Seasonal DOC accumulation in the Black Sea: a regional explanation for a general mechanism

Cauwet, Gustave; Deliat, Gaëlle; Krastev, Anton; Shtereva, G.; Becquevort, Sylvie; Lancelot, Christiane; Momzikoff, André; Saliot, A.; Cociasu, Adriana; Popa, L.

doi:10.1016/s0304-4203(02)00064-6

Cited by 48 publications

(27 citation statements)

References 38 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In our study, DOC showed a regular and highly pronounced annual pattern: a progressive rise over summer, followed by a gradual decline, a pattern similar to that observed by Avril (2002) (68.2 μM), but, on average, it was 24.1 μM, lower than that determined by Pettine et al (2001) for the North Adriatic area off the Po River delta, by Doval et al (2001) for the eastern North Atlantic-Azores Front region (168 μM) and by Cauwet et al (2002) for the Black Sea (ca. 100 μM).…”

Section: Doc Dynamicssupporting

confidence: 80%

Major inter-annual variations in microbial dynamics in the Gulf of Trieste (northern Adriatic Sea) and their ecosystem implications

Umani¹,

Negro²,

Larato³

et al. 2007

Aquat. Microb. Ecol.

View full text Add to dashboard Cite

Section: Doc Dynamicssupporting

confidence: 80%

Major inter-annual variations in microbial dynamics in the Gulf of Trieste (northern Adriatic Sea) and their ecosystem implications

Umani¹,

Negro²,

Larato³

et al. 2007

Aquat. Microb. Ecol.

View full text Add to dashboard Cite

“…Zweifel et al (1993) showed that the addition of nutrients to samples from a nutrientdepleted system promoted DOC breakdown, which also implies that the lack of nutrients favours DOC preservation. Cauwet et al (2002) reported that during nutrient deficiency, bacteria are unable to utilize a carbon-rich organic substrate like carbohydrates. Therefore as suggested by Thingstad et al (1997) and Tanaka and Rassoulzadegan (2002), this surface accumulated DOC could indicate long term malfunctioning of the microbial loop; this could be related to bacteria-phytoplankton competition for inorganic nutrients that reduce DOC remineralization in nutrient-depleted water.…”

Section: Discussionmentioning

confidence: 99%

Distribution of inorganic and organic nutrients in the South Pacific Ocean − evidence for long-term accumulation of organic matter in nitrogen-depleted waters

2008

View full text Add to dashboard Cite

Abstract. During the BIOSOPE cruise the RV Atalante was dedicated to study the biogeochemical properties in the South Pacific between the Marquesas Islands (141 • W-8 • S) and the Chilean upwelling (73 • W-34 • S). Over the 8000 km covered by the cruise, several different trophic situations were encountered, in particular strong oligotrophic conditions in the South Pacific Gyre (SPG, between 123 • W and 101 • W). In this isolated region, nitrate was undetectable between the surface and 160-180 m and only trace quantities (<20 nmoles l −1 ) of regenerated nitrogen (nitrite and ammonium) were detected, even in the subsurface maximum. Integrated nitrate over the photic layer, which reached 165 m, was close to zero. Despite this severe nitrogendepletion, phosphate was always present in significant concentrations (≈0.1 µmoles l −1 ), while silicic acid was maintained at low but classical oceanic levels (≈1 µmoles l −1 ). In contrast, the Marquesas region (MAR) to the west and Chilean upwelling (UPW) to the east were characterized by high nutrient concentrations, one hundred to one thousand fold higher than in the SPG. The distribution of surface chlorophyll reflected the nitrate gradient, the lowest concentrations (0.023 nmoles l −1 ) being measured at the centre of the SPG, where integrated value throughout the photic layer was very low (≈ 10 mg m −2 ). However, due to the relatively high concentrations of chlorophyll-a encountered in the DCM (0.2 µg l −1 ), chlorophyll-a concentrations throughout the photic layer were less variable than nitrate concentrations (by a factor 2 to 5). In contrast to chlorophyll-a, integrated particulate organic matter (POM) remained more or less constant along the study area (500 mmoles m −2 , 60 mmoles m −2 and 3.5 mmoles m −2 for particulate organic carbon, particulate organic nitrogen and particulate organic phosphorus, Correspondence to: P. Raimbault (patrick.raimbault@univmed.fr) respectively), with the exception of the upwelling, where values were two fold higher. The residence time of particulate carbon in the surface water was only 4-5 days in the upwelling, but up to 30 days in the SPG, where light isotopic δ 15 N signal noted in the suspended POM suggests that N 2 -fixation provides a dominant supply of nitrogen to phytoplankton. The most striking feature was the large accumulation of dissolved organic matter (DOM) in the SPG compared to the surrounding waters, in particular dissolved organic carbon (DOC) where concentrations were at levels rarely measured in oceanic waters (>100 µmoles l −1 ). Due to this large pool of DOM in the SPG photic layer, integrated values followed a converse geographical pattern to that of inorganic nutrients with a large accumulation in the centre of the SPG. Whereas suspended particulate matter in the mixed layer had a C/N ratio largely conforming to the Redfield stochiometry (C/N≈6.6), marked deviations were observed in this excess DOM (C/N≈16 to 23). The marked geographical trend suggests that a net in situ source exists, mainly due to biologic...

show abstract

“…1). Average concentrations of nitrogen organic forms are estimated for the three shelf rivers (Cauwet et al, 2002;Reschke et al, 2002;Walling and Fang, 2003). When multiplied by the considered discharges, this leads to a total load of 10.1 Gmol N yr −1 (7, 0.8 and 2.3 for Danube, Dnieper and Dniester, respectively).…”

Section: A Capet Et Al: Seasonal Hypoxia In the Black Sea Northwestmentioning

confidence: 99%

Drivers, mechanisms and long-term variability of seasonal hypoxia on the Black Sea northwestern shelf – is there any recovery after eutrophication?

Capet

Beckers²,

Grégoire

2013

Biogeosciences

View full text Add to dashboard Cite

Abstract. The Black Sea northwestern shelf (NWS) is a shallow eutrophic area in which the seasonal stratification of the water column isolates the bottom waters from the atmosphere. This prevents ventilation from counterbalancing the large consumption of oxygen due to respiration in the bottom waters and in the sediments, and sets the stage for the development of seasonal hypoxia. A three-dimensional (3-D) coupled physical–biogeochemical model is used to investigate the dynamics of bottom hypoxia in the Black Sea NWS, first at seasonal and then at interannual scales (1981–2009), and to differentiate its driving factors (climatic versus eutrophication). Model skills are evaluated by a quantitative comparison of the model results to 14 123 in situ oxygen measurements available in the NOAA World Ocean and the Black Sea Commission databases, using different error metrics. This validation exercise shows that the model is able to represent the seasonal and interannual variability of the oxygen concentration and of the occurrence of hypoxia, as well as the spatial distribution of oxygen-depleted waters. During the period 1981–2009, each year exhibits seasonal bottom hypoxia at the end of summer. This phenomenon essentially covers the northern part of the NWS – which receives large inputs of nutrients from the Danube, Dniester and Dnieper rivers – and extends, during the years of severe hypoxia, towards the Romanian bay of Constanta. An index H which merges the aspects of the spatial and temporal extension of the hypoxic event is proposed to quantify, for each year, the intensity of hypoxia as an environmental stressor. In order to explain the interannual variability of H and to disentangle its drivers, we analyze the long time series of model results by means of a stepwise multiple linear regression. This statistical model gives a general relationship that links the intensity of hypoxia to eutrophication and climate-related variables. A total of 82% of the interannual variability of H is explained by the combination of four predictors: the annual riverine nitrate load (N), the sea surface temperature in the month preceding stratification (Ts), the amount of semi-labile organic matter accumulated in the sediments (C) and the sea surface temperature during late summer (Tf). Partial regression indicates that the climatic impact on hypoxia is almost as important as that of eutrophication. Accumulation of organic matter in the sediments introduces an important inertia in the recovery process after eutrophication, with a typical timescale of 9.3 yr. Seasonal fluctuations and the heterogeneous spatial distribution complicate the monitoring of bottom hypoxia, leading to contradictory conclusions when the interpretation is done from different sets of data. In particular, it appears that the recovery reported in the literature after 1995 was overestimated due to the use of observations concentrated in areas and months not typically affected by hypoxia. This stresses the urgent need for a dedicated monitoring effort in the Black Sea NWS focused on the areas and months concerned by recurrent hypoxic events.

show abstract

Seasonal DOC accumulation in the Black Sea: a regional explanation for a general mechanism

Cited by 48 publications

References 38 publications

Major inter-annual variations in microbial dynamics in the Gulf of Trieste (northern Adriatic Sea) and their ecosystem implications

Major inter-annual variations in microbial dynamics in the Gulf of Trieste (northern Adriatic Sea) and their ecosystem implications

Distribution of inorganic and organic nutrients in the South Pacific Ocean − evidence for long-term accumulation of organic matter in nitrogen-depleted waters

Drivers, mechanisms and long-term variability of seasonal hypoxia on the Black Sea northwestern shelf – is there any recovery after eutrophication?

Contact Info

Product

Resources

About