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There were over 100 talks at this year’s Challenger 2012 conference. We have already covered four of the keynote lectures by Jorge Sarmiento, David Righton, Ken Buessler and Phyllis Lam. Below are summaries of some of the short talks that took place:

Simeon Hill (British Antarctic Survey): Projecting climate effects on the growth habitat of Antarctic Krill

The largest blooms of krill, occurring off the south-east coast of South America, have a biomass comparable to the entire human race (215 million tonnes), with a very high turnover rate – it is these blooms that support much of the amazing Antarctic marine life captured by programs such as Frozen Planet. The speaker mentioned that a biomass decline occurred between the 70s and 90s, and suggested this may be due to sea-ice loss (juvenile krill are dependent on sea-ice). The speaker then went on to talk about a model, designed to examine future krill growth potential (for estimating biomass and abundance changes), taking into account sea-surface temperature predictions (from a number of models), chlorophyll concentrations (from satellite data), and assuming a starting length for krill of 40mm (I’m not sure why, and forgot to ask). Under all climate change scenarios, growth potential was predicted to decrease – by up to 20% under the worst case scenario. It is anticipated that this will have large knock-on effects higher up the Antarctic food web, especially for large sea-mammals with restricted foraging ranges. The speaker is keen to point out, however, that there are large uncertainties in these predictions: the inherent uncertainties surrounding climate models, when combined with what is yet to be discovered about the life-history of krill, results in large uncertainties when working with this model.

Corinne Le Quéré (University of East Anglia): Grazing control on Southern Ocean Biomass

‘High nutrients low chlorophyll’ (HNLC) regions in the Southern Ocean are well known to oceanographers as areas of low primary productivity — generally considered to be the result of limiting concentrations of iron (which is required in small quantities by phytoplankton). However, global models that take iron limitation into account, although performing better than simple models, have had little success in reproducing HNLC regions – they still predict excessive chlorophyll build-up during the summer (which doesn’t occur in reality). The speaker talked about a model, devised by her research group, that takes into account 6 groups of phytoplankton, 3 groups of zooplankton, and bacteria. The model reproduces Southern Ocean chlorophyll concentrations (but only when zooplankton are included), throughout the year, very closely – suggesting that plankton biomass in the Southern Ocean is controlled, not just by iron limitation, but also by zooplankton grazing. The speaker finishes by saying that geo-engineering predictions from iron fertilisation experiments (such as those picked up by the media a few months ago) will be unreliable until the full ecosystem response is understood.

Alex Beaton (National Oceanography Centre, Southampton): Lab-on-a-chip analyser for in situ nitrate and nitrite determination in natural waters

Jorge Sarmiento’s talked about the future of biogeochemistry in the oceans (see our post here): deploying Argo Floats equipped with a range of autonomous biogeochemical sensors. Here, Alex Beaton talked about the development of a ‘Lab-on-a-chip’ sensor (a small sensor, not a sensor deployed on a potato-based snack) that could be deployed in the near future to measure in situ nitrate concentrations. Using microfluidics, a technology that miniaturises chemical analytical methods usually undertaken in the laboratory, the speaker has designed an analyser capable of being deployed on oceanographic sensor platforms, and measuring nitrate concentrations as low as 0.025 micromolar (suitable for all natural waters, except in the open oligotrophic ocean). The speaker presented data from a field test where the sensor was deployed in an estuarine environment for a month: results compare favourably when compared with current standardised methods for measuring nitrate. The speaker says that these tests demonstrate the potential of this sensor to collect data with high temporal resolution; further reductions in power consumption may make the deployment of this sensor on Argo Floats, or other oceanographic sensing platforms, a real possibility in the not so distant future.

Micheal Cunliffe (Marine Biological Association of the United Kingdom): Bacterial genomes reveal new insights into the importance of mixotrophy in the marine carbon cycle

The application of genomics (the study of an organism’s genome) to bacterioplankton communities has indicated that many of these organisms are capable of using supplementary energy sources. A full compliment of genes for using thiosulphate as an energy source have been found in the genome of several marine Roseobacter (a genus of bacteria commonly found in the ocean). In laboratory studies, designed to test the functionality of these genes, one species grew faster, had increased respiratory rates, and showed greater biomass increases when grown mixotrophically on a combination of glucose and thiosulphate compared to cells grown on glucose alone. The speaker also talked about experiments on the an Arctic Roseobacter species. Its genome contains genes for a functional rhodopsin (light capturing pigment), suggesting it may be capable of supplementing heterotrophic growth with light energy. Once again, experiments confirmed the functionality of the genes present, showing that growth was enhanced in the presence of light. The speaker concludes that these experiments demonstrate the potential first step of linking genes discovered in genomes (and metagenomes) with ecosystem function.

Peter Williams (University of Bangor): Are the oligotrophic oceans net heterotrophic?

Maps of net community production suggest that about 80 % of the ocean is net heterotrophic. However, the speaker suggests that this is likely to be an error. First of all, it is suggested that the other 20% of the ocean that is net autotrophic balances the other 80% that is heterotrophic – there is a major flaw, however, if this is the case: if these two processes are in balance, that would essentially eliminate the ‘biological pump’. There needs to be an excess of carbon fixation to account for the biological pump, and even revised analysis can only account for about 1/5 of the carbon exported out of the surface waters. The speaker goes on to point out that sustained heterotrophy would require an input of organic matter into the gyres: either from the atmosphere, lateral transfer from adjacent water masses, or upwelling from the deep ocean – it is pointed out that none of these sources could possibly be large enough to sustain the amount of heterotrophy that is observed. Although the speaker points out that there are other scientists that disagree, he concludes that there cannot be sustained heterotrophy in the oligotrophic gyres, and suggests that there must be an error in the methods currently being used. He suggests that the source of this error is likely to be a feature unique to gyres. My own suspicion, which is probably entirely wrong, is that there is a lot of variability (not just seasonal variability, but also variability caused by physical processes) in oligotrophic gyres that does not get resolved by many ship-based sampling programs, potentially causing underestimations of autotrophy.

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David Aldridge has a PhD in Marine Science from The National Oceanography Centre, Southampton. He is now planning his escape from academia. He is the founder and editor of Words in mOcean.