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

Journal of Earth System Science (Impact Factor: 1.04). 04/2012; 109(4):433-441. DOI: 10.1007/BF02708331
Source: OAI


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.

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Available from: Sarma Vvss, Jan 20, 2014
    • "Strength of the physical forces and their biological response vary spatially and seasonally in the Arabian Sea. Seasonal variability of this nature has been observed from ship measurements and documented by a number of scientists (Prasanna Kumar et al. 2000; Dickey et al. 1998; Wiggert et al. 2005). However, spatial as well as temporal variability in the productivity can be studied with satellite data more effectively without requiring multiple ship cruises. "
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    ABSTRACT: Northern Arabian Sea is considered as an ecologically sensitive area as it experiences a massive upwelling and long-lasting algal bloom, Noctiluca scintillans (green tide) during summer and spring-winter, respectively. Diatom bloom is also found to be co-located with N. scintillans and both have an impact on ecology of the basin. In-house technique of detecting species of these blooms from Moderate Resolution Imaging Spectroradiometer (MODIS)-Aqua data was used to generate a time-series of images revealing their spatial distribution. A study of spatial-temporal variability of these blooms using satellite data expressed a cyclic pattern of their spread over a period of 13 years. An average distribution of the blooms for January–March period revealed a peak in 2015 and minimum in 2013. Subsequently, a time-series of phytoplankton species images were generated for these 2 years to study their inter-annual variability and the associated factors. Species images during active phase of the bloom (February) in 2015 indicated development of N. scintillans and diatom in the central Arabian Sea also, up to 12° N. This observation was substantiated with relevant oceanic parameters measured from the ship as well as satellite data and the same is highlight of the paper. While oxygen depletion and release of ammonia associated with N. scintillans are detrimental for waters on the western side; it is relatively less extreme and supports the entire food chain on the eastern side. In view of these contrasting eco-sensitive events, it is a matter of concern to identify biologically active persistent areas, hot spots, in order to study their ecology in detail. An ecological index, persistence of the bloom, was derived from the time-series of species images and it is another highlight of our study.
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    • "The cold sea surface, weak wind stresses and high evaporation increases the densification of the sea surface of Arabian Sea derive convective mixing, increasing mixed layer depth and upwelling of nutrient rich water and hence increases biomassAli et al, 2005;Wiggert et al, 2000;Pattabiraman et al, 2012). The spatio-temporal plots of temperature and salinity data recorded by Argo float 29000134 which was dropped in the Gulf of Oman is shown in Figure 7Figure 8) which is in confirmation toKumar et al. (2000). The result of analysis for summer monsoon (Figure 9) exhibits the dynamics of high southwestern wind stresses. "

    Full-text · Article · Jan 2015
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    • "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). "
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    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.
    Full-text · Dataset · Feb 2014
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