Deep-Water Circulation over the Last Two Glacial Cycles Reconstructed from Authigenic Neodymium Isotopes in the Equatorial Indian Ocean (Core HI1808-GPC04)

AbstractWe reconstructed the past deep-water character of the equatorial Indian Ocean using the isotope ratio of neodymium (εNd) in the Fe–Mn coating of mixed-species foraminifera. When compared with previous εNd records at the same site (ODP 758) and at another site to the west (SK 129), the three datasets were consistent and showed glacial-interglacial variations, even though the other two records were extracted from different media (cleaned foraminifera and bulk sediment leach). This confirms that while the foraminiferal coating is the preferred medium for reconstructing past bottom water εNd records, for carbonate-dominated lithologies, weak acid extraction of bulk sediment is also a viable option offering high-resolution capabilities. When the lithology includes volcanic particles or high organics, the extraction protocol may need to be adjusted to guard against detrital contamination or a slight correction may need to be applied. During glacials, the deep waters bathing the equatorial Indian Ocean had a larger AABW component and during interglacials a larger NADW component. Our HI1808-GPC04 record supplements the ODP 758 record in the interval with prominent AABW signal (MIS 6/5 transition and MIS 7) and reveals regional effects in some non-radiogenic intervals. The smaller differences between the HI1808-GPC04/ODP 758 and SK 129 records seem to reflect regional Nd input from river systems and non-radiogenic Nd from the boundaries.

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Estimates of High Resolution Ventilation Age from the Equatorial Indian Ocean during Last 40 ka: Implications to Paleo Deep Water Circulation

10.46427/gold2020.182 ◽

2020 ◽

Author(s):

Nisha Bharti ◽

Ravi Bhushan ◽

M Muruganantham

Keyword(s):

High Resolution ◽

Indian Ocean ◽

Deep Water ◽

Equatorial Indian Ocean ◽

Water Circulation

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The Sources and Mixing Characteristics of the Agulhas Current

Journal of Physical Oceanography ◽

10.1175/jpo2964.1 ◽

2006 ◽

Vol 36 (11) ◽

pp. 2060-2074 ◽

Cited By ~ 47

Author(s):

Lisa M. Beal ◽

Teresa K. Chereskin ◽

Yueng D. Lenn ◽

Shane Elipot

Keyword(s):

Indian Ocean ◽

Potential Vorticity ◽

Vertical Mixing ◽

Equatorial Indian Ocean ◽

Agulhas Current ◽

The North ◽

Deep Waters ◽

Stream Potential ◽

Lateral Mixing ◽

Potential Inhibitors

Abstract Recent observations taken at four principal latitudes in the Agulhas Current show that the watermass properties on either side of its dynamical core are significantly different. Inshore of its velocity core are found waters of predominantly Arabian Sea, Red Sea, and equatorial Indian Ocean origin, while offshore waters are generally from the Atlantic Ocean, the Southern Ocean, and the southeast Indian Ocean. For the most part, the inshore waters approach the Agulhas Current through the Mozambique Channel, while those offshore are circulated within the southern Indian Ocean subtropical gyre before joining the current. These disparate water masses remain distinct during their 1000-km journeys along the South African continental slope, despite the convergence, extreme velocity shears, and high eddy kinetic energies found within the Agulhas Current. Both potential vorticity conservation and kinematic arguments are discussed as potential inhibitors of along-isopycnal mixing. It is concluded that a high cross-stream gradient of potential vorticity is the dominant mechanism for watermass separation near the surface, while the kinematic steering of water particles by the current is dominant at intermediate depths, where cross-stream potential vorticity is homogeneous. Hence, three lateral mixing regimes for the Agulhas Current are suggested. The surface and thermocline waters are always inhibited from mixing, by the presence of both a strong, cross-frontal potential vorticity gradient and kinematic steering. At intermediate depths mixing is inhibited by steering alone, and thus in this regime periodic mixing is expected during meander events (such as Natal pulses), when the steering level will rise and allow cross-frontal exchange. Below the steering level in the deep waters, there is a regime of free lateral mixing. The deep waters of the Agulhas Current are homogeneous in the cross-stream sense, being from the same North Atlantic source, and their salinity steadily (and rather rapidly) decreases to the north. Here, it is suggested that mixing must be dominated by vertical processes and a large vertical mixing coefficient of order 10 cm2 s−1 is estimated.

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Impacts of the Middle Miocene Climatic Transition on deep-water carbonate preservation and oxygenation in the equatorial Indian Ocean

Palaeogeography Palaeoclimatology Palaeoecology ◽

10.1016/j.palaeo.2021.110511 ◽

2021 ◽

pp. 110511

Author(s):

Karlos G.D. Kochhann ◽

Wolfgang Kuhnt ◽

Ann E. Holbourn ◽

Yoichi Usui ◽

Julia Lübbers ◽

...

Keyword(s):

Indian Ocean ◽

Deep Water ◽

Middle Miocene ◽

Equatorial Indian Ocean ◽

Climatic Transition ◽

Water Carbonate ◽

Middle Miocene Climatic Transition

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Mineralogical and Geochemical Signatures of Metalliferous Sediments in Wocan-1 and Wocan-2 Hydrothermal Sites on the Carlsberg Ridge, Indian Ocean

Minerals ◽

10.3390/min9010026 ◽

2019 ◽

Vol 9 (1) ◽

pp. 26 ◽

Cited By ~ 2

Author(s):

Samuel Olatunde Popoola ◽

Xiqiu Han ◽

Yejian Wang ◽

Zhongyan Qiu ◽

Ying Ye ◽

...

Keyword(s):

Indian Ocean ◽

Volcanic Glass ◽

Mineral Chemistry ◽

Hydrothermal Systems ◽

Bulk Sediment ◽

Sediment Samples ◽

Metalliferous Sediments ◽

Metalliferous Sediment ◽

Carlsberg Ridge ◽

Hydrothermal Environments

In this paper, we conduct a comparative study on the mineralogy and geochemistry of metalliferous sediment collected near the active hydrothermal site (Wocan-1) and inactive hydrothermal site (Wocan-2) from Wocan Hydrothermal Field, on the Carlsberg Ridge (CR), northwest Indian Ocean. We aim to understand the spatial variations in the primary and post-depositional conditions and the intensity of hydrothermal circulations in the Wocan hydrothermal systems. Sediment samples were collected from six stations which includes TVG-07, TVG-08 (Wocan-1), TVG-05, TVG-10 (Wocan-2), TVG-12 and TVG-13 (ridge flanks). The mineralogical investigations show that sediment samples from Wocan-1 and Wocan-2 are composed of chalcopyrite, pyrite, sphalerite, barite, gypsum, amorphous silica, altered volcanic glass, Fe-oxides, and hydroxides. The ridge flank sediments are dominated by biogenic calcite and foraminifera assemblages. The bulk sediment samples of Wocan-1 have an elevated Fe/Mn ratio (up to ~1545), with lower U contents (<7.4 ppm) and U/Fe ratio (<~1.8 × 10−5). The sulfide separates (chalcopyrite, pyrite, and sphalerite) are enriched in Se, Co, As, Sb, and Pb. The calculated sphalerite precipitation temperature (Sph.PT) yields ~278 °C. The sulfur isotope (δ34S) analysis returned a light value of 3.0–3.6‰. The bulk sediment samples of Wocan-2 have a lower Fe/Mn ratio (<~523), with high U contents (up to 19.6 ppm) and U/Fe ratio (up to ~6.2 × 10−5). The sulfide separates are enriched in Zn, Cu, Tl, and Sn. The calculated Sph.PT is ~233 °C. The δ34S returned significant values of 4.1–4.3‰ and 6.4–8.7‰ in stations TVG-10 and TVG-05, respectively. The geochemical signatures (e.g., Fe/Mn and U/Fe ratio, mineral chemistry of sulfides separates, and S-isotopes and Sph.PT) suggest that sediment samples from Wocan-1 are located near intermediate–high temperature hydrothermal discharge environments. Additionally, relatively low δ34S values exhibit a lower proportion (less than 20%) of seawater-derived components. The geochemical signatures suggest that sediment samples from Wocan-2 has undergone moderate–extensive oxidation and secondary alterations by seawater in a low–intermediate temperature hydrothermal environments. Additionally, the significant δ34S values of station TVG-05 exhibit a higher estimated proportion (up to 41%) of seawater-derived components. Our results showed pervasive hydrothermal contributions into station TVG-08 relative to TVG-07, it further showed the increased process of seafloor weathering at TVG-05 relative to TVG-10.

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A biological Indian Ocean Dipole event in 2019

Scientific Reports ◽

10.1038/s41598-021-81410-5 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Wei Shi ◽

Menghua Wang

Keyword(s):

Biological Activity ◽

Indian Ocean ◽

Indian Ocean Dipole ◽

Infrared Imaging ◽

Equatorial Indian Ocean ◽

The West ◽

Indian Ocean Dipole Event ◽

Chl A ◽

Positive Indian Ocean Dipole ◽

Dipole Response

AbstractThe 2019 positive Indian Ocean Dipole (IOD) event in the boreal autumn was the most serious IOD event of the century with reports of significant sea surface temperature (SST) changes in the east and west equatorial Indian Ocean. Observations of the Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the Suomi National Polar-orbiting Partnership (SNPP) between 2012 and 2020 are used to study the significant biological dipole response that occurred in the equatorial Indian Ocean following the 2019 positive IOD event. For the first time, we propose, identify, characterize, and quantify the biological IOD. The 2019 positive IOD event led to anomalous biological activity in both the east IOD zone and west IOD zone. The average chlorophyll-a (Chl-a) concentration reached over ~ 0.5 mg m−3 in 2019 in comparison to the climatology Chl-a of ~ 0.3 mg m−3 in the east IOD zone. In the west IOD zone, the biological activity was significantly depressed. The depressed Chl-a lasted until May 2020. The anomalous ocean biological activity in the east IOD zone was attributed to the advection of the higher-nutrient surface water due to enhanced upwelling. On the other hand, the dampened ocean biological activity in the west IOD zone was attributed to the stronger convergence of the surface waters than that in a normal year.

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