399 research outputs found
Cruise Report and preliminary results. DUSTTRAFFIC IV: Transatlantic fluxes of Saharan dust. Cruise No. JC134, 19 March â 16 April 2016 St Johns, Antigua â Sta Cruz, Tenerife (Spain)
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The mysterious long-range transport of giant mineral dust particles
Giant mineral dust particles (>75 ”m diameter) found far from their source have puzzled scientists for a long time. These wind-blown particles impact the atmosphereâs radiation balance, clouds and the ocean carbon cycle but are generally ignored in models. Here we report new observations of individual giant Saharan dust particles of up to 450 ”m in diameter sampled in air over the Atlantic Ocean at 2,400 and 3,500 km from the west African coast. Past research points to fast horizontal transport, turbulence, uplift in convective systems and electrical levitation of particles as possible explanations for this fascinating phenomenon. We present a critical assessment of these mechanisms using order-of-magnitude estimates and backward trajectories. Results show that established concepts are merely able to explain our new observations. Therefore we propose several lines of research we deem promising to further advance our understanding and modelling
Precipitation as the main driver of Neoglacial fluctuations of Gualas glacier, Northern Patagonian Icefield
© The Author(s), 2012. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Climate of the Past 8 (2012): 519-534, doi:10.5194/cp-8-519-2012.Glaciers are frequently used as indicators of climate change. However, the link between past glacier fluctuations and climate variability is still highly debated. Here, we investigate the mid- to late-Holocene fluctuations of Gualas Glacier, one of the northernmost outlet glaciers of the Northern Patagonian Icefield, using a multi-proxy sedimentological and geochemical analysis of a 15 m long fjord sediment core from Golfo Elefantes, Chile, and historical documents from early Spanish explorers. Our results show that the core can be sub-divided into three main lithological units that were deposited under very different hydrodynamic conditions. Between 5400 and 4180 cal yr BP and after 750 cal yr BP, sedimentation in Golfo Elefantes was characterized by the rapid deposition of fine silt, most likely transported by fluvio-glacial processes. By contrast, the sediment deposited between 4130 and 850 cal yr BP is composed of poorly sorted sand that is free of shells. This interval is particularly marked by high magnetic susceptibility values and Zr concentrations, and likely reflects a major advance of Gualas glacier towards Golfo Elefantes during the Neoglaciation. Several thin silt layers observed in the upper part of the core are interpreted as secondary fluctuations of Gualas glacier during the Little Ice Age, in agreement with historical and dendrochronological data. Our interpretation of the Golfo Elefantes glaciomarine sediment record in terms of fluctuations of Gualas glacier is in excellent agreement with the glacier chronology proposed for the Southern Patagonian Icefield, which is based on terrestrial (moraine) deposits. By comparing our results with independent proxy records of precipitation and sea surface temperature, we suggest that the fluctuations of Gualas glacier during the last 5400 yr were mainly driven by changes in precipitation in the North Patagonian Andes.This research was supported by an EU FP6
Marie Curie Outgoing Fellowship to S.B. Cruise NBP0505 was
funded by the US National Science Foundation, Office of Polar
Programs grant number NSF/OPP 03-38137 to J. Anderson (Rice
University) and J. Smith Wellner (University of Houston). The
Cimar-7 Program was supported by the Chilean National Oceanographic
Committee (CONA, Grant C7F 01-10 to S. Pantoja)
Microscale spatial distributions of microbes and viruses in intertidal photosynthetic microbial mats
Intertidal photosynthetic microbial mats from the Wadden Sea island Schiermonnikoog were examined for microscale (millimetre) spatial distributions of viruses, prokaryotes and oxygenic photoautotrophs (filamentous cyanobacteria and benthic diatoms) at different times of the year. Abundances of viruses and prokaryotes were among the highest found in benthic systems (0.05â5.43 Ă 1010 viruses gâ1 and 0.05â2.14 Ă 1010 prokaryotes gâ1). The spatial distribution of viruses, prokaryotes and oxygenic photoautotrophs were highly heterogeneous at mm scales. The vertical distributions of both prokaryotic and viral abundances were related to the depth of the oxygenic photoautotrophic layer, implying that the photosynthetic mat fuelled the microbial processes in the underlying layer. Our data suggest that viruses could make an important component in these productive environments potentially affecting the biodiversity and nutrient cycling within the mat
Assessing the relationship between Saharan dust input and export of organic material in the deep eastern Mediterranean Sea using a one-year sediment-trap record
Atmospheric deposition of iron from mineral aerosols to the ocean
Atmospheric deposition of iron (Fe) from mineral aerosols to the ocean has been suggested to increase the amount of ocean uptake of CO2 and emissions of marine biogenic aerosols. The marine organic material may be an important source of ice-nucleating particles in remote marine environment such as the Southern Ocean, North Pacific Ocean, and North Atlantic Ocean. Significant progress has been made in our understanding of atmospheric inputs of labile Fe from natural and anthropogenic sources to the surface oceans. Different emission sources and transformation processes affect aerosol Fe solubility. Mineral dust contains a small amount of labile Fe (e.g., ferrihydrite) on the surface (about 1% of Fe solubility) and thus may deliver insignificant labile Fe fluxes to the polar oceans in present days. However, about 10% of mean Fe solubility is measured for the Last Glacial Maximum (LGM) aerosols in Antarctica. If this value is applied to mineral dust during the LGM, the atmospheric input of labile Fe could be comparable to that provided by upwelling in present days. However, there are still large uncertainties regarding the relative importance of different sources of Fe and the effects of atmospheric aerosols on dissolved Fe in the ocean. Here, we use atmospheric chemistry transport model and ocean ecosystem model to investigate the effects of atmospheric deposition of Fe from mineral aerosols to dissolved Fe in the ocean, based on measurements in the North Atlantic. When a constant Fe solubility of 2% was used in the ocean model, the model overestimated the dissolved Fe concentration in the surface ocean downwind from the North African dust plume. Considering different degrees of atmospheric Fe processing reduced the overestimates. However, the atmospheric model underestimated labile Fe concentration over the Southern Ocean. Further investigation of the mechanisms of emissions, transport, and deposition of Fe-containing particles over the oceans is needed to improve our understanding of labile Fe supply to open ocean.Abstract A14B-08 presented at 2018 Fall Meeting, AGU, Washington D. C., 10-14 Dec
Response of coccolithophore communities to oceanographic and atmospheric processes across the North- and Equatorial Atlantic
Changes in coccolithophore productivity in response to climate-driven ocean warming are likely to have cascading biogeochemical effects that feed back to the changing climate. This paper investigates the role (and interplay) of large-scale oceanographic and atmospheric processes across the North- and Equatorial Atlantic, including Saharan dust deposition, on the distribution of coccolithophore communities. The study is based on biological and hydrological data collected across the photic zone of the ocean, and aerosol data collected from the lower atmosphere, across 50°Nâ1°S during the Atlantic Meridional Transect in boreal Autumn of 2018 (AMT28), in synergy with Earth Observations. Results confirm existing understanding of the distribution of coccolithophore communities which are related to major meridional hydrological gradients across the North Atlantic. Dynamic, oxygenated and microphytoplankton-enriched waters at higher-latitudes were characterized by less diverse coccolithophore populations, dominated by placolith-bearing r-selected coccolithophores. In contrast, the heavily stratified and picoplankton-enriched waters of the subtropical gyre revealed more diverse populations, dominated by umbelliform coccolithophores and holococcolithophores at the surface, and by floriform taxa in the lower photic zone. Mean concentrations of 14.4Ă103 cells/L present in the North Atlantic Tropical Gyre Province (30â12°N), only slightly lower compared to 17.7Ă103 cells/L produced in the North Atlantic Drift province (50â40°N), provide a snapshot perspective on the importance of coccolithophore production in heavily stratified gyre conditions. Higher concentrations of 19â-Hexanoyloxyfucoxanthin (HexFuco) in regions of enhanced production of r-selected placolith-bearing species suggest that this pigment should not be generalized as a proxy for the entire coccolithophore community. Enhanced abundances of fast-blooming Emiliania huxleyi and Gephyrocapsa oceanica, and of cyanobacteria (including both picoplankton and N2-fixing Trichodesmium spp.) at the surface of the region of more persistent Saharan dust deposition (at ~12-10°N) appeared to result from dust-born nutrient input. Underneath this stratified surface layer, enhanced productivity in the deep chlorophyll maximum (DCM) appeared decoupled from that on the surface, fueled by geostrophic eastward shoaling of the nutricline across the tropical North Atlantic. As this was the region of highest macronutrient concentrations measured along and below the nutricline, our data suggest that the NE tropical Atlantic may act as a permanent dust-born nutrient depocenter as previously hypothesized
Photocatalytic chlorine atom production on mineral dustâsea spray aerosols over the North Atlantic
Active chlorine in the atmosphere is poorly constrained and so is its role in the oxidation of the potent greenhouse gas methane, causing uncertainty in global methane budgets. We propose a photocatalytic mechanism for chlorine atom production that occurs when Sahara dust mixes with sea spray aerosol. The mechanism is validated by implementation in a global atmospheric model and thereby explaining the episodic, seasonal, and location-dependent 13C depletion in CO in air samples from Barbados [J.E. Mak, G. Kra, T. Sandomenico, P. Bergamaschi, J. Geophys. Res. Atmos. 108 (2003)], which remained unexplained for decades. The production of Cl can also explain the anomaly in the CO:ethane ratio found at Cape Verde [K. A. Read et al., J. Geophys. Res. Atmos. 114 (2009)], in addition to explaining the observation of elevated HOCl [M. J. Lawler et al., Atmos. Chem. Phys. 11, 7617â7628 (2011)]. Our model finds that 3.8 Tg(Cl) yâ1 is produced over the North Atlantic, making it the dominant source of chlorine in the region; globally, chlorine production increases by 41%. The shift in the methane sink budget due to the increased role of Cl means that isotope-constrained topâdown models fail to allocate 12 Tg yâ1 (2% of total methane emissions) to 13C-depleted biological sources such as agriculture and wetlands. Since 2014, an increase in North African dust emissions has increased the 13C isotope of atmospheric CH4, thereby partially masking a much greater decline in this isotope, which has implications for the interpretation of the drivers behind the recent increase of methane in the atmosphere
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