–28 km‐thick low wavespeed sedimentary cover and a 6–8 km‐thick gradient zone overlying 100 km‐thick high wavespeed upper mantle. The ocean‐basement interface dips gently northward, remaining a positive impedance contrast to ∼50 km depth at ∼250 km north of the coast where it disappears as the basaltic/gabbroic oceanic crust has probably transformed to eclogite. Further north, a weak arrival at ∼5 s in the receiver functions appears, grading northward into the Moho arrival of the continental Iranian Plateau. This disruption in the seismic signature of the Moho occurs in the forearc region where the dip of the subducting oceanic plate steepens. The southern Iranian Plateau's continental crust has an average Vs of 3.55 ± 0.05 km s−1, an almost flat Moho 40–45 km deep, and a sub‐Moho mantle Vs of 3.75 ± 0.05 km s−1 in the 50–80 km depth range. Weak Moho conversions probably result from ∼20% serpentinization of peridotite in the mantle wedge. Receiver functions indicate a flat continental Moho – no crustal root beneath the high topography region of the volcanic belt, which therefore must be compensated by low upper mantle densities. The high Vp/Vs ratio observed for the mantle wedge suggests ∼1%–2% partial melt.

Piracy and Maritime Security in the North-Western Indian Ocean: From the Gulf of Oman to the Waters off the Somali Coast

There are a daunting number of maritime security threats and challenges in the north-western Indian Ocean region, both extant and potential. Indeed, the mere fact that the Indian Ocean constitutes the world’s largest swath of maritime space that is prone to the major menace of piracy (in the Gulf of Oman, the Arabian Sea, the Gulf of Aden and in the waters off the north-east African coastline), as well as the sporadic threat of terrorism (by Islamic militias of Al-Shabaab in Somalia and Al-Qaeda in the Arabian Peninsula in Yemen), signifies that the region will arguably remain the maritime area with the greatest array of security challenges. However, while anti-piracy measures ought to have shaped regional policymaking, and the resources that a large and diverse group of states has devoted to addressing these maritime challenges have never been adequate to the task, largely successful coalition-building exercises and joint naval task-force operations have been encouraging. The transformation of Somali piracy from a haphazard activity into a highly organised, professionalised criminal enterprise is briefly elucidated by greed-grievance theory and supplemented by the theory of crime, also known as routine-activity theory.

Dissolved iron cycling in the Arabian Sea and sub-tropical gyre region of the Indian Ocean

Understanding the sources and biogeochemical processes influencing the dissolved iron (DFe) distribution is crucial because of its coupled role in C- and N-fixation in the oceans. Vertical depth profiles of DFe in the northwestern Indian Ocean along two meridional transects (∼65 °E and ∼57 °E) during spring and fall seasons are presented here under the GEOTRACES-INDIA initiative. The DFe in the surface waters exhibited both spatial and seasonal variabilities; N-S gradient with higher values in the north; and notably higher concentrations in the fall season. The photic zone-integrated DFe (57.5 ± 13.4 µmol m−2) was double in the Arabian Sea compared to the subtropical Indian Ocean (31.81 ± 7.63 µmol m−2) with a significant positive correlation with the photic zone integrated primary production. This suggests higher availability of DFe is responsible for high primary production in the Arabian Sea compared to the subtropical Indian Ocean. Lateral and vertical advection along with particle dissolution from the atmospheric dust fluxes and scavenging-adsorption processes could play prominent role in controlling photic DFe concentrations in the Arabian Sea. The continental margin sources, redox chemistry, and remineralization are responsible for the observed high DFe concentration within the intense oxygen minimum zone. The in-situ remineralization ratios of Fe to C in the Arabian Sea are higher than any other region of the Indian Ocean. It could be due to the high uptake of Fe during primary production in the Arabian Sea, despite huge spatio-temporal variations in the abundance of phytoplankton communities. Our DFe data from the undersampled region over the Carlsberg Ridge suggests the presence of chronic/event plumes contributing to the DFe inventory in the western Arabian Sea region.We have approximated the geochemical budget of Fe in the top 100 m for open ocean waters of the Arabian Sea. These preliminary estimates suggest that lateral and vertical fluxes for DFe are prominent in the region compared to soluble atmospheric Fe dust fluxes and these sources are balanced by the biotic and abiotic removal processes in the region. Based on these estimated fluxes, the calculated residence time of DFe varies from ∼0.1 to 1 year in photic waters of the Arabian Sea. Our results highlight the intrusion of Fe-deficit Southern Ocean waters in the Arabian Sea and the upwelling of Fe-starved deep waters alongside the northwest of the Murray Ridge are likely responsible for Fe limitation in the region.

Flow fields and outputs of the hydrothermal plume at the Wocan-1 field based on an <italic>in-situ</italic> video

<p indent="0mm">Deep-sea hydrothermal plumes are an essential medium for exchanging the heat and elements between the lithosphere and hydrosphere and contribute to elemental cycling and marine chemistry evolution. In this paper, based on field video footage of a black smoker recorded at the Wocan-1 hydrothermal field on the slow-spreading Carlsberg Ridge in the northwestern Indian Ocean, the flow fields of the “Huoyanshan” hydrothermal plume were calculated using a cross-correlation algorithm. In addition, the heat and chemical outputs of the hydrothermal vent are investigated using the estimated source volume flux and fluid properties obtained from <italic>in-situ</italic> measurements. The results reveal that as the plume rises, the vertical velocity along the plume centerline increases, reaching a maximum value of approximately <sc>15.5 cm/s.</sc> This tendency is attributed to the combined effect of initial momentum flux and buoyancy flux. The maximum horizontal velocity along the plume centerline is approximately <sc>10.3 cm/s,</sc> indicating a strong deep ocean current on the Carlsberg Ridge. Due to plume entrainment, the volume flux of the hydrothermal vent linearly increases with increasing plume rise. Furthermore, the heat and iron outputs from the “Huoyanshan” hydrothermal vent were estimated as <sc>1.35±0.11 MW</sc> and <sc>3661±323 kg/a,</sc> respectively. These results provide valuable insights into the plume dynamics of submarine hydrothermal vents and the deep-sea thermal and elements balance.

Global mapping of 10-day differences of temperature and salinity in the intermediate layer observed with Argo floats

The authors examine small-scale spatiotemporal variability of the layer nearly 2000-m depth, which is the “bottom” of the present Argo observation system, using all of available Argo float data. The 10-day change, ΔT10, is defined as the difference of temperature between two successive observations with an interval of nearly 10 days for each individual float at an isobaric surface. |ΔT10| is large along the western boundary currents at 1000 dbar, and becomes less remarkable with depth. At 1950 dbar, mean |ΔT10| is noticeable in the northeastern Atlantic Ocean (NEAO), the Argentine basin, and the northwestern Indian Ocean. In the Southern Ocean, large |ΔT10| is localized in some areas located over the ridges or leeward of the plateau. Basically, ΔT10 at isobaric surfaces is accounted for by the heave component, but the spiciness component is dominant or comparable to the other in the NEAO and the Argentine basin. ΔT10 decreases with depth monotonically most of the world, suggesting that wind energy input is attenuated with depth. In some areas in the Southern Ocean, however, the vertical profile of |ΔT10| implies enhanced bottom-induced turbulence. |ΔT10| peaks at 1300 dbar in the NEAO, corresponding to the spread of the Mediterranean Outflow Water. |ΔT10| is smaller in the Pacific Ocean compared with the other oceans, but is enhanced along the equator, the Kuroshio and its Extension, the Kuril, Aleutian, Hawaii, and Mariana Islands, and the Emperor Seamount Chain.

Tigriopus iranicus sp. nov., a new species of Harpacticidae (Copepoda, Crustacea) from Iran, with a redescription of T. raki Bradford, 1967.

The first representative of Tigriopus Norman, 1869 from the north-western Indian Ocean is described from rock pools on the Iranian coast. Tigriopus iranicussp. nov. is distinguishable from its congeners by i) the possession of two maxillary endites, each with two setae; ii) a two-segmented mandibular endopod; iii) P1enp-3 with one pinnate claw, a well-developed geniculate spine and a small seta; and iv) female P6 with two setae. Additionally, we present a complete redescription of Tigriopus raki Bradford, 1967 on the basis of paratype material and a key to the species of the genus.

Habitat wise variability in the diversity of sea cucumbers in Lakshadweep Archipelago, North-Western Indian Ocean

The coral reefs of the Lakshadweep archipelago harbour significant sea cucumber resources. The paper discusses the habitat-wise variability of sea cucumbers observed during a series of surveys in this atolls. The western side lagoon areas and eastern intertidal areas of the atolls showed maximum diversity and species richness. One of the northernmost atolls of this archipelago, Kiltan showed an exceptional abundance of the green sea cucumber Stichopus chloronotus. The information provided will be useful for developing conservation strategies for this important group of coral reef dwellers.

Notes on batoid fishes of the Socotra Archipelago (north-western Indian Ocean), with four new records.

The species composition of batoid fishes from coastal waters of the Socotra Archipelago is reviewed, with confirmed records of the wedgefish Rhynchobatus djiddensis (Forsskål, 1775) and four new records of sharkrays, wedgefishes, and guitarfishes based on collected specimens, including one species from Abd al-Kuri Island, Rhina ancylostoma Bloch Schneider, 1801 (Rhinidae), and three species from the main island Socotra, Acroteriobatus salalah (Randall Compagno, 1995) and Rhinobatos punctifer Compagno Randall, 1987 (Rhinobatidae), and Rhynchobatus australiae Whitley, 1939 (Rhinidae). Among the new records for the Socotra Archipelago, R. australiae represents the first verified record for the Arabian region. In addition, records of four stingray species (Dasyatidae) are verified based on underwater observations accompanied with photographs. All recorded batoid fishes are commercial species caught in the local small-scale fishery. Information on the identification and distribution of each species is provided.

Spreading and Vertical Structure of the Persian Gulf and Red Sea Outflows in the Northwestern Indian Ocean

AbstractIn the Indian Ocean, salty water masses from the Persian Gulf and Red Sea are important sources of salt, heat, and nutrients. Across the Arabian Sea, these outflows impact human and biological activities, their thermohaline characteristics and shapes exhibiting important spatial and seasonal variability. The knowledge of the water masses properties is important to validate realistic simulations of the Indian Ocean. A classical approach to study these water masses is to track them on specific isopycnal levels. Nevertheless, their peaking thermohaline characteristics are not always found at a specific density but rather spread over a range. Here, we develop a detection algorithm able to capture the full vertical structure of the outflows, that we applied to a data set of about 126,000 vertical profiles. We are thus able to quantify the changes in their thermohaline signatures and in their vertical structures, characterized here by the intensity of the salinity peaks of the water masses and lateral injection of fresh and salty waters, and describe their spatial variability. Across the northwestern Indian Ocean, the salty outflows undergo several changes, diminishing their thermohaline signatures and peaks and layering. In their early stages in the narrow Gulf of Oman and Aden, the outflows present configurations indicative of diapycnal mixing. In the same regions and along the western edge of the Arabian Sea, these water masses are subject to lateral mixing. All over the Arabian Sea, salt fingering conditions are met for lower layers of the outflows.

Otobothrium muscatense n. sp. (Trypanorhyncha: Otobothriidae) from Rhabdosargus sarba (Forsskål) (Sparidae), with new locality records of larval trypanorhynchs off the Sultanate of Oman.

In the evaluation of the larval trypanorhynch fauna off the Sultanate of Oman, a total of 188 bony fishes belonging to 16 species were studied, which led to the description of a new species with the establishment of new host and locality records. A new otobothriid species, Otobothrium muscatense n. sp., is described from Rhabdosargus sarba (Forsskål). Based on scolex morphology and tentacular armature, the new species closely resembles the small-sized Otobothrium Linton, 1890 species described as Otobothrium cysticum (Mayer, 1842) and O. crenacolle Linton, 1890. However, it differs from them in the basal armature by a more robust shape of the first principal and the triangular shape of the billhooks as well as by the retractor muscle originating inthe posterior part of the tentacle sheath, attaching to a thickening of thetentacle sheath wall,with a muscular branch continuing and attaching atfrontpart of the bulb. It differs from the other species of Otobothrium by size, the combination of six principal hooksand a single intercalary hook in the metabasal armature, and the plane of reflection through the tentacle surfaces. New locality records of the tentaculariids Nybelinia indica Chandra, 1986, Heteronybelinia yamagutii (Dollfus, 1960), Tentacularia coryphaenae Bosc, 1797, and Mixonybelinia lepturi Palm, 2004, together with the lacistorhynchids Pseudogrillotia multiminacantha Palm, 2004 and Callitetrarhynchus gracilis (Rudolphi, 1819), and the pseudotobothriid Parotobothrium balli (Southwell, 1929) off the Muscat region are established. Of the reported species, especially P. multiminacantha and M. lepturi occurring in Trichiurus lepturus L. further demonstrate the relatedness between the Indonesian and the northwestern Indian Ocean fauna, increasing the number of joint records between Indonesia and Omani waters to 14 species.

Deep water circulation in the Arabian Sea during the last glacial cycle: Implications for paleo-redox condition, carbon sink and atmospheric CO2 variability

Global overturning circulation plays a vital role in atmospheric CO2 and climate variability during glacial-interglacial (G-I) cycles; however, the exact mechanism remains elusive due to inadequate knowledge on past deep water circulation in the global ocean. Since no deep water is formed in the northern Indian Ocean, it ventilates from the south and acts only as a host for deep water circulation. Absence of any active deep water formation makes the northern Indian Ocean an ideal location to assess the extent of southern source waters and its role on past CO2 variability during the G-I climate cycles. This study provides the first record of deep water circulation in the Arabian Sea, the northwestern Indian Ocean, during the past 136 ka based on authigenic Nd isotope record (εNd). The Arabian Sea εNd record shows large variability ranging from −8.8 to −6.5 with more radiogenic values during the glacial stages (MIS 2 & 6) and less radiogenic values during the interglacial stages (MIS 1 & 5) indicating changes in water mass sources. The observation of more radiogenic εNd values similar to the glacial Antarctic Bottom Water (AABW) indicates enhanced flow of AABW (95–100%) and substantial reduction and/or almost complete retreat of North Atlantic Deep Water (NADW, 0–5%) during the glacials, whereas less radiogenic values indicate enhanced flow of NADW (∼20–40%) during the interglacials. The Arabian Sea εNd record followed exactly similar pattern to that of the equatorial Indian Ocean (EIO). However, amplitude of their variations differed significantly during the interglacials (MIS 1 & 5); the Arabian Sea εNd values were more radiogenic than the EIO. This suggests that during the interglacials, the Arabian Sea received more fraction of AABW through the western pathway, whereas the EIO received more fraction of NADW through the central pathway. This highlights differences in deep water exports from the Southern Ocean to the Arabian Sea and the EIO during the interglacials whereas export of similar water masses and its uniform distribution up to the northern Indian Ocean during the glacials. Our findings of significant G-I changes in AABW and NADW exports to the Indian Ocean and intra-basinal differences in their distribution have important implications for regional biogeochemical processes, paleo-redox conditions in the water column, carbon sink (organic and inorganic) and atmospheric CO2 variability during the G-I climate transitions.