An assessment of upper ocean carbon and nitrogen export fluxes on the boreal continental shelf: A 3‐year study in the open Baltic Sea comparing sediment traps, <sup>234</sup>Th proxy, nutrient, and oxygen budgets

Gustafsson, Örjan; Gelting, Johan; Andersson, Per; Larsson, Ulf; Roos, Per

doi:10.4319/lom.2013.11.495

Cited by 30 publications

(26 citation statements)

References 54 publications

(114 reference statements)

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“…The direct evidence for organotrophic denitrification found in this study shows that N turnover processes in the water column are more directly coupled to the organic carbon export than previously thought. In the Baltic Sea, carbon export increases by up to a factor five during the spring bloom and significant interannual variations occur (Gustafsson et al ). These strong seasonal and interannual variations also imply a high temporal variability of N loss.…”

Section: Discussionmentioning

confidence: 99%

Denitrification and DNRA at the Baltic Sea oxic-anoxic interface: Substrate spectrum and kinetics

et al. 2016

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The dependence of denitrification and dissimilatory nitrate reduction to ammonium (DNRA) on different electron donors was tested in the nitrate‐containing layer immediately below the oxic–anoxic interface (OAI) at three stations in the central anoxic basins of the Baltic Sea. Additionally, pathways and rates of fixed nitrogen transformation were investigated with 15N incubation techniques without addition of donors. Denitrification and anammox were always detected, but denitrification rates were higher than anammox rates. DNRA occurred at two sites and rates were two orders of magnitude lower than denitrification rates. Separate additions of dissolved organic carbon and sulfide stimulated rates without time lag indicating that both organotrophic and lithotrophic bacterial populations were simultaneously active and that they could carry out denitrification or DNRA. Manganese addition stimulated denitrification and DNRA at one station, but it is not clear whether this was due to a direct or indirect effect. Ammonium oxidation to nitrite was detected on one occasion. During denitrification, the production of nitrous oxide (N2O) was as important as dinitrogen (N2) production. A high ratio of N2O to N2 production at one site may be due to copper limitation, which inhibits the last denitrification step. These data demonstrate the coexistence of a range of oxidative and reductive nitrogen cycling processes at the Baltic OAI and suggest that the dominant electron donor supporting denitrification and DNRA is organic matter. Organotrophic denitrification is more important for nitrogen budgets than previously thought, but the large temporal variability in rates calls for long‐term seasonal studies.

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Section: Discussionmentioning

confidence: 99%

Denitrification and DNRA at the Baltic Sea oxic-anoxic interface: Substrate spectrum and kinetics

et al. 2016

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“…With stainless steel spatulas, we manually transferred the upper 0–2 cm into polyethylene containers that were frozen immediately afterward. Sinking particulate matter was collected with a cylindrical sediment trap system [ Gustafsson et al ., ] that was bottom anchored with ∼40 kg railway tracks and galvanized chains. The trap (one array per mooring) consisted of three PVC cylinders each holding a straight cylindrical glass tube (500 × 100 mm) and was positioned at 6–10 m water depth (YS‐4 at 22 m), below the mixed surface layer (5–9 m deep), and as far above the bottom (4–9 m) as possible (Table and supporting information Figure S1).…”

Section: Methodsmentioning

confidence: 99%

Preferential burial of permafrost‐derived organic carbon in Siberian‐Arctic shelf waters

et al. 2014

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The rapidly changing East Siberian Arctic Shelf (ESAS) receives large amounts of terrestrial organic carbon (OC) from coastal erosion and Russian-Arctic rivers. Climate warming increases thawing of coastal Ice Complex Deposits (ICD) and can change both the amount of released OC, as well as its propensity to be converted to greenhouse gases (fueling further global warming) or to be buried in coastal sediments. This study aimed to unravel the susceptibility to degradation, and transport and dispersal patterns of OC delivered to the ESAS. Bulk and molecular radiocarbon analyses on surface particulate matter (PM), sinking PM and underlying surface sediments illustrate the active release of old OC from coastal permafrost. Molecular tracers for recalcitrant soil OC showed ages of 3.4-13 14 C-ky in surface PM and 5.5-18 14 C-ky in surface sediments. The age difference of these markers between surface PM and surface sediments is larger (i) in regions with low OC accumulation rates, suggesting a weaker exchange between water column and sediments, and (ii) with increasing distance from the Lena River, suggesting preferential settling of fluvially derived old OC nearshore. A dual-carbon end-member mixing model showed that (i) contemporary terrestrial OC is dispersed mainly by horizontal transport while being subject to active degradation, (ii) marine OC is most affected by vertical transport and also actively degraded in the water column, and (iii) OC from ICD settles rapidly and dominates surface sediments. Preferential burial of ICD-OC released into ESAS coastal waters might therefore lower the suggested carbon cycle climate feedback from thawing ICD permafrost.

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“…The major annual phytoplankton blooms in the Baltic Sea, occurring in spring and late summer, provide massive but transient input of fresh and reactive organic matter. Highest export fluxes have been determined during spring blooms, while sedimentation was shown to strongly decrease during early summer (Höglander et al, 2004;Gustafsson et al, 2013). This study examines the coupling between primary production and bacterial organic matter recycling under various oxygen regimes during early summer.…”

Section: Discussionmentioning

confidence: 99%

Relevance of Nutrient-Limited Phytoplankton Production and Its Bacterial Remineralization for Carbon and Oxygen Fluxes in the Baltic Sea

et al. 2019

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The Baltic Sea is prone to oxygen deficiency due to the restricted water exchange with the North Sea in coincidence with a high biological oxygen demand. The partitioning of organic carbon between respiration, accumulation and export is co-determined by phytoplankton primary production and its subsequent bacterial remineralization. Here, we investigated net phytoplankton primary production, heterotrophic bacterial biomass production and dark CO 2 fixation by on-board incubations with radiolabeled tracers in the Baltic Proper and in the Gulf of Riga after the main spring bloom. Results show that low phytoplankton standing stocks of ≤1.6 µg chlorophyll a L −1 sustained net primary production of 161-724 mg C m −2 d −1 under nitrogen limitation. Estimates of bacterial carbon remineralization suggest that freshly produced organic carbon was supplied to the aphotic zone at all stations. In the southern Baltic Proper, net primary production exceeded the bacterial carbon demand in the surface mixed layer, suggesting that organic matter derived from nutrient-limited primary production was available for export to bacterial communities below the oxycline. On average, 46% of heterotrophic bacterial production was mediated in oxygen minimum zones, revealing the high importance of organic matter recycling under hypoxic and anoxic conditions for the carbon budget. Dark CO 2 fixation of up to 4.33 µg C L −1 d −1 in sulfide-free waters equaled 9-54% of the co-inciding heterotrophic bacterial carbon demand and may have provided another organic carbon source for heterotrophic activity. Substantially higher dark CO 2 fixation up to 25.46 µg C L −1 d −1 was determined in sulfidic waters. Since our study was conducted 5 months after the major Baltic inflow event in winter 2014/2015, potential effects of deep water ventilation could be investigated. In the Gotland Basin, heterotrophic bacterial production in renewed oxygen-rich bottom water was similar to that in the uplifted oxygen-deficient former bottom water, while it was significantly reduced in sulfidic waters. Hence, our results suggest that the removal of hydrogen sulfide by inflow events has a high potential to increase bacterial carbon remineralization.

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An assessment of upper ocean carbon and nitrogen export fluxes on the boreal continental shelf: A 3‐year study in the open Baltic Sea comparing sediment traps, ²³⁴Th proxy, nutrient, and oxygen budgets

Abstract: Six different approaches for estimating the upper ocean export of carbon and nitrogen has been assessed using 2-3 years of observations in the open Baltic Sea. The long-term average export ratios, relative to primary production, were similar from approaches based on upper ocean N budget (

Cited by 30 publications

References 54 publications

Denitrification and DNRA at the Baltic Sea oxic-anoxic interface: Substrate spectrum and kinetics

Denitrification and DNRA at the Baltic Sea oxic-anoxic interface: Substrate spectrum and kinetics

Preferential burial of permafrost‐derived organic carbon in Siberian‐Arctic shelf waters

Relevance of Nutrient-Limited Phytoplankton Production and Its Bacterial Remineralization for Carbon and Oxygen Fluxes in the Baltic Sea

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An assessment of upper ocean carbon and nitrogen export fluxes on the boreal continental shelf: A 3‐year study in the open Baltic Sea comparing sediment traps, 234Th proxy, nutrient, and oxygen budgets

Abstract: Six different approaches for estimating the upper ocean export of carbon and nitrogen has been assessed using 2-3 years of observations in the open Baltic Sea. The long-term average export ratios, relative to primary production, were similar from approaches based on upper ocean N budget (

Cited by 30 publications

References 54 publications

Denitrification and DNRA at the Baltic Sea oxic-anoxic interface: Substrate spectrum and kinetics

Denitrification and DNRA at the Baltic Sea oxic-anoxic interface: Substrate spectrum and kinetics

Preferential burial of permafrost‐derived organic carbon in Siberian‐Arctic shelf waters

Relevance of Nutrient-Limited Phytoplankton Production and Its Bacterial Remineralization for Carbon and Oxygen Fluxes in the Baltic Sea

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An assessment of upper ocean carbon and nitrogen export fluxes on the boreal continental shelf: A 3‐year study in the open Baltic Sea comparing sediment traps, ²³⁴Th proxy, nutrient, and oxygen budgets