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Alkenones are found in diverse prymnesiophytes including Emiliania huxleyi , which ranges throughout the world ocean. The number of double bonds in alkenones corresponds with growth temperature, and calibrations between sea surface temperature and alkenone unsaturation have been used to establish alkenone unsaturation as a temperature proxy in ancient sediments. Here we report virus infection causes a relative increase in the proportion of diunsaturated alkenones in E. huxleyi strain CCMP 374. As virus infection routinely terminates E. huxleyi blooms in the ocean, it is possible that this contributes to the variance in alkenone-based temperature estimates for core-top sediments.

SummaryPhytoplankton blooms are ephemeral events of exceptionally high primary productivity that regulate the flux of carbon across marine food webs [1–3]. Quantification of bloom turnover [4] is limited by a fundamental difficulty to decouple between physical and biological processes as observed by ocean color satellite data. This limitation hinders the quantification of bloom demise and its regulation by biological processes [5, 6], which has important consequences on the efficiency of the biological pump of carbon to the deep ocean [7–9].Here, we address this challenge and quantify algal blooms’ turnover using a combination of satellite and in situ data, which allows identification of a relatively stable oceanic patch that is subject to little mixing with its surroundings. Using a newly developed multisatellite Lagrangian diagnostic, we decouple the contributions of physical and biological processes, allowing quantification of a complete life cycle of a mesoscale (∼10–100 km) bloom of coccolithophores in the North Atlantic, from exponential growth to its rapid demise. We estimate the amount of organic carbon produced during the bloom to be in the order of 24,000 tons, of which two-thirds were turned over within 1 week. Complimentary in situ measurements of the same patch area revealed high levels of specific viruses infecting coccolithophore cells, therefore pointing at the importance of viral infection as a possible mortality agent. Application of the newly developed satellite-based approaches opens the way for large-scale quantification of the impact of diverse environmental stresses on the fate of phytoplankton blooms and derived carbon in the ocean.

This study focuses on the potential explanations for a Phaeocystis antarctica summer bloom occurred in stratified waters of Terra Nova Bay (TNB) - which is part of the Antarctic Special Protected Area (n.161) in the Ross Sea - trough a multi-parameter correlative approach. Many previous studies have highlighted that water column stratification typically favors diatom dominance compared to the colonial haptophyte P. antarctica, in the Ross Sea, and this correlation has often been used to explain the historic dominance of diatoms in TNB. To explore the spatial and temporal progression of P. antarctica bloom in coastal waters, four stations were sampled three times each between December 31, 2009 and January 13, 2010. Taxonomic and pigment composition of phytoplankton communities, macro-nutrient concentrations and various different indices, all indicated the relative dominance of P. antarctica. Cell abundances revealed that P. antarctica contributed 79% of total cell counts in the upper 25 m and 93% in the lower photic zone. Similarly, a strong correlation was observed between Chl-a and the Hex:Fuco pigment ratio, corroborating the microscopic analyses. Recent studies have shown that iron can trigger colonial P. antarctica blooms. Based on the Hex:Chl-c3 proxy for iron limitation in P. antarctica, we hypothesize that anomalously higher iron fluxes were responsible for the unusual bloom of colonial P. antarctica observed in TNB.

During two cruises to the Ross Sea, Antarctica in austral spring and summer, fast repetition rate fluorometry was used to investigate the relationship between phytoplankton photophysiology and water mass characteristics, micronutrient availability, and composition. Particulate organic matter proxies for phytoplankton biomass (chlorophyll a, particulate organic carbon and nitrogen, and biogenic silica) were all elevated in the photic zone during spring and summer. Biogenic silica concentrations were an order of magnitude higher in summer relative to spring, reflecting a shift in composition from Phaoecystis antarctica to diatoms. Quantum yields of PS II (Fv/Fm) were generally higher in spring relative to summer, coincident with weaker vertical and horizontal gradients in hydrographic properties. Reduced Fv/Fm values (

We report results from two surveys of pCO2, biological O2 saturation (DO2/Ar) and dimethylsulfide (DMS) in surface waters of the Ross Sea polynya. Measurements were made during early spring (November 2006–December 2006) and mid-summer (December 2005–January 2006) using ship-board membrane inlet mass spectrometry (MIMS) for high spatial resolution (i.e. sub-km) analysis. During the early spring survey, the polynya was in the initial stages of development and exhibited a rapid increase in open water area and phytoplankton biomass over the course of our � 3 week occupation. We observed a rapid transition from a net heterotrophic ice-covered system (supersaturated pCO2 and undersaturated O2) to a high productivity regime associated with a Phaeocystis-dominated phytoplankton bloom. The timing of the early spring phytoplankton bloom was closely tied to increasing sea surface temperature across the polynya, as well as reduced wind speeds and ice cover, leading to enhanced vertical stratification. There was a strong correlation between pCO2, DO2/Ar, DMS and chlorophyll a (Chl a) during the spring phytoplankton bloom, indicating a strong biological imprint on gas distributions. Box model calculations suggest that pCO2 drawdown was largely attributable to net community production, while gas exchange and shoaling mixed layers also exerted a strong control on the re-equilibration of mixed layer O2 with the overlying atmosphere. DMS concentrations were closely coupled to Phaeocystis biomass across the early spring polynya, with maximum concentrations exceeding 100 nM. During the summer cruise, we sampled a large net autotrophic polynya, shortly after the seasonal peak in phytoplankton productivity. Both diatoms and Phaeocystis were abundant in the phytoplankton assemblages during this time. Minimum pCO2 was less than 100 ppm, while DO2/Ar exceeded 30% in some regions. Mean DMS concentrations were � 2-fold lower than during the spring, although the range of concentrations was similar between the two surveys. There was a significant correlation between pCO2, DO2/Ar and Chl a across the summer polynya, but the strength of these correlations and the slope of O2 vs. CO2 relationship were significantly lower than during the early spring. Summertime DMS concentrations were not significantly correlated to phytoplankton biomass (Chl a), pCO2 or DO2/Ar. In contrast to the early spring time, there were no clear temporal trends in summertime gas concentrations. Rather, small-scale spatial variability, likely resulting from mixing and localized sea-ice melt, was clearly evident in surface gas distributions across the polynya. Analysis of length-scale dependent variability demonstrated that much of the spatial variance in surface water gases occurred at scales of o20 km, suggesting that high resolution analysis is needed to fully capture biogeochemical heterogeneity in this system.

14 pages,11 figures The major source of reduced sulfur in the remote marine atmosphere is the biogenic compound dimethylsulfide (DMS), which is ubiquitous in the world’s oceans and released through food web interactions. Relevant fluxes and concentrations of DMS, its phytoplankton-produced precursor, dimethylsulfoniopropionate (DMSP) and related parameters were measured during an intensive Lagrangian field study in two mesoscale eddies in the Sargasso Sea during July–August 2004, a period characterized by high mixed-layer DMS and low chlorophyll—the so-called ‘DMS summer paradox’. We used a 1-D vertically variable DMS production model forced with output from a 1-D vertical mixing model to evaluate the extent to which the simulated vertical structure in DMS and DMSP was consistent with changes expected from field-determined rate measurements of individual processes, such as photolysis, microbial DMS and dissolved DMSP turnover, and air–sea gas exchange. Model numerical experiments and related parametric sensitivity analyses suggested that the vertical structure of the DMS profile in the upper 60 m was determined mainly by the interplay of the two depth variable processes—vertical mixing and photolysis—and less by biological consumption of DMS. A key finding from the model calibration was the need to increase the DMS(P) algal exudation rate constant, which includes the effects of cell rupture due to grazing and cell lysis, to significantly higher values than previously used in other regions. This was consistent with the small algal cell size and therefore high surface area-to-volume ratio of the dominant DMSP-producing group—the picoeukaryotes. We gratefully acknowledge the financial assistance provided through NSF Biocomplexity funding (OPP-0083078) and an Australian Research Council Discovery Grant. We are grateful to the comments by D.J. Kieber. We recognize the participation and help of K. Bailey, J. Bisgrove, B. Blomquist, I. Forn, H. Harada, B. Huebert, D. Jones, L. Maroney, A. Neely, S. Riseman, C. Smith, J. Stefels, K. Tinklepaugh, M. Vila-Costa, G. Westby, H. Zemmelink and the R/V Seward Johnson crew. DiTullio et al., 2001; Simo ́ and Dachs, 2002; Simon and Azam, 1989; Zemmelink et al., 2005

The upwelling of nutrients and iron (Fe) sustains biological production in much of the Southern Ocean. Using a shipboard natural community continuous culture system (Ecostat), we supplied a single added Fe concentration at two dilution rates chosen to examine the effects of variations in realistic growth and loss rates on an Fe-limited algal community in the Antarctic Zone south of Australia. A parallel growout experiment provided “no-dilution” +Fe and −Fe controls. In the continuous flow experiment, phytoplankton biomass was lower and more constant throughout the incubation and major nutrients were never depleted. Nanophytoplankton abundance remained similar in both growout treatments, and therefore, growth of this group did not appear to be Fe-limited. The addition of Fe in a continuous fashion resulted in a community co-dominated by both small diatoms and nanophytoplankton. Increases in dilution rate favored diatom species that were smaller and faster-growing, as well as non-silicified algal groups. Particulate carbon (PC) to particulate nitrogen (PN) ratios increased above the Redfield ratio when Fe was added in a continuous fashion, while biogenic silica (BSi) to PC and PN ratios decreased 2–3 fold in the continuous flow experiment compared to the initial conditions and the parallel growout control experiment. Photosynthetic efficiency increased in the continuous flow treatments above the control but remained significantly lower than in the 1.4 nM Fe addition. The results of our shipboard continuous flow experiments are compared and contrasted with those of the mesoscale Southern Ocean Iron RElease Experiment (SOIREE) carried out at the same site. Our results suggest that increases in natural dilution rates (i.e. vertical turbulent diffusion) in polar Antarctic waters could shift the algal community towards smaller, faster-growing algal species, thus having a major effect on nutrient cycling and carbon export in the Southern Ocean.

Surface water transects and vertical profiles for dissolved iron, macronutrients, chlorophyll a (Chl a), and hydrographic data were obtained in the Peru upwelling regime during August and September 2000. The supply of the micronutrient iron, relative to that of the macronutrients nitrate, phosphate and silicic acid, is shown to play a critical role in allowing extensive diatom blooms to develop in the Peru upwelling system. The extremely high-chlorophyll bbrown waters of PeruQ (with Chl a concentrations between 20 and 45 Ag/l) result from massive diatom blooms with maximal photochemical efficiencies (Fv/Fm N0.6) occurring in the iron-rich upwelling region observed over the broad continental shelf off northern and central Peru. The source of the upwelled water in this region is the nutrient-rich subsurface countercurrent in contact with the organicrich shelf sediments. This subsurface shelf water is suboxic and has extremely high concentrations of dissolved Fe (N50 nM) in the near-bottom waters. In marked contrast, relatively low-chlorophyll bblue watersQ (Chl a b2 Ag/l) with low concentrations of dissolved Fe (b0.1 nM) and high unutilized macronutrient concentrations are observed in the coastal upwelled waters along the southern coast of Peru and in the offshore regions of the Peru Current. Southern Peru is a region without a wide shelf to serve as a source of iron and, as a result, dissolved Fe concentrations in the near-bottom suboxic waters of this region are an order-ofmagnitude lower than observed off northern and central Peru. In addition, the offshore Peru Current is a broad, Fe-limited, highnitrate, lower than expected chlorophyll region extending hundreds of kilometers offshore into the northeast region of the South Pacific subtropical gyre and northwestward into the South Equatorial Pacific. D 2004 Elsevier B.V. All rights reserved.

Over the last two decades, escalating rates of coastal development have altered macro- and micronutrient loading patterns to many southeastern U.S. estuaries. This study addresses a potential consequence of urbanization-associated coastal deforestation that may have important implications for estuarine ecosystem productivity: a reduction in bioavailable Fe. We compared the potential for Fe limitation at representative sites in two neighboring South Carolina salt marsh estuaries, one (“Parsonage Creek” site in Murrells Inlet estuary) impacted by urbanization-associated clear-cutting, and the other (“Oyster Landing” site in North Inlet estuary) undeveloped and surrounded by forests. The urbanized estuarine site was marked by lower dissolved Fe concentrations compared to the forested estuarine site. In bioassay experiments conducted from 1996 to 1999, the addition of chelated Fe to natural phytoplankton populations stimulated chlorophyll a concentrations in water from Parsonage Creek on 6 of 11 sampling dates. Chlorophyll responses in Oyster Landing water also were observed on two of those sampling times, dates that followed periods of relatively low rainfall. In one experiment, the addition of Fe+NO 3 − to Parsonage Creek water led to significantly higher chlorophyll concentrations than when NO 3 − was added alone, but Fe+NH 4 + addition did not result in higher chlorophyll than NH 4 + addition alone. It was hypothesized that the difference in NO 3 − and NH 4 + responses was related to a greater tendency towards Si depletion in Fe-stressed NO 3 − -grown samples, or alternatively, to the higher Fe requirement for NO 3 − assimilation relative to that needed for NH 4 + assimilation. In bioassay experiments using Fe-deplete semi-continuous cultures of Synechococcus WH8101, Fe addition did not affect the net growth rate of cultures transferred to water from either estuary, but increased the chlorophyll a content of cells transferred to Parsonage Creek water. Finally, photosynthesis vs. irradiance parameters ( α , P max ) obtained from Oyster Landing samples ( Synechococcus continuous cultures, while the same parameters derived from Parsonage Creek samples were much lower and comparable to those from Fe-deplete cultures. The results indicate that phytoplankton population growth from high salinity salt marsh estuaries can be Fe-limited. Also, the potential for Fe limitation was more prevalent in a urbanized deforested estuary than in an undeveloped forested estuary, consistent with the hypothesis that organically bound Fe from coastal forests plays an important role in supplying Fe for the growth of estuarine phytoplankton.

Dimethylsulfide (DMS), particulate dimethylsulfoniopropionate (DMSPp) and phytoplankton pigments were measured on three transects in the Ross Sea, Antarctica during February 1992. Although relatively low chl a levels (mean of 0.7 μg l−1) were encountered, the DMS inventory in the photic zone ranged from 81 to 3484 μol m−2. In comparison, the DMSOp standing stock was very low (range of 13–298μol m−2) and accounted for only 11% of the average integrated DMS concentration. DMS:chl a ratios (58–78 nmol μg−1) were significantly higher in waters dominated by Phaeocystis antarctica compared to diatom-dominated waters (2–12 nmol μg−1). A strong DMS gradient was observed from south to north with the highest DMS concentrations (123 nM) measured in the southern Ross Sea and the lowest (

Primary production was measured on four cruises to the subarctic Pacific Ocean as an integral component of the SUPER Project (SUbarctic Pacific Ecosystem Research). Results from 26 in situ experiments and 9 simulated in situ experiments yielded production rates that were significantly higher than measured during the earlier Canadian Weather Station program. The new estimate of annual primary production is ca 170g C m−2y−1, over three times greater than previously thought. Maximum production rates of over 1g C m−2d−1 also exceeded recent measurements made with ultraclean sampling technique. Photosynthesis versus irradiance experiments yielded average light-saturated, chlorophyll-specific assimilation rates of ca. 60mgC mgChl−1d−1, which, when combined with local estimates of algal C/Chl, suggested that the specific growth rate of phytoplankton exceeded one doubling per day under optimum conditions of irradiance. Although no spring phytoplankton blooms have ever been observed in the offshore subarctic Pacific, the primary production rates in this region are among the highest reported in any open-ocean environment; production per unit biomass does not seem limited to any extent. Removal processes, such as grazing and sinking, must necessarily play a major role in controlling the standing crop of phytoplankton in the subarctic Pacific.

During the ADIOS I (Asian Dust Input to the Oceanic System) expedition to 26°N, 155°W in the North Pacific Central Gyre (NPCG) atmospheric-oceanic disturbances caused significant changes in phytoplankton community dynamics. A low pressure disturbance and several major dust deposition events resulted in a 37 and 25% increase in autotrophic carbon and nitrogen assimilation rates, respectively, relative to the pre-storm rates. The integrated submicron autotrophic N-assimilation rate increased by 72%. This submicron autotrophic community was responsible for 63 ± 7% of total autotrophic N-assimilation. New production increased by up to a factor of 4 as a result of the disturbances. The areal Chl a concentration doubled with the most significant increase observed near the base of the photic zone. Chemotaxonomic identification by HPLC pigment analyses indicated that the characteristic pigment concentrations of all major phytoplankton classes (except prokaryotic algae) increased as a result of the disturbances. Water column stability estimates and NO 3 − gradient measurements indicated that turbulent vertical transport of NO 3 − across the pycnocline could not explain the observed increases in photosynthetic parameters. Near surface NO 3 − concentrations increased following a dust deposition event. In addition, a positive temporal correlation was observed between the atmospheric Al concentration and the near-surface Chl a concentration. The data suggested that atmospheric deposition of NO 3 − and Fe stimulated autotrophic growth. Atmospheric deposition of NO 3 − and Fe may significantly enhance new production rates in the NPCG, especially during episodic dust events.

Primary production rates and concentrations of photosynthetic pigments were measured on 5 days during March and April 1987, at 26°N, 155°W in the North Pacific subtropical gyre. The primary production measurements were carried out using on-deck incubators with blue and blue-violet filters which simulated both the intensity and spectral characteristics of submarine light. Dawn-to-dusk production rates averaged 777±219 mg C m−2. The quantum requirements implied by photosynthetic rates measured near the base of the euphotic zone approached the theoretical minimum of 8 Ein mol−1C if the chlorophyll a-specific absorption coefficient ( k c ) was assumed to equal 16 m2 g−1 Chl a. Both the absorption characteristics of extracted pigments and of particulate material collected on glass fiber filters indicated that k c was constant and equal to 16.0±1.6 m2 g−1 Chl a over the depth of the euphotic zone if submarine light were assumed to have the same spectral characteristics as surface light. When the spectral characteristics of submarine light were properly modeled, k c was found to increase by about a factor of three between the surface and approximately the 14% light level and to equal 44±7 m2 g−1 Chl a throughout the lower 75% of the euphotic zone. The dramatic difference in the ability of phytoplankton to absorb equal quantum fluxes of white and blue light implies that areal primary production rates can be underestimated by about a factor of two in the open ocean if incubations are conducted using surface light attenuated with neutral density filters.

Primary productivity (14C) and mass flux measurements using a free-drifting sediment trap deployed at 900 m were made at four stations in the Pacific Ocean between 12°N and 6°S at 153°W. The latitudinal variations in productivity were consistent with historical patterns showing the equator as a zone of high production and the oligotrophic waters north of the equatorial region as an area of low productivity. The correlation coefficient between the two sets of independent measurements was 0.999, indicating that in this oceanic area the activity of the primary producers was closely related to the total mass flux. A re-examination of historical data suggests that the downward flux of particulate organic carbon varies in direct proportion to the quotient of surface primary production raised to the 1.4 power and depth raised to the 0.63 power.

Phytoplankton photosynthetic rates and relative and absolute growth rates were estimated using 14 C techniques at five stations in the Carribean Sea and two stations in the western Atlantic. Integral photosynthetic rates at the Caribbean stations averaged (±1 S.D.) 633 ± 77 mg C m −2 d −1 . Light-saturated growth rates were about 0.6 d −1 . Relative growth rates averaged 85% in the surface mixed layer and 93% in the lower euphotic zone. Uptake of 14 C at night accounted for 26% of the integral production at the Caribbean stations. The specific activity of Chl a carbon increased at night, and growth rates inferred from this increase were highly correlated with nocturnal 14 C uptake. Based on the Chl a carbon specific activity data, about 76% of the nocturnal 14 C uptake was attributed to phytoplankton. This uptake may have represented assimilation of labeled DOC excreted during the photoperiod. Over 80% of the Chl a in the chlorophyll maximum layers fell in the picoplankton size range. Incubation of these populations at higher irradiance levels revealed no indication of light adaptation over a 24 h period, a result consistent with recent studies of Synechococcus . Chlorophyll maximum populations occurred at about the 3% light level and were estimated to be growing with a doubling time of a little over 2 days. Estimated phytoplankton carbon concentrations were virtually identical in the mixed layers and chlorophyll maxima. The latter were therefore the result of adaptation of the phytoplankton to low irradiance levels and did not represent biomass maxima.

A comparison of nitrogen assimilation rates based on uptake of 15 NH 4 + and incorporation of 14 CO 2 into protein at three stations near the Hawaiian Islands indicates that heterotrophic processes accounted for at least 50 to 75% of the NH 4 + uptake. These results suggest that bacteria may compete effectively with phytoplankton for inorganic nutrients in the sea.