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Acoustic Identification of Dolphin Whistle Types in Deep Waters of Arabian Sea Using Wavelet Threshold Denoising Approach

Mahanty Madan Mohan, Cheenankandy Sanjana M., Latha Ganesan, Raghuraman Govindan, Venkatesan Ramasamy

Archives of Acoustics

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2023

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Vol. 48, No. 1

39--48

EN

In situ time series measurements of ocean ambient noise, have been made in deep waters of the Arabian Sea, using an autonomous passive acoustic monitoring system deployed as part of the Ocean Moored buoy network in the Northern Indian Ocean (OMNI) buoy mooring operated by the National Institute of Ocean Technology (NIOT), in Chennai during November 2018 to November 2019. The analysis of ambient noise records during the spring (April–June) showed the presence of dolphin whistles but contaminated by unwanted impulsive shackle noise. The frequency contours of the dolphin whistles occur in narrow band in the range 4–16 kHz. However, the unwanted impulsive shackle noise occurs in broad band with the noise level higher by ~20 dB over the dolphin signals, and it reduces the quality of dolphin whistles. A wavelet based threshold denoising technique followed by a subtraction method is implemented. Reduction of unwanted shackle noise is effectively done and different dolphin whistle types are identified. This wavelet denoising approach is demonstrated for extraction of dolphin whistles in the presence of challenging impulsive shackle noise. Furthermore, this study should be useful for identifying other cetacean species when the signal of interest is interrupted by unwanted mechanical noise.

2

Historical occurrences of marine microalgal blooms in Indian peninsula : Probable causes and implications

Oyeku Oyeshina Gideon, Mandal Subir Kumar

Oceanologia

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2021

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No. 63 (1)

51--70

EN

The Indian marine environment supports employment for over 200 million people, including revenue of nearly $7 billion per annum. However, ecological goods and services of the shallow coast and the marine environment of the Indian peninsula are being affected by recurrent blooms of microalgae. One hundred and six published literature, starting from the first report in 1908 to 2017, were reviewed to investigate the historical occurrences of marine microalgal blooms (MMBs) around the Indian peninsula. 154 MMBs comprising 24 genera and 7 classes were reported during the study period. Noctiluca (dinophyceae) and Trichodesmium (cyanophyceae) bloom contributed 34.4% and 31.8% of total blooms. PCA revealed that high sea surface temperature (SST) and salinity were significant driving forces for Trichodesmium blooms formation, while high nutrients (NO3-N, PO4-P, and SiO4-Si) and low salinity triggered prymnesiophyceae, raphidophyceae, bacillariophyceae and most of the dinophyceae blooms. Noctiluca blooms were linked with both eutrophication and the abundance of prey organisms. HABs were generally dinophyceae dominated and were associated with mass mortality of aquatic fauna, human intoxication, paralytic, and ciguatera shellfish poisoning and even death. Increasing SST and anthropogenic influences around the Indian peninsula could increase the occurrences of MMBs (including HABs) and the number of causative taxa. Proper safety measures such as routine monitoring of phycotoxin levels in the environment and local seafood are required to be put in place in other to protect the health of the public.

3

A study on loops and eddies identified from the trajectories of drifters in the North Indian Ocean

Dora Shrikant, Aparna Sreekumar G.

Oceanologia

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2021

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No. 63 (4)

516--530

EN

We identify loops and eddies from the trajectories of the drifters in the North Indian Ocean (NIO) from October 1985 to March 2019. We use the geometric identification method to identify loops and eddies and compare them with the loops identified from loopers provided by Lumpkin (2016). In NIO, the number of loops estimated from loopers is less than the number of loops and eddies identified by the geometric identification method. A total of 761 loops are identified, of which 346 are eddies, whereas the loops identified from loopers are only 149. Larger radii loops and eddies are observed in the western and central Bay of Bengal (BoB) and the southwestern part of the Arabian Sea (AS). Temporal variation of loops and eddies shows a peak during April–May in the AS and September–October in the BoB. In the BoB, the temporal variation of cyclonic eddies matches with the variation in chlorophyll.

4

The geomorphology of the Makran Trench in the context of the geological and geophysical settings of the Arabian Sea

Lemenkova Polina

Geology, Geophysics and Environment

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2020

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Vol. 46, no. 3

205--222

EN

The study focuses on the Makran Trench in the Arabian Sea basin, in the north Indian Ocean. The area is tectonically active, with a system of ridges and fracture zones morphologically separating the Arabian Sea. The study examined the relationships between the topographic structure of the Makran Trench and the regional settings of the Arabian Sea: geomorphology, sediment thickness, geophysical fields, geology and tectonic lineaments. The methodology is based on the GMT scripting toolset. The spatial analysis includes high-resolution datasets GEBCO, EGM2008, GlobSed and data on tectonics, geology, geophysics, sediment thickness and topographic terrain model visualized by GMT. The paper also defined a way in which the proprietary ESRI data format can be transformed into the freely available GMT geospatial data of the geoid EGM2008 model. The geomorphological modeling included the automatic digitization of 300-km width cross-section profiles of the trench demonstrating its submarine relief. The analysis showed a correlation between the geological and tectonic structures, asymmetric geomorphology and geophysical anomaly fields. Gravity data indicate a crustal structure with anomalies generated by the bending of the lithosphere into the Makran subduction zone and density variations in the mantle reflected on the gravity maps. The gravity correlates with lineaments of the geomorphic structures. Bathymetric analysis revealed the most frequent depth (448 samples) at −3,250 to −3,500 m, followed by intervals: −3,000 to −3,250 m, −2,750 to −3,000 m. The declining continental slope correlates with gradually decreasing depths as equally distributed bins: 124 samples (−2,500 to −2,750 m), 96 (−2,250 to −2,500 m), 86 (−2,000 to −2,250 m). The trench is an asymmetric form with a high steepness on the continental slope of Pakistan and low steepness with a flat valley on the oceanward side. The multi-source data integration is important for seafloor mapping and the geomorphological analysis of oceanic trenches hidden to direct observations. The machine learning methods of GMT and cartographic modeling provide possibilities for the effective visualization of the trench. The comparison of the geomorphology with gravity anomalies, tectonic lineation, geological structures and topographical variations provides more detail to studies of the seafloor in the Arabian Sea.

5

Spatio-temporal variations in sulfur-oxidizing and sulfate-reducing bacterial activities during upwelling, off south-west coast of India

Kamaleson A. Sam, Gonsalves Maria-Judith, Kumar Swatantar, Jineesh V. K., LokaBharathi P. A.

Oceanologia

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2019

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No. 61 (4)

427--444

EN

The Arabian Sea, off SW India, is becoming more anoxic in recent years. Poor ventilation affects microbial degradation of organic matter in the oxygen minimum zone (≤ 2.85 ml l-1 O2, ≤ 0.02 μM NO2) and the anoxic marine zone (≤ 0.09 ml l-1 O2, ≥ 0.5 μM NO2). We posit that one of the reasons at the microbial level could be due to a more prominent increase in sulfate-reducing activity (SRA), than sulfur-oxidizing activity (SOA). Hence, the objective was to measure the extent to which SOA can counter the effect of SRA. We, therefore examined these activities along with relevant environmental variables from 2009 to 2011 off Kochi (9.55°N-75.33°E) and Trivandrum (8.26°N-76.50°E), covering the three phases of upwell-ing. SRA was measured radiometrically using 35S, and SOA by iodometry. Off Kochi, the SOA of the water column increased 6 x (194-1151 μM d-1) and SRA 4 x (13-54 nM d-1) from phase I to III. Off Trivandrum, the increase in SOA was 1.7 x (339-560 μM d-1) and SRA 7 x (24-165 nM d-1) contributing to the build-up of reducing/oxidizing conditions. This increase in SOA moderates the effect of increase in SRA. Besides, the average concentrations of dissolved oxygen and nitrite off Trivandrum were 1.80 ± 1.66, 1.48 ± 1.55, 1.93 ± 1.86 ml l-1 and 0.14 ± 0.14, 1.69 ± 0.67, 0.34 ± 0.42 μM during the three phases respectively. Hence, it is suggested that the coastal waters examined in this study could probably be between oxygen minimum zone (OMZ) and anoxic minimum zone (AMZ) in patches temporarily. The present paper highlights the interactions between sulfate-reducing and sulfur-oxidizing activities, during upwelling for the first time in these waters. These observations give an important and timely insight into the implications.

6

Investigating the role of air-sea forcing on the variability of hydrography, circulation, and mixed layer depth in the Arabian Sea and Bay of Bengal

Srivastava A., Dwivedi S., Mishra A. K.

Oceanologia

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2018

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No. 60 (2)

169--186

EN

An effort is made to understand and quantify the influence of near surface zonal and meridional winds, incoming shortwave radiation, and freshwater flux air-sea forcings on the seasonal variability of the hydrography, circulation, and mixed layer depth of the Arabian Sea (AS) and Bay of Bengal (BoB). Sensitivity experiments using an ocean general circulation model are carried out for this purpose in the Indian ocean around 65°-95°E, 5°-22°N during 1998-2014 (17 years). In the absence of near surface wind forcing, the sea surface temperature of the region greatly increases in all the seasons, whereas, in the absence of incoming shortwave radiation forcing, exactly opposite is the case. The sea surface salinity of the AS and BoB decreases in the absence of wind and shortwave radiation forcings, whereas, in the northern BoB it increases in the absence of freshwater flux forcing. The sub-surface changes in the stratification of temperature and salinity are also investigated. The influence of the air-sea forcings on the mixed layer depth of the region is found to be highly seasonally dependent. The effect of air-sea forcings on the seasonal variability of the upper ocean vertical stability is studied using the vertical shear of the horizontal velocity, buoyancy frequency, and energy required for mixing as quantifiers. The near surface wind forcing has highest contribution in changing the surface circulation of the region.

7

Wielokilometrowe przeprawy nad Morzem Arabskim

Januszek M.

Geoinżynieria : drogi, mosty, tunele

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2018

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nr 1

56--57

PL

Połączenie autostradowe Bandra-Worli (Indie) o długości 5,6 km poprowadzone zostało betonowo-stalowym mostem, przekraczającym Morze Arabskie. Obiekt przekazano do użytku w marcu 2010 r., a teraz planowane jest jego przedłużenie aż o 10 km. Jeszcze dłuższą przeprawę zaplanowano, by połączyć Mumbaj, położony na wyspie Salsette, z jednym z jego miast satelitarnych – Navi Mumbaj. Most osiągnie długość 22 km.

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Performance of operational satellite bio-optical algorithms in different water types in southeastern Arabian Sea

Minu P., Lotliker A. A., Shaju S. S., Ashraf P. M., Kumar T. S., Meenakumari B.

Oceanologia

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2016

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No. 58 (4)

317--326

EN

The in situ remote sensing reflectance (Rrs) and optically active substances (OAS) measured using hyperspectral radiometer, were used for optical classification of coastal waters in the southeastern Arabian Sea. The spectral Rrs showed three distinct water types, that were associated with the variability in OAS such as chlorophyll-a (chl-a), chromophoric dissolved organic matter (CDOM) and volume scattering function at 650 nm (β650). The water types were classified as Type-I, Type-II and Type-III respectively for the three Rrs spectra. The Type-I waters showed the peak Rrs in the blue band (470 nm), whereas in the case of Type-II and III waters the peak Rrs was at 560 and 570 nm respectively. The shifting of the peak Rrs at the longer wavelength was due to an increase in concentration of OAS. Further, we evaluated six bio-optical algorithms (OC3C, OC4O, OC4, OC4E, OC3M and OC4O2) used operationally to retrieve chl-a from Coastal Zone Colour Scanner (CZCS), Ocean Colour Temperature Scanner (OCTS), Sea-viewing Wide Field-of-view Sensor (SeaWiFS), MEdium Resolution Imaging Spectrometer (MERIS), Moderate Resolution Imaging Spectroradiometer (MODIS) and Ocean Colour Monitor (OCM2). For chl-a concentration greater than 1.0 mg m−3, algorithms based on the reference band ratios 488/510/520 nm to 547/550/555/560/565 nm have to be considered. The assessment of algorithms showed better performance of OC3M and OC4. All the algorithms exhibited better performance in Type-I waters. However, the performance was poor in Type-II and Type-III waters which could be attributed to the significant co-variance of chl-a with CDOM.

9

An Arabian Sea. Chart if the Middle Ages

Shivandra S.

Prace Wydziału Nawigacyjnego Akademii Morskiej w Gdyni

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1998

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Z. 6

108--126