The Eocene Arctic Azolla bloom: environmental conditions, productivity and carbon drawdown.

Enormous quantities of the free-floating freshwater fern Azolla grew and reproduced in situ in the Arctic Ocean during the middle Eocene, as was demonstrated by microscopic analysis of microlaminated sediments recovered from the Lomonosov Ridge during Integrated Ocean Drilling Program (IODP) Expedition 302. The timing of the Azolla phase (approximately 48.5 Ma) coincides with the earliest signs of onset of the transition from a greenhouse towards the modern icehouse Earth. The sustained growth of Azolla, currently ranking among the fastest growing plants on Earth, in a major anoxic oceanic basin may have contributed to decreasing atmospheric pCO2 levels via burial of Azolla-derived organic matter. The consequences of these enormous Azolla blooms for regional and global nutrient and carbon cycles are still largely unknown. Cultivation experiments have been set up to investigate the influence of elevated pCO2 on Azolla growth, showing a marked increase in Azolla productivity under elevated (760 and 1910 ppm) pCO2 conditions. The combined results of organic carbon, sulphur, nitrogen content and 15N and 13C measurements of sediments from the Azolla interval illustrate the potential contribution of nitrogen fixation in a euxinic stratified Eocene Arctic. Flux calculations were used to quantitatively reconstruct the potential storage of carbon (0.9-3.5 10(18) gC) in the Arctic during the Azolla interval. It is estimated that storing 0.9 10(18) to 3.5 10(18) g carbon would result in a 55 to 470 ppm drawdown of pCO2 under Eocene conditions, indicating that the Arctic Azolla blooms may have had a significant effect on global atmospheric pCO2 levels through enhanced burial of organic matter.

Spiniferites cruciformis: a fresh water dinoflagellate cyst?

Palynological studies of cored lacustrine sediments from the late Quaternary of Lake Kastoria, northern Greece, revealed a Late Glacial interval with abundant dinoflagellate cysts. Cyst assemblages include two identifiable species, Spiniferites cruciformis and Gonyaulax apiculata. The presence of the fresh water species G. apiculata is consistent with the lacustrine setting of these deposits, but that of S. cruciformis is anomalous. Previously, this species has only been recorded in abundance from presumed brackish marine sediments from the Black Sea and Marmara Sea sediments where geochemical data clearly record brackish salinities. Therefore, it has been regarded as a low salinity cyst type with a wide range of morphological variation that some workers have suggested to reflect salinity fluctuations. Specimens from Greece display only part of the range of morphological variability previously described from these (brackish) marine settings. Encountered morphological variation includes ellipsoidal/pentameral and cruciform endocyst shapes with rare intermediate shapes, and highly variable septa development. Specimens characterized by extremely reduced ornamentation known from (brackish) marine environments have not been recorded. Our records of S. cruciformis indicate that: (1) it could thrive in fresh water conditions; and (2) that apparently most of the strong morphological variations of the cysts are an intrinsic phenomenon for this taxon, and may only partly be linked to salinity variations as suggested earlier. We suggest that S. cruciformis essentially is a fresh water taxon, and that its records in (brackish) marine environments, with the exception of specimens with strongly reduced ornamentation, may be due to transportation, to short-lived fresh water surface conditions in such environments, or to tolerance of the species to brackish conditions.

Two unusual new dinoflagellate cyst genera from the Bunde Borehole, Maastrichtian type area, southern Netherlands.

Maastrichtian and Danian deposits from the Bunde Borehole in the Maastrichtian type area contain the morphologically unusual dinoflagellate species Spumadinium felderorum gen. et sp. nov. and Lasagniella herngreenii gen. et sp. nov., both of which have archeopyles formed by the loss of several paraplates. In S. felderorum the paraplates forming the operculum or opercular pieces appear to be the third and fourth precingulars (3"-4") plus the first and second anterior intercalaries (1a-2a). This suggests that Spumadinium, although having a wall resembling some cribroperidinioids, is a cladopyxiinean. L. herngreenii is unique in having up to eight wall layers, separated and supported by buttresses. The archeopyle is also a combination type but formed by loss of one apical (3'), three anterior intercalary (1a-3a) and three precingular (3"-5") paraplates. Thus, Lasagniella is assignable to the Peridiniales. The distinctive morphology and restricted ranges of the two genera make them useful stratigraphic markers for the Upper Maastrichtian-Danian.

The terminal Paleozoic fungal event: evidence of terrestrial ecosystem destabilization and collapse.

Because of its prominent role in global biomass storage, land vegetation is the most obvious biota to be investigated for records of dramatic ecologic crisis in Earth history. There is accumulating evidence that, throughout the world, sedimentary organic matter preserved in latest Permian deposits is characterized by unparalleled abundances of fungal remains, irrespective of depositional environment (marine, lacustrine, fluviatile), floral provinciality, and climatic zonation. This fungal event can be considered to reflect excessive dieback of arboreous vegetation, effecting destabilization and subsequent collapse of terrestrial ecosystems with concomitant loss of standing biomass. Such a scenario is in harmony with predictions that the Permian-Triassic ecologic crisis was triggered by the effects of severe changes in atmospheric chemistry arising from the rapid eruption of the Siberian Traps flood basalts.