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[1] Sea-air differences of CO 2 partial pressures (DpCO 2 ) and surface chlorophyll a (chl-a) concentration have been determined during 22 cruises in various seasons for 2000-2006 over the Patagonia Sea and shelf break. From spring to autumn, the nearshore waters act as a source of atmospheric CO 2 , while the midshelf and slope are a CO 2 sink, leading to highly negative areal means of sea-air CO 2 flux and DpCO 2 . The DpCO 2 and CO 2 flux in spring reach values of À67 matm and À7 Â 10 À3 mol m À2 d À1 , respectively, and are close to equilibrium in winter. Sea-air DpCO 2 and chl-a over the shelf are negatively correlated, suggesting that photosynthesis is one of the main processes responsible for the large CO 2 sequestration. The annual areal mean DpCO 2 and sea-air CO 2 flux are À31 matm and À3.7 Â 10 À3 mol m À2 d À1 , respectively, indicating that the Patagonia Sea is one of the strongest CO 2 sinks per unit area in the World Ocean.

Abstract. The photosynthetic performance of marine phytoplankton varies in response to a variety of factors, environmental and taxonomic. One of the aims of the MArine primary Production: model Parameters from Space (MAPPS) project of the European Space Agency is to assemble a global database of photosynthesisirradiance (P-E) parameters from a range of oceanographic regimes as an aid to examining the basin-scale variability in the photophysiological response of marine phytoplankton and to use this information to improve the assignment of P-E parameters in the estimation of global marine primary production using satellite data. The MAPPS P-E database, which consists of over 5000 P-E experiments, provides information on the spatiotemporal variability in the two P-E parameters (the assimilation number, P B m , and the initial slope, α B , where the superscripts B indicate normalisation to concentration of chlorophyll) that are fundamental inputs for models (satellite-based and otherwise) of marine primary production that use chlorophyll as the state variable. Qualitycontrol measures consisted of removing samples with abnormally high parameter values and flags were added to denote whether the spectral quality of the incubator lamp was used to calculate a broad-band value of α B . The MAPPS database provides a photophysiological data set that is unprecedented in number of observations and in spatial coverage. The database will be useful to a variety of research communities, including marine ecologists, Published by Copernicus Publications.

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.

Several satellite models classify phytoplankton functional types (PFT) based on cell size. In this study we used field data from the Argentine Sea on both the photosynthetic and the bio-optical properties of phytoplankton to distinguish photosynthetic and bio-optical phytoplankton types (PBPT). Cluster analyses were run using data from 70 stations sampled during 3 periods to distinguish different PBPT, and principal component analysis was used to describe them. We examined the main taxonomic composition and percentage of chl a in the < 5 µm size fraction found within the PBPT. The distribution of PBPT in relation to hourly primary production and environmental conditions was also investigated. The results showed a high degree of variability in biooptical and photosynthetic properties, e.g. the specific absorption coefficient of phytoplankton, a B ph (440), varied between 0.015 and 0.067 m 2 (mg chl a) −1 , and the maximum production at light saturation, P B m , varied between 0.68 and 10.05 mg C (mg chl a) −1 h −1. This resulted in the discrimination of 11 PBPT. Some had similar average cell sizes but differed in their bio-optical or photosynthetic characteristics, e.g. PBPT1 (with diatoms < 5 µm and Emiliania huxleyi 2-5 µm) and PBPT6 (with diatoms < 5 µm and coccal cells ~2 µm) had markedly different P B m values (PBPT1: 1.20 mg C (mg chl a) −1 h −1 and PBPT6: 6.71 mg C (mg chl a) −1 h −1). This variability in the bio-optical and physiological properties is most likely the result of adaptation by phytoplankton communities to the high heterogeneity in environmental conditions in this region. These results indicate that satellite models describing the distribution of PFT based on cell size alone will not provide a realistic representation of the phytoplankton composition in this highly productive and heterogeneous area.