scholarly journals Impact of Climate Change on Past Indian Monsoon and Circulation: A Perspective Based on Radiogenic and Trace Metal Geochemistry

Atmosphere ◽  
2021 ◽  
Vol 12 (3) ◽  
pp. 330
Author(s):  
Harunur Rashid ◽  
Yang Wang ◽  
Alexandra T. Gourlan
Keyword(s):  
Indian Ocean ◽  
Bay Of Bengal ◽  
Indian Subcontinent ◽  
North Indian Ocean ◽  
Sea Surface ◽  
Andaman Sea ◽  
Northern Indian Ocean ◽  
Hafnium Isotopes ◽  
Neodymium Isotopes ◽  
The Last Glacial

The Indian summer monsoon (ISM), one of the dramatic illustrations of seasonal hydrological variability in the climate system, affects billions of lives. The ISM dominantly controls the northern Indian Ocean sea-surface salinity, mostly in the Bay of Bengal and the Andaman Sea, by the Ganga-Brahmaputra-Meghna and Irrawaddy-Salween rivers outflow and direct rainfall. In the past decade, numerous studies have used radiogenic neodymium (εNd) isotopes of seawater to link Indian subcontinent erosion and the ensuing increase in discharge that results in changes in the north Indian Ocean sea surface. Here we synthesized the state of the ISM and ocean circulation using the neodymium and hafnium isotopes from north Indian Ocean deep-sea sediments. Our data suggest that the Bay of Bengal and north Indian Ocean sea-surface conditions were most likely modulated by changes in the ISM strength during the last glacial-interglacial cycle. These findings contrast to the hypothesis that suggests that the bottom water neodymium isotopes of the northern Indian Ocean were modulated by switching between two distant sources, namely North Atlantic Deep Water and Antarctic bottom water. Furthermore, the consistency between the neodymium and hafnium isotopes during the last glacial maximum and Holocene suggests a weak and dry ISM and strong and wet conditions, respectively. These data also indicate that the primary source of these isotopes was the Himalayas. Our results support the previously published paleo-proxy records, indicating weak and strong monsoons for the same periods. Moreover, our data further support the hypothesis that the northern Indian Ocean neodymium isotopes were decoupled from the global ocean neodymium budget due to the greater regional influence by the great Ganga-Brahmaputra-Meghna and Irrawaddy-Salween discharge draining the Indian subcontinent to the Bay of Bengal and the Andaman Sea.

Description of Rhinobatos ranongensis sp. nov. (Rhinopristiformes: Rhinobatidae) from the Andaman Sea and Bay of Bengal with a review of its northern Indian Ocean congeners

Zootaxa ◽  
2019 ◽  
Vol 4576 (2) ◽  
pp. 257
Author(s):  
PETER R. LAST ◽  
BERNARD SÉRET ◽  
GAVIN J.P. NAYLOR
Keyword(s):  
Indian Ocean ◽  
Bay Of Bengal ◽  
Intraspecific Variability ◽  
Andaman Sea ◽  
Nominal Species ◽  
Northern Indian Ocean ◽  
Additional Material ◽  
Tissue Samples ◽  
New Material ◽  
Colour Morphs

A new species of guitarfish, Rhinobatos ranongensis sp. nov., is described from 5 preserved specimens, and images and tissue samples of additional material, collected from the Andaman Sea and Bay of Bengal. This species co-occurs in the eastern sector of the northern Indian Ocean with two poorly defined congeners, R. annandalei Norman and R. lionotus Norman, which have been misidentified and confused with Indo-Pacific congeners since they were first described in 1926. Norman’s species are rediagnosed based on limited new material and a re-examination of the types. In the western sector of the northern Indian Ocean, Rhinobatos annandalei has been confused in recent literature with the sympatric R. punctifer Compagno and Randall, which is represented by four primary colour morphs, including a white-spotted colour morph resembling R. annandalei. Rhinobatos punctifer also displays strong intraspecific variability and sexual dimorphism in some body dimensions. These four species of Rhinobatos have unique MtDna sequences and belong to a clade of Indo-West Pacific species that are morphologically similar. Despite the relatively small numbers of specimens available for investigation, these species exhibit some clear differences in body proportions, meristics and squamation. Rhinobatos ranongensis sp. nov. differs from its northern Indian Ocean congeners through a combination of a relatively narrow disc and mouth, high vertebral count, long snout, low dorsal fins, and being largely plain coloured. A new lectotype and a paralectotype are designated for the syntypes of R. annandalei, and the four primary colour forms of R. punctifer, the plain, white-spotted and ocellated morphs, are described and the three nominal species rediagnosed. A key is provided to the four known members of the genus in the northern Indian Ocean. 

scholarly journals ΔR Correction Values for the Northern Indian Ocean

Radiocarbon ◽  
2001 ◽  
Vol 43 (2A) ◽  
pp. 483-488 ◽  
Author(s):  
Koushik Dutta ◽  
Ravi Bhushan ◽  
B L K Somayajulu
Keyword(s):  
Indian Ocean ◽  
Bay Of Bengal ◽  
Arabian Sea ◽  
Andaman Sea ◽  
Northern Indian Ocean ◽  
Northern Arabian Sea ◽  
Ocean Region ◽  
Thermocline Ventilation ◽  
Ventilation Rates ◽  
Made In

Apparent marine radiocarbon ages are reported for the northern Indian Ocean region for the pre-nuclear period, based on measurements made in seven mollusk shells collected between 1930 and 1954. The conventional 14C ages of these shells range from 693 ± 44 to 434 ± 51 BP in the Arabian Sea and 511 ± 34 to 408 ± 51 BP in the Bay of Bengal. These ages correspond to mean ΔR correction values of 163 ± 30 yr for the northern Arabian Sea, 11 ± 35 yr for the eastern Bay of Bengal (Andaman Sea) and 32 ± 20 yr for the southern Bay of Bengal. Contrasting reservoir ages for these two basins are most likely due to differences in their thermocline ventilation rates.

Pseudanthias vizagensis, a junior synonym of Pseudanthias pillai Heemstra & Akhilesh, 2012 (Perciformes: Serranidae)

Zootaxa ◽  
2020 ◽  
Vol 4890 (1) ◽  
pp. 135-147
Author(s):  
K.V. AKHILESH ◽  
T.G. KISHORE ◽  
M. MUKTHA ◽  
M.W. LISHER ◽  
GOP P. AMBARISH ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Bay Of Bengal ◽  
Andhra Pradesh ◽  
Arabian Sea ◽  
Original Description ◽  
Junior Synonym ◽  
Andaman Sea ◽  
Northern Indian Ocean ◽  
Additional Material ◽  
Bay Of Bengal Coast

Pseudanthias vizagensis Krishna, Rao and Venu, 2017 was described from 44 specimens, collected from Visakhapatnam (Andhra Pradesh), on the Bay of Bengal coast of India, but without clear designation of a holotype. The characters used for differentiating the species from its nearest congener Pseudanthias pillai Heemstra & Akhilesh, 2012, a species currently known only from the northern Indian Ocean, were limited, poor and substantially overlapping. Examination of additional material of P. pillai from the Arabian Sea, Bay of Bengal, Andaman Sea, and comparison with the original description and images of P. vizagensis revealed that the latter is a junior synonym of P. pillai. Diagnostic characters are reviewed, additional morphological details and fresh colouration, including sexual dimorphic characters not covered in previous works are provided. 

Towards long-term (2002-present) reconstruction of northern Indian Ocean Sea Surface Salinity based on AMSR-E and L-band Radiometer data

2021 ◽  
Author(s):  
Marie Montero ◽  
Nicolas Reul ◽  
Clément de Boyer Montégut ◽  
Jérôme Vialard ◽  
Jean Tournadre
Keyword(s):  
Indian Ocean ◽  
North Indian Ocean ◽  
Sea Surface ◽  
Sea Surface Salinity ◽  
Northern Indian Ocean ◽  
Surface Salinity ◽  
The North ◽  
X Band ◽  
L Band

<p>Salinity plays an important role in the oceanic circulation, because of its impact on pressure gradients and the upper ocean stability. This is particularly the case in the North Indian Ocean where freshwater inputs from monsoonal rain and rivers into the Bay of Bengal and strong evaporation in the Arabian Sea leads to high salinity contrasts, and a strong variability tied to the large monsoonal currents seasonal cycle.</p><p>In situ salinity data is however too sparse to allow a detailed study of the contrasted and variable Northern Indian Ocean Sea Surface Salinity (SSS). This situation has changed since the launch of SMOS in 2009, and the advent of L-band-based SSS remote sensing with a much higher spatio-temporal sampling. Here, we explore the capacity of C and X-band measurements, such as those of AMSR-E (May 2002-October 2011) to reconstruct Northern Indian Ocean SSS prior 2009. Previous studies have indeed demonstrated the ability of C- and X-band products to reconstruct SSS in high-contrast regions like river estuaries, especially at high Sea Surface Temperature (SST), like in the Northern Indian Ocean.</p><p> </p><p>We are currently focusing on the development of the algorithm to reconstruct salinity from the C- and X-band data of AMSR-E. The ESA Climate Change Initiative (CCI) SSS dataset build from a merge of SMOS, Aquarius and SMAP data, provides a reference SSS that is both used for training our algorithm and for validation, over the common AMSR-E and CCI period (January 2010 to October 2011).</p><p>Our first results are encouraging: spatial contrast between the low-SSS values close to estuaries and along the coast and higher SSS in the middle of the Bay of Bengal as well as some aspects of the seasonal cycle are reproduced. However, spurious signals linked to either radio frequency interferences still need to be filtered out and signals associated with other residual geophysical contributions (e.g. wind, atmospheric vapor content) need to be better estimated. The long-term goal of this work is to merge the C-, X-, and L-band data with in-situ measurements and thus provide a long-term reconstruction of monthly SSS in the north Indian Ocean with a ~50km resolution.</p>

Assessing the long-term physical-biogeochemical interactions in the North Indian Ocean using a coupled relocatable model

2021 ◽  
Author(s):  
Jenny Jardine ◽  
Anna Katavouta ◽  
Dale Partridge ◽  
Jeff Polton ◽  
Jason Holt ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Large Scale ◽  
Indian Subcontinent ◽  
North Indian Ocean ◽  
Scale Model ◽  
Northern Indian Ocean ◽  
Climate Fluctuations ◽  
The North ◽  
Run Off ◽  
Large Scale Model

<p><br>The Indian Ocean is a dynamic region that is heavily influenced by immense freshwater runoff, extreme meteorological events and the seasonal reversal of monsoonal currents. Providing essential resources for over one-third of the global population, the Northern Indian Ocean is a key area of research: increased freshwater run-off, low overturning velocities and high air-sea fluxes result in the region being highly susceptible to climate fluctuations, and execess nutrients, particularly nitrates accumulated through agricultural run-off, directly influence marine biogeochemical cycles. The South Asia Nitrogen Hub (SANH) is a GCRF project designed to assess, monitor and predict the physical and biogeochemical response of the Northern Indian Ocean to such anthropogenic changes. To address key questions in SANH, a relocatable physical-biogeochemical (NEMO-ERSEM) was configured across the region, which includes the Eastern Arabian Sea and the Bay of Bengal. A 22-year hindcast run (1993-2015) at ~11km resolution allows the physical-biogeochemical processes (including from mesoscale eddies, extreme meteorological events and varying runoff) to be viewed at scale that is otherwise impossible with observational campaigns. In conjunction with the large-scale model domain, 6 smaller high-resolution (~1-2km) coastal models were configurated around the Indian subcontinent, allowing a more focussed view at processes that directly impact coastal populations. Here, we will present initial results from the large-scale hindcast run, the coastal regions, and explore the advantages and caveats of relocatable modelling.<br><br></p>

scholarly journals Wind-Driven Response of the Northern Indian Ocean to Climate Extremes*

2007 ◽  
Vol 20 (13) ◽  
pp. 2978-2993 ◽  
Author(s):  
Tommy G. Jensen
Keyword(s):  
Indian Ocean ◽  
Ocean Circulation ◽  
Bay Of Bengal ◽  
El Niño ◽  
Arabian Sea ◽  
El Nino ◽  
Ocean Model ◽  
La Niña ◽  
Northern Indian Ocean ◽  
La Nina

Abstract Composites of Florida State University winds (1970–99) for four different climate scenarios are used to force an Indian Ocean model. In addition to the mean climatology, the cases include La Niña, El Niño, and the Indian Ocean dipole (IOD). The differences in upper-ocean water mass exchanges between the Arabian Sea and the Bay of Bengal are investigated and show that, during El Niño and IOD years, the average clockwise Indian Ocean circulation is intensified, while it is weakened during La Niña years. As a consequence, high-salinity water export from the Arabian Sea into the Bay of Bengal is enhanced during El Niño and IOD years, while transport of low-salinity waters from the Bay of Bengal into the Arabian Sea is enhanced during La Niña years. This provides a venue for interannual salinity variations in the northern Indian Ocean.

scholarly journals Seven year satellite observations of the mean structures and variabilities in the regional aerosol distribution over the oceanic areas around the Indian subcontinent

2005 ◽  
Vol 23 (6) ◽  
pp. 2011-2030 ◽  
Author(s):  
S. K. Nair ◽  
K. Parameswaran ◽  
K. Rajeev
Keyword(s):  
Indian Ocean ◽  
Southern Hemisphere ◽  
Bay Of Bengal ◽  
Arabian Sea ◽  
Indian Subcontinent ◽  
Monsoon Season ◽  
Dry Season ◽  
Aerosol Transport ◽  
Summer Monsoon Season ◽  
Aerosol Distribution

Abstract. Aerosol distribution over the oceanic regions around the Indian subcontinent and its seasonal and interannual variabilities are studied using the aerosol optical depth (AOD) derived from NOAA-14 and NOAA-16 AVHRR data for the period of November 1995–December 2003. The air-mass types over this region during the Asian summer monsoon season (June–September) are significantly different from those during the Asian dry season (November–April). Hence, the aerosol loading and its properties over these oceanic regions are also distinctly different in these two periods. During the Asian dry season, the Arabian Sea and Bay of Bengal are dominated by the transport of aerosols from Northern Hemispheric landmasses, mainly the Indian subcontinent, Southeast Asia and Arabia. This aerosol transport is rather weak in the early part of the dry season (November–January) compared to that in the later period (February–April). Large-scale transport of mineral dust from Arabia and the production of sea-salt aerosols, due to high surface wind speeds, contribute to the high aerosol loading over the Arabian Sea region during the summer monsoon season. As a result, the monthly mean AOD over the Arabian Sea shows a clear annual cycle with the highest values occurring in July. The AOD over the Bay of Bengal and the Southern Hemisphere Indian Ocean also displays an annual cycle with maxima during March and October, respectively. The amplitude of the annual variation is the largest in coastal Arabia and the least in the Southern Hemisphere Indian Ocean. The interannual variability in AOD is the largest over the Southeast Arabian Sea (seasonal mean AOD varies from 0.19 to 0.42) and the northern Bay of Bengal (seasonal mean AOD varies from 0.24 to 0.39) during the February–April period and is the least over the Southern Hemisphere Indian Ocean. This study also investigates the altitude regions and pathways of dominant aerosol transport by combining the AOD distribution with the atmospheric circulation. Keywords. Atmospheric composition and structure (Aerosols and particles) – Meteorology and atmospheric dynamics (Climatology) – Oceanography: physical (Ocean fog and aerosols)

scholarly journals Reviews and syntheses: Present, past, and future of the oxygen minimum zone in the northern Indian Ocean

2020 ◽  
Vol 17 (23) ◽  
pp. 6051-6080
Author(s):  
Tim Rixen ◽  
Greg Cowie ◽  
Birgit Gaye ◽  
Joaquim Goes ◽  
Helga do Rosário Gomes ◽  
...  
Keyword(s):  
Oxygen Consumption ◽  
Indian Ocean ◽  
Nitrogen Cycle ◽  
Bay Of Bengal ◽  
Arabian Sea ◽  
Oxygen Supply ◽  
Northern Indian Ocean ◽  
Minimum Zone ◽  
Oxygen Minimum ◽  
Oxygen Concentrations

Abstract. Decreasing concentrations of dissolved oxygen in the ocean are considered one of the main threats to marine ecosystems as they jeopardize the growth of higher organisms. They also alter the marine nitrogen cycle, which is strongly bound to the carbon cycle and climate. While higher organisms in general start to suffer from oxygen concentrations < ∼ 63 µM (hypoxia), the marine nitrogen cycle responds to oxygen concentration below a threshold of about 20 µM (microbial hypoxia), whereas anoxic processes dominate the nitrogen cycle at oxygen concentrations of < ∼ 0.05 µM (functional anoxia). The Arabian Sea and the Bay of Bengal are home to approximately 21 % of the total volume of ocean waters revealing microbial hypoxia. While in the Arabian Sea this oxygen minimum zone (OMZ) is also functionally anoxic, the Bay of Bengal OMZ seems to be on the verge of becoming so. Even though there are a few isolated reports on the occurrence of anoxia prior to 1960, anoxic events have so far not been reported from the open northern Indian Ocean (i.e., other than on shelves) during the last 60 years. Maintenance of functional anoxia in the Arabian Sea OMZ with oxygen concentrations ranging between > 0 and ∼ 0.05 µM is highly extraordinary considering that the monsoon reverses the surface ocean circulation twice a year and turns vast areas of the Arabian Sea from an oligotrophic oceanic desert into one of the most productive regions of the oceans within a few weeks. Thus, the comparably low variability of oxygen concentration in the OMZ implies stable balances between the physical oxygen supply and the biological oxygen consumption, which includes negative feedback mechanisms such as reducing oxygen consumption at decreasing oxygen concentrations (e.g., reduced respiration). Lower biological oxygen consumption is also assumed to be responsible for a less intense OMZ in the Bay of Bengal. According to numerical model results, a decreasing physical oxygen supply via the inflow of water masses from the south intensified the Arabian Sea OMZ during the last 6000 years, whereas a reduced oxygen supply via the inflow of Persian Gulf Water from the north intensifies the OMZ today in response to global warming. The first is supported by data derived from the sedimentary records, and the latter concurs with observations of decreasing oxygen concentrations and a spreading of functional anoxia during the last decades in the Arabian Sea. In the Arabian Sea decreasing oxygen concentrations seem to have initiated a regime shift within the pelagic ecosystem structure, and this trend is also seen in benthic ecosystems. Consequences for biogeochemical cycles are as yet unknown, which, in addition to the poor representation of mesoscale features in global Earth system models, reduces the reliability of estimates of the future OMZ development in the northern Indian Ocean.

scholarly journals Trend of shift in the area of cyclo-genesis over north Indian Ocean

MAUSAM ◽  
2021 ◽  
Vol 58 (1) ◽  
pp. 49-58
Author(s):  
CHARAN SINGH ◽  
B. R. LOE
Keyword(s):  
Standard Deviation ◽  
Indian Ocean ◽  
Bay Of Bengal ◽  
Arabian Sea ◽  
North Indian Ocean

ABSTRACT. Cyclo-genesis over north Indian Ocean (Bay of Bengal and the Arabian Sea) has been studied with reference to the formation and shift of cyclo-genesis area. The frequency of formation of cyclones during a particular month and year for the period of study has been presented. The study has shown that the maximum number of cyclo-genesis occurred during the month of July followed by August and September. Cyclo-genesis was about three times more in the Bay of Bengal as compared to that in the Arabian Sea. Areas favourable for cyclo-genesis were found between Lat. 15.0° N to 22.5° N and Long. 86.0° E to 92.0° E over the Bay of Bengal and Lat. 7.0° N to 12.5° N and 60.0° E to 74.0° E over the Arabian sea while meander over north Indian ocean, some times its shift significantly. Standard deviation of number of cyclones has been computed for the decades from 1891-2000. It was found that it was maximum (1.96) during 1941-1950 followed by 1981-1990 (1.92).

Variations of the Indian Ocean Walker circulation since the Last Glacial Maximum revealed by reconstructed and simulated zonal wind intensity

2021 ◽  
Author(s):  
Xinquan Zhou ◽  
Stéphanie Duchamp-Alphonse ◽  
Masa Kageyama ◽  
Franck Bassinot ◽  
Xiaoxu Shi ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Surface Temperature ◽  
Equatorial Indian Ocean ◽  
Walker Circulation ◽  
Sea Surface ◽  
The Indian Ocean ◽  
Sst Anomaly ◽  
Mean Circulation ◽  
The Last Glacial Maximum ◽  
The Last Glacial

&lt;p&gt;Today, precipitation and wind patterns over the equatorial Indian Ocean and surrounding lands are paced by monsoon and Walker circulations that are controlled by the seasonal land-sea temperature contrast and the inter-annual convection over the Indo-Pacific Warm Pool, respectively. The annual mean surface westerly winds are particularly tied to the Walker circulation, showing interannual variability coupled with the gradient of Sea Surface Temperature (SST) anomaly between the tropical western and southeastern Indian Ocean, namely, the Indian Ocean Dipole (IOD). While the Indian monsoon pattern has been widely studied in the past, few works deal with the evolution of Walker circulation despite its crucial impacts on modern and future tropical climate systems. Here, we reconstruct the long-term westerly (summer) and easterly (winter) wind dynamics of the equatorial Indian Ocean (10&amp;#176;S&amp;#8722;10&amp;#176;N), since the Last Glacial Maximum (LGM) based on i) primary productivity (PP) records derived from coccolith analyses of sedimentary cores MD77-191 and BAR94-24, retrieved off the southern tip of India and off the northwestern tip of Sumatra, respectively and ii) the calculation of a sea surface temperature (SST) anomaly gradient off (south) western Sumatra based on published SST data. We compare these reconstructions with atmospheric circulation simulations obtained with the general coupled model AWI-ESM-1-1-LR (Alfred Wegener Institute Earth System Model).&lt;/p&gt;&lt;p&gt;Our results show that the Indian Ocean Walker circulation was weaker during the LGM and the early/middle Holocene than present. Model simulations suggest that this is due to anomalous easterlies over the eastern Indian Ocean. The LGM mean circulation state may have been comparable to the year 1997 with a positive IOD, when anomalously strong equatorial easterlies prevailed in winter. The early/mid Holocene mean circulation state may have been equivalent to the year 2006 with a positive IOD, when anomalously strong southeasterlies prevailed over Java-Sumatra in summer. The deglaciation can be seen as a transient period between these two positive IOD-like mean states.&lt;/p&gt;

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