OCB Summer Workshop WHOI, July 16-19,

Transcription

1 Transformation and fluxes of carbon in a changing Arctic Ocean and it s impact on ocean acidification, the Atlantic view Leif G. Anderson Department t of Chemistry and Molecular l Biology University of Gothenburg Sweden

2 Layout: The Atlantic ti view Overview of carbon fluxes & transformation in the AO Changes in carbon transformation & fluxes, e.g. feedbacks Effect on Ocean Acidification Concluding remarks

3 The Atlantic view

4 The atmospheric pressure field determines much of the oceanic water transport to the Arctic Ocean. High NAO-index!

5 The only deep water connection with the global oceans is through the Fram Strait and thus waters of Atlantic origin fills up most of the Arctic Ocean deeper than a few hundred meters. Atlantic water influences the Eurasian shelf seas all from the Barents Sea to the East Siberian Sea. Rivers are an important part of the Arctic Ocean carbon cycle, and they are largely feed by evaporation from the Atlantic Ocean. Circulation of the Atlantic-derived halocline waters and distribution of the Eurasian Basin shelf input and the Pacific water, respectively. Rudels et al., Observations in the Ocean, Chapter 4 in Lemke and Jacobi (eds.), Arctic Climate Change: The ACSYS Decade and Beyond

6 The Atlantic view Overview of carbon fluxes & transformation in the AO Changes in carbon transformation & fluxes, e.g. feedbacks Effect on Ocean Acidification Concluding remarks

7 The water that builds up the surface water in the central Arctic Ocean largely flows over shelves seas. Here primary production occurs in the summer and cooling throughout the year.

8 Both decreases pco 2 and thus most surface waters in the central AO are under-saturated

9 In winter, sea ice formation promotes air sea exchange of gases

10 Polynyas y Ice factories and active CO 2 flux regions. Kvalvagen

11 epth (metres) D p CO 2 (µatm) DIC (µmol/kg) One example Stn. 2 Stn. 3 Stn. 5 Stn. 6 Stn. 7 Stn Observations from Storfjorden, 0.5 April The changes in pco 2 and DIC was not -0.5 followed by corresponding changes in -1.0 oxygen or nutrients, illustrating that -1.5 biogeochemistry was not the cause of increasing DIC with depth (and S). Temp perature ( o C) Salinity Anderson, Falck, Jones, Jutterström, and Swift, J. Geophys. Res., 109, 2004.

12 What is the Pan-Arctic importance of sea ice production as a conveyor for air-sea CO 2 flux? High S brine enriched water is mainly produced in the Atlantic sector as surface water S is higher. h But sea ice production also impact TA of the brine and the sea ice melt-water through chemogenic CaCO 3 (s) formation. 2 TA is trapped pco 2 decreases in sea ice melt-water 1 Brine TA is depleted pco 2 increases in the brine

13 Where can enough salty water be produced? Dethleff (2010) used models and sea ice data to compute volume and salinities of brine induced shelf plumes. For the regions A1-A3, E and F the result was ~0.5 Sv in the salinity range Dethleff, D. Dense water formation in the Laptev Sea flaw lead, J. Geophys. Res., 115, C12022, doi: /2009jc006080, 2010.

14 Transport of carbon to intermediate and deep waters of the Arctic Ocean also occurs through ocean ventilation, one important conveyor being cooling in the Barents Sea

15 Section from Kara Sea to Lomonosov Ridge, Polarstern 1996 Θ Penetration ti n of the Barents Sea branch along the continental margin down to ~1500 m depth. Colder and fresher water. This is a conveyor for sequestration of anthropogenic CO 2. S

16 How about the biological C pump? Phosphate profiles from the Canadian and Eurasian Basins Constant values below ~2000 m depth minimal sedimentation

17 Si(OH) 4 and O 2 show more variability in the deep waters than PO 4 Phosphate Oxygen Silicate Beringia 2005

18 Transient tracers show long residence times of the deep waters, mixing age ~500 y in CB and ~200 y in EB CB EB Thus, the sedimentation below ~2000 m is, at present, negligible!

19 The Atlantic view Overview of carbon fluxes & transformation in the AO Changes in carbon transformation & fluxes, e.g. feedbacks Effect on Ocean Acidification Concluding remarks

20 Changes in plankton productivity? The abundance of calcifies, such as coccolithophores, has increased in the Barents Sea during the last decades

21 And of course the decreasing sea ice coverage, with its impact on: Biological activity Sea ice formation Coastal erosion.

22 Air pressure field August September CO 2 oversaturated surface waters west of ~160 o E (Atlantic domain) and even more so along the coast H Surface water p CO in situ 2 How come and is it new?

23 How? Surface water PO 4 concentration But NO 3 concentrations are low in the surface water of all areas, while there is an excess of PO 4 in the ESS & CS. This reveals that marine primary production occurs in all areas. Surface water NO 3 concentration Hence, areas of high pco 2 have a source of OM low in nuts that decays, most likely terrestrial OM.

24 A section of biochemical constituents across the Laptev Sea give even more support to the importance of terrestrial OM Close to zero Close to zero Phosphate Nitrate Silicate (µmol/kg) (µmol/kg) (µmol/kg) Not oversaturated Laptev Sea section Laptev Sea 385 Oversaturated AOU (µmol/k g) East Siberian Sea pco 2 (µatm) Chukchi Sea

25 The Atlantic view Overview of carbon fluxes & transformation in the AO Changes in carbon transformation & fluxes, e.g. feedbacks Effect on Ocean Acidification Concluding remarks

26 High biogenic activity in the Siberian shelf seas Properties at bottom sample reveal a hot spot with a signature of microbial decay of organic matter. High nuts, high fco 2, high AOU & low ph. PO 4 (µmol/kg) SiO 2 (µmol/kg) fco 2 (µatm) ph tot (15 o C) AOU = [O 2 ] saturation [O 2 ] measured AOU (µmol/kg)

27 Impact on the solubility of calcium carbonate Omega Aragonite in the bottom water Omega Calcite in the bottom water The aragonite degree of saturation ti is both impacted by S and by microbial decay of organic matter, where the former mainly sets the surface water degree.

28 The exchange with the deep basin Omega calcite Omega aragonite The under-saturation of, especially aragonite, is spread far out into the deep basin at a depth close to the surface where life exist.

29 The Atlantic view Overview of carbon fluxes & transformation in the AO Changes in carbon transformation & fluxes, e.g. feedbacks Effect on Ocean Acidification Concluding remarks

30 Concluding remarks The central AO is, at least up to now, a region of low C transformation and fluxes The shelf seas are biogeochemical very dynamic As a result of ocean ventilation, the anthropogenic CO 2 sink is high per unit area Climate change will alter C fluxes, the question is how Some future challenges More open water in summer promotes ice production and thus deep water ventilation More open water in summer promotes PP and sedimentation of POM Thawing of permafrost promotes coastal erosion and runoff DOC supply, leading to increased pco 2 in shelf seas

31 Thanks for listening and to all colleagues that have contributed in the field and to the evaluation of the data Vanja Alling, Per Andersson, Göran Björk, Ylva Ericson, Örjan Gustafsson, Martin Jakobsson, Emil Jeansson, Peter Jones, Sara Jutterström, Irina Pipko, Bert Rudels, Natalia Shakhova, Igor Semiletov, Bill Smethie Jr., Jim Swift, Toste Tanhua, Doug Wallace, Iréne Wåhlström