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Transport of Pacific water into the Canada Basin

Transport of Pacific water into the Canada Basin. R. Pickart, Woods Hole Oceanographic Institution M. Spall, Woods Hole Oceanographic Institution B. Corlett Woods Hole Oceanographic Institution Min Li University of the Chinese Academy of Sciences

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Transport of Pacific water into the Canada Basin

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  1. Transport of Pacific water into the Canada Basin R. Pickart, Woods Hole Oceanographic Institution M. Spall, Woods Hole Oceanographic Institution B. Corlett Woods Hole Oceanographic Institution Min LiUniversity of the Chinese Academy of Sciences Peigen Lin Woods Hole Oceanographic Institution, Motoyo Itoh, Takashi KikcuchiJAMSTEC Yiquan Qi Hohai University USCGC Healy in the Chukchi Sea Photo by A. Kowalski

  2. Outline • Brief introduction (motivation, data, numerical model) • Description of how Pacific water progresses from the • Chukchi shelf to the Canada basin • Modified versus unmodified Pacific water • Seasonality of Pacific water transport • Role of the Beaufort Gyre

  3. Pacific water circulation on the Chukchi shelf ~1 Sv of Pacific water ~ 1 Sv of Pacific water

  4. Question: How does Pacific water get from the shelf to the Canada Basin? Hypothesis #1: Primarily advected offshore of Barrow Canyon Hypothesis #2: Subducted across the Chukchi shelfbreak

  5. Hypothesis #1: The Chukchi Slope Current Corlett and Pickart (2017) estimate that the slope current advects 0.5Sv of Pacific Water

  6. Hypothesis #2: Transport across the Chukchi shelf edge Timmermanns et al. (2017) estimate that 0.4 Sv of Pacific water subducts from the mixed-layer of the Chukchi Sea into the Canada Basin halocline

  7. Data used in the study 3 mooring arrays 46 shipboard sections 2002-14 Shipboard data Mooring data plus climatological Bering Strait mooring data from Woodgate et al. (2005)

  8. MIT general circulation model Canada Basin Two-year integration Chukchi Sea

  9. The Chukchi Slope Current Average Section Pot. Temp. Chukchi Slope Current Shelfbreak Jet Shipboard data Abs. Geos. Vel.

  10. The Chukchi Slope Current Average Section PSW PWW AW Pot. Temp. Chukchi Slope Current Shelfbreak Jet Shipboard data Abs. Geos. Vel.

  11. The Chukchi Slope Current Average Section PSW PWW AW Pot. Temp. Chukchi Slope Current Shelfbreak Jet Shipboard data Abs. Geos. Vel.

  12. Pacific water circulation scheme

  13. Pacific water circulation scheme (revised)

  14. Chukchi shelf mass budget Long Strait

  15. Chukchi shelf mass budget Long Strait

  16. Chukchi shelf mass budget Long Strait

  17. Chukchi shelf mass budget Long Strait

  18. Chukchi shelf mass budget Long Strait

  19. Chukchi shelf mass budget Long Strait

  20. Chukchi shelf mass budget Long Strait

  21. The Chukchi Slope Current – mooring data Average Section Pot. Temp. Chukchi Slope Current Shelfbreak Jet Abs. Geos. Vel. Year long depth-integrated vectors 2013-14

  22. The Chukchi Slope Current – mooring data Average Section Chukchi Slope Current Shelfbreak Jet Pot. Temp. Chukchi Slope Current Alongstream velocity Shelfbreak Jet Abs. Geos. Vel. Year-long mean vertical section of alongstream velocity 2013-14

  23. The Chukchi Slope Current – mooring data Seasonal mean sections Average Section summer fall Pot. Temp. Chukchi Slope Current Shelfbreak Jet winter spring Abs. Geos. Vel.

  24. The Chukchi Slope Current – mooring data Seasonal mean sections Average Section summer fall Does the Chukchi Slope Current really emanate from Barrow Canyon? Pot. Temp. Chukchi Slope Current Shelfbreak Jet winter spring Abs. Geos. Vel.

  25. Origin of the Chukchi Slope Current Evidence from surface drifters Stabeno et al. (2018)

  26. Mean depth-integrated flow from the model Beaufort Gyre

  27. Chukchi Slope current from model Chukchi Slope Current Shelfbreak Jet Depth (m) Chukchi Slope Current Shelfbreak Jet Model

  28. Chukchi Slope current from model Chukchi Slope Current Chukchi Slope Current Shelfbreak Jet Depth (m) Shelfbreak Jet Chukchi Slope Current Shipboard Data Model Shelfbreak Jet Mooring Data

  29. MIT general circulation model compute transport across 60m isobath

  30. Model transport across the Chukchi shelfbreak Sverdrups Herald Canyon Barrow Canyon Integrated transport from the western end of the shelf to Barrow Canyon

  31. Model transport across the Chukchi shelfbreak Sverdrups Herald Canyon Barrow Canyon Integrated transport from the western end of the shelf to Barrow Canyon Importantly: We find no evidence of wind-driven subduction distributed along the shelfbreak, casting doubt on hypothesis #1

  32. Two tracers were introduced into the model • Pacific water tracer: given a value of 1 in Bering Strait • Ventilation tracer: continuously set to 1 at the surface of the Chukchi Sea • and set to 0 below the surface only at Bering Strait

  33. Pacific water tracer Barrow Canyon Snapshot of PW tracer concentration at 47 m depth

  34. Pacific water tracer Chukchi Slope Current Shelfbreak Jet Barrow Canyon Snapshot of PW tracer concentration at 47 m depth Mean vertical section of PW tracer across the Chukchi slope

  35. Question: Is the Pacific water modified by air-sea interaction as it crosses the Chukchi shelf? • The product of the PW tracer and the ventilation tracer indicates the • Pacific water that was modified in the surface mixed-layer

  36. Question: Is the Pacific water modified by air-sea interaction as it crosses the Chukchi shelf? • The product of the PW tracer and the ventilation tracer indicates the • Pacific water that was modified in the surface mixed-layer • The product of the PW tracer and one minus the ventilation tracer • indicates unmodified Pacific water

  37. Volume of unventilated Pacific water entire shelf

  38. Volume of unventilated Pacific water (entire shelf) entire shelf Canada Basin

  39. Volume of unventilated Pacific water (entire shelf) entire shelf Canada Basin 25% of the Pacific water transported into the Canada Basin is not ventilated on the Chukchi shelf

  40. Model seasonality of Pacific water transport Bering Strait Transport in Sverdrups

  41. Model seasonality of Pacific water transport Bering Strait Barrow Canyon Transport in Sverdrups

  42. Model seasonality of Pacific water transport Bering Strait Barrow Canyon Chukchi slope current Transport in Sverdrups

  43. Model seasonality of Pacific water transport Bering Strait Barrow Canyon Chukchi slope current Barrow Canyon stratification Transport in Sverdrups

  44. Observed seasonality of Pacific water transport Bering Strait Mooring measurements

  45. Observed seasonality of Pacific water transport Bering Strait Barrow Canyon Mooring measurements

  46. Observed seasonality of Pacific water transport Bering Strait Barrow Canyon Chukchi slope current Mooring measurements

  47. Observed seasonality of Pacific water transport Bering Strait Barrow Canyon Chukchi slope current Beaufort shelfbreak jet Mooring measurements

  48. Relationship between the Beaufort Gyre and Chukchi slope current Solution with no Bering Strait inflow

  49. Relationship between the Beaufort Gyre and Chukchi slope current Solution with no Bering Strait inflow Solution with only Bering Strait inflow

  50. Relationship between the Beaufort Gyre and Chukchi slope current Mean section of alongstream velocity

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