Alfred Wegener Institute for Polar and Marine Research
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Regional pollen-based Holocene temperature and precipitation patterns depart from the Northern Hemisphere mean trends
Get PDFA mismatch between model-and proxy-based Holocene climate change, known as the "Holocene conundrum", may partially originate from the poor spatial coverage of climate reconstructions in, for example, Asia, limiting the number of grid cells for model-data comparisons. Here we investigate hemispheric, latitudinal, and regional mean time series and time-slice anomaly maps of pollen-based reconstructions of mean annual temperature, mean July temperature, and annual precipitation from 1908 records in the Northern Hemisphere extratropics. Temperature trends show strong latitudinal patterns and differ between (sub-)continents. While the circum-Atlantic regions in Europe and eastern North America show a pronounced Middle Holocene temperature maximum, western North America shows only weak changes, and Asia mostly shows a continuous Holocene temperature increase. Likewise, precipitation trends show certain regional peculiarities such as the pronounced Middle Holocene precipitation maximum between 40 and 50gN in Asia and Holocene increasing trends in Europe and western North America, which can all be linked with Holocene changes in the regional circulation pattern responding to temperature change. Given a background of strong regional heterogeneity, we conclude that the calculation of global or hemispheric means, which initiated the Holocene conundrum debate, should focus more on understanding the spatiotemporal patterns and their regional drivers
Healthy living on a healthy planet
Get PDFOur lifestyle is making us ill and is destroying the natural life-support systems. In the vision of ‘healthy living on a healthy planet’, human spheres of life – what we eat, how we move, where we live – are designed to be both healthy and environmentally compatible, and planetary risks – climate change, biodiversity loss, pollution – have been overcome. Health systems harness their transformative potential; education and science promote societal change. The vision can only be realized with international cooperation and requires what the WBGU terms global urgency governance
Transient Suppression of Bacterial Populations Associated with Gut Health is Critical in Success of Exclusive Enteral Nutrition for Children with Crohn’s Disease
Get PDFBackground and Aims: Exclusive enteral nutrition [EEN] is a dietary intervention to induce clinical remission in children with active luminal Crohn's disease [CD]. While changes in the gut microbial communities have been implicated in achieving this remission, a precise understanding of the role of microbial ecology in the restoration of gut homeostasis is lacking. Methods: Here we reconstructed genomes from the gut metagenomes of 12 paediatric subjects who were sampled before, during and after EEN. We then classified each microbial population into distinct 'phenotypes' or patterns of response based on changes in their relative abundances throughout the therapy on a per-individual basis. Results: Our data show that children achieving clinical remission during therapy were enriched with microbial populations that were either suppressed or that demonstrated a transient bloom as a function of EEN. In contrast, this ecosystem-level response was not observed in cases of EEN failure. Further analysis revealed that populations that were suppressed during EEN were significantly more prevalent in healthy children and adults across the globe compared with those that bloomed ephemerally during the therapy. Conclusions: These observations taken together suggest that successful outcomes of EEN are marked by a temporary emergence of microbial populations that are rare in healthy individuals, and a concomitant reduction in microbes that are commonly associated with gut homeostasis. Our work is a first attempt to highlight individual-specific, complex environmental factors that influence microbial response in EEN. This model offers a novel, alternative viewpoint to traditional taxonomic strategies used to characterize associations with health and disease states
A Review of Seismic Surveys on the Lomonosov Ridge: Conclusions on its Structural Segmentation and Influence on Arctic Ocean Paleoceanography
Get PDFThe Lomonosov Ridge presents a major morphologic feature in the Arctic Ocean. Its tectonic evolution influenced the development of the ocean current system, deposition realm, glacial processes and ecosystem essentially. Based on morphological differences, the Lomonosov Ridge can be divided into three segments: the North American leg north off Greenland, the central part, and the Siberian leg.
The contribution presents an overview on a set of seismic surveys along the Ridge, and across into the adjacent Eurasian and Amerasia Basins. The data image the entire sedimentary cover, as well as the ridge’s basement surface. Prominent reflectors, reflector configuration, as well as the reflection pattern of seismic units were correlated with coring information and magnetic anomalies to establish a seismostratigraphic model.
Aim of the study is to investigate if the structure of the sedimentary cover can be related to the segmentation of the Lomonosov Ridge, and thus, can provide information on the subsidence history of the different legs. Drift bodies, sediment waves, and erosional structures are examined for indications on the Paleoceanography, such as first passages for water mass exchanges between the Amerasia and Eurasia Basins, and the onset of a modern ocean circulation system and paleo-bottom current activity in the Arctic Ocean
The tidal effects in the Finite-volumE Sea ice–Ocean Model (FESOM2.1): a comparison between parameterised tidal mixing and explicit tidal forcing
Get PDFTides are proved to have a significant effect on the ocean and climate. Previous modelling research either adds a tidal mixing parameterisation or an explicit tidal forcing to the ocean models. However, no research compares the two approaches in the same framework. Here we implement both schemes in a general ocean circulation model and assess both methods by comparing the results. The aspects for comparison involve hydrography, sea ice, meridional overturning circulation (MOC), vertical diffusivity, barotropic streamfunction and energy diagnostics. We conclude that although the mesh resolution is poor in resolving internal tides in most mid-latitude and shelf-break areas, explicit tidal forcing still shows stronger tidal mixing at the Kuril-Aleutian Ridge and the Indonesian Archipelago than the tidal mixing parameterisation. Beyond that, the explicit tidal forcing method leads to a stronger upper cell of the Atlantic MOC by enhancing the Pacific MOC and the Indonesian Throughflow. Meanwhile, the tidal mixing parameterisation leads to a stronger lower cell of the Atlantic MOC due to the tidal mixing in deep oceans. Both methods maintain the Antarctic Circumpolar Current at a higher level than the control run by increasing the meridional density gradient. We also show several phenomena that are not considered in the tidal mixing parameterisation, for example, the changing of energy budgets in the ocean system, the bottom drag induced mixing on the continental shelves and the sea ice transport by tidal motions. Due to the limit of computational capacity, an internal-tide-resolving simulation is not feasible for climate studies. However, a high-resolution short-term tidal simulation is still required to improve parameters and parameterisation schemes in climate studies
Globally coherent water cycle response to temperature change during the past two millennia
Get PDFThe response of the global water cycle to changes in global surface temperature remains an outstanding question in future climate projections and in past climate reconstructions. The stable hydrogen and oxygen isotope compositions of precipitation (δprecip), meteoric water (δMW) and seawater (δSW) integrate processes from microphysical to global scales and thus are uniquely positioned to track global hydroclimate variations. Here we evaluate global hydroclimate during the past 2,000 years using a globally distributed compilation of proxies for δprecip, δMW and δSW. We show that global mean surface temperature exerted a coherent influence on global δprecip and δMW throughout the past two millennia, driven by global ocean evaporation and condensation processes, with lower values during the Little Ice Age (1450–1850) and higher values after the onset of anthropogenic warming (~1850). The Pacific Walker Circulation is a predominant source of regional variability, particularly since 1850. Our results demonstrate rapid adjustments in global precipitation and atmospheric circulation patterns—within decades—as the planet warms and cools
Ecophysiological and behavioural response of juveniles of the Chilean cold-water coral Caryophyllia (Caryophyllia) huinayensis to increasing sediment loads
Get PDFChilean Patagonia is a hotspot of biodiversity, harbouring cold-water corals (CWCs) that populate steep walls and overhangs of fjords and channels. Through anthropogenic activities such as deforestation, roadworks, aquafarming and increased landslide frequency, sediment input increases in the fjord region. While the absence of CWCs on moderately steep slopes has been suggested to reflect high vulnerability to sedimentation, experimental evidence has been lacking. Here, we investigated the sensitivity of CWCs to sediment stress, using juvenile Caryophyllia (Caryophyllia) huinayensis as a model. A 12-week aquarium experiment was conducted with three sediment loads: the average natural sediment concentration in Comau Fjord, 100- and 1000-fold higher sediment levels, expected from gravel road use and coastal erosion. Changes in coral mass and calyx dimensions, polyp expansion, tissue retraction and respiration were measured. For CWCs exposed to two and three order of magnitude higher sediment concentrations, 32% and 80% of the animals experienced a decrease in tissue cover, respectively, along with a decrease in respiration rate of 34% and 66%. Under the highest concentration corals showed reduced polyp expansion and a significantly reduced growth of ~ 95% compared to corals at natural concentration. The results show that C. huinayensis is affected by high sediment loads. As human activities that increase sedimentation steadily intensify, coastal planners need to consider detrimental effects on CWCs
Future climate conditions alter biomass of salt marsh plants in the Wadden Sea
Get PDFUnderstanding how the salt marsh vegetation will evolve under future climate conditions is essential for predicting the role of marsh ecosystem services in a warmer climate with higher CO2-concentrations. In a mesocosm experiment in the northern Wadden Sea, the impact of increased temperature (+ 3 °C) and CO2 (800 ppm) on salt marsh vegetation was investigated, assessing biomass production in the pioneer zone and low marsh. The pioneer zone, which was dominated by Spartina anglica and exposed to natural tidal inundations, demonstrated a differentiated response between belowground and aboveground biomass. Aboveground biomass increased in response to enhanced CO2 availability, and belowground biomass increased in response to raised temperatures. Other plant species accounted for less than 18% of the aboveground biomass, and their biomass was suppressed under high CO2 availability. Increased biomass by Spartina anglica may improve resilience toward sea level rise. Hence, the pioneer zone is expected to maintain its coastal protection and blue carbon storage capacity under future climate conditions. The low marsh, which was dominated by Elymus athericus, was exposed to higher than usual tidal inundations and resembled a scenario with increased sea level. The low marsh showed no response in biomass to increased CO2 or temperature, which may be due to the increased flooding. The positive response of Spartina anglica (C4 plant) and the lack of response in Elymus athericus (C3 plant) counter the notion that C3 plants are more productive under future climate conditions and demonstrate that C4 plants can also thrive in future salt marshes