scholarly journals Challenges in modelling spatiotemporally varying phytoplankton blooms in the Northwestern Arabian Sea and Gulf of Oman

2015 ◽  
Vol 12 (13) ◽  
pp. 9651-9693 ◽  
Author(s):  
S. Sedigh Marvasti ◽  
A. Gnanadesikan ◽  
A. A. Bidokhti ◽  
J. P. Dunne ◽  
S. Ghader
Keyword(s):  
Interannual Variability ◽  
Arabian Sea ◽  
Regional Scale ◽  
Height Anomaly ◽  
Phytoplankton Blooms ◽  
Gulf Of Oman ◽  
The North ◽  
Sea Surface Height Anomaly ◽  
One Year ◽  
The Persian Gulf

Abstract. We examine interannual variability of phytoplankton blooms in northwestern Arabian Sea and Gulf of Oman. Satellite data (SeaWIFS ocean color) shows two climatological blooms in this region, a wintertime bloom peaking in February and a summertime bloom peaking in September. A pronounced anti-correlation between the AVISO sea surface height anomaly (SSHA) and chlorophyll is found during the wintertime bloom. On a regional scale, interannual variability of the wintertime bloom is thus dominated by cyclonic eddies which vary in location from one year to another. These results were compared against the outputs from three different 3-D Earth System models. We show that two coarse (1°) models with the relatively complex biogeochemistry (TOPAZ) capture the annual cycle but neither eddies nor the interannual variability. An eddy-resolving model (GFDL CM2.6) with a simpler biogeochemistry (miniBLING) displays larger interannual variability, but overestimates the wintertime bloom and captures eddy-bloom coupling in the south but not in the north. The southern part of the domain is a region with a much sharper thermocline and nutricline relatively close to the surface, in which eddies modulate diffusive nutrient supply to the surface (a mechanism not previously emphasized in the literature). We suggest that for the model to simulate the observed wintertime blooms within cyclones, it will be necessary to represent this relatively unusual nutrient structure as well as the cyclonic eddies. This is a challenge in the Northern Arabian Sea as it requires capturing the details of the outflow from the Persian Gulf.

scholarly journals Challenges in modeling spatiotemporally varying phytoplankton blooms in the Northwestern Arabian Sea and Gulf of Oman

2016 ◽  
Vol 13 (4) ◽  
pp. 1049-1069 ◽  
Author(s):  
S. Sedigh Marvasti ◽  
A. Gnanadesikan ◽  
A. A. Bidokhti ◽  
J. P. Dunne ◽  
S. Ghader
Keyword(s):  
Interannual Variability ◽  
Annual Cycle ◽  
Harmful Algal Blooms ◽  
Algal Blooms ◽  
Arabian Sea ◽  
Regional Scale ◽  
Phytoplankton Productivity ◽  
Gulf Of Oman ◽  
The North ◽  
The Persian Gulf

Abstract. Recent years have shown an increase in harmful algal blooms in the Northwest Arabian Sea and Gulf of Oman, raising the question of whether climate change will accelerate this trend. This has led us to examine whether the Earth System Models used to simulate phytoplankton productivity accurately capture bloom dynamics in this region – both in terms of the annual cycle and interannual variability. Satellite data (SeaWIFS ocean color) show two climatological blooms in this region, a wintertime bloom peaking in February and a summertime bloom peaking in September. On a regional scale, interannual variability of the wintertime bloom is dominated by cyclonic eddies which vary in location from one year to another. Two coarse (1°) models with the relatively complex biogeochemistry (TOPAZ) capture the annual cycle but neither eddies nor the interannual variability. An eddy-resolving model (GFDL CM2.6) with a simpler biogeochemistry (miniBLING) displays larger interannual variability, but overestimates the wintertime bloom and captures eddy-bloom coupling in the south but not in the north. The models fail to capture both the magnitude of the wintertime bloom and its modulation by eddies in part because of their failure to capture the observed sharp thermocline and/or nutricline in this region. When CM2.6 is able to capture such features in the Southern part of the basin, eddies modulate diffusive nutrient supply to the surface (a mechanism not previously emphasized in the literature). For the model to simulate the observed wintertime blooms within cyclones, it will be necessary to represent this relatively unusual nutrient structure as well as the cyclonic eddies. This is a challenge in the Northern Arabian Sea as it requires capturing the details of the outflow from the Persian Gulf – something that is poorly done in global models.

scholarly journals Mesoscale variability of water masses in the Arabian Sea as revealed by ARGO floats

Ocean Science ◽  
2012 ◽  
Vol 8 (2) ◽  
pp. 227-248 ◽  
Author(s):  
X. Carton ◽  
P. L'Hegaret ◽  
R. Baraille
Keyword(s):  
Arabian Sea ◽  
Regional Scale ◽  
Water Masses ◽  
Gulf Of Aden ◽  
Mesoscale Variability ◽  
Energy Distributions ◽  
Sea Level Anomaly ◽  
Persian Gulf Water ◽  
The Persian Gulf ◽  
Anomalous Water

Abstract. By analysing ARGO float data over the last four years, a few aspects of the mesoscale variability of water masses in the Arabian Sea are described. The Red Sea Outflow Water (RSOW) is concentrated in the Southwestern Gulf of Aden, in particular when a cyclonic gyre predominates in this region. Salinities of 36.5 and temperatures of 16 °C are found in this area at depths between 600 and 1000 m. RSOW is more dilute in the eastern part of the Gulf, where intense and relatively barotropic gyres mix it with Indian ocean Central Water. RSOW is also detected along the northeastern coast of Socotra, and fragments of RSOW are found between one and three degrees of latitude north of this island. In the whole Gulf of Aden, the correlation between the deep motions of the floats and the sea-level anomaly measured by altimetry is strong, at regional scale. The finer scale details of the float trajectories are not sampled by altimetry and are often related to the anomalous water masses that the floats encounter. The Persian Gulf Water (PGW) is found in the float profiles near Ras ash Sharbatat (near 57° E, 18° N), again with 36.5 in salinity and about 18–19 °C in temperature. These observations were achieved in winter when the southwestward monsoon currents can advect PGW along the South Arabian coast. Fragments of PGW were also observed in the Arabian Sea between 18 and 20° N and 63 and 65° E in summer, showing that this water mass can escape the Gulf of Oman southeastward, during that season. Kinetic energy distributions of floats with respect to distance or angle share common features between the two regions (Gulf of Aden and Arabian Sea), in particular peaks at 30, 50 and 150 km scales and along the axis of monsoon currents. Hydrological measurements by floats are also influenced by the seasonal variations of PGW and RSOW in these regions.

scholarly journals NUMERICAL SIMULATION OF TROPICAL CYCLONES AND STORM SURGES IN THE ARABIAN SEA

2018 ◽  
pp. 11
Author(s):  
Mohsen Soltanpour ◽  
Zahra Ranji ◽  
Tomoyo Shibayama ◽  
Sarmad Ghader ◽  
Shinsaku Nishizaki
Keyword(s):  
Tropical Cyclones ◽  
Persian Gulf ◽  
Arabian Sea ◽  
Storm Surges ◽  
Ocean Model ◽  
Gulf Of Oman ◽  
The Persian Gulf ◽  
The Impact ◽  
Landfall Location ◽  
Good Agreement

Winds, waves and storm surges of Gonu and Ashobaa, as two recent cyclones in the Arabian Sea and Gulf of Oman, are simulated by a system of WRF-FVCOM-SWAN. The employed models are separately calibrated using the available data. Surges are found to be highly dependent on coastal geometry and landfall location, rather than the storm intensity. Comparisons at different stations reveal that the results of models are in a good agreement with measured parameters. Negative surges are also observed in the enclosed basins of the Persian Gulf and Red Sea. The calibrated atmosphere-wave-ocean model can be utilized for the prediction of extreme events, expected to increase in future due to the impact of the climate change.

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