195 research outputs found
Seasonal contribution of terrestrial organic matter and biological oxygen demand to the Baltic Sea from three contrasting river catchments
To examine the potential influence of terrestrially derived DOM on the Baltic
Sea, a year-long study of dissolved organic matter (DOM) was performed in
three river catchments in Sweden. One catchment drains into the Bothnian Sea,
while two southern catchments drain into the Baltic proper. Dissolved organic
carbon (DOC) concentrations were positively correlated with discharge from
forested catchments over the year. While the overall concentrations of DOC
were several times higher in the southern two catchments, higher discharge in
the northern catchment resulted in the annual loadings of DOC being on the
same order of magnitude for all three catchments. Biological oxygen demand
(BOD) was used as a proxy for the lability of carbon in the system. The range
of BOD values was similar for all three catchments, however, the ratio of BOD
to DOC (an indication of the labile fraction) in Ume river was four times
higher than in the southern two catchments. Total annual BOD loading to the
Baltic Sea was twice as high in the northern catchment than in the two
southern catchments. Lower winter temperatures and preservation of organic
matter in the northern catchment combined with an intense spring flood help
to explain the higher concentrations of labile carbon in the northern
catchment. Lower lability of DOM as well as higher colour in the southern
catchments suggest that wetlands (i.e. peat bogs) may be the dominant source
of DOM in these catchments, particularly in periods of low flow. With climate
change expected to increase precipitation events and temperatures across the
region, the supply and quality of DOM delivered to the Baltic Sea can also be
expected to change. Our results indicate that DOM supply to the Baltic Sea
from boreal rivers will be more stable throughout the year, and potentially
have a lower bioavailability
OpenFluor- an online spectral library of auto-fluorescence by organic compounds in the environment
An online repository of published organic fluorescence spectra has been developed, which can be searched for quantitative matches with any set of unknown spectra. It fills a critical gap by increasing access to measured and modelled (PARAFAC) spectra, and linking across studies and systems to reveal "global" fluorescence trends
USING FLUORESCENT DISSOLVED ORGANIC MATTER TO TRACE ARCTIC SURFACE FRESH WATER
Climate change affects the Arctic environment with regards to permafrost thaw, changes in the riverine runoff and subsequent export of fresh water and terrestrial material to the Arctic Ocean. In this context, the Fram Strait represents a major pathway for export to the Atlantic basin. We assess the potential of visible wavelength dissolved organic matter fluorescence (VIS-FDOM) to trace the origin of Arctic outflow waters. Oceanographic surveys were performed in the Fram Strait, as well as on the east Greenland shelf (following the East Greenland Current), in late summer 2012 and 2013. Meteoric (fmw), sea-ice melt (fsim), Atlantic (faw) and Pacific (fpw) water fractions were determined and FDOM components were identified by PARAFAC modeling. In Fram Strait and east Greenland shelf, a robust correlation between VIS-FDOM and fmw was apparent, suggesting it as a reliable tracer of polar waters. However, variability was observed in the origin of polar waters, in relation to contribution of faw and fpw, between the sampled years. VIS-FDOM traced this variability, and distinguished between the origins of the halocline waters as originating in either the Eurasian or Canada basins. The findings presented highlight the potential of designing in situ DOM fluorometers to trace the freshwater origins and decipher water mass dynamics in the region
TRACING THE COMPOSITION OF DOM IN THE ARCTIC OCEAN WITH FLUORESCENCE SPECTROSCOPY
The Arctic Ocean consists of a large pool of dissolved organic matter (DOM), receiving considerable input of terrigenous carbon mobilized from high latitude carbon-rich soils and peatlands. This study aims at characterizing the DOM fluorescent components in two Arctic environments: the Lena River delta region (September 2013) and the Polar (Arctic) waters in the Fram Strait (June 2014). In addition, optical indices of DOM modification were evaluated together with the amount of DOM (expressed as the absorption at 350nm; a350). The colored and fluorescent fractions of DOM (CDOM and FDOM, respectively) were analyzed using fluorescence spectroscopy and PARAFAC modeling. The amount of DOM (a350) decreased with increasing salinity (varying from 15.7m-1 in the Lena delta to 0.34m-1 in the Fram strait), with strong removal at low salinity. Six fluorescent components were identified in the Lena delta region and three of those components were validated in the Fram Strait. The allochthonous humic-like signal was the dominant fraction of DOM within both sampled regions, with the highest relative contributions to total FDOM associated to low salinity. Conversely, autochthonous signal (e.g. protein- and/or marine humic-like) presented higher contribution in relation to total FDOM at high salinity. All the components were inversely related to salinity with the highest removal rates observed at low salinity. Optical indices of DOM modification (CDOM absorption slope, SUVA, fluorescence index, humification index and biological activity index) showed decrease on the humification degree and aromaticity of DOM towards high salinity. Strong removal at low salinity in the Lena delta region is presumed to be driven mostly by photodegradation and flocculation. The lower a350 values observed in the Fram strait indicates low removal through the Arctic Ocean. Further analyses will be conducted to evaluate the main drivers of the DOM removal through the open Arctic Ocean
Turnover time of fluorescent dissolved organic matter in the dark global ocean
Research articleMarine dissolved organic matter (DOM) is one of the largest reservoirs of reduced carbon on
Earth. In the dark ocean (4200 m), most of this carbon is refractory DOM. This refractory
DOM, largely produced during microbial mineralization of organic matter, includes humic-like
substances generated in situ and detectable by fluorescence spectroscopy. Here we show two
ubiquitous humic-like fluorophores with turnover times of 435±41 and 610±55 years, which
persist significantly longer than the B350 years that the dark global ocean takes to renew. In
parallel, decay of a tyrosine-like fluorophore with a turnover time of 379±103 years is also
detected. We propose the use of DOM fluorescence to study the cycling of resistant DOM
that is preserved at centennial timescales and could represent a mechanism of carbon
sequestration (humic-like fraction) and the decaying DOM injected into the dark global
ocean, where it decreases at centennial timescales (tyrosine-like fraction).Versión del editor10,015
Fluorescent dissolved organic matter as a biogeochemical tracer in the Davis Strait
Climate change affects the Arctic environment with regards to permafrost thaw, sea-ice melt, alterations to the freshwater budget and increased export of terrestrial material to the Arctic Ocean. The Davis Strait, together with the Fram Strait, represents the major gateways connecting the Arctic and Atlantic. Oceanographic survey was performed in the Davis Strait in late summer 2013, where hydrographical data and water samples were collected. Meteoric (fmw), sea-ice melt, Atlantic (faw) and Pacific (fpw) water fractions were determined. The underlying fluorescence properties of dissolved organic matter (FDOM) were characterized by applying Parallel Factor Analysis (PARAFAC), which isolated three fluorescent components. Visible wavelength FDOM (VIS-FDOM), associated to terrestrial humic-like material, was capable of tracing the Arctic outflow due to high values observed in association to Arctic Polar waters (PW) exiting through Davis Strait. Furthermore, VIS-FDOM was correlated to apparent oxygen utilization and traced deep-water turnover of DOM and also allowed to distinguish between surface waters from eastern (Atlantic + modified PW) and western (Canada-basin PW) sectors. The presented findings highlight the potential of designing in situ DOM fluorometers to trace the freshwater origins and decipher water mass mixing dynamics in the region and the potential of FDOM as a biogeochemical tracer
- …