Description: Arctic coastal ecosystems are rapidly changing due to climate warming. This makes modeling their produc- tivity crucially important to better understand future changes. System primary production in these systems is highest dur- ing the pronounced spring bloom, typically dominated by di- atoms. Eventually the spring blooms terminate due to sili- con or nitrogen limitation. Bacteria can play an important role for extending bloom duration and total CO2 fixation through ammonium regeneration. Current ecosystem mod- els often simplify the effects of nutrient co-limitations on al- gal physiology and cellular ratios and simplify nutrient re- generation. These simplifications may lead to underestimations of primary production. Detailed biochemistry- and cell- based models can represent these dynamics but are difficult to tune in the environment. We performed a cultivation experiment that showed typical spring bloom dynamics, such as extended algal growth via bacterial ammonium remineralization, reduced algal growth and inhibited chlorophyll synthesis under silicate limitation, and gradually reduced nitrogen assimilation and chlorophyll synthesis under nitrogen limitation. We developed a simplified dynamic model to represent these processes. Overall, model complexity in terms of the number of parameters is comparable to the phytoplankton growth and nutrient biogeochemistry formulations in common ecosystem models used in the Arctic while improv- ing the representation of nutrient-co-limitation-related processes. Such model enhancements that now incorporate in- creased nutrient inputs and higher mineralization rates in a warmer climate will improve future predictions in this vulnerable system.

Description: Future supplies of rare minerals for global industries with high-tech products may depend on deep-sea mining. However, environmental standards for seafloor integrity and recovery from environmental impacts are missing. We revisited the only midsize deep-sea disturbance and recolonization experiment carried out in 1989 in the Peru Basin nodule field to compare habitat integrity, remineralization rates, and carbon flow with undisturbed sites. Plough tracks were still visible, indicating sites where sediment was either removed or compacted. Locally, microbial activity was reduced up to fourfold in the affected areas. Microbial cell numbers were reduced by ~50% in fresh “tracks” and by 〈30% in the old tracks. Growth estimates suggest that microbially mediated biogeochemical functions need over 50 years to return to undisturbed levels. This study contributes to developing environmental standards for deep-sea mining while addressing limits to maintaining and recovering ecological integrity during large-scale nodule mining.

Description: Industrial-scale mining of deep-sea polymetallic nodules will remove nodules in large areas and impact the physical integrity of the seafloor. However, environmental standards for seafloor integrity and studies of recovery from environmental impacts are still largely missing. Further we have only a poor understanding of the role of nodules in shaping benthic microbial diversity and element cycles. We revisited the deep-sea disturbance and recolonization experiment carried out with a towed plough harrow in 1989 in the Peru Basin nodule field within a circular area of approx. 3.5 km diameter (〉4100 m water depth). In the experimental area, the 26 years old plough tracks were still visible and showed different types and levels of disturbance such as removal and compaction of surface sediments. Microbial communities and their diversity were studied in disturbance tracks and undisturbed sites and related to habitat integrity, remineralization rates, and carbon flow. Locally, microbial activity was reduced up to 4 times in the impacted areas. Microbial cell numbers were reduced by ~50% in fresh, and by 〈30% in the old tracks. Our data suggest that microbially-mediated biogeochemical functions need more than 50 years to return to undisturbed levels in the sediments. In areas with nodules (i.e., outside the disturbance tracks) microbial communities in the nodules themselves were studied. Nodule communities were distinct from sediments and showed a lower diversity and a higher proportion of sequences related to potential metal-cycling bacteria (i.e. Magnetospiraceae, Hyphomicrobiaceae), bacterial and archaeal nitrifiers (i.e. AqS1, unclassified Nitrosomonadaceae, Nitrosopumilus, Nitrospina, Nitrospira), as well as bacterial sequences typically found in ocean crust, hydrothermal deposits and sessile fauna. Our results confirm that nodules host specific microbial communities with potentially significant contributions to organic carbon remineralization and metal cycling. This study contributes to developing environmental standards for deep-sea mining and highlights the limits for maintaining and recovering ecological integrity and functions during large-scale nodule mining.

Description: Der Tiefseebergbau wird als eine neue Möglichkeit diskutiert, um wichtige Rohstoffe zu fördern. Entsprechende Technologien befinden sich in der Entwicklung. Wir sprechen mit Forschenden vom Max-Planck-Institut für Marine Mikrobiologie, vom Alfred-Wegener-Institut und vom GEOMAR, die sich mit den Auswirkungen des Abbaus von Rohstoffen in der Tiefsee auf das dortige Ökosystem befassen.

Description: A rapidly warming Arctic Ocean and associated sea-ice decline is resulting in changing sea-ice protist communities, affecting productivity of under-ice, pelagic, and benthic fauna. Quantifying such effects is hampered by a lack of biomarkers suitable for tracing specific basal resources (primary producers and microorganisms) through food webs. We investigate the potential of δ13C values of essential amino acids (EAAs) (δ13CEAA values) to estimate the proportional use of diverse basal resources by organisms from the under-ice (Apherusa glacialis), pelagic (Calanus hyperboreus) and benthic habitats (sponges, sea cucumber), and the cryo-pelagic fish Boreogadus saida. Two approaches were used: baseline δ13CEAA values, that is, the basal resource specific δ13CEAA values, and δ13CEAA fingerprints, or mean-centred baseline δ13CEAA values. Substantial use of sub-ice algae Melosira arctica by all studied organisms suggests that its role within Arctic food webs is greater than previously recognized. In addition, δ13CEAA fingerprints from algae-associated bacteria were clearly traced to the sponges, with an individually variable kelp use by sea cucumbers. Although mean-centred δ13CEAA values in A. glacialis, C. hyperboreus, and B. saida tissues were aligned with microalgae resources, they were not fully represented by the filtered pelagic- and sea-ice particulate organic matter constituting the spring diatom-dominated algal community. Under-ice and pelagic microalgae use could only be differentiated with baseline δ13CEAA values as similar microalgae clades occur in both habitats. We suggest that δ13CEAA fingerprints combined with microalgae baseline δ13CEAA values are an insightful tool to assess the effect of ongoing changes in Arctic basal resources on their use by organisms.