Dataset: Primary productivity estimates from the incubation of seawater collected at the Bermuda Atlantic Time-series Study (BATS) site from December 1988 through June 2024

Primary production is measured in situ as part of the monthly Bermuda Atlantic Time Series (BATS) cruises. Research was conducted on many research vessels including R/V Weatherbird I, R/V Weatherbird II, R/V Cape Henlopen, R/V Cape Hatteras, R/V Oceanus, R/V Endeavor, R/V Atlantic Explorer. Nominal deployment location at BATS site  (31 40'N, 64 10'W).  Numerous Chief Scientists: Tony Knap, Rachel Dow, Anthony Michaels, Kjell Gundersen, Rodney Johnson, Ann Close, Deborah Steinberg, Paul Lethaby, Julian Mitchell, Vivienne Lochhead, Deborah Lomas, Steven Bell, Jonathan Whitefield, Gwyn Evans, James Sadler, Samuel Monk, Samuel Stevens, Afonso Goncalves, Matt Enright, Fernando Pacheco, Zac Anderson, Claire Medley, Dominic Smith.

Scope and field of application
Primary production is a fundamental ecological variable for understanding the flow of energy into an ecosystem as it supports the availability of organic material as building blocks for higher trophic levels. This method uses a radiocarbon ¹⁴C spike and liquid scintillation counter (LSC) techniques to quantify the rate of primary production. This procedure describes the method for the determination of primary production in seawater, expressed as milligrams of carbon per cubic meter per day (mg C m⁻³ day⁻¹) . This method is suitable for the assay of all levels of primary production found in the ocean.

 Primary production is defined as the rate of uptake of inorganic carbon (DIC) into particulate organic carbon (POC),

                                      DIC_n * POC¹⁴C * 1.05
                C uptake   =   -----------------------------    , where
                                              DIC¹⁴C 

C uptake = rate of carbon fixation (mg Carbon m⁻³ day⁻¹) 
DIC_n = naturally occurring dissolved inorganic carbon
POC¹⁴C = ¹⁴C spiked particulate organic carbon
DIC¹⁴C = ¹⁴C spiked dissolved inorganic carbon
1.05 = metabolic discrimination factor due to biological isotopic fractionation (preferable uptake of lighter isotopes)

Principle of analysis
The rate of carbon fixation by autotrophs in seawater is measured by tracing the uptake of radioactive ¹⁴C from the inorganic form to the particulate organic form. Radiocarbon is added at an assumed ratio to the total inorganic carbon content of the seawater sample. The uptake of radiocarbon by the particulate phytoplankton is converted to total carbon uptake by the application of this radiocarbon: total carbon ratio. Inorganic carbon is not measured because samples are acidified before analysis. The seawater is collected using the CTD at discrete depths every 20 meters from the surface to 140 meters. The radioactive ¹⁴C spike is added and samples are incubated in situ at their respective depths using a free-floating array. The array is deployed prior to first light and recovered after sunset to capture the dawn to dusk light cycle.

A liquid scintillation counter (LSC) is used to calculate the level of radioactivity in the sample and therefore the amount of ¹⁴C particulate organic carbon. The LSC measures the conversion of radioactive decay events into photons of light, which are detected by photomultiplier tubes and converted into electrical pulses. In order to aid the detection of radioactivity, a liquid scintillation cocktail is added (Ultima gold for this method). The cocktail contains both solvent and scintillator molecules. The radioactive decay from the ¹⁴C excites the solvent molecule, and the energy is transferred to the scintillator which re-emits the energy in the form of light. Often more than one type of scintillator is present in the cocktail to allow for the emission of light at a suitable wavelength to be detected by the photomultiplier tubes. The resulting electrical signal that is generated is recorded as counts per minute (CPM). 

For additional details, please see Protocols for the Bermuda Atlantic Time-series Study Core Measurements.