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We used more than 25,000 nutrient samples to elucidate for the first time basin-scale distributions and seasonal changes of surface ammonium (NH ) and nitrite (NO ) concentrations in the Pacific Ocean. The highest NH , NO , and nitrate (NO ) concentrations were observed north of 40°N, in the coastal upwelling region off the coast of Mexico, and in the Tasman Sea. NH concentrations were elevated during May-October in the western subarctic North Pacific, May-December in the eastern subarctic North Pacific, and June-September in the subtropical South Pacific. NO concentrations were highest in winter in both hemispheres. The seasonal cycle of NH was synchronous with NO , NO , and satellite chlorophyll a concentrations in the western subtropical South Pacific, whereas it was synchronous with chlorophyll- a but out of phase with NO and NO in the subarctic regions. [ABSTRACT FROM AUTHOR]

This study presents the results of the first field application of a flow-through multi-wavelength Fast Repetition Rate fluorometer (FRRF) equipped with two excitation channels (458 and 593 nm). This device aims to improve the measurement of mixed cyanobacteria and algae community's photosynthetic parameters and was designed to be easily incorporated into existing ferrybox systems. We present a spatiotemporal analysis of the maximum photochemical efficiency (F v /F m ) and functional absorption cross section (σ PSII ) recorded from April to August 2014 on a ship-of-opportunity commuting twice per week between Helsinki (Finland) and Travemünde (Germany). Temporal variations of F v /F m and σ PSII differed between areas of the Baltic Sea. However, even though the Baltic Sea is characterized by several physico-chemical gradients, no gradient was observed in F v /F m and σ PSII spatial distribution suggesting complex interactions between biotic and abiotic controls. σ PSII was sensitive to phytoplankton seasonal succession and thus differed according to the wavelength used to excite photosystems II ( PSI I) pigments. This was particularly true in summer when high σ PSII (593) values were observed later and longer than high σ PSII (458) values, reflecting the role of cyanobacteria in photosynthetic light uptake measured at community scale. In contrast, F v /F m variations were similar after excitation at 458 nm or 593 nm suggesting that the adjustment of F v /F m in response to environmental factors was similar for the different groups (algae vs. cyanobacteria) present within the phytoplankton community. [ABSTRACT FROM AUTHOR]

Abstract: Distribution of cyanobacteria cannot be evaluated using chlorophyll a (Chla) in vivo fluorescence, as most of their Chla is located in non-fluorescing photosystem I. Phycobilin fluorescence, in turn, is noted as a useful tool in the detection of cyanobacterial blooms. We applied phycocyanin (PC) fluorometer in the monitoring of the filamentous cyanobacterial bloom in the Baltic Sea. For the bloom forming filamentous cyanobacteria Aphanizomenon flos-aquae and Nodularia spumigena, PC fluorescence maximum was identified using the excitation–emission fluorescence matrix. Consequently, the optical setup of our instrument was noted to be appropriate for the detection of PC, and with minor or no interference from Chla and phycoerythrin fluorescence, respectively. During summer 2005, the instrument was installed on a ferryboat commuting between Helsinki (Finland) and Travemünde (Germany), and data were collected during 32 transects providing altogether 200 000 fluorescence records. PC in vivo fluorescence was compared with Chla in vivo fluorescence and turbidity measured simultaneously, and with Chla concentration and biomass of the bloom forming filamentous cyanobacteria determined from discrete water samples. PC fluorescence showed a linear relation to the biomass of the bloom forming filamentous cyanobacteria, and the other sources of PC fluorescence are considered minor in the open Baltic Sea. Estimated by PC fluorescence, cyanobacterial bloom initiated late June at the Northern Baltic Proper, rapidly extended to the central Baltic Proper and the Gulf of Finland, and peaked in the mid-July with values up to 10mgl−1 (fresh weight). In late July, bloom vanished in most areas. During single transects, or for the whole summer, the variability in Chla concentrations was explained more by PC fluorescence than by Chla fluorescence. Thus, filamentous cyanobacteria dominated the overall variability in phytoplankton biomass. Consequently, we show that during the cyanobacterial blooms, the estimation of Chla concentration using only Chla in vivo fluorescence is not applicable, but PC in vivo fluorescence is required as a predictor as well. [Copyright &y& Elsevier]