Catastrophic reduction of seaice in the Arctic Ocean - its impact on the marine ecosystems in the polar region-

Transcription

1 1/12 Catastrophic reduction of seaice in the Arctic Ocean - its impact on the marine ecosystems in the polar region- KAKENHI No Naomi Harada (JAMSTEC) J. Onodera, E. Watanabe, K. Matsuno, K. Kimoto, M. Honda, M. J. Kishi, T. Kikuchi, Y. Tanaka

2 2/12 Phytoplankton responses on the sea-ice reduction Introduction If sea-ice reduced in the Arctic Ocean, l Light Sea ice reduction contributes to the improvement of light condition in the sea water l Temperature Increasing the light promotes to be warm l Nutrients Concentration of nutrients decrease by sea-ice melting. Light and fresh water prevents upwelling the nutrients from deep layer Sun light Sea-ice Sun light Nuts Does sea-ice reduction promote or prevent phytoplankton production?

3 3/12 Influence on biogeochemical cycle in the water Introduction l Is biological pump accelerated? l Does Arctic Ocean become a sink of atmospheric CO 2?

4 4/12 Limited biogeochemical observation research in the Arctic Ocean Aims To understand the impact of sea-ice reduction on productivity and biogeochemical cycles Current climate model is insufficient to reconstruct the environment of the Arctic Ocean Collaboration study between observation and model to understand the temporal and spatial variability R/V Mirai and Ice Breaker Earth simulator

5 5/12 Sampling site and method Observation area Northwind Abyssal Plain NAP Canada Basin Nansen Basin Amundsen Basin N. Atlantic Greenland Chukchi shelf region Siberia NAP Chukchi shelf region Canada Basin Alaska 180m 1300m Okhotsk Sea Bering Sea N. Pacific Previous sediment trap observation sites

6 6/12 Biological particles collected by time series sediment trap system Result of biological fluxes Flux was maximum in the beginning of winter and composed of quite old and fresh particles Pteropods Result Fresh zooplankton from trap Copepods Fresh particles 1mm 1mm Bivalves Oncaea parila 1mm mm 0.1mm

7 7/12 Arctic sea ice-ocean physicsecosystem model Method Sea ice-ocean physics model: COCO Marine ecosystem model: NEMURO [m] Siberia Europe NAP Greenland 80N 70N Bering strait 45N Canada Spin up Annual variability exp. (Atmospheric condition (Atmospheric condition during in 1979) ) 10 yrs integration 33 yrs integration Seasonal variability exp. (Atmospheric condition in 2010) 1 yr integration 25km mesh 5km mesh Simulation with 5 km mesh can provide eddy scale current, current along the complicated ocean floor and lower trophic level ecosystem

8 8/12 Enhanced biogenic particle fluxes into the deep layer at beginning of polar night season Nov W NAP 75N 80N Comparison between model simulation and observation data of seasonal change in biogenic particle fluxes Model Obs. in 2010 Obs. in 2011 [µμmol- N/m 2 /day] Result 180m 1300m Bering Strait Barrow Model simulation at 1300m depth 140W [µμmol- N/m2 /day] Model simulated biogenic particle fluxes l reconstructed the double peak observed in summer and autumn l showed large settling in the southern part of Canada Basin

9 9/12 Meso scale eddy transports the shelf water and incubates the lower trophic level organisms Aug x NAP x km Result 50cm/s 10 9 x x Barrow x 100m depth Temp&Eddy x x [ºC] 7 6 Cold eddy x x x x 9 Warm eddy x 8 Eddy observed in Oct, 2010 (R/V Mirai) Nishino et al. [2011] SST from MODIS satellite Sep, 2003 Watanabe [2011] Eddy transports the water mass from the shelf break Turbulent mixing (inside the eddy) promotes nutrient input from subsurface to surface in the eddy-matured period Biogenic particle flux would enhance depending on the timing and location of eddy occurrence

10 10/12 Lower trophic ecosystem responses on the sea-ice reduction Result (a) Lateral transport of lithogenic and old organic particles from shelf break into more oceanic area (b) Fresh organic particles, which were incubated inside the eddy, are added If sea ice edge moved back... Accelerated eddy occurrence+ Enhanced current system Promoted lower trophic level organisms production

11 11/12 Comparison of model simulated organic nitrogen fluxes between 1990 s and after 2005 Model result 2010M Ice2.0 Ice0.5 Result 80% increase of eddy appearance PON fluxes Sea-ice NAP 2010M Ice2.0 Ice0.5 Bering Strait Barrow [µμmol- N/m 2 /day] Area: 140W-160W &75N-1000m depth contour Oct. 1 Average flux on Nov. in the southern part of Canada Basin

12 12/12 Summary Time series sediment trap experiment and sea ice ocean physics-marine ecosystem model provided new findings regarding the lower trophic production Pacific side of Arctic Ocean. Maximum fluxes of biogenic particles appeared in the beginning of sea ice season. The shelf water transportation by meso scale eddies might be important. Biological pump associated with eddy occurrences would be enhanced in the Northwind abyssal plain, because eddy formation is considered to be more accelerated if no seaice condition expands in near future. Watanabe et al., 2014 Nature Comm, doi: /ncomms4950 Matsuno et al., 2013 J Plankton Res, 36, Watanabe, E Ocean Modelling, doi: /j.ocemod Watanabe et al., 2012 J Oceanogr 68, Nishino et al., 2011 J Oceanogr 67,