Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
  • BCO-DMO Processing Description
  • Problem Description
• Related Publications
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

Underway fluoresence sampling from the western Eastern Indian Ocean Upwelling region on the R/V Roger Ravelle in January - March 2022 (BLOOFINZ).

When the instrument is used for underway sampling, the ALF is connected to the ship’s uncontaminated seawater flow-through system allowing for continuous measurements in water drawn from approximately 5m below the surface

The  Automatic Laser Fluorometric Analyzer (ALFA)  is a state-of-the-art instrument, that combines high-resolution spectral measurements of blue (405 nm) and green (532 nm) laser-stimulated fluorescence, with spectral deconvolution techniques to estimate CDOM, phytoplankton variable fluorescence (Fv/Fm), Chl a and three types of phycobiliprotein pigments.

The fluorescence intensities attributable to each of the variables are normalized to the water Raman and expressed as relative fluorescence units (RFU). The Raman–normalized Chl a (679nm) and CDOM (508nm) fluorescence signals stimulated by the blue laser allow for measurements of Chl a and CDOM, respectively, while the Raman-normalized PE fluorescence signatures stimulated with the green laser allow for detection and quantitative assessment of three PE-containing groups of phytoplankton. These include the:

1. PE-1 peak at 565nm from blue water oligotrophic cyanobacteria with high phycourobilin/phycoerythrobilin (PUB/PEB) ratios,
2. PE-2 peak at 578nm from green water cyanobacteria with low-PUB/PEB ratios that usually thrive in coastal mesohaline waters, and
3. PE-3 peak at 590 nm attributable to eukaryotic photoautotrophic cryptophytes that are rich in phycobiliproteins and often abundant in coastal, and estuarine environments and in enclosed bays (Chekalyuk and Hafez, 2008; Chekalyuk et al., 2012, Goes et al. 2014).

* Converted date and time notation to ISO format notation
* Renamed fields to comply with database requirements
* Removed row 70259 with date 10-01-08 and row 138180 with date 06-19-13 from original dataset due to inconsistent date notation, approved by submitter

NSF Award Abstract:
Phytoplankton constitute the base of the marine food web. Their diversity, productivity and abundance have a huge influence on fisheries. For example, seasonal increases in phytoplankton biomass caused by the surge of deep ocean nutrient rich waters into the upper sunlit layers in the Equatorial Indian Ocean lead to an increase in tuna stocks. However, non-periodic increases of sea surface temperatures in the Seychelles-Chagos Thermocline Ridge region in the eastern Equatorial Indian Ocean, a phenomenon known as the Indian Ocean Dipole, weakens deep ocean water surge, which seems to alter phytoplankton community structure and to reduce phytoplankton’s productivity to the detriment of tuna stocks. Yet, the impact from such unpredictable events is not fully understood. This project investigates the impacts of an ongoing Indian Ocean Dipole, one of the most severe on record, on phytoplankton. The broader impacts of the project relate to its value to inform fisheries management plans in that area. Data derived from this study is valuable to understand and predict wider changes in the food web in a region that is coming under increasing pressures of global warming. All the data is made publicly available.

The research team is working with South Korean collaborators to understand how changes in phytoplankton biomass and in deep chlorophyll maxima may be linked to changes in phytoplankton productivity and growth rates due nutrient and/or iron limitation as a result of the weakening of deep-water upwelling. The team is also investigating the impact of the dipole event on cell size of dominating phytoplankton populations. Finally, they are testing if the phytoplankton community rely primarily on recycled as opposed to new nitrogenous nutrients for photosynthesis and growth during dipole events. The hypotheses are tested through extensive biological, hydro-chemical and biogeochemical measurements that include: 1) microscopic, Flow Cytometry, FlowCAM and HPLC pigment based analysis of phytoplankton biomass, community composition and size structure and Fast Repetition Rate based measurements of phytoplankton photosynthetic competency along a cruise track and different depths in the water column, and 2) on-deck incubation based photosynthesis and nutrient uptake experiments. In situ measurements and sample collection is carried out as part of the Korea-US inDian Ocean Scientific (KUDOS) Research Program cruise (April-May 2020) on board the Korea Institute of Ocean Sciences and Technology Ship R/V Isabu, one of the only multi-disciplinary oceanographic cruises planned for the Seychelles-Chagos Thermocline Ridge region during the dipole event.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.