Pelagic Iron Recycling in the Southern Ocean: Exploring the Contribution of Marine Animals

The availability of iron controls primary productivity in large areas of the Southern Ocean. Iron is largely supplied via atmospheric dust deposition, melting ice, the weathering of shelf sediments, upwelling, sediment resuspension, mixing (deep water, biogenic, and vertical mixing) and hydrothermal vents with varying degrees of temporal and spatial importance. However, large areas of the Southern Ocean are remote from these sources, leading to regions of low primary productivity. Recent studies suggest that recycling of iron by animals in the surface layer could enhance primary productivity in the Southern Ocean. The aim of this review is to provide a quantitative and qualitative assessment of the current literature on pelagic iron recycling by marine animals in the Southern Ocean and highlight the next steps forward in quantifying the retention and recycling of iron by higher trophic levels in the Southern Ocean. Phytoplankton utilize the iron in seawater to meet their metabolic demand. Through grazing, pelagic herbivores transfer the iron in phytoplankton cells into their body tissues and organs. Herbivores can recycle iron through inefficient feeding behavior that release iron into the water before ingestion, and through the release of fecal pellets. The iron stored within herbivores is transferred to higher trophic levels when they are consumed. When predators consume iron beyond their metabolic demand it is either excreted or defecated. Waste products from pelagic vertebrates can thus contain high concentrations of iron which may be in a form that is available to phytoplankton. Bioavailability of fecal iron for phytoplankton growth is influenced by a combination of the size of the fecal particle, presence of organic ligands, the oxidation state of the iron, as well as biological (e.g., remineralization, coprochaly, coprorhexy, and coprophagy) and physical (e.g., dissolution, fragmentation) processes that lead to the degradation and release of fecal iron. The flux of dissolved iron from pelagic recycling is comparable to other sources in the region such as atmospheric dust, vertical diffusivity, vertical flux, lateral flux and upwelling, but lower than sea ice, icebergs, sediment resuspension, and deep winter mixing. The temporal and seasonal importance of these various factors requires further examination

Report on the European BioEco observing system

This deliverable provides (1) updates to D1.2 ‘Map the current state of biological observations in Europe’, (2) a report on the two workshops and global review undertaken to progress capacity and coordination of ocean observation, and (3) outlines key steps forward that will improve our capacity to predict biological and ecosystem changes under a changing climate

Map of BioEco Observing networks/capability

This deliverable maps the locations and properties of sustained biological observing networks through Europe including identifying coordinating groups and data aggregators. Data come from a global survey of networks, supplemented by an analysis of sustained observations in OBIS (that receives all biological data from EMODNet)

Examining the Interaction Between Free‐Living Bacteria and Iron in the Global Ocean

International audienceMarine free-living (FL) bacteria play a key role in the cycling of essential biogeochemical elements, including iron (Fe), during their uptake, transformation and release of organic matter throughout the water column. Similar to phytoplankton, the growth of FL bacteria is regulated by nutritive resources such as Fe, and the low availability of these resources may influence bacterial interactions with phytoplankton, causing knock-on effects for biogeochemical cycling. Yet, knowledge of the factors limiting the growth of FL bacteria and their role within the Fe cycle is poorly constrained. Here, we explicitly represent FL, carbon-oxidizing bacteria in a three-dimensional global ocean biogeochemistry model to address these questions. We find that although Fe can emerge as proximally limiting in the tropical Pacific and in high-latitude regions during summer, the growth of FL bacteria is ultimately controlled by the availability of labile dissolved organic carbon over most of the world's oceans. In Fe-limited regions, FL bacterial biomass is sensitive to their Fe uptake capability in seasonally Fe-limitation regions and to their minimum Fe requirements in regions perennially low in Fe. Fe consumption by FL bacteria is significant in the upper ocean in our model, and their competition with phytoplankton for Fe affects phytoplankton growth dynamics and can make bacteria become more carbon limited. The impact of FL bacteria on the Fe distribution in the ocean interior is small due to a tight coupling between Fe uptake and release. Moving forward, future work that considers other bacteria groups and different bacterial metabolisms is needed to explore the broader role of bacteria in ocean Fe cycling. In this context, the global growing’ omics data from ocean observing programs can play a crucial role

Pelagic Iron Recycling in the Southern Ocean: Exploring the Contribution of Marine Animals

The availability of iron controls primary productivity in large areas of the Southern Ocean. Iron is largely supplied via atmospheric dust deposition, melting ice, the weathering of shelf sediments, upwelling, sediment resuspension, mixing (deep water, biogenic, and vertical mixing) and hydrothermal vents with varying degrees of temporal and spatial importance. However, large areas of the Southern Ocean are remote from these sources, leading to regions of low primary productivity. Recent studies suggest that recycling of iron by animals in the surface layer could enhance primary productivity in the Southern Ocean. The aim of this review is to provide a quantitative and qualitative assessment of the current literature on pelagic iron recycling by marine animals in the Southern Ocean and highlight the next steps forward in quantifying the retention and recycling of iron by higher trophic levels in the Southern Ocean. Phytoplankton utilize the iron in seawater to meet their metabolic demand. Through grazing, pelagic herbivores transfer the iron in phytoplankton cells into their body tissues and organs. Herbivores can recycle iron through inefficient feeding behavior that release iron into the water before ingestion, and through the release of fecal pellets. The iron stored within herbivores is transferred to higher trophic levels when they are consumed. When predators consume iron beyond their metabolic demand it is either excreted or defecated. Waste products from pelagic vertebrates can thus contain high concentrations of iron which may be in a form that is available to phytoplankton. Bioavailability of fecal iron for phytoplankton growth is influenced by a combination of the size of the fecal particle, presence of organic ligands, the oxidation state of the iron, as well as biological (e.g., remineralization, coprochaly, coprorhexy, and coprophagy) and physical (e.g., dissolution, fragmentation) processes that lead to the degradation and release of fecal iron. The flux of dissolved iron from pelagic recycling is comparable to other sources in the region such as atmospheric dust, vertical diffusivity, vertical flux, lateral flux and upwelling, but lower than sea ice, icebergs, sediment resuspension, and deep winter mixing. The temporal and seasonal importance of these various factors requires further examination

Resource Colimitation Drives Competition Between Phytoplankton and Bacteria in the Southern Ocean

International audienc

Carbon to phosphorus ratio in krill and whales (mol mol⁻¹).

<p>Data point above the third quartile for whale faeces is 3 or more times higher than the interquartile range.</p

Summary of dissolved and particulate trace element concentrations in surface waters from the literature (nmol L⁻¹).

<p>Data from Frew <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114067#pone.0114067-Frew1" target="_blank">[69]</a> and Bowie <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114067#pone.0114067-Bowie1" target="_blank">[44]</a> in the Australasian-Pacific sector are from non-fertilised surface waters.</p><p>Summary of dissolved and particulate trace element concentrations in surface waters from the literature (nmol L⁻¹).</p

A preliminary model of iron fertilisation by baleen whales and Antarctic krill in the Southern Ocean: Sensitivity of primary productivity estimates to parameter uncertainty

International audienceLarge marine animals may play a crucial role in storing and recycling bioavailable iron in surface waters by consuming iron-rich prey and subsequent defecation of iron that is excess to their requirements. This biological recycling of iron could enhance primary productivity in iron-limited waters. However, quantifying the effects of marine animals on ocean primary productivity remains challenging because of a limited understanding of the key biogeochemical processes involved. In this paper, we develop a preliminary model that explores these uncertainties and examines the potential effects of historical populations of blue, fin and humpback whales, and the biomass of Antarctic krill required to support the whale populations, on primary productivity in the Southern Ocean.ăăOur results suggest that, despite conservative estimates for key processes in our model, pre-exploitation populations of blue whales and, to a lesser extent fin and humpback whales, could have contributed to iron recycling, resulting in enhanced phytoplankton production in iron-limited Southern Ocean waters. Iron-rich defecation by un-exploited whale populations in the Southern Ocean, and the biomass Antarctic krill required to support them, could have resulted in a contribution to primary productivity of between 1.5 × 10−4 to 23.4 g C m−2 yr−1 (blue whales), 1.4 × 10−4 to 13.9 g C m−2 yr−1 (fin whales), and 2.4 × 10−5 to 1.7 g C m−2 yr−1 (humpback whales). However, only when all parameter estimates are at their upper limits does there appear to be this significant role for whales in enhancing primary productivity, and thus we need to assess the likelihood of these values arising.ăăThe high degree of uncertainty around the magnitude of these increases in primary productivity is mainly due to our limited quantitative understanding of key biogeochemical processes. To reduce uncertainty regarding the effect of whales on Southern Ocean primary productivity, future research will need to refine our understanding of five influential model parameters: iron content in krill; krill consumption rates by whales; persistence of whale faecal iron in the photic zone; bioavailability of this retained iron; and the carbon-to-iron ratio of phytoplankton