Dissolved organic matter composition and bioavailability reflect ecosystem productivity in the Western Arctic Ocean

Shen, Yuan; Fichot, Cédric G.; Benner, Ronald

doi:10.5194/bg-9-4993-2012

Cited by 65 publications

(76 citation statements)

References 62 publications

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“…The values of absorption coefficients (e.g., a g 355) observed in the eastern Bering Sea were generally lower than those reported for the western Arctic Ocean shelf region influenced by the McKenzie River (Gueguen et al, 2005) and comparable to values (∼ 0.2 to 0.3 m −1 ) reported for the shelf break region of the midAtlantic Bight (Del Vecchio and Blough, 2004). The DOC concentrations were similar to those reported for the summer in the Chukchi Sea shelf (77 ± 12 µM) (Shen et al, 2012). Although the salinity-a g 355 relationship shows three broad trends (Fig.…”

Section: Dom Characteristics In the Eastern Bering Sea And The Cold Psupporting

confidence: 59%

Absorption and fluorescence properties of chromophoric dissolved organic matter of the eastern Bering Sea in the summer with special reference to the influence of a cold pool

et al. 2014

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Abstract. The absorption and fluorescence properties of chromophoric dissolved organic matter (CDOM) are reported for the inner shelf, slope waters and outer shelf regions of the eastern Bering Sea during the summer of 2008, when a warm, thermally stratified surface mixed layer lay over a cold pool (< 2 • C) that occupied the entire middle shelf. CDOM absorption at 355 nm (a g 355) and its spectral slope (S) in conjunction with excitationemission matrix (EEM) fluorescence and parallel factor analysis (PARAFAC) revealed large variability in the characteristics of CDOM in different regions of the Bering Sea. PARAFAC analysis aided in the identification of three humic-like (components one, two and five) and two proteinlike (a tyrosine-like component three, and a tryptophanlike component four) components. In the extensive shelf region, average absorption coefficients at 355 nm (a g 355, m −1 ) and DOC concentrations (µM) were highest in the inner shelf (0.342 ± 0.11 m −1 , 92.67 ± 14.60 µM) and lower in the middle (0.226 ± 0.05 m −1 , 78.38 ± 10.64 µM) and outer (0.185 ± 0.05 m −1 , 79.24 ± 18.01 µM) shelves, respectively. DOC concentrations, however were not significantly different, suggesting CDOM sources and sinks to be uncoupled from DOC. Mean spectral slopes S were elevated in the middle shelf (24.38 ± 2.25 µm −1 ) especially in the surface waters (26.87 ± 2.39 µm −1 ) indicating high rates of photodegradation in the highly stratified surface mixed layer, which intensified northwards in the northern middle shelf likely contributing to greater light penetration and to phytoplankton blooms at deeper depths. The fluorescent humic-like components one, two, and five were most elevated in the inner shelf most likely from riverine inputs. Along the productive "green belt" in the outer shelf/slope region, absorption and fluorescence properties indicated the presence of fresh and degraded autochthonous DOM. Near the Unimak Pass region of the Aleutian Islands, low DOC and a g 355 (mean 66.99 ± 7.94 µM; 0.182 ± 0.05 m −1 ) and a high S (mean 25.95 ± 1.58 µm −1 ) suggested substantial photobleaching of the Alaska Coastal Water, but high intensities of humic-like and protein-like fluorescence suggested sources of fluorescent DOM from coastal runoff and glacier meltwaters during the summer. The spectral slope S vs. a g 355 relationship revealed terrestrial and oceanic end members along with intermediate water masses that were modeled using nonlinear regression equations that could allow water mass differentiation based on CDOM optical properties. Spectral slope S was negatively correlated (r 2 = 0.79) with apparent oxygen utilization (AOU) for waters extending from the middle shelf into the deep Bering Sea indicating increasing microbial alteration of CDOM with depth. Although our data show that the CDOM photochemical environment of the Bering Sea is complex, our current information on its optical properties will aid in better understanding of the biogeochemical role of CDOM in carbon budgets in relation to the annual sea ic...

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Section: Dom Characteristics In the Eastern Bering Sea And The Cold Psupporting

confidence: 59%

Absorption and fluorescence properties of chromophoric dissolved organic matter of the eastern Bering Sea in the summer with special reference to the influence of a cold pool

et al. 2014

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“…A particularity of the Southern Ocean surface waters are the lower DOC concentrations compared to other oceans (i.e., ∼ 50 vs. 70-80 µM) (Hansell, 2013). Here, AA accounted for only 0.9-4.4 % of DOC, which is in the range of values found in other regions (Benner, 2002;Bourgoin and Tremblay, 2010;Shen et al, 2012). However, AA yields in the DOC of HNLC surface water (2.7 %) were about twice that measured in the oligotrophic North Pacific near Hawaii (Kaiser and Benner, 2008).…”

Section: Amino Acids In the Southern Oceanmentioning

confidence: 51%

“…The measured concentrations, yields, and relative distributions of AA in POM and DOM were in the range of values previously found in the open equatorial Pacific (Lee et al, 2000), the coastal waters of the Arctic (Dittmar et al, 2001;Shen et al, 2012) and North Atlantic Ocean (Bourgoin and Tremblay, 2010), and in the polar front zone of the Southern Ocean (Panagiotopoulos et al, 2002). THAA represented between 21 and 25 % of POC in the surface waters of bloom sites, which is close to the 27 % measured in suspended particles at the chlorophyll maximum depth in the equatorial Pacific (Lee et al, 2000).…”

Section: Amino Acids In the Southern Oceanmentioning

confidence: 65%

Origin and fate of particulate and dissolved organic matter in a naturally iron-fertilized region of the Southern Ocean

et al. 2015

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Abstract. Natural iron fertilization of high-nutrient lowchlorophyll (HNLC) waters induces annually occurring spring phytoplankton blooms off the Kerguelen Islands (Southern Ocean). To examine the origin and fate of particulate and dissolved organic matter (POM and DOM), D-and L-amino acids (AA) were quantified at bloom and HNLC stations. Total hydrolyzable AA accounted for 21-25 % of surface particulate organic carbon (%POC AA ) at the bloom sites, but for 10 % at the HNLC site. A marked decrease in %POC AA with depth was observed at the most productive stations leading to values between 3 and 5 % below 300 m depth. AA contributed to only 0.9-4.4 % of dissolved organic carbon (%DOC AA ) at all stations. The only consistent vertical trend was observed at the most productive station (A3-2) where %DOC AA decreased from ∼ 2 % in the surface waters to 0.9 % near 300 m. These AA yields revealed that POM and DOM were more rapidly altered or mineralized at the bloom sites compared to the HNLC site. Alteration state was also assessed by trends in C / N ratio, %D-AA and degradation index. Different molecular markers indicated that POM mostly originated from diatoms and bacteria. The estimated average proportion of POM from intact phytoplankton cells in surface waters was 45 % at the bloom station A3-2, but 14 % at the HNLC site. Estimates based on D-AA yields indicated that ∼ 15 % of POM and ∼ 30 % of DOM was of bacterial origin (cells and cell fragments) at all stations. Surprisingly, the DOM in HNLC waters appeared less altered than the DOM from the bloom, had slightly higher dissolved AA concentrations, and showed no sign of alteration within the water column. Unfavorable conditions for bacterial degradation in HNLC regions can explain these findings. In contrast, large inputs of labile organic molecules and iron likely stimulate the degradation of organic matter (priming effect) and the production of more recalcitrant DOM (microbial carbon pump) during iron-fertilized blooms.

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“…Overall, DOM in groundwater is a mixture of components derived from various sources and altered by multiple processes, making it difficult to predict the composition and bioreactivity of DOM solely from bulk DOM analyses (Chapelle et al 2009;Shen et al 2012a).The regional chromatography model is presented as a conceptual framework for understanding the sources and processes influencing the properties of DOM during its transport from the surface litter layer to groundwater. Additional studies of water transit times and pathways through soils would provide further insights about the processes shaping the concentration, composition, and bioavailability of DOM in groundwater.…”

Section: Bacterial Contributions To Dom In Groundwatermentioning

confidence: 99%

“…Molecular analyses of specific biochemical components of DOM can provide qualitative and quantitative insights about the bioavailability and diagenetic alteration of DOM without conducting bioassay experiments (Benner 2003;Davis and Benner 2007;Shen et al 2012a). Amino acids are bioreactive components of DOM and have been used as molecular indicators of bioavailable DOM in marine environments (Benner 2003;Davis et al 2009) and have been applied recently to groundwater (Chapelle et al 2009).…”

mentioning

confidence: 99%

Origins and bioavailability of dissolved organic matter in groundwater

et al. 2014

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Dissolved organic matter (DOM) in groundwater influences water quality and fuels microbial metabolism, but its origins, bioavailability and chemical composition are poorly understood. The origins and concentrations of dissolved organic carbon (DOC) and bioavailable DOM were monitored during a long-term (2-year) study of groundwater in a fractured-rock aquifer in the Carolina slate belt. Surface precipitation was significantly correlated with groundwater concentrations of DOC, bioavailable DOM and chromophoric DOM, indicating strong hydrological connections between surface and ground waters. The physicochemical and biological processes shaping the concentrations and compositions of DOM during its passage through the soil column to the saturated zone are conceptualized in the regional chromatography model. The model provides a framework for linking hydrology with the processes affecting the transformation, remineralization and microbial production of DOM during passage through the soil column. Lignin-derived phenols were relatively depleted in groundwater DOM indicating substantial removal in the unsaturated zone, and optical properties of chromophoric DOM indicated lower molecular weight DOM in groundwater relative to surface water. The prevalence of glycine, caminobutyric acid, and D-enantiomers of amino acids indicated the DOM was highly diagenetically altered. Bioassay experiments were used to establish DOCnormalized yields of amino acids as molecular indicators of DOM bioavailability in groundwater. A relatively small fraction (8 ± 4 %) of DOC in groundwater was bioavailable. The relatively high yields of specific D-enantiomers of amino acids indicated a substantial fraction (15-34 %) of groundwater DOC was of bacterial origin.

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Dissolved organic matter composition and bioavailability reflect ecosystem productivity in the Western Arctic Ocean

Cited by 65 publications

References 62 publications

Absorption and fluorescence properties of chromophoric dissolved organic matter of the eastern Bering Sea in the summer with special reference to the influence of a cold pool

Absorption and fluorescence properties of chromophoric dissolved organic matter of the eastern Bering Sea in the summer with special reference to the influence of a cold pool

Origin and fate of particulate and dissolved organic matter in a naturally iron-fertilized region of the Southern Ocean

Origins and bioavailability of dissolved organic matter in groundwater

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