Understanding Variations of Volume & Freshwater Fluxes through CAA: Potential Application in Projecting

Future Changes

Youyu Lu, Simon Higginson, Shannon Nudds

Bedford Institute of Oceanography, DFO

Arctic-North Atlantic Interaction(from G Holloway)

Focusing on NW Atlantic:

• Key for global “conveyor belt”

• Freshwater inputs important for deep convection

• Two routes: east or west of Greenland – which one is more important?

Monitoring at Key Locations (DFO Involved)

CAA Not Resolved by Climate Models (due to complicated small-scale geometry)

An Approach to Forecasting/Projecting Long-term Changes in CAA

1. High-resolution simulations – limited duration

2. Analysis to understand forcing mechanisms

3. Derive statistical relationship with large-scale forcing

4. Forecasting/projecting with outputs of large-scale forcing from climate models

This combined dynamical + statistical approach can be applied to a wide range of problems

NEMO Configurations: BIO pan-NEMO Configurations: BIO pan-ArcticArctic

• Pan-Arctic 18 km grids;

also include nested CAA 6 km grids;

• Pan-Arctic 6 km

• Grid spacing nearly uniform

Validation Example: Sea-ice Drift Model vs Ice Buoy

June 1999 December 1999

Sea-ice Drift: Model vs Ice Buoy

June 1999 December 1999

Volume Fluxes Through CAA

High correlation between BIO 6 km Arctic model & GLORYS v2 global ocean reanalysis

Freshwater Fluxes Through CAA

Less correlated than volume flux – due to difference in salinity field. Needs further validation/study.

Mean Fluxes during 1998-2007Location Model Volume

Flux (Sv)FW Flux (mSv)

FW Flux Ice (mSv)

Nares Strait Glorys2v1 0.79 (0.27) 10.17 (3.90) 3.34 (3.29)

Arctic 6km 1.14 (0.56) 25.05 (12.57) 5.48 (5.01)

Lancaster Sound Glorys2v1 1.31 (0.23) 61.40 (12.62) 6.63 (3.85)

Arctic 6km 0.98 (0.32) 45.60 (11.79) 7.30 (5.07)

Barrow Strait Glorys2v1 1.42 (0.27) 65.20 (17.31) 7.45 (5.14)

Arctic 6km 1.15 (0.35) 54.93 (15.00) 9.33 (6.57)

Davis Strait Glorys2v1 2.43 (0.55) 55.62 (16.27) 13.53 (14.65)

Arctic 6km 2.07 (0.80) 71.28 (12.67) 12.91 (14.25)

Fram Strait Glorys2v1 1.73 (0.96) 5.70 (4.50) 69.57 (40.29)

Arctic 6km 1.62 (1.57) 19.85 (10.36) 22.23 (18.53)

Indeed, FW transport from CAA is larger than that from east of Greenland.

What drives Fluxes Through CAA?

Upstream influence – wind in Beaufort

Sea (Peterson et al)

What drives Fluxes Through CAA?

Downstream influence – Sea level in Baffin Bay (McGeehan & Maslowski 2012)

Analysis of 6 km Model: Seasonal Cycle in Barrow Strait

Model agrees quite well with obs at southern side

Seasonal Cycle in Davis Strait

Clear difference between western & eastern sides

Seasonal Cycle in Fram Strait

Clear difference between western & eastern sides

Seasonal Cycles of Volume & FW Fluxes

Further Work

• Analyze correlation with forcing

• Determine how forcings operate: barotropic or baroclinic processes?

• Develop regression models: link flux variations to large-scale forcing

Summary

• Model results suggest that freshwater transport though CAA is larger than that from east of Greenland

• Two forcing mechanisms (up- & down-stream) have been proposed by previous studies. This analysis suggests that both mechanisms operate – depending on seasons & locations

• Understanding mechanisms may help to develop regression models: linking CAA transports to large-scale forcing

• This combined dynamical + statistical approach can help climate projection, and is useful for solving a lot of other problems