Alkenon concentrations of Creatcesous sediments of DSDP Hole 76-534A (Table 1)

We here report the discovery of unusual distributions of long-chain alkenones (C37-C42) in two Cretaceous black shales from the Blake-Bahama Basin, western North Atlantic. These sediments are Cenomanian (c. 95 Ma) and mid-Albian (c. 105 Ma) in age, thus significantly extending the geological range of these compounds. The precise source of these lipids is, as yet, unknown, although they may derive from an ancient ancestor of Emiliania huxleyi.

Calcareous nannofossils in Neogene sediments of ODP Leg 117 holes

Calcareous nannofossils were studied in 574 Neogene samples recovered from eight sites drilled in block-faulted basins on the continental margin of Oman. This portion of the Arabian Sea experiences seasonal upwelling associated with the southwest monsoon. Not surprisingly, some of the more typical Neogene warm-water nannoplankton are either missing entirely or are extremely rare in these sediments. Coccolithus pelagicus, a typical cold-water indicator, is extremely abundant in many samples of late Pliocene to early Pleistocene age. These intervals correspond to periods of Northern Hemisphere glaciation. Reworked Late Cretaceous and Cenozoic nannofossils are found in a majority of the samples. They were probably carried from the Arabian Peninsula or the continent of Africa on strong southwest summer winds. Ages for the various nannofossil events were calculated by projecting the nannofossil datums onto the magnetostratigraphic scale for Sites 724, 727, and 728. These are the first ages for the various nannofossil datums derived from Oman Margin sediments. The following ages have been calculated for these nannofossil events: FAD Emiliania huxleyi, 0.23 Ma; LAD Pseudoemiliania lacunosa, 0.38 Ma; FAD Helicosphaera inversa, 0.42 Ma; top of acme of Reticulofenestra sp. A, 0.70 Ma; FAD Gephyrocapsaparallela, 0.85 Ma; LAD Gephyrocapsa spp. (large), 1.07 Ma; LAD Helicosphaera sellii, 1.34 Ma; LAD Calcidiscus macintyrei, 1.47 Ma; FAD Gephyrocapsa oceanica, 1.53 Ma; FAD Gephyrocapsa caribbeanica, 1.80 Ma; LAD Discoaster brouweri, 2.03 Ma; LAD Discoasterpentaradiatus, 2.31 Ma; LAD Discoaster surculus, 2.42; LAD Discoaster tamalis, 2.77 Ma; LAD Sphenolithus abies, 3.44 Ma; and LAD Reticulofenestra pseudoumbilica, 3.44 Ma.

Calcareous nannofossil abundance and datums of ODP Leg 189 sites

Quaternary sediments were recovered at all five sites drilled during Ocean Drilling Program (ODP) Leg 189 in the Tasmanian Gateway. Two of these sites lie north of the present-day Subtropical Front (STF), and three sites lie south of the STF. Quaternary sediments recovered at Sites 1168, 1170, 1171, and 1172 were studied in detail to determine the calcareous nannofossil biostratigraphy and construct an age model for these sediments. The Pliocene/Pleistocene boundary was identified by the last occurrence (LO) of Discoaster brouweri at Site 1172 and approximated by the LO of Calcidiscus macintyrei at the other sites because of a lack of discoasterids. A hiatus encompassing the entire Helicosphaera sellii Zone was tentatively identified at Sites 1168 and 1172 by the coincident LOs of C. macintyrei and H. sellii. Similar hiatuses have been noted at ODP Site 1127 on the Great Australian Bight, Deep Sea Drilling Project Site 282 off the Tasman subcontinent, and ODP Site 1165 in Prydz Bay, Antarctica.

Calcareous nannofossils in Pliocene and Quaternary sediments of ODP Leg 117 holes

A total of 21 calcareous nannofossil datums was found in the upper Pliocene and Quaternary sediments recovered from the ocean floor of the North Atlantic during DSDP Leg 94. These datums were correlated to magnetostratigraphy, and ages were estimated by interpolation between magnetic reversals. Calcareous nannofossil assemblages from 549 samples recovered during ODP Leg 117 were studied in order to estimate the age of the sediments of Sites 720, 721, 722, and 731 drilled at the Indus Fan and the Owen Ridge in the Arabian Sea, Indian Ocean. We also showed that the datums above mentioned can be traced into the Indian Ocean. Two new species, namely Helicosphaera omanica and Reticulofenestra ampla, are described.

Abundance of living coccolithophores in the northern Arabian Sea (Table 2)

The present study was conducted to provide information about living coccolithophores from the northern Arabian Sea as potential proxies in palaeoceanographic studies. In all, 71 plankton samples from 16 stations collected in September 1993 were analysed for their contents of living coccolithophores. Absolute abundances range from less than 400 coccospheres per litre in surface waters to 35 000 spheres per litre at intermediate water depths. From 49 identified taxa, nine species contribute significant cell numbers of more than 2000 coccospheres per litre and comprise more than 10% of the communities in at least one sample. Important species are (in approximate order of cell abundances): Gephyrocapsa oceanica, Florisphaera profunda, Oolithotus antillarum, Calciosolenia murrayi, Umbellosphaera irregularis, Emiliania huxleyi, Umbellosphaera tenuis, Calciopappus rigidus, and Algirosphaera robusta. At most profiles, a vertical succession of coccolithophore species was found. Calciosolenia murrayi and C. rigidus were restricted to surface waters, whereas high numbers of F. profunda and A. robusta occurred at depths below 40 m. The coccolithophore communities reflected the local oceanographic situation and seemed to be more dependent on mixed layer depth and nutrient availability than on temperature and salinity changes. Additionally, synecologic competition with diatoms in part controlled the species composition and generally reduced the abundance of coccolithophores. Synecological and ecological tolerances of species were discussed with the help of cluster analysis.

Theoretical model simulations for variations in thermal reaction norms

Thermal reaction norms for growth rates of six Emiliania huxleyi isolates originating from the central Atlantic (Azores, Portugal) and five isolates from the coastal North Atlantic (Bergen, Norway) were assessed. We used the template mode of variation model to decompose variations in growth rates into modes of biological interest: vertical shift, horizontal shift, and generalist-specialist variation. In line with the actual habitat conditions, isolates from Bergen (Bergen population) grew well at lower temperatures, and isolates from the Azores (Azores population) performed better at higher temperatures. The optimum growth temperature of the Azores population was significantly higher than that of the Bergen population. Neutral genetic differentiation was found between populations by microsatellite analysis. These findings indicate that E. huxleyi populations are adapted to local temperature regimes. Next to between-population variation, we also found variation within populations. Genotype-by-environment interactions resulted in the most pronounced phenotypic differences when isolates were exposed to temperatures outside the range they naturally encounter. Variation in thermal reaction norms between and within populations emphasizes the importance of using more than one isolate when studying the consequences of global change on marine phytoplankton. Phenotypic plasticity and standing genetic variation will be important in determining the potential of natural E. huxleyi populations to cope with global climate change.

Dimethylsulphide (DMS), dimethylsulphonioproionate (DMSP) and halocarbon concentrations taken from 25m integrated samples during the 2011 SOPRAN Bergen Raunefjord Mesocosm experiment, Norway

The human-induced rise in atmospheric carbon dioxide since the industrial revolution has led to increasing oceanic carbon uptake and changes in seawater carbonate chemistry, resulting in lowering of surface water pH. In this study we investigated the effect of increasing CO2 partial pressure (pCO2) on concentrations of volatile biogenic dimethylsulfide (DMS) and its precursor dimethylsulfoniopropionate (DMSP), through monoculture studies and community pCO2 perturbation. DMS is a climatically important gas produced by many marine algae: it transfers sulfur into the atmosphere and is a major influence on biogeochemical climate regulation through breakdown to sulfate and formation of subsequent cloud condensation nuclei (CCN). Overall, production of DMS and DMSP by the coccolithophore Emiliania huxleyi strain RCC1229 was unaffected by growth at 900 µatm pCO2, but DMSP production normalised to cell volume was 12 % lower at the higher pCO2 treatment. These cultures were compared with community DMS and DMSP production during an elevated pCO2 mesocosm experiment with the aim of studying E. huxleyi in the natural environment. Results contrasted with the culture experiments and showed reductions in community DMS and DMSP concentrations of up to 60 and 32 % respectively at pCO2 up to 3000 µatm, with changes attributed to poorer growth of DMSP-producing nanophytoplankton species, including E. huxleyi, and potentially increased microbial consumption of DMS and dissolved DMSP at higher pCO2. DMS and DMSP production differences between culture and community likely arise from pH affecting the inter-species responses between microbial producers and consumers.

Adaptive evolution of a key phytoplankton species to ocean acidification

Ocean acidification, the drop in seawater pH associated with the ongoing enrichment of marine waters with carbon dioxide from fossil fuel burning, may seriously impair marine calcifying organisms. Our present understanding of the sensitivity of marine life to ocean acidification is based primarily on short-term experiments, in which organisms are exposed to increased concentrations of CO2. However, phytoplankton species with short generation times, in particular, may be able to respond to environmental alterations through adaptive evolution. Here, we examine the ability of the world's single most important calcifying organism, the coccolithophore Emiliania huxleyi, to evolve in response to ocean acidification in two 500-generation selection experiments. Specifically, we exposed E. huxleyi populations founded by single or multiple clones to increased concentrations of CO2. Around 500 asexual generations later we assessed their fitness. Compared with populations kept at ambient CO2 partial pressure, those selected at increased partial pressure exhibited higher growth rates, in both the single- and multiclone experiment, when tested under ocean acidification conditions. Calcification was partly restored: rates were lower under increased CO2 conditions in all cultures, but were up to 50% higher in adapted compared with non-adapted cultures. We suggest that contemporary evolution could help to maintain the functionality of microbial processes at the base of marine food webs in the face of global change.

Coccolithophore abundance and biometry in the South China Sea, 2014

Coccolithophore contributions to the global marine carbon cycle are regulated by the calcite content of their scales (coccoliths), and the relative cellular levels of photosynthesis and calcification. All three of these factors vary between coccolithophore species, and with response to the growth environment. Here, water samples were collected in the northern basin of the South China Sea (SCS) during summer 2014 in order to examine how environmental variability influenced species composition and cellular levels of calcite content. The vertical structure of the coccolithophore community was strongly regulated by mesoscale eddies. All living coccolithophores produced within the euphotic zone (1 % of surface irradiance), and Florisphaera profunda was a substantial coccolithophore and coccolith-calcite producer in the Deep Chlorophyll-a Maximum (DCM), especially in most oligotrophic anti-cyclonic eddy centers. Placolith-bearing coccolithophores, plus F. profunda, and other larger and numerically rare species made almost equal contributions to coccolith-based calcite in the water column. For Emiliania huxleyi biometry measurements, coccolith size positively correlated with nutrients, and it is suggested that coccolith length is influenced by nutrient and light related growth rates. However, larger sized coccoliths were related to low pH and calcite saturation, although it is not a simple cause and effect relationship. Genotypic or ecophenotypic variation may also be linked to coccolith size variation.

Alkenones and alkenes in surface waters and sediments of the Southern Ocean

The concentration of C37-C39 long-chain alkenones and alkenes were determined in surface water and surface sediment samples from the subpolar waters of the Southern Ocean. Distributions of these compounds were similar in both sample sets indicating little differential degradation between or within compound classes. The relative amounts of the tri- to tetra-unsaturated C37 alkenones increased with increasing temperature for temperatures below 6°C similar to the di- and tri-unsaturated C37 alkenones. The C37 di-, tri-, and tetra-unsaturated methyl alkenones are used in paleotemperature calculations via the U37K and the U37K ratios. In these datasets, the relative abundances of the C37:2 and the C37.3 alkenones as a proportion of the total C37 alkenones were opposite and strongly related to temperature (the latter with more scatter), but the abundance of the C37:4 alkenone showed no relationship with temperature. The original definition of U37K includes the abundance of 37:4 in both the numerator and denominator, and thus it is perhaps not surprising that there is considerable scatter in the values obtained for U37K at low temperatures. Of the two, we suggest that U37K' is the better parameter for use in paleotemperature estimations, even in cold locations. U37K' values in the sediments fall on virtually the same regression line obtained for the water column samples of Sikes and Volkman (1993, doi:10.1016/0016-7037(93)90120-L), indicating that their calibration is suitable for use in Southern Ocean sediments. The comparison of water column data with sedimentary temperature estimates suggests that the alkenone distributions are dominated by contributions from the summer when the biomass of Emiliania huxleyi and presumably flux to the sediment, is expected to be high.