Table of Contents

• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Data Files
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

Phytoplankton abundance for diatoms, dinoflagellate and Trichodesmium, nutrients and ctd data from Northern Arabian Sea, 2009-2011.

The data are subject to restricted access.  Please contact the PI for access, jgoes@bigelow.org.

During the cruise, seawater samples were collected with a 5-l Niskin® sampler mounted on a Sea Bird Electronics® CTD rosette using JGOFS prescribed clean techniques (Knap et al., 1996). Calibrated sensors mounted on the CTD provided vertical profiles of salinity, temperature and dissolved O2. The salinity sensor was calibrated against Autosal® Salinometer measurements, while the dissolved O2 sensor was calibrated against measurements using the Winkler method with the high-precision amperometric end point detection (Langdon, 1984). Quality control was guided by the National Oceanographic Data Center Report and included duplicate profile, depth duplication and inversion checks, as well as data range and large temperature and inversion checks (Boyer and Levitus, 1994).

Chlorophyll-a concentrations corrected for phaeophytin were measured by the fluorometric method, whereas phytoplankton production rates were measured using 14C labeled NaHCO3 incubations under simulated in-situ conditions in plexiglass tanks placed on the deck in full sunlight and in running seawater (Knap et al., 1996).

Microscopic identification and enumeration of phytoplankton was undertaken on duplicate samples that were fixed with 1% Lugol’s iodine in 3% buffered formaldehyde solution and stored in cool and dark conditions to allow the cells to settle. Prior to microscopic analysis, samples were concentrated to 5-10 ml by carefully siphoning out the top layer through a 10um Nitex® filter wrapped around the tip of a thin tube. Although examination of the siphoned layer under the microscope indicated that no visible cells were lost by this method of concentration, cell abundance estimated using this method only applies to >10um cells. Cell density was counted by transferring 1ml replicates of the concentrated sample on to a Sedgwick-Rafter® slide and counted with an Olympus Inverted microscope (Model IX 50) at 200x magnification. Identification of phytoplankton was based on standard taxonomic keys, and was in most cases undertaken up to the species level (Tomas, 1997).

Sampling and Analytical Methodology:
Methodologies are provided in Knap, A., A. Michaels, A. Close, H. Ducklow, and A. Dickson (1996), Protocols for the Joint Global Ocean Flux Study (JGOFS) core measurementsRep. 19 170 pp, Scientific Committee on Oceanic Research, International Council of Scientific Unions. Intergovernmental Oceanographic Commission, Bergen, Norway.
The analytical precisions and limits of detection of each of the variables measured are provided in Knap et al (1996).

References:
Boyer, T. & Levitus, S. Quality control of oxygen, temperature and salinity data. 65 National Oceanographic Data Center, Washington, D.C. (1994).
Knap, A., A. Michaels, A. Close, H. Ducklow, and A. Dickson (1996), Protocols for the Joint Global Ocean Flux Study (JGOFS) core measurementsRep. 19 170 pp, Scientific Committee on Oceanic Research, International Council of Scientific Unions. Intergovernmental Oceanographic Commission, Bergen, Norway.
Langdon, C. Dissolved oxygen monitoring system using a pulsed electrode: design, performance and evaluation. Deep Research I 31, 1357-1367 (1984).
Tomas, C. R. Identifying Marine Phytoplankton. 858 (Academic Press, 1997).

Until the late 90's Noctiluca miliaris, a large heterotrophic dinoflagellate was a minor component of phytoplankton populations in the northern Arabian Sea, appearing in bloom form only sporadically during the Southwest Monsoon (SWM, summer monsoon) and in coastal regions predisposed to upwelling and deep slope water intrusions. Since then N. miliaris blooms have increased in frequency, intensity and distribution, but with the majority of blooms being observed during the Northeast monsoon (NEM, winter monsoon). Large blooms of these organisms have now become more pervasive and widespread throughout the Gulf of Oman and in the western and central Arabian Sea replacing diatom-dominating blooms of the NEM that were seen frequently during the multi-disciplinary Arabian Sea, Joint Global Ocean Flux Studies (JGOFS). There is particular concern that the emergence of N. miliaris blooms and their association with waters that are nutrient-rich and undersaturated with respect to oxygen may be indicative of eutrophication of the Arabian Sea ecosystem. Such concerns are consistent with recent indications that the Arabian Sea is becoming more productive and that its permanent oxygen minimum zone is intensifying due to increased organic matter export from the euphotic zone. There is also concern that the replacement of diatoms by N. miliaris is potentially having a large impact on the food web and carbon cycling in the Arabian Sea.

This project will carry out a targeted field program aimed at understanding the emergence and fate of N. miliaris blooms. In particular the project will investigate 1) the environmental conditions facilitating large N. miliaris blooms in the Arabian Sea and 2) the trophic role of N. miliaris blooms and 3) implications of these blooms for carbon cycling and biogeochemical processes in the Arabian Sea. This field study has been devised in consultation with colleagues at the National Institute of Oceanography (NIO) & the Space Applications Centre in India who have offered ship time on board the India's research vessel R/V Sagar Kanya and laboratory facilities at NIO at no cost to this project. An existing collaboration with the Sultan Qaboos University (SQU), Oman will also allow access to data from an ongoing field program in the northern Arabian Sea.

This project will provide training to two US undergraduate students at Bigelow Laboratory and one graduate student from Univ. Texas (UT) will be involved full time. This project will provide an opportunity for students from the US to work alongside students from India. Through this truly international collaborative effort the project will encourage scientific curiosity about the response of marine ecosystems to climate change as well as foster a cross-cultural exchange of ideas. The investigators will leverage education and outreach efforts through development of a website which will be linked to Bigelow Laboratory's existing algal blooms and the Univ. Maine COSEE-OESS website. This website will be translated into Hindi, the official language of India and into Arabic, the language of Oman. This web-based resource will be tailored for non-specialist audiences with strong emphasis on visuals. At the UT Marine Science Institute. a radio segment on this research will be written for Science and the Sea, a radio program produced for National Public Radio, and played on most public radio stations nationwide (http://scienceandthesea.org/)

Associated programs: OCB Ocean Chemistry and Biochemistry) and SIBER (Sustained Indian Ocean Biochemistry and Ecosystem Research).  SIBER is cosponsored by IMBER (Integrated Marine Biogeochemistry and Ecosystem Research) and IOGOOS (Indian Ocean Global Ocean Observing System).