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Primary Production, an Index of Climate Change in the Ocean: Satellite-Based Estimates over Two Decades. Although this is a substantial increase in the estimate of primary production, the results of the sensitivity analysis in which the photosynthesis versus irradiance parameters were varied by ±1 standard deviation and, importantly, the observed trends in regional and global annual primary production are largely unchanged. The main corrections increased our estimate of global annual primary production on average by +23.9% between 1998 and 2018, while the correction of the rounding error in the PAR products increased global annual primary production between 2003 and 2018 by +0.9%. Global annual primary production remained close to the range of earlier observations (32.0-70.7 Gt C y SP -1 sp ) [2,4,5,22] when both P-I parameters were adjusted by +1 standard deviation (+1 SD) (70.8-76.2 Gt C y SP -1 sp ), but adjustments by -1 standard deviation (-1 SD) resulted in considerably lower global annual primary production rates (25.7-27.8 Gt C y SP -1 sp ). [Extracted from the article]

Primary production by marine phytoplankton is one of the largest fluxes of carbon on our planet. In the past few decades, considerable progress has been made in estimating global primary production at high spatial and temporal scales by combining in situ measurements of primary production with remote-sensing observations of phytoplankton biomass. One of the major challenges in this approach lies in the assignment of the appropriate model parameters that define the photosynthetic response of phytoplankton to the light field. In the present study, a global database of in situ measurements of photosynthesis versus irradiance (P-I) parameters and a 20-year record of climate quality satellite observations were used to assess global primary production and its variability with seasons and locations as well as between years. In addition, the sensitivity of the computed primary production to potential changes in the photosynthetic response of phytoplankton cells under changing environmental conditions was investigated. Global annual primary production varied from 38.8 to 42.1 Gt C yr − 1 over the period of 1998–2018. Inter-annual changes in global primary production did not follow a linear trend, and regional differences in the magnitude and direction of change in primary production were observed. Trends in primary production followed directly from changes in chlorophyll-a and were related to changes in the physico-chemical conditions of the water column due to inter-annual and multidecadal climate oscillations. Moreover, the sensitivity analysis in which P-I parameters were adjusted by ±1 standard deviation showed the importance of accurately assigning photosynthetic parameters in global and regional calculations of primary production. The assimilation number of the P-I curve showed strong relationships with environmental variables such as temperature and had a practically one-to-one relationship with the magnitude of change in primary production. In the future, such empirical relationships could potentially be used for a more dynamic assignment of photosynthetic rates in the estimation of global primary production. Relationships between the initial slope of the P-I curve and environmental variables were more elusive. [ABSTRACT FROM AUTHOR]

We analyzed the relationship between population abundance and cell size in phytoplankton assemblages from coastal, shelf, and open-ocean environments. Our results show that across the entire size spectrum considered, population abundance increases over two orders of magnitude from subtropical to coastal regions. We find a highly significant linear relationship between nutrient concentration and the intercept of the log-log relationship between population abundance and cell size. In contrast to overall patterns reported mainly for vascular plants and animals, marine phytoplankton diversity does not show any consistent trend along either latitudinal or productivity gradients. These results imply that large-scale (biogeographic) variations in phytoplankton standing stocks are controlled by changes in population abundances rather than by systematic variations in species richness. These findings provide a mechanistic connection among nutrient availability, population dynamics, and phytoplankton diversity over macroecological scales. [ABSTRACT FROM AUTHOR]