Robert Strzepek

Robert Strzepek
University of Tasmania · Institute for Marine and Antarctic Studies (IMAS)

PhD

About

82
Publications
11,616
Reads
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Introduction
Research Interests Marine biogeochemical cycles of bioactive metals; biological oceanography; physiological ecology and evolution of marine phytoplankton, particularly species indigenous to the Southern Ocean; adaptations of phytoplankton to low iron availability, specifically the effects of iron availability on photosynthetic physiology and photoacclimatory strategies; marine proteomics and transcriptomics
Additional affiliations
January 2018 - present
University of Tasmania
Position
  • Research Associate
October 2011 - March 2016
Australian National University
Position
  • Research Associate
January 2002 - September 2011
The University of Otago
Education
September 1996 - September 2003
University of British Columbia - Vancouver
Field of study
  • Botany and Oceanography

Publications

Publications (82)
Article
Full-text available
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 li...
Article
Full-text available
Plain Language Summary Phytoplankton fluorescence is a relatively easy and consistent measurement that can be made in the ocean. The measured fluorescence stems directly from the chlorophyll contained in phytoplankton cells and is therefore very specific to the tiny plants. Great oceanic coverage of fluorescence measurements is achieved because flu...
Article
Full-text available
The influence of global change on Southern Ocean productivity will have major ramifications for the future management of polar living resources. A prior laboratory study investigated the response of a batch-cultured subantarctic diatom to global ocean change (concurrent increases in temperature/CO2/irradiance/iron; decreased macronutrients), reveal...
Article
Full-text available
The trace metal iron (Fe) controls the diversity 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 phyt...
Preprint
Full-text available
Ocean alkalinity enhancement (OAE) is a proposed method for removing carbon dioxide (CO2) from the atmosphere by the accelerated weathering of (ultra-) basic minerals to increase alkalinity – the chemical capacity of seawater to store CO2. During the weathering of OAE-relevant minerals relatively large amounts of trace metals will be released and m...
Preprint
Full-text available
The Subantarctic Southern Ocean is far away from terrestrial iron inputs. Low dissolved iron (DFe) supply strongly limits the growth of phytoplankton in subpolar surface waters. However, phytoplankton benefit from vertical Fe supply from a subsurface reservoir (termed new Fe) which triggers the beginning of the phytoplankton growth season. However,...
Preprint
Full-text available
Submission to Journal of Plankton Research - Horizons Article (topical and provocative reviews). In the article we ask the question: 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-...
Article
Full-text available
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 c...
Article
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...
Article
Full-text available
Model projections for the Southern Ocean indicate that light, iron (Fe) availability, temperature and carbon dioxide (CO2) 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 u...
Article
Full-text available
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 phytoplan...
Article
Full-text available
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...
Article
Full-text available
The Southern Ocean is responsible for approximately 40% of oceanic carbon uptake through biological and physical processes. In the Southern Ocean, phytoplankton growth is limited by low iron (Fe) and light supply. Climate model projections for the Southern Ocean indicate that temperature, underwater irradiance and Fe supply are likely to change sim...
Article
Full-text available
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 limits phytoplankton productivity, such as the Southern Ocean. Assessment of photosynthetic competency on large scales remains challenging, but phytoplankton...
Article
Full-text available
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 follow...
Article
A mesocosm experiment was used to investigate the fractionation of silicon (Si)isotopes in subtropical surface waters east of New Zealand. Surface waters in this region were characterised by relatively low concentrations of silicic acid (Si(OH) 4 )(~2 μmol L ⁻¹ )and higher nitrate (~5 μmol L ⁻¹ )and dissolved iron (Fe)concentrations (~0.4 nmol L ⁻¹...
Article
Full-text available
Phytoplankton productivity in the polar Southern Ocean (SO) plays an important role in the transfer of carbon from the atmosphere to the ocean’s interior, a process called the biological carbon pump, which helps regulate global climate. SO productivity in turn is limited by low iron, light, and temperature, which restrict the efficiency of the carb...
Article
Full-text available
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 e...
Article
Zinc (Zn) isotope fractionation by the coccolithophore Emiliania huxleyi (a Tasman Sea isolate) was investigated by culturing it across a range of free Zn2+ ion concentrations (1.2 pmol L−1 to 3.2 nmol L−1), which span the natural range observed in the global oceans. Across the range of free Zn2+ ion concentrations tested, the amount of bio-availab...
Article
Full-text available
Phaeocystis antarctica is an abundant phytoplankton species in the Southern Ocean, where growth is frequently limited by iron and light. Being able to grow under low iron conditions is essential to the species’ success, but there have been hints that this ability differs among clones. Here, we compare the growth, cell size and chlorophyll a concent...
Data
Average cell volume of the P. antarctica clones grown under different iron- and light-conditions. This table provides the average cell volume (fL cell-1) measured for each of the four P. antarctica clones grown under different iron- and light-conditions. Each biological replicate was measured three times, and the standard error of the mean cell vol...
Data
Percentage of solitary cells of the four P. antarctica clones grown under different iron- and light-conditions. This table provides the percentage of solitary cells (out of the total solitary + colonial cells) of the four P. antarctica clones grown under different iron- and light-conditions. Each biological replicate was measured three times, and t...
Data
Intracellular chlorophyll a concentrations of the four P. antarctica clones grown under different iron- and light-conditions. This table provides the intracellular cell volume-normalized chlorophyll a concentrations (mmol chlorophyll a LCV-1) of the four P. antarctica clones grown under different iron- and light-conditions. Each biological replicat...
Data
Criteria used to determine whether clones exhibit a particular response to the iron limiting treatments. This table shows the statistical significance (p-value) and fold-change (FC) thresholds which were used to identify clones that exhibit particular responses, such as a change in cell size or growth limitation, to the iron limiting treatments. Th...
Data
Cell surface area to volume ratios (μm-1) of the P. antarctica clones grown under different iron- and light-conditions. This table provides the cell surface area to volume ratios (μm-1) of the four P. antarctica clones grown under different iron- and light-conditions. Each biological replicate was measured three times, and the standard error of the...
Article
The fractionation of silicon (Si) isotopes was measured in two Southern Ocean diatoms (Proboscia inermis and Eucampia Antarctica) and a coastal diatom (Thalassiosira pseudonana) that were grown under varying iron (Fe) concentrations. Varying Fe concentrations had no effect on the Si isotope enrichment factor (ε) in T. pseudonana, whilst E. Antarcti...
Article
We investigated the effects of iron (Fe) limitation on the elemental stoichiometry, silicic acid (Si(OH)4) uptake kinetics and cell morphology in two Southern Ocean diatoms Eucampia antarctica and Proboscia inermis and the temperate diatom Thalassiosira pseudonana. An increase in Fe-stress resulted in reductions in specific growth rate and decrease...
Article
Full-text available
Relief of iron (Fe) limitation in the surface Southern Ocean has been suggested as one driver of the regular glacial-interglacial cycles in atmospheric carbon dioxide (CO2). The proposed cause is enhanced deposition of Fe-bearing atmospheric dust to the oceans during glacial intervals, with consequent effects on export production and the carbon cyc...
Data
Apparatus for sublimation of ice-core material for dry extraction of large masses of ice core dust (based on [24]). (TIF)
Data
Calculating Eucampia antarctica cell volume. (DOCX)
Article
Full-text available
2016 Conway et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.Relief of iron (Fe) limitation in the surface Southern Ocean has been suggested as one driver of...
Article
Full-text available
Dissolved iron supply is pivotal in setting global phytoplankton productivity and pelagic ecosystem structure. However, most studies of the role of iron have focussed on carbon biogeochemistry within pelagic ecosystems, with less effort to quantify the iron biogeochemical cycle. Here we compare mixed‐layer biotic iron inventories from a low‐iron (~...
Article
Full-text available
The supply and bioavailability of dissolved iron sets the magnitude of surface productivity for ∼40% of the global ocean. The redox state, organic complexation, and phase (dissolved versus particulate) of iron are key determinants of iron bioavailability in the marine realm, although the mechanisms facilitating exchange between iron species (inorga...
Article
Full-text available
Phytoplankton growth rates are limited by the supply of iron (Fe) in approximately one third of the open ocean, with major implications for carbon dioxide sequestration and carbon (C) biogeochemistry. To date, understanding how alteration of Fe supply changes phytoplankton physiology has focused on traditional metrics such as growth rate, elemental...
Article
Full-text available
“ It takes a village to finish (marine) science these days ” Paraphrased from Curtis Huttenhower (the Human Microbiome project) The rapidity and complexity of climate change and its potential effects on ocean biota are challenging how ocean scientists conduct research. One way in which we can begin to better tackle these challenges is to conduct...
Data
The individual reactions norms (specific growth rates per day) of all measured strains and cultures obtained by fitting a thermal tolerance function (see Methods) to these data. (TIF)
Data
Intraspecific variation in thermal reaction norms for species in which only one strain was available. (TIF)
Data
A summary of temperature optima (°C) obtained here (red boxes) and from the literature (blue boxes), expressed as box and whiskers plots, for each of the species used in our study (red). The thick black line in each box represents the median temperature. (TIF)
Data
A summary of temperature optima, maximum growth rates and niche width – expressed as box and whiskers plots - for each of the species used in our study. The black bands denote the median value, the bottom and top of the box represent the 1st and 3rd quartile of the data, respectively. The ‘whiskers’ extending from the boxes indicate the positions o...
Data
A summary of niche width (°C), expressed as box and whiskers plots - for each of the species used in our study. (TIF)
Data
A summary of maximum growth rate expressed as box and whiskers plots - for each of the species used in our study. (TIF)
Data
A plot of niche widths versus annual temperature range. Data points are coloured by species. This plot omits the niche widths that are poorly resolved (i.e. the 6 T. pseudonana +1 A. sanguinea strain). Niche widths increase as the annual temperature range increases, in accordance with the climate variability hypothesis. (TIF)
Article
Full-text available
The rate of carbon fixation by phytoplank- ton in marine surface waters is often tied to the supply of growth-limiting nutrients such as iron (Fe). While average cellular requirements and ratios for various elements are well known in the literature, especially through laboratory culture work, the plasticity of these relationships in natural plankto...
Article
Full-text available
1] Diatom blooms play a central role in supporting food-webs and sequestering biogenic carbon to depth. Oceanic conditions set bloom initiation, whereas both environmental and ecological factors determine bloom magnitude and lon-gevity. Our study reveals another fundamental determinant of bloom dynamics. A diatom spring bloom in offshore New Zealan...
Conference Paper
Full-text available
Subantarctic water (SA) close to New Zealand belongs to high nutrient low chlorophyll (HNLC) region. HNLC water is Fe limited. Low Fe concentration in water limits primary production. Oceanographic studies in the last 10 years have shown that Fe in subnanomolar concentration plays a significant role in primary production. However Fe is not only the...
Article
Full-text available
In laboratory experiments we examined the interplay of light and iron availability on the intracellular iron concentrations, specific growth rates, and photosynthetic physiology of Southern (S.) Ocean diatoms (Eucampia antarctica and Proboscia inermis) and the haptophyte Phaeocystis antarctica. Intracellular iron concentrations and iron : carbon (F...
Article
Full-text available
1] The emerging field of ocean iron biogeochemistry has prompted interest in the identification and quantification of Fe supply mechanisms. However, less attention has been given to estimating biological Fe utilization, and using the magnitude of Fe utilization to enhance our understanding of modes of supply. Here, we combine regionally validated d...
Article
Full-text available
We report results of laboratory studies examining the effect of low levels of iron (Fe) availability on the intracellular Fe concentrations and specific growth rates in Southern Ocean diatoms (Fragilariopsis kerguelensis, Eucampia antarctica, Proboscia inermis, and Thalassiosira antarctica) and Phaeocystis antarctica. All species grew on Fe complex...
Article
Full-text available
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 picocyanobac...
Article
This study compares intracellular Cd content (Cd:C) of cultured marine phytoplankton grown under various Fe levels, with estimated particulate Cd:P ratios derived from regression slopes of Cd versus PO43− relationships from a global dataset. A 66-fold difference in Cd:C ratios was observed among the seven species grown under identical Fe concentrat...