NOPR Collection:

Evolution mechanism of contrasting phases of consecutive IOD events from 1994 to 1998

Thu, 01 Jul 2021 00:00:00 GMT

Title: Evolution mechanism of contrasting phases of consecutive IOD events from 1994 to 1998 Authors: Anil, N; M R, Ramesh Kumar; Sajeev, R; Saji, P K Abstract: The Dipole Mode Index (DMI), an Index used to represent the Indian Ocean Dipole (IOD), shows a back to back occurrence of positive and negative IOD events during the period 1994 to 1998. The year 1994 was a strong positive IOD year and was followed by a strong negative IOD in 1996. The positive IOD in 1997 and negative IOD in 1998 were co-occurred with the strong El-Nino and strong La-Nina, respectively. In the present study, we have looked into the evolution of consecutive IOD events during the period 1994 to 1998 and analyzed the differences in their formation, features and association with Indian Summer Monsoon Rainfall (ISMR) for various homogenous regions of the Indian subcontinent. We have found that the El-Nino and La-Nina enhances the IOD-induced positive SST anomalies in the western and eastern parts of the Indian Ocean during the co-occurred years, respectively. The evolution of positive IOD in 1997 is driven by the strong easterly wind anomalies associated with strong El-Nino. The positive anomalies of SST in the western equatorial Indian Ocean is maintained by the El-Nino which results in the long life span of positive IOD in the year 1997 than that of pure positive IOD year 1994. The westward propagating Rossby wave generated due to PIOD is maintained by strong El-Nino in the year 1997. The vertical dynamics, represented by D20, showed minor differences during the pure and co-occurred IOD events. The positive IOD years with El-Nino had good correlation with the Peninsular India and Central North East India regions rainfall. Since we have used only limited samples or cases under the different categories, our present results are preliminary in nature. Page(s): 521-532

A preliminary study on the environmental factors triggering frequent bloom of diatom Asterionellopsis glacialis (Castracane) Round 1990 along west coast of Bay of Bengal

Thu, 01 Jul 2021 00:00:00 GMT

Title: A preliminary study on the environmental factors triggering frequent bloom of diatom Asterionellopsis glacialis (Castracane) Round 1990 along west coast of Bay of Bengal Authors: Padhi, S K; Patro, S; Sahu, B K; Baliarsingh, S K; Sahu, K C Abstract: A time-series observation of Asterionellopsis glacialis (Castracane) Round 1990 bloom in the surf zone of east coast of India and associated physico-chemical parameters, was carried out during pre-monsoon period (May 2018). This study also reviews the species status as a surf-zone diatom and its temporal characteristics. Referring to the earlier study, the temporal characteristic of A. glacialis bloom in Indian context can be classified as ―sporadic‖ due to the alteration of blooming community and may be also further investigated for its seasonality as the bloom mostly observed during the pre-monsoon season. Among the nutrients, silicate is identified as a major factor controlling the bloom of A. glacialis. The present study highlights the introduction of biogenic silica attributed to precipitation induced land runoff and the effect of wind as important environmental factors responsible for A. glacialis proliferation in nearshore waters of east coast of India. Page(s): 533-541

Variabilities in the community structure of phytoplankton in the upwelled and non-upwelled waters of southeastern Arabian Sea during the early summer monsoon

Thu, 01 Jul 2021 00:00:00 GMT

Title: Variabilities in the community structure of phytoplankton in the upwelled and non-upwelled waters of southeastern Arabian Sea during the early summer monsoon Authors: Twinkle, S; Thomas, L C; Padmakumar, K B Abstract: The community structure of microphytoplankton was assessed along the southeastern Arabian Sea during the early phase of the summer monsoon. The study records an intense coastal upwelling along the southernmost region (off Thiruvananthapuram), which decreased further north. High chlorophyll-a (10.8 mg m^-3) and nutrient concentration was recorded in the coastal waters of Thiruvananthapuram. Even though off Mangalore (12° N) and off Goa (15° N) where upwelling was confined to narrow coastal zone, also showed high chlorophyll-a concentration, 3.98 mg m-3 and 6.31 mg m^-3, respectively. The upwelled waters were dominated by centric diatoms (Thalassiosira sp.) and the non-upwelled waters (12° N and 15° N) were dominated by dinoflagellates. Microphytoplankton cell density was the highest along off Thiruvananthapuram (4.8×10⁴ cells L^-1), with maximum cell density along the coastal waters (1.4×10⁴ cells L^-1). Phytoplankton community of upwelled and non-upwelled waters showed significant variations with 60 % similarity between phytoplankton communities of upwelled waters. Page(s): 542-549

Acute toxicity of two organophosphorus pesticides to the early-life stage of flathead grey mullet, Mugil cephalus (Linnaeus, 1758)

Thu, 01 Jul 2021 00:00:00 GMT

Title: Acute toxicity of two organophosphorus pesticides to the early-life stage of flathead grey mullet, Mugil cephalus (Linnaeus, 1758) Authors: Dake, A S; Pawar, A P; Sanaye, S V; Sreepada, R A Abstract: The acute toxicity (96 h LC₅₀) of two organophosphorus pesticides (OPs), chlorpyrifos (CPF) and dimethoate (DMT) to the early-life stage (fry) of flathead grey mullet, Mugil cephalus (total length, 22±2 mm, wet weight, 285±4 mg) was evaluated. M. cephalus were exposed to concentrations of CPF (2, 4, 6, 8, and 10 μg/L) and DMT (300, 750, 1500, 3000 and 4500 μg/L) for 96 h. Values of 96 h LC₅₀ indicated that CPF (3.45 μg/L; 95 % confidence limits, lower = 2.77 and upper = 4.06 μg/L) was found to be highly toxic to M. cephalus fry compared to DMT (854.10 μg/L; 95 % confidence limits, lower = 558.23 and upper = 1176.77 μg/L). Data obtained during the present study would be helpful in monitoring OP pollution in coastal waters with M. cephalus as key bioindicator species. Page(s): 550-556