Hydrographic characterization of southeast Arabian Sea during the wane of southwest monsoon and spring intermonsoon

Abstract

Seasonal variation of the hydrography along the southeast Arabian Sea is described using data collected onboard FORV Sagar Sampada in September--October 2003 (later phase of Southwest monsoon, SWM) and March--April 2004 (Spring inter monsoon, SIM). During the later phase of the SWM, upwelling was in the withdrawal phase and the frontal structure was clearer in the northern sections (13 and 15 degrees N lat) indicating strong upwelling in the area. The driving force of upwelling is identified as the combination of alongshore wind stress and remote forcing with a latitudinal variability. Although a more prominent upwelling was found in the north, a maximum surface Chlorophyll-a was found in the south (10 degrees N). During the SIM, the area was characterized by oligotrophic water with relatively high Sea Surface Temperature (>29 degrees C) and low salinity (33.8 to 35.4). During March, the surface hydrography was found to be controlled mainly by the intrusion of low-saline waters from the south, while during September by the high saline water from the north. The presence of various water masses [Arabian Sea High Salinity Water (ASHSW), Persian Gulf Water (PGW), Red Sea Water (RSW)] and their seasonal variations in the region is discussed and their decreasing influence towards the south is noted during both periods of observation. During the SWM, the dynamic topography showed the equator-ward flow of the West India Coastal Current (WICC) at the surface and a pole-ward coastal under current at sub-thermocline depth. During the SIM, surface circulation revealed the WICC flowing pole-ward north of 13 degrees N, but equator-ward flow in the south, with a clockwise circulation around the Lakshadweep High.

Picophytoplankton Distribution and Their Contribution to Particulate Organic Carbon in the Northern Indian Ocean

“…The intermonsoon period, which occurs between the southwest (summer) and northeast (winter) monsoons, represents a critical transitional phase characterized by a weakening of monsoonal forcing. This period is associated with changes in upper ocean stratification, nutrient dynamics, and circulation patterns, which collectively influence biological processes such as phytoplankton community succession and trophic interactions (Lévy et al, 2007;Smith et al, 1998;Vimal Kumar et al, 2008). However, our understanding of picophytoplankton ecology during the fall intermonsoon remains limited.…”

Picophytoplankton Distribution and Their Contribution to Particulate Organic Carbon in the Northern Indian Ocean

“…The intermonsoon period, which occurs between the southwest (summer) and northeast (winter) monsoons, represents a critical transitional phase characterized by a weakening of monsoonal forcing. This period is associated with changes in upper ocean stratification, nutrient dynamics, and circulation patterns, which collectively influence biological processes such as phytoplankton community succession and trophic interactions (Lévy et al, 2007;Smith et al, 1998;Vimal Kumar et al, 2008). However, our understanding of picophytoplankton ecology during the fall intermonsoon remains limited.…”

Characterizing the circulation off the Kenyan‐Tanzanian coast using an ocean model

“…A better understanding of the ocean circulation at temporal and spatial resolutions appropriate to these environmental issues will be valuable. However, this part of the East African coastal ocean has been grossly undersampled in comparison to neighboring areas such as the Somali coast and the Arabian Gulf [e.g., Vimal Kumar et al ., ; Smith et al ., ], the Red Sea [e.g., Roman and Lutjeharms , ], and the Mozambique Channel [e.g., van der Werf et al ., ; Ridderinkhof et al ., ; da Silva et al ., ; Nauw et al ., ; Matano et al ., ]. Historically, the undersampling is due to economical constraints of the local countries and the remoteness of the region, far from major oceanographic research institutes.…”

Picophytoplankton Distribution and Their Contribution to Particulate Organic Carbon in the Northern Indian Ocean

“…The intermonsoon period, which occurs between the southwest (summer) and northeast (winter) monsoons, represents a critical transitional phase characterized by a weakening of monsoonal forcing. This period is associated with changes in upper ocean stratification, nutrient dynamics, and circulation patterns, which collectively influence biological processes such as phytoplankton community succession and trophic interactions (Lévy et al, 2007;Smith et al, 1998;Vimal Kumar et al, 2008). However, our understanding of picophytoplankton ecology during the fall intermonsoon remains limited.…”

Characterizing the circulation off the Kenyan‐Tanzanian coast using an ocean model

“…A better understanding of the ocean circulation at temporal and spatial resolutions appropriate to these environmental issues will be valuable. However, this part of the East African coastal ocean has been grossly undersampled in comparison to neighboring areas such as the Somali coast and the Arabian Gulf [e.g., Vimal Kumar et al ., ; Smith et al ., ], the Red Sea [e.g., Roman and Lutjeharms , ], and the Mozambique Channel [e.g., van der Werf et al ., ; Ridderinkhof et al ., ; da Silva et al ., ; Nauw et al ., ; Matano et al ., ]. Historically, the undersampling is due to economical constraints of the local countries and the remoteness of the region, far from major oceanographic research institutes.…”

Picophytoplankton Distribution and Their Contribution to Particulate Organic Carbon in the Northern Indian Ocean

“…The intermonsoon period, which occurs between the southwest (summer) and northeast (winter) monsoons, represents a critical transitional phase characterized by a weakening of monsoonal forcing. This period is associated with changes in upper ocean stratification, nutrient dynamics, and circulation patterns, which collectively influence biological processes such as phytoplankton community succession and trophic interactions (Lévy et al, 2007;Smith et al, 1998;Vimal Kumar et al, 2008). However, our understanding of picophytoplankton ecology during the fall intermonsoon remains limited.…”

Characterizing the circulation off the Kenyan‐Tanzanian coast using an ocean model

“…A better understanding of the ocean circulation at temporal and spatial resolutions appropriate to these environmental issues will be valuable. However, this part of the East African coastal ocean has been grossly undersampled in comparison to neighboring areas such as the Somali coast and the Arabian Gulf [e.g., Vimal Kumar et al ., ; Smith et al ., ], the Red Sea [e.g., Roman and Lutjeharms , ], and the Mozambique Channel [e.g., van der Werf et al ., ; Ridderinkhof et al ., ; da Silva et al ., ; Nauw et al ., ; Matano et al ., ]. Historically, the undersampling is due to economical constraints of the local countries and the remoteness of the region, far from major oceanographic research institutes.…”