Regional Studies in Marine Science 10 (2017) 116–134 Contents lists available at ScienceDirect Regional Studies in Marine Science journal homepage: www.elsevier.com/locate/rsma Nutrient dynamics of northern Bay of Bengal (nBoB)—Emphasizing the role of tides Sourav Das a,∗ , Sandip Giri a , Isha Das a , Abhra Chanda a , Amit Ghosh a , Anirban Mukhopadhyay a , Anirban Akhand b , S.B. Choudhury c , V.K. Dadhwal d , Sourav Maity e , T. Srinivasa Kumar e , Aneesh A. Lotliker e , D. Mitra f , Sugata Hazra a a School of Oceanographic Studies, Jadavpur University, Jadavpur, 188, Raja S. C. Mullick Road, Kolkata - 700032, West Bengal, India b Coastal Ecosystems Division, Port and Airport Research Institute, 3-1-1, Nagase, Yokosuka 239-0826, Japan c National Remote Sensing Centre (Department of Space, Government of India), Balanagar, Hyderabad - 500042, Telangana, India d Indian Institute of Space Science and Technology, Thiruvananthapuram - 695547, Kerala, India e Indian National Centre for Ocean Information Services, Kukatpally, Hyderabad - 500090, Telengana, India f Marine and Atmospheric Sciences Division, Indian Institute of Remote Sensing (Department of Space, Government of India), 4, Kalidas Road, Dehradun - 248001, Uttaranchal, India article info Article history: Received 20 July 2016 Received in revised form 16 January 2017 Accepted 17 January 2017 Available online 23 January 2017 Keywords: Nutrient Tide Chlorophyll-a Shallow continental shelf Northern Bay of Bengal abstract The variability of nutrient concentrations (dissolved inorganic nitrogen, DIN; dissolved inorganic phosphorus, DIP; and dissolved inorganic silicate, DSi) along with salinity, total suspended matter (TSM), chlorophyll-a (chl-a) and dissolved oxygen (DO) were investigated in the shallow continental shelf waters of the northern Bay of Bengal. The sampling was conducted during the high tide and low tide conditions (day time) of the spring and neap phases throughout two annual cycles (February, 2013 to January, 2015). All analyses were carried out to evaluate the hypothesis—tidal processes principally regulate the nutrient variability in short-term scale. Results portrayed that DIN, DIP and DSi concentrations varied significantly between spring and neap phases as well as between high and low tides (p < 0.05). Short-term spring–neap and high tide-low tide contrast was most prominent in pre-monsoon and post- monsoon season. Considering the entire dataset, DIN, DSi and DIP concentrations were 8.83±3.45 mg l −1 , 8.43 ± 3.32 mg l −1 and 0.61 ± 0.36 mg l −1 during the spring phase and 9.79 ± 3.61 mg l −1 ,9.24 ± 3.19 mg l −1 and 0.73 ± 0.41 mg l −1 during the neap phase respectively. TSM exhibited strongest positive correlation with DIN and DSi (R 2 = 0.9) followed by a strong negative correlation with salinity (R 2 = 0.7), however, DIP showed a moderate correlation with both salinity and TSM. Salinity and TSM being a proxy of tidal variability, significant correlation between these two parameters and nutrient concentrations enabled the proposed hypothesis to be accepted. Moreover, this region exhibited low abundance of chl-a (∼0.1 to 3.5 mgm −3 throughout the study period) though nutrient values were quite high, as this region was phosphate limited in the post-monsoon, and for the rest of the year it was light limited. © 2017 Elsevier B.V. All rights reserved. 1. Introduction Whenever two completely different natural waters (freshwater and seawater) unite they generate a unique surroundings— estuaries are one such distinctive ecosystems where freshwater from river mixes with steadily intruding seawater. Considering the volume, these regions are relatively small; however, they have a ∗ Corresponding author. Fax: +91 33 2414 6242. E-mail address: sourav.biooptics@gmail.com (S. Das). major contribution to global primary productivity (Alheit, 2009). This type of transition region between land and open marine system experiences high fluxes of freshwater bringing dissolved nutrients and organic matter from adjoining rivers, resulting in relatively high primary productivity (Laane et al., 2005). Owing to this enhanced productivity, these areas generally serve as breeding grounds for marine organisms, nursery for juveniles and a potential fishery habitat. The degree of estuarine inputs of freshwater, dissolved nutrients, organic material and sediments to the coastal ocean is principally regulated by the changes in the quantum of freshwater discharge, rainfall pattern and tidal cycle (Schubel and Pritchard, 1986; Balls, 1994), the estuarine types (Webb and http://dx.doi.org/10.1016/j.rsma.2017.01.006 2352-4855/© 2017 Elsevier B.V. All rights reserved.