Studies included in the meta-analysis.

Data were collected during cruises undertaken as part of the Atlantic Meridional Transect (AMT) Program, individual cruises to the Celtic Sea, Baltic Sea, North Sea, other UK and European shelf waters and the Pacific, as well as part of time series studies in the Gulf of Finland, Massachusetts Bay (USA), Ariake Bay (Japan) and Bedford Basin (Canada). Methodological differences existed in the way data were corrected for spectral discrepancies between the fluorometer and 14C-incubator light source (σPSIIspec), in the estimates of the number of photosystem II (nPSII), and in the approach used to compare electron transport rates (ETR) and 14C fixation.
+ spectral corrections applied according to Moore et al. [11]. In some samples, a spectral correction factor of 1.75 was used while a spectral correction was n.a. denotes not applicable because primary productivity was measured on samples incubated in the cuvette holder of a FASTact Fluorometer.
nPSII was assumed to be constant (0.0033 or 0.0020 mol RCII (mol chla)−1) or calculated either according to (‡) nPSII = 500 (Fv/Fm)/0.65 or (†) Oxborough et al.[7]. ETRs were either measured in situ or on discrete samples using a 1FASTtrecka, or 2FASTact FRR fluorometer, a 3FIRe benchtop fluorometer or a 4FRRFDiving Flash. Superscript 5 denotes photosynthesis irradiance curves measured on samples incubated for 1–4 hours using a photosynthetron [32] or equivalent incubator, 6 denotes 2 hour in situ bottle incubations, while 7 indicates rapid light curves carried out in on-deck laboratories under temperature controlled conditions. SIS stands for 24 hour on deck ‘simulated in situ’ incubations, and N is the number of observations for each study. a) Silsbe and Ylöstalo unpublished, b) Lawrenz, Capuzzo, Forster, Suggett unpublished, c) Suggett and Forget unpublished, d) Prášil, Gorbunov, Babin, Huot unpublished, e) Ylöstalo et al. unpublished.