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Using marine sediment traps (named RESPIRE for REspiration of Sinking Particles In the subsu Rface oc Ean) designed to collect sinking particles and associated microbial communities in situ, we collected and incubated marine aggregates/particles in the southern Pacific Ocean from separate phytoplankton bloom events in situ. We determined the phylogenetic affiliation for the microorganisms growing on aggregates by pyrosequencing partial 16S rRNA gene amplicons. Water column samples were also collected and sequenced for comparison between sinking-particle-associated and planktonic bacterial communities. Statistically significant differences were found between the water column and sediment trap bacteria. Relative abundances of Pelagibacter sp. and multiple members of the Flavobacteria, Actinobacteria, and α- Proteobacteria were elevated in water column samples, while trap samples contained members of the Roseobacter clade of α- Proteobacteria in high relative abundances. Our findings indicated that rapid changes - within 24 h of collection - occurred to the microbial community associated with aggregates from either bloom type. There was a little change in the bacterial assemblage after the initial 24-h incubation period. The most abundant early colonizer was a Sulfitobacter sp. This study provides further evidence that Roseobacters are rapid colonizers of marine aggregates and that colonization can occur on short timescales. This study further demonstrates that particle origin may be insignificant regarding the heterotrophic bacterial population that degrades them. [ABSTRACT FROM AUTHOR]

Some of the largest scientific manipulation experiments conducted on our planet have enriched broad swaths of the surface ocean with iron. Surface ocean signatures of these iron enrichment experiments have covered areas up to > 1,000 km² and have been conspicuous from space. Twelve of these multidisciplinary studies have been conducted since the early 1990s in three specific ocean regions-- the Southern Ocean, and equatorial and sub-Arctic areas of the Pacific Ocean-- where plant nutrients are perennially high (termed high nutrient low chlorophyll, or HNLC). In addition, a combined phosphorus and iron enrichment experiment was conducted in the oligotrophic North Atlantic Ocean. Together, these studies represent a unique set of physical, chemical, optical, biological, and ecological data. The richness of these data sets is captured in an open-access relational database at the Biological and Chemical Oceanography Data Management Office (BCO_DMO; http://osprey.bco-dmo.org/program.cfm?flag=viewp&id=10&sortby=program). It is a product of Working Group 131 (The Legacy of in situ Iron Enrichment: Data Compilation and Modeling; http://www.scor-int.org/Working_Groups/wg131.htm) of the Scientific Committee on Oceanic Research. The purpose of this article is to make the wider community aware of this resource. It also presents the merits and provides examples of the utility of this database for exploring emerging topics in oceanography, such as the links between ecosystem processes and biogeochemical cycles; the feasibility and many side effects of oceanic geoengineering; and how understanding the coupling among physical, chemical, and biological processes at the mesoscale can inform the emerging field of submesoscale biogeochemistry. [ABSTRACT FROM AUTHOR]

We initiated and mapped a diatom bloom in the northeast subarctic Pacific by concurrently adding dissolved iron and the tracer sulfur hexafluoride to a mesoscale patch of high-nitrate, low-chlorophyll waters. The bloom was dominated by pennate diatoms and was monitored for 25 d, which was sufficiently long to observe the evolution and termination of the bloom and most of the decline phase. Fast repetition--rate fluorometry indicated that the diatoms were iron-replete until day 12, followed by a 4-5-d transition to iron limitation. This transition period was characterized by relatively high rates of algal growth and nutrient uptake, which pointed to diatoms using intracellularly stored iron. By days 16-17, the bloom was probably limited simultaneously by both iron and silicic acid supply, because low silicic acid concentrations were evident. Modeling simulations, using data from our study, provided an estimate of the critical threshold for algal aggregation. Observed diatom abundances during the bloom exceeded this threshold between days 13 and 17. Mass sedimentation of diatoms and diatom aggregates was recorded in surface-tethered free-drifting sediment traps at 50 m in depth on day 21. Although the termination of the bloom was probably controlled by the availability of both iron and silicic acid, we cannot rule out the role of algal aggregation. The bloom decline was likely triggered by the onset of mass sedimentation. During our study, evidence of both diatom species succession and species-specific aggregation point to important links between algal nutrient stress and the initiation of algal aggregation. [ABSTRACT FROM AUTHOR]

Provides information on a study which measured the heterotrophic bacterial biomass, production, and respiration rates during winter, spring and summer in the subarctic northeast Pacific from September 1995 to June 1997. Understanding of bacterial influences on the ocean carbon budget; Methodology of the study; Results and discussion; Conclusions.

Provides information on a study which dealt with the co-limitation of phytoplankton growth by light and iron in the northeast subarctic Pacific. Analysis of environmental conditions in winter at Ocean Station Papa (OSP); Physical, biological and chemical parameters at OSP; Iron requirements of phytoplankton growth at different light levels; Effects of increasing light levels and iron concentrations.

Heterotrophic bacterial abundance and productivity were measured in the euphotic zone over 4 years during winter, late spring, and late summer in the subarctic NE Pacific from September 1995 to February 1999. Sampling took place during 11 cruises at five hydrographic stations spaced along the east/west line-P transect from slope waters at P4 (1200 m depth) to the open-ocean waters at Ocean Station Papa (OSP) (4250 m depth). P4 exhibits a spring bloom and summer nutrient depletion, whereas OSP exhibits no spring bloom, consistently replete macronutrients, and iron limitation of primary productivity. Bacterial biomass, derived from cell abundance (assuming 10fgC cell[sup -1]), ranged from an average of ∼6 µg C1[sup -1] in the winter to 10 and 14 µg CI[sup -1] in the spring and summer all along line-P. Factors for converting the uptake of radiolabeled substrate to bacterial productivity were determined empirically from dilution experiments. The empirically derived conversion factors for both thymidine and leucine were positively correlated to in situ cell abundance. Bacterial productivity estimated from [³H]-thymidine and [[sup 14]C]-leucine incorporation rates was lowest in the winter (∼ 0.2 µg Cl[sup -1] d[sup -1]), with little spatial variability. Bacterial productivity increased 4-10-fold in spring at P4 compared with 04-fold at the more oceanic stations. Between 1995 and 1998, the average summer bacterial abundance all along line-P decreased by ∼ 50%, while bacterial productivity decreased by ∼90%. These decreases reduced summer bacterial productivity and growth rates to nearly winter levels in both the open-ocean and slope waters during late summer 1998. The average bacterial productivity at OSP is similar to other open-ocean regions while bacterial abundance is slightly higher providing for relatively lower growth rates and inferring lower associated loss rates. [ABSTRACT FROM AUTHOR]

We investigated the Southern Ocean (SO) prokaryote community structure via zero-radius operational taxonomic unit (zOTU) libraries generated from 16S rRNA gene sequencing of 223 full water column profiles. Samples reveal the prokaryote diversity trend between discrete water masses across multiple depths and latitudes in Indian (71-99°E, summer) and Pacific (170-174°W, autumn-winter) sectors of the SO. At higher taxonomic levels (phylum-family) we observed water masses to harbour distinct communities across both sectors, but observed sectorial variations at lower taxonomic levels (genus-zOTU) and relative abundance shifts for key taxa such as Flavobacteria, SAR324/Marinimicrobia, Nitrosopumilus and Nitrosopelagicus at both epi- and bathy-abyssopelagic water masses. Common surface bacteria were abundant in several deep-water masses and vice-versa suggesting connectivity between surface and deep-water microbial assemblages. Bacteria from same-sector Antarctic Bottom Water samples showed patchy, high beta-diversity which did not correlate well with measured environmental parameters or geographical distance. Unconventional depth distribution patterns were observed for key archaeal groups: Crenarchaeota was found across all depths in the water column and persistent high relative abundances of common epipelagic archaeon Nitrosopelagicus was observed in deep-water masses. Our findings reveal substantial regional variability of SO prokaryote assemblages that we argue should be considered in wide-scale SO ecosystem microbial modelling., (© 2022 The Authors. Environmental Microbiology published by Society for Applied Microbiology and John Wiley & Sons Ltd.)

Seasonal drawdown of dissolved inorganic carbon (DIC) in the subtropical upper ocean makes a significant contribution to net community production (NCP) globally. Although NCP requires macronutrient supply, surface macronutrients are chronically depleted, and their supply has been unable to balance the NCP demand. Here, we report nanomolar increases in surface nitrate plus nitrite (N+N, ~20 nM) and phosphate (PO 4 , ~15 nM) from summer to winter in the western subtropical North Pacific. Molar ratios of upward fluxes of DIC:N+N:PO 4 to the euphotic zone (< 100 m) were in near-stoichiometric balance with microbial C:N:P ratios (107~243:16~35:1). Comparison of these upward influxes with other atmospheric and marine sources demonstrated that total supply is largely driven by the other sources for C and N (93~96%), but not for P (10%), suggesting that nanomolar upward supply of P and its preferential recycling play a vital role in sustaining the NCP.

Anthropogenically-modulated reductions in pH, termed ocean acidification, could pose a major threat to the physiological performance, stocks, and biodiversity of calcifiers and may devalue their ecosystem services. Recent debate has focussed on the need to develop approaches to arrest the potential negative impacts of ocean acidification on ecosystems dominated by calcareous organisms. In this study, we demonstrate the role of a discrete (i.e. diffusion) boundary layer (DBL), formed at the surface of some calcifying species under slow flows, in buffering them from the corrosive effects of low pH seawater. The coralline macroalga Arthrocardia corymbosa was grown in a multifactorial experiment with two mean pH levels (8.05 'ambient' and 7.65 a worst case 'ocean acidification' scenario projected for 2100), each with two levels of seawater flow (fast and slow, i.e. DBL thin or thick). Coralline algae grown under slow flows with thick DBLs (i.e., unstirred with regular replenishment of seawater to their surface) maintained net growth and calcification at pH 7.65 whereas those in higher flows with thin DBLs had net dissolution. Growth under ambient seawater pH (8.05) was not significantly different in thin and thick DBL treatments. No other measured diagnostic (recruit sizes and numbers, photosynthetic metrics, %C, %N, %MgCO3) responded to the effects of reduced seawater pH. Thus, flow conditions that promote the formation of thick DBLs, may enhance the subsistence of calcifiers by creating localised hydrodynamic conditions where metabolic activity ameliorates the negative impacts of ocean acidification.

Ocean acidification and greenhouse warming will interactively influence competitive success of key phytoplankton groups such as diatoms, but how long-term responses to global change will affect community structure is unknown. We incubated a mixed natural diatom community from coastal New Zealand waters in a short-term (two-week) incubation experiment using a factorial matrix of warming and/or elevated pCO2 and measured effects on community structure. We then isolated the dominant diatoms in clonal cultures and conditioned them for 1 year under the same temperature and pCO2 conditions from which they were isolated, in order to allow for extended selection or acclimation by these abiotic environmental change factors in the absence of interspecific interactions. These conditioned isolates were then recombined into 'artificial' communities modelled after the original natural assemblage and allowed to compete under conditions identical to those in the short-term natural community experiment. In general, the resulting structure of both the unconditioned natural community and conditioned 'artificial' community experiments was similar, despite differences such as the loss of two species in the latter. pCO2 and temperature had both individual and interactive effects on community structure, but temperature was more influential, as warming significantly reduced species richness. In this case, our short-term manipulative experiment with a mixed natural assemblage spanning weeks served as a reasonable proxy to predict the effects of global change forcing on diatom community structure after the component species were conditioned in isolation over an extended timescale. Future studies will be required to assess whether or not this is also the case for other types of algal communities from other marine regimes.

The oceanic biological pump drives sequestration of carbon dioxide in the deep sea via sinking particles. Rapid biological consumption and remineralization of carbon in the "twilight zone" (depths between the euphotic zone and 1000 meters) reduce the efficiency of sequestration. By using neutrally buoyant sediment traps to sample this chronically understudied realm, we measured a transfer efficiency of sinking particulate organic carbon between 150 and 500 meters of 20 and 50% at two contrasting sites. This large variability in transfer efficiency is poorly represented in biogeochemical models. If applied globally, this is equivalent to a difference in carbon sequestration of more than 3 petagrams of carbon per year.