Planktonic foraminiferal abundance and flux in the Porcupine Seabight, Northeast Atlantic

Modern planktonic foraminifera collected with a sediment trap and subfossil assemblages from surface sediments from Galway Mound in the Porcupine Seabight off southwestern Ireland, northeastern Atlantic, were studied to show recent assemblage variations. The sediment trap operated from April to August 2004 and covers the spring bloom and early summer conditions with sampling intervals of 8 days. Eleven different species were recorded. Glorotalia hirsuta, Turborotalita quinqueloba and Globigerinita glutinata appeared predominately in spring. Neogloboquadrina incompta, Globigerina bulloides and Globorotalia inflata were abundant in spring and summer. The highest foraminiferal tests flux occured in June. The faunal composition was similar to subfossil assemblages from surface sediments, but the species proportions were different. This was mainly affected by the subtropical G. hirsuta, which was frequent in 2004 and rare in surface sediment samples and in earlier plankton collections from the southern Porcupine Seabight that were performed during the 1990s. The weight of deposited foraminifera is mainly influenced by spring bloom as indicated by sea-surface chlorophyll-a data. The top three-ranked species, G. hirsuta, N. incompta and G. bulloides contributed 87 % to the foraminiferal carbonate flux at Galway Mound. Foraminiferal carbonate and shell flux as well as the shell size revealed variations, which are related to lunar periodicity. The data infer a lunar pacing of reproduction for the main species as well as for G. glutinata and G. inflata, which was not recorded before.

Radiocarbon dating on cold-water corals, grain size, Corg, and benthic foraminfera assemblage of two sediment cores from the Ionian Sea

Continuous sedimentary records from an eastern Mediterranean cold-water coral ecosystem thriving in intermediate water depths (~600 m) reveal a temporary extinction of cold-water corals during the Early to Mid Holocene from 11.4-5.9 cal kyr BP. Benthic foraminiferal assemblage analysis shows low-oxygen conditions of 2 ml l**-1 during the same period, compared to bottom-water oxygen values of 4-5 ml l**-1 before and after the coral-free interval. The timing of the corals' demise coincides with the sapropel S1 event, during which the deep eastern Mediterranean basin turned anoxic. Our results show that during the sapropel S1 event low oxygen conditions extended to the rather shallow depths of our study site in the Ionian Sea and caused the cold-water corals temporary extinction. This first evidence for the sensitivity of cold-water corals to low oceanic oxygen contents suggests that the projected expansion of tropical oxygen minimum zones resulting from global change will threaten cold-water coral ecosystems in low latitudes in the same way that ocean acidification will do in the higher latitudes.

Accumulation rates of dinoflagellate cysts at trap sites CB2, CB3, CB4, and CB9 off Cape Blanc

A 5-year sediment trap survey in the upwelling area off Cape Blanc (NW Africa) provides information on the seasonal and annual resting cyst production of dinoflagellates, their sinking characteristics and preservation potential. Strong annual variation in cyst production characterizes the region. Cyst production of generally all investigated species, including Alexandrium pseudogonyaulax (Biecheler) T. Horig. ex T. Kita et Fukuyo (cyst genus Impagidinium) and Gonyaulax spinifera (Clap. et J. Lachm.) Diesing (cyst genus Nematosphaeropsis) was enhanced with increasing upper water nutrient and trace-element concentrations. Cyst production of Lingulodinium polyedrum (F. Stein) J. D. Dodge was the highest at the transition between upwelling and upwelling-relaxation. Cyst production of Protoperidinium americanum (Gran et Braarud) Balech, Protoperidinium monospinum (Paulsen) K. A. F. Zonn. et B. Dale, and Protoperidinium stellatum (D. Wall) Balech, and heterotrophic dinoflagellates forming Brigantedinium spp. and Echinidinium aculeatum Zonn., increased most pronouncedly during upwelling episodes. Production of Protoperidinium conicum (Gran) Balech and Protoperidinium pentagonum (Gran) Balech cysts and total diatom valves were related, providing evidence of a predator-prey relationship. The export cyst-flux of E. aculeatum, P. americanum, P. monospinum, and P. stellatum was strongly linked to the flux of total diatom valves and CaCO3, whereas the export production of Echinidinium granulatum Zonn. and Protoperidinium subinerme (Paulsen) A. R. Loebl. correlated with total organic carbon, suggesting potential consumption of diatoms, prymnesiophytes, and organic matter, respectively. Sinking velocities were at least 274 m · d**-1, which is in range of the diatom- and coccolith-based phytoplankton aggregates and "slower" fecal pellets. Species-selective degradation did not occur in the water column, but on the ocean floor.