Coccolithophore species as indicators of surface oceanographic conditions in the vicinity of Azores islands

Abstract

During summer 2008 and spring 2009, surface oceanographic surveys were carried out around three islands of the Azores archipelago (Terceira, São Miguel and Santa Maria) to assess the phytoplankton distribution and associated physico-chemical processes. The Azores archipelago is a major feature in the biogeochemical North Atlantic Subtropical Gyre (NAST) province although its influence on the productivity of the surrounding ocean is poorly known. Surface phytoplankton was studied by microscopy and HPLC (High Precision Liquid Chromatography). The mean values for biomass proxy Chlorophyll a (Chla) ranged from 0.04 to 0.55 mg L À1 (Chla maximum ¼ 0.86 mg L À1) and coccolithophores were the most abundant group, followed by small flagellates, Cyanobacteria, diatoms and dinoflagellates being the least abundant group. The distribution of phytoplankton and coccolithophore species in particular presented seasonal differences and was consistent with the nearshore influence of warm subtropical waters from the south Azores current and colder subpolar waters from the north. The satellite-derived circulation patterns showed southward cold water intrusions off Terceira and northward warm water intrusions off Santa Maria. The warmer waters signal was confirmed by the subtropical coccolithophore assemblage, being Discosphaera tubifera a constant presence under these conditions. The regions of enhanced bio-mass, either resulting from northern cooler waters or from island induced processes, were characterized by the presence of Emiliania huxleyi. Diatoms and dinoflagellates indicated coastal and regional processes of nutrient enrichment and areas of physical stability, respectively.

The Azores Confluence Zone

“…The most striking results from this study were that: (i) the west group of islands are affected mostly by the Gulf Stream (bifurcation) filaments, meanders and eddies; whereas (ii) the east group is affected by westward-propagating eddies, most likely the ones pinching off from the Azores current. This also helps explain the different phytoplankton communities observed in the northern vs. southern islands as reported by Silva et al (2013); (iii) regional Ekman transport seems to be responsible for the confluence of these mesoscale phenomena in the Azores Archipelago; (iv) the differing physical nature of the dominant oceanographic processes that affect the west and the east groups are imprinted in their water mass composition as well as in their nutrient (climatological) profiles. At the surface, a tilted frontal region denotes the asymmetry between the dominant processes that affect both ends-i.e., west and east island groups; (v) the biological enrichment is very seasonal and very dependent on the shallowing of the nutricline; it often reaches the islands from the north from the Gulf Stream, or from the east (Azores Current); far-field enrichment strongly surpasses the intensity of the observed local enrichment.…”

“…The maximum value of phosphate concentration is located at a slightly shallower depth (800 m). This E-W asymmetry can also help explain the differences in phytoplankton organisms observed by Silva et al (2013), as well as suggest the incursion of sub-tropical warm waters (via filaments and/or eddies) from the Gulf Stream into the archipelago.…”

“…Most recently, Silva et al (2013) studied the seasonal differences of the nearshore phytoplankton communities and their probable relationship with a "southward intrusion of cold water, " and with a "northward incursion of sub-tropical warm water." Nonetheless, there were no attempts to relate these different observations to the regional ocean circulation patterns.…”

Seasonal variability of the carbonate system and coccolithophore Emiliania huxleyi at a Scottish Coastal Observatory monitoring site

“…The presence of E. huxleyi has been used as proxy of oceanographic conditions (Silva et al, 2008(Silva et al, , 2013. In the North Sea the occurrence of E. huxleyi has been related to the inflows of water from the Atlantic and from the shelf west of Scotland, especially during the early summer (Holligan et al, 1993).…”

Spatial and temporal variability in coccolithophore abundance and distribution in the NW Iberian coastal upwelling system

“…In a study of the vertical distribution of extant coccolithophores, Baumann et al (2008) describe C. leptoporus as a deep-dwelling species, along with F. profunda. This species has shown broad tolerance to environmental conditions and has been related to warm and oligotrophic waters (Giraudeau, 1992;Silva et al, 2013) as well as to colder, fresher, and eutrophic waters (Baumann et al, 2016), in this and other regions. In this study, CCA points to a clear relationship of C. leptoporus with saltier, warmer, and poor-nutrient waters, and low levels of irradiance (Fig.…”