ORCID Profile
0000-0003-1060-7140
Current Organisations
University of Adelaide
,
Australian Antarctic Division
,
University of Tasmania
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Publisher: Elsevier BV
Date: 11-2011
Publisher: Elsevier BV
Date: 09-2016
Publisher: American Geophysical Union (AGU)
Date: 04-2015
DOI: 10.1002/2014GB004936
Publisher: Copernicus GmbH
Date: 11-01-2018
Abstract: Abstract. High-latitude oceans are anticipated to be some of the first regions affected by ocean acidification. Despite this, the effect of ocean acidification on natural communities of Antarctic marine microbes is still not well understood. In this study we exposed an early spring, coastal marine microbial community in Prydz Bay to CO2 levels ranging from ambient (343 µatm) to 1641 µatm in six 650 L minicosms. Productivity assays were performed to identify whether a CO2 threshold existed that led to a change in primary productivity, bacterial productivity, and the accumulation of chlorophyll a (Chl a) and particulate organic matter (POM) in the minicosms. In addition, photophysiological measurements were performed to identify possible mechanisms driving changes in the phytoplankton community. A critical threshold for tolerance to ocean acidification was identified in the phytoplankton community between 953 and 1140 µatm. CO2 levels ≥ 1140 µatm negatively affected photosynthetic performance and Chl a-normalised primary productivity (csGPP14C), causing significant reductions in gross primary production (GPP14C), Chl a accumulation, nutrient uptake, and POM production. However, there was no effect of CO2 on C : N ratios. Over time, the phytoplankton community acclimated to high CO2 conditions, showing a down-regulation of carbon concentrating mechanisms (CCMs) and likely adjusting other intracellular processes. Bacterial abundance initially increased in CO2 treatments ≥ 953 µatm (days 3–5), yet gross bacterial production (GBP14C) remained unchanged and cell-specific bacterial productivity (csBP14C) was reduced. Towards the end of the experiment, GBP14C and csBP14C markedly increased across all treatments regardless of CO2 availability. This coincided with increased organic matter availability (POC and PON) combined with improved efficiency of carbon uptake. Changes in phytoplankton community production could have negative effects on the Antarctic food web and the biological pump, resulting in negative feedbacks on anthropogenic CO2 uptake. Increases in bacterial abundance under high CO2 conditions may also increase the efficiency of the microbial loop, resulting in increased organic matter remineralisation and further declines in carbon sequestration.
Publisher: Elsevier BV
Date: 08-2013
Publisher: American Geophysical Union (AGU)
Date: 11-2021
DOI: 10.1029/2020GB006921
Abstract: Despite widespread iron (Fe) limitation in the Southern Ocean, intense phytoplankton blooms are observed around productive coastal regions such as the Mertz Polynya (off George V Land and Adelie Land, East Antarctica 140–155°E). Sources of Fe across coastal East Antarctica vary, with limited data available for late summer months. We investigated the sources of dissolved Fe (dFe .2 μm) at 19 oceanographic stations in the Mertz Glacier Region (64–67°S 138–154°E), between January and March of 2019. Concentrations of dFe ranged from below detection limit (0.03 nM) at the surface, to 0.34 nM above the base of the mixed layer (35 m), reaching 0.59 nM at depth (520 m). Using oceanographic features and trace element ratios (manganese and titanium), we identified Circumpolar Deep Water (CDW) and shelf sediment resuspension in modified CDW as contributors of dFe to the region over this period. Microbial Fe remineralization was evident where nutrient‐rich water met highly oxygenated waters over the continental shelf. Reduced Fe concentrations in the mixed layer and euphotic zones suggested rapid biological uptake prior to s ling. Despite proposals for pelagic Fe recycling by marine animals, preliminary investigations reveal no significant spatial relationship between animal presence and surface ocean Fe concentrations over the study area. Further research is required to identify seasonal changes to Fe supply in coastal areas which will strengthen our understanding of the Fe cycle and its influence on microbial and primary productivity in this globally significant region.
Publisher: Oxford University Press (OUP)
Date: 10-09-2004
Publisher: Inter-Research Science Center
Date: 23-06-2016
DOI: 10.3354/MEPS11742
Publisher: Frontiers Media SA
Date: 04-08-2022
DOI: 10.3389/FMARS.2022.948772
Abstract: The availability of iron (Fe) to marine microbial communities is enhanced through complexation by ligands. In Fe limited environments, measuring the distribution and identifying the likely sources of ligands is therefore central to understanding the drivers of marine productivity. Antarctic coastal marine environments support highly productive ecosystems and are influenced by numerous sources of ligands, the magnitude of which varies both spatially and seasonally. Using competitive ligand exchange adsorptive cathodic stripping voltammetry (CLE-AdCSV) with 2-(2-thiazolylazo)- p -cresol (TAC) as a competing artificial ligand, this study investigates Fe-binding ligands (FeL) across the continental shelf break in the Mertz Glacier Region, East Antarctica (64 - 67°S 138 - 154°E) during austral summer of 2019. The average FeL concentration was 0.86 ± 0.5 nM Eq Fe, with strong conditional stability constants (Log K FeL ) averaging 23.1 ± 1.0. The strongest binding ligands were observed in modified circumpolar deep water (CDW), thought to be linked to bacterial Fe remineralisation and potential siderophore release. High proportions of excess unbound ligands (L’) were observed in surface waters, as a result of phytoplankton Fe uptake in the mixed layer and euphotic zone. However, FeL and L’ concentrations were greater at depth, suggesting ligands were supplied with dissolved Fe from upwelled CDW and particle remineralisation in benthic nepheloid layers over the shelf. Recent sea-ice melt appeared to support bacterial production in areas where Fe and ligands were exhausted. This study is included within our newly compiled Southern Ocean Ligand (SOLt) Collection, a database of publicly available Fe-binding ligand surveys performed south of 50°S. A review of the SOLt Collection brings attention to the paucity of ligand data collected along the East Antarctic coast and the difficulties in pinpointing sources of Fe and ligands in coastal environments. Elucidating poorly understood ligand sources is essential to predicting future Fe availability for microbial populations under rapid environmental change.
Publisher: International Glaciological Society
Date: 2013
Abstract: Freezing temperatures, desiccation and high levels of solar radiation make the surface of the Antarctic ice sheet one of Earth’s harshest habitats. However, our study in the Vestfold Hills area of East Antarctica shows that favourable conditions for microbial production become established just beneath the surface of blue-ice areas, which collectively cover about 2% of the ice-sheet periphery. Their translucent, wind-polished surface allows solar heating to create meltwater in a greenhouse-type environment at depths of up to 1 m. Melting is intensified around dark debris particles, or cryoconite, where we found microbiological activity to be greatest. Rates of photosynthesis (average 2060 ng C (g cryoconite) −1 d −1 ) were adapted to low light intensities (∼10% of surface irradiance values) and most likely dominated by cyanobacteria and Chloroplastida. A heterotrophic bacterial community was also found to be active within the cryoconite, although average bacterial growth rates (5.7 ng C (g cryoconite) −1 d −1 ) were far lower than average community respiration (1870 ng C (g cryoconite) −1 d −1 ). The majority of the respired carbon was most likely associated with the autotrophs and several protists. Therefore, blue-ice areas constitute oases for microbial life around the periphery of Earth’s coldest ice sheet.
Publisher: Wiley
Date: 03-2004
DOI: 10.1002/RRA.725
Publisher: Elsevier BV
Date: 09-2016
Publisher: Elsevier BV
Date: 2018
Publisher: Elsevier BV
Date: 11-2011
Publisher: Elsevier BV
Date: 05-2010
Publisher: Inter-Research Science Center
Date: 23-02-2018
DOI: 10.3354/MEPS12420
Publisher: Copernicus GmbH
Date: 02-2011
Abstract: Abstract. The roles of iron and light in controlling biomass and primary productivity are clearly established in the Southern Ocean. However, their influence on net community production (NCP) and carbon export remains to be quantified. To improve our understanding of NCP and carbon export production in the Subantarctic Zone (SAZ) and the northern reaches of the Polar Frontal Zone (PFZ), we conducted continuous onboard determinations of NCP as part of the Sub-Antarctic Sensitivity to Environmental Change (SAZ-Sense) study, which occurred in January–February 2007. Biological O2 supersaturation was derived from measuring O2/Ar ratios by equilibrator inlet mass spectrometry. Based on these continuous measurements, NCP during the austral summer 2007 in the Australian SAZ was approximately 43 mmol O2 m−2 d−1. NCP showed significant spatial variability, with larger values near the Subtropical front, and a general southward decrease. For shallower mixed layers ( m), dissolved Fe concentrations and Fe sufficiency, estimated from variable fluorescence, correlated strongly with NCP. The strong correlation between NCP and dissolved Fe may be difficult to interpret because of the correlation of dissolved Fe to MLD and because the concentration of iron may not be a good indicator of its availability. At stations with deeper mixed layers, NCP was consistently low, regardless of iron sufficiency, consistent with light availability also being an important control of NCP. Our new observations provide independent evidence for the critical roles of iron and light in mediating carbon export from the Southern Ocean mixed layer.
Publisher: Elsevier BV
Date: 11-2011
Publisher: Copernicus GmbH
Date: 11-11-2015
Abstract: Abstract. Our current knowledge of broad-scale patterns of primary production in the Southern Ocean is derived from satellite ocean-colour estimates of chlorophyll a (Chl a) in the open ocean, typically in spring-summer. Here, we provide evidence that large-scale intra-ice phytoplankton surface aggregation occur off the coast of Antarctica during austral autumn, and that these "blooms" are largely undetected in satellite ocean-colour time series (which mask the ice-covered ocean). We present an analysis of (i) true-colour (visible) satellite imagery in combination with (ii) conventional ocean-colour data, and (iii) direct s ling from a research vessel, to identify and characterise a large-scale intra-ice algal occurrence off the coast of East Antarctica in early autumn (March) 2012. We also present evidence of these autumn "blooms" in other regions (for ex le, Princess Astrid Coast in 2012) and other years (for ex le, Terra Nova Bay in 2015) implying regular and widespread occurrence of these phenomena. The occurrence of such undetected algal accumulations implies that the magnitude of primary production in the Southern Ocean is currently underestimated.
Publisher: Elsevier BV
Date: 11-2011
Publisher: Elsevier BV
Date: 10-2022
Publisher: Public Library of Science (PLoS)
Date: 19-08-2013
Publisher: American Geophysical Union (AGU)
Date: 08-2018
DOI: 10.1029/2018JC013932
Publisher: Inter-Research Science Center
Date: 2004
DOI: 10.3354/AME037033
Publisher: American Physiological Society
Date: 07-1995
DOI: 10.1152/JAPPL.1995.79.1.256
Abstract: In resting euthermic mammals, hypoxia elicits a hyperventilation that results from a combination of hyperpnea and hypometabolism. Often accompanying the hypoxia-induced hypometabolism is a drop in body temperature. To separate the synergic effects of hypothermia per se from the direct effects of hypoxia on metabolic rate, ventilation (VE), and O2 consumption (VO2) were measured in anesthetized rats fitted with abdominal heat exchangers and maintained at either normothermic (37.5 degrees C) or hypothermic (35 degrees C) body temperatures while exposed to either normoxia or hypoxia (7% O2). Hypothermia induced parallel decreases in VE and VO2, thereby maintaining VE/VO2. Hypoxia resulted in a hyperventilation achieved with the same relative decrease in VO2 and increase in VE in both normothermic and hypothermic rats. The results suggest that 1) the changes in metabolic rate and VE during hypothermia reflect a direct effect of cold and, 2) because of similar levels of hypoxic hyperventilation in the hypothermic and normothermic rats, relative to metabolic rate, respiratory gain has not been depressed in hypothermic rats.
Publisher: Walter de Gruyter GmbH
Date: 07-1994
DOI: 10.1515/JBCPP.1994.5.3-4.227
Abstract: Male Hooded Wistar rats were exposed to three five-minute periods of hypoxia in which they breathed a gas mixture comprising 7% O2 and 93% N2. Before the second and third hypoxic exposures rats were injected (i.m.) with aminophylline (an adenosine antagonist) at a dose of 15 mg.kg-1. In control animals, hypoxia caused an increase in ventilation which was greater during the first than during the fifth minute of hypoxia. Each injection of aminophylline significantly increased ventilation in air-breathing rats. However, the first dose of the drug did not significantly alter the hypoxic ventilatory response. The second dose of aminophylline had two effects on ventilation during hypoxia. It reduced the ventilatory response during the first minute of hypoxia, and also prevented the fall in ventilation between the first and fifth minute of exposure. Ethylenediamine injections had no effect on ventilation or the responses to hypoxia. The results suggest that adenosine has a dual role in respiratory control during hypoxia, one excitatory and the other inhibitory. Although previous studies have already identified such roles for adenosine, the present study may represent the first time in which these have been demonstrated in a single animal model.
Publisher: Elsevier BV
Date: 05-2010
No related grants have been discovered for Karen Westwood.