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In 2015, the largest recorded harmful algal bloom (HAB) occurred in the Northeast Pacific, causing nearly 100 million dollars in damages to fisheries and killing many protected marine mammals. Dominated by the toxic diatom Pseudo-nitzschia australis , this bloom produced high levels of the neurotoxin domoic acid (DA). Through molecular and transcriptional characterization of 52 near-weekly phytoplankton net-tow samples collected at a bloom hotspot in Monterey Bay, California, we identified active transcription of known DA biosynthesis ( dab ) genes from the three identified toxigenic species, including P. australis as the primary origin of toxicity. Elevated expression of silicon transporters ( sit1 ) during the bloom supports the previously hypothesized role of dissolved silica (Si) exhaustion in contributing to bloom physiology and toxicity. We find that coexpression of the dabA and sit1 genes serves as a robust predictor of DA one week in advance, potentially enabling the forecasting of DA-producing HABs. We additionally present evidence that low levels of iron could have colimited the diatom population along with low Si. Iron limitation represents an overlooked driver of both toxin production and ecological success of the low-iron-adapted Pseudo-nitzschia genus during the 2015 bloom, and increasing pervasiveness of iron limitation may fuel the escalating magnitude and frequency of toxic Pseudo-nitzschia blooms globally. Our results advance understanding of bloom physiology underlying toxin production, bloom prediction, and the impact of global change on toxic blooms., Competing Interests: Competing interests statement:The authors declare no competing interest.

Nitrification, the microbial oxidation of ammonium to nitrate, is a central part of the nitrogen cycle. In the ocean's surface layer, the process alters the distribution of inorganic nitrogen species available to phytoplankton and produces nitrous oxide. A widely held idea among oceanographers is that nitrification is inhibited by light in the ocean. However, recent evidence that the primary organisms involved in nitrification, the ammonia-oxidizing archaea (AOA), are present and active throughout the surface ocean has challenged this idea. Here we show, through field experiments coupling molecular genetic and biogeochemical approaches, that competition for ammonium with phytoplankton is the strongest regulator of nitrification in the photic zone. During multiday experiments at high irradiance a single ecotype of AOA remained active in the presence of rapidly growing phytoplankton. Over the course of this three day experiment, variability in the intensity of competition with phytoplankton caused nitrification rates to decline from those typical of the lower photic zone (60 nmol L-1 d-1) to those in well-lit layers (<1 nmol L-1 d-1). During another set of experiments, nitrification rates exhibited a diel periodicity throughout much of the photic zone, with the highest rates occurring at night when competition with phytoplankton is lowest. Together, the results of our experiments indicate that nitrification rates in the photic zone are more strongly regulated by competition with phytoplankton for ammonium than they are by light itself. This finding advances our ability to model the impact of nitrification on estimates of new primary production, and emphasizes the need to more strongly consider the effects of organismal interactions on nutrient standing stocks and biogeochemical cycling in the surface of the ocean.

Marine photosynthetic plankton are responsible for approximately 50 petagrams (10(15)) of carbon per year of net primary production, an amount equivalent to that on land. This primary production supports essentially all life in the oceans and profoundly affects global biogeochemical cycles and climate. This review discusses the general distribution of primary production in the sea, the processes that regulate this distribution, and how marine primary production is sensitive to climate variability and change. Statistical modes of ocean variability and their characteristic interannual to multi-decadal timescales over the last century are described. Recent in situ and satellite time-series of primary production can be clearly linked to interannual ocean variability. Global marine primary production appears to have increased over the past several decades in association with multi-decadal variations. A paleoclimate record extends discussion to the centennial scale, providing contrasting insights into how marine primary production might vary in the future.

Among eukaryotes, four major phytoplankton lineages are responsible for marine photosynthesis; prymnesiophytes, alveolates, stramenopiles, and prasinophytes. Contributions by individual taxa, however, are not well known, and genomes have been analyzed from only the latter two lineages. Tiny "picoplanktonic" members of the prymnesiophyte lineage have long been inferred to be ecologically important but remain poorly characterized. Here, we examine pico-prymnesiophyte evolutionary history and ecology using cultivation-independent methods. 18S rRNA gene analysis showed pico-prymnesiophytes belonged to broadly distributed uncultivated taxa. Therefore, we used targeted metagenomics to analyze uncultured pico-prymnesiophytes sorted by flow cytometry from subtropical North Atlantic waters. The data reveal a composite nuclear-encoded gene repertoire with strong green-lineage affiliations, which contrasts with the evolutionary history indicated by the plastid genome. Measured pico-prymnesiophyte growth rates were rapid in this region, resulting in primary production contributions similar to the cyanobacterium Prochlorococcus. On average, pico-prymnesiophytes formed 25% of global picophytoplankton biomass, with differing contributions in five biogeographical provinces spanning tropical to subpolar systems. Elements likely contributing to success include high gene density and genes potentially involved in defense and nutrient uptake. Our findings have implications reaching beyond pico-prymnesiophytes, to the prasinophytes and stramenopiles. For example, prevalence of putative Ni-containing superoxide dismutases (SODs), instead of Fe-containing SODs, seems to be a common adaptation among eukaryotic phytoplankton for reducing Fe quotas in low-Fe modern oceans. Moreover, highly mosaic gene repertoires, although compositionally distinct for each major eukaryotic lineage, now seem to be an underlying facet of successful marine phytoplankton.

In situ enrichment experiments have shown that the growth of bloom-forming diatoms in the major high-nitrate low-chlorophyll (HNLC) regions of the world's oceans is limited by the availability of iron. Yet even the largest of these manipulative experiments represents only a small fraction of an ocean basin, and the responses observed are strongly influenced by the proliferation of rare species rather than the growth of naturally dominant populations. Here we link unique fluorescence attributes of phytoplankton to specific physiological responses to nutrient stress, and use these relationships to evaluate the factors that constrain phytoplankton growth in the tropical Pacific Ocean on an unprecedented spatial scale. On the basis of fluorescence measurements taken over 12 years, we delineate three major ecophysiological regimes in this region. We find that iron has a key function in regulating phytoplankton growth in both HNLC and oligotrophic waters near the Equator and further south, whereas nitrogen and zooplankton grazing are the primary factors that regulate biomass production in the north. Application of our findings to the interpretation of satellite chlorophyll fields shows that productivity in the tropical Pacific basin may be 1.2-2.5 Pg C yr(-1) lower than previous estimates have suggested, a difference that is comparable to the global change in ocean production that accompanied the largest El Niño to La Niña transition on record.

The availability of iron is known to exert a controlling influence on biological productivity in surface waters over large areas of the ocean and may have been an important factor in the variation of the concentration of atmospheric carbon dioxide over glacial cycles. The effect of iron in the Southern Ocean is particularly important because of its large area and abundant nitrate, yet iron-enhanced growth of phytoplankton may be differentially expressed between waters with high silicic acid in the south and low silicic acid in the north, where diatom growth may be limited by both silicic acid and iron. Two mesoscale experiments, designed to investigate the effects of iron enrichment in regions with high and low concentrations of silicic acid, were performed in the Southern Ocean. These experiments demonstrate iron's pivotal role in controlling carbon uptake and regulating atmospheric partial pressure of carbon dioxide.

Much is known about how broad eukaryotic phytoplankton groups vary according to nutrient availability in marine ecosystems. However, genus- and species-level dynamics are generally unknown, although important given that adaptation and acclimation processes differentiate at these levels. We examined phytoplankton communities across seasonal cycles in the North Atlantic (BATS) and under different trophic conditions in the eastern North Pacific (ENP), using phylogenetic classification of plastid-encoded 16S rRNA amplicon sequence variants (ASVs) and other methodologies, including flow cytometric cell sorting. Prasinophytes dominated eukaryotic phytoplankton amplicons during the nutrient-rich deep-mixing winter period at BATS. During stratification ('summer') uncultured dictyochophytes formed ∼35 ± 10% of all surface plastid amplicons and dominated those from stramenopile algae, whereas diatoms showed only minor, ephemeral contributions over the entire year. Uncultured dictyochophytes also comprised a major fraction of plastid amplicons in the oligotrophic ENP. Phylogenetic reconstructions of near-full length 16S rRNA sequences established 11 uncultured Dictyochophyte Environmental Clades (DEC). DEC-I and DEC-VI dominated surface dictyochophytes under stratification at BATS and in the ENP, and DEC-IV was also important in the latter. Additionally, although less common at BATS, Florenciella -related clades (FC) were prominent at depth in the ENP. In both ecosystems, pelagophytes contributed notably at depth, with PEC-VIII (Pelagophyte Environmental Clade) and (cultured) Pelagomonas calceolata being most important. Q-PCR confirmed the near absence of P. calceolata at the surface of the same oligotrophic sites where it reached ∼1,500 18S rRNA gene copies ml–1 at the DCM. To further characterize phytoplankton present in our samples, we performed staining and at-sea single-cell sorting experiments. Sequencing results from these indicated several uncultured dictyochophyte clades are comprised of predatory mixotrophs. From an evolutionary perspective, these cells showed both conserved and unique features in the chloroplast genome. In ENP metatranscriptomes we observed high expression of multiple chloroplast genes as well as expression of a selfish element (group II intron) in the psaA gene. Comparative analyses across the Pacific and Atlantic sites support the conclusion that predatory dictyochophytes thrive under low nutrient conditions. The observations that several uncultured dictyochophyte lineages are seemingly capable of photosynthesis and predation, raises questions about potential shifts in phytoplankton trophic roles associated with seasonality and long-term ocean change. [ABSTRACT FROM AUTHOR]

Coastal upwelling regions are hotspots of biological productivity, supporting diverse communities of microbial life and metabolisms. Monterey Bay (MB), a coastal ocean embayment in central California, experiences seasonal upwelling of cold, nutrient-rich waters that sustain episodes of high phytoplankton production in surface waters. While productivity in surface waters is intimately linked to metabolisms of diverse communities of Archaea and Bacteria, a comprehensive understanding of the microbial community in MB is missing thus far, particularly in relation to the distinct hydrographic seasons characteristic of the MB system. Here we present the results of a 2-year microbial time-series survey in MB, investigating community composition and structure across spatiotemporal gradients. In deciphering these patterns, we used unique sequence variants (SVs) of the 16S rRNA gene (V4–V5 region), complemented with metagenomes and metatranscriptomes representing multiple depth profiles. We found clear depth-differentiation and recurring seasonal abundance patterns within planktonic communities, particularly when analyzed at finer taxonomic levels. Compositional changes were more pronounced in the upper 0–40 m of the water column, whereas deeper depths were characterized by temporally stable populations. In accordance with the dynamic nutrient profiles, the system appears to change from a Bacteroidetes- and Rhodobacterales-dominated upwelling period to an oceanic season dominated by oligotrophic groups such as SAR11 and picocyanobacteria. The cascade of environmental changes brought about by upwelling and relaxation events thus impacts microbial community structure in the bay, with important implications for the temporal variability of nutrient and energy fluxes within the MB ecosystem. Our observations emphasize the need for continued monitoring of planktonic microbial communities in order to predict and manage the behavior of this sensitive marine sanctuary ecosystem, over projected intensification of upwelling in the region. [ABSTRACT FROM AUTHOR]

A three‐dimensional physical‐biological model was used to study the dynamics of physical and biological processes in the central California Current System (CCS) from 1993 to 2016 and investigate its response to different climate modes. The variations of new production (NP) and nitrate fluxes in the central CCS showed robust seasonal and interannual variability. In the coastal upwelling region (0–150 km offshore), the variability of NP was associated with both coastal upwelling and alongshore nitrate advection. In the coastal transition zone (150–300 km offshore), it was related to nitrate fluxes that were determined primarily by the physics rather than nitrate concentration, with vertical mixing and offshore transport being dominant factors. In the offshore oceanic region (California Current; 300–1,000 km offshore), nitrate concentrations played a more important role in the variations of nitrate fluxes, and the NP variability was dominated by the nutrient supplies of vertical mixing and lateral transports. Although El Niño–Southern Oscillation can affect coastal upwelling, alongshore currents, and nitrate fluxes, the coastal NP responded to El Niño–Southern Oscillation mostly in the frequencies of <1 and >6 years. Pacific Decadal Oscillation and North Pacific Gyre Oscillation may affect the CCS ecosystem through large‐scale winds and stratification, modifying the circulation in the upper layer and leading to changes in nitrate concentration and NP. Plain Language Summary The central California Current System (CCS) is one of the most productive ecosystems in the global ocean, because strong coastal upwelling brings a large amount of subsurface nutrients to the sunlit layer and supports abundant phytoplankton growth. Understanding the response of this system to varying physical forcing is of great importance in predicting how marine ecosystem will evolve with global change. By using a three‐dimensional model, this study demonstrates that biological properties in the central CCS show strong interannual variability. The dominant driver leading to this variability varies in different subregions moving from the coast to offshore. Over the CCS, climate variability can cause variations in surface wind, stratification, sea level, and circulations at different time scales, which contribute to changes in nutrient supply and phytoplankton production. [ABSTRACT FROM AUTHOR]

Abstract Monterey Bay, California, has been sampled by ship at 2–3 week intervals during 1989–2011. Here we present the resulting time series of temperature, salinity, nitrate, chlorophyll and primary production over the 23-year record and correlate the nonseasonal anomalies and four Pacific Basin-scale climate indices. About half of Monterey Bay variability was captured by the seasonal cycle while half remained in the anomalies. Correlations revealed strong associations between temperature, salinity and nitrate, and weaker correlations between these anomalies and euphotic zone-integrated chlorophyll and primary production. Sub-euphotic zone physical and particularly nitrate anomalies were better predictors of the euphotic zone biological variables than were their surface anomalies. The strongest correlations between temperature, salinity and nitrate anomalies occurred in spring and summer (e.g. during upwelling). Conversely, spring and summer nitrate were less well correlated with the biological variables than during the remaining months due to nonlinearity in the biological response. Lagged cross-correlations generally showed decreasing correlation with increasing lag (0–12 months). The Monterey Bay anomalies were then correlated with four Pacific Basin-scale climate indices --- the Multivariate ENSO Index (MEI), the Pacific Decadal Oscillation (PDO), the El Niño Modoki Index (EMI), and the North Pacific Gyre Oscillation (NPGO). Temperature, salinity and nitrate were well-correlated to the indices (accounted for 20–25% of the variance) whereas chlorophyll and primary production were weakly- and often insignificantly-correlated with the indices (accounted for 4–10% of the variance). The MEI was most strongly and the EMI least strongly (usually insignificantly) correlated with the anomalies. Most indices were also significantly cross-correlated over the observation period. Seasonally, the MEI produced strong winter and weaker summer associations with temperature, salinity and nitrate, and weak negative correlations with the biological anomalies all year. The PDO showed similar but weaker associations. The EMI correlations were weak but revealed seasonal cycles similar in phasing to those of the MEI. The NPGO exhibited positive relationships with salinity, nitrate and the biological anomalies, all peaking in summer and fall, and a weak negative association with temperature. Index-leads-anomaly correlations did not generally strengthen with lag (0–12 months). All the anomalies exhibited trends, with temperature decreasing and salinity, nitrate and the biological anomalies increasing. Except for 200 m temperature, these trends were significant and substantial, with surface nitrate and euphotic-zone integrated chlorophyll and primary production increasing 1.69 uM, 7.27 mg m−2 and 510 mgC m−2 d−1 per decade, respectively. These Monterey Bay trends are consistent with other California Current results and Pacific Basin index trends over the same period, indicating that Monterey Bay fluctuates with the California Current and North Pacific Basin. [ABSTRACT FROM AUTHOR]

For terrestrial and marine benthic ecologists, landscape ecology provides a framework to address issues of complexity, patchiness, and scale—providing theory and context for ecosystem based management in a changing climate. Marine pelagic ecosystems are likewise changing in response to warming, changing chemistry, and resource exploitation. However, unlike spatial landscapes that migrate slowly with time, pelagic seascapes are embedded in a turbulent, advective ocean. Adaptations from landscape ecology to marine pelagic ecosystem management must consider the nature and scale of biophysical interactions associated with organisms ranging from microbes to whales, a hierarchical organization shaped by physical processes, and our limited capacity to observe and monitor these phenomena across global oceans. High frequency, multiscale, and synoptic characterization of the 4-D variability of seascapes are now available through improved classification methods, a maturing array of satellite remote sensing products, advances in autonomous sampling of multiple levels of biological complexity, and emergence of observational networks. Merging of oceanographic and ecological paradigms will be necessary to observe, manage, and conserve species embedded in a dynamic seascape mosaic, where the boundaries, extent, and location of features change with time. [ABSTRACT FROM AUTHOR]

The regulation of seasonal satellite-derived primary production (PP) was investigated within a 150 km coastal box in four eastern boundary upwelling systems (EBUS): California, Peru, Northwest Africa and Benguela. The following regulating factors were considered: (1) wind-driven nitrate supply; (2) iron supply inferred from proxies (shelf mud belt width, modeled atmospheric iron deposition, river discharge); (3) temperature; (4) light and (5) physical export consisting of offshore export, eddy-driven and wind-driven subduction. The ratio of potential new production (carbon-equivalent of nitrate supply) to primary production, termed the N-ratio, is shown to be an indicator of PP limitation by nitrate supply (low N-ratios) vs. inhibition by other factors (high N-ratios). The factors regulating PP were assessed by analyzing the N-ratios and computing spatial correlations between PP and each factor each month. The regulation of primary production was found to vary spatially, seasonally and from one EBUS to another. Macronutrient supply is shown to be the dominant regulating factor off Northwest Africa and during some seasons and locations in other systems. Light regulation within the mixed layer occurs in all EBUS in winter but may only inhibit PP (high N-ratios) off Peru and Benguela. Evidence for iron limitation was found in each EBUS (except Northwest Africa) at varying levels and was greatest off Peru during austral winter when iron demand by phytoplankton increases due to low light levels. Rapid offshore advection combined with wind-driven and/or eddy-driven subduction may inhibit PP off California. A simple generalization regarding the regulation of primary production in EBUS is not forthcoming. [ABSTRACT FROM AUTHOR]

The occurrence of nitrification in the oceanic water column has implications extending from local effects on the structure and activity of phytoplankton communities to broader impacts on the speciation of nitrogenous nutrients and production of nitrous oxide. The ammonia-oxidizing archaea, responsible for carrying out the majority of nitrification in the sea, are present in the marine water column as two taxonomically distinct groups. Water column group A (WCA) organisms are detected at all depths, whereas Water column group B (WCB) are present primarily below the photic zone. An open question in marine biogeochemistry is whether the taxonomic definition of WCA and WCB organisms and their observed distributions correspond to distinct ecological and biogeochemical niches. We used the natural gradients in physicochemical and biological properties that upwelling establishes in surface waters to study their roles in nitrification, and how their activity-ascertained from quantification of ecotype-specific ammonia monooxygenase (amoA) genes and transcripts-varies in response to environmental fluctuations. Our results indicate a role for both ecotypes in nitrification in Monterey Bay surface waters. However, their respective contributions vary, due to their different sensitivities to surface water conditions. WCA organisms exhibited a remarkably consistent level of activity and their contribution to nitrification appears to be related to community size. WCB activity was less consistent and primarily constrained to colder, high nutrient and low chlorophyll waters. Overall, the results of our characterization yielded a strong, potentially predictive, relationship between archaeal amoA gene abundance and the rate of nitrification. [ABSTRACT FROM AUTHOR]

Coupled measurements of nitrate (NO3-), nitrogen (N), and oxygen (O) isotopic composition (δ15NNO3 and δ18ONO3) were made in surface waters of Monterey Bay to investigate multiple N cycling processes occurring within surface waters. Profiles collected throughout the year at three sites exhibit a wide range of values, suggesting simultaneous and variable influence of both phytoplankton NO3- assimilation and nitrification within the euphotic zone. Specifically, increases in δ18ONO3 were consistently greater than those in δ15NNO3. A coupled isotope steady state box model was used to estimate the amount of NO3- supplied by nitrification in surface waters relative to that supplied from deeper water. The model highlights the importance of the branching reaction during ammonium (NH4+) consumption, in which NH4+ either serves as a substrate for regenerated production or for nitrification. Our observations indicate that a previously unrecognized proportion of nitrate-based productivity, on average 15 to 27%, is supported by nitrification in surface waters and should not be considered new production. This work also highlights the need for a better understanding of isotope effects of NH4+ oxidation, NH4+ assimilation, and NO3- assimilation in marine environments. [ABSTRACT FROM AUTHOR]

Provides information on a study which estimated primary production using phytoplankton utilization of nitrate for the Monterey Bay, California region. Model description; Results and discussion.

Presents research which measured dissolvable iron in transects across the California Current System (CCS) in March, 1997 and March, 1998. Role of iron availability in phytoplankton primary productivity; Results of upwelling in the CCS; Results of iron addition to CCS samples; Effects of the 1998 El Nino on iron levels; Primary source of iron in the CCS.

Abstract: This work quantifies the role of tropical instability waves (TIWs) in modulating nutrient and chlorophyll distributions in the equatorial Pacific through an analysis of satellite data and a case study of in situ observations. A TIW index is constructed to differentiate periods of strong and weak TIW activity. TIW impacts are first examined in monthly averaged satellite SST and chlorophyll data for three distinct regions north of the equator where TIWs are most active. The chlorophyll data are high-pass filtered to preserve the seasonal cycle and remove long-term trends. Although SST follows a predictable relationship with the TIW index, chlorophyll concentrations do not. Periods of high TIW activity are characterized by cooler SSTs but consistently low chlorophyll. A case study of individual TIW vortices demonstrates that their impact on nutrients and chlorophyll is a function of intensity. Strong TIWs drive reductions in nutrients and chlorophyll due to the subduction of nutrient-replete water north of the equator and the advection of nutrient-poor water toward the equator from adjacent to the upwelling zone. Weak TIWs do not drive these advective processes to the same degree, so retain elevated nutrients that fuel chlorophyll increases. The most positive effect on nutrients and chlorophyll by TIWs was observed during boreal winter, likely owing to thermocline topography. A shallower thermocline in combination with weak TIWs results in elevated nutrients and chlorophyll north of the equator. Given the variability associated with TIW intensity and season, generalizing TIW effects has proven difficult, but targeted Lagrangian studies will better characterize these dynamic features and their impact on elemental fluxes. [Copyright &y& Elsevier]

We used a 3-dimensional individual-based model (3-D IBM) of Peruvian anchovy to examine how spatial variation in environmental conditions affects larval and juvenile growth and survival, and recruitment. Temperature, velocity, and phytoplankton and zooplankton concentrations generated from a coupled hydrodynamic Nutrients–Phytoplankton–Zooplankton–Detritus (NPZD) model, mapped to a three dimensional rectangular grid, were used to simulate anchovy populations. The IBM simulated individuals as they progressed from eggs to recruitment at 10 cm. Eggs and yolk-sac larvae were followed hourly through the processes of development, mortality, and movement (advection), and larvae and juveniles were followed daily through the processes of growth, mortality, and movement (advection plus behavior). A bioenergetics model was used to grow larvae and juveniles. The NPZD model provided prey fields which influence both food consumption rate as well as behavior mediated movement with individuals going to grids cells having optimal growth conditions. We compared predicted recruitment for monthly cohorts for 1990 through 2004 between the full 3-D IBM and a point (0-D) model that used spatially-averaged environmental conditions. The 3-D and 0-D versions generated similar interannual patterns in monthly recruitment for 1991–2004, with the 3-D results yielding consistently higher survivorship. Both versions successfully captured the very poor recruitment during the 1997–1998 El Niño event. Higher recruitment in the 3-D simulations was due to higher survival during the larval stage resulting from individuals searching for more favorable temperatures that lead to faster growth rates. The strong effect of temperature was because both model versions provided saturating food conditions for larval and juvenile anchovies. We conclude with a discussion of how explicit treatment of spatial variation affected simulated recruitment, other examples of fisheries modeling analyses that have used a similar approach to assess the influence of spatial variation, and areas for further model development. [ABSTRACT FROM AUTHOR]

Abstract: Nitrate supply by coastal upwelling has been estimated for four eastern boundary regions (Benguela, California, Northwest Africa and Peru) by combining surface winds measured from space and in situ vertical nitrate profiles. We use a QuikSCAT weekly wind product to assess the seasonal vertical transport induced by wind forcing. The calculation is made from the coast to 150km offshore and the wind-driven upwelling is partitioned into that contributed by Ekman transport and pumping. We assume that on the upwelling event time scale (days) the water brought to the surface originates from a depth of 60m. Seasonal climatologies are used to estimate in situ nitrate concentration at 60m, and nitrate supply is calculated as the product of nitrate concentration times the vertical transport obtained from QuikSCAT. This represents the potential new production, i.e. the amount of nitrate available for phytoplankton primary production, for each region. We find that Benguela, Northwest Africa and Peru have similar levels of nitrate supply and potential new production while California has about 60% of the other three. [Copyright &y& Elsevier]

Abstract: It has recently been shown that inner shelf waters of NE Monterey Bay, California function as an “extreme bloom incubator”, frequently developing dense “red tide” blooms that can rapidly spread. Located within the California Current upwelling system, this open bay is strongly influenced by oceanographic dynamics resulting from cycles of upwelling favorable winds and their relaxation and/or reversal. Different wind forcing causes influx of different water types that originate outside the bay: cold nutrient-rich waters during upwelling and warm nutrient-poor waters during relaxation. In this study, we examine how the bay''s bloom incubation area can interact with highly variable circulation to cause red tide spreading, dispersal and retention. This examination of processes is supported by satellite, airborne and in situ observations of a major dinoflagellate bloom during August and September of 2004. Remote sensing of high spatial, temporal and spectral resolution shows that the bloom originated in the NE bay, where it was highly concentrated in a narrow band along a thermal front. Upwelling circulation rapidly spread part of the bloom, mixing cool waters of an upwelling filament with warm bloom source waters as they spread. Vertical migration of the dinoflagellate populations was mapped by autonomous underwater vehicle surveys through the spreading bloom. Following bloom expansion, a two-day wind reversal forced intrusion of warm offshore waters that dispersed much of the bloom. Upwelling winds then resumed, and the bloom was further dispersed by an influx of cold water. Throughout these oceanographic responses to changing winds, an intense bloom persisted in sheltered waters of the NE bay, where extreme blooms are most frequent and intense. Microscopic examination of surface phytoplankton samples from the central bay showed that spreading of the bloom from the NE bay and mixing with regional water masses resulted in significantly increased abundance of dinoflagellates and decreased abundance of diatoms. Similar dinoflagellate bloom incubation sites are indicated in other areas of the California Current system and other coastal upwelling systems. Through frequent bloom development and along-coast transports, relatively small incubation sites may significantly influence larger regions of the coastal marine ecosystems in which they reside. [Copyright &y& Elsevier]

Abstract: On two cruises in August and September 2003 (hereafter cruises 2 and 3) during wind relaxations and transitions to upwelling conditions, thin layers of phytoplankton were observed in or a few meters below the stratified transition layer at the mixed layer base and in regions of sheared flow on the flanks of eddies, filaments, and fronts near Monterey Bay, California. On an earlier cruise in August (cruise 1), no thin layers were found after a prolonged wind relaxation. Chlorophyll concentrations and shear were both an order of magnitude less than on cruises 2 and 3. Our vertical profiles were made using a fluorometer mounted on a conductivity–temperature–depth package, which was lowered from the ship as slowly as every 10km on five cross-shore transects. Remotely sensed sea-surface temperature, chlorophyll, and currents are required to understand the temporal and spatial evolution of the circulation and to interpret the quasi-synoptic in situ data. Decorrelation scales are from lagged temperature and salinity covariances. Objectively mapped sections of the in situ data indicate the waters containing thin layers were recently upwelled at either the Point Sur or Point Año Nuevo upwelling centers. Spatially limited distributions of phytoplankton at the coastal upwelling centers ( alongshore, 20km cross-shore, and 30m thick) were transformed into thin layers by current shear and isolated from wind-driven vertical mixing by the stratification maximum of the transition layer. Vertically sheared horizontal currents on the flanks of the eddies, filaments, and fronts horizontally stretched and vertically thinned phytoplankton distributions. These thin, elongated structures were then observed as thin layers of phytoplankton in vertical fluorescence profiles at four stations on cruise 2 and eight stations on cruise 3. Light winds during relaxations did not mix away these thin layers. On cruise 2, thin layers were found at eddies at the inshore and offshore ends of a 100-km-long filament, while broader subsurface chlorophyll maxima were found along the filament. This result suggests that higher-resolution sampling along and across a filament may find thin layers forming and dissipating along its length. On cruise 3, thin layers were found at three adjacent stations across an upwelling front and may have extended continuously for , but neither species composition nor bio-optical data are available to confirm this conjecture. The thin layers were 1–5m thick in the vertical at full width half maximum and had peak fluorescence values from . (Bottle chlorophyll samples showed fluorometer chlorophyll readings may have been large, but the scatter in this relation was considerable especially at the larger fluorescence values detected in thin layers.) While sheared currents thinned an initially thick subsurface chlorophyll maximum into thin layers, the peak values in these thin layers exceeded concentrations in the upwelled source waters and were unexplained by our data. [Copyright &y& Elsevier]

Abstract: The eastern tropical Pacific includes 28 million km2 of ocean between 23.5°N and S and Central/South America and 140°W, and contains the eastern and equatorial branches of the north and South Pacific subtropical gyres plus two equatorial and two coastal countercurrents. Spatial patterns of primary production are in general determined by supply of macronutrients (nitrate, phosphate) from below the thermocline. Where the thermocline is shallow and intersects the lighted euphotic zone, biological production is enhanced. In the eastern tropical Pacific thermocline depth is controlled by three interrelated processes: a basin-scale east/west thermocline tilt, a basin-scale thermocline shoaling at the gyre margins, and local wind-driven upwelling. These processes regulate supply of nutrient-rich subsurface waters to the euphotic zone, and on their basis we have divided the eastern tropical Pacific into seven main regions. Primary production and its physical and chemical controls are described for each. Enhanced rates of macronutrient supply maintains levels of primary production in the eastern tropical Pacific above those of the oligotrophic subtropical gyres to the north and south. On the other hand lack of the micronutrient iron limits phytoplankton growth (and nitrogen fixation) over large portions of the open-ocean eastern tropical Pacific, depressing rates of primary production and resulting in the so-called high nitrate-low chlorophyll condition. Very high rates of primary production can occur in those coastal areas where both macronutrients and iron are supplied in abundance to surface waters. In these eutrophic coastal areas large phytoplankton cells dominate; conversely, in the open-ocean small cells are dominant. In a ‘shadow zone’ between the subtropical gyres with limited subsurface ventilation, enough production sinks and decays to produce anoxic and denitrified waters which spread beneath very large parts of the eastern tropical Pacific. Seasonal cycles are weak over much of the open-ocean eastern tropical Pacific, although several eutrophic coastal areas do exhibit substantial seasonality. The ENSO fluctuation, however, is an exceedingly important source of interannual variability in this region. El Niño in general results in a depressed thermocline and thus reduced rates of macronutrient supply and primary production. The multi-decadal PDO is likely also an important source of variability, with the ‘El Viejo’ phase of the PDO resulting in warmer and lower nutrient and productivity conditions similar to El Niño. On average the eastern tropical Pacific is moderately productive and, relative to Pacific and global means, its productivity and area are roughly equivalent. For example, it occupies about 18% of the Pacific Ocean by area and accounts for 22–23% of its productivity. Similarly, it occupies about 9% of the global ocean and accounts for 10% of its productivity. While representative, these average values obscure very substantial spatial and temporal variability that characterizes the dynamics of this tropical ocean. [Copyright &y& Elsevier]

We report measurements of dissolvable and particulate iron, particulate Al, nutrients and phytoplankton biomass in surface waters during the termination of one upwelling event and the initiation of a second event in August 2000. These events occurred in the area of the An˜o Nuevo upwelling center off the coast of central California. The first event was observed after ∼8 days of continuous upwelling favorable winds, while the second event was observed through the onset of upwelling favorable winds to wind reversals ∼3 days later. Coincident with the upwelling signatures of low temperature and high salinity were significantly elevated concentrations of nitrate and silicate with average concentrations greater than 15 and 20 μM, respectively, during both upwelling events. Dissolvable Fe concentrations (TD-Fe) were significantly higher in the second event, 6.5 versus 1.2 nM Fe found in the first event. Nitrate was reduced by ∼5 μM day−1 within this second upwelled plume as compared to a drawdown of ∼2 μM day−1 within the first plume. Silicate was reduced in a ratio of 1.2 mol Si:mol NO3 in the high Fe waters of the second plume as compared to a ratio of 2.2 in the lower Fe waters of the first plume. The observed differences in nutrient utilization are consistent with some degree of iron limitation. The area of increased dissolvable Fe in the second upwelling event was coincident with elevated particulate Fe concentrations, indicating the particulate pool as a possible source of the observed increase in TD-Fe. The elevated particulate Fe in surface waters was a result of resuspended sediments in the bottom boundary layer (BBL) of the shallow shelf being transported to the surface during upwelling. Particulate (and dissolvable) iron concentrations were significantly reduced as upwelling continued. This was most probably due to a decoupling of the BBL from upwelled source waters as the upwelling front moved offshore and/or reduced turbulence in the BBL as upwelling continued. The observed reduction in both particulate and dissolvable Fe, as upwelling continued to deliver macronutrients to surface waters, may result in varying levels of Fe limitation. [Copyright &y& Elsevier]

Unusual large-scale accumulations of phytoplankton occurred across 10,000 km of the equatorial Pacific during the 1998 transition from El Nin˜o to La Nin˜a. The forcing and dynamics of these phytoplankton blooms were studied using satellite-based observations of sea surface height, temperature and chlorophyll, and mooring-based observations of winds, hydrography and ocean currents. During the bloom period, the thermocline (nutricline) was anomalously shallow across the equatorial Pacific. The relative importance of processes that enhanced nutrient flux into the euphotic zone differed between the western and eastern regions of the blooms. In the western bloom region, the important vertical processes were turbulent vertical mixing and wind-driven upwelling. In contrast, the important processes in the eastern bloom region were wave-forced shoaling of nutrient source waters directly into the euphotic zone, along-isopycnal upwelling, and wind-driven upwelling. Advection by the Equatorial Undercurrent spread the largest bloom 4500 km east of where it began, and advection by meridional currents of tropical instability waves transported the bloom hundreds of kilometers north and south of the equator. Many processes influenced the intricate development of these massive biological events. Diverse observations and novel analysis methods of this work advance the conceptual framework for understanding the complex dynamics and ecology of the equatorial Pacific. [Copyright &y& Elsevier]