DOI: 10.5884/13254
title: Fast Repetition Rate fluorometry-based measurements of phytoplankton photo-physiology in the Canadian Arctic Archipelago, Aug 2019

description: We employed Fast Repetition Rate fluorometry (FRRF) for high-resolution mapping of phytoplankton photo-physiology in Lancaster Sound and Barrow Strait regions of the Canadian Arctic Archipelago. For exact details of sampling locations, see the Latitude and Longitude fields of this dataset. The sampling period took place onboard the CCGS Amundsen from Aug 2-14, 2019. Continuous ship-board measurements of Chlorophyll a (Chla) fluorescence transients were made using a Soliense LIFT FRRF with a 12 minute interval between sampling events using a single-turnover flash protocol. Within each sampling event, 40 Chla fluorescence transients were measured under low light (5 μmol photons per m-2 s-1), and 40 under high light (150 μmol photons per m-2 s-1) on an isolated sample from the ship’s seawater line. Each fluorescence transient has a 1s interval. Between sampling events, a pump custom fit to the FRRF flushed the sampling cuvette and was synchronized to stop pumping 10 minutes prior to the next measurement sequence to allow phytoplankton dark acclimation within the sampling cuvette. Thus, measurements were continuous and fully automated. Each fluorescence transient curve was fit to the biophysical model described by Kolber et al., 1998 to retrieve the following diagnostics of phytoplankton photo-physiology: UTC time of measurement, julian day of measurement, actinic light provided during flash measurements (μmol photons per m-2 s-1), model fit Chi sq, baseline fluorescence (relative units), maximum inducible fluorescence (relative units), functional absorption area of Photosystem II (Å2 Reaction Center II-1), the probability of energy transfer between reaction centers (fractional), the time constants for the three components of Qa reoxidation (μs) and their relative weights (fractional), the signal to noise ratio, and the surface PAR at time of measurements (μmol photons per m-2 s-1). Together, these parameters of phytoplankton light harvesting and utilization efficiency can be used to estimate phytoplankton photochemistry yields, which power the photosynthetic electron transport chain, and ultimately provide an upper limit for photosynthetic carbon uptake.
description: This dataset was collected for high spatiotemporal analysis of phytoplankton photophysiological characteristics, to elucidate fine-scale variability in phytoplankton photosynthetic capacities as they relate to hydrographic conditions, nutrient abundances, and light influences. Such oceanographic conditions are highly dynamic and rapidly evolving in the Canadian Arctic Archipelago where sampling took place. Therefore documenting environmental influences on Arctic phytoplankton photophysiology requires ocean observing methods capable of high resolution measurements. For this reason, we deployed Fast Repetition Rate fluorometry to rapidly and simultaneously measure phytoplankton light harvesting and light utilization efficiencies. We were thus able to produce a map of phytoplankton photo-physiology along the cruise track through Baffin Bay and Lancaster Sound. Our high resolution measurements enabled us to relate spatial variability in photophysiology to localized regions of enhanced nutrient abundances due to riverine inputs and tidal mixing, while temporal variability in photophysiology was related to diel solar cycles. Hydrographic variables complimentary to this dataset were measured by Amundsen Science and are available here doi: 10.5884/12715.