Consequences of inhibition of mixed-layer deepening by the West India Coastal Current for winter phytoplankton bloom in the northeastern Arabian Sea

Abstract We review bio-optical and physical data from three mooring experiments, the Marine Light–Mixed Layers programme in spring 1989 and 1991 in the Iceland Basin (59°N/21°W), and the Forced Upper Ocean Dynamics Experiment in the central Arabian Sea from October 1994 to 1995 (15.5°N/61.5°E). In the Iceland Basin, from mid-April to mid-June in 1989, chlorophyll-a concentrations are sensitive to small changes in stratification, with intermittent increases early in the record. The spring increase occurs after 20 May, coincident with persistent water column stratification. In 1991, the bloom occurs 2 weeks earlier than in 1989, with a background of strong short-term and diurnal variability in mixed layer depth and minimal horizontal advection. In the Arabian Sea, the mixing response to the northeast and southwest monsoons, plus the response to mesoscale eddies, produces four blooms over the annual cycle. The mixed layer depth in the Arabian Sea never exceeds the euphotic zone, allowing interactions between phytoplankton and grazer populations to become important. For all three mooring experiments, change in water column stratification is key in producing phytoplankton blooms.

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Origins of Coupled Model Biases in the Arabian Sea Climatological State

Journal of Climate ◽

10.1175/jcli-d-17-0417.1 ◽

2018 ◽

Vol 31 (5) ◽

pp. 2005-2029 ◽

Cited By ~ 4

Author(s):

Motoki Nagura ◽

J. P. McCreary ◽

H. Annamalai

Keyword(s):

Mixed Layer ◽

Persian Gulf ◽

Arabian Sea ◽

Coupled Model ◽

Sea Surface Salinity ◽

Western Boundary ◽

Coastal Current ◽

Surface Cooling ◽

Surface Salinity ◽

High Salinity Water

This study investigates biases of the climatological mean state of the northern Arabian Sea (NAS) in 31 coupled ocean–atmosphere models. The focus is to understand the cause of the large biases in the depth of the 20°C isotherm [Formula: see text] that occur in many of them. Other prominent biases are the depth [Formula: see text] and temperature [Formula: see text] of Persian Gulf water (PGW) and the wintertime mixed-layer thickness (MLT) along the northern boundary. For models that lack a Persian Gulf (group 1), [Formula: see text] is determined by the wintertime MLT bias [Formula: see text] through the formation of an Arabian Sea high-salinity water mass (ASHSW) that is too deep. For models with a Persian Gulf (group 2), if [Formula: see text] > MLT (group 2B), PGW remains mostly trapped to the western boundary and, again, [Formula: see text] directly controls [Formula: see text]. If [Formula: see text] MLT (group 2A), PGW spreads into the NAS and impacts [Formula: see text] because [Formula: see text] > 20°C; nevertheless [Formula: see text] still influences [Formula: see text] indirectly through its impact on [Formula: see text]. The thick wintertime mixed layer is driven primarily by surface cooling [Formula: see text] during the fall. Nevertheless, variations in ΔMLT among the models are more strongly linked to biases in the density stratification (jump) across the bottom of the mixed layer than to [Formula: see text] biases. The jump is in turn determined primarily by sea surface salinity biases (ΔSSS) advected into the NAS by the West India Coastal Current, and the source of ΔSSS is the rainfall deficit associated with the models’ weak summer monsoon. Ultimately, then, ΔD20 is linked to this deficit.

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Physicochemical controls on the initiation of phytoplankton bloom during the winter monsoon in the Arabian Sea

Scientific Reports ◽

10.1038/s41598-021-92897-3 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

R. S. Lakshmi ◽

Satya Prakash ◽

Aneesh A. Lotliker ◽

Sanjiba K. Baliarsingh ◽

Alakes Samanta ◽

...

Keyword(s):

Mixed Layer ◽

Arabian Sea ◽

Phytoplankton Bloom ◽

Inorganic Nitrogen ◽

Euphotic Zone ◽

Winter Monsoon ◽

Stoichiometric Ratio ◽

Stressed Condition ◽

Critical Depth ◽

Northern Arabian Sea

AbstractOccurrence of phytoplankton bloom in the northern Arabian Sea (NAS) during the winter monsoon is perplexing. The convective mixing leads to a deeper and well-oxygenated (> 95% saturation) mixed layer. We encountered low chlorophyll conditions though the nutrient conditions were favorable for a bloom. The mean ratio of silicate (Si) to DIN (Dissolved Inorganic Nitrogen: nitrate + nitrite + ammonium) in the euphotic zone was 0.52 indicating a “silicate-stressed” condition for the proliferation of diatoms. Also, the euphotic depth was much shallower (~ 49 m) than the mixed layer (~ 110 m) suggesting the Sverdrup critical depth limitation in the NAS. We show that the bloom in this region initiates only when the mixed layer shoals towards the euphotic zone. Our observations further suggest that two primary factors, the stoichiometric ratio of nutrients, especially the Si/DIN ratio, in the mixed layer and re-stratification of the upper water column, govern the phytoplankton blooming in NAS during the later winter monsoon. The important finding of the present study is that the Sverdrup’s critical depth limitation gives rise to the observed low chl-a concentration in the NAS, despite having enough nutrients.

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TEMPERATURE VARIABILITY AT SENUNU BAY, WEST SUMBAWA

Jurnal Ilmu dan Teknologi Kelautan Tropis ◽

10.29244/jitkt.v5i2.7555 ◽

2013 ◽

Vol 5 (2) ◽

Author(s):

Syamsul Hidayat ◽

Mulia Purba ◽

Jorina Waworuntu

Keyword(s):

Layer Thickness ◽

Mixed Layer ◽

Cross Correlation ◽

Sea Surface ◽

Thermocline Depth ◽

Kelvin Wave ◽

The West ◽

Sea Bottom ◽

Annual Period ◽

Regional Processes

The purposes of this study were to determine the variability of temperature and its relation to regional processes in the Senunu Bay. The result showed clear vertical stratifications i.e., mixed layer thickness about 39-119 m with isotherm of 27°C, thermocline layer thickness about 83-204 m with isotherm of 14–26°C, and the deeper layer from the thermocline lower limit to the sea bottom with isotherm <13°C. Temperature and the thickness of each layers varied with season in which during the Northwest Monsoon the temperature was warmer and the mixed layer was thicker than those during Southeast Monsoon. During Southeast Monsoon, the thermocline layer rose about 24 m. The 2001, 2006, and 2009 (weak La Nina years), the Indonesia Throughflow (ITF) carried warmer water, deepening thermocline depth and reducing upwelling strength. In 2003 and 2008 thickening of mixed layer occurred in transition season was believed associated with the arrival of Kelvin Wave from the west. In 2002 and 2004 (weak El Nino period,) ITF carries colder water shallowing thermocline depth and enhancing upwelling strength. In 2007 was believed to be related with positive IODM where the sea surface temperature were decreasing due to intensification of southeast wind which induced strong upwelling. The temperature spectral density of mixed layer and thermocline was influenced by annual, semi-annual, intra-annual and inter-annual period fluctuations. The cross-correlation between wind and temperature showed significant value in the annual period. Keywords: temperature, thermocline, variability, ENSO, IODM.

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Observed variability of the West India Coastal Current on the continental shelf from 2010–2017

Journal of Earth System Science ◽

10.1007/s12040-021-01603-4 ◽

2021 ◽

Vol 130 (2) ◽

Author(s):

Anya Chaudhuri ◽

P Amol ◽

D Shankar ◽

S Mukhopadhyay ◽

S G Aparna ◽

...

Keyword(s):

Continental Shelf ◽

Coastal Current ◽

The West

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The phytoplankton bloom in the northwestern Arabian Sea during the southwest monsoon of 1979

Journal of Geophysical Research Atmospheres ◽

10.1029/91jc01711 ◽

1991 ◽

Vol 96 (C11) ◽

pp. 20623 ◽

Cited By ~ 112

Author(s):

John C. Brock ◽

Charles R. McClain ◽

Mark E. Luther ◽

William W. Hay

Keyword(s):

Arabian Sea ◽

Phytoplankton Bloom ◽

Southwest Monsoon

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Prehistoric Man Round Bombay

Proceedings of the Prehistoric Society of East Anglia ◽

10.1017/s0958841800026351 ◽

1932 ◽

Vol 7 (1) ◽

pp. 35-42 ◽

Cited By ~ 2

Author(s):

K. R. U. Todd

Keyword(s):

Arabian Sea ◽

Maximum Height ◽

The West ◽

Fishing Village ◽

Red Earth ◽

The Hill ◽

Steep Hill

The purpose of this paper is to put on record the discovery of various sites, containing traces of prehistoric man, in the neighbourhood of Bombay.The area of greatest importance is that of Worli. It is a cotton milling suburb of Bombay, distant some 4 miles from the Fort, and is situated on low lying marshy ground and bounded to the West by a low steep hill having a maximum height of 100 ft. O.D., and consisting of igneous basalt overlying amygdaloidal trap with a dyke of F.W. strata between. This dyke contains fossils of marsh tortoises, frogs and plants resembling bulrushes. The basalt is capped with red earth which is decomposing trap, and contains nodules of agate and blocks of chert. West of the hill is the Arabian Sea. The northern extremity of this hill ends in a spur which juts out into the sea, and here is the fishing village of Koliwada, consisting of mud huts.

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Seasonal variations of the dinoflagellate algae Noctiluca scintillans abundance in the western Arabian Sea and the northern Black Sea

10.5194/egusphere-egu21-1479 ◽

2021 ◽

Author(s):

Sergey Piontkovski ◽

Khalid Al Hashmi ◽

Yuliya Zagorodnaya ◽

Irina Serikova ◽

Vladislav Evstigneev ◽

...

Keyword(s):

Black Sea ◽

Mixed Layer ◽

Algal Blooms ◽

Arabian Sea ◽

Temporal Dynamics ◽

The Black Sea ◽

Northeast Monsoon ◽

Major Peak ◽

Noctiluca Scintillans ◽

Upper Mixed Layer

Seasonal variability is a powerful component of the spatio-temporal dynamics of plankton communities, especially in the regions with oxygen-depleted waters. The Arabian Sea and the Black Sea are typical representatives of these regions. In both, the dinoflagellate Noctiluca scintillans (Macartney) Kofoid & Swezy, 1921, is one of the abundant plankton species which forms algal blooms. Sampling on coastal stations in the upper mixed layer by the plankton nets with the 120-140 &#181;m mesh size was carried out in 2004-2010. Monthly data were averaged over years. A comparison of seasonal patterns of Noctiluca abundance pointed to the persistence of a bimodal seasonal cycle in both regions. The major peak was observed during spring in the Black Sea and during the winter (Northeast) monsoon in the Arabian Sea. The timing of the second (minor) peak was different over regions as well. This peak was modulated by advection of seasonally fluctuating velocity of coastal currents which transport waters enriched by nutrients by coastal upwelling. The abundance of Noctiluca of the major peak (with the concentration around 1.5*106 cells m-3) was from one to two orders as much high in the western Arabian Sea compared to the northern Black Sea. The remotely sensed chlorophyll-a concentration during the time of the major seasonal peak exhibited a fivefold difference over these regions. In terms of nutrientconcentration in the upper mixed layer (in particular, nitrates and silicates), a difference of about one order of magnitude was observed.

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