Carbon cycling in the Baltic Sea — The fate of allochthonous organic carbon and its impact on air–sea CO2 exchange

Gustafsson, Erik; Deutsch, Barbara; Gustafsson, Bo; Humborg, Christoph; Mörth, Carl‐Magnus

doi:10.1016/j.jmarsys.2013.07.005

Cited by 63 publications

(117 citation statements)

References 66 publications

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“…The horizontal areas at different water depths are based on real hypsography of the various subbasins of the system. Mixing and advection is simulated in a hydrodynamic module (Gustafsson 2000, while the dynamics of nutrients and plankton (Savchuk 2002;Gustafsson et al 2012;Savchuk et al 2012) as well as organic carbon and the carbonate system processes (Gustafsson et al 2014a(Gustafsson et al , b, 2015 are simulated in a biogeochemical module.…”

Section: Model Descriptionmentioning

confidence: 99%

“…Total organic C, N, and P (TOC, TON, and TOP) represent the sums of dissolved and particulate organic C, N, and P respectively. DOC in the model is distributed between four individual state variables, allowing a separation between marine and terrestrial DOC, and further between refractory and labile fractions (Gustafsson et al 2014a). The separation between marine and terrestrial fractions is for consistency also applied to POC in the water column as well as organic carbon in the active sediment layer.…”

Section: Model Descriptionmentioning

confidence: 99%

“…For that reason we have no estimates of basin-wide mean C concentrations based on observations. Simulated organic and inorganic carbon concentrations have however been validated in earlier publications (Gustafsson et al 2014a(Gustafsson et al , 2015, and average basin-wide simulated concentrations of TC, TOC, and DIC are presented in Table 3.…”

Section: Pools and Ratiosmentioning

confidence: 99%

“…Stepanauskas et al 2002). Organic carbon supplied from land and by atmospheric depositions has been assumed to be on average separated into 40% degradable and 60% refractory matter (Gustafsson et al 2014a) (see further below). The fact that the overall simulated TON concentration in the system is overestimated could imply that the prescribed degradable fraction of organic N in land loads is too low.…”

Section: Pools and Ratiosmentioning

confidence: 99%

“…The present version of BALTSEM (cf. Gustafsson et al 2014a) explicitly includes DIC, DIN, and DIP, as well as dissolved and particulate organic C, N, and P, allowing separate budget calculations for organic, inorganic, and total C, N, and P pools and fluxes. Our calculations include pelagic pools and their transformations as well as storage and transformations in the active sediment layer, which allows a complete coverage of the overall C, N, and P cycling.…”

Section: Introductionmentioning

confidence: 99%

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Key processes in the coupled carbon, nitrogen, and phosphorus cycling of the Baltic Sea

et al. 2017

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In this study we examine pools of carbon (C), nitrogen (N), and phosphorus (P) in the Baltic Sea, both simulated and reconstructed from observations. We further quantify key fluxes in the C, N, and P cycling. Our calculations include pelagic reservoirs as well as the storage in the active sediment layer, which allows a complete coverage of the overall C, N, and P cycling on a system-scale. A striking property of C versus N and P cycling is that while the external supplies of total N and P (TN and TP) are largely balanced by internal removal processes, the total carbon (TC) supply is mainly compensated by a net export out of the system. In other words, external inputs of TN and TP are, in contrast to TC, rather efficiently filtered within the Baltic Sea. Further, there is a net export of TN and TP out of the system, but a net import of dissolved inorganic N and P (DIN and DIP). There is on the contrary a net export of both the organic and inorganic fractions of TC. While the pelagic pools of TC and TP are dominated by inorganic compounds, TN largely consists of organic N because allochthonous organic N is poorly degradable. There are however large basin-wise differences in C, N, and P elemental ratios as well as in inorganic versus organic fractions. These differences reflect both the differing ratios in external loads and differing oxygen conditions determining the redox-dependent fluxes of DIN and DIP.

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Section: Model Descriptionmentioning

confidence: 99%

Section: Model Descriptionmentioning

confidence: 99%

Section: Pools and Ratiosmentioning

confidence: 99%

Section: Pools and Ratiosmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Key processes in the coupled carbon, nitrogen, and phosphorus cycling of the Baltic Sea

et al. 2017

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External total alkalinity loads versus internal generation: The influence of nonriverine alkalinity sources in the Baltic Sea

Gustafsson

Wällstedt

Humborg

et al. 2014

Global Biogeochemical Cycles

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In this study we first present updated riverine total alkalinity (TA) loads to the various Baltic Sea sub-basins, based on monthly measurements in 82 of the major rivers that represent 85% of the total runoff. Simulations in the coupled physical-biogeochemical BALTSEM (BAltic sea Long-Term large Scale Eutrophication Model) model show that these river loads together with North Sea water inflows are not sufficient to reproduce observed TA concentrations in the system, demonstrating the large influence from internal sources. Budget calculations indicate that the required internal TA generation must be similar to river loads in magnitude. The nonriverine source in the system amounts to about 2.4 mmol m À2 d À1 on average. We argue here that the majority of this source is related to denitrification together with unresolved sediment processes such as burial of reduced sulfur and/or silicate weathering. This hypothesis is supported by studies on sediment processes on a global scale and also by data from sediment cores in the Baltic Sea. In a model simulation with all internal TA sources and sinks switched on, the net absorption of atmospheric CO 2 increased by 0.78 mol C m À2 yr À1compared to a simulation where TA was treated as a passive tracer. Our results clearly illustrate how pelagic TA sources together with anaerobic mineralization in coastal sediments generate a significant carbon sink along the aquatic continuum, mitigating CO 2 evasions from coastal and estuarine systems.

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Tracing terrestrial DOC in the Baltic Sea—A 3‐D model study

Fransner

Nycander

Mörth

et al. 2016

Global Biogeochemical Cycles

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The fate of terrestrial organic matter brought to the coastal seas by rivers and its role in the global carbon cycle are still not very well known. Here the degradation rate of terrestrial dissolved organic carbon (DOCter) is studied in the Baltic Sea, a subarctic semienclosed sea, by releasing it as a tracer in a 3‐D circulation model and applying linear decay constants. A good agreement with available observational data is obtained by parameterizing the degradation in two rather different ways: one by applying a decay time on the order of 10 years to the whole pool of DOCter and one by dividing the DOCter into one refractory pool and one pool subject to a decay time on the order of 1 year. The choice of parameterization has a significant effect on where in the Baltic Sea the removal takes place, which can be of importance when modeling the full carbon cycle and the CO2 exchange with the atmosphere. In both cases the biogeochemical decay operates on time scales less than the water residence time. Therefore, only a minor fraction of the DOCter reaches the North Sea, whereas approximately 80% is removed by internal sinks within the Baltic Sea. This further implies that DOCter mineralization is an important link in land‐sea‐atmosphere cycling of carbon in coastal and shelf seas that are heavily influenced by riverine DOC.

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Carbon cycling in the Baltic Sea — The fate of allochthonous organic carbon and its impact on air–sea CO2 exchange

Cited by 63 publications

References 66 publications

Key processes in the coupled carbon, nitrogen, and phosphorus cycling of the Baltic Sea

Key processes in the coupled carbon, nitrogen, and phosphorus cycling of the Baltic Sea

External total alkalinity loads versus internal generation: The influence of nonriverine alkalinity sources in the Baltic Sea

Tracing terrestrial DOC in the Baltic Sea—A 3‐D model study

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