ALBERT

Description: Background: In mammals, ABCB1 constitutes a cellular "first line of defense" against a wide array of chemicals and drugs conferring cellular multidrug or multixenobiotic resistance (MDR/MXR). We tested the hypothesis that an ABCB1 ortholog serves as protection of the sensitive developmental processes in zebrafish embryos against adverse compounds dissolved in the water. Results: Indication for ABCB1-type efflux counteracting the accumulation of chemicals in zebrafish embryos comes from experiments with fluorescent and toxic transporter substrates and inhibitors. With inhibitors present, levels of fluorescent dyes in embryo tissue and sensitivity of embryos to toxic substrates were generally elevated. We verified two predicted sequences from zebrafish, previously annotated as abcb1, by cloning; our synteny analyses, however, identified them as abcb4 and abcb5, respectively. The abcb1 gene is absent in the zebrafish genome and we explored whether instead Abcb4 and/or Abcb5 show toxicant defense properties. Quantitative real-time polymerase chain reaction (qPCR) analyses showed presence of transcripts of both genes throughout the first 48 hrs of zebrafish development. Similar to transporter inhibitors, morpholino knock-down of Abcb4 increased accumulation of fluorescent substrates in embryo tissue and sensitivity of embryos toward toxic compounds. In contrast, morpholino knock-down of Abcb5 did not exert this effect. ATPase assays with recombinant protein obtained with the baculovirus expression system confirmed that dye and toxic compounds act as substrates of zebrafish Abcb4 and inhibitors block its function. The compounds tested comprised model substrates of human ABCB1, namely the fluorescent dyes rhodamine B and calcein-am and the toxic compounds vinblastine, vincristine and doxorubicin; cyclosporin A, PSC833, MK571 and verapamil were applied as inhibitors. Additionally, tests were performed with ecotoxicologically relevant compounds: phenanthrene (a polycyclic aromatic hydrocarbon) and galaxolide and tonalide (two polycyclic musks). Conclusions: We show that zebrafish Abcb4 is a cellular toxicant transporter and provides protection of embryos against toxic chemicals dissolved in the water. Zebrafish Abcb4 thus is functionally similar to mammalian ABCB1, but differs to mammalian ABCB4, which is not involved in cellular resistance to chemicals but specifically transports phospholipids in liver. Our data have important implications: Abcb4 could affect bioavailability - and thus toxicologic and pharmacologic potency - of chemicals to zebrafish embryos and inhibition of Abcb4 therefore causes chemosensitization, i.e., enhanced sensitivity of embryos to toxicants. These aspects should be considered in (eco)toxicologic and pharmacologic chemical screens with the zebrafish embryo, a major vertebrate model.

Description: One of the controlling factors of net ecosystem exchange that is highly sensitive to changes in climate is fire activity. A model study to describe these controlling factors is validated using multiple proxies to understand fire activity on a continental scale. We present results form a transient integration with the fully coupled Earth System Model (ESM) ECHAM5/MPI-OM1/JSBACH of the Max-Planck-Institute for Meteorology covering the last 6000 years. The model comprises dynamical components for atmosphere, ocean, and biosphere including an approach to simulate fire dynamics. The simulation is analyzed with a focus on land carbon and fire dynamics. A range of observational products are used to constrain the models ability to simulate fire distribution and changes in fire regimes over the course of the last 6000 years. On the global land scale, the model run shows a small decrease of the global mean temperature and a decline in annual precipitation. For the land carbon storage there is a significant decrease. Due to the changes in the orbital parameters with time, regionally the effect on precipitation and temperature is stronger, which results in a shift of the tropical rain belt combined with changes in vegetation. Striking is for example a reduction in the vegetation cover in central East Asia over the last 6000 years with a subsequent decreasing trend in land carbon. Related to climatic changes the fire activity is changing as well. We simulate a reduction of 5% in annual global burned area within the last 6000 years. Regionally, the simulation points out trends in the fire activity corresponding to the changes in vegetation shifts: e.g. there is an increase of 15% in central East Asia and a reduction of about 20% in tropical West Africa in burned area mainly a result of the redistribution of fuel abundance. Simulated changes in fire activity are compared to fire activity records reported in the global charcoal database (Power et al., 2008) and levoglucosan values out of ice cores. As the charcoal data and levoglucosan data show opposite trends, we demonstrate the sensitivity of the modeled and observed trend to the chosen grid boxes of the model domain. Whereas the charcoal sites are biased to North-America and show an opposite trend than the ice-core data from Kilimanjaro, the investigation of levoglucosan data out of remote ice cores (EPICA or NEEM) are additional used to get a global view on the trend in fire activity.

Description: One of the controlling factors of NEE that is highly sensitive to changes in climate is fire activity. Here we present results form a transient integration with the fully coupled MPI- Earth System Model (MPI-ESM) of the Max-Planck-Institute for Meteorology covering the last 6000 years. The model comprises dynamical components for atmosphere, ocean, and biosphere including an approach to simulate fire dynamics. The simulation is analyzed with a focus on land carbon and fire dynamics. A range of observational products is used to constrain the models ability to simulate fire distribution and changes in fire regimes over the course of the last 6000 years. On the global land scale, the model run shows a small decrease of the global mean temperature and a decline in annual precipitation. For the land carbon storage there is a significant decrease. On the regional scale, the effect on temperature and precipitation due to changes in the orbital parameters with time is much stronger. A shift of the tropical rain belt combined with changes in vegetation is simulated. Striking is for example a reduction in the vegetation cover in central East Asia over the last 6000 years with a subsequent decreasing trend in land carbon. Related to these climatic changes the fire activity is changing as well. We simulate a reduction of 5% in annual global burned area within the last 6000 years. Regionally, the simulation points out trends in the fire activity corresponding to the changes in vegetation shifts: e.g. there is an increase of ~ +15% in central East Asia and a reduction of about 20% in tropical West Africa in burned area mainly a result of the redistribution of fuel abundance. Simulated changes in fire activity are compared to fire activity records reported in the global charcoal database (Power et al., 2008) and levoglucosan values out of ice cores. A special focus of the analysis will lie on an assessment of correlation between fire activity and large-scale climate indexes (e.g. ENSO, NAO). Focusing on the last 100 yrs the modeled variability is checked against a reconstruction of a yearly global fire history (Mouillot et al., 2005). This comparison points out regions with a significant influence of anthropogenic disturbed fires, which are not represented in the ESM, but play a major role in the last few decades.

Description: Two model studies based on the Earth System Model (ESM) ECHAM5/MPI-OM1/JSBACH of the Max-Planck-Institute for Meteorology will be presented showing the vegetation response to orbital forcing. A 6000 years transient simulation of the Holocene and a time-slice model experiment for the Eemian are investigated. The model comprises dynamical components for atmosphere, ocean, and biosphere including an approach to simulate vegetation disturbance by fire dynamics and wind. The model results show reasonable patterns for temperature and precipitation changes (compared to present day climate). For the Holocene the annual mean global temperature is slightly decreasing (approximately 0.1 K), but the regional and seasonal changes are much larger. For example, Arctic temperatures are in winter up to 5 K higher (for the Holocene) and differences of up to -3 K are simulated for tropical west Africa, but only minor changes in the precipitation patterns related to changes within the tropical rain belt are simulated by MPI-ESM. At the same time shifts in the fractional vegetation cover are computed. Striking is for example the shift of the boreal tree line and the greening of West Africa during the early Holocene. The patterns derived from the Eemian snap-shot simulation feature similar, but more pronounced changes. All these vegetation changes are also reflected in the carbon storage on land. The amount of carbon stored in biomass decreases during the transient 6000 years from the Holocene to present day, as the fraction of forest covered area decreases with time and is replaced by grass and shrubs.

Description: One of the controlling factors of net ecosystem exchange that is highly sensitive to changes in climate is fire activity. A model study to describe these controlling factors is validated using multiple proxies to understand fire activity on a continental scale. We present results form a transient integration with the fully coupled Earth System Model (ESM) ECHAM5/MPI-OM1/JSBACH of the Max-Planck-Institute for Meteorology covering the last 6000 years. The model comprises dynamical components for atmosphere, ocean, and biosphere including an approach to simulate fire dynamics. The simulation is analyzed with a focus on land carbon and fire dynamics. A range of observational products are used to constrain the models ability to simulate fire distribution and changes in fire regimes over the course of the last 6000 years. On the global land scale, the model run shows a small decrease of the global mean temperature and a decline in annual precipitation. For the land carbon storage there is a significant decrease. Due to the changes in the orbital parameters with time, regionally the effect on precipitation and temperature is stronger, which results in a shift of the tropical rain belt combined with changes in vegetation. Striking is for example a reduction in the vegetation cover in central East Asia over the last 6000 years with a subsequent decreasing trend in land carbon. Related to climatic changes the fire activity is changing as well. We simulate a reduction of 5% in annual global burned area within the last 6000 years. Regionally, the simulation points out trends in the fire activity corresponding to the changes in vegetation shifts: e.g. there is an increase of 15% in central East Asia and a reduction of about 20% in tropical West Africa in burned area mainly a result of the redistribution of fuel abundance. Simulated changes in fire activity are compared to fire activity records reported in the global charcoal database (Power et al., 2008) and levoglucosan values out of ice cores. As the charcoal data and levoglucosan data show opposite trends, we demonstrate the sensitivity of the modeled and observed trend to the chosen grid boxes of the model domain. Whereas the charcoal sites are biased to North-America and show an opposite trend than the ice-core data from Kilimanjaro, the investigation of levoglucosan data out of remote ice cores (EPICA or NEEM) are additional used to get a global view on the trend in fire activity.

Description: Orbital forcing does not only exert direct insolation effects, but also alters climate indirectly through feedback mechanisms that modify atmosphere and ocean dynamics and meridional heat and moisture transfers. We investigate the regional effects of these changes by detailed analysis of atmosphere and ocean circulation and heat transports in a coupled atmosphere-ocean-sea ice-biosphere general circulation model (ECHAM5/JSBACH/MPI-OM). We perform long term quasi equilibrium simulations under pre-industrial, mid-Holocene (6000 years before present – yBP), and Eemian (125 000 yBP) orbital boundary conditions. Compared to pre-industrial climate, Eemian and Holocene temperatures show generally warmer conditions at higher and cooler conditions at lower latitudes. Changes in sea-ice cover, ocean heat transports, and atmospheric circulation patterns lead to pronounced regional heterogeneity. Over Europe, the warming is most pronounced over the north-eastern part in accordance with recent reconstructions for the Holocene. We attribute this warming to enhanced ocean circulation in the Nordic Seas and enhanced ocean-atmosphere heat flux over the Barents Shelf in conduction with retreat of sea ice and intensified winter storm tracks over northern Europe.