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1

Distribution and biogeochemical perspectives of nutrients in the Eastern Equatorial Indian Ocean

Paul Madhusudan, Sanyal Prasun, Mukherjee Rishmita, Gupta Vandana Kumari, Bakshi Sneha, Acharya Avanti, Bhattacharya Trishneeta, Chakraborty Kunal, Mukhopadhyay Sandip Kumar

Oceanologia

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2024

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Vol. 66 (2)

381--393

EN

The seasonal reversal of ocean circulation associated with seasonal change in the direction of prevailing winds and the occurrence of several anomalous events in the Eastern Equatorial Indian Ocean (EEIO) make this region dynamic and complex in terms of its biogeochemical characteristics. Two multidisciplinary cruises were conducted to measure nutrients and associated physicochemical parameters across the water column (up to 1000 m) of the EEIO during boreal summer and winter monsoons to understand the distribution of nutrients and their spatio-temporal variability from a biogeochemical perspective. The seasonality in the thermohaline structure of the region is indistinct except for surface salinity drop during summer monsoon due to more precipitation on-site and in adjoining areas. Low concentrations of chlorophyll at the surface and in the deep chlorophyll maxima represent the oligotrophic nature of this region. Surface water was found nutrient-depleted (0.03–0.4 µM Nitrate, 0.02–0.13 µM Phosphate). The maxima of vertical profiles of nitrate and phosphate were recorded at a shallower depth (150–200 m) when compared to its maxima in usual oceanic conditions, but a silicate maximum was recorded in deeper water. In the surface and upper mixed layer paucity of nutrients resulted in low N:P and N:Si ratios. Therefore, nitrogen limitation is evident. The overall ratio of N:P yielded a mean value of 15.33 and matched with the representative literature value for the Indian Ocean. The minimum oxygen values (<50 µM) in the deep water (150–200 m) indicated a hypoxic condition. No signature of denitrification and a moderate nitrate deficit were observed in deep waters. The negative values of Nitrate anomaly (N-tracer) at 50–100 m depth were attributed to a Watermass influenced by denitrification. The prevailing oligotrophic condition caused limited synthesis of organic matter and subsequently little decomposition in deep water. The maxima in the apparent oxygen utilization (AOU) profile are confined to 150 to 200 m depth and represent the most active zone for regeneration that is limited to shallow depth. Regenerated nutrients reached maxima at shallower depth and primarily control material cycling in this region. Supply of nitrate to the surface water based on the preformed values of prevailing water mass was primarily by Bay of Bengal water. According to the findings of this study, preformed nitrate concentrations between 100 and 200 metres below the surface were found very low, indicating that Indonesian Through Flow (ITF) has little impact on the distribution of nutrients in this area.

2

The Effect of ENSO on the Upwelling Intensity in the Seas along the Northern Coast of Papua: A Case Study of the 2015-2016 El Niño and the 2010-2011 La Niña Events

Lesmana Petrik Siano Okta Prima, Wirasatriya Anindya, Setiyono Heryoso, Suryoputro Agus Anugroho Dwi, Wijaya Yusuf Jati, Ismunarti Dwi Haryo, Haryanti Dwi, Abdillah Muhammad Rais

Ecological Engineering & Environmental Technology

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2024

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Vol. 25, iss. 2

243--253

EN

The seas along the Northern Coast of Papua constitute a region with complex oceanographic conditions as they are situated within the Indo-Pacific warm pool (IPWP). The geographical location in the southern hemisphere induces upwelling during the west monsoon season (December-January-February). Additionally, interannual phenomena such as the El Niño Southern Oscillation (ENSO) can impact the intensity of upwelling in these waters. This study aimed to compare the upwelling intensity in the seas along the Northern Coast of Papua during neutral phases and ENSO phases. The main indicators of upwelling are sea surface temperature (SST) and Ekman mass transport (EMT). The data utilized in this study include SST from GHRSST and surface wind from ASCAT. The data processing employed the monthly composite method with spatiotemporal analysis based on anomaly results derived from monthly climatology. The analysis results reveal that El Niño 2015–2016 led to an increase in upwelling intensity ranging from 1.82 to 4.00 m/s2, while La Niña 2010–2011 resulted in a weakening of upwelling intensity ranging from 4.95 to 6.56 m/s2 in the seas along the Northern Coast of Papua. On the basis of correlation and regression analysis, it can be concluded that offshore EMT significantly influences upwelling anomalies in the southeastern waters, whereas the northwestern waters are more influenced by the shifting IPWP during ENSO.

3

The shoemaker spinefoot Siganus sutor (Valenciennes, 1835) in the marine waters of Iraq: second appearance and the northernmost record in the northern Indian Ocean

Jawad Laith, Abed Jassim, Resen Amjed Kadhum, Al-Yassein Rajaa, Kulw Ali M.

Oceanological and Hydrobiological Studies

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2023

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Vol. 52, No. 2

166--171

EN

A new record of Siganus sutor from inland artificial marine extension Shatt al-Basrah canal, south of Iraq, is reported.Two specimens were collected during an ichthyologic survey on 2 November 2021. The specimens are 127 and 129 mm in total length. This record from Iraqi waters represents the species’ second and northernmost appearance in thenorthern Indian Ocean.

4

Remotely induced storm effects on the coastal flooding along the southwest coast of India

Swathy Krishna P.S., Aboobacker Valliyil Mohammed, Ramesh Madipally, Nair L. Sheela

Oceanologia

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2023

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Vol. 65 (3)

503--516

EN

The southwest coast of India is exposed to long-period swells propagated from the South Indian Ocean during pre- and post-monsoon seasons. Although swells from the Southern Ocean and Atlantic Ocean were identified in the North Indian Ocean, their existence and impact along the southwest coast of India were not well investigated. On 19 March 2019, the Valiyathura-Shangumukham coastal stretch along the southwest coast of India experienced an unexpected coastal inundation without having a prompt forecast/warning, and not induced by a storm/cyclone in its vicinity. The present study investigates the causative forces of this inundation and estimates the wave runup and inundation. The study reveals that an unusual swell system was developed in the Indian-Atlantic-Southern Oceans (IASO) interface during 10–12 March and propagated towards the southwest coast of India. The measured wave spectra off Varkala clearly depicts the presence of long-period swells (Tp>18 s), which dominantly occurred as single-peaked. Wave modelling has been carried out to characterize the wave transformation associated with the “IASO interface swells” along the southern Kerala coast. A wave runup of up to 0.93 m height and a coastal inundation of up to 83 m onshore have been estimated during this event.

5

Generation and Assessment of ARGO Sea Surface Temperature Climatology for the Indian Ocean Region

Jha Ravi Kumar, Bhaskar T.V.S. Udaya

Oceanologia

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2023

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Vol. 65 (2)

343--357

EN

ARGO program was conceived with an aim to generate near real-time ocean observations as the primary in-situ sources for use in operational oceanography studies. Two decades-long ARGO near-surface temperature data set was used for generating monthly gridded ARGO sea surface temperature (ASST) product on a climatological scale. Data interpolating variational analysis (DIVA) method was employed for generating the product with a spatial resolution of 0.25° x 0.25° for the Tropical Indian Ocean. This monthly ASST product was evaluated using five different climatological SST products derived from in-situ and satellite measurements. Various statistics such as BIAS, RMSE, coefficient of correlation, and skill scores were generated to evaluate the reliability of the ASST product. Further, the ASST product was validated with climatological in-situ SST obtained from RAMA and OMNI moorings deployed in the Indian Ocean. Statistical comparisons showed low BIAS and RMSE, and high correlation and skill scores with most of the buoys locations and the gridded SST products. Results concluded that the near-surface temperature data from ARGO can be used along with other SST data sets in the generation of high-resolution blended SST products.

6

Piractwo somalijskie

Banasiewicz Paulina, Gramala Sara

Roczniki Studenckie Akademii Wojsk Lądowych

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2020

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R. 4

45--58

PL

Piractwo jest bardzo ważnym problemem, które pośrednio dotyczy, praktycznie każdego człowieka. Każdy korzysta bowiem z dóbr, które były transportowane drogą morską. Morza i oceany zajmują bardzo dużą powierzchnię kuli ziemskiej, społeczeństwo nie jest w stanie ich kontrolować. Geneza piractwa wiąże się bezpośrednio z powstaniem żeglugi morskiej, świadczy to o tym, iż ludzie od zarania dziejów muszą zmagać się z tym problemem. Szczególnie niebezpiecznym regionem w kwestii piractwa jest Ocean Indyjski, Zatoka Adeńska i Róg Afryki. Zaangażowanie organizacji międzynarodowych sprawiło, iż obecnie piractwo na tych obszarach ustępuje, nie zmienia to faktu, iż należy nieustannie kontrolować sytuację i inwigilować obiekty, które przemieszczają się tamtejszymi trasami.

EN

Piracy is a very important problem that indirectly affects practically every person. Everyone uses the goods that were transported by sea. The origin of piracy is related to the emergence of shipping. A particulary dangerous area for piracy is the Indian Ocean, the Gulf of Aden and the Horn of Africa. Due to the involvement of international organizations, piracy in these areas is now subsiding, but this doesn't change the fact that the situation should be constantly monitored and objects that move along these routes must be constantly monitored.

7

Indian Ocean wind speed variability and global teleconnection patterns

Sinha Mourani, Jha Somnath, Chakraborty Paromita

Oceanologia

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2020

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No. 62 (2)

126--138

EN

The influence of the local sea surface temperature (SST) and remote ENSO (El Niño-Southern Oscillation) indices on the wind speed (WS) data were explored for the Indian Ocean region. Relationships among the parameters were studied using spatial correlation plots and significant correlation ranges. Two months (July and January) representing opposite monsoon phases were selected for analysis for the period 1950-2016. There was a significant negative correlation between WS and SST over the Bay of Bengal (BOB) during July. Although different ENSO indices correlated differently in different areas of the Indian Ocean, the region off the coast of Sri Lanka was most significantly teleconnected. The southwest monsoon locally impacted the WS and SST relationship and the WS parameter was remotely teleconnected in both the monsoon seasons. Further empirical orthogonal function (EOF) analysis was applied on the 67 years WS data of the BOB region to extract the dominant mode representing maximum variability of the total variance. The temporal pattern of the first principal component (PC1) of WS data was linked to the North Atlantic Oscillations in January and the Atlantic Multidecadal Oscillation in July respectively. The continuous wavelet power spectra of the PC1 of WS showed significant regions in the 2-4-year band resembling the ENSO variability. Wavelet coherence applied between PC1 of WS and the ENSO indices showed greatest values for January in the 8-16-year band and for July in the 0-4-year band. A close relationship was established between the WS variability in BOB and the ENSO indices.

8

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.

9

Analysis of Coseismic Fault Slip Models of the 2012 Indian Ocean Earthquake: Importance of GPS Data for Crustal Deformation Studies

Gunawan E., Maulida P., Meilano I., Irsyam M., Efendi J.

Acta Geophysica

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2016

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Vol. 64, no. 6

2136--2150

EN

Based on continuous GPS data, we analyze coseismic deformation due to the 2012 Indian Ocean earthquake. We use the available coseismic slip models of the 2012 earthquake, derived from geodetic and/or seismic waveform inversion, to calculate the coseismic displacements in the Andaman-Nicobar, Sumatra and Java. In our analysis, we employ a spherical, layered model of the Earth and we find that Java Island experienced coseismic displacements up to 8 mm, as also observed by our GPS network. Compared to coseismic offsets measured from GPS data, a coseismic slip model derived from multiple observations produced better results than a model based on a single type of observation.

10

Geopolityka i geostrategia wybranych mocarstw w regionie Oceanu Indyjskiego i Zachodniego Pacyfiku

Skrzyp J.

Zeszyty Naukowe AON

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2013

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nr 1(90)

5-37

EN

The Asian Development Bank forecasts that within 40 years Asia will catch up with Europe and North America which means that it will regain its dominating position in the global economy. Among many countries in this region China, which has already become world great power, deserves special attention. A dynamic progress is also the characteristic of India, a country which competes with China for the access to energy resources. Thus, a great race of those countries has commenced to have access to those resources as well as to secure the routes of their transport. Due to the above situation, the Indian Ocean and the West Pacific have gain special significance hence the Middle East and Africa are for the aforementioned countries a resource base. This, moreover, overlaps with strategic interests of the USA, Russia and other countries. As a result it is the beginning of a big game between China and India and the prize is the security of communication routes on the Indian Ocean and the West Pacific, where also the USA have their strategic interests. A big game between China, the USA, and Russia is also carried put in order to gain access to natural resources in Central Asia including the Caspian Sea and the Middle East. In the above situation, the ASEAN countries have become important being the passage area between the Indian Ocean and the Pacific. This is because of the Strait of Malacca which is located in this area and passed by 50 thousand ships yearly.

11

Response of eastern Indian Ocean (ODP Site 762B) benthic foraminiferal assemblages to the closure of the Indonesian seaway

Rai A. K., Singh W. B.

Oceanologia

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2012

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No. 54 (3)

449-472

EN

Pliocene-Pleistocene deep sea benthic foraminifera from ODP Site 762B in the eastern Indian Ocean were examined to understand the tectonically/climatically induced palaeoceanographic changes. In addition to already published data on this site by Rai & Singh (2001), some more faunal parameters were considered in the present work. Characteristic benthic foraminiferal assemblages as well as more diverse fauna during the early Pliocene (before 3.5 Ma) reflected relatively oligotrophic and warm bottom water conditions. At the beginning of the late Pliocene (i.e. ~3 š 0.5 Ma) relative abundances of Uvigerina proboscidea, infaunal taxa and high productivity taxa increased, whereas faunal diversity showed a distinct decline, suggesting the development of pronounced upwelling resulting in higher surface water productivity. The strongly reduced inflow of warm and oligotrophic water masses as the South Equatorial Current (SEC) from the South Pacific to the eastern Indian Ocean due to the effective closure of the Indonesian seaway increased the surface water productivity. The closing of the Indonesian seaway during the late Pliocene was also responsible for the cessation of the warm, southward-flowing Leeuwin Current (LC) and the greater influence of the cold, deep and northward-flowing Western Australian Current (WAC) in the eastern Indian Ocean.

12

Ambient noise induced by large-amplitude internal waves in the ocean

Serebryany A., Aredov A., Okhrimenko N.

Hydroacoustics

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2009

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Vol. 12

209-216

EN

Experimental data on the ambient noise generated by large-amplitude internal waves in the ocean are considered. The data are obtained by us during oceanic expeditions in the Indian Ocean and South China Sea. In both cases the generation of noise was caused by solitary internal waves with 50-m amplitudes. The internal waves were accompanied by strong orbital currents (up to 1.5 m/s) which created intense convergence with choppy surface waves at the sea surface. Simultaneous observations of internal waves and parameters of the ambient noise were carried out from a drifting vessel during calm weather. In both cases, the increase in the level of the ambient noise coincided with the passages of internal waves. The analysis of experimental data and the data of numerically modeling are presented.

13

The Pliocene-Pleistocene boundary in pelagic oozes off Reunion Island, western Indian Ocean

Duczmal-Czerniewicz A., Jugowiec-Nazarkiewicz M., Szydło A.

Acta Geologica Polonica

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2006

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Vol. 56, no. 4

407-419

EN

Nannoplankton and foraminifera from the pelagic oozes from a water depth of 3 684 meters, 150 km southeast of Reunion Island, Indian Ocean, prove the NN18 and NN19 nannoplankton zones, indicating the Pliocene.Pleistocene boundary. The Pliocene.Pleistocene boundary was established at 220.230 cm depth. The abundance of Globorotalia truncatulinoides increases from about 50 cm below the sea floor. The microfossil assemblages and clay mineral components of the sediments may be correlated with changes of climatic conditions influenced by glaciations.

14

Problem potencjału stresowego górotworu (refleksje po kataklizmie w rejonie Oceanu Indyjskiego)

Adamczewski Z., Larsen L.

Przegląd Geodezyjny

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2005

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R. 77, nr 2

3-5