  Fast Repetition Rate fluorometry (FRRf) generates high-resolution measures of
phytoplankton primary productivity as electron transport rates (ETRs). How ETRs
scale to corresponding inorganic carbon (C) uptake rates (the so-called
electron requirement for carbon fixation, e,C), inherently describes the extent
and effectiveness with which absorbed light energy drives C-fixation. However,
it remains unclear whether and how e,C follows predictable patterns for
oceanographic datasets spanning physically dynamic, and complex, environmental
gradients. We utilise a unique high-throughput approach, coupling ETRs and
14C-incubations to produce a semi-continuous dataset of e,C (n = 80),
predominantly from surface waters, along the Australian coast (Brisbane to the
Tasman Sea), including the East Australian Current (EAC). Environmental
conditions along this transect could be generally grouped into cooler, more
nutrient-rich waters dominated by larger size-fractionated Chl-a (>10 um)
versus warmer nutrient-poorer waters dominated by smaller size-fractionated
Chl-a (< 2 um). Whilst e,C was higher for warmer water samples, environmental
conditions alone explained less than 20% variance of e,C, and changes in
predominant size-fraction(s) distributions of Chl-a (biomass) failed to explain
variance of e,C. Instead, NPQNSV was a better predictor of e,C, explaining 55%
of observed variability. NPQNSV is a physiological descriptor that accounts for
changes in both long-term driven acclimation in non-radiative decay, and
quasi-instantaneous PSII downregulation, and thus may prove a useful predictor
of e,C across physically-dynamic regimes, provided the slope describing their
relationship is predictable.

Populations and Evolution