The impact of northern Indian Ocean rivers on the Bay of Bengal using NEMO global ocean model

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.

Download Full-text

Antarctic ice sheet fertilises the Southern Ocean

Biogeosciences ◽

10.5194/bg-11-2635-2014 ◽

2014 ◽

Vol 11 (10) ◽

pp. 2635-2643 ◽

Cited By ~ 53

Author(s):

R. Death ◽

J. L. Wadham ◽

F. Monteiro ◽

A. M. Le Brocq ◽

M. Tranter ◽

...

Keyword(s):

Southern Ocean ◽

Ice Sheet ◽

Ocean Model ◽

Coastal Sediments ◽

Global Ocean ◽

Iron Cycling ◽

Antarctic Ice Sheet ◽

Significant Control ◽

Subglacial Meltwater ◽

The Impact

Abstract. Southern Ocean (SO) marine primary productivity (PP) is strongly influenced by the availability of iron in surface waters, which is thought to exert a significant control upon atmospheric CO2 concentrations on glacial/interglacial timescales. The zone bordering the Antarctic Ice Sheet exhibits high PP and seasonal plankton blooms in response to light and variations in iron availability. The sources of iron stimulating elevated SO PP are in debate. Established contributors include dust, coastal sediments/upwelling, icebergs and sea ice. Subglacial meltwater exported at the ice margin is a more recent suggestion, arising from intense iron cycling beneath the ice sheet. Icebergs and subglacial meltwater may supply a large amount of bioavailable iron to the SO, estimated in this study at 0.07–0.2 Tg yr−1. Here we apply the MIT global ocean model (Follows et al., 2007) to determine the potential impact of this level of iron export from the ice sheet upon SO PP. The export of iron from the ice sheet raises modelled SO PP by up to 40%, and provides one plausible explanation for seasonally very high in situ measurements of PP in the near-coastal zone. The impact on SO PP is greatest in coastal regions, which are also areas of high measured marine PP. These results suggest that the export of Antarctic runoff and icebergs may have an important impact on SO PP and should be included in future biogeochemical modelling.

Download Full-text

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

Biogeosciences ◽

10.5194/bg-17-6051-2020 ◽

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.

Download Full-text

Antarctic Ice Sheet fertilises the Southern Ocean

Biogeosciences Discussions ◽

10.5194/bgd-10-12551-2013 ◽

2013 ◽

Vol 10 (7) ◽

pp. 12551-12570 ◽

Cited By ~ 8

Author(s):

R. Death ◽

J. L. Wadham ◽

F. Monteiro ◽

A. M. Le Brocq ◽

M. Tranter ◽

...

Keyword(s):

Southern Ocean ◽

Ice Sheet ◽

Ocean Model ◽

Coastal Sediments ◽

Global Ocean ◽

Iron Cycling ◽

Antarctic Ice Sheet ◽

Significant Control ◽

Subglacial Meltwater ◽

The Impact

Abstract. Southern Ocean (SO) marine primary productivity (PP) is strongly influenced by the availability of iron in surface waters, which is thought to exert a significant control upon atmospheric CO2 concentrations on glacial/interglacial timescales. The zone bordering the Antarctic Ice Sheet exhibits high PP and seasonal plankton blooms in response to light and variations in iron availability. The sources of iron stimulating elevated SO PP are in debate. Established contributors include dust, coastal sediments/upwelling, icebergs and sea ice. Subglacial meltwater exported at the ice margin is a more recent suggestion, arising from intense iron cycling beneath the ice sheet. Icebergs and subglacial meltwater may supply a large amount of bioavailable iron to the SO, estimated in this study at 0.07–1.0 Tg yr−1. Here we apply the MIT global ocean model (Follows et al., 2007) to determine the potential impact of this level of iron export from the ice sheet upon SO PP. The export of iron from the ice sheet raises modelled SO PP by up to 40%, and provides one plausible explanation for very high seasonally observed PP in the near-coastal zone. The impact on SO PP is greatest in coastal regions, which are also areas of high observed marine PP. These results suggest that the export of Antarctic runoff and icebergs may have an important impact on SO PP and should be included in future biogeochemical modelling.

Download Full-text

Beaching patterns of plastic debris along the Indian Ocean rim

10.5194/os-2020-50 ◽

2020 ◽

Author(s):

Mirjam van der Mheen ◽

Erik van Sebille ◽

Charitha Pattiaratchi

Keyword(s):

Indian Ocean ◽

Bay Of Bengal ◽

Plastic Material ◽

Monsoon Season ◽

Southwest Monsoon ◽

Plastic Waste ◽

Ocean Dynamics ◽

Global Ocean ◽

The Indian Ocean ◽

Southwest Monsoon Season

Abstract. A large percentage of global ocean plastic waste enters the northern hemisphere Indian Ocean (NIO). Despite this, it is unclear what happens to buoyant plastics in the NIO. Because the subtropics in the NIO is blocked by landmass, there is no subtropical gyre and no associated subtropical garbage patch in this region. We therefore hypothesise that plastics "beach" and end up on coastlines along the Indian Ocean rim. In this paper, we determine the influence of beaching plastics by applying different beaching conditions to Lagrangian particle tracking simulation results. Our results show that a large amount of plastic likely ends up on coastlines in the NIO, while some crosses the equator into the southern hemisphere Indian Ocean (SIO). In the NIO, the transport of plastics is dominated by seasonally reversing monsoonal currents, which transport plastics back and forth between the Arabian Sea and the Bay of Bengal. All buoyant plastic material in this region beaches within a few years in our simulations. Countries bordering the Bay of Bengal are particularly heavily affected by plastics beaching on coastlines. This is a result of both the large sources of plastic waste in the region, as well as ocean dynamics which concentrate plastics in the Bay of Bengal. During the intermonsoon period following the southwest monsoon season (September, October, November), plastics can cross the equator on the eastern side of the NIO basin into the SIO. Plastics that escape from the NIO into the SIO beach on eastern African coastlines and islands in the SIO or enter the subtropical SIO garbage patch.

Download Full-text

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 ◽

10.11646/zootaxa.4576.2.3 ◽

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.

Download Full-text

A report on epibionts and new record of two ciliates Ephelota plana and Ephelota gigantea in the coastal waters of Bay of Bengal, Northern Indian Ocean

Symbiosis ◽

10.1007/s13199-019-00659-7 ◽

2019 ◽

Vol 80 (2) ◽

pp. 217-230 ◽

Cited By ~ 1

Author(s):

Jasmine Purushothaman ◽

Aishee Bhowal ◽

Alfisa Siddique ◽

Sanu V. Francis ◽

Chelladurai Raghunathan

Keyword(s):

Indian Ocean ◽

Bay Of Bengal ◽

Coastal Waters ◽

New Record ◽

Northern Indian Ocean

Download Full-text

ΔR Correction Values for the Northern Indian Ocean

Radiocarbon ◽

10.1017/s0033822200038376 ◽

2001 ◽

Vol 43 (2A) ◽

pp. 483-488 ◽

Cited By ~ 89

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.

Download Full-text

Modeling Decadal Changes on the Indian Ocean Section I5 at 32°S

Journal of Climate ◽

10.1175/jcli4160.1 ◽

2007 ◽

Vol 20 (13) ◽

pp. 3106-3130 ◽

Cited By ~ 4

Author(s):

R. J. Murray ◽

Nathaniel L. Bindoff ◽

C. J. C. Reason

Keyword(s):

Indian Ocean ◽

Ocean Model ◽

Global Ocean ◽

Late Winter ◽

Intermediate Water ◽

Mode Water ◽

Density Class ◽

The Indian Ocean ◽

1960S And 1970S ◽

The 1960S

Abstract A near-global ocean model with resolution enhanced in the southern Indian Ocean has been spun up to seasonal equilibrium and then driven by NCEP–NCAR reanalysis 1 monthly mean forcings and Hadley SSTs over the period 1948–2002. The aim was to simulate changes in the subsurface properties observed in hydrographic surveys at 32°S in the Indian Ocean in 1965, 1987, and 2002. These surveys showed a zonally averaged cooling on isopycnals of 0.5° and 0.3°C in mode and intermediate waters between 1965 and 1987 and a warming of the mode water coupled with a continued cooling of the intermediate water between 1987 and 2002. The major changes in isopycnal depth and temperature modeled in this study were confined to the mode water and were qualitatively similar to those observed but concentrated in a lower density class and in the eastern half of the section. The dominant changes here were multidecadal, with maximum temperatures on the σθ = 26.7 kg m−3 isopycnal being reached in 1968 and minimum temperatures in 1990. The simulations showed a propagation of interannual anomalies toward the section from a region of deep late winter mixed layers in the southeast Indian Ocean within a period of several years. Surface temperatures in this region were lowest in the 1960s and highest in the late 1980s. Temperatures on isopycnals showed the opposite variation, consistent with SST having the controlling effect on mixed layer density and depth. Isopycnal depths within the mode water were strongly correlated with temperature, implying a redistribution of mode water density classes, the greatest volume of mode water being produced in a higher density class (σθ = 26.8–27.0 kg m–3) during the period of cooler surface forcing in the 1960s and 1970s than during the warmer period following (σθ = 26.6–26.8 kg m–3).

Download Full-text

Impact of biogeochemistry feedbacks on the projected climate change signal over the Indian Continent

10.5194/egusphere-egu2020-19402 ◽

2020 ◽

Author(s):

Dmitry Sein ◽

William Cabos ◽

Pankaj Kumar ◽

Vladimir Ryabchenko ◽

Stanislav Martyanov ◽

...

Keyword(s):

Climate Change ◽

Marine Ecosystem ◽

Regional Model ◽

Ocean Model ◽

Global Ocean ◽

Future Climate Change ◽

Climate Change Signal ◽

Water Type ◽

Substantial Impact ◽

The Impact

There are few studies dedicated to assessing the impact of biogeochemistry feedbacks on the climate change signal. In this study, we evaluate this impact in a future climate change scenario over the Indian subcontinent with the coupled regional model ROM in the Indian CORDEX area.In ROM a global ocean model (MPIOM) with regionally high horizontal resolution (up to 15 km resolution in the Bay of Bengal) is coupled to an atmospheric regional model (REMO, with 25 km resolution) and global terrestrial hydrology model. The ocean and the atmosphere are interacting within the region covered by the atmospheric domain. Outside this domain, the ocean model is not coupled to the atmosphere, being driven by prescribed atmospheric forcing, thus running in so-called stand-alone mode.To assess the impact of biogeochemical feedbacks on the climate change signal, we compare two simulations with ROM. In both simulations, the model is driven by data from a climate change simulation under the RCP 8.5 scenario with the MPI-ESM global model and differ only in the activation of the biochemistry module of MPIOM. In the first simulation, we use a light attenuation parameterization based on the Jerlov water types, when the attenuation coefficient varies spatially depending on the water type specified but does not vary in time. In the second simulation, we introduce the biochemical feedbacks as implemented in the global ocean biogeochemistry model HAMOCC. &#160;Both simulations capture the main features of the present time atmospheric and oceanic variability in the region and the model with HAMOCC reproduces well the intra-annual dynamics of the marine ecosystem in the northern Indian Ocean.A comparison of the simulated changes in atmospheric variables shows that the feedbacks have a substantial impact on the climate change signal for precipitation and air temperature, especially over the central Indian region.Acknowledgement: The work was supported by the Russian Science Foundation (Project 19-47-02015) and Indian project no. DST/INT/RUS/RSF/P-33/G.

Download Full-text