Murat V. Ardelan

Shelf-derived iron inputs drive biological productivity in the southern Drake Passage

water entrainment while Fe/ 228 Ra ratios were used to calculate the Fe flux. In the summer of 2006 we found rapid mixing and significant lateral iron export, namely, a dissolved iron flux of 1.1 � 10 5 mol d � 1 and total acid leachable iron flux of 1.1 � 10 6 mol d � 1 all of which is transported in the mixed layer from the shelf region offshore. This dissolved iron flux is significant, especially considering that the bloom observed in the offshore region (0.5–2 mg chl a m � 3 ) had an iron demand of 1.1 to 4 � 10 5 mol Fe. Net vertical export fluxes of particulate Fe derived from 234 Th/ 238 U disequilibrium and Fe/ 234 Th ratios accounted for only about 25% of the dissolved iron flux. On the other hand, vertical upward mixing of iron rich deeper waters provided only 7% of the lateral dissolved iron flux. We found that similarly to other studies in iron-fertilized regions of the Southern Ocean, lateral fluxes overwhelm vertical inputs and vertical export from the water column and support significant phytoplankton blooms in the offshore regions of the Drake Passage.

Assessing the micro-phytoplankton response to nitrate in Comau Fjord (42°S) in Patagonia (Chile), using a microcosms approach

Anthropogenic (aquaculture) changes in environment nutrient concentrations may affect phytoplankton (biomass and taxa composition) in marine coastal waters off the Chilean Patagonia. The effects of adding nitrate (NO3−) to natural phytoplankton assemblages were evaluated considering biomass, cell abundance, and taxonomic composition. Microcosm experiments were performed in the spring, summer, and winter in the Comau Fjord located in Subantarctic Patagonia. At the end of the experiments, NO3− decreased rapidly and was undetectable in treatments, indicating a strong NO3− deficiency associated with an exponential increase in Chl-a concentrations, particulate organic nitrogen, and carbon in these treatments. Moreover, given the depleted nitrate concentrations of the spring and summer experiments, the micro-phytoplankton taxa structure shifted from mixed diatom and dinoflagellate assemblages (Ceratium spp., Dinophysis spp., Coscinodiscus sp., Rhizosolenia pungens) to assemblages dominated by blooms of the classic chain-forming diatoms found in temperate and cold waters such as Chaetoceros spp., Skeletonema spp., and Thalassiosira spp. Thus, nitrogen sources (i.e., nitrate, ammonia) may influence phytoplankton abundance and biomass accumulation dynamics in the northern section of Patagonia. It also emphasizes the importance of diatom taxa in regards to the short-term response of phytoplankton to changing environmental nutrient conditions due to natural (decreasing freshwater stream flow) and anthropogenic (aquaculture) events. This situation may be one of the future scenarios in the Patagonian fjords, thus stressing the needs for active environmental monitoring and impact assessment.

Stakeholder Perceptions of Links between Environmental Changes to their Socio-Ecological System and their Adaptive Capacity in the Region of Troms, Norway

Climate change affects the marine environment at all levels of governance. At a global level, researchers expect the projected increase in sea surface temperature to facilitate large changes in the marine food web, which in turn will affect both global fisheries and aquaculture. At the local level, government and stakeholders want to know whether and how this affects their local communities and their adaptive capacity in light of this. Research suggests that risk communication of the effects of changes in the marine food web suffers from stakeholders` short-term mentality and narrow boundaries. This in turn can lead to an underestimation of the potential risks associated with climate change. We explore this theory by mapping the perceptions of marine stakeholders in the region of Troms, Norway. We first developed cognitive maps in a workshop setting, and then used system conceptualization to analyze the feedback mechanisms of the system qualitatively using fuzzy cognitive mapping. We examined the outcomes and compared them for different scenarios using a simple MatLab script. Results demonstrated that stakeholders did not underestimate their risks to climate change. They were aware of environmental changes, and they perceived that a changing climate was the cause of this change, and that it was indeed affecting their livelihoods – and would continue to do so in the future.

Size‐spectrum based differential response of phytoplankton to nutrient and iron‐organic matter combinations in microcosm experiments in a Chilean Patagonian Fjord

The Patagonian fjords have been recognized as a major region of relatively high primary productivity systems during spring–summer bloom periods, where iron‐organic matter forms may be essential complexes involved in key growth processes connected to the carbon and nitrogen cycles. We used two dissolved organic matter (DOM) types, marine polysaccharide and siderophore, as a model to understand how they affect the bioavailability of Fe to phytoplankton and bacteria and to assess their ecological role in fjord systems. A 10‐day microcosm study was performed in the Comau Fjord during summer conditions (March 2012). Pico‐, nano‐, and microphytoplankton abundance, total chlorophyll‐a and bacteria abundance, and bacterial secondary production estimates were analyzed in five treatments: (i) control (no additions), (ii) only nutrients (NUT: PO4, NO3, Si), (iii) nutrients + Fe(II), (iv) polysaccharide (natural diatoms extracted: 1–3 beta Glucan), and (v) Hexandentate Desferroxiamine B (DFB, siderophore). Our results showed that while DFB reduced Fe bioavailability for almost all phytoplankton assemblages in the fjord, polysaccharide did not have effects on the iron bioavailability. At Nutrients + Fe and Polysaccharide treatments, chlorophyll‐a concentration abruptly increased from 0.9 to 20 mg m−3 during the first 4–6 days of the experimental period. Remarkably, at the Nutrients + Fe treatment, the development of the bloom was accompanied by markedly high abundances of Synechococcus, picoeukaryotes, and autotrophic nanoflagellates within the first 4 days of the experiment. Our study indicated that small plankton (phytoplankton <20 μm and bacteria) were the first to respond to dissolved Nutrients + Fe compared to large sized micro‐phytoplankton cells (>20 μm). This could be at least partially attributed to biological utilization of Fe (2 to 3 nM) by <20 μm phytoplankton and bacteria through the interaction with organic ligands released by bacteria that eventually could increase solubility of the Fe dissolved fraction thus having a positive effect on the small‐sized phytoplankton community.

Anthropogenic impact on marine ecosystem health: A comparative multi-proxy investigation of recent sediments in coastal waters

Hazardous substances entering the sea, and ultimately deposited in bottom sediments, pose a growing threat to marine ecosystems. The present study characterized two coastal areas exposed to significant anthropogenic impact - Gulf of Gdańsk (Poland), and Oslofjord/Drammensfjord (Norway) - by conducting a multi-proxy investigation of recent sediments, and comparing the results in light of different available thresholds for selected contaminants. Sediment samples were analyzed for benzo(a)pyrene (B(a)P) and other polycyclic aromatic hydrocarbons (PAHs), nonylphenols (NPs), organotin compounds (OTs), toxic metals (Cd, Hg, Pb), as well as mutagenic, genotoxic and endocrine-disrupting activities (in CALUX bioassays). In general, a declining trend in the deposition of contaminants was observed. Sediments from both basins were not highly contaminated with PAHs, NPs and metals, while OT levels may still give rise to concern in the Norwegian fjords. The results suggest that the contamination of sediments depends also on water/sediment conditions in a given region.

Effect of Siderophore on Iron Availability in a Diatom and a Dinoflagellate Species: Contrasting Response in Associated Bacteria

Organic ligands play a key role controlling trace metal bioavailability in the world oceans, yet the species-specific requirements determining whether certain iron forms can be metabolized largely remain unclear. Siderophores are considered relevant within this pool of ligands keeping iron soluble. We used desferrioxamine B (DFB) to study the siderophore effect on cultures of Skeletonema costatum and Alexandrium catenella. The experimental approach used semi-continuous additions of iron(II) and DFB over time, reaching final concentrations of 1 and 10 nM Fe and 10-10000 nM DFB. The negative effect of DFB over growth in S. costatum was evident and sharp until day 9 for treatments above 500 nM. Delayed growth occurred at 10000 nM, reaching ~ 80 % of cell density in Controls under both iron conditions. A. catenella exhibited a more attenuated negative effect of DFB over growth, only significant at 10000 nM, while growth was enhanced at lowest DFB. Total bacterial abundance in diatom and dinoflagellate cultures presented inversed trends. While negatively correlated to DFB in diatom cultures, bacteria in high DFB treatments in dinoflagellate cultures reached highest abundances. Delayed growth exhibited in S. costatum at the highest DFB, indicates favorable changes for Fe uptake occurred over time, suggesting involvement of other mechanism facilitating the diatom cell membrane reduction. Overall unaffected growth in A. catenella suggests the potential to utilize FeDFB and therefore capacity to access strongly complexed Fe sources. Contrasting responses in the bacterial community associated with each species, highlight the complexity of these interactions, while suggest that for A. catenella it may represent an advantage for acquiring Fe. The DFB effect exhibited the capacity for different uptake strategies among phytoplankton species of different functional groups and underlines the necessity to broaden the study of iron bioavailability on a species basis, alongside interaction with other microbial components such bacteria, to reflect interactions in natural ecosystems.