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Climate warming increasingly drives changes in large-scale ocean physics and biogeochemistry, and affects the kinetics of biological reactions. Together these factors govern phytoplankton productivity, thereby shaping the responses of ocean carbon and nutrient cycles to global change. Here we bring together results from experimental, observational and modelling studies to highlight how interactive feedbacks between warming and nutrient limitation can affect the responses of biogeochemically critical marine primary producers. The availability of many bioactive elements in seawater will be altered markedly in the future, thereby shifting resource deficiencies. These modifications to nutrient limitation when compounded by concurrent warming can change phytoplankton optimum growth temperatures and elemental use efficiencies in group-specific and nutrient-specific ways. The biogeochemical impacts of these nutrient and warming interactions reflect a distinction between the thermal reactivity of major cellular structural elements like nitrogen (N) and catalytic micronutrients like iron (Fe). Integrating the mechanistic feedbacks between warming, nutrient availability and primary productivity into Earth system models is necessary to improve confidence in projections of ocean biogeochemical cycle transformations in a changing climate.

Marine microbial communities in coastal environments are subject to both seasonal fluctuations and anthropogenic alterations of environmental conditions. The separate influences of temperature and resource‐dependency on phytoplankton growth, community, and ecosystem metabolism are relatively well understood. However, winners and losers in the ocean are determined based on the interplay among often rapidly changing biological, chemical and physical drivers. The direct, indirect, and interactive effects of these conditions on planktonic food web structure and function are poorly constrained. Here, we investigated how simultaneous manipulation of temperature and nutrient availability affects trophic transfer from phytoplankton to herbivorous protists, and their resulting implications at the ecosystem level. Temperature directly affected herbivorous protist composition; ciliates dominated (66%) in colder treatment and dinoflagellates (60%) at warmer temperatures. Throughout the experiments, grazing rates were < 0.1 d−1, with higher rates at subzero temperatures. Overall, the nutrient–temperature interplay affected trophic transfer rates antagonistically when nutrients were amended, and synergistically, when nutrients were not added. This interaction resulted in higher percentages of primary production consumed under nutrient unamended compared to nutrient amended conditions. At the ecosystem level, these changes may determine the fate of primary production, with most of the production likely exported out of the pelagic zone in high‐temperature and nutrient conditions, while high‐temperature and low‐nutrient availability strengthened food web coupling and enhanced trophic transfer. These results imply that in warming oceans, management of coastal nutrient loading will be a critical determinant of the degree of primary production removal by microzooplankton and dependent ecosystem production.

Ocean warming (OW) and acidification (OA) are recognized as two major climatic conditions influencing phytoplankton growth and nutritional or toxin content. However, there is limited knowledge on the responses of harmful algal bloom species that produce toxins. Here, the study provides quantitative and mechanistic understanding of the acclimation and adaptation responses of the domoic acid (DA) producing diatom Pseudo-nitzschia multiseriesto rising temperature and pCO2using both a one-year in situ bulk culture experiment, and an 800-day laboratory acclimation experiment. Ocean warming showed larger selective effects on growth and DA metabolism than ocean acidification. In a bulk culture experiment, increasing temperature +4 °C above ambient seawater temperature significantly increased DA concentration by up to 11-fold. In laboratory when the long-term warming acclimated samples were assayed under low temperatures, changes in growth rates and DA concentrations indicated that P. multiseriesdid not adapt to elevated temperature, but could instead rapidly and reversibly acclimate to temperature shifts. However, the warming-acclimated lines showed evidence of adaptation to elevated temperatures in the transcriptome data. Here the core gene expression was not reversed when warming-acclimated lines were moved back to the low temperature environment, which suggested that P. multiseriescells might adapt to rising temperature over longer timescales. The distinct strategies of phenotypic plasticity to rising temperature and pCO2demonstrate a strong acclimation capacity for this bloom-forming toxic diatom in the future ocean.

Ocean warming (OW) and acidification (OA) are recognized as two major climatic conditions influencing phytoplankton growth and nutritional or toxin content. However, there is limited knowledge on the responses of harmful algal bloom species that produce toxins. Here, the study provides quantitative and mechanistic understanding of the acclimation and adaptation responses of the domoic acid (DA) producing diatom Pseudo-nitzschia multiseriesto rising temperature and pCO2using both a one-year in situ bulk culture experiment, and an 800-day laboratory acclimation experiment. Ocean warming showed larger selective effects on growth and DA metabolism than ocean acidification. In a bulk culture experiment, increasing temperature +4?°C above ambient seawater temperature significantly increased DA concentration by up to 11-fold. In laboratory when the long-term warming acclimated samples were assayed under low temperatures, changes in growth rates and DA concentrations indicated that P. multiseriesdid not adapt to elevated temperature, but could instead rapidly and reversibly acclimate to temperature shifts. However, the warming-acclimated lines showed evidence of adaptation to elevated temperatures in the transcriptome data. Here the core gene expression was not reversed when warming-acclimated lines were moved back to the low temperature environment, which suggested that P. multiseriescells might adapt to rising temperature over longer timescales. The distinct strategies of phenotypic plasticity to rising temperature and pCO2demonstrate a strong acclimation capacity for this bloom-forming toxic diatom in the future ocean.

In the nitrogen-limited subtropical gyres, diazotrophic cyanobacteria, including Crocosphaera, provide an essential ecosystem service by converting dinitrogen (N2) gas into ammonia to support primary production in these oligotrophic regimes. Natural gradients of phosphorus (P) and iron (Fe) availability in the low-latitude oceans constrain the biogeography and activity of diazotrophs with important implications for marine biogeochemical cycling. Much remains unknown regarding Crocosphaera’s physiological and molecular responses to multiple nutrient limitations. We cultured C. watsoniiunder Fe, P, and Fe/P (co)-limiting scenarios to link cellular physiology with diel gene expression and observed unique physiological and transcriptional profiles for each treatment. Counterintuitively, reduced growth and N2fixation resource use efficiencies (RUEs) for Fe or P under P limitation were alleviated under Fe/P co-limitation. Differential gene expression analyses show that Fe/P co-limited cells employ the same responses as single-nutrient limited cells that reduce cellular nutrient requirements and increase responsiveness to environmental change including smaller cell size, protein turnover (Fe-limited), and upregulation of environmental sense-and-respond systems (P-limited). Combined, these mechanisms enhance growth and RUEs in Fe/P co-limited cells. These findings are important to our understanding of nutrient controls on N2fixation and the implications for primary productivity and microbial dynamics in a changing ocean.

Nickel is a biologically essential element for marine life, with the potential to influence diverse processes, including methanogenesis, nitrogen uptake and coral health, in both modern and past oceans. However, an incomplete view of oceanic Ni cycling has stymied understanding of how Ni may impact marine life in these modern and ancient oceans. Here we combine data-constrained global biogeochemical circulation modelling with culture experiments and find that Ni in oligotrophic gyres is both chemically and biologically labile and only minimally incorporated into diatom frustules. We then develop a framework for understanding oceanic Ni distributions, and in particular the two dominant features of the global marine Ni distribution: the deep concentration maximum and the residual pool of approximately 2 nM Ni in subtropical gyres. We suggest that slow depletion of Ni relative to macronutrients in upwelling regions can explain the residual Ni pool, and reversible scavenging or slower regeneration of Ni compared with macronutrients contributes to the distinct Ni vertical distribution. The strength of these controls may have varied in the past ocean, impacting Ni bioavailability and setting a fine balance between Ni feast and famine for phytoplankton, with implications for both ocean chemistry and climate state.

A complex interplay of environmental variables impacts phytoplankton community composition and physiology. Temperature and nutrient availability are two principal factors driving phytoplankton growth and composition, but are often investigated independently and on individual species in the laboratory. To assess the individual and interactive effects of temperature and nutrient concentration on phytoplankton community composition and physiology, we altered both the thermal and nutrient conditions of a cold‐adapted spring phytoplankton community in Narragansett Bay, Rhode Island, when surface temperature was 2.6°C and chlorophyll > 9 μg L−1. Water was incubated in triplicate at −0.5°C, 2.6°C, and 6°C for 10 d. At each temperature, treatments included both nutrient amendments (N, P, Si addition) and controls (no macronutrients added). The interactive effects of temperature and resource availability altered phytoplankton growth and community structure. Nutrient amendments resulted in species sorting and communities dominated by larger species. Under replete nutrients, warming tripled phytoplankton growth rates, but under in situ nutrient conditions, increased temperature acted antagonistically, reducing growth rates by as much as 33%, suggesting communities became nutrient limited. The temperature–nutrient interplay shifted the relative proportions of each species within the phytoplankton community, resulting in more silica rich cells at decreasing temperatures, irrespective of nutrients, and C : N that varied based on resource availability, with nutrient limitation inducing a 47% increase in C : N at increasing temperatures. Our results illustrate how the temperature–nutrient interplay can alter phytoplankton community dynamics, with changes in temperature amplifying or exacerbating the nutrient effect with implications for higher trophic levels and carbon flux.

A small subset of marine microbial enzymes and surface transporters have a disproportionately important influence on the cycling of carbon and nutrients in the global ocean. As a result, they largely determine marine biological productivity and have been the focus of considerable research attention from microbial oceanographers. Like all biological catalysts, the activity of these keystone biomolecules is subject to control by temperature and pH, leaving the crucial ecosystem functions they support potentially vulnerable to anthropogenic environmental change. We summarize and discuss both consensus and conflicting evidence on the effects of sea surface warming and ocean acidification for five of these critical enzymes [carbonic anhydrase, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), nitrogenase, nitrate reductase, and ammonia monooxygenase] and one important transporter (proteorhodopsin). Finally, we forecast how the responses of these few but essential biocatalysts to ongoing global change processes may ultimately help to shape the microbial communities and biogeochemical cycles of the future greenhouse ocean.

The ocean is home to a diverse and metabolically versatile microbial community that performs the complex biochemical transformations that drive the nitrogen cycle, including nitrogen fixation, assimilation, nitrification and nitrogen loss processes. In this Review, we discuss the wealth of new ocean nitrogen cycle research in disciplines from metaproteomics to global biogeochemical modelling and in environments from productive estuaries to the abyssal deep sea. Influential recent discoveries include new microbial functional groups, novel metabolic pathways, original conceptual perspectives and ground-breaking analytical capabilities. These emerging research directions are already contributing to urgent efforts to address the primary challenge facing marine microbiologists today: the unprecedented onslaught of anthropogenic environmental change on marine ecosystems. Ocean warming, acidification, nutrient enrichment and seawater stratification have major effects on the microbial nitrogen cycle, but widespread ocean deoxygenation is perhaps the most consequential for the microorganisms involved in both aerobic and anaerobic nitrogen transformation pathways. In turn, these changes feed back to the global cycles of greenhouse gases such as carbon dioxide and nitrous oxide. At a time when our species casts a lengthening shadow across all marine ecosystems, timely new advances offer us unique opportunities to understand and better predict human impacts on nitrogen biogeochemistry in the changing ocean of the Anthropocene.

In the nitrogen-limited subtropical gyres, diazotrophic cyanobacteria, including Crocosphaera, provide an essential ecosystem service by converting dinitrogen (N2) gas into ammonia to support primary production in these oligotrophic regimes. Natural gradients of phosphorus (P) and iron (Fe) availability in the low-latitude oceans constrain the biogeography and activity of diazotrophs with important implications for marine biogeochemical cycling. Much remains unknown regarding Crocosphaera’s physiological and molecular responses to multiple nutrient limitations. We cultured C. watsoniiunder Fe, P, and Fe/P (co)-limiting scenarios to link cellular physiology with diel gene expression and observed unique physiological and transcriptional profiles for each treatment. Counterintuitively, reduced growth and N2fixation resource use efficiencies (RUEs) for Fe or P under P limitation were alleviated under Fe/P co-limitation. Differential gene expression analyses show that Fe/P co-limited cells employ the same responses as single-nutrient limited cells that reduce cellular nutrient requirements and increase responsiveness to environmental change including smaller cell size, protein turnover (Fe-limited), and upregulation of environmental sense-and-respond systems (P-limited). Combined, these mechanisms enhance growth and RUEs in Fe/P co-limited cells. These findings are important to our understanding of nutrient controls on N2fixation and the implications for primary productivity and microbial dynamics in a changing ocean.

Diatoms have well‐recognized roles in fixing and exporting carbon and supplying energy to marine ecosystems, but only recently have we begun to explore the diversity and importance of nano‐ and pico‐diatoms. Here, we describe a small (ca. 5 μm) diatom from the genus Chaetocerosisolated from a wintertime temperate estuary (2°C, Narragansett Bay, Rhode Island), with a unique obligate specialization for low‐light environments (< 120 μmol photons m−2s−1). This diatom exhibits a striking interaction between irradiance and thermal responses whereby as temperatures increase, so does its susceptibility to light stress. Historical 18S rRNA amplicon data from our study site show this isolate was abundant throughout a 6‐yr period, and its presence strongly correlates with winter and early spring months when light and temperature are low. Two amplicon sequence variants matching this isolate had a circumpolar distribution in Tara Polar Ocean Circle samples, indicating its unusual light and temperature requirements are adaptations to life in a cold, dark environment. We expect this isolate's low light, psychrophilic niche to shrink as future warming‐induced stratification increases both light and temperature levels experienced by high latitude marine phytoplankton.

Arsenic pollution is a widespread threat to marine life, but the ongoing rise pCO2levels is predicted to decrease bio-toxicity of arsenic. However, the effects of arsenic toxicity on marine primary producers under elevated pCO2are not well characterized. Here, we studied the effects of arsenic toxicity in three globally distributed diatom species (Phaeodactylum tricornutum, Thalassiosira pseudonana, and Chaetoceros mulleri) after short-term acclimation (ST, 30 days), medium-term exposure (MT, 750 days), and long-term (LT, 1460 days) selection under ambient (400 µatm) and elevated (1000 and 2000 µatm) pCO2. We found that elevated pCO2alleviated arsenic toxicity even after short acclimation times but the magnitude of the response decreased after mid and long-term adaptation. When fed with these elevated pCO2selected diatoms, the scallop Patinopecten yessoensishad significantly lower arsenic content (3.26–52.83%). Transcriptomic and biochemical analysis indicated that the diatoms rapidly developed arsenic detoxification strategies, which included upregulation of transporters associated with shuttling harmful compounds out of the cell to reduce arsenic accumulation, and upregulation of proteins involved in synthesizing glutathione (GSH) to chelate intracellular arsenic to reduce arsenic toxicity. Thus, our results will expand our knowledge to fully understand the ecological risk of trace metal pollution under increasing human activity induced ocean acidification.

Arsenic pollution is a widespread threat to marine life, but the ongoing rise pCO2levels is predicted to decrease bio-toxicity of arsenic. However, the effects of arsenic toxicity on marine primary producers under elevated pCO2are not well characterized. Here, we studied the effects of arsenic toxicity in three globally distributed diatom species (Phaeodactylum tricornutum, Thalassiosira pseudonana, and Chaetoceros mulleri) after short-term acclimation (ST, 30 days), medium-term exposure (MT, 750 days), and long-term (LT, 1460 days) selection under ambient (400 µatm) and elevated (1000 and 2000 µatm) pCO2. We found that elevated pCO2alleviated arsenic toxicity even after short acclimation times but the magnitude of the response decreased after mid and long-term adaptation. When fed with these elevated pCO2selected diatoms, the scallop Patinopecten yessoensishad significantly lower arsenic content (3.26–52.83%). Transcriptomic and biochemical analysis indicated that the diatoms rapidly developed arsenic detoxification strategies, which included upregulation of transporters associated with shuttling harmful compounds out of the cell to reduce arsenic accumulation, and upregulation of proteins involved in synthesizing glutathione (GSH) to chelate intracellular arsenic to reduce arsenic toxicity. Thus, our results will expand our knowledge to fully understand the ecological risk of trace metal pollution under increasing human activity induced ocean acidification.

Throughout the open ocean, a minimum in dissolved iron concentration (dFe) overlaps with the deep chlorophyll maximum (DCM), which marks the lower limit of the euphotic zone. Maximizing light capture in these dim waters is expected to require upregulation of Fe-bearing photosystems, further depleting dFe and possibly leading to co-limitation by both iron and light. However, this effect has not been quantified for important phytoplankton groups like Prochlorococcus, which contributes most of the productivity in the oligotrophic DCM. Here, we present culture experiments with Prochlorococcusstrain MIT1214, a member of the Low Light 1 ecotype isolated from the DCM in the North Pacific subtropical gyre. Under a matrix of iron and irradiance matching those found at the DCM, the ratio of Fe to carbon in ProchlorococcusMIT1214 cells ranged from 10–40?×?10-6?mol Fe:mol C and increased with light intensity and growth rate. These results challenge theoretical models predicting highest Fe:C at lowest light intensity, and are best explained by a large photosynthetic Fe demand that is not downregulated at higher light. To sustain primary production in the DCM with the rigid Fe requirements of low-light-adapted Prochlorococcus, dFe must be recycled rapidly and at high efficiency.

Throughout the open ocean, a minimum in dissolved iron concentration (dFe) overlaps with the deep chlorophyll maximum (DCM), which marks the lower limit of the euphotic zone. Maximizing light capture in these dim waters is expected to require upregulation of Fe-bearing photosystems, further depleting dFe and possibly leading to co-limitation by both iron and light. However, this effect has not been quantified for important phytoplankton groups like Prochlorococcus, which contributes most of the productivity in the oligotrophic DCM. Here, we present culture experiments with Prochlorococcusstrain MIT1214, a member of the Low Light 1 ecotype isolated from the DCM in the North Pacific subtropical gyre. Under a matrix of iron and irradiance matching those found at the DCM, the ratio of Fe to carbon in ProchlorococcusMIT1214 cells ranged from 10–40 × 10-6mol Fe:mol C and increased with light intensity and growth rate. These results challenge theoretical models predicting highest Fe:C at lowest light intensity, and are best explained by a large photosynthetic Fe demand that is not downregulated at higher light. To sustain primary production in the DCM with the rigid Fe requirements of low-light-adapted Prochlorococcus, dFe must be recycled rapidly and at high efficiency.

Average sea surface temperatures are expected to rise 4° this century, and marine phytoplankton and bacterial community composition, biogeochemical rates, and trophic interactions are all expected to change in a future warmer ocean. Thermal experiments typically use constant temperatures; however, weather and hydrography cause marine temperatures to fluctuate on diel cycles and over multiple days. We incubated natural communities of phytoplankton collected from California coastal waters during spring, summer, and fall under present-day and future mean temperatures, using thermal treatments that were either constant or fluctuated on a 48?h cycle. As assayed by marker-gene sequencing, the emergent microbial communities were consistent within each season, except when culture temperatures exceeded the highest temperature recorded in a 10-year local thermal dataset. When temperature treatments exceeded the 10-year maximum the phytoplankton community shifted, becoming dominated by diatom amplicon sequence variants (ASVs) not seen at lower temperatures. When mean temperatures were above the 10-year maximum, constant and fluctuating regimes each selected for different ASVs. These findings suggest coastal microbial communities are largely adapted to the current range of temperatures they experience. They also suggest a general hypothesis whereby multiyear upper temperature limits may represent thresholds, beyond which large community restructurings may occur. Now inevitable future temperature increases that exceed these environmental thresholds, even temporarily, may fundamentally reshape marine microbial communities and therefore the biogeochemical cycles that they mediate.

Average sea surface temperatures are expected to rise 4° this century, and marine phytoplankton and bacterial community composition, biogeochemical rates, and trophic interactions are all expected to change in a future warmer ocean. Thermal experiments typically use constant temperatures; however, weather and hydrography cause marine temperatures to fluctuate on diel cycles and over multiple days. We incubated natural communities of phytoplankton collected from California coastal waters during spring, summer, and fall under present-day and future mean temperatures, using thermal treatments that were either constant or fluctuated on a 48 h cycle. As assayed by marker-gene sequencing, the emergent microbial communities were consistent within each season, except when culture temperatures exceeded the highest temperature recorded in a 10-year local thermal dataset. When temperature treatments exceeded the 10-year maximum the phytoplankton community shifted, becoming dominated by diatom amplicon sequence variants (ASVs) not seen at lower temperatures. When mean temperatures were above the 10-year maximum, constant and fluctuating regimes each selected for different ASVs. These findings suggest coastal microbial communities are largely adapted to the current range of temperatures they experience. They also suggest a general hypothesis whereby multiyear upper temperature limits may represent thresholds, beyond which large community restructurings may occur. Now inevitable future temperature increases that exceed these environmental thresholds, even temporarily, may fundamentally reshape marine microbial communities and therefore the biogeochemical cycles that they mediate.

Increased stratification and mixed layer shoaling of the surface ocean resulting from warming can lead to exposure of marine dinitrogen (N2)‐fixing cyanobacteria to higher levels of inhibitory ultraviolet (UV) radiation. These same processes also reduce vertically advected supplies of the potentially limiting nutrient phosphorus (P) to N2fixers. It is currently unknown how UV inhibition and P limitation interact to affect the biogeochemical cycles of nitrogen and carbon in these biogeochemically critical microbes. We investigated the responses of the important and widespread marine N2‐fixing cyanobacteria Crocosphaera(strain WH0005) and Trichodesmium(strains IMS 101 and GBR) to UV‐A and UV‐B under P‐replete and P‐limited conditions. Growth, N2fixation, and carbon dioxide (CO2) fixation rates of TrichodesmiumIMS 101 and Crocosphaerawere negatively affected by UV exposure. This inhibition was greater for TrichodesmiumIMS 101 than for Crocosphaera, which fixes N2only during the night and so avoids direct UV damage. Negative effects of UV on both IMS 101 and Crocosphaerawere less in P‐limited cultures than in P‐replete cultures. In contrast, no UV inhibition was observed in GBR, regardless of P availability. UV inhibition was related to different amounts of UV‐absorbing compounds produced by these isolates. Responses to UV radiation and P availability interactions were taxon‐specific, but our results indicated that in general, UV radiation effects on Trichodesmiumand Crocosphaerarange from negative to neutral. UV inhibition and its interactions with P limitation may thus have a substantial influence on the present day and future nitrogen and carbon cycles of the ocean.

In the Anthropocene, in which we now live, climate change is impacting most life on Earth. Microorganisms support the existence of all higher trophic life forms. To understand how humans and other life forms on Earth (including those we are yet to discover) can withstand anthropogenic climate change, it is vital to incorporate knowledge of the microbial ‘unseen majority’. We must learn not just how microorganisms affect climate change (including production and consumption of greenhouse gases) but also how they will be affected by climate change and other human activities. This Consensus Statement documents the central role and global importance of microorganisms in climate change biology. It also puts humanity on notice that the impact of climate change will depend heavily on responses of microorganisms, which are essential for achieving an environmentally sustainable future.

The signs of climate change are undeniable, and the inevitable impact for Earth and all its inhabitants is a serious concern. Ice is melting, sea levels are rising, biodiversity is declining, precipitation has increased, atmospheric levels of carbon dioxide and greenhouse gases are alarmingly high, and extreme weather conditions are becoming increasingly common. But what role do microorganisms have in this global challenge? In this Viewpoint article, several experts in the field discuss the microbial contributions to climate change and consider the effects of global warming, extreme weather, flooding and other consequences of climate change on microbial communities in the ocean and soil, on host–microbiota interactions and on the global burden of infectious diseases and ecosystem processes, and they explore open questions and research needs. In this Viewpoint article, several experts discuss the microbial contributions to climate change and consider the effects of global warming, extreme weather and other consequences of climate change on microbial communities in the ocean and soil, host–microbiota interactions and the global burden of infectious diseases and ecosystem processes, and they explore open questions and research needs.

Phytoplankton growth in the seasonally productive Southern Ocean is typically limited by iron (Fe). In the next century, however, Fe inputs and temperature are predicted to increase. Dissolved concentrations of nitrogen (N) and phosphorus (P) may also change due to physical and biological drivers, altering the stoichiometric N:P ratio of the water column. Two separate experiments were conducted to study how these predicted changes will impact nutrient utilization by two natural microbial communities from the Ross Sea, Antarctica. The first investigation focused on a Terra Nova Bay community amended with Fe and grown under a wide range of seven different N:P ratios. Building on the results of the first study, a McMurdo Sound community was incubated under a factorial design at high, medium (ambient), and low N:P ratios, with and without Fe addition, and at ambient versus elevated temperature. In both experiments absolute uptake rates of bicarbonate, nitrate, and amino acids by two size fractions (0.7–5.0 μm and > 5.0 μm) of microorganisms were measured using stable isotopes. For Terra Nova Bay microorganisms, significant differences in nutrient uptake rates occurred when the N:P ratio was elevated, and nitrate uptake rates significantly increased early in the experiment but were not different at the end. For McMurdo Sound microorganisms, changing the N:P supply ratio did not have a clear effect, while temperature elevation and/or Fe addition significantly increased nutrient uptake. Results indicate that changing the dissolved N:P ratio can potentially alter nutrient uptake rates; however, the impact of temperature and Fe are greater. The Southern Ocean is one of the most biologically important ecosystems on our planet. Microscopic plants, called phytoplankton, form the base of the food web in the Southern Ocean and play a direct role in regulating how much and how fast elements like nitrogen and carbon are cycled throughout the world ocean. The goal of this research was to determine how predicted changes in the environment will impact how fast phytoplankton use these elements. The conditions that we tested included elevated temperature, addition of iron, and the proportion of nitrogen to phosphorus in the seawater. These parameters were selected because temperatures are increasing in the Southern Ocean, and the relative availability of nutrients can alter what species of phytoplankton are present and how fast they grow. Phytoplankton were collected from two locations in the Ross Sea, Antarctica, and grown for a few weeks under experimental conditions. Our results demonstrate that all three parameters, warmer temperatures, the addition of iron, and changing nitrogen to phosphorus ratios will increase how fast phytoplankton use nitrogen and carbon, but the impact of elevated temperature and the addition of iron had a much larger impact than the nitrogen to phosphorus ratio. Responses of Ross Sea microorganisms to changing dissolved N:P ratios, temperature, and Fe vary seasonally and among taxaIncreasing the N:P ratio of the seawater increased nitrate uptake rates, but only over short time scales and during the late‐season bloomTemperature elevation and Fe addition are more significant drivers of change than N:P supply ratios when Phaeocystisis dominant

The cyanobacterium Trichodesmiumfixes as much as half of the nitrogen (N2) that supports tropical open-ocean biomes, but its growth is frequently limited by iron (Fe) availability1,2. How future ocean warming may interact with this globally widespread Fe limitation of TrichodesmiumN2fixation is unclear3. Here, we show that the optimum growth temperature of Fe-limited Trichodesmiumis ~5 °C higher than for Fe-replete cells, which results in large increases in growth and N2fixation under the projected warmer Fe-deplete sea surface conditions. Concurrently, the cellular Fe content decreases as temperature rises. Together, these two trends result in thermally driven increases of ~470% in Fe-limited cellular iron use efficiencies (IUEs), defined as the molar quantity of N2fixed by Trichodesmiumper unit time per mole of cellular Fe (mol N2fixed h–1mol Fe–1), which enables Trichodesmiumto much more efficiently leverage the scarce available Fe supplies to support N2fixation. Modelling these results in the context of the IPCC representative concentration pathway (RCP) 8.5 global warming scenario4predicts that IUEs of N2fixers could increase by ~76% by 2100, and largely alleviate the prevailing Fe limitation across broad expanses of the tropical Pacific and Indian Oceans. Thermally enhanced cyanobacterial IUEs could increase future global marine N2fixation by ~22% over the next century, and thus profoundly alter the biology and biogeochemistry of open-ocean ecosystems.

Lateral input of dissolved organics may play a significant role to support productivity in oligotrophic ocean although associated biogeochemical evidences are lacking in the field. Ammonia oxidation (AO), the first step of nitrification that bridges organic remineralization and nitrate, is potentially an immediate responder. By using 15N‐NH4+, the spatial distribution of AO was investigated in the northern South China Sea, where Kuroshio Current intrudes frequently. AO ranged widely (0.001 to 134 nmol · L−1· day−1) in space and the depth‐integrated (200 m) AO peaked where the Kuroshio influence is moderate suggesting that enhanced AO had occurred due to lateral mixing. Since oligotrophic Kuroshio is characterized by high dissolved organic nitrogen (DON), such lateral mixing not only introduces external DON into the northern South China Sea but also enhances NH4+regeneration and subsequent oxidation to complicate the conventional new production in the boundary zone with DON gradient. The horizontal mixing is widespread in oligotrophic ocean; however, the mixing‐induced biogeochemical response is hard to detect and remains less explored. We measured ammonia oxidation (AO), a critical process immediately responds to remineralization of dissolved organic matter (DOM), along the pathway of Kuroshio intrusion into the South China Sea. We found AO peaked at stations where the influence of Kuroshio Current intrusion is moderate. We hypothesized that intrusion of oligotrophic water brings on‐site recalcitrant DOM into marginal seas and enriches ammonium level via bacteria decomposition of the foreign DOM. Accompanied is the enhancement of AO, which transfers DOM into nitrate, further complicating the conventional concept of N‐based new production. Such lateral intrusion or transport appears also along a meridional direction. For example, the western boundary current (warm and saline) carrying DOM‐rich water flows toward higher latitudes where nutrients are high. According to our findings, such hemispheric scale transport may exert considerable influence on high‐latitude nitrogen biogeochemistry. Knowledge of the impact of Kuroshio intrusion on AO in the northern South China Sea was a step forward in documenting this type of response in frontal zone, but more studies will be needed to validate the underlying mechanisms. The spatial distribution of ammonia oxidation was reported for the first time in the northern South China SeaEnhanced ammonia oxidation was associated with the Kuroshio Current intrusionRemineralization of DON introduced by the Kuroshio Current was likely a stimulator to enhance the ammonia oxidation in the northern South China Sea

Marine ecosystems are facing multiple anthropogenic global changes, including ocean acidification, warming, and reduced nutrient supplies. Together, these will challenge phytoplankton including large centric diatoms such as Coscinodiscussp., a group that is important to ocean food webs and carbon export. We investigated the interactive effects of warming, elevated CO2, and nitrate availability on Coscinodiscusgrowth, elemental stoichiometry, and Fe and C uptake rates in a four‐treatment factorial experiment combining two CO2levels (∼400 ppm and 800 ppm) and two temperatures (16°C and 20°C) across seven nitrate concentrations (1–100 μmol L−1). Higher temperatures led to higher maximum growth rates (μmax), but also higher half‐saturation constants for nitrate (K1/2), while elevated CO2increased K1/2only at the warmer temperature. Lower μmax/K1/2ratios under warming and rising CO2indicated a higher nitrate requirement at these conditions. High temperature decreased cellular P and Si contents and consequently increased N : P and C : Si ratios, especially at ambient CO2. Fe : C uptake ratios responded positively to lower nitrate levels, lower CO2, and warming. Significant interactions between nitrate availability and temperature or CO2were observed for specific growth rates, chlorophyll aand Si contents, Fe : C, N : P, and Si : C, while temperature and CO2interactions were only significant for μmax/K1/2and cellular P content. The mutual interactions among CO2concentrations, temperature, and nitrate supply may all affect future growth, physiology, and carbon export by Coscinodiscussp., however, in general warming and nitrate availability appear to be more influential than CO2.

The seas are acidifying as a result of carbon dioxide emissions. It now emerges that this will alter the solubility of the shells of marine organisms called diatoms — and thereby change the distribution of nutrients and plankton in the ocean.

The nitrogen (N)-fixing cyanobacterium Trichodesmium is globally distributed in warm, oligotrophic oceans, where it contributes a substantial proportion of new N and fuels primary production. These photoautotrophs form macroscopic colonies that serve as relatively nutrient-rich substrates that are colonized by many other organisms. The nature of these associations may modulate ocean N and carbon (C) cycling, and can offer insights into marine co-evolutionary mechanisms. Here we integrate multiple omics-based and experimental approaches to investigate Trichodesmium-associated bacterial consortia in both laboratory cultures and natural environmental samples. These efforts have identified the conserved presence of a species of Gammaproteobacteria (Alteromonas macleodii), and enabled the assembly of a near-complete, representative genome. Interorganismal comparative genomics between A. macleodii and Trichodesmium reveal potential interactions that may contribute to the maintenance of this association involving iron and phosphorus acquisition, vitamin B12exchange, small C compound catabolism, and detoxification of reactive oxygen species. These results identify what may be a keystone organism within Trichodesmium consortia and support the idea that functional selection has a major role in structuring associated microbial communities. These interactions, along with likely many others, may facilitate Trichodesmium’s unique open-ocean lifestyle, and could have broad implications for oligotrophic ecosystems and elemental cycling.

The nitrogen (N)-fixing cyanobacterium Trichodesmiumis globally distributed in warm, oligotrophic oceans, where it contributes a substantial proportion of new N and fuels primary production. These photoautotrophs form macroscopic colonies that serve as relatively nutrient-rich substrates that are colonized by many other organisms. The nature of these associations may modulate ocean N and carbon (C) cycling, and can offer insights into marine co-evolutionary mechanisms. Here we integrate multiple omics-based and experimental approaches to investigate Trichodesmium-associated bacterial consortia in both laboratory cultures and natural environmental samples. These efforts have identified the conserved presence of a species of Gammaproteobacteria (Alteromonas macleodii), and enabled the assembly of a near-complete, representative genome. Interorganismal comparative genomics between A. macleodiiand Trichodesmiumreveal potential interactions that may contribute to the maintenance of this association involving iron and phosphorus acquisition, vitamin B12exchange, small C compound catabolism, and detoxification of reactive oxygen species. These results identify what may be a keystone organism within Trichodesmiumconsortia and support the idea that functional selection has a major role in structuring associated microbial communities. These interactions, along with likely many others, may facilitate Trichodesmium’sunique open-ocean lifestyle, and could have broad implications for oligotrophic ecosystems and elemental cycling.

Gephyrocapsa oceanicais a widespread species of coccolithophore that has a significant impact on the global carbon cycle through photosynthesis and calcium carbonate precipitation. We investigated combined effects of light (50 µmol m-2s-1, 190 µmol m-2s-1, and 400 µmol m-2s-1) and the nitrogen sources NO3-and NH4+on its physiological performance under nitrogen-limited conditions. The specific growth rate was highest at the mid-range light level of 190 µmol m-2s-1, where it was further accelerated by NH4+relative to NO3-. There were no significant growth rate differences between NO3-- and NH4+-grown cells at the two light levels either above or below this optimum irradiance. Cellular particulate organic carbon (POC) and nitrogen (PON) content were not significantly affected by different light intensities and nitrogen sources. However, both the cellular particulate inorganic carbon (PIC) content and the PIC to POC ratio were greatly decreased by increased light levels, and were further decreased by NH4+only at the highest light level. Non-photochemical quenching (NPQ) increased with increasing light intensity, and was higher in NO3-rather than in NH4+-grown cells at medium and high light intensities. Our results demonstrate that under low, relatively realistic oceanic nitrogen concentrations, increasing light intensity and the replacement of NO3-by NH4+would have a significant negative effect on the calcification of the coccolithophore G. oceanica. If these findings are also applicable to other coccolithophore species, the future ocean carbon cycle may be greatly affected.

A low‐cost micro‐stereolithography technique with the ability to additively manufacture dense piezoelectric ceramic components is reported. This technique enables the layer‐wise production of functional devices with a theoretical in‐plane resolution of ∼20 μm and an out‐of‐plane resolution of <1 μm without suffering a significant reduction in the piezoelectric properties when compared to conventionally produced ceramics of the same composition. The ability to fabricate devices in complex geometries and with different material properties means that conventional limits of manufacturing are not present. A hollow, spherical shell of the piezoelectric material 0.65Pb(Mg⅓Nb⅔)O3–0.35PbTiO3, built without tooling or recourse to additional equipment or processes, is shown generating ultrasound in the MHz range.

A regional scale TEMPEST208airborne electromagnetic survey was flown in north-east Namibia in 2011. With broad line spacing (4 km) and a relatively low-powered, fixed-wing system, the approach was intended to provide a regional geo-electric map of the area, rather than direct detection of potential mineral deposits.A key component of the geo-electric profiling was to map the relative thickness of the Kalahari sediments, which is up to 200 m thick and obscures most of the bedrock in the area. Knowledge of the thickness would allow explorers to better predict the costs of exploration under the Kalahari. An additional aim was to determine if bedrock conductors were detectable beneath the Kalahari cover.The system succeeded in measuring the Kalahari thickness where this cover was relatively thin and moderately conductive. Limitations in depth penetration mean that it is not possible to map the thickness in the centre of the survey area, and much of the northern half of the survey area. Additional problems arise due to the variable conductivity of the Kalahari cover. Where the conductivity of the Kalahari sediment is close to that of the basement, there is no discernable contrast to delineate the base of the Kalahari.Basement conductors are visible beneath the more thinly covered areas such as in the north-west and south of the survey area. The remainder of the survey area generally comprises deeper, more conductive cover and for the most part basement conductors cannot be detected.A qualitative comparison with VTEM data shows comparable results in terms of regional mapping, and suggests that even more powerful systems such as the VTEM may not detect discrete conductors beneath the thick conductive parts of the Kalahari cover.

Coastal upwelling regimes associated with eastern boundary currents are the most biologically productive ecosystems in the ocean. As a result, they play a disproportionately important role in the microbially mediated cycling of marine nutrients. These systems are characterized by strong natural variations in carbon dioxide concentrations, pH, nutrient levels and sea surface temperatures on both seasonal and interannual timescales. Despite this natural variability, changes resulting from human activities are starting to emerge. Carbon dioxide derived from fossil fuel combustion is adding to the acidity of upwelled low-pH waters. Low-oxygen waters associated with coastal upwelling systems are growing in their extent and intensity as a result of a rise in upper ocean temperatures and productivity. And nutrient inputs to the coastal ocean continue to grow. Coastal upwelling systems may prove more resilient to changes resulting from human activities than other ocean ecosystems because of their ability to function under extremely variable conditions. Nevertheless, shifts in primary production, fish yields, nitrogen gain and loss, and the flux of climate-relevant gases could result from the perturbation of these highly productive and dynamic ecosystems.

Much of the bioavailable nitrogen that supports open ocean food webs and biogeochemical cycles is fixed from the atmosphere by marine cyanobacteria of the genera Trichodesmium and Crocosphaera. In previous experiments carried out with a limited set of cyanobacterial isolates, rates of cyanobacterial nitrogen fixation were shown to increase with carbon dioxide concentrations. Here, we report results from a series of laboratory experiments in which we grew seven strains of Trichodesmium and Crocosphaera from the Atlantic and Pacific oceans under a wide range of carbon dioxide concentrations, and monitored rates of nitrogen fixation and growth. We document large, strain-specific differences in the relationship between nitrogen fixation and carbon dioxide concentration, suggesting that individual strains within each genus are adapted to grow and fix nitrogen at different concentrations of carbon dioxide. We apply kinetic constants from the individual carbon dioxide response curves to an illustrative biogeochemical model of the ocean in 2100, which suggests that strains adapted to high carbon dioxide concentrations could potentially be favoured in a future acidified ocean. We suggest that surface ocean carbon dioxide concentrations could constitute a previously unrecognized selective force that shapes the community composition and diversity of nitrogen-fixing cyanobacteria.

Carbon dioxide and light are two major prerequisites of photosynthesis. Rising CO2levels in oceanic surface waters in combination with ample light supply are therefore often considered stimulatory to marine primary production. Here we show that the combination of an increase in both CO2and light exposure negatively impacts photosynthesis and growth of marine primary producers. When exposed to CO2concentrations projected for the end of this century, natural phytoplankton assemblages of the South China Sea responded with decreased primary production and increased light stress at light intensities representative of the upper surface layer. The phytoplankton community shifted away from diatoms, the dominant phytoplankton group during our field campaigns. To examine the underlying mechanisms of the observed responses, we grew diatoms at different CO2concentrations and under varying levels (5–100%) of solar radiation experienced by the phytoplankton at different depths of the euphotic zone. Above 22–36% of incident surface irradiance, growth rates in the high-CO2-grown cells were inversely related to light levels and exhibited reduced thresholds at which light becomes inhibitory. Future shoaling of upper-mixed-layer depths will expose phytoplankton to increased mean light intensities. In combination with rising CO2levels, this may cause a widespread decline in marine primary production and a community shift away from diatoms, the main algal group that supports higher trophic levels and carbon export in the ocean.

The detection of specific chemicals when concealed behind a layer of clothing is reported using near infrared (NIR) spectroscopy. It is found that concealment modifies the spectrum of a particular chemical when recorded at stand-off ranges of three meters in a diffuse reflection experiment. Chemometric analysis of the spectra has been performed with neural network-based pattern recognition/classification to deal with this problem. Neural networks help to overcome nonlinearities within the calibration/training dataset, affording more robust modelling. The work has been shown to both allow detection of specific chemicals concealed behind a single intervening layer of fabric material, and to estimate the concentration of hydrogen peroxide using partial least squares regression (PLSR).

The detection of specific chemicals when concealed behind a layer of clothing is reported using near infrared (NIR) spectroscopy. Concealment modifies the spectrum of a particular chemical when recorded at stand-off ranges of three meters in a diffuse reflection experiment. The subsequent analysis to identify a particular chemical has involved employing calibration models such as principal component regression (PCR) and partial least squares regression (PLSR). Additionally, detection has been attempted with good results using neural networks. The latter technique serves to overcome nonlinearities in the calibration/training dataset, affording more robust modelling. Finally, lock-in amplification of spectral data collected in through-transmission arrangement has been shown to allow detection at SNR as low as -60dB. The work has been shown to both allow detection of specific chemicals concealed behind a single intervening layer of fabric material, and to estimate the concentration of certain liquids.

Measurements are presented which demonstrate that near infrared (NIR) spectroscopy can be used to identify chemicals concealed behind clothing. This has been achieved for detector stand-off distances of 3 m. The optical properties of a range of clothing materials have been investigated, and the transmission of NIR signals found to be sufficient for spectroscopy. The study has shown that granular solid materials can be identified when hidden behind a layer of clothing. Examples of chemicals used in this study include ammonium nitrate and other ammonium salts. Details of the current measurements and results are given, together with suggestions for increasing detection sensitivity.

Climate change will alter concurrently many environmental factors that exert control over oceanic phytoplankton. Recent laboratory culture work, shipboard experiments, and field surveys reveal many remaining unknowns about the bottom‐up controls for five globally important algal groups. Increasing uncertainties exist, respectively, for picocyanobacteria, diatoms, Phaeocystisspp., N2‐fixing cyanobacteria, and coccolithophores. This missing information about current environmental controls will hinder progress in modeling how these phytoplankton will be influenced by climate change. A review of conceptual approaches used to elucidate the relationship between environmental controls and phytoplankton dominance, from Margalef's mandala to functional traits, uncovered limitations regarding their application to climate‐change scenarios. For example, these previous approaches have insufficient scope or dimensions to take into account the confounding effects of synergistic and antagonistic interactions of multiple environmental change variables. A new approach is needed that considers all of the different environmental properties altered by climate change and their interactions while at the same time permitting a subset of the most significant controls for a specific phytoplankton group to be isolated and evaluated in factorial matrix perturbation experiments. We advocate three new interlinked approaches, including environmental clusters that incorporate all factors (temperature, CO2, light, nutrients, and trace metals), which both exert control over present‐day floristics and will be altered by climate change. By carefully linking a holistic conceptual approach to a reductionist experimental design, the future responses of open‐ocean phytoplankton groups to a complex, rapidly changing environment can be better predicted.

As a key intermediate in the nitrogen cycle, nitrite is involved in multiple biological pathways that regulate the distribution and availability of nitrogen in the ocean. In the oligotrophic gyres, nitrite accumulates near the base of the euphotic zone, demonstrating a subsurface maximum, termed the primary nitrite maximum; while in subpolar regions, nitrite concentrations are elevated in the near‐surface ocean. As yet, the mechanisms controlling this meridional pattern remain unclear. Here, we present vertically resolved profiles of rates of nitrite production and consumption extending from the Subtropical Gyre to the Subarctic Front in the North Pacific Ocean. Our results indicate that the latitudinal distributions of nitrite across this basin are influenced by variations in phytoplankton‐nitrifier interactions. In the well‐lit oligotrophic surface, phytoplankton dominates rapid nitrite cycling via coupled release and re‐assimilation; below the euphotic zone, diminished light stress on nitrite oxidizers results in rapid turnover and limits nitrite. By contrast, in subpolar regions where nitrate concentrations are elevated in the euphotic zone, nitrite is released during assimilative nitrate reduction and competition between phytoplankton and nitrifiers for ammonium is relaxed, facilitating ammonia oxidation. These processes, together with differential light sensitivities of ammonia and nitrite oxidizers, allow net accumulation of nitrite. Furthermore, we demonstrate a substantial contribution of urea oxidation in forming the primary nitrite maximum and balancing the two steps of marine nitrification. Our findings reveal physical‐biological interactive controls on nitrite cycling and distributions in the ocean and help disentangle the complex effect of phytoplankton‐microbe interactions on marine nitrogen biogeochemistry. Nitrite is a key intermediate between reduced and oxidized forms of nitrogen that is involved in numerous biological processes in the marine nitrogen cycle. Throughout the world's oceans, concentrations of nitrite vary spatially, with concentrations in the subtropics often demonstrating a subsurface maximum, while concentrations are often elevated in the euphotic zone in the tropics and subpolar regions. To date, the mechanisms and processes governing the vertical distributions of nitrite remain controversial. By investigating a suite of processes catalyzing nitrite cycling across the Northwestern Pacific, we show that spatially variable interactions between phytoplankton and planktonic nitrifiers regulate pathways and rates of nitrite cycling. These processes together shape nitrite distribution patterns at the basin scale. Additionally, we demonstrate the significance of urea oxidation in marine nitrogen recycling in terms of contributing to the primary nitrite maximum formation and maintaining the homeostasis of the two steps of nitrification. At the basin scale, the PNM exhibits a unique meridional patternNitrate‐dependent phytoplankton‐nitrifier interactions result in distinctive nitrite accumulation patterns in different ocean regionsFollowing ammonia oxidation, urea oxidation represents the second largest nitrite source playing an essential role to form the PNM At the basin scale, the PNM exhibits a unique meridional pattern Nitrate‐dependent phytoplankton‐nitrifier interactions result in distinctive nitrite accumulation patterns in different ocean regions Following ammonia oxidation, urea oxidation represents the second largest nitrite source playing an essential role to form the PNM

Diese Arbeit unternimmt den Versuch einer gemeinsamen Interpretation der geologischen und geophysikalischen Daten der oberkretarzischen Intrusivkomplexe von Messum-Krater und Brandberg. Beide Komplexe sind durch starke magnetische Anomalien gekennzeichnet. Für Messum vorliegende Schweredaten und refraktionsseismische Profile zeigen im Bereich des Kraters eine positive Schwereanomalie und anomal hohe P-Wellengeschwindigkeiten in der mittleren und unteren Kruste. Der Messum-Komplex besteht vorwiegend aus einer konzentrischen Abfolge von Gabbro- und Syenitintrusionen, die nur ein geringes topographisches Relief aufweisen. Dagegen erhebt sich der Brandberg 1500 m über die Ebene der Namib-Wüste und besteht – abgesehen von einer kleinen monzonitischen Vorläuferintrusion – ausschließlich aus Granit. Unser Modell für die Krustenstruktur des Messum zeigt eine subvertikale Intrusionszone, deren Breite den Ausmaßen des Kraters an der Oberfläche nahe kommt. Dichte- und seismischer Geschwindigkeitskontrast zu den unintrudierten Bereich der Sektion sind entlang des vertikalen Krustenprofils unter Messum konstant und deuten damit auf ein gleichbleibendes Verhältnis von intrudiertem Material und Nebengestein hin. Modellierungen der magnetischen und der Schweredaten lassen bis hinab zur Moho auf einen Anteil von ca. 30% Gabbro schließen. Dies steht im Gegensatz zu der Annahme, dass der Messum-Krater das Eruptionszentrum für 8500 km3 felsischer Vulkanite der Paraná-Etendeka-Provinz ist. Unser mit den magnetischen Daten des Brandbergs übereinstimmendes Krustenmodell zeigt eine geschichtete Intrusion mit einer gabbroiden Basis. Das Modell ist konsistent mit den petrologischen Daten, die eine Mantelherkunft des Brandbergs-Granits anzeigen. Obwohl die Geometrie des Modells einige Unsicherheiten aufweist, sind doch bestimmte Eigenschaften als gesichert einzustufen. Zunächst sind weder der Granit noch der Monzonit allein in der Lage, die beobachtete magnetische Anomalie zu erklären. Es muss ein Körper wesentlich höherer Suszeptibilität unter dem Granit und dem Monzonit vorhanden sein, bei dem es sich unserer Ansicht nach um einen Mantel-abgeleiteten gabbroiden Körper handelt, der im Prozess der Fraktionierung die Granitoide produziert hat. Weiterhin verlangt die Form der magnetischen Anomalie, dass die gabbroide Intrusion in der Oberkruste liegt, ihre Breite größer ist als die des anstehenden Granits und ihre Ränder nach außen einfallen.