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Coccolithophore export fluxes were investigated via the analysis of sinking matter, obtained from Eastern Mediterranean time-series sediment traps moored in three open sites of the north-eastern Mediterranean Sea located in the Athos Basin of North Aegean (M2 site), Cretan Sea of South Aegean (M3 site) and at Ionian Sea (Nestor site). The aim of our study was to determine the spatial, temporal and seasonal variability in coccolithophore fluxes, as well as to estimate coccolith biogenic carbonate contribution to the sedimentation process. Data from an additional time-series sediment trap located in the southwestern Black Sea were also considered for the comparison of the oligotrophic Eastern Mediterranean setting with the eutrophic Black Sea. Coccolithophore fluxes revealed a highly seasonal pattern during February–March in the North Aegean (peak in late February 2015: 85.6 x 105 coccospheres m−2 day−1; 27.9 x 108 coccoliths m−2 day−1), during March–May in the Cretan Sea (peak in late March 2015: 33.7 x 105 coccospheres m−2 day−1; 19.5 x 108 coccoliths m−2 day−1) and during February–March and May–June in the Ionian Sea (peak in late May 2012: 14.3 x 105 coccospheres m−2 day−1; 1.53 x 108 coccoliths m−2 day−1). The recorded maxima coincide with low sea surface temperatures, increased precipitation and high PIC fluxes. Coccosphere fluxes were dominated by Emiliania huxleyi comprising ~70% of the total abundance, in the North Aegean and ~50% in the Cretan and Ionian Seas. Syracosphaera pulchra was also prominent in the study sites, where its abundance reached 14% in the North Aegean and ~10% in the Cretan and Ionian Seas respectively. Florisphaera profunda represented one of the major taxa in the coccolith fluxes of all three Eastern Mediterranean sites (~25% in North Aegean, ~20% in Cretan and Ionian Seas), while Algirosphaera robusta and Umbilicosphaera sibogae were the most abundant among the minor taxa. The North Aegean Sea exhibited a considerably higher coccolith flux when compared to other sediment traps due to the prominent seasonal peak of E. huxleyi during winter (February–March) (>95% of the total abundance). In contrast to the Eastern Mediterranean sediment traps, the time-series data from the Black Sea showed presence of monospecific E. huxleyi assemblage increasing its abundance during late September–November (max 320 x 105 coccospheres m−2 day−1; at least 7.79 x 108 coccoliths m−2 day−1, coccolith flux derived only from coccospheres converted to coccoliths). In the Eastern Mediterranean, biogenic carbonate fluxes followed the general pattern of the total mass flux in all investigated areas, with the Black Sea coccolithophore CaCO3 flux being the lowest due to low the E. huxleyi coccolith mass. Overall, in the North Aegean Sea, coccolithophore fluxes are strongly dependent on surface waters nutrients enrichment due to winter vertical water column mixing, riverine inputs and Black Sea water inflows, while the fertilization and/or formation of fast-sinking aggregates due to episodic dust input event are affecting the coccolithophore fluxes in the Cretan and Ionian Seas. The intercomparison of the coccolith export fluxes in the studied NE-SW mooring transects implies a north-south and east-west decreasing pattern, depending on the variable oceanographic regimes and the associated environmental factors controlling the investigated areas. © 2019 Elsevier Ltd

The export production of coccolithophores has been measured from Black Sea, North Aegean Sea, Cretan Sea, South Cretan margin and Ionian Sea, and compared in order to define the spatial and seasonal variability in theirassemblage composition. Α sediment trap mooring has been deployed for one year (10/2007- 9/2008) at 1000 m water depth, in western Black Sea. The maximum coccosphere fluxes, with almost monospecific assemblage of Emiliania huxleyi, have been recorded during May, June and September (max. 3.2 x108 coccospheres m-2 day-1). The seasonally controlled coccolithophore patterns are strongly related to those of sea surface temperature and accumulated rainfall in the area, triggering riverine nutrient input Coccosphere fluxes in North Aegean Sea have been calculated from a sediment trap deployment at 500 m (1/2011-12/2011). E. huxleyi is the dominant species, followed by Rhabdosphaera spp., Syracosphaera spp. and Florisphaera profunda as minor assemblage components. Maximum fluxes have been observed in February and June (max. summer 2.9 x105 coccospheres m-2 day-1). A single mooring with two sediment traps (500 and 1700 m) was deployed at the southern margin of the Cretan Sea (Triantaphyllou et al., 2004). The results obtained from 500 m depth show that the highest flux values were observed between late March to late June (max. 9.4 x105 coccospheres m-2 day-1). The pattern was characterized by three main phases that correlate well with the gradual increase in SST from January till September. Coccosphere sinking assemblages were characterized by high abundances of E. huxleyi, followed by F. profunda, Rhabdosphaera spp. and Syracosphaera spp. Six moorings have been deployed at different sites along the south–west margin of Crete, providing a total of eight sediment-trap time series (6/ 2005-5/2006), (Malinverno et al., 2009). Maximum coccosphere fluxes were recorded in between March to June (4.3 x 105 –3.4 x106 coccospheres m−2 day−1), featured by dominance of E. huxleyi and subordinate Helicosphaera carteri, Umbilicosphaera spp. and Syracosphaera pulchra; intermediate fluxes from June to November, with high abundance of the deep photic zone species Algirosphaera robusta, F. profunda, Gladiolithus flabellatus; low fluxes from November to February, with high flux of A. robusta, S. pulchra and Syracosphaera spp. These three periods correspond to the seasonal changes in sea surface temperature and surface mixed layer depth. Coccolithophore fluxes from the central part of the Ionian Sea have been studied from a sediment trap mooring (9/1999-6/2001) at 500 m water depth (Malinverno et al., 2014). Peak coccolithophore export production is observed in May (3.5 x105 coccospheres m-2 day-1), a secondary peak is observed in September-October. The assemblage is dominated year-round by the cosmopolitan species E. huxleyi, followed by the deep-dwelling F. profunda and by several minor species (Syracosphaera spp., Rhabdosphaera spp., A. robusta, G. flabellatus) which are most abundant during the summer period of upper water column stratification. NESTOR mooring line (4500m depth) was deployed at the deepest basin of the SE Ionian Sea (36ο 2.96 N, 21ο 28.93 E). The mooring line was instrumented with five pairs of sediment traps, set at 700, 1200, 2000, 3200, and 4300m depth. The Ionian Sea displays high seasonal variability with maximum productivity rates observed during the late winter/spring convective mixing period (Stavrakakis et al., 2013). Our coccolithophore flux study from the shallower trap (700 m) for an overall interval between 6/2010 and 8/2012, reveals a peak during late spring- early summer (max. May 2012; 1.43 x106 coccospheres m-2 day-1) that is in accordance with the peak of total mass flux. The assemblage is dominated by E. huxleyi, followed by A. robusta, Syracosphaera spp., H. carteri, Umbilicosphaera sibogae. A high seasonal pattern characterizes the assemblages; the export production and fluxes are strongly dependent on the nutrient influx, the vertical mixing/ and or intermediate waters upwelling, SST of the water column and the influence of episodic dust input events leading to enhanced fluxes of lithogenic matter, in a north - south and east - west transient.

Α sediment trap mooring has been deployed for one year (10/2007- 9/2008) at 1000 m water depth, in western Black Sea. The maximum coccosphere fluxes, with almost monospecific assemblage of Emiliania huxleyi, have been recorded during May and June. The seasonally controlled coccolithophore patterns are strongly related to those of sea surface temperature and accumulated rainfall in the area, triggering riverine nutrient input. Coccosphere fluxes in North Aegean Sea have been calculated from a sediment trap deployment at 500 m (1/2011-12/2011). E. huxleyi is the dominant species, followed by Syracosphaera pulchra, Rhabdosphaera clavigera as minor assemblage components. Maximum fluxes have been observed in between May-June. A single mooring with two sediment traps (500 and 1700 m) was deployed at the southern margin of the Cretan Sea (1/2001-2/2002) [1]. The results obtained from 500 m depth show that the highest productivity season was recorded from January till late September with the highest flux values observed between late March to late June. During this period the pattern was characterized by three main phases that correlate well with the gradual increase in SST from January till September. Coccosphere sinking assemblages were characterized by high abundances of E. huxleyi, followed by Florisphaera profunda, R. clavigera and Syracosphaera spp. Six moorings have been deployed at different sites along the south–west margin of Crete, providing a total of eight sediment-trap time series (6/2005- 5/2006) [2]. Maximum coccosphere fluxes were recorded in between March to June, featured by dominance of E. huxleyi and subordinate Helicosphaera carteri, Umbilicosphaera spp. and S. pulchra; intermediate fluxes from June to November, with high abundance of the deep photic zone species Algirosphaera robusta, F. profunda, Gladiolithus flabellatus; and low fluxes from November to February, with high flux of A. robusta, S. pulchra and Syracosphaera spp. These three periods correspond to the seasonal changes in sea surface temperature and surface mixed layer depth. Coccolithophore fluxes from the central part of the Ionian Sea have been studied from a sediment trap mooring (9/1999-6/2001) at 500 and 2800 m water depth [3]. Peak coccolithophore export production is observed in May, a secondary peak is observed in September-October. The assemblages is dominated year-round by the cosmopolitan species E. huxleyi, followed by the deep-dwelling F. profunda and by several minor species (Syracosphaera pulchra, R. clavigera, A. robusta, G. flabellatus, Calcidiscus leptoporus, Umbellosphaera tenuis and small Syracosphaera spp.) which are most abundant during the summer period of upper water column stratification. A high seasonal pattern characterizes the coccolithophore assemblages from all the investigated areas of eastern Mediterranean and Black seas. The export production and biogenic carbonate fluxes are strongly dependent on the nutrient influx, the vertical mixing and sea surface temperatures of the water column, in a north-south and east-west transient.

Coccolithophore export fluxes were investigated via the analysis of sinking matter, obtained from Eastern Mediterranean time-series sediment traps moored in three open sites of the north-eastern Mediterranean Sea located in the Athos Basin of North Aegean (M2 site), Cretan Sea of South Aegean (M3 site) and at Ionian Sea (Nestor site). The aim of our study was to determine the spatial, temporal and seasonal variability in coccolithophore fluxes, as well as to estimate coccolith biogenic carbonate contribution to the sedimentation process. Data from an additional time-series sediment trap located in the southwestern Black Sea were also considered for the comparison of the oligotrophic Eastern Mediterranean setting with the eutrophic Black Sea. Coccolithophore fluxes revealed a highly seasonal pattern during February–March in the North Aegean (peak in late February 2015: 85.6 x 105 coccospheres m−2 day−1; 27.9 x 108 coccoliths m−2 day−1), during March–May in the Cretan Sea (peak in late March 2015: 33.7 x 105 coccospheres m−2 day−1; 19.5 x 108 coccoliths m−2 day−1) and during February–March and May–June in the Ionian Sea (peak in late May 2012: 14.3 x 105 coccospheres m−2 day−1; 1.53 x 108 coccoliths m−2 day−1). The recorded maxima coincide with low sea surface temperatures, increased precipitation and high PIC fluxes. Coccosphere fluxes were dominated by Emiliania huxleyi comprising ~70% of the total abundance, in the North Aegean and ~50% in the Cretan and Ionian Seas. Syracosphaera pulchra was also prominent in the study sites, where its abundance reached 14% in the North Aegean and ~10% in the Cretan and Ionian Seas respectively. Florisphaera profunda represented one of the major taxa in the coccolith fluxes of all three Eastern Mediterranean sites (~25% in North Aegean, ~20% in Cretan and Ionian Seas), while Algirosphaera robusta and Umbilicosphaera sibogae were the most abundant among the minor taxa. The North Aegean Sea exhibited a considerably higher coccolith flux when compared to other sediment traps due to the prominent seasonal peak of E. huxleyi during winter (February–March) (>95% of the total abundance). In contrast to the Eastern Mediterranean sediment traps, the time-series data from the Black Sea showed presence of monospecific E. huxleyi assemblage increasing its abundance during late September–November (max 320 x 105 coccospheres m−2 day−1; at least 7.79 x 108 coccoliths m−2 day−1, coccolith flux derived only from coccospheres converted to coccoliths). In the Eastern Mediterranean, biogenic carbonate fluxes followed the general pattern of the total mass flux in all investigated areas, with the Black Sea coccolithophore CaCO3 flux being the lowest due to low the E. huxleyi coccolith mass. Overall, in the North Aegean Sea, coccolithophore fluxes are strongly dependent on surface waters nutrients enrichment due to winter vertical water column mixing, riverine inputs and Black Sea water inflows, while the fertilization and/or formation of fast-sinking aggregates due to episodic dust input event are affecting the coccolithophore fluxes in the Cretan and Ionian Seas. The intercomparison of the coccolith export fluxes in the studied NE-SW mooring transects implies a north-south and east-west decreasing pattern, depending on the variable oceanographic regimes and the associated environmental factors controlling the investigated areas.