ORCID Profile
0000-0002-6442-7121
Current Organisation
University of Tasmania
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Ecological Impacts of Climate Change | Biological Oceanography | Chemical Oceanography | Oceanography
Antarctic and Sub-Antarctic Oceanography | Marine Oceanic Processes (excl. climate related) |
Publisher: Wiley
Date: 06-2022
Publisher: Elsevier BV
Date: 10-2006
Publisher: CSIRO Publishing
Date: 2020
DOI: 10.1071/MF19200
Abstract: In this study we investigated the distribution of dissolved and particulate zinc (dZn and pZn respectively) and its isotopes in the Subantarctic Zone as part of a Geotraces Process voyage. dZn and pZn depth profiles contrasted each other, with dZn showing depletion within the euphotic zone while pZn profiles showed enrichment. Fitting a power law equation to the pZn profiles produced an attenuation factor of 0.82, which contrasted values for particulate phosphorus, cadmium and copper. The results indicate that zinc has a longer regeneration length scale than phosphorus and cadmium, but shorter than copper. The differential regeneration of pZn relative to that of particulate phosphorus likely explains why dZn appears to have a deeper regeneration profile than that of phosphate. The dZn isotope (δ66Zndissolved) profiles collected across the Subantarctic Zone showed differing profile structures. For one station collected within an isolated cold-core eddy (CCE), δ66Zndissolved showed surface enrichment relative to deep waters. The corresponding pZn isotope profiles within the CCE did not show enrichment rather, they were subtly depleted in surface waters and then converged to similar values at depth. Zinc isotope fractionation can be explained through a combination of fractionation processes associated with uptake by phytoplankton, zinc complexation by natural organic ligands and zinc regeneration from particulate matter.
Publisher: American Geophysical Union (AGU)
Date: 04-10-2005
DOI: 10.1029/2005GB002481
Publisher: Oxford University Press (OUP)
Date: 09-01-2018
Abstract: Observations from two research cruises made in 2008 and 2012 to east of New Zealand are put into context with satellite data to contrast and compare surface chlorophyll a evolution in the two years in order to explore mechanisms of phytoplankton bloom development in the southwest Pacific Ocean. In 2008, surface chlorophyll a largely followed the long-term climatological cycle, and 2008 can be considered a canonical year, where the autumn bloom is triggered by increasing vertical mixing at the end of summer and the spring bloom is triggered by decreasing vertical mixing at the end of winter. In contrast, 2012 was anomalous in that there was no autumn bloom, and in early spring there were several periods of sustained increase in surface chlorophyll a that did not become fully developed spring blooms. (In this region, we consider spring blooms to occur when surface chlorophyll a exceeds 0.5 mg m-3). These events can be related to alternating episodes of increased or decreased vertical mixing. The eventual spring bloom in October was driven by increased ocean cooling and wind stress (i.e. increased mixing) and paradoxically was driven by mechanisms considered more appropriate for autumn rather than spring blooms.
Publisher: Authorea, Inc.
Date: 14-06-2023
DOI: 10.22541/ESSOAR.168677216.63458355/V1
Abstract: Deep Chlorophyll Maxima (DCMs) are ubiquitous in low-latitude oceans, and of recognized biogeochemical and ecological importance. DCMs have been observed in the Southern Ocean, initially from ships and recently from profiling robotic floats, but with less understanding of their onset, duration, underlying drivers, or whether they are associated with enhanced biomass features. We report the characteristics of a DCM and DBM (Deep Biomass Maximum) in the Inter-Polar-Frontal-Zone (IPFZ) south of Australia from CTD profiles, shipboard-incubated s les, a towbody, and a BGC-ARGO float. The DCM and DBM were ~20 m thick and co-located with the nutricline, in the vicinity of a subsurface ammonium maximum characteristic of the IPFZ, but ~100 m shallower than the ferricline. Towbody transects demonstrated that the co-located DCM/DBM was broadly present across the IPFZ. Large healthy diatoms, with low iron requirements, resided within the DCM/DBM, and fixed up to 20 mmol C m-2 d-1. The BGC-ARGO float revealed the DCM/DBM persisted for months. We propose a dual environmental mechanism to drive DCM/DBM formation and persistence within the IPFZ: sustained supply of both recycled iron within the subsurface ammonium maxima and upward silicate transport from depth. DCM/DBM cell-specific growth rates were considerably slower than those in the overlying mixed layer, implying that phytoplankton losses are also reduced, possibly as a result of heavily silicified diatom frustules. The light-limited seasonal termination of the observed DCM/DBM did not result in a ‘diatom dump’, rather ongoing diatom downward export occurred throughout its multi-month persistence.
Publisher: Wiley
Date: 24-04-2021
DOI: 10.1002/LNO.11772
Abstract: Manganese (Mn) is an abundant element in the Earth's crust. However, its concentrations in open ocean seawater are low, where external inputs are scarce. In this study, we report the dissolved Mn and particulate Mn distributions in the Southern Ocean, measured along the GEOTRACES—SR3 transect, from Tasmania (Australia) to Antarctica in the Southern Ocean, during the austral summer 2018. Both dissolved Mn and particulate Mn concentrations were generally low away from localized sources ( 0.3 nmol L −1 and 0.1 nmol L −1 , respectively) along the transect. Our observations of a lower labile particulate fraction than previously measured suggest the Southern Ocean has a unique particulate Mn composition. Low surface dissolved Mn concentrations were attributed to biological uptake and few external sources. Our results suggest biological control of the Mn cycle was higher above the Antarctic continental slope, compared to the rest of the section, and our particulate Mn : P ratios indicated the presence of iron‐stressed diatoms south of the Sub‐Antarctic Front. We suggest low dissolved Mn surface concentrations may (co‐)limit phytoplankton growth in this region. Localized higher dissolved Mn concentrations were observed due to external sources, such as sedimentary and hydrothermal inputs. The presence of an eddy at the same latitude as a hydrothermal plume induced an upwelling of hydrothermally enriched waters up to 1000 m however, no dissolved Mn inputs to the surface waters were observed. We suggest previous dissolved Mn inputs to the surface layer may be obscured by biological uptake.
Publisher: Elsevier BV
Date: 2001
Publisher: Public Library of Science (PLoS)
Date: 10-07-2017
Publisher: American Geophysical Union (AGU)
Date: 08-2023
DOI: 10.1029/2022GB007613
Abstract: Manganese (Mn) is an essential element involved in photosynthesis, yet its concentrations in Southern Ocean open waters are very low, arising from biological uptake and limited external inputs. At southern latitudes, waters overlying the Antarctic shelf are expected to have much higher Mn concentrations due to their proximity to external sources. In this study, we investigated the potential export of Mn‐rich Antarctic shelf waters toward depleted open Southern Ocean waters. Our results showed that while high Mn concentrations were observed over the shelf, biological uptake decreased dissolved Mn concentrations in surface waters north of the South Antarctic Circumpolar Current Front ( .1 nmol kg −1 ), limiting its export. Conversely, mixing between Mn‐rich Antarctic Bottom Waters and Mn‐depleted Lower Circumpolar Deep Waters combined with oxidative and scavenging processes led to a decrease in dissolved Mn concentrations within bottom waters, with distance from the coast. Particulate Mn concentrations also showed a decreasing trend with distance from the coast. A comparison with other Antarctic coastal regions suggests this bottom water Mn removal may be widespread and that East Antarctica may be characterized by lower Mn concentrations compared to other regions. Still, subsurface dissolved Mn maxima (0.3–0.6 nmol kg −1 ) represented a potential reservoir for surface waters. We hypothesize that these high subsurface values result from external sources near the shelf. Overall, these results suggest that the moderate lateral export of trace metal‐enriched waters contributes to the extremely low and potentially limiting Mn concentrations previously reported further north in this Southern Ocean region.
Publisher: Inter-Research Science Center
Date: 18-03-2013
DOI: 10.3354/AME01611
Publisher: Public Library of Science (PLoS)
Date: 16-10-2013
Publisher: Frontiers Media SA
Date: 30-08-2017
Publisher: Proceedings of the National Academy of Sciences
Date: 20-02-2019
Abstract: Controls on phytoplankton productivity in the extreme environment of the Southern Ocean has received widespread attention. This polar region presents three challenges to primary producers: how to subsist under the joint constraints of low temperatures, low light, and growth-limiting concentrations of the essential trace element iron. The resident phytoplankton have overcome these extreme environmental conditions with a unique combination of physiological adaptations. They have modified parts of their photosynthetic machinery to harvest low levels of light without substantially increasing their iron requirements, and in a way that may exploit the low temperature in their environment. Together, these adaptations enable them to use iron and light more efficiently and grow faster than environmental conditions should otherwise permit.
Publisher: American Geophysical Union (AGU)
Date: 06-2012
DOI: 10.1029/2011JC007726
Publisher: Oxford University Press (OUP)
Date: 08-06-2022
Abstract: The necessity to understand the influence of global ocean change on biota has exposed wide-ranging gaps in our knowledge of the fundamental principles that underpin marine life. Concurrently, physiological research has stagnated, in part driven by the advent and rapid evolution of molecular biological techniques, such that they now influence all lines of enquiry in biological oceanography. This dominance has led to an implicit assumption that physiology is outmoded, and advocacy that ecological and biogeochemical models can be directly informed by omics. However, the main modeling currencies are biological rates and biogeochemical fluxes. Here, we ask: how do we translate the wealth of information on physiological potential from omics-based studies to quantifiable physiological rates and, ultimately, to biogeochemical fluxes? Based on the trajectory of the state-of-the-art in biomedical sciences, along with case-studies from ocean sciences, we conclude that it is unlikely that omics can provide such rates in the coming decade. Thus, while physiological rates will continue to be central to providing projections of global change biology, we must revisit the metrics we rely upon. We advocate for the co-design of a new generation of rate measurements that better link the benefits of omics and physiology.
Publisher: Wiley
Date: 08-05-2017
DOI: 10.1002/LNO.10578
Publisher: American Geophysical Union (AGU)
Date: 12-2005
DOI: 10.1029/2005GB002490
Publisher: Inter-Research Science Center
Date: 03-06-2009
DOI: 10.3354/AME01284
Publisher: American Geophysical Union (AGU)
Date: 12-2005
DOI: 10.1029/2005GB002494
Publisher: American Society for Microbiology
Date: 27-04-2023
DOI: 10.1128/MSYSTEMS.01260-22
Abstract: The biology and ecology of marine microbial eukaryotes is known to be constrained by oceanic conditions. In contrast, how viruses that infect this important group of organisms respond to environmental change is less well known, despite viruses being recognized as key microbial community members.
Publisher: Wiley
Date: 18-09-2017
DOI: 10.1002/LNO.10658
Publisher: Public Library of Science (PLoS)
Date: 06-07-2016
Publisher: Wiley
Date: 19-04-2010
Publisher: Springer Science and Business Media LLC
Date: 10-2000
DOI: 10.1038/35037500
Abstract: Changes in iron supply to oceanic plankton are thought to have a significant effect on concentrations of atmospheric carbon dioxide by altering rates of carbon sequestration, a theory known as the 'iron hypothesis'. For this reason, it is important to understand the response of pelagic biota to increased iron supply. Here we report the results of a mesoscale iron fertilization experiment in the polar Southern Ocean, where the potential to sequester iron-elevated algal carbon is probably greatest. Increased iron supply led to elevated phytoplankton biomass and rates of photosynthesis in surface waters, causing a large drawdown of carbon dioxide and macronutrients, and elevated dimethyl sulphide levels after 13 days. This drawdown was mostly due to the proliferation of diatom stocks. But downward export of biogenic carbon was not increased. Moreover, satellite observations of this massive bloom 30 days later, suggest that a sufficient proportion of the added iron was retained in surface waters. Our findings demonstrate that iron supply controls phytoplankton growth and community composition during summer in these polar Southern Ocean waters, but the fate of algal carbon remains unknown and depends on the interplay between the processes controlling export, remineralisation and timescales of water mass subduction.
Publisher: Inter-Research Science Center
Date: 20-01-2022
DOI: 10.3354/MEPS13923
Abstract: Model projections for the Southern Ocean indicate that light, iron (Fe) availability, temperature and carbon dioxide (CO 2 ) will change concurrently in the future. We investigated the physiological responses of Southern Ocean phytoplankton to multiple variables by culturing the haptophyte Phaeocystis antarctica and the diatom Chaetoceros flexuosus under various combinations of light, Fe, temperature and CO 2 . Using statistical models, the influence of each environmental variable was analysed for each physiological response, ultimately predicting how ‘future’ conditions (high temperature and high CO 2 ) would influence the 2 phytoplankton species. Under future conditions, cellular chlorophyll a and carbon to nitrogen molar ratios were modelled to increase for both species in all light and Fe treatments, but at times were inconsistent with measured values. Measured and modelled values of the photochemical efficiency of photosystem II ( F v / F m ) declined in cultures of P. antarctica due to concurrent increases in temperature and CO 2 , under all light and Fe treatments. The trends in F v / F m for C. flexuosus were less clear. Our model and observations suggest that when temperature and CO 2 are concurrently increased, the growth of both species remains largely unchanged. This modelling analysis reveals that high CO 2 exerts a strong negative influence on the growth of both phytoplankton, and any ‘future’ increase in growth can be attributed to the positive effect of warming rather than a CO 2 fertilisation effect.
Publisher: Wiley
Date: 07-2012
Publisher: Elsevier BV
Date: 07-2019
Publisher: American Geophysical Union (AGU)
Date: 07-2015
DOI: 10.1002/2014GB005014
Publisher: Springer Science and Business Media LLC
Date: 06-06-2023
DOI: 10.1038/S42003-023-04962-4
Abstract: Carbon dioxide removal (CDR) and emissions reduction are essential to alleviate climate change. Ocean macroalgal afforestation (OMA) is a CDR method already undergoing field trials where nearshore kelps, on rafts, are purposefully grown offshore at scale. Dissolved iron (dFe) supply often limits oceanic phytoplankton growth, however this potentially rate-limiting factor is being overlooked in OMA discussions. Here, we determine the limiting dFe concentrations for growth and key physiological functions of a representative kelp species, Macrocystis pyrifera , considered as a promising candidate for OMA. dFe additions to oceanic seawater ranging 0.01-20.2 nM Fe′ ‒ Fe′ being the sum of dissolved inorganic Fe(III) species ‒ result in impaired physiological functions and kelp mortality. Kelp growth cannot be sustained at oceanic dFe concentrations, which are 1000-fold lower than required by M. pyrifera . OMA may require additional perturbation of offshore waters via dFe fertilisation.
Publisher: Elsevier BV
Date: 09-2022
Publisher: Wiley
Date: 19-09-2011
Publisher: Copernicus GmbH
Date: 17-02-2020
Abstract: Abstract. Evaluation of photosynthetic competency in time and space is critical for better estimates and models of oceanic primary productivity. This is especially true for areas where the lack of iron (Fe) limits phytoplankton productivity, such as the Southern Ocean. Assessment of photosynthetic competency on large scales remains challenging, but phytoplankton chlorophyll a fluorescence (ChlF) is a signal that holds promise in this respect as it is affected by, and consequently provides information about, the photosynthetic efficiency of the organism. A second process affecting the ChlF signal is heat dissipation of absorbed light energy, referred to as non-photochemical quenching (NPQ). NPQ is triggered when excess energy is absorbed, i.e. when more light is absorbed than can be used directly for photosynthetic carbon fixation. The effect of NPQ on the ChlF signal complicates its interpretation in terms of photosynthetic efficiency, and therefore most approaches relating ChlF parameters to photosynthetic efficiency seek to minimize the influence of NPQ by working under conditions of sub-saturating irradiance. Here, we propose that NPQ itself holds potential as an easily acquired optical signal indicative of phytoplankton physiological state with respect to Fe limitation. We present data from a research voyage to the Subantarctic Zone south of Australia. Incubation experiments confirmed that resident phytoplankton were Fe-limited, as the maximum quantum yield of primary photochemistry, Fv∕Fm, measured with a fast repetition rate fluorometer (FRRf), increased significantly with Fe addition. The NPQ “capacity” of the phytoplankton also showed sensitivity to Fe addition, decreasing with increased Fe availability, confirming previous work. The fortuitous presence of a remnant warm-core eddy in the vicinity of the study area allowed comparison of fluorescence behaviour between two distinct water masses, with the colder water showing significantly lower Fv∕Fm than the warmer eddy waters, suggesting a difference in Fe limitation status between the two water masses. Again, NPQ capacity measured with the FRRf mirrored the behaviour observed in Fv∕Fm, decreasing as Fv∕Fm increased in the warmer water mass. We also analysed the diel quenching of underway fluorescence measured with a standard fluorometer, such as is frequently used to monitor ambient chlorophyll a concentrations, and found a significant difference in behaviour between the two water masses. This difference was quantified by defining an NPQ parameter akin to the Stern–Volmer parameterization of NPQ, exploiting the fluorescence quenching induced by diel fluctuations in incident irradiance. We propose that monitoring of this novel NPQ parameter may enable assessment of phytoplankton physiological status (related to Fe availability) based on measurements made with standard fluorometers, as ubiquitously used on moorings, ships, floats and gliders.
Publisher: Wiley
Date: 10-11-2022
DOI: 10.1002/LOL2.10223
Abstract: It has recently been shown that Southern Ocean phytoplankton species have evolved to optimize their light‐harvesting potential without increasing the high iron‐requiring proteins used for photosynthesis. We measured molecular and physiological responses of phytoplankton cultures under a combination of iron and light conditions. While iron‐replete cultures mostly increased biovolume, photochemical efficiency ( F v / F m ) and the relative abundance of photosystem II (PSII) and Cytochrome b 6 f protein compared to iron‐limited cultures, light also regulated cellular chlorophyll a content and played a role in controlling PSII protein abundance. Investment of protein resources into the carbon fixing enzyme Ribulose 1,5‐bisphosphate carboxylase oxygenase (Rubisco) was species‐specific, but increased growth rates correlated with increased investment into Rubisco for all species. Our results suggest that Proboscia inermis uses a ergent molecular strategy to compete for nutrients, light, and CO 2 in the Southern Ocean.
Publisher: Elsevier BV
Date: 02-2013
Publisher: Frontiers Media SA
Date: 11-2019
Publisher: Public Library of Science (PLoS)
Date: 21-05-2013
Publisher: Springer Science and Business Media LLC
Date: 11-02-2020
DOI: 10.1038/S41467-020-14464-0
Abstract: Mesoscale eddies are ubiquitous in the iron-limited Southern Ocean, controlling ocean-atmosphere exchange processes, however their influence on phytoplankton productivity remains unknown. Here we probed the biogeochemical cycling of iron (Fe) in a cold-core eddy. In-eddy surface dissolved Fe (dFe) concentrations and phytoplankton productivity were exceedingly low relative to external waters. In-eddy phytoplankton Fe-to-carbon uptake ratios were elevated 2–6 fold, indicating upregulated intracellular Fe acquisition resulting in a dFe residence time of ~1 day. Heavy dFe isotope values were measured for in-eddy surface waters highlighting extensive trafficking of dFe by cells. Below the euphotic zone, dFe isotope values were lighter and coincident with peaks in recycled nutrients and cell abundance, indicating enhanced microbially-mediated Fe recycling. Our measurements show that the isolated nature of Southern Ocean eddies can produce distinctly different Fe biogeochemistry compared to surrounding waters with cells upregulating iron uptake and using recycling processes to sustain themselves.
Publisher: Proceedings of the National Academy of Sciences
Date: 22-12-2014
Abstract: The supply and bioavailability of dissolved iron sets the magnitude of surface productivity for approximately 40% of the global ocean however, our knowledge of how it is transferred between chemical states and pools is poorly constrained. Here we utilize the isotopic composition of dissolved and particulate iron to fingerprint its transformation in the surface ocean by abiotic and biotic processes. Photochemical and biological reduction and dissolution of particulate iron in the surface ocean appear to be key processes in regulating its supply and bioavailability to marine biota. Iron isotopes offer a new window into our understanding of the internal cycling of Fe, thereby allowing us to follow its biogeochemical transformations in the surface ocean.
Publisher: Authorea, Inc.
Date: 26-03-2023
DOI: 10.22541/ESSOAR.167979670.07996683/V1
Abstract: Abstract Ocean Iron Fertilization (OIF) aims to remove carbon dioxide (CO2) from the atmosphere by stimulating phytoplankton carbon-fixation and subsequent deep ocean carbon sequestration in iron-limited oceanic regions. Transdisciplinary assessments of OIF have revealed overwhelming challenges around the detection and verification of carbon sequestration and wide-ranging environmental side-effects, thereby d ening enthusiasm for OIF. Here, we utilize 5 requirements that strongly influence whether OIF can lead to atmospheric CO2 removal (CDR): The requirement (1) to use preformed nutrients from the lower overturning circulation cell (2) for prevailing Fe-limitation (3) for sufficient underwater light for photosynthesis (4) for efficient carbon sequestration (5) for sufficient air-sea CO2 transfer. We systematically evaluate these requirements using observational, experimental, and numerical data to generate circumpolar maps of OIF (cost-)efficiency south of 60°S. Results suggest that (cost-)efficient CDR is restricted to locations on the Antarctic Shelf. Here, CDR costs can be US$/tonne CO2 while they are mainly US$/tonne CO2 in offshore regions of the Southern Ocean, where mesoscale OIF experiments have previously been conducted. However, sensitivity analyses underscore that (cost-)efficiency is in all cases associated with large variability and are thus difficult to predict, which reflects our insufficient understanding of the relevant biogeochemical and physical processes. While OIF implementation on Antarctic shelves appears most (cost-)efficient, it raises legal questions because regions close to Antarctica fall under 3 overlapping layers of international law. Furthermore, the constraints set by efficiency and costs reduce the area suitable for OIF, thereby likely reducing its maximum CDR potential.
Publisher: Wiley
Date: 25-06-2022
DOI: 10.1002/LNO.12175
Abstract: The influence of global change on Southern Ocean productivity will have major ramifications for future management of polar life. A prior laboratory study investigated the response of a batch‐cultured subantarctic diatom to projected change simulating conditions for 2100 (increased temperature/CO 2 /irradiance/iron decreased macronutrients), showed a twofold higher chlorophyll‐derived growth rate driven mainly by temperature and iron. We translated this design to the field to understand the phytoplankton community response, within a subantarctic foodweb, to 2100 conditions. A 7‐d shipboard study utilizing 250‐liter mesocosms was conducted in March 2016. The outcome mirrors lab‐culture experiments, yielding twofold higher chlorophyll in the 2100 treatment relative to the control. This trend was also evident for intrinsic metrics including nutrient depletion. Unlike the lab‐culture study, photosynthetic competence revealed a transient effect in the 2100 mesocosm, peaking on day 3 then declining. Metaproteomics revealed significant differences in protein profiles between treatments by day 7. The control proteome was enriched for photosynthetic processes (c.f. 2100) and exhibited iron‐limitation signatures the 2100 proteome exposed a shift in cellular energy production. Our findings of enhanced phytoplankton growth are comparable to model simulations, but underlying mechanisms (temperature, iron, and/or light) differ between experiments and models. Batch‐culture approaches hinder cross‐comparison of mesocosm findings to model simulations (the latter are akin to “continuous‐culture chemostats”). However, chemostat techniques are problematic to use with mesocosms, as mesozooplankton will evade seawater flow‐through, thereby accumulating. Thus, laboratory, field, and modeling approaches reveal challenges to be addressed to better understand how global change will alter Southern Ocean productivity.
Publisher: Wiley
Date: 27-10-2022
Publisher: American Geophysical Union (AGU)
Date: 09-2012
DOI: 10.1029/2012GL053448
Publisher: American Geophysical Union (AGU)
Date: 13-06-2022
DOI: 10.1029/2021GL097616
Abstract: The ratio between fluorescence (F) and chlorophyll‐a (Chl)—where fluorescence is measured with a saturating fluorometer—is variable in the world's oceans, with the highest ratios and highest variability observed in the Southern Ocean. While species composition and Chl packaging per cell are strong drivers for the observed variability, additional factors, including iron limitation, have to this date not specifically been evaluated. Radiometers on biogeochemical (BGC)‐Argo floats allow for an independent estimate of Chl concentration that is based on the light attenuation coefficient, K d . Making use of 4,000 radiometry profiles from BGC‐Argo floats in the Southern Ocean, we estimate Chl based on K d and investigate the variability in F/Chl. Our analysis reveals a positive correlation between F/Chl and a proxy for iron limitation based on non‐photochemical quenching dynamics. The strong influence of iron limitation on F/Chl is further corroborated by data from Southern Ocean phytoplankton cultures.
Publisher: Wiley
Date: 13-12-2021
Publisher: Wiley
Date: 13-12-2021
Publisher: MDPI AG
Date: 16-08-2022
DOI: 10.3390/MICROORGANISMS10081655
Abstract: In the Subantarctic sector of the Southern Ocean, vertical entrainment of iron (Fe) triggers the seasonal productivity cycle but diminishing physical supply during the spring to summer transition forces microbial assemblages to rapidly acclimate. Here, we tested how phytoplankton and bacteria within an isolated eddy respond to different dissolved Fe (DFe)/ligand inputs. We used three treatments: one that mimicked the entrainment of new DFe (Fe-NEW), another in which DFe was supplied from bacterial regeneration of particles (Fe-REG), and a control with no addition of DFe (Fe-NO). After 6 days, 3.5 (Fe-NO, Fe-NEW) to 5-fold (Fe-REG) increases in Chlorophyll a were observed. These responses of the phytoplankton community were best explained by the differences between the treatments in the amount of DFe recycled during the incubation (Fe-REG, 15% recycled c.f. 40% Fe-NEW, 60% Fe-NO). This additional recycling was more likely mediated by bacteria. By day 6, bacterial production was comparable between Fe-NO and Fe-NEW but was approximately two-fold higher in Fe-REG. A preferential response of phytoplankton (haptophyte-dominated) relative to high nucleic acid (HNA) bacteria was also found in the Fe-REG treatment while the relative proportion of diatoms increased faster in the Fe-NEW and Fe-NO treatments. Comparisons between light and dark incubations further confirmed the competition between picophytoplankton and HNA for DFe. Overall, our results demonstrate great versatility by microorganisms to use different Fe sources that results in highly efficient Fe recycling within surface waters. This study also encourages future research to further investigate the interactions between functional groups of microbes (e.g. HNA and cyanobacteria) to better constraint modeling in Fe and carbon biogeochemical cycles.
Publisher: Springer Science and Business Media LLC
Date: 07-2022
DOI: 10.1038/S43705-022-00132-5
Abstract: The trace metal iron (Fe) controls the ersity and activity of phytoplankton across the surface oceans, a paradigm established through decades of in situ and mesocosm experimental studies. Despite widespread Fe-limitation within high-nutrient, low chlorophyll (HNLC) waters, significant contributions of the cyanobacterium Synechococcus to the phytoplankton stock can be found. Correlations among differing strains of Synechococcus across different Fe-regimes have suggested the existence of Fe-adapted ecotypes. However, experimental evidence of high - versus low-Fe adapted strains of Synechococcus is lacking, and so we investigated the transcriptional responses of microbial communities inhabiting the HNLC, sub-Antarctic region of the Southern Ocean during the Spring of 2018. Analysis of metatranscriptomes generated from on-deck incubation experiments reflecting a gradient of Fe-availabilities reveal transcriptomic signatures indicative of co-occurring Synechococcus ecotypes adapted to differing Fe-regimes. Functional analyses comparing low-Fe and high-Fe conditions point to various Fe-acquisition mechanisms that may allow persistence of low-Fe adapted Synechococcus under Fe-limitation. Comparison of in situ surface conditions to the Fe-titrations indicate ecological relevance of these mechanisms as well as persistence of both putative ecotypes within this region. This Fe-titration approach, combined with transcriptomics, highlights the short-term responses of the in situ phytoplankton community to Fe-availability that are often overlooked by examining genomic content or bulk physiological responses alone. These findings expand our knowledge about how phytoplankton in HNLC Southern Ocean waters adapt and respond to changing Fe supply.
Publisher: Elsevier BV
Date: 08-2009
Publisher: Frontiers Media SA
Date: 07-07-2017
Publisher: Springer Science and Business Media LLC
Date: 17-03-2004
DOI: 10.1038/NATURE02437
Abstract: Iron supply has a key role in stimulating phytoplankton blooms in high-nitrate low-chlorophyll oceanic waters. However, the fate of the carbon fixed by these blooms, and how efficiently it is exported into the ocean's interior, remains largely unknown. Here we report on the decline and fate of an iron-stimulated diatom bloom in the Gulf of Alaska. The bloom terminated on day 18, following the depletion of iron and then silicic acid, after which mixed-layer particulate organic carbon (POC) concentrations declined over six days. Increased particulate silica export via sinking diatoms was recorded in sediment traps at depths between 50 and 125 m from day 21, yet increased POC export was not evident until day 24. Only a small proportion of the mixed-layer POC was intercepted by the traps, with more than half of the mixed-layer POC deficit attributable to bacterial remineralization and mesozooplankton grazing. The depletion of silicic acid and the inefficient transfer of iron-increased POC below the permanent thermocline have major implications both for the biogeochemical interpretation of times of greater iron supply in the geological past, and also for proposed geo-engineering schemes to increase oceanic carbon sequestration.
Publisher: Springer Science and Business Media LLC
Date: 10-2004
DOI: 10.1038/NATURE02954
Abstract: Diatoms are a key taxon of eukaryotic phytoplankton and a major contributor to global carbon fixation. They are ubiquitous in the marine ecosystem despite marked gradients in environmental properties, such as dissolved iron concentrations, between coastal and oceanic waters. Previous studies have shown that offshore species of diatoms and other eukaryotic algae have evolved lower iron requirements to subsist in iron-poor oceanic waters, but the biochemical mechanisms responsible for their decreased iron demand are unknown. Here we show, using laboratory-cultured model species, a fundamental difference between a coastal and an oceanic diatom in their photosynthetic architecture. Specifically, the oceanic diatom had up to fivefold lower photosystem I and up to sevenfold lower cytochrome b6f complex concentrations than a coastal diatom. These changes to the photosynthetic apparatus markedly decrease the cellular iron requirements of the oceanic diatom but not its photosynthetic rates. However, oceanic diatoms might have also sacrificed their ability to acclimate to rapid fluctuations in light intensity--a characteristic of dynamic and turbid coastal waters. We suggest that diatoms, and probably other eukaryotic algal taxa, exploited this difference in the underwater light climate between oceanic and coastal waters, enabling them to decrease their iron requirements without compromising photosynthetic capacity. This adaptation probably facilitated the colonization of the open ocean by diatoms, and contributes to their persistence in this iron-impoverished environment.
Start Date: 07-2022
End Date: 06-2025
Amount: $470,342.00
Funder: Australian Research Council
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