Article

Physical control of primary productivity on a seasonal scale in central and eastern Arabian Sea

Journal of Earth System Science (Impact Factor: 0.79). 04/2012; 109(4):433-441. DOI: 10.1007/BF02708331
Source: OAI

ABSTRACT Usingin situ data collected during 1992–1997, under the Indian programme of Joint Global Ocean Flux Study (JGOFS), we show that the biological
productivity of the Arabian Sea is tightly coupled to the physical forcing mediated through nutrient availability. The Arabian
Sea becomes productive in summer not only along the coastal regions of Somalia, Arabia and southern parts of the west coast
of India due to coastal upwelling but also in the open waters of the central region. The open waters in the north are fertilized
by a combination of divergence driven by cyclonic wind stress curl to the north of the Findlater Jet and lateral advection
of nutrient-rich upwelled waters from Arabia. Productivity in the southern part of the central Arabian Sea, on the other hand,
is driven by advection from the Somalia upwelling. Surface cooling and convection resulting from reduced solar radiation and
increased evaporation make the northern region productive in winter. During both spring and fall inter-monsoons, this sea
remains warm and stratified with low production as surface waters are oligotrophic. Inter-annual variability in physical forcing
during winter resulted in one-and-a-half times higher production in 1997 than in 1995.

Download full-text

Full-text

Available from: Sarma Vvss, Jan 20, 2014
0 Followers
 · 
127 Views
  • Source
    • "All the above arguments show the fundamental role of variations in the physical environment on the spring bloom, associated with phytoplankton dynamics. The potential physical factors could be one or some of the changing events originating in the ocean, in the atmosphere and on the land: wind speed and direction (Furuya et al., 1993), air temperature (Sharples et al., 2006), precipitation and river discharge (Cloern, 1996; Greenan et al., 2004), upwelling (Kumar et al., 2000), external water intrusion (Thomas et al., 2003), meso-scale eddies (Kahru et al., 1990) and deep convection (Gacic et al., 2002; Backhaus et al., 2003). The effects of weather, through controls of the light field and wind mixing, on the spring bloom are examined in a series of modeling papers (Townsend et al., 1994; Dutkiewicz et al., 2001). "
    [Show abstract] [Hide abstract]
    ABSTRACT: The development of phytoplankton bloom and its association with physical forcing is examined through an interdisciplinary field-work conducted in the vicinity of the central trough of the southern Yellow Sea during March-April 2009, with the aid of a surface Lagrangian drifter deployed at the bloom site. Bloom patches were detected using an empirical value and two of them were traced by the drifter for a period of several days respectively. Both of them appears as thin-layer subsurface chlorophyll a maximum (SCM) throughout the tracing, although their dominant phytoplankton species are not identical at all. The magnitude as well as the onset of these two blooms is different from each other, but both found to be relevant to local oceanic and meteorological conditions. Both of them demonstrate that the changes in the stability of hydrographical structure, especially at layers around the SCM, take a substantial role in triggering or terminating the blooming processes. Those changes in meteorological conditions, like wind speed and directions, solar radiation, are short and cause daily or synoptic scale variations in phytoplankton concentrations, but the frequency of northerly wind events predating the bloom season has a positive effect on the occurrence of spring blooms. The horizontal advection is another contributing factor indicated by the drifter which accounts for the bloom extinction at the station B20. In addition, due to the weak orbital horizontal movement, the bloom above the central trough persists longer and larger.
  • Source
    • "In boreal winter the land-sea pressure gradient is reverse and moderate, dry and cold northeastern winds flow from the Indian-Tibetan high-pressure zone toward the southward shifted ITCZ, which is located at about 10°S. Northeasterly winds induce convective mixing along the coast, generating a second, smaller productivity maximum in the northeastern Arabian Sea [Reichart et al., 1998; Kumar et al., 2000]. The winter monsoon is characterized by overall drier conditions and lower dust input into the Arabian Sea [Sirocko and Lange, 1991; Clemens, 1998; Prins and Weltje, 1999]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Dansgaard-Oeschger oscillations and Heinrich events described in North Atlantic sediments and Greenland ice are expressed in the climate of the tropics, for example, as documented in Arabian Sea sediments. Given the strength of this teleconnection, we seek to reconstruct its range of environmental impacts. We present geochemical and sedimentological data from core SO130-289KL from the Indus submarine slope spanning the last ~ 80 kyr. Elemental and grain size analyses consistently indicate that interstadials are characterized by an increased contribution of fluvial suspension from the Indus River. In contrast, stadials are characterized by an increased contribution of aeolian dust from the Arabian Peninsula. Decadal-scale shifts at climate transitions, such as onsets of interstadials, were coeval with changes in productivity-related proxies. Heinrich events stand out as especially dry and dusty events, indicating a dramatically weakened Indian summer monsoon, potentially increased winter monsoon circulation, and increased aridity on the Arabian Peninsula. This finding is consistent with other paleoclimate evidence for continental aridity in the northern tropics during these events. Our results strengthen the evidence that circum-North Atlantic temperature variations translate to hydrological shifts in the tropics, with major impacts on regional environmental conditions such as rainfall, river discharge, aeolian dust transport, and ocean margin anoxia.
    Paleoceanography 02/2014; 29(2):99-114. DOI:10.1002/2013PA002509 · 3.92 Impact Factor
  • Source
    • "All the above arguments show the fundamental role of variations in the physical environment on the spring bloom, associated with phytoplankton dynamics. The potential physical factors could be one or some of the changing events originating in the ocean, in the atmosphere and on the land: wind speed and direction (Furuya et al., 1993), air temperature (Sharples et al., 2006), precipitation and river discharge (Cloern, 1996; Greenan et al., 2004), upwelling (Kumar et al., 2000), external water intrusion (Thomas et al., 2003), meso-scale eddies (Kahru et al., 1990) and deep convection (Gacic et al., 2002; Backhaus et al., 2003). The effects of weather, through controls of the light field and wind mixing, on the spring bloom are examined in a series of modeling papers (Townsend et al., 1994; Dutkiewicz et al., 2001). "
    [Show abstract] [Hide abstract]
    ABSTRACT: The development of phytoplankton bloom and its association with physical forcing is examined through an interdisciplinary field-work conducted in the vicinity of the central trough of the southern Yellow Sea during March-April 2009, with the aid of a surface Lagrangian drifter deployed at the bloom site. Bloom patches were detected using an empirical value and two of them were traced by the drifter for a period of several days respectively. Both of them appears as thin-layer subsurface chlorophyll a maximum (SCM) throughout the tracing, though their dominant phytoplankton species are not identical at all. The magnitude as well as the onset of these two blooms is different from each other, but both found to be relevant to local oceanic and meteorological conditions. Both of them demonstrate that the changes in the stability of hydrographical structure, especially at layers around the SCM, take a substantial role in triggering or terminating the blooming processes. Those changes in meteorological conditions, like wind speed and directions, solar radiation, are short and cause daily or synoptic scale variations in phytoplankton concentrations, but the frequency of northerly wind events predating the bloom season has a positive effect on the occurrence of spring blooms. The horizontal advection is another contributing factor indicated by the drifter which accounts for the bloom extinction at the station B20. In addition, due to the weak orbital horizontal movement, the bloom above the central tough persists longer and larger. %\ 2013-06-06 11:45:00
    Deep Sea Research Part II Topical Studies in Oceanography 12/2013; 97. DOI:10.1016/j.dsr2.2013.05.001 · 2.76 Impact Factor
Show more