(Table 1) Sample levels of diatom and silicoflagellate datums at DSDP Holes 69-504 and 69-505

A standard biostratigraphic system, based upon diatom datum levels previously correlated to the paleomagnetic record, was applied to Deep Sea Drilling Project Sites 501/504 and 505. Sedimentation appears to have been constant at the three sites, averaging 50 m/m.y. at Sites 501/504 and 60 m/m.y. at Site 505. Calcium carbonate is rather poorly preserved at both sites, because of depth of water and, at Sites 501/504, alteration by diagenesis. Siliceous microfossils are common and moderately well preserved at the three sites; at Sites 501/504, diatoms disappear abruptly below the first occurrence of chert. The uppermost Miocene diatom assemblage occurs just above chert and is characterized by a strong dominance of Thalassionema and Thalassiothrix, which implies very high silica production during the latest Miocene; the chert probably is derived from a similar assemblage. In the earliest Pliocene, silica production appears to have decreased sharply; about 3 Ma, preservation of calcium carbonate also diminished, suggesting a shoaling of the CCD. At 2 Ma, there occurred a short interval of low production of both calcium carbonate and silica, which lasted into the earliest Pleistocene.

Geochemistry and diatom abundances in sediment trap samples of Effingham Inlet, Canada

Sediment traps were deployed inside the anoxic inner basin of Effingham Inlet and at the oxygenated mouth of the inlet from May 1999 to September 2000 in a pilot study to determine the annual depositional cycle and impact of the 1999-2000 La Niña event within a western Canadian inlet facing the open Pacific Ocean. Total mass flux, geochemical parameters (carbon, nitrogen, opal, major and minor element contents, and stable isotope ratios) and diatom assemblages were determined and compared with meteorological and oceanographic data. Deposition was seasonal, with coarser grained terrestrial components and benthic diatoms settling in the autumn and winter, coincident with the rainy season. Marine sedimentary components and abundant pelagic diatoms were coincident with coastal upwelling in the spring and summer. Despite the seasonal differences in deposition, the typical temperate-zone Thalassiosira-Skeletonema-Chaetoceros bloom succession was muted. A July 1999 total mass flux peak and an increase in biogenous components coincided with a rare bottom-water oxygen renewal event in the inlet. Likewise, there were cooler-than-average sea surface temperatures (SSTs) just outside the inlet, and unusually high abundances of a previously undescribed cool-water marine diatom (Fragilariopsis pacifica sp. nov.) within the inlet. Each of these occurrences likely reflects a response to the strong La Niña that followed the year after the strongest-ever recorded El Niño event of 1997-1998. By the autumn of 1999, SSTs had returned to average, and F. pacifica had all but disappeared from the remaining trap record, indicating that oceanographic conditions had returned to normal. Oxygenation events were not witnessed in the inlet in the years before or after 1999, suggesting that a rare oceanographic and climatic event was captured by this sediment trap time series. The data from this record can therefore be used as a benchmark for identifying anomalous environmental conditions on this coast.

Photochemical responses of the diatom Skeletonema costatum grown under elevated CO2 concentrations to short-term changes in pH

Variability in pH is a common occurrence in many aquatic environments, due to physical, chemical and biological processes. In coastal waters, lagoons, estuaries and inland waters, pH can change very rapidly (within seconds or hours) in addition to daily and seasonal changes. At the same time, progressive ocean acidification caused by anthropogenic CO2 emissions is superimposed on these spatial and temporal pH changes. Photosynthetic organisms are therefore unavoidably subject to significant pH variations at the cell surface. Whether this will affect their response to long-term ocean acidification is still unknown, nor is it known whether the short-term sensitivity to pH change is affected by the pCO2 to which the cells are acclimated. We posed the latter open question as our experimental hypothesis: Does acclimation to seawater acidification affect the response of phytoplankton to acute pH variations? The diatom Skeletonema costatum, commonly found in coastal and estuarine waters where short-term acute changes in pH frequently occur, was selected to test the hypothesis. Diatoms were grown at both 390 (pH 8.2, low CO2; LC) and 1000 (pH 7.9, high CO2; HC) µatm CO2 for at least 20 generations, and photosynthetic responses to short-term and acute changes in pH (between 8.2 and 7.6) were investigated. The effective quantum yield of LC-grown cells decreased by ca. 70% only when exposed to pH 7.6; this was not observed when exposed to pH 7.9 or 8.2. HC-grown cells did not show significant responses in any pH treatment. Non-photochemical quenching showed opposite trends. In general, our results indicate that while LC-grown cells are rather sensitive to acidification, HC-grown cells are relatively unresponsive in terms of photochemical performance.

Diatom abundances in sediment core CESAR_83-006

The modern Arctic Ocean is regarded as a barometer of global change and amplifier of global warming (Graversen et al., 2008, doi:10.1038/nature06502) and therefore records of past Arctic change are critical for palaeoclimate reconstruction. Little is known of the state of the Arctic Ocean in the greenhouse period of the Late Cretaceous epoch (65-99 million years ago), yet records from such times may yield important clues to Arctic Ocean behaviour in near-future warmer climates. Here we present a seasonally resolved Cretaceous sedimentary record from the Alpha ridge of the Arctic Ocean. This palaeo-sediment trap provides new insight into the workings of the Cretaceous marine biological carbon pump. Seasonal primary production was dominated by diatom algae but was not related to upwelling as was previously hypothesized (Kitchell and Clark, 1982, doi:10.1016/0031-0182(82)90087-6). Rather, production occurred within a stratified water column, involving specially adapted species in blooms resembling those of the modern North Pacific subtropical gyre (Dore et al., 2008, doi:10.1016/j.pocean.2007.10.002), or those indicated for the Mediterranean sapropels (Kemp et al., 1999, doi:10.1038/18001). With increased CO2 levels and warming currently driving increased stratification in the global ocean (Sarmiento et al., 1998, doi:10.1038/30455), this style of production that is adapted to stratification may become more widespread. Our evidence for seasonal diatom production and flux testify to an ice-free summer, but thin accumulations of terrigenous sediment within the diatom ooze are consistent with the presence of intermittent sea ice in the winter, supporting a wide body of evidence for low temperatures in the Late Cretaceous Arctic Ocean (Falcon-Lang et al., 2004, doi:10.1016/j.palaeo.2004.05.016; Amiot et al., 2004, doi:10.1016/j.epsl.2004.07.015; Otto-Bliesner et al., 2002, doi:10.1029/2001JD000821), rather than recent suggestions of a 15 °C mean annual temperature at this time (Jenkyns et al., 2004, doi:10.1038/nature03143).

Effects of high CO2 levels on the ecophysiology of the diatom Thalassiosira weissflogii differ depending on the iron nutritional status

Iron availability in seawater, namely the concentration of dissolved inorganic iron ([Fe']), is affected by changes in pH. Such changes in the availability of iron should be taken into account when investigating the effects of ocean acidification on phytoplankton ecophysiology because iron plays a key role in phytoplankton metabolism. However, changes in iron availability in response to changes in ocean acidity are difficult to quantify specifically using natural seawater because these factors change simultaneously. In the present study, the availability of iron and carbonate chemistry were manipulated individually and simultaneously in the laboratory to examine the effect of each factor on phytoplankton ecophysiology. The effects of various pCO2 conditions (390, 600, and 800 µatm) on the growth, cell size, and elemental stoichiometry (carbon [C], nitrogen [N], phosphorus [P], and silicon [Si]) of the diatom Thalassiosira weissflogii under high iron ([Fe'] = 240 pmol/l) and low iron ([Fe'] = 24 pmol/l) conditions were investigated. Cell volume decreased with increasing pCO2, whereas intracellular C, N, and P concentrations increased with increasing pCO2 only under high iron conditions. Si:C, Si:N, and Si:P ratios decreased with increasing pCO2. It reflects higher production of net C, N, and P with no corresponding change in net Si production under high pCO2 and high iron conditions. In contrast, significant linear relationships between measured parameters and pCO2 were rarely detected under low iron conditions. We conclude that the increasing CO2 levels could affect on the biogeochemical cycling of bioelements selectively under the iron-replete conditions in the coastal ecosystems.

Diatom biostratigraphy, Argon ages and chronology of ODP Hole 183-1138A

A thick Neogene section was recovered in the upper ~300 m of Ocean Drilling Program Hole 1138A, drilled on the Central Kerguelen Plateau in the Indian sector of the Southern Ocean. Sediment lithologies consist primarily of mixed carbonate and biosiliceous clays and oozes, with several thin (1-3 cm) tephra horizons. The tephras are glass rich, well sorted, and dominantly trachytic to rhyolitic in composition. Volcaniclastic material in these horizons is interpreted to have originated from Heard Island, 180 km northwest of Site 1138, and was likely emplaced through both primary ash fall and turbiditic, submarine flows. A Neogene age-depth model for Hole 1138A is constructed primarily from 36 diatom biostratigraphic datums. Nannofossil and planktonic foraminifer biostratigraphy provides supporting age information. Additionally, four high-precision 40Ar-39Ar ages are derived from ash and tephra horizons, and these radiometric ages are in close agreement with the biostratigraphic ages. The integrated age-depth model reveals a reasonably complete lower Miocene to upper Pleistocene section in Hole 1138A, with the exception of a ~1-m.y. hiatus at the Miocene/Pliocene boundary. Another possible hiatus is also identified at the Oligocene/Miocene boundary. High Neogene sedimentation rates and the presence of both calcareous and siliceous microfossils, combined with datable tephra horizons, establish Site 1138 as a suitable target for future drilling legs with paleoceanographic objectives. This report also proposes two new diatom species, Fragilariopsis heardensis and Azpeitia harwoodii, from Pliocene strata of Hole 1138A.

Effects of pCO2 and iron on the elemental composition and cell geometry of the marine diatom Pseudo-nitzschia pseudodelicatissima//(Bacillariophyceae)

Partial pressure of CO2 (pCO2) and iron availability in seawater show corresponding changes due to biological and anthropogenic activities. The simultaneous change in these factors precludes an understanding of their independent effects on the ecophysiology of phytoplankton. In addition, there is a lack of data regarding the interactive effects of these factors on phytoplankton cellular stoichiometry, which is a key driving factor for the biogeochemical cycling of oceanic nutrients. Here, we investigated the effects of pCO2 and iron availability on the elemental composition (C, N, P, and Si) of the diatom Pseudo-nitzschia pseudodelicatissima (Hasle) Hasle by dilute batch cultures under 4 pCO2 (~200, ~380, ~600, and ~800 µatm) and five dissolved inorganic iron (Fe'; ~5, ~10, ~20, ~50, and ~100 pmol /L) conditions. Our experimental procedure successfully overcame the problems associated with simultaneous changes in pCO2 and Fe' by independently manipulating carbonate chemistry and iron speciation, which allowed us to evaluate the individual effects of pCO2 and iron availability. We found that the C:N ratio decreased significantly only with an increase in Fe', whereas the C:P ratio increased significantly only with an increase in pCO2. Both Si:C and Si:N ratios decreased with increasing pCO2 and Fe'. Our results indicate that changes in pCO2 and iron availability could influence the biogeochemical cycling of nutrients in future oceans with high- CO2 levels, and, similarly, during the time course of phytoplankton blooms. Moreover, pCO2 and iron availability may also have affected oceanic nutrient biogeochemistry in the past, as these conditions have changed markedly over the Earth's history.

Light-modulated responses of growth and photosynthetic performance to ocean acidification in the model diatom Phaeodactylum tricornutum

Ocean acidification (OA) due to atmospheric CO2 rise is expected to influence marine primary productivity. In order to investigate the interactive effects of OA and light changes on diatoms, we grew Phaeodactylum tricornutum, under ambient (390 ppmv; LC) and elevated CO2 (1000 ppmv; HC) conditions for 80 generations, and measured its physiological performance under different light levels (60 µmol/m**2/s, LL; 200 µmol/m**2/s, ML; 460 µmol/m**2/s, HL) for another 25 generations. The specific growth rate of the HC-grown cells was higher (about 12-18%) than that of the LC-grown ones, with the highest under the ML level. With increasing light levels, the effective photochemical yield of PSII (Fv'/Fm') decreased, but was enhanced by the elevated CO2, especially under the HL level. The cells acclimated to the HC condition showed a higher recovery rate of their photochemical yield of PSII compared to the LC-grown cells. For the HC-grown cells, dissolved inorganic carbon or CO2 levels for half saturation of photosynthesis (K1/2 DIC or K1/2 CO2) increased by 11, 55 and 32%, under the LL, ML and HL levels, reflecting a light dependent down-regulation of carbon concentrating mechanisms (CCMs). The linkage between higher level of the CCMs down-regulation and higher growth rate at ML under OA supports the theory that the saved energy from CCMs down-regulation adds on to enhance the growth of the diatom.

Abundance of diatom cells in sediments from the Okhotsk and Bering Seas and the Northwest Pacific Ocean

The present investigation was targeted at diatom composition studies in the surface sediments (0-1 cm) sampled in the Sea of Okhotsk and the northwest Pacific in the depth range from 130 to 6110 m. The taxonomic analysis, as well as the quantitative (the diatom cell abundance per sediment dry weight unit) content and ecological group definition, was applied. Ten diatom taxa are the main body (80-100%) of the diatom assemblages: Bacterosira bathyomphala, Chaetoceros spp. (spores), Actinocyclus curvatulus, Thalassiosira latimarginata (group), T. antarctica (spores), Neodenticula seminae, Rhizosolenia hebetata f. hiemalis, Thalassiothrix longissima, Coscinodiscus marginatus, Coscinodiscus oculus iridis. The relative content of these species reflects the sedimentation conditions for different parts of the sea: the shelf, the continental slope, the open sea, and the ocean. The highest diatom content (45.6.3-60.0 mln per g of dry weight) was found for the surface sediments in the central part of the Sea of Okhotsk and the continental slope of western Kamchatka.