Cruise No. EP01-2

Access URI: https://doi.org/10.6084/m9.figshare.19434197.v3

Alternate Title: Second Scientific Cruise Under IIOE-2

Brief Description (Abstract):

The growth of marine phytoplankton is primarily limited by the reactive forms of nitrogen. Dinitrogen (N2)-fixing organisms (termed diazotrophs) supplement this need by providing a natural fertilizer, ammonium. Biological N2 fixation is meagerly explored in the Bay of Bengal (Bay). Stratified, warm, oligotrophic (but relatively high iron and phosphate) and oxygen minimum zone (OMZ) waters of the Bay might be a niche for diazotrophs. Therefore, we conducted N2 fixation rate measurements in the euphotic zone, the OMZ and below the OMZ down to 1,500 m depth near the coastal and in the central Bay at seven stations aboard ORV Sindhu Sankalp (SSK-127) between 5 and 15 April 2019. We further assessed primary production and cyanobacterial community composition along with their potential environmental controlling parameters. We hypothesized that N2 fixation rates in the dark-oxygenated waters (below the OMZ) should be lower than the rates in the OMZ owing to incompatibility of dark-waters prevailing non-cyanobacterial diazotrophs with O2. N2 fixation rates in the euphotic zone were low (0.02 to 0.38 nmol N L-1 d-1) and their contribution to primary production was small (less than 2%). Despite conducive conditions for diazotrophy in the Bay, the reason for the relatively low euphotic zone and OMZ N2 fixation rates remained unclear and enigmatic. Interestingly, significantly higher N2 fixation rates occurred below the OMZ, ranging from 0.06 to 0.11 nmol N L-1 d-1 where oxygen concentrations ranged between 0.5 and 1.6 mL L-1, rather than within the OMZ where rates ranged from 0.02 to 0.08 nmol N L-1 d-1 and oxygen concentrations were less than 0.5 mL L-1. Euphotic zone N2 fixation showed seasonality in the Bay with increasing rates from spring to summer season, perhaps owing to increasing iron flux as the summer monsoon approaches its peak.

Status: Completed

Purpose: To investigate the potential environmental controlling parameters of N2 fixation in the Bay of Bengal

Credit(s): Dr. Arvind Singh

Presentation Format: TableDigital

Distribution Format: Unknown

Distribution Format Version: Unknown

Supplemental Information:

IIOE-2 endorsed project.The project aligns with IIOE-2 Science Theme 6 (Unique geological, physical, biogeochemical, and ecological features of the Indian Ocean).The primary objective of the Cruise No. EP01-2 was to measure N2 fixation rate during the spring inter-monsoon in the euphotic zone, the OMZ and below the OMZ down to 1,500 m depth near the coastal and in the central Bay of Bengal. The other major objectives were to assess primary production and cyanobacterial community composition along with their potential environmental controlling parameters.

Keyword(s): Earth Science-Oceans-Ocean Chemistry-Organic Matter, Earth Science-Oceans-Ocean Chemistry-Oxygen, Earth Science-Oceans-Ocean Chemistry-Phosphate, Earth Science-Oceans-Ocean Chemistry-Silicate, Earth Science-Oceans-Ocean Chemistry-Stable Isotopes, Earth Science-Oceans-Ocean Chemistry-Nitrogen, Earth Science-Oceans-Ocean Chemistry-Biogeochemical Cycles, Earth Science-Oceans-Ocean Temperature-Sea Surface Temperature, Earth Science-Oceans-Ocean Temperature-Ocean Mixed Layer, Earth Science-Oceans-Ocean Temperature-Water Temperature, Earth Science-Oceans-Salinity/Density-Conductivity, Earth Science-Oceans-Salinity/Density-Density, Earth Science-Oceans-Salinity/Density-Salinity, Earth Science-Oceans, Earth Science-Oceans-Ocean Chemistry-Chlorophyll, Earth Science-Oceans-Ocean Chemistry-Nitrite, Earth Science-Oceans-Ocean Chemistry-Nitrate, Earth Science-Oceans-Ocean Chemistry-Nutrients, Earth Science-Oceans-Ocean Chemistry-Organic Carbon,

Place/Location(s): Bay of Bengal,

Project: IIOE-2,

Topic Category(s): GeoScientific Information,

Date(s): 2023-09-14 (Publication), 2023-12-11 (Creation),

Resource Contact(s):
1. Name : Dr. Arvind Singh
    Position : Scientist
    Role : PrincipalInvestigator
    Phone : +91 79 2631 4153
    E-Mail : arvinds [ at ] prl.res.in
    Organization Name : Physical Research Laboratory (PRL)
    Address : Geosciences Division, Physical Research Laboratory, Navrangpura
    City : Ahmedabad
    State : Gujarat
    Postal Code : 380 009
    Country : IND

Distributor Contact(s):
1. Name : Dr S. Rajan
    Position : JPO INDIA IIOE-2 Coordinator
    Role : Distributor
    Phone : +91-40-23886142
    E-Mail : iioe-2 [ at ] incois.gov.in
    Organization Name : Indian National Centre for Ocean Information Services (INCOIS)
    Address : Ocean Valley, Pragathi Nagar (BO), Nizampet (SO)
    City : Hyderabad
    State : Telangana
    Postal Code : 500090
    Country : IND

Metadata Contact(s):
1. Name : Dr. Arvind Singh
    Position : Scientist
    Role : PointOfContact
    Phone : +91 79 2631 4153
    E-Mail : arvinds [ at ] prl.res.in
    Organization Name : Physical Research Laboratory (PRL)
    Address : Geosciences Division, Physical Research Laboratory, Navrangpura
    City : Ahmedabad
    State : Gujarat
    Postal Code : 380 009
    Country : IND

Extent:
Start Date : 2019-04-07
End Date   : 2019-04-14