dr Simon Belanger – Université du Québec à Rimouski, Québec, Canada
dr Atsushi Matsuka – Laval University, Takuvik Joint International Laboratory Quebec, Canada
prof. Huixiang Xie – Université du Québec à Rimouski, Québec, Canada
dr Philippe Massicotte – Aarhus University, Department of Bioscience, Roskilde, Denmark
dr Simon Belanger
Université du Québec à Rimouski, Québec, Canada.
Simon Bélanger is a professor in remote sensing at the Université du Québec a Rimouski (UQAR). He has more than fifteen years of experience in the field of ocean colour remote sensing. SB worked successively for the department of fisheries and oceans of Canada at Maurice Lamontagne Institute, the European Space Agency (ESA-ESRIN ; Italy) and ACRI-ST (France). Dr Bélanger obtained his PhD in 2006 entitled « Response of light-related carbon fluxes in the Arctic Ocean to climate change: Quantification and monitoring of dissolved organic matter photo-oxidation in the Beaufort Sea using satellite remote sensing » under the direction of Dr Marcel Babin at the Laboratoire d’Océanographie de Villefranche (LOV), France. His research interests are broad, from ocean color remote sensing problems (improvement of atmospheric correction or bio-optical algorithms) to applications of remote sensing to ocean biogeochemistry problems (primary production and photochemical processes from space). He has created in 2009 the AquaTel lab (Laboratoire d’optique aquatique et de télédétection) at UQAR. He is a member of the International Ocean Colour Coordinating Group (IOCCG), Québec-Océan, Arcticnet, Centre d’études Nordiques and BORÉAS.
Exports of CDOM and FDOM from boreal watersheds into the Gulf of St. Lawrence: implications of river damming and seasonality
River inputs of particulate and dissolved organic matter (POM and DOM) play a structural role for the coastal ecosystems. The supply of DOM and inorganic nutrients fuels both autotrophic and heterotrophic microorganisms. Simultaneously, colored dissolved organic matter (CDOM) and POM strongly attenuate solar radiation in the water column, reducing photosynthetically usable radiation. Here we study the seasonal variability in nutrients, bulk chemical composition and optical properties of CDOM in nine large river systems on the north shore of the Estuary and Gulf of St Lawrence (EGSL). These rivers account for up to 16% of the total freshwater discharged to the EGSL and four of them are regulated by large hydroelectric dams. The rivers regulated by dams showed a greater proportion of dissolved inorganic nitrogen (essentially nitrate) readily available for microorganisms. Unlike other boreal rivers, the export of silicate were similar between natural and dammed rivers. As expected, the regulation of the river flow, however, impeded large differences in the timing of the peak in nutrient and DOM exports to the coastal zone. For example, for the regulated rivers, small seasonal variations of the exports of dissolved organic carbon (DOC) were observed : ∼33% in winter and ∼25% in spring, compare to < 10% and ~50% for natural systems. The optical properties of CDOM (absorption and fluorescence), suggested that DOM in all systems was primarily derived from terrestrial ecosystems. The spectral slope of the CDOM absorption spectra exhibit higher values in regulated rivers indicating that DOM was made up of smaller molecules. Based on the PARAFAC decomposition of exitation-emission matrices, DOM in natural systems tends to be more labile than in regulated ones
dr Atsushi Matsuka
Laval University, Takuvik Joint International Laboratory Quebec, Canada
Atsushi Matsuoka received his doctorate in Oceanography and marine bio-optics in 2008 from Hokkaido University, Japan. He spent three years as a postdoctoral fellow in the marine bio-optics and remote sensing group at the Laboratoire d'Océanographie de Villefranche (LOV), France before joining Takuvik Joint International Laboratory, Québec City Canada in 2011 for his second postdoctoral fellowship. To better understand physical and biogeochemical response to climate change, Dr. Matsuoka has intensively studies the optical properties of the Arctic Ocean, knowledge of which is useful for satellite ocean colour remote sensing. Based on these findings, his research further extends to tracing the budget of dissolved organic carbon from space.
Roles of colored dissolved organic matters in the Arctic Ocean
Light absorption of colored dissolved organic matter (CDOM) is a useful quantity that provides insight into both physical and biogeochemical processes. While marine optical properties have been widely examined at lower latitudes, those for Arctic waters have been restricted both temporally and geographically due to sea ice. Since the early 2000s, partly in response to a significant reduction of summer Arctic sea ice, a number of in situ datasets have been acquired, but they are sparse and individually insufficient to draw a general view of the basin-wide spatial and temporal variations in absorption. To address this problem, I built a large absorption database (total, particulate, and CDOM) of the Arctic Ocean by pooling the majority of published datasets and merging them with newly-acquired datasets. This database allows us to examine the important roles of CDOM in the cold environments.
My talk will be presented in two sections. In the first section, CDOM absorption properties in relation to hydrography, photo-oxidation, and microbial activity will be presented based on in situ observations. In the second section, I will extend the observational perspective to satellite ocean color platforms including estimation of dissolved organic carbon (DOC) concentration from space.
prof. Huixiang Xie
Université du Québec à Rimouski, Québec, Canada
Dr. Xie obtained a doctoral degree in oceanography from Dalhousie University in 1998. He then worked for three years as a postdoctoral fellow at the Woods Hole Oceanographic Institution and at the National Exposure Research Laboratory affiliated with the U.S. Environmental Protection Agency. He is currently a professor of chemical oceanography at the Institut des sciences de la mer de Rimouski, Université du Québec à Rimouski. Dr. Xie’s research interests are mainly focused on 1) photochemical transformation of organic matter and its implication for carbon and nutrient cycling in marine waters; 2) biogeochemical cycling of trace gases such as carbon monoxide (CO), dimethyl sulfide (DMS), and methane (CH4) in the ocean.
Carbon monoxide: A probe of organic matter photoreactivity and microbial uptake of trace solutes in marine waters
The ocean is a source of atmospheric carbon monoxide (CO), which regulates the oxidizing capacity of the troposphere. Photoproduction and microbial uptake are the primary source and sink for oceanic CO and their interplay often leads to large diel variations in CO concentrations ([CO]) in the upper ocean. As the second most abundant inorganic carbon product from chromophoric dissolved organic matter (CDOM) photooxidation, CO per se is a significant component of the marine carbon cycle. More recently, it has been recognized that CO can also be photochemically produced from particulate organic matter (POM) in both coastal and open-ocean waters. Because it can be measured easily and precisely, CO is the most studied carbon photoproduct and has been frequently used as a proxy for the major but difficult-to-measure photoproducts, such as CO2 and biolabile organic carbon. Microbial CO oxidation not only modulates CO air-sea flux, but also potentially influences the flow of organic carbon in the food web and the respiratory CO2 budget. CO is also a short-lived tracer for modeling couplings among optics, photochemistry, biology, mixing dynamics, and gas exchange.
The efficiency of an organic matter photochemical process is often expressed as an apparent quantum yield (AQY), which is defined as the moles of a product photochemically produced or a reactant photochemically destroyed divided by the moles of photons absorbed by the organic matter at a given wavelength. One focus of this presentation is to use the AQY of CO (AQYCO) as a tool to probe the photoreactivity of CDOM and POM from diverse aquatic environments and to evaluate the effects of various environmental factors (e.g. temperature, salinity, pH, and dilution) on the organic matter photoreactivity. The AQYCO for CDOM (AQYCO-CDOM) is generally linearly correlated to the absorption coefficients of CDOM in the ultra violet (UV) regime; this relationship holds for salinity ranges covering estuarine, coastal, and open-ocean waters. CO photoproduction from CDOM is moderately temperature-dependent with low-salinity waters showing stronger dependence than saline waters. Increases in salinity and pH, and physical dispersion during estuarine mixing can explain a large part of the seaward decrease in AQYCO-CDOM observed in many estuaries. The spectra of AQY for POM-based CO photoproduction (AQYCO-POM) are flatter than the corresponding AQYCO-CDOM spectra, rendering visible radiation to be relatively more important for POM-based CO photoproduction than for the CDOM term. In particle-rich estuarine and coastal waters, POM photochemistry can prevail over CDOM photochemistry in terms of CO photoproduction.
A second focus of this presentation addresses the kinetics of microbial uptake of CO in marine waters. Microbial CO uptake often follows first-order kinetics at ambient [CO], particularly in warm waters, but saturation, inhibition, and Hill-type kinetics are not unusual in the cold, Arctic environments. Seasonal variations and temperature dependences of microbial CO uptake are discussed. The diverse kinetics revealed by microbial CO uptake at ambient [CO] demonstrate that CO is a useful substrate for studying microbial uptake kinetics of trace solutes in marine waters.
dr Philippe Massicotte
Aarhus University, Department of Bioscience, Roskilde, Denmark
Philippe obtained his PhD in environmental sciences in 2012, followed by two-years as a post-doc in Quebec, Canada. In recent years, he has been working on projects aiming to determine how the surrounding landscapes of aquatic ecosystems influence their functioning. He has investigated: 1) how tributaries and land use interact with the quality and quantity of DOM in the water column and 2) how DOM and suspended inorganic particulate matter influence watercolor. Most of the projects that he led have involved the use of spectral imagery, GIS and several spatial analyzes. The unifying theme of his future research will be to better understand the factors that determine underwater light characteristics, DOM biogeocycling and subsequently aquatic ecosystem functioning. He is currently working at Aarhus University in Denmark with Prof. Stiig Markager. The theme of his current research project is to better understand bio-optics and the dynamics of colored dissolved organic matter innatural aquatic ecosystems.
Using a Gaussian decomposition approach to model absorption spectra of chromophoric dissolved organic matter
The chromophoric fraction of dissolved organic matter (CDOM) is responsible for the optical proprieties of most natural waters and plays a key role in ecosystem functioning. The spectral slope (S) describing the approximate exponential decline in CDOM absorption with increasing wavelength is widely used for tracing changes in the chemical composition of CDOM. However, the usefulness of S for characterizing CDOM is limited by the spectral range over which is it calculated. The lack of consensus in the choice of the spectral range severely limits our ability to compare results from the literature and thus our understanding on how S varies in different aquatic ecosystems on the global scale. We propose a new method for modeling CDOM absorption spectra based on a Gaussian decomposition approach that removes the limitations associated with the choice of the spectral range used to estimate S. Using simulations (n = 1000), we show that our framework provides robust estimates of S by exploiting all the information contained in CDOM spectra. On average, the error on S estimations were of 0.16% for the proposed method compared to 27% and 11% for the traditional modeling approaches fitted over 300-700 nm and 240-700 nm respectively. We further demonstrate the ability of the framework to decompose and model chromophores present in complex spectra from different aquatic environments ranging from freshwater to deep oceanic water samples from around the world. The proposed modeling framework opens avenues for long-term or cross-site comparison studies about the biogeochemical cycling of CDOM.