Kitidis, Vassilis: A Carbon-budget for the north-west European shelf - limitations and uncertainties.
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The document summarizes a study quantifying the carbon budget of the north-west European shelf. The primary motivation was to quantify the air-sea carbon dioxide flux and determine where carbon goes long-term. The estimated net carbon flux was 23 teragrams of carbon per year entering the ocean. However, there are uncertainties including non-measured organic carbon fluxes, interpolation errors, and difficulties directly measuring net carbon burial. The study aims to provide information relevant to ocean acidification, long-term carbon storage, and potential reductions in atmospheric carbon burden.
![Primary motivation was to quantify the air to sea flux of CO2
[UK research programme + ICOS + Ferrybox…]
Question: • Where does the Carbon go?
• Is there long term C-storage?
• How big are other fluxes?](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
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Kitidis, Vassilis: A Carbon-budget for the north-west European shelf - limitations and uncertainties.
- 1. Carbon-budget for the north-west European shelf – limitations and uncertainties Kitidis, Vassilis (vak@pml.ac.uk), Shutler Jamie D., Ashton Ian, Warren Mark, Brown Ian, Findlay Helen, Hartman Sue E., Sanders Richard, Humphreys Matthew, Kivimäe Caroline , Greenwood Naomi, Hull Tom, Pearce David, McGrath Triona, Stewart Brian M., Walsham Pamela, McGovern Evin, Bozec Yann, Gac Jean-Philippe , Marrec Pierre, van Heuven Steven M.A.C., Hoppema Mario, Schuster Ute, Johannessen Truls, Omar Abdirahman, Lauvset Siv, Skjelvan Ingunn, Olsen Are, Steinhoff Tobias, Körtzinger Arne, Becker Meike, Lefevre Nathalie, Diverrès Denis, Gkritzalis Thanos, Cattrijsse André, Petersen Wilhelm, Voynova Yoana G., Chapron Bertrand, Grouazel Antoine, Land Peter E., Sharples Jonathan, Nightingale Philip D https://www.nature.com/articles/s41598-019-56363-5
- 2. Primary motivation was to quantify the air to sea flux of CO2 [UK research programme + ICOS + Ferrybox…] Question: • Where does the Carbon go? • Is there long term C-storage? • How big are other fluxes?
- 3. NW European Shelf C-budget (fluxes in Tg C y-1) https://www.nature.com/articles/s41598-019-56363-5 “Policy relevant”: 1. Ocean Acidification, 2. C-burial (reduces atmospheric burden), 3. Potential export (reduces atmospheric burden) 1. 2. 3.
- 4. https://www.nature.com/articles/s41598-019-56363-5 NW European Shelf C-budget (fluxes in Tg C y-1) Literature FluxesIN - FluxesOUT
- 5. Uncertainties [air to sea CO2 flux was 23 Tg C y-1]: ● Non CO2, non CH4 organic C from the atmosphere – not included, but could be 1.9 ± 1.4 Tg C y-1 [http://dx.doi.org/10.1016/j.atmosenv.2016.06.006]. ● Interpolation – quantified as 16% of annual surface ocean CO2 field [https://www.nature.com/articles/s41598-019-56363-5 ]. ● Net C-burial – Largest proportional uncertainty in budget, although a small term (1.3 ± 3.1 Tg C y-1 . Extrapolated by sediment type from seasonal data from Celtic Sea. Limited spatial data extent and indirect calculation – difficult to measure [https://www.nature.com/articles/s41598-019-56363-5 ]. Respiration + N-cycle C:N; O:C C-remineralised Assume 97% recycled Gross C+N-deposited & Sediment-Water return Flux Measured Sediment-Water N-flux Check this
- 6. Uncertainties – fate of riverine-C [air to sea CO2 flux was 23 Tg C y-1]: Estuary & Coastal Open shelf Thomas et al. 2005 18.9 Tg C y−1 DIC and 2.1 Tg C y−1 DOC Ciais et al. 2008 (scaled) 2.0 Tg C y−1 DIC and 2.6 Tg C y−1 DOC Borges, Chen, Cai (scaled) 24.4 ± 10.4 Tg C y−1 CO2, River Large/urban estuary bias Scaled by Area:Coastline assumes homogeneity Easy to measure Difficult
- 7. Can ICOS do this exercise? ? ? ?
Editor's Notes
- This work started life as an exercise to quantify the air to sea flux of CO2. This was prompted by a targeted UK programme which prompted us to ask for help in compiling a large dataset of surface “ocean” CO2. Colleagues brought ICOS and Ferrybox funding to the table. The resulting net annual flux was from air to sea over most of the shelf. This raised a number of sequential questions: 1) Where does the C go? 2) Where does the C go in the long term since there is annual influx to the sea? 3) How big are other fluxes?
- These questions prompted a simple budget where the NW European shelf is treated as a box with C flowing in and out of the box (anti-clockwise from top): atmospheric influx, river- and Baltic Sea-influx, net burial in sediments (shells and organic C) and export, mostly to the Norwegian Sea. In the centre of the box we have C-accumulation which causes Ocean Acidification. The observations to note are that atmospheric influx of CO2 is the largest flux in, followed by the Baltic while export to the Norwegian Sea is the largest flux out. Also of note, is the relatively small contribution of organic-C input from rivers/Baltic (~10% of total C from these sources. The fluxes which are ultimately most interesting to wider society are 1) Ocean Acidification, 2) burial and 3) “potential” C-entrainment in deep water - the term “Export” refers to export from the box, not necessarily into deep water.
- Each of these fluxes carries uncertainty. The fluxes in the red boxes were calculated from the literature, others were calculated by us and finally, what was left over was the Export term, largely to the Norwegian Sea / North Atlantic. This term ensures the principle of “conservation of mass”, so what goes in has to either stay in the box (DIC accumulation – the cause of Acidification) or leave.
- Organic C-deposition (wet or dry) is highly uncertain due to paucity of data. Interpolation was quantified by comparing interpolated data with measurements not included in the original analysis. Net C burial is a highly uncertain term and difficult to measure in disturbed (trawled) shelf sediments. We quantified this indirectly by converting Respiration and N-cycling rates into C-remineralisation. Assuming that this represented 97% of gross-C-deposition, we can calculate the sediment-water nutrient flux and check this against measurements to validate the 97% recycling assumption.
- The river to estuary DIC flux was x10 greater than the estuary to open shelf DIC flux. Estuaries are supersaturated with CO2 and its efflux can account for this discrepancy, but carries high uncertainty and is biased to large/urbanised estuaries which may not be representative. Scaling assumed a fixed Estuarine Area to Coastline length ratio and hence homogeneity in morphology which may not be realistic. The river to estuary flux is simpler to quantify (accessible river-banks, boats, flux is unidirectional). In contrast, the coastal to open shelf flux is more difficult to reach, larger and the flux is tidally bidirectional.
- The air to sea flux of CO2 and DIC accumulation can be quantified with existing infrastructure. Infrastructure is currently not representative of the diversity of estuaries in order to quantify the estuarine CO2 efflux to the atmosphere. Riverine inputs are monitored nationally and RINGO has made recommendations regarding their integration. The Baltic influx is not quantified, but this may not be necessary if it is included in the box. There are no sustained observations of Net C-burial at present (ICOS or otherwise). There are few observation from which to calculate the “Export” term to the Norwegian Sea and they are outside ICOS. Conclusion: Modelling has a crucial role to play in filling the observational gaps, particularly “burial” and “export”.