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Phytoplankton plays an important role in ocean processes, and is well-known to have an enormous positive impact on climate change or more specifically on global warming, by reducing atmospheric CO2 levels through the sinking of produced organic and inorganic matter to the deep ocean (Falkowski, 2012; Beardall and Raven, 2013). However, climate change, with consequences of elevated seawater temperatures and decreased pH levels (Beardall and Raven, 2013), influences phytoplankton dynamics, changing phytoplankton composition, geography and biomass in the oceans (Falkowski and Oliver, 2007; Boyd et al., 2015; Jonkers et al., 2019). Temperature increases could also drive temporal shifts in the onset of the regular annual blooms, their composition, duration and amplitude as well as mismatches in timing between trophic levels (Hinder et al., 2012; Mikaelyan et al., 2015). The overall impact of increased temperature on phytoplankton is not easy to assess due to variable and complex repercussions. For example, increasing temperatures can lead to more stratified waters, especially in summer months, and prevent nutrient replenishment at the ocean surface. info:eu-repo/semantics/publishedVersion

Abundance and carbon biomass of different phytoplankton groups obtained by microscopy were compared with taxonomy derived from pigment measurements and CHEMTAX analysis of samples collected in June 2006 in the NW Black Sea. The diatom Chaetoceros curvisetus was dominant in terms of carbon biomass based on cell volume at inshore stations, while the coccolithophore Emiliania huxleyi was prevalent at offshore. Emiliania huxleyi reached bloom abundance of 3.3 × 106 cells L− 1. The chlorophyll a (chl a) concentration within phytoplankton groups as allocated by CHEMTAX was in agreement with microscopy derived carbon biomasses of the taxonomic groups diatoms, dinoflagellates and cryptophytes only. Carbon biomass of less abundant phytoplankton taxa (cyanophytes, euglenophytes and chlorophytes) did not correlate with group-specific chl a. It was not possible to detect E. huxleyi bloom by CHEMTAX analysis probably due to much higher biomass of other species containing 19’-hexanoyloxyfucoxanthin. Nutrient concentrations were generally high in the waters where diatom and dinoflagellates dominated the community but low in the area of E. huxleyi bloom. A good correlation between total carbon biomass of phytoplankton and chl a was found and the estimated C:chl a ratio of phytoplankton varied between 36 and 256 (in average 124 ± 50).

Effects of atmospheric deposition and other environmental factors on phytoplankton dynamics were evaluated from an open (having offshore characteristics) and a coastal station in the northeastern Mediterranean between December 2000 and December 2001. Data on phytoplankton, chlorophyll a, nutrients, temperature and salinity were obtained at bi-weekly or more intense intervals during 1 yr, whilst transport of Saharan dust towards the sampling region was monitored daily by SeaWiFS (sea-viewing wide field-of-view sensor) images. Diatoms were the group of highest average biomass during the entire investigation period. Although coccolithophores (mainly Emiliania huxleyi) numerically dominated at the open station during the study period, their maximum abundance was as low as 50 x 10 3 cells l -1 . The intensity of dust transport was observed to be highest in spring. Less intense transports were observed in summer and autumn. Several intense episodic dry and wet dust deposition events during the spring season observed by SeaWiFS images caused little or no increase in phytoplankton abundance and biomass in the following days and weeks. Nevertheless, it appears that less intense dust transport events increased phytoplankton abundance and biomass in August, September and October 2001, when water column stratification was at its peak. However, these increases were much weaker than the major winter-early spring bloom (in February and March), which was caused by upwelling, mixing the water column. We suggest that the impact of atmospheric nutrient input on phytoplankton in the Mediterranean is rather low on a yearly basis.

The species composition, abundance, and biomass of micro- (>15 μm) and nano- (

Lessardia elongata Saldarriaga & Taylor is identified for the first time in the north-western Black Sea in the present study. This species has probably been recorded with different names in the Black Sea due to lack of detailed investigations with scanning electron microscopy (SEM) or fluorescence microscopy. Our identification is based on observations with an electron microscope in September 2004 and with an epifluorescence and light microscope in June 2006. Cells were 5–10 µm wide, 22–30 µm long in formaldehyde fixed samples, fusiform, transparent, and had a faint broad girdle. Epitheca was slightly larger than the hypotheca and recently ingested prey could often be seen in the antapical half of the cell within very conspicuous vacuoles. Thin and faint thecal plates were hardly visible under epifluorescence microscope after staining the cells with fluorescence brightener 28 in the fixed samples. Cell abundances up to 18,400 cells l–1 and 87,000 cells l–1 were observed in September 2004 and June 2006, respectively.

The chemical composition of suspended particulate organic matter (SPOM) in the Black Sea water column has been characterized by pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS). The results are discussed in terms of the hydro-chemical properties of the water column. Phytoplankton cultures grown in the lab also were analyzed to provide reference information for the euphotic zone SPOM. The composition of SPOM in the Black Sea displays important vertical variations dependent on specific distinct biochemical processes in the water column. Identical pyrolysis markers indicative for proteins, lipids, carbohydrates and chlorophylls were obtained from SPOM in the euphotic zone of the Black Sea and the phytoplankton cultures. Nevertheless, the relative contribution of lipids and carbohydrates to Black Sea SPOM was higher than in phytoplankton cultures. The lipid to protein ratio throughout the water column seems to determine the C/N ratio of SPOM. Below the oxycline, the relative contribution of proteins to the SPOM pool increased while the lipid content of the SPOM decreased. The protein composition changed substantially in the suboxic/anoxic transition zone, as expressed by the increase in pyrrole/indole ratio. Elemental sulfur was observed in particulates suspended at the upper anoxic zone, and the relative intensity of the S8 peak varied regionally with more intense multi-peaks in SW shelf-break station, in agreement with the lateral flux of O2. Sulfur-containing organic compounds (e.g. thiophenes), including organic polysulphides (e.g. 1,2-dithiole-3-thiones) were detected in some deep anoxic samples, indicating that sulphurization of organic matter may be active in the water column.