Fine scale variability in methanol uptake and oxidation in the micro-layer and near-surface waters of the Atlantic

The aim of this research was to make the first depth profiles of the microbial assimilation of methanol carbon and its oxidation to carbon dioxide and use as an energy source from the microlayer to 1000 m. Some of the highest reported methanol oxidation rate constants of 0.5–0.6 d−1 were occasionally found in the microlayer and immediately underlying waters (10 cm depth), albeit these samples also showed the greatest heterogeneity compared to other depths down to 1000 m. Methanol uptake into the particulate phase was exceptionally low in microlayer samples, suggesting that any methanol utilised by microbes in this environment is for energy generation. The sea surface microlayer and 10 cm depth also showed a higher proportion of bacteria with a low DNA content, and bacterial leucine uptake rates in surface microlayer samples were either less than or the same as those in the underlying 10 cm layer. The average methanol oxidation and particulate rates were however statistically the same throughout the depths sampled, although the latter were highly variable in the near-surface 0.25–2 m compared to deeper depths. The statistically significant relationship demonstrated between uptake of methanol into particles and bacterial leucine incorporation suggests that many heterotrophic bacteria could be using methanol carbon for cellular growth. On average, methanol bacterial growth efficiency (BGEm) in the top 25 m of the water column is 6% and decreases with depth. Although, for microlayer and 10 cm-depth samples, BGEm is less than the near-surface 25–217 cm, possibly reflecting increased environmental UV stress resulting in increased maintenance costs, i.e. energy required for survival. We conclude that microbial methanol uptake rates, i.e. loss from seawater, are highly variable, particularly close to the seawater surface, which could significantly impact upon seawater concentrations and hence the air–sea flux.

Fine-scale variability in methanol uptake and oxidation: from the microlayer to 1000 m.

The aim of this research was to make the first depth profiles of the microbial assimilation of methanol carbon and its oxidation to carbon dioxide and use as an energy source from the microlayer to 1000 m. Some of the highest reported methanol oxidation rate constants of 0.5–0.6 d−1 were occasionally found in the microlayer and immediately underlying waters (10 cm depth), albeit these samples also showed the greatest heterogeneity compared to other depths down to 1000 m. Methanol uptake into the particulate phase was exceptionally low in microlayer samples, suggesting that any methanol utilised by microbes in this environment is for energy generation. The sea surface microlayer and 10 cm depth also showed a higher proportion of bacteria with a low DNA content, and bacterial leucine uptake rates in surface microlayer samples were either less than or the same as those in the underlying 10 cm layer. The average methanol oxidation and particulate rates were however statistically the same throughout the depths sampled, although the latter were highly variable in the near-surface 0.25–2 m compared to deeper depths. The statistically significant relationship demonstrated between uptake of methanol into particles and bacterial leucine incorporation suggests that many heterotrophic bacteria could be using methanol carbon for cellular growth. On average, methanol bacterial growth efficiency (BGEm) in the top 25 m of the water column is 6% and decreases with depth. Although, for microlayer and 10 cm-depth samples, BGEm is less than the near-surface 25–217 cm, possibly reflecting increased environmental UV stress resulting in increased maintenance costs, i.e. energy required for survival. We conclude that microbial methanol uptake rates, i.e. loss from seawater, are highly variable, particularly close to the seawater surface, which could significantly impact upon seawater concentrations and hence the air–sea flux.

In hot water: zooplankton and climate change

An overview is provided of the observed and potential future responses of zooplankton communities to global warming. I begin by describing the importance of zooplankton in ocean ecosystems and the attributes that make them sensitive beacons of climate change. Global warming may have even greater repercussions for marine ecosystems than for terrestrial ecosystems, because temperature influences water column stability, nutrient enrichment, and the degree of new production, and thus the abundance, size composition, diversity, and trophic efficiency of zooplankton. Pertinent descriptions of physical changes in the ocean in response to climate change are given as a prelude to a detailed discussion of observed impacts of global warming on zooplankton. These manifest as changes in the distribution of individual species and assemblages, in the timing of important life-cycle events, and in abundance and community structure. The most illustrative case studies, where climate has had an obvious, tangible impact on zooplankton and substantial ecosystem consequences, are presented. Changes in the distribution and phenology of zooplankton are faster and greater than those observed for terrestrial groups. Relevant projected changes in ocean conditions are then presented, followed by an exploration of potential future changes in zooplankton communities from the perspective of different modelling approaches. Researchers have used a range of modelling approaches on individual species and functional groups forced by output from climate models under future greenhouse gas emission scenarios. I conclude by suggesting some potential future directions in climate change research for zooplankton, viz. the use of richer zooplankton functional groups in ecosystem models; greater research effort in tropical systems; investigating climate change in conjunction with other human impacts; and a global zooplankton observing system.

Reduction in photosystem II efficiency during a virus-controlled Emiliania huxleyi bloom

During viral infection of Emiliania huxleyi, laboratory studies have shown that photo-system (PS) II efficiency declines during the days post-infection and is thought to be associated with viral-induced interruption of electron transport rates between photosystems. However,measuring the impact of viral infection on PSII function in E. huxleyi populations from natural,taxonomically diverse phytoplankton communities is difficult, and whether this phenomenon occurs in nature is presently unknown. Here, chlorophyll fluorescence analysis was used to assess changes in PSII efficiency throughout an E. huxleyi bloom during a mesocosm experiment off the coast of Norway. Specifically, we aimed to determine whether a measurable suppression of the efficiency of PSII photochemistry could be observed due to viral infection of the natural E. huxleyi populations. During the major infection period prior to bloom collapse, there was a significant reduction in PSII efficiency with an average decrease in maximum PSII photochemical efficiency (Fv/Fm) of 17% and a corresponding 75% increase in maximum PSII effective absorption cross section(σPSII); this was concurrent with a significant decrease in E. huxleyi growth rates and an increase in E. huxleyi virus (EhV) production. As E. huxleyi populations dominated the phytoplankton community and potentially contributed up to 100% of the chlorophyll a pool, we believe that the variable chlorophyll fluorescence signal measured during this period was derived predominantly from E. huxleyi and, thus, reflects changes occurring within E. huxleyi cells. This is the first demonstration of suppression of PSII photochemistry occurring during viral infection of natural coccolithophore populations.