Colored Dissolved Organic Matter Distribution Research Articles

Remote-sensing monitoring of colored dissolved organic matter in the Arctic Ocean

In the Arctic Ocean, variations in the colored dissolved organic matter (CDOM) have important value and significance. This study proposed and evaluated a novel method by combining the Google Earth Engine with a multilayer back-propagation neural network to retrieve CDOM concentration. This model performed well on the testing data and independent validation data (R2 = 0.76, RMSE = 0.37 m−1, MAPD = 35.43 %), and it was applied to Moderate Resolution Imaging Spectroradiometer (MODIS) images. The CDOM distribution in the Arctic Ocean and its main sea areas was first depicted during the ice-free period from 2002 to 2021, with average CDOM concentration in the range of 0.25 and 0.31 m−1. High CDOM concentration appeared in coastal areas affected by rivers on the Siberian side. The CDOM concentration was highly correlated with salinity (r = −0.92) and discharge (r > 0.68), while melting sea ice diluted seawater and CDOM concentration.

Application of airborne hyperspectral imagery to retrieve spatiotemporal CDOM distribution using machine learning in a reservoir

• A CDOM absorption coefficient was selected from seven reference wavelengths. • The optimal combinations of R rs wavelengths were determined by random forest. • The optimal random forest model with CDOM absorption coefficient was revealed. • Spatiotemporal distribution and characteristics of CDOM were confirmed. • Results can be used to reveal temporal and spatial variation in CDOM distributions. Colored dissolved organic matter (CDOM) in inland waters is used as a proxy to estimate dissolved organic carbon (DOC) and may be a key indicator of water quality and nutrient enrichment. CDOM is optically active fraction of DOC so that remote sensing techniques can remotely monitor CDOM with wide spatial coverage. However, to effectively retrieve CDOM using optical algorithms, it may be critical to select the absorption coefficient at an appropriate wavelength as an output variable and to optimize input reflectance wavelengths. In this study, we constructed a CDOM retrieval model using airborne hyperspectral reflectance data and a machine learning model such as random forest. We evaluated the best combination of input wavelength bands and the CDOM absorption coefficient at various wavelengths. Seven sampling events for airborne hyperspectral imagery and CDOM absorption coefficient data from 350 nm to 440 nm over two years (2016–2017) were used, and the collected data helped train and validate the random forest model in a freshwater reservoir. An absorption coefficient of 355 nm was selected to best represent the CDOM concentration. The random forest exhibited the best performance for CDOM estimation with an R 2 of 0.85, Nash-Sutcliffe efficiency of 0.77, and percent bias of 3.88, by using a combination of three reflectance bands: 475, 497, and 660 nm. The results show that our model can be utilized to construct a CDOM retrieving algorithm and evaluate its spatiotemporal variation across a reservoir.

Characterization of colored dissolved organic matter in the northeastern South China Sea using EEMs-PARAFAC and absorption spectroscopy

Three-dimensional fluorescence excitation-emission matrix spectroscopy with parallel factor analysis (EEMs-PARAFAC) and absorption spectroscopy were used to characterize the colored dissolved organic matter (CDOM) in the northeastern South China Sea. The results showed that fluorescence components were identified as humic-like, tryptophan-like, tyrosine-like substances. The fluorescence indices indicated the CDOM in deep and subsurface waters had strong autogenous source characteristics, which were significantly affected by the activities of phytoplankton and bacteria in water. CDOM in surface waters was affected by both endogenous and exogenous sources. The content of CDOM in the horizontal spatial gradually decreased and then increased from nearshore areas to far-shore areas, indicating the coastal areas were affected by human activities, and in the open sea, the activities of organisms were strong. The redundancy analysis results showed that total phosphorus, ammonia nitrogen and dissolved oxygen were key environmental factors affecting the distribution of CDOM.

Optical Absorption Characteristics, Spatial Distribution, and Source Analysis of Colored Dissolved Organic Matter in Wetland Water around Poyang Lake

Colored dissolved organic matter (CDOM) is an important part of aquatic ecosystems and plays a key role in the biogeochemical cycle. In this study, CDOM absorption spectrum curves and water quality parameters from 30 sampling sites in the wetlands of Poyang Lake, Jiangxi Province, China, were collected in October 2016. The optical absorption characteristics and spatial distribution of CDOM, the correlation between the absorption coefficient of CDOM at a wavelength of 355 nm (ag(355)), and the concentration of dissolved organic carbon (DOC) were analyzed. Spectral characteristic parameters—namely, E2/E3 (the ratio of the CDOM absorption coefficient at a wavelength of 250 nm to the CDOM absorption coefficient at a wavelength of 365 nm), SUVA254 (the ratio of the CDOM absorption coefficient at a wavelength of 254 nm to the DOC concentration), and spectral slopes—were used to infer the composition and sources of CDOM in the Poyang Lake wetlands. The results showed the following: (1) the CDOM absorption spectrum of water of the Poyang Lake wetlands presented significant spatial variation, showing a trend of south > west > north > east; (2) there was a strong linear correlation between the CDOM absorption coefficient and the DOC concentration in the water of the Poyang Lake wetlands (ag(355) = 1.075DOC–0.659 (r2 = 0.723, p < 0.001, n = 30)); (3) the analysis of the spectral characteristic parameters E2/E3, SUVA254, and spectral slopes showed that the CDOM in the Poyang Lake wetlands has relatively high aromaticity and molecular weight, which were shown to be mainly affected by terrestrial inputs. The results showed that the molecular weight and aromaticity of CDOM were higher in the south of the lake than in other parts.

An Automatic Stationary Water Color Parameters Observation System for Shallow Waters: Designment and Applications.

Measurements of the above-water spectrum and concerned water color parameters (WCPs) are crucial for research and applications in water environment remote sensing. Due to the lack of system integration and automatization, conventional methods are labor-intensive, time-consuming, and prone to subjective influences. To obtain a highly accurate and long-term consistent spectrum and concurrent WCPs (Chl-a (chlorophyll-a), turbidity, and CDOM (Colored Dissolved Organic Matter)) data with a relatively low cost, an Automatic Stationary Water Color Parameters Observation System (AFWCPOS) was developed. Controlled by an automatic platform, the spectral and WCPs data were collected by TriOS RAMSES hyperspectral spectroradiometers and WETLabs ECO (Environmental Characterization Optics) fluorometers following the measurement protocol. Experiment and initial validations of AFWCPOS were carried out in Poyang Lake, the largest freshwater lake in China, from 20 to 28 July 2013. Results proved that the spectral data from AFWCPOS were highly consistent with the commonly used portable SVC (Spectra Vista Corporation) HR-1024 field spectroradiometer, with the coefficient of determination (R2) of 0.96, unbiased percent difference (UPD) of 0.14, and mean relative difference (MRD) of 0.078. With advantages of continuous and high degrees of automation monitoring, the AFWCPOS has great potential in capture diurnal and inter-diurnal variations in the test site of Poyang Lake, as well as another high-dynamic shallow coastal and inland waters, which will benefit routine water quality monitoring with high quality and high-frequency time-series observations. In addition, a successful case based on Landsat 8 OLI (Operational Land Imager) image and in-situ data collected by AFWCPOS showed it’s potential in remote sensing applications. The spatial distribution of Chl-a, turbidity, and CDOM were mapped, which were explainable and similar to previous researches. These results showed our system was able to obtain reliable and valuable data for water environment monitoring.

Spatio-temporal variations of CDOM in shallow inland waters from a semi-analytical inversion of Landsat-8

Bottom reflectance is often the main cause of high uncertainty in Colored Dissolved Organic Matter (CDOM) estimation for optically shallow waters. This study presents a Landsat-8 based Shallow Water Bio-optical Properties (SBOP) algorithm to overcome bottom effects so as to successfully observe spatial and temporal CDOM dynamics in inland waters. We evaluated the algorithm via 58 images and a large set of field measurements collected across seasons of multiple years in the Saginaw Bay, Lake Huron. Results showed that the SBOP algorithm reduced estimation errors by as much as 4 times (RMSE = 0.17 and R2 = 0.87 in the Saginaw Bay) when compared to the QAA-CDOM algorithm that did not take into account bottom reflectance. These improvements in CDOM estimation are consistent and robust across broad range CDOM absorption. Our analysis revealed: 1) the proposed remote sensing algorithm resulted in significant improvements in tracing spatial-temporal CDOM inputs from terrestrial environments to lakes, 2) CDOM distribution captured with high resolution land-viewing satellite is useful in revealing the impacts of terrestrial ecosystems on the aquatic environment, and 3) Landsat-8 OLI, with its 16 days revisit time, provides valuable time series data for studying CDOM seasonal variations at land-water interface and has the potential to reveal its relationship to adjacent terrestrial biogeography and hydrology. The study presents a shallow water algorithm for studying freshwater or coastal ecology, as well as carbon cycling science.

The dynamic observation of dissolved organic matter in the Zhujiang (Pearl River) Estuary in China from space

The distributions of estuarine colored dissolved organic matter (CDOM) are the combined results of physicalbiogeochemical processes. Remote sensing is needed to monitor highly dynamically estuarine CDOM. Using in situ data from four seasonal cruises, an algorithm is developed to estimate CDOM absorption coefficient at 400 nm (aCDOM(400)) in the Zhujiang (Pearl River) Estuary (ZJE). The algorithm uses band ratios of Rrs(667)/Rrs(443) and Rrs(748)/Rrs(412). By applying it to moderate resolution imaging spectroradiometer onboard Aqua satellite (MODIS/Aqua) data from 2002 to 2014, seasonal climatology aCDOM(400) in the ZJE is calculated. CDOM distributions are majorly influenced by water discharge from the Zhujiang River and underwater topography. Along the section vertical to a water depth gradient, the seasonal aCDOM(400) exponentially decreased (y=aebx, b<0), but with great differences among seasons. Riverine fresh water is the primary source of CDOM in the ZJE. Fulvic acid fraction decreases with increasing salinity. Using developed algorithms, conservative CDOM mixing equation, and river discharge, effective riverine end-member concentration and flux of dissolved organic carbon (DOC) in summer and winter from 2002 to 2014 are first estimated from the MODIS/Aqua data. Both effective riverine end-member DOC concentration and flux are positively related to the river discharge, significantly in summer with R2 of 0.698 for concentration and 0.965 7 for flux.

Monitoring seasonal variations of colored dissolved organic matter for the Saginaw River based on Landsat-8 data

Abstract Remote sensing is an effective tool for studying CDOM (colored dissolved organic matter) variations and its relevant environmental factors. Monitoring CDOM distribution and dynamics in small water is often limited by the coarse spatial resolution of traditional ocean color sensors. In this study, because of its high spatial resolution of 30 m, Landsat-8 data were used to assess seasonal variations of CDOM in the Saginaw River, by using an empirical statistic model. Pearson correlation analysis between CDOM variations and other environmental factors, such as temperature, discharge, and dissolved oxygen, shows that temperature was negatively correlated to CDOM variations and discharge played a positive role. We also calculated the monthly mean aCDOM(440) (the absorption coefficient of CDOM at 440 nm) for the Saginaw River between April and November from 2013 to 2016. This study demonstrates a good example for future applications in small waters: observing CDOM variations and other relevant environmental factors change by using Landsat remote sensing, so that we can know more about water quality and ecosystem health of small waters as well as the climate change impact on regional watersheds.

High colored dissolved organic matter (CDOM) absorption in surface waters of the central-eastern Arctic Ocean: Implications for biogeochemistry and ocean color algorithms.

As consequences of global warming sea-ice shrinking, permafrost thawing and changes in fresh water and terrestrial material export have already been reported in the Arctic environment. These processes impact light penetration and primary production. To reach a better understanding of the current status and to provide accurate forecasts Arctic biogeochemical and physical parameters need to be extensively monitored. In this sense, bio-optical properties are useful to be measured due to the applicability of optical instrumentation to autonomous platforms, including satellites. This study characterizes the non-water absorbers and their coupling to hydrographic conditions in the poorly sampled surface waters of the central and eastern Arctic Ocean. Over the entire sampled area colored dissolved organic matter (CDOM) dominates the light absorption in surface waters. The distribution of CDOM, phytoplankton and non-algal particles absorption reproduces the hydrographic variability in this region of the Arctic Ocean which suggests a subdivision into five major bio-optical provinces: Laptev Sea Shelf, Laptev Sea, Central Arctic/Transpolar Drift, Beaufort Gyre and Eurasian/Nansen Basin. Evaluating ocean color algorithms commonly applied in the Arctic Ocean shows that global and regionally tuned empirical algorithms provide poor chlorophyll-a (Chl-a) estimates. The semi-analytical algorithms Generalized Inherent Optical Property model (GIOP) and Garver-Siegel-Maritorena (GSM), on the other hand, provide robust estimates of Chl-a and absorption of colored matter. Applying GSM with modifications proposed for the western Arctic Ocean produced reliable information on the absorption by colored matter, and specifically by CDOM. These findings highlight that only semi-analytical ocean color algorithms are able to identify with low uncertainty the distribution of the different optical water constituents in these high CDOM absorbing waters. In addition, a clustering of the Arctic Ocean into bio-optical provinces will help to develop and then select province-specific ocean color algorithms.

Coastal and inland water monitoring using a portable hyperspectral laser fluorometer

The potential for a ship-mounted laser fluorometer to provide rapid, non-intrusively measurements in both coastal and lake conditions are investigated. The instrument consists of a high pulse repetition frequency (10-kHz) microchip laser for fluorescence excitation, a broadband hyperspectral micro spectrometer for spectral detection, and a confocal reflective fluorescent probe for signal collection; it weighs only about 1.7kg. Chlorophyll a (chl-a) and colored dissolved organic matter (CDOM) measured by the new instrument were observed to agree well with those measured by traditional time-consuming laboratory methods in Hangzhou Bay seawater and Qiandao Lake inland water. Subsequently, laser fluorescence distribution and characteristics of chl-a and CDOM in these regions were analyzed, which will improve our understanding of biogeochemical processes in these optically complex aquatic systems. The portable system is promising for water environment monitoring, especially in coastal and inland water.

Optical assessment of colored dissolved organic matter and its related parameters in dynamic coastal water systems

Prediction of the curve of the absorption coefficient of colored dissolved organic matter (CDOM) and differentiation between marine and terrestrially derived CDOM pools in coastal environments are hampered by a high degree of variability in the composition and concentration of CDOM, uncertainties in retrieved remote sensing reflectance and the weak signal-to-noise ratio of space-borne instruments. In the present study, a hybrid model is presented along with empirical methods to remotely determine the amount and type of CDOM in coastal and inland water environments. A large set of in-situ data collected on several oceanographic cruises and field campaigns from different regional waters was used to develop empirical methods for studying the distribution and dynamics of CDOM, dissolved organic carbon (DOC) and salinity. Our validation analyses demonstrated that the hybrid model is a better descriptor of CDOM absorption spectra compared to the existing models. Additional spectral slope parameters included in the present model to differentiate between terrestrially derived and marine CDOM pools make a substantial improvement over those existing models. Empirical algorithms to derive CDOM, DOC and salinity from remote sensing reflectance data demonstrated success in retrieval of these products with significantly low mean relative percent differences from large in-situ measurements. The performance of these algorithms was further assessed using three hyperspectral HICO images acquired simultaneously with our field measurements in productive coastal and lagoon waters on the southeast part of India. The validation match-ups of CDOM and salinity showed good agreement between HICO retrievals and field observations. Further analyses of these data showed significant temporal changes in CDOM and phytoplankton absorption coefficients with a distinct phase shift between these two products. Healthy phytoplankton cells and macrophytes were recognized to directly contribute to the autochthonous production of colored humic-like substances in variable amounts within the lagoon system, despite CDOM content being partly derived through river run-off and wetland discharges as well as from conservative mixing of different water masses. Spatial and temporal maps of CDOM, DOC and salinity products provided an interesting insight into these CDOM dynamics and conservative behavior within the lagoon and its extension in coastal and offshore waters of the Bay of Bengal. The hybrid model and empirical algorithms presented here can be useful to assess CDOM, DOC and salinity fields and their changes in response to increasing runoff of nutrient pollution, anthropogenic activities, hydrographic variations and climate oscillations.

Seasonal Variation of Colored Dissolved Organic Matter in Barataria Bay, Louisiana, Using Combined Landsat and Field Data

Coastal bays, such as Barataria Bay, are important transition zones between the terrigenous and marine environments that are also optically complex due to elevated amounts of particulate and dissolved constituents. Monthly field data collected over a period of 15 months in 2010 and 2011 in Barataria Bay were used to develop an empirical band ratio algorithm for the Landsat-5 TM that showed a good correlation with the Colored Dissolved Organic Matter (CDOM) absorption coefficient at 355 nm (ag355) (R2 = 0.74). Landsat-derived CDOM maps generally captured the major details of CDOM distribution and seasonal influences, suggesting the potential use of Landsat imagery to monitor biogeochemistry in coastal water environments. An investigation of the seasonal variation in ag355 conducted using Landsat-derived ag355 as well as field data suggested the strong influence of seasonality in the different regions of the bay with the marine end members (lower bay) experiencing generally low but highly variable ag355 and the freshwater end members (upper bay) experiencing high ag355 with low variability. Barataria Bay experienced a significant increase in ag355 during the freshwater release at the Davis Pond Freshwater Diversion (DPFD) following the Deep Water Horizon oil spill in 2010 and following the Mississippi River (MR) flood conditions in 2011, resulting in a weak linkage to salinity in comparison to the other seasons. Tree based statistical analysis showed the influence of high river flow conditions, high- and low-pressure systems that appeared to control ag355 by ~28%, 29% and 43% of the time duration over the study period at the marine end member just outside the bay. An analysis of CDOM variability in 2010 revealed the strong influence of the MR in controlling CDOM abundance in the lower bay during the high flow conditions, while strong winds associated with cold fronts significantly increase CDOM abundance in the upper bay, thus revealing the important role these events play in the CDOM dynamics of the bay.

First autonomous bio-optical profiling float in the Gulf of Mexico reveals dynamic biogeochemistry in deep waters.

Profiling floats equipped with bio-optical sensors well complement ship-based and satellite ocean color measurements by providing highly-resolved time-series data on the vertical structure of biogeochemical processes in oceanic waters. This is the first study to employ an autonomous profiling (APEX) float in the Gulf of Mexico for measuring spatiotemporal variability in bio-optics and hydrography. During the 17-month deployment (July 2011 to December 2012), the float mission collected profiles of temperature, salinity, chlorophyll fluorescence, particulate backscattering (bbp), and colored dissolved organic matter (CDOM) fluorescence from the ocean surface to a depth of 1,500 m. Biogeochemical variability was characterized by distinct depth trends and local “hot spots”, including impacts from mesoscale processes associated with each of the water masses sampled, from ambient deep waters over the Florida Plain, into the Loop Current, up the Florida Canyon, and eventually into the Florida Straits. A deep chlorophyll maximum (DCM) occurred between 30 and 120 m, with the DCM depth significantly related to the unique density layer ρ = 1023.6 (R2 = 0.62). Particulate backscattering, bbp, demonstrated multiple peaks throughout the water column, including from phytoplankton, deep scattering layers, and resuspension. The bio-optical relationship developed between bbp and chlorophyll (R2 = 0.49) was compared to a global relationship and could significantly improve regional ocean-color algorithms. Photooxidation and autochthonous production contributed to CDOM distributions in the upper water column, whereas in deep water, CDOM behaved as a semi-conservative tracer of water masses, demonstrating a tight relationship with density (R2 = 0.87). In the wake of the Deepwater Horizon oil spill, this research lends support to the use of autonomous drifting profilers as a powerful tool for consideration in the design of an expanded and integrated observing network for the Gulf of Mexico.

Colored Dissolved Organic Matter Dynamics in the Northern Gulf of Mexico from Ocean Color and Numerical Model Results

Chaichitehrani, N.; D’Sa, E.J.; Ko, D.S.; Walker, N.D.; Osburn, C.L., and Chen, R.F., 2014. Colored dissolved organic matter dynamics in the Northern Gulf of Mexico from ocean color and numerical model results. Journal of Coastal Research, 30(4), 800–814. Coconut Creek (Florida), ISSN 0749-0208. Colored dissolved organic matter (CDOM) absorption and salinity relationships were assessed and used in conjunction with the salinity and current outputs of a numerical model (Navy Coastal Ocean Model [NCOM]) to study CDOM dynamics in the northern Gulf of Mexico. In situ CDOM absorption and salinity obtained from multiple field campaigns were inversely correlated seasonally (winter–spring and summer) and latitudinally (inner- and outer-shelf zones), suggesting conservative behavior of CDOM distribution. A weaker correlation, during summer in the outer-shelf zone, however, indicated stronger effects of photooxidation and lower masking effects from riverine CDOM. Applying these relationships to simulated salinity resulted in hourly maps of CDOM that revealed similarities to CDOM patterns derived from SeaWiFS satellite imagery. Further, matchup comparisons between model-derived and in situ CDOM absorption were statistically sound for the summer (bias ¼� 0.016, root mean square error ¼ 0.059, r 2 ¼ 0.51 SI ¼ 0.28) and the winter–spring periods (bias ¼ 0.033, root mean square error ¼ 0.099, r 2 ¼ 0.52, SI ¼ 0.21). Overlaying the modelderived CDOM maps on the simulated currents revealed the strong influence of currents on CDOM advection. Downcoast currents during the nonsummer months led to persistent advection of CDOM westward interrupted by frequent cold front events that flush CDOM-laden waters out of the coastal bays onto the inner and outer continental shelves. In contrast, the upcoast current regime, though less well organized, produces a more significant seaward advection of CDOM, likely due to the Ekman transport and subsequent entrainment by mesoscale eddies over the continental slope.

Characterisation of colored dissolved organic matter in Hudson Bay and Hudson Strait using parallel factor analysis

Composition and concentration of colored dissolved organic matter (CDOM) have been determined in Hudson Bay and Hudson Strait by excitation emission matrix spectroscopy (EEM) and parallel factor analysis (PARAFAC). Based on 63 surface samples, PARAFAC identified three fluorescent components, which were attributed to two humic- and one protein-like components. One humic-like component was identified as representing terrestrial organic matter and showed a conservative behaviour in Hudson Bay estuaries. The second humic-like component, traditionally identified as peak M, originated both from land and produced in the marine environment. Component 3 had spectra resembling protein-like material and thought to be plankton-derived. The distribution and composition of CDOM were largely controlled by water mass mixing with protein-like component being the least affected. Distinctive fluorescence patterns were also found between Hudson Bay and Hudson Strait, suggesting different sources of CDOM. The optically active fraction of DOC (both absorbing and fluorescing) was very high in the Hudson Bay (up to 89%) suggesting that fluorescence and absorbance can be used as proxies of the DOC concentration.

Influence of extreme storm events on West Florida Shelf CDOM distributions

Colored Dissolved Organic Matter (CDOM) distribution and signatures provide vital information about the amount and composition of organic material in aquatic environments. This information is critical for deciphering the sources and biogeochemical pathways of organic carbon, and thus vital to the understanding of carbon cycling and budgets. Waters of the West Florida Shelf are heavily influenced by many river systems on Florida's Gulf Coast that, to the first order, control CDOM distributions on the shelf. Three storm events during 2004 and 2005 (Hurricane Charley, Hurricane Wilma, and a Winter Storm) profoundly altered the typical distribution of CDOM fluorescence and absorption properties on the Southern West Florida Shelf. Seasonal surveys revealed that changes in the underwater light field as a result of major hurricanes and resuspension events are linked closely with a number of factors prior to a storm's passing such as the presence of persistent blooms, rainfall and discharge. Additionally, storm track and wind direction were found to play a significant role in CDOM signatures.

Algorithm development and validation for satellite‐derived distributions of DOC and CDOM in the U.S. Middle Atlantic Bight

Oceanographic cruises were conducted within the U.S. Middle Atlantic Bight (MAB) to collect field measurements to develop algorithms to retrieve surface ocean colored dissolved organic matter (CDOM) and dissolved organic carbon (DOC) from NASA's MODIS‐Aqua and SeaWiFS satellite sensors and to investigate the processes that influence the distributions of CDOM and DOC. In order to develop empirical algorithms for CDOM and DOC, the CDOM absorption coefficient (aCDOM) was correlated with in situ remote sensing reflectance band ratios, and DOC was then derived from aCDOM through the aCDOM to DOC relationships. Our validation analyses demonstrate successful retrieval of DOC and CDOM using MODIS and SeaWiFS with mean absolute percent differences from field measurements of 9.3 ± 7.3% for DOC, 19 ± 14% for aCDOM(355), 15.5 ± 12% for aCDOM(443), and 8.6 ± 4.9% for the CDOM spectral slope. To our knowledge, the algorithms presented here represent the first validated algorithms for satellite retrieval of aCDOM, DOC, and CDOM spectral slope in the coastal ocean. Satellite imagery demonstrates the importance of riverine/estuarine discharge from Chesapeake Bay and Delaware Bay to the export of CDOM and DOC to the coastal ocean. Between spring and summer, photooxidation has a significant impact on CDOM distributions resulting in a pronounced decrease in aCDOM between the midshelf and continental slope region of the MAB. The satellite‐derived DOC products demonstrate the net ecosystem production of DOC of 12 to 34 μmol C L−1 between spring and summer. The aCDOM algorithms presented here are applicable to other coastal regions and can also be used to retrieve DOC using region‐specific aCDOM to DOC relationships.

Colored dissolved organic matter dynamics across the shelf‐basin interface in the western Arctic Ocean

Spatial variations in the concentration and nature of colored dissolved organic matter (CDOM) in the western Arctic Ocean were examined by three‐dimensional excitation/emission matrix (3‐D EEM) spectroscopy. CDOM profiles showed distinctive features well correlated with hydrographic characteristics. CDOM fluorescence was particularly high at depths between 40 and 200 m (up to 3 fluorescence units (Fl.U.)) in both Chukchi Sea and Beaufort Sea transects. Penetration of the high CDOM signal, formed on the shelves, into the Canada Basin was confined to the upper halocline layer (salinity of ∼33.1). This layer had distinctive 3‐D EEM fingerprints in fluorescence spectra, showing a marked terrestrial humic signature. The presence of CDOM in the halocline layer likely resulted from two main processes: the brine rejection during sea ice formation and transport across the sediment‐water interface during early diagenesis. Despite the high primary productivity in the Chukchi shelf, CDOM contribution from in situ production seemed to have little influence on the overall CDOM distributions in the study area.

Colored dissolved organic matter in Tampa Bay, Florida

Absorption and fluorescence of colored dissolved organic matter (CDOM) and concentrations of dissolved organic carbon (DOC), chlorophyll and total suspended solids in Tampa Bay and its adjacent rivers were examined in June and October of 2004. Except in Old Tampa Bay (OTB), the spatial distribution of CDOM showed a conservative relationship with salinity in June, 2004 ( a CDOM(400) = − 0.19 × salinity + 6.78, R 2 = 0.98, n = 17, salinity range = 1.1–32.5) with little variations in absorption spectral slope and fluorescence efficiency. This indicates that CDOM distribution was dominated by mixing. In October, 2004, CDOM distribution was nonconservative with an average absorption coefficient ( a CDOM(400), ∼ 7.76 m − 1 ) about seven times higher than that in June (∼ 1.11 m − 1 ). The nonconservative behavior was caused largely by CDOM removal at intermediate salinities (e.g., a CDOM(400) removal > 15% at salinity ∼ 13.0), which likely resulted from photobleaching due to stronger stratification. The spatial and seasonal distributions of CDOM in Tampa Bay showed that the two largest rivers, the Alafia River (AR) and Hillsborough River (HR) were dominant CDOM sources to most of the bay. In OTB, however, CDOM showed distinctive differences: lower absorption coefficient, higher absorption spectral slopes, and lower ratios of CDOM absorption to DOC and higher fluorescence efficiency. These differences may have stemmed from (1) changes in CDOM composition by more intensive photobleaching due to the longer residence time of water mass in OTB; (2) other sources of CDOM than the HR/AR inputs, such as local creeks, streams, groundwater, and/or bottom re-suspension. Average CDOM absorption in Tampa Bay at 443 nm, a CDOM(443), was about five times higher in June and about ten times higher in October than phytoplankton pigment absorption, a ph(443), indicating that blue light attenuation in the water column was dominated by CDOM rather than by phytoplankton absorption throughout the year.

Distributions and characteristics of colored dissolved organic matter in the Western Arctic Ocean

Terrigenous dissolved organic matter (DOM) is continuously discharged by rivers into the ocean, yet its distribution and reactivity within ocean basins remain poorly defined. With high concentrations of terrestrial DOM in arctic rivers and a disproportionate share of global riverine discharge on a volume basis to the Arctic Ocean, the influence of terrigenous DOM on marine carbon budgets and the global carbon cycle can be significant. In this paper, we report the detection of terrestrial DOM using optical properties of surface waters in the Western Arctic Ocean. The distribution of absorption and fluorescence of colored dissolved organic matter (C-DOM) and dissolved organic carbon (DOC) were recorded. Mixing of C-DOM was conservative at low and mid-salinity ( S>25‰), indicating a terrestrial origin for this material and the absence of strong in situ sources and sinks. However, at higher salinities (>25‰), C-DOM distribution was highly scattered due to the mixing of water masses of statistically different optical properties. Higher absorption coefficients and C-DOM and DOC concentrations reflect the higher contribution of terrigenous DOM. The region most influenced by land-derived DOM is the Mackenzie Shelf where the 3D excitation/emission matrix spectra show a strong signature of continental inputs. Furthermore, the absence of a typical marine DOM signal indicates that a terrigenous component dominated C-DOM composition throughout the entire Western Arctic Ocean.