Der Eisenkreislauf im Ozean, Rolle im Klimasystem und Beeinflussung durch Staub, Ozeanzirkulation und Biologie

Eine wesentliche Erkenntnis in der Meeresforschung der letzten drei Dekaden war die wichtige Rolle von Eisen im marinen Kohlenstoffkreislauf, und - da dieser den Kohlenstoffgehalt der Atmosphäre zu grossen Teilen bestimmt - im Klima. Eisen ist ein essentieller Mikronährstoff, nicht nur für Pflanzen; ein Mangel an Eisen schränkt gegenwärtig das Wachstum von Phytoplankton in mehr als 30% der Weltozeane ein, und dies obwohl Eisen eines der häufigsten Elemente der Erdkruste ist. Der Grund hierfür ist die extrem geringe Löslichkeit von Eisenhydroxiden in oxischem Meerwasser, die dazu führt, dass gelöstes Eisen eine starke Tendenz hat, sich an Partikel anzusetzen und so gegenüber den anderen löslicheren Nährstoffen, wie Nitrat oder Phosphat abgereichert wird. Die zentrale Rolle von Eisen im marinen Kohlenstoffkreislauf bietet Möglichkeiten für Rückkopplungen mit dem Klima. Ein Beispiel hierfür ist etwa die Hypothese, dass ein erhöhter Eiseneintrag über Staub im trockenen und kalten Klima der Eiszeiten beigetragen hat zu einer größeren Speicherung von Kohlenstoff im Ozean und so zu einer weiteren Abkühlung. Globale biogeochemische Modelle sind jedoch stark auf die Darstellung der gegenwärtigen Eisenverteilung hinoptimiert, was ihre Aussagefähigkeit für andere Klimazustände einschränkt. Das liegt daran, dass eine Reihe von Prozessen, die im Eisenkreislauf eine grosse Rolle spielen, komplex sind und in den Modellen oft sehr einfach parameterisiert werden. Beispiele hierfür sind etwa die Rolle von Kolloiden und Mikropartikeln beim Verlust von Eisen aus der gelösten Phase, der Einfluß von organischen Molekülen zu der Löslichkeit von Eisen, oder der Beitrag von Photochemie bei der Lösung von Eisen aus Staubpartikeln

The multiple roles of dust in ocean biogeochemistry

ithogenic material, carried by the atmosphere and deposited as dust, is a major source of nutrients and trace metals to the ocean. In the tropical Atlantic, which receives at least half of the global deposition flux to the oceans, dust is very likely to be the dominant source especially of iron. Iron is an important micronutrient for marine biology, so the delivery of dust couples the atmosphere, the global carbon cycle and climate. There are several ways how mankind is influencing this process, e.g. by changing dust emissions, but also by influencing dust particle composition, and hence iron solubility. But how much of the dust-deposited iron becomes bioavailable also depends on the seawater side: Iron is hardly soluble in oxic seawater and rapidly scavenged onto particle surfaces. Dust deposition also is a source of particles, and hence can act as a sink for dissolved iron. This talk will give an overview about the role of dust for marine biological productivity and carbon exchange between ocean and atmosphere, and how it is affected by chemistry of iron in the ocean. I will then focus on the double role of iron as a source and sink of iron, using insights from modelling and a series of recent measurements in the tropical Atlantic. Finally I will outline gaps in our current understanding and modelling of the marine iron cycle and point to ways forward

Simulating the distribution of stable silicon isotopes in the Last Glacial Maximum

Variations in the silicon stable isotopic composition (δ30Si) of sedimentary biogenic silica (BSi) are used to reconstruct the utilization level of dissolved silicic acid (DSi) by diatoms in the geological past and to explore the influence of diatoms on past oceanic biogeochemistry and climate. A Last Glacial Maximum (LGM) climate simulation has been performed with a coupled ocean-sediment model that includes a prognostic formulation of BSi production with concurrent silicon isotopic fractionation. The model results show reduced DSi utilization by diatoms in high latitudes during the LGM, likely due to the extended ice cover in the model. There is a decrease in BSi export production in the Southern Ocean during the LGM compared to a present-day climate experiment. This leads to an increased equator-ward transport of DSi in Subantarctic Mode Water and Antarctic Intermediate Water, and a shift in the distribution of DSi from the deep Pacific into the deep Atlantic. The mean δ30Si value of DSi in the upper ocean shows a 0.14 per mil decrease in the LGM experiment, while there is an increase in the low-latitude Pacific compared with the present-day experiment. In the Pacific and Indian Ocean the slopes of the surface Si(OH)4

Modelling Silicate - Nitrate - Ammonium Co-Limitation of Algal Growth and the Importance of Bacterial Remineralisation Based on an Experimental Arctic Coastal Spring Bloom Culture Study

Arctic coastal ecosystems are rapidly changing due to climate warming, which makes modelling their productivity crucially important to better understand future changes. System primary production in these systems is highest during the pronounced spring bloom, typically dominated by diatoms. Eventually the spring blooms terminate due to silicon or nitrogen limitation. Bacteria can play an important role for extending bloom duration and total CO2 fixation through ammonium regeneration. Current ecosystem models often simplify the effects of nutrient co-limitations on algal physiology and cellular ratios and neglect bacterial driven regeneration, leading to an underestimation 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 bacteria ammonium remineralisation, and 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. The model also highlights the importance of organic matter excretion, and post bloom ammonium accumulation. Overall, model complexity is comparable to other ecosystem models used in the Arctic while improving the representation of nutrient co-limitation related processes. Such model enhancements that now incorporate increased nutrient inputs and higher mineralization rates in a warmer climate will improve future predictions in this vulnerable system

Differences in Fabry Cardiomyopathy Between Female and Male Patients Consequences for Diagnostic Assessment

ObjectivesWe hypothesized that Fabry cardiomyopathy in female patients might differ substantially from that in male patients and sought to prove this hypothesis in a large cohort consisting of 104 patients with Fabry disease.BackgroundFabry cardiomyopathy in male patients is characterized by left ventricular (LV) hypertrophy, impaired myocardial function, and subsequent progressive myocardial fibrosis. In contrast, the occurrence of these 3 cardiomyopathic hallmarks in female patients remains unknown.MethodsIn 104 patients (58 females, age 42 ± 16 years; 46 males, age 42 ± 13 years) with genetically proven Fabry disease, LV hypertrophy, regional myocardial deformation and myocardial fibrosis were assessed by standard echocardiography, strain rate imaging, and cardiac magnetic resonance (CMR) imaging–guided late enhancement (LE).ResultsIn men, end-diastolic left ventricular wall thickness (LVWT) ranged from 6 to 19.5 mm (LV mass CMR 55 to 200 g/m2), and LE was never seen with LVWT <12 mm (LV mass <99 g/m2). In contrast in female patients, LVWT ranged from 5 to 15.5 mm, LV mass ranged from 39 to 146 g/m2, and LE was already detectable with an LVWT of 9 mm (LV mass 56 g/m2). When LV mass was examined in CMR, LE was detected in 23% of the female patients without hypertrophy (n = 9), whereas LE was never seen in male patients with normal LV mass. LE was always associated with low systolic strain rate, but the severity of impairment was independent of LVWT in female patients (lateral strain rate in patients with LV hypertrophy with LE −0.7 ± 0.2 s−1; patients without LV hypertrophy with LE −0.8 ± 0.2 s−1; p = 0.45).ConclusionsIn contrast to male patients, the loss of myocardial function and the development of fibrosis do not necessarily require myocardial hypertrophy in female patients with Fabry disease. Thus, in contrast to actual recommendations, initial cardiac staging and monitoring should be based on LV hypertrophy and on replacement fibrosis in female patients with Fabry disease

Activated regulatory T-cells promote duodenal bacterial translocation into necrotic areas in severe acute pancreatitis

Objective In acute pancreatitis (AP), bacterial translocation and subsequent infection of pancreatic necrosis are the main risk factors for severe disease and late death. Understanding how immunological host defence mechanisms fail to protect the intestinal barrier is of great importance in reducing the mortality risk of the disease. Here, we studied the role of the Treg/Th17 balance for maintaining the intestinal barrier function in a mouse model of severe AP. Design AP was induced by partial duct ligation in C57Bl/6 or DEREG mice, in which regulatory T-cells (Treg) were depleted by intraperitoneal injection of diphtheria toxin. By flow cytometry, functional suppression assays and transcriptional profiling we analysed Treg activation and characterised T-cells of the lamina propria as well as intraepithelial lymphocytes (IELs) regarding their activation and differentiation. Microbiota composition was examined in intestinal samples as well as in murine and human pancreatic necrosis by 16S rRNA gene sequencing. Results The prophylactic Treg-depletion enhanced the proinflammatory response in an experimental mouse model of AP but stabilised the intestinal immunological barrier function of Th17 cells and CD8+/γδTCR+ IELs. Treg depleted animals developed less bacterial translocation to the pancreas. Duodenal overgrowth of the facultative pathogenic taxa Escherichia/Shigella which associates with severe disease and infected necrosis was diminished in Treg depleted animals. Conclusion Tregs play a crucial role in the counterbalance against systemic inflammatory response syndrome. In AP, Treg-activation disturbs the duodenal barrier function and permits translocation of commensal bacteria into pancreatic necrosis. Targeting Tregs in AP may help to ameliorate the disease course