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It concerns the open access paper published as a Review paper by Baker et al., Sci. Adv. 2021; 7 : eabd8800 7 July 2021, with the following abstract "Anthropogenic emissions to the atmosphere have increased the flux of nutrients, especially nitrogen, to the ocean, but they have also altered the acidity of aerosol, cloud water, and precipitation over much of the marine atmosphere. For nitrogen, acidity-driven changes in chemical speciation result in altered partitioning between the gas and particulate phases that subsequently affect long-range transport. Other important nutrients, notably iron and phosphorus, are affected, because their soluble fractions increase upon exposure to acidic environments during atmospheric transport. These changes affect the magnitude, distribution, and deposition mode of individual nutrients supplied to the ocean, the extent to which nutrient deposition interacts with the sea surface microlayer during its passage into bulk seawater, and the relative abundances of soluble nutrients in atmospheric deposition. Atmospheric acidity change therefore affects ecosystem composition, in addition to overall marine productivity, and these effects will continue to evolve with changing anthropogenic emissions in the future. "

Iron supply is thought to regulate primary production in high nitrate, low chlorophyll (HNLC) regions of the sea in both the past and the present. A critical aspect of this relationship is acquisition of iron (Fe) by phytoplankton, which occurs through a complex series of extracellular reactions that are influenced by Fe chemistry and speciation. During the first in situ mesoscale Fe-enrichment experiment in the Southern Ocean (Southern Ocean iron release experiment [SOIREE]), we monitored the uptake of Fe by three size classes of plankton and their ensuing physiological response to the Fe enrichment. Rates of Fe uptake from both inorganic Fe (Fe') and organic Fe complexes (FeL) were initially fast, indicative of Fe-limitation. After Fe enrichment phytoplankton down-regulated Fe uptake and optimized physiological performance, but by day 12 they had greatly increased their capacity to acquire Fe from FeL. The increase in Fe uptake from FeL coincided with a sixfold decrease in Fe' that followed the production of Fe-binding organic ligands. Phytoplankton were able to use organically bound Fe at rates sufficient to maintain net growth for more than 42 d. Adaptation to such shifts in Fe chemistry may contribute to bloom longevity in these polar HNLC waters.

Vivaspin6 (R) ultrafiltration units with molecular weight "cut-off" membranes of 5, 10, 30, 50, and 100 kDa were used together to examine the size distribution of newly formed iron (Fe) colloids in natural seawater samples and in the presence of several different Fe chelators with varying Fe binding strength. Artificial Fe chelators, such as TAC, and 2 kDG, when added at equimolar levels to Fe, supported the formation of a continuum of Fe-ligand colloids between 5 and 100 kDa. More than 90% of the added Fe-55 in these solutions occurred in Fe aggregates/particles larger than 100 kDa. The strong siderophore DFO held the majority of the added Fe-55 in the "truly" soluble fraction = 10 kDa showed similar "cut-off" properties on natural seawater samples collected in the water column off the Peruvian coast. Fe solubility determined with these membranes was approximately six times greater than Fe solubility determined with the 5 kDa membrane and the 0.02 mu m syringe filters. This suggests that a seamless size continuum of organic chelators (

Iron (Fe) is a limiting nutrient for phytoplankton productivity in many different oceanic regions. A critical aspect underlying iron limitation is its low solubility in seawater as this controls the distribution and transport of iron through the ocean. Processes which enhance the solubility of iron in seawater, either through redox reactions or organic complexation, are central to understanding the biogeochemical cycling of iron. In this work we combined iron solubility measurements with parallel factor (PARAFAC) data analysis of CDOM fluorescence along a meridional transect through the Atlantic (PS ANT XXVI-4) to examine the hypothesis that marine humic fluorescence is a potential proxy for iron solubility in the surface ocean. PARAFAC analysis revealed 4 components, two humic like substances and two protein-like. Overall none of the 4 components were significantly correlated with iron solubility, though humic-like components were weakly correlated with iron solubility in iron replete waters. Our analysis suggests that the ligands responsible for maintaining iron in solution in the euphotic zone are sourced from both remineralisation processes and specific ligands produced in response to iron stress and are not easily related to bulk CDOM properties. The humic fluorescence signal was sharply attenuated in surface waters presumably most likely due to photo bleaching, though there was only a weak correlation with the transient photo product H2O2, suggesting longer lifetimes in the photic zone for the fluorescent components identified here. Key Points: - humic-like components correlated with Fe solubility in iron repleted water - ligands are sourced from remineralisation processes produced to Fe stress - humic flu sharply attenuated in surface waters, but only weak corr. with H2O2

Surface water distributions of dissolved Al (dAl) and dissolved Ti (dTi) were investigated along a meridional Atlantic transect and related to dust deposition estimates. In the zone of Saharan dust deposition, highest dAl concentrations occurred in the tropical salinity minimum and suggest increasing Al dissolution from Saharan aerosols with wet deposition. By contrast, the dTi distribution is not related to precipitation but agrees with the pattern of annual dust deposition. In the zone of Patagonian dust deposition, elevated dTi concentrations contrasted with decreased dAl concentrations, indicating excess dAl scavenging onto biogenic particles in surface waters. Estimated residence times range from months to years for dAl and are ∼10 times higher for dTi. This suggests that dAl reflects seasonal changes in dust deposition, while dTi is related to longer temporal scales. However, spatial variations in input and removal processes complicate the quantification of dust deposition from surface water concentrations.

Seventeen inorganic germanium and silicon concentration profiles collected from the Atlantic, southwest Pacific, and Southern oceans are presented. A plot of germanium concentration versus silicon concentration produced a near-linear line with a slope of 0.760 × 10−6 (±0.004) and an intercept of 1.27 (±0.24) pmol L−1 (r2 = 0.993, p < 0.001). When the germanium-to-silicon ratios (Ge/Si) were plotted versus depth and/or silicon concentrations, higher values are observed in surface waters (low in silicon) and decreased with depth (high in silicon). Germanium-to-silicon ratios in diatoms (0.608–1.03 × 10−6) and coupled seawater samples (0.471–7.46 × 10−6) collected from the Southern Ocean are also presented and show clear evidence for Ge/Si fractionation between the water and opal phases. Using a 10 box model (based on PANDORA), Ge/Si fractionation was modeled using three assumptions: (1) no fractionation, (2) fractionation using a constant distribution coefficient (KD) between the water and solid phase, and (3) fractionation simulated using Michaelis-Menten uptake kinetics for germanium and silicon via the silicon uptake system. Model runs indicated that only Ge/Si fractionation based on differences in the Michaelis-Menten uptake kinetics for germanium and silicon can adequately describe the data. The model output using this fractionation process produced a near linear line with a slope of 0.76 × 10−6 and an intercept of 0.92 (±0.28) pmol L−1, thus reflecting the oceanic data set. This result indicates that Ge/Si fractionation in the global ocean occurs as a result of subtle differences in the uptake of germanium and silicon via diatoms in surface waters.

The oceans are by far the largest global reservoir of carbon that is available on climate relevant timescales (< 1000 yrs). A fraction of this oceanic carbon pool, comparable in magnitude with the CO2 inventory of today’s atmosphere, is transformed via biological assimilation of inorganic carbon into dissolved or particulate organic material within the sun-lit surface ocean. Subsequently this material can be respired, returning to the ocean as CO2, or it can sink to the sediments and this forms the basis of the ‘biological pump’. The efficiency of this pump is limited by the availability of nutrients, which are essential prerequisites for the growth of phytoplankton. We now know that vast areas of the surface ocean have extremely low nutrient concentrations limiting productivity. For instance, in the subtropical oceanic gyres, which comprise more than 40% of the Earth’s surface, the macronutrients nitrate, nitrite, ammonia and phosphate are depleted to trace levels which limit phytoplankton abundance so strongly such that the term “oceanic desert” was coined for these regions.

A Synechococcus sp. strain PCC 7002 Fe bioreporter was constructed containing the isiAB promoter fused to the Vibrio harveyi luxAB genes. Bioreporter luminescence was characterized with respect to the free ferric ion concentration in trace metal-buffered synthetic medium. The applicability of the Fe bioreporter to assess Fe availability in the natural environment was tested by using samples collected from the Baltic Sea and from the high-nutrient, low-chlorophyll subarctic Pacific Ocean. Parallel assessment of dissolved Fe and bioreporter response confirmed that direct chemical measurements of dissolved Fe should not be considered alone when assessing Fe availability to phytoplankton.

An improved knowledge of iron biogeochemistry is needed to better understand key controls on the functioning of high-nitrate low-chlorophyll (HNLC) oceanic regions. Iron budgets for HNLC waters have been constructed using data from disparate sources ranging from laboratory algal cultures to ocean physics. In summer 2003 we conducted FeCycle, a 10-day mesoscale tracer release in HNLC waters SE of New Zealand, and measured concurrently all sources (with the exception of aerosol deposition) to, sinks of iron from, and rates of iron recycling within, the surface mixed layer. A pelagic iron budget (timescale of days) indicated that oceanic supply terms (lateral advection and vertical diffusion) were relatively small compared to the main sink (downward particulate export). Remote sensing and terrestrial monitoring reveal 13 dust or wildfire events in Australia, prior to and during FeCycle, one of which may have deposited iron at the study location. However, iron deposition rates cannot be derived from such observations, illustrating the difficulties in closing iron budgets without quantification of episodic atmospheric supply. Despite the threefold uncertainties reported for rates of aerosol deposition (Duce et al., 1991), published atmospheric iron supply for the New Zealand region is ∼50-fold (i.e., 7- to 150-fold) greater than the oceanic iron supply measured in our budget, and thus was comparable (i.e., a third to threefold) to our estimates of downward export of particulate iron. During FeCycle, the fluxes due to short term (hours) biological iron uptake and regeneration were indicative of rapid recycling and were tenfold greater than for new iron (i.e. estimated atmospheric and measured oceanic supply), giving an “fe” ratio (uptake of new iron/uptake of new + regenerated iron) of 0.17 (i.e., a range of 0.06 to 0.51 due to uncertainties on aerosol iron supply), and an “Fe” ratio (biogenic Fe export/uptake of new + regenerated iron) of 0.09 (i.e., 0.03 to 0.24).

Nitrogen fixation supports new production in the oligotrophic oceans and removes dinitrogen and carbon dioxide from mixed layer waters. N‐fixation rates have been estimated in various ways but measurements are still too rare and factors limiting N‐fixation are not yet fully understood. Here we present data from a transect along 10°N through the tropical Atlantic on the Meteor Cruise 55 where N‐fixation rates between 3.7 and 255 μmol N*m−2*d−1 were recorded. The highest rates occurred off Africa in the eastern tropical North Atlantic (ETNA), and in the Amazon River plume in the West and contributed to 1–12.2% of the N‐demand of primary production. N‐fixation rates correlated with dissolved Fe concentrations, which were 20–280 times greater than the estimated demand. High atmospheric Fe inputs combined with the shallow nutricline make the ETNA a favourable environment for N‐fixers.

H2O2 was measured in the upper water column (0–200 m) along a west-east transect through the Equatorial Atlantic as part of the German SOLAS (Surface Ocean Lower Atmosphere) cruise Meteor 55 (M55). Vertical profiles of H2O2 showed characteristic exponential decay consistent with light profiles and rainwater inputs. Integrated (0–100 m) water column H2O2 inventories ranged from 1.1–8.9 mmol m−2 with the highest values in the Amazon Plume. H2O2 inventories were also higher at the Equatorial Upwelling and after heavy rain showers in the region of the Inter Tropical Convergence Zone (ITCZ). Analysis of rain water samples collected during the cruise gave a volume weighted mean of 10.8 μmol L−1 (range 1.5–22.3 μmol L−1). This work highlights the importance of rainwater as a major source for H2O2 in the surface waters under the ITCZ.

Measurements of dissolved (DFe) and total iron (TFe) in the upper water column are presented from the German SOLAS (Surface Ocean ‐ Lower Atmosphere Study) cruise (M55), along a west to east transect at 10°N, in the equatorial Atlantic in October/November 2002. Aerosol samples were collected simultaneously during this time and are used to estimate an iron flux to the surface waters. Resulting flux estimates combined with iron inventories in the near surface waters reveal extremely short fractional mean residence times (6–62 days) for total (dissolved and particulate) iron in waters directly under the path of Saharan dust plumes. These results suggest that individual dust storms can supply a significant amount of the present iron upper water column inventory which is subsequent rapidly removed by aggregation and sinking.

Marine litter and microplastics in particular have for some time now been postulated to be of environmental concern. Despite the ever-increasing amount of microplastic studies, conclusive evidence of the adverse effects of microplastics in the pelagic realm is currently deficient. Specifically, there is a need to look at contamination of key species in the environment and to conduct well-constructed cause and effect studies in order to make tangible conclusions about the potential environmental risks of microplastics. This type of study proves to be particularly challenging for the pelagic realm due to its diversity and dynamic nature. The work presented within this thesis aimed to assess how key ecological players interact with microplastics in the pelagic realm and what potential adverse effects these interactions present to the environment. Study organisms were chosen along two gradients, being organism size (macro to micro) and environmental nutrient saturation (eutrophic to oligotrophic). By doing so I was able to gain important insights into the pathways of microplastics in the pelagic realm. Microplastic contamination of seven species of mesopelagic fishes, sampled from a nutrient rich warm-core eddy in the Northwest Atlantic, was investigated. With 73% of all of 233 assessed fish containing microplastics these fish seem to be particularly prone to microplastic contamination. Internalisation of microplastics could have happened either through direct ingestion from the sea water or through transfer from their planktivorous prey. Similarity in microplastic colour, size and shape to those sampled from the seawater indicates direct ingestion. Nevertheless, through the application of small mesh sizes of microplastic-retaining filters, this is the first study reporting microplastics in the gut contents of these fishes which overlap in size with food targeted by their planktivorous prey. Such high rates of microplastic contamination may have knock-on effects on individual fish health and those of their predators. For the gelatinous filter-feeding salps, which were exposed to microplastics in the laboratory, an effect on an individual level is unlikely as microplastics were simply in- and subsequently egested through incorporation into their faecal pellets. The incorporation of microplastics into salp faecal pellets did, however, slow down the pellets’ sinking speed. High sinking velocities are a pivotal characteristic of this type of particulate organic matter as these allow it to bypass recycling in the upper water column and thus enable carbon sequestration to the ocean floor. Therefore, I show that microplastics may pose a threat to the distribution of organic matter in the water column and the cycling of carbon within the biological pump. Lastly, microplankton communities sampled in the oligotrophic waters of the subtropical South Pacific were exposed to nanoplastic particles and ingestion by microzooplankton was investigated. Through experimental observations and encounter rate calculations it was shown that ingestion by microzooplankton is unlikely. For waters containing higher amounts of organic matter, coagulation of nanoplastics with such matter was demonstrated. This re-packages nanoplastics in a way that allows for their dispersal in the water column and increases their bioavailability. In waters where such matter is not sufficiently present a likely pathway could be filter-feeding ingestion by mucous grazers such as larvaceans and salps.

The late-Caledonian granites of south Connemara occupy a key location in the western Irish Caledonides. The granites comprise the Galway Granite Batholith and its satellite plutons of Roundstone, Inish, Omey and Letterfrack. The granite's 80 km long, WNW-trending axis reflects a stitching relationship between the granite and the EW-trending Skird Rocks Fault which is one of a number of major strike-slip faults that parallel the Iapetus suture in the British and Irish Caledonides. The NNE-SSW-trending Shannawona and the NNW-SSE-trending Barna Faults, divide the batholith into three blocks i.e. the Western, Central and Eastern Blocks. This study was focussed on a ~34 km2 area of the Western Block i.e. the Kilkieran Sector located ~60 km west of Galway city. Detailed geological mapping has identified five main granite types i.e. the Microgranite, the Glenaruid Layered Granite, the Megacrystic Porphyritic Granite, the Scainnimh Coarse Grained Granite and the Northern Coarse Grained Granite. A suite of NNE-SSW trending dikes were emplaced during final consolidation of the granite. Locally these display margins marked by brecciation and intricate injectional patterns with the host granite. Digital datasets were used to generate a 3D geological model for the area. Petrographic and whole rock geochemical studies of 45 samples show that the granites range from Monzo-Granite to Syeno-Granites while the Mafic Microgranular Enclaves plot in the Diorite field. Major and trace element bivariate and trivariate plots define linear differentiation trends from the less silicic coarse grained granites to the more silicic microgranites data. Rare Earth Element (REE) plots for the granites display LREE enrichment, negative Eu anomalies and HREE depletion similar to those displayed by granites elsewhere in the batholith. Hornblende-plagioclase geothermobarometry, from eight new locations in the batholith, place pressure constraints on crystallisation that range from 3.16 ±0.6 kb to 4.13 ±0.8 kb. Estimated crystallisation temperatures range from ~690oC to ~730oC. U-Pb zircon geochronometry was carried out on five samples i.e. the study area (3), the Carna Granite (1) and the Lough Fadda Granodiorite (1). All three samples from the study area yield an age of ~402 Ma, The Carna Granite sample yields an age of ~412 Ma and the Lough Fadda Granodiorite sample yields an age of 393 ±3.4 Ma. Re-Os molybenite geochronometry on a sample of An Maoileann Microgranite yields an age of 402.2 ±1.1 Ma. The Re-Os and U-Pb age determinations for this microgranite provide a maximum age for timing of emplacement of the dacite dike suite and by inference a maximum age for their host granites. The geobarometric and geochronometric data for all of the batholith are integrated with the spatial distribution and structural relationships of the granites to develop a Pressure-time model for the emplacement of the Galway Batholith.