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Day 3 - Marine ecosystems

Title: Long term changes in phytoplankton populations between Tasmania and Antarctica observed via pigment analysis, microscopy and satellite

Presenter: Simon Wright

Australian Antarctic Division
Antarctic Climate and Ecosystems CRC
Institute of Marine and Antarctic Studies, University of Tasmania

Authors: S Wright1,2,3, P Strutton3, R Johnson3, R van den Enden1, C Woolridge1, F Scott1, A Davidson1,2

1 - Australian Antarctic Division

2 - Antarctic Climate and Ecosystems CRC

3 - Institute of Marine and Antarctic Studies, University of Tasmania


Shipboard and satellite observations showed significant changes in the phytoplankton populations between Tasmania and Antarctica, which differed across the region but were each correlated with the Southern Annular Mode. Regular shipboard observations from the polar vessel MV l’Astrolabe (56 crossings, 2002-present) showed that chlorophyll concentrations varied five-fold between years and increased 28% on average across the region (140-145°E). CHEMTAX analysis of phytoplankton pigment data suggested that the increases in chlorophyll concentrations were mainly due to diatoms in the south and haptophytes and/or dinoflagellates in the north. Satellite observations (1997-present) across a wider region (135-145°E) also showed increases in chlorophyll concentrations, but only at high latitudes (60-65°S). They showed a general decrease in chlorophyll concentrations at mid latitudes (45-55°S) that was not seen in the shipboard data. Differences between shipboard and satellite observations were probably due to strong longitudinal gradients in the oceanography between 135°E and 145°E. However both sets of data showed significant correlations between chlorophyll concentrations and the strength of the Southern Annular Mode, which determines wind patterns in the region. These results confirm predictions that increases in the strength of the Southern Annular Mode due to climate change could have significant effects on phytoplankton populations and hence the rest of the food web that depends on them.

Title: Top down or bottom up? How about an end-to-end approach to Southern Ocean ecosystem research and management?

Presenter: Stuart Corney

Antarctic Climate and Ecosystems Cooperative Research Centre

Authors: Stuart Corney1, Jess Melbourne-Thomas1,2, Andrew Constable1,2

1 - Antarctic Climate and Ecosystems Cooperative Research Centre, Private Bag 80, Hobart Tasmania 7001, Australia

2 - Australian Antarctic Division, Channel Highway, Kingston, Tasmania 7050 Australia


End-to-end ecosystem models enable us to represent complex social-ecological systems, integrating the feedbacks between sub-components that are usually considered separately. They are essential for identifying key knowledge gaps and data needs. They are also important tools for simulating and evaluating scenarios to help identify uncertainties about the future behaviours of ecosystems, or the implications of different management options.

The field of end-to-end ecosystem modelling has seen rapid advances in recent years and there is now good agreement on what constitutes such a model. However, many different model frameworks are available that resolve, to various levels of detail, interactions between oceanography, the broader environment (e.g. climate or cryosphere), biogeochemical cycles, food web dynamics and human industries and markets.

In this presentation we seek to synthesise the available tools and approaches, and to identify key gaps that might affect the continued (and increasing) development and use of end-to-end models in decision-making. We will categorise the components, mechanics and applications that exist across the range of end-to-end models now available for marine ecosystems and use this to identify the specific challenges that lie ahead in attempting to integrate the physical environment, food webs and human components into modelling frameworks useful for management.

Title: Ice Acidification: Response of sea ice brine algae to changes in CO2 concentration

Presenter: Andrew McMinn

University of Tasmania, IMAS

Authors: Andrew McMinn1, Marius Müller1, Tom Coad1, Andrew Martin2, Ken Ryan2

1 - University of Tasmania, IMAS, Private Bag 129, Hobart 7001,,,

2 - Victoria University of Wellington, School of Biological Sciences,,


During sea ice formation internal gas concentrations in brine channels are heavily modified by changes to gas solubility at high salinity and low temperature, often resulting in supersaturation, degassing and a steep decline in pH. Brine channel and surface sea ice communities have only limited access to the outside and consequently their CO2 (and nutrient) supply becomes severely restricted. Thus, unlike planktonic ecosystems where CO2 is rarely in short supply, in sea ice brine systems the shortage is often acute and the addition CO2 as a result of ocean acidification is likely to partially alleviate this stress. During sea ice formation there is an initial abiotic drop in pH associated with increasing ionic strength. However, in spring and summer this trend is usually overridden by the photosynthetic activity of often dense microalgal communities that cause the pH to rise as a result of the depletion of the dissolved CO2. Values of up to 8.9, for instance, have been reported from platelet iceand up to 9.9 in brine channels.

In 2011 and 2012 the effect of elevated CO2 and reduced pH on brine algae was examined at Cape Evans, McMurdo Sound. In each year the brine algae, which was a monoculture of the dinoflagellate Polarella glacialis, responded strongly to increased CO2 by an increase in growth rate and an alleviation of stress. In 2012, effects caused by pH were differentiated from those caused by CO2 by manipulating the DIC while keeping pH constant. Growth, maximum quantum yield and photosynthetic capacity were greater than the control in all treatments.

The response of brine algae in pack ice was examined on the SIPEX2 voyage. This community, which was dominated by diatoms, showed a smaller response and high levels of CO2 mostly caused a decline in growth and photosynthetic parameters.

Title: Mapping phytoplankton iron utilization provides insights into Southern Ocean supply mechanisms

Presenter: Philip Boyd

Institute of Marine and Antarctic Studies

Authors: Philip W Boyd1, Kevin R Arrigo2

1 - Institute of Marine and Antarctic Studies, Hobart, University of Tasmania,

2 - Stanford University, Stanford, CA 94305,


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 datasets (1997-2007) on remotely-sensed net primary production (NPP) with the iron:carbon (Fe:C) molar ratios for resident phytoplankton to produce Southern Ocean maps of Fe utilization. This approach exploits the resolution of remotely-sensed data to investigate the spatial patterns, areal extent and interannual variability of Fe utilization, and relates it to published temporal and spatial trends for Fe supply mechanisms. We estimate that Southern Ocean Fe utilization averaged ~ 3.3+0.3 x 108 mol Fe a-1. This utilization varied little between years (7.8-9.6 µmol Fe m-2 a-1), was greatest for subpolar waters, particularly in the Atlantic (up to 53.0 µmol Fe m-2 a-1), and was lowest for the polar waters of the Indian sector. Application of maps corresponding to the location and areal extent of Fe supply regions (e.g. dust deposition) revealed that Fe utilization was highest in waters supplied by Patagonian dust, and to a lesser extent, where sediment resuspension (i.e. <500 m depth) probably supplies the majority of the Fe. The Atlantic sector has regions where multiple supply mechanisms are evident, resulting in perennially high productivity. This approach provides a better assessment of the relative importance, realm of influence, and areal extent of different Fe supply mechanisms to Southern Ocean waters.

Title: Phytoplankton dynamics underpin different ecosystem structures in the Southern Ocean: Alternative community states under identical environmental conditions

Presenter: Craig Johnson

Institute of Marine and Antarctic Studies, University of Tasmania

Authors: Craig Johnson, Simon Wotherspoon
Institute of Marine and Antarctic Studies, University of Tasmania


In the Southern Ocean it is sometimes observed that at different times, in the same location and season, the pelagic system may be dominated by either salps and/or jellyfish, or by large crustaceans. This observation raises the question of whether these different community configurations arise from external environmental forcing or whether they represent alternative stable states that can arise under identical environmental conditions. Simple models of interactions between large diatoms and nanophytoplankton as two distinct phytoplankton functional groups show that, dependent on the magnitude of interspecific competition and nature of the initial phytoplankton inoculum in a water mass, the ecological dynamic can demonstrate hysteresis so that for a fixed rate of iron delivery the system dynamic can move either to domination by large diatoms or nanoplankton. In this circumstance, when interspecific competition is high, iron levels affect total production but have relatively little effect on community composition. In contrast, if interspecific competition if weak then there is no hysteresis and the system is readily forced by iron, with low iron leading to domination by nanoplankton and high iron leading to domination by large diatoms. Statistical qualitative modelling of food web dynamics shows clearly that systems dominated by nanophytoplankton lead to proliferation of salps and other jellies, while those dominated by large diatoms lead to domination by large crustacean and fish larvae.

Title: Spatial and temporal comparisons of sea ice algal communities in the Ross Sea, Antarctica

Presenter: Ken Ryan

School of Biological Sciences, Victoria University of Wellington

Authors: Francisca A. H. Vermeulen, Ken G. Ryan
School of Biological Sciences, Victoria University of Wellington, PO Box 600, Wellington, New Zealand,,


The community compositions of microalgae within fast ice in the Ross Sea from 1980 to 2012 were compared. Compositions varied over long and short periods, with geographical location, and with vertical position within the ice. The highest biomass was always found in the bottom 10cm of the sea ice while increasing snow cover correlated with decreased algal and EPS biomass, as well as with changes in species composition. Large variations in sea ice biomass of up to two orders of magnitude were observed in different years in McMurdo Sound sites. At Terra Nova Bay, the ice thickness and snow cover was extremely variable, resulting in large changes of biomass and quite distinct species compositions from year to year. Our analysis of previous studies in McMurdo Sound sea ice showed that there has been an increasing prevalence of Berkeleya adeliensis and Fragillariopsis spp. from about the mid-1990s. This is unlikely to be due to misidentifications in earlier studies as these species were identified in other parts of the Southern Ocean by the same authors. During Nov-Dec 2011, diatoms formed the largest carbon source in the bottom of the sea ice up to 9,000 µgC.L-1 (90% of TOC), while the interior of the sea ice was dominated by EPS at ~350 µgC.L-1 (90% of TOC). Algal biomass and EPS biomass were strongly correlated indicating algae were the main EPS producers, however as algal biomass increased, the relative contribution of EPS to TOC declined. Reasons for this observation will be discussed.

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Key dates

  • 11th June 2013
    Registrations close
  • 21st June 2013
    Registrations at the AAD open for staff
  • 24th June 2013
    Registrations at the venue open
  • 24th June 2013
    Conference commences
  • 26th June 2013
    Conference concludes

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This page was last modified on 6 June 2013.