Schauer, Ursula

Tsubouchi, Takamasa

von Appen, Wilken-Jon

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The Arctic Ocean volume, heat and freshwater transports during 2004-2010by Dr. R. Curry at WHOI21 March 2017ASOF meeting @ IOPANTakamasa Tsubouchi Wilken-Jon von AppenUrsula SchauerARCGATE: Maximizing the potential of Arctic Ocean Gateway arrayArctic boundary observationFig. Mooring array during 2008-09, modified from Dickson et al. [2009]Little is known about oceanic heat temporal variabilityThe heat budget in the Arctic OceanThe pan-Arctic approach: progress so farTsubouchi et al. [2012, JGR]• Quasi-synoptic estimate in summer 2005 [Tsubouchi et al., 2012].• First seasonal cycle during 2005-06 [Tsubouchi et al. under review].Objective of this studyQuantify “observation based” multi-year monthly volume, heat, FW transports during 2004-10.Focus period: Oct. 2004 - May 2010 (68 months)Data during 2004-2010Fig. Mooring array in the Arctic four main gates• ~1,000 moored instruments: microCAT (T, S: blue), RCM (T, (S), V: red),  ADCP (V: green).• 37 Repeat CTD sections in south of BSO.• PIOMAS sea ice thickness & velocity data [Zhang and Rothrock, 2003]Filtering and Gridding • De-tided and smoothed with Butterworth filter (27 days cutoff).• Data gaps (> 30days) are filled by its mean annual cycle.• Linear interpolation is applied vertically and horizontally.Daily de-tided (black)Daily smoothed (green)Monthly mean (red)N-S velocity (cm s-1)Monthly Temperature fields• Captures major water mass distributions & variabilities• AW in WSC and BSO, Polar water, large variability in Bering Strait.Temperature at 50m.Monthly in black,average in red.Davis Fram BSO BeringMonthly initial volume transport imbalance• Initial imbalances is -3.0±2.2 Sv.• Of which, below 1,500m accounts for -2.4±0.9 Sv.Full depth (black), above 1,500m (grey).Inverse model: unknowns & constraints• 1287 unknowns are derived from 12 constraints.• Bottom vel (639), Sea ice (639), FW input (1), Diapycnal (8)• Volume & Salt: 5 layers and whole layerObtain volume and salt conserved monthly velocity field for consecutive 68 months.Dickson et al. (2006)Results pan-Arctic volume, heat & FW boundary transports Mean velocity field during 2004-2010(Sv) This study referenceDavis -1.9±1.0 -1.6±0.5(*1)Fram -1.4±1.2 -2.0±2.7 (*2)BSO 2.2±1.0 2.0 (*3)Bering 1.0±0.5 0.8 (*4)Net -0.10±0.06 -0.8*1 Curry et al., 2014, *2 Schauer et al., 2008,  *3 Smerdsrud et al., 2010, *4 Woodgate et al., 2005Table: volume transport comparisonFig. (top) mean volume & salt closed velocity field. (Bottom) cumulative full depth volume transport.• Captures major current system.• Polar water outflow,  AW inflow, PW inflow.  Volume transports: each gateway • Net transport is almost zero in each month.• Seasonality.• Strong BSO inflow in winter.• Strong Bering inflow in summer.(Sv) long term JFM JASDavis -1.9±1.0 -1.8 -2.4Fram -1.4±1.2 -2.0 -1.2BSO 2.2±1.0 +2.9 +2.2Bering 1.0±0.5 +0.8 +1.4Volume transports: water mass • Double cell overturning structure.• AW inflow: strong in winter, weak in summer.• DW outflow (-1.4±0.8 Sv) may be too strong.(Sv) mean JFM JASSURF+UAW -1.0 -1.8 -0.3AW +4.5 +6.0 +3.2IW+DW -3.5 -4.3 -2.9The Heat transports• The heat transport is 180±57 TW (68 monthly ave & std).• Seasonality: ~250TW in Nov, ~100 TW in May.• Inter-annual variability: 196±56 TW in 2004-05, 165±71 TW in 2007-08.*12 monthly ave & std from Oct to following Sep.The FW transports• The FW transport is 156±91 mSv (68 monthly ave & std).• Seasonality: ~250 mSv in Nov-Mar, ~50 mSv in Jun-Aug.• Inter-annual variability: 163±79 mSv in 2004-05, 121±103 mSv in 2007-08.*12 monthly ave & std from Oct to following Sep.Putting into a big picture• Heat budget• 180±57 TW ~ 15.9±5.0 Wm-2• MERRA has the best agreement.NRA ERA40 JRA25 MERRA5 11 14 19Long-term air-sea heat fluxes north of 70˚N (Wm-2)Porter et al. [2010], Cullather & Bosilovich [2012]Note that 10W/m2 is equivalent to 1m sea ice melt in a year.• FW budget• Boundary: 156±91 mSv• Surface: ~214 mSv. Haine et al. [2015]• FW content: ~25 mSv. Rabe et al. [2014]• Imbalance of ~33 mSv - significant?Putting into a big pictureWhat changes by changing Tref?• Total heat transport DOES NOT change.• Temperature transport in each piece of section DOES change.• e.g. WSC: 33±14 TW-eq (1.01±0.18˚C), 113±34 TW-eq (-1.8˚C).Fig.  Accumulative full depth heat transport along sections.What changes by changing Sref?• Total FW transport DOES NOT change (almost).• FW transport in each piece of section DOES change.• e.g. EGC: -4±11 mSv-eq (34.70±0.02), 95±21 mSv-eq (35.2).Fig.  Accumulative full depth FW transport along sections.Take home message• Mass & salt conserved velocity field is crucial to calculate heat & FW transport.• Choice of reference value is arbitrary.• For heat, any value is possible. • For FW, sensible values (34.7-35.2) only introduce error of ~1%.• Recognise the impact of choice of reference values.• Total heat & FW DOES NOT change (For FW, almost).• Partial sectional values DOES change.Data on PANGAEA• One year data is available.• Search Tsubouchi, then you will find it.• 68 month data will be available in this summer.ASOF’s role to promote this study• Endorsement• Gateway to the PANGAEA web link• Present the time series as scientific deliverableWhat is next break though?• Include Greenland-Scotland Ridge section in the box inverse model.• Two boxes - Arctic Ocean & Nordic Seas.• Initial focus period would be 2004-2010 (same as this study).AaGaard et al. [1985, JGR] Eldevik & Nilsen. [2013, JC] Tsubouchi et al. [2012, JGR] Summary• Oceanic volume, heat & FW transports under mass and salt constraints during Oct 2004 - May 2010.• Volume tra. has Seasonality in each gateway and water masses.• Double cell over-turning structure and its seasonality.• Heat transport is 180±57 TW ~ 15.9±5.0 Wm-2• FW transport is 156±91 mSv.• The seasonal & interannual variability in the Heat & FW transports• I am looking for a job. - ideally related work.Acknowledgement• The Arctic main gateways have been measured by six research institutes in the world: UW for Davis Strait and for the US side of Bering Strait; NPI and AWI for Fram Strait; IMR for BSO; UAF and AARI for the Russian side of Bering Strait. • The pan-Arctic approach is developed under two UK NERC projects, ASBO and TEA-COSI. • This work is supported by EU Marie Curie project, ARCGATE. 

The Arctic Ocean volume, heat and freshwater transports during 2004-2010

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