On the Possible Mechanisms for Saltening of the Bay of Bengal

The Bay of Bengal (BoB) is a low saline basin owing to large influx of freshwater from precipitation and river runoff. To maintain the salt balance of the BoB, the incessant lowering of salinity is to be balanced by the inflow of saltier water into the basin. In the present work, various processes that contribute to the saltening of the BoB, viz. coastal upwelling, eddies and their interaction, lateral advection from Arabian Sea and tropical cyclones are discussed. In the near-shore regions, the coastal upwelling due to wind induced Ekman transport plays a dominant role in increasing the surface salinity. On the other hand, in the open ocean, the divergence induced by eddies and their mutual interaction contributes significantly to the salt water pumping. In the southern BoB, the advection from the Arabian Sea increases the salinity. The formation of cyclones in the BoB also leads to an increase in the surface salinity. However, the magnitude of saltening of the Bay due to these processes varies from north to south. The uplift of saltier water from subsurface levels increases the salinity in the surface layers thereby creating a salinity gradient and a salinity front.

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Modelling an alkenone-like proxy record in the NW African upwelling

Biogeosciences ◽

10.5194/bg-3-251-2006 ◽

2006 ◽

Vol 3 (3) ◽

pp. 251-269 ◽

Cited By ~ 5

Author(s):

X. Giraud

Keyword(s):

Ocean Circulation ◽

Coastal Upwelling ◽

Biogeochemical Model ◽

Physiological Factors ◽

Adaptive Grid Refinement ◽

Near Shore ◽

Temperature Records ◽

Temperature Proxy ◽

Set Up ◽

Lateral Advection

Abstract. A regional biogeochemical model is applied to the NW African coastal upwelling between 19° N and 27° N to investigate how a water temperature proxy, alkenones, are produced at the sea surface and recorded in the slope sediments. The biogeochemical model has two phytoplankton groups: an alkenone producer group, considered to be coccolithophores, and a group comprising other phytoplankton. The Regional Ocean Modelling System (ROMS) is used to simulate the ocean circulation and takes advantage of the Adaptive Grid Refinement in Fortran (AGRIF) package to set up an embedded griding system. In the simulations the alkenone temperature records in the sediments are between 1.1 and 2.3°C colder than the annual mean SSTs. Despite the seasonality of the coccolithophore production, this temperature difference is not mainly due to a seasonal bias, nor to the lateral advection of phytoplankton and phytodetritus seaward from the cold near-shore waters, but to the production depth of the coccolithophores. If coretop alkenone temperatures are effectively recording the annual mean SSTs, the amount of alkenone produced must vary among the coccolithophores in the water column and depend on physiological factors (e.g. growth rate, nutrient stress).

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Frontal variability and its impact on chlorophyll in the Arabian Sea

10.5194/egusphere-egu2020-9188 ◽

2020 ◽

Author(s):

Yuntao Wang ◽

Wentao Ma ◽

Feng Zhou ◽

Chai Fei

Keyword(s):

Arabian Sea ◽

Coastal Upwelling ◽

Cold Water ◽

Southwest Monsoon ◽

Ocean Dynamics ◽

Ekman Transport ◽

Spatial And Temporal Variability ◽

Anomalous Field ◽

The North ◽

The Impact

<p>Sixteen years satellite observations are used to investigate the frontogenesis, frontal variability and its impact on chlorophyll in the Arabian Sea. Large frontal probability (FP) and high chlorophyll mainly happens near the coast, e.g., near Somalia and Oman, and its value generally decreases with offshore distance. An Empirical Orthogonal Function (EOF) is used to disentangle the spatial and temporal variability of front and chlorophyll. Prominent seasonal cycle of frontal activities is identified, peaking in summer when southwest wind prevails. The seasonality for chlorophyll is same with wind and front near Somalia, which largely impacted by monsoon. During summer, the southwest monsoon drives offshore Ekman transport and induces coastal upwelling. It transports subsurface cold water and nutrients to the surface layer, which generates fronts and enhances chlorophyll, respectively. The frontal activities can be used as an indicator to determine the chlorophyll level that high chlorophyll happens when frontal probability gets higher than 2%. At anomalous field, stronger wind can induce higher frontal activities and chlorophyll. The impact of wind on frontogenesis can extend 1,000km offshore and a simplified linear regression is applied to quantify their relationship. The variability of wind leads chlorophyll by lags increasing with distance, indicating a horizontal offshore transport of coastal water. In winter, the northeast wind is not upwelling favorable, thus the frontal activities and chlorophyll are greatly reduced off Somalia. During this period, large chlorophyll is found in the north off Oman because of mixing, thus its relationship with front is less pronounced. In the upwelling regions, fronts act as an intermedia process that connecting the wind forcing and responses of ecosystem. The frontal activities in Arabian Sea is fundamentally important to improve our understanding of monsoon related ocean dynamics.</p>

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Past 100 ky surface salinity-gradient response in the Eastern Arabian Sea to the summer monsoon variation recorded by δ18O of G. sacculifer

Global and Planetary Change ◽

10.1016/j.gloplacha.2004.10.008 ◽

2005 ◽

Vol 47 (2-4) ◽

pp. 135-142 ◽

Cited By ~ 18

Author(s):

Anjali R. Chodankar ◽

Virupaxa K. Banakar ◽

Tadamichi Oba

Keyword(s):

Summer Monsoon ◽

Arabian Sea ◽

Salinity Gradient ◽

Surface Salinity ◽

Eastern Arabian Sea

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Statistical Assessment of Sea-Surface Salinity from SMAP: Arabian Sea, Bay of Bengal and a Promising Red Sea Application

Remote Sensing ◽

10.3390/rs12030447 ◽

2020 ◽

Vol 12 (3) ◽

pp. 447 ◽

Cited By ~ 3

Author(s):

Viviane V. Menezes

Keyword(s):

Red Sea ◽

Ocean Circulation ◽

Bay Of Bengal ◽

Arabian Sea ◽

Hydrological Cycle ◽

North Indian Ocean ◽

Sea Surface ◽

Sea Surface Salinity ◽

Surface Salinity ◽

The North

Sea-surface salinity (SSS) is an essential climate variable connected to Earth’s hydrological cycle and a dynamical component of ocean circulation, but its variability is not well-understood. Thanks to Argo floats, and the first decade of salinity remote sensing, this is changing. While satellites can retrieve salinity with some confidence, accuracy is regionally dependent and challenging within 500–1000 km offshore. The present work assesses the first four years of the National Aeronautics and Space Administration’s Soil Moisture Active Passive (SMAP) satellite in the North Indian Ocean. SMAP’s improved spatial resolution, better mitigation for radio-frequency interference, and land contamination make it particularly attractive to study coastal areas. Here, regions of interest are the Bay of Bengal, the Arabian Sea, and the extremely salty Red Sea (the last of which has not yet received attention). Six SMAP products, which include Levels 2 and 3 data, were statistically evaluated against in situ measurements collected by a variety of instruments. SMAP reproduced SSS well in both the Arabian Sea and the Bay of Bengal, and surprisingly well in the Red Sea. Correlations there were 0.81–0.93, and the root-mean-square difference was 0.38–0.67 for Level 3 data.

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Cyclogenesis in the Bay of Bengal and the Arabian Sea

Tellus ◽

10.3402/tellusa.v22i6.10279 ◽

1970 ◽

Vol 22 (6) ◽

pp. 716-718

Author(s):

K. G. Mowla

Keyword(s):

Bay Of Bengal ◽

Arabian Sea

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Differences in Northward Propagation of Convection Over the Arabian Sea and Bay of Bengal During Boreal Summer

Journal of Geophysical Research Atmospheres ◽

10.1029/2019jd031648 ◽

2020 ◽

Vol 125 (3) ◽

Author(s):

Nirupam Karmakar ◽

Vasubandhu Misra

Keyword(s):

Bay Of Bengal ◽

Arabian Sea ◽

Boreal Summer ◽

Northward Propagation

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

Journal of Climate ◽

10.1175/jcli4150.1 ◽

2007 ◽

Vol 20 (13) ◽

pp. 2978-2993 ◽

Cited By ~ 22

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.

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Diagnosis of 3D Vertical Circulation in the Upwelling and Frontal Zones East of Hainan Island, China

Journal of Physical Oceanography ◽

10.1175/jpo-d-16-0192.1 ◽

2017 ◽

Vol 47 (4) ◽

pp. 755-774 ◽

Cited By ~ 7

Author(s):

Lingling Xie ◽

Enric Pallàs-Sanz ◽

Quanan Zheng ◽

Shuwen Zhang ◽

Xiaolong Zong ◽

...

Keyword(s):

Coastal Upwelling ◽

Frontal Zone ◽

Dominant Role ◽

Subsurface Layer ◽

Vertical Mixing ◽

Hainan Island ◽

Eddy Diffusivity ◽

Vertical Circulation ◽

Forcing Term ◽

Advection Term

AbstractUsing the generalized omega equation and cruise observations in July 2012, this study analyzes the 3D vertical circulation in the upwelling region and frontal zone east of Hainan Island, China. The results show that there is a strong frontal zone in subsurface layer along the 100-m isobath, which is characterized by density gradient of O(10−4) kg m−4 and vertical eddy diffusivity of O(10−5–10−4) m2 s−1. The kinematic deformation term SDEF, ageostrophic advection term SADV, and vertical mixing forcing term SMIX are calculated from the observations. Their distribution patterns are featured by banded structure, that is, alternating positive–negative alongshore bands distributed in the cross-shelf direction. Correspondingly, alternating upwelling and downwelling bands appear from the coast to the deep waters. The maximum downward velocity reaches −5 × 10−5 m s−1 within the frontal zone, accompanied by the maximum upward velocity of 7 × 10−5 m s−1 on two sides. The dynamic diagnosis indicates that SADV contributes most to the coastal upwelling, while term SDEF, which is dominated by the ageostrophic component SDEFa, plays a dominant role in the frontal zone. The vertical mixing forcing term SMIX, which includes the momentum and buoyancy flux terms SMOM and SBUO, is comparable to SDEF and SADV in the upper ocean, but negligible below the thermocline. The effect of the vertical mixing on the vertical velocity is mainly concentrated at depths with relatively large eddy diffusivity and eddy diffusivity gradient in the frontal zone.

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