Coccolithophore biogeographic trends and export production in the Eastern Mediterranean and Black Seas

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.