1 / 21

1 Climate and Global Dynamics Division, National Center for Atmospheric Research

Role of Bering Strait in the Thermohaline Circulation’s Response to Freshwater Forcing under Present Day and LGM Conditions. 1 Aixue Hu, 1 Bette L. Otto-Bliesner, 1 Gerald A. Meehl, 2 Weiqing Han, 3 Carrie Morrill, 1 Esther C. Brady and 1 Bruce Briegleb.

justine-noel
Download Presentation

1 Climate and Global Dynamics Division, National Center for Atmospheric Research

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Role of Bering Strait in the Thermohaline Circulation’s Response to Freshwater Forcing under Present Day and LGM Conditions 1Aixue Hu, 1Bette L. Otto-Bliesner, 1Gerald A. Meehl, 2Weiqing Han, 3Carrie Morrill, 1Esther C. Brady and 1Bruce Briegleb 1Climate and Global Dynamics Division, National Center for Atmospheric Research 2Department of Atmospheric and Oceanic Sciences, University of Colorado 3NOAA Paleoclimatology Program, National Climatic Data Center J. of Climate, 21, 2239-2258 ahu@ucar.edu

  2. Introduction: Bering Strait The thermohaline circulation is a global ocean circulation. It is driven by differences in the density of the sea water which is controlled by temperature (thermal) and salinity (haline).

  3. Facts about Bering Strait: Present: ~150 km wide; ~50 m deep; 0.8 Sv Flow; 0.08 Sv FW. Sverdrup (Sv) ≡ 106 m3s-1 Question: Does the opening of the Bering Strait at 11,000 yr ago contribute to the Holocene stable climate?

  4. CAM3 with T42 horizontally and 26 levels vertically POP with 1 degree horizontally and 40 levels vertically CSIM5 CLM3 Last Glacial Maximum (LGM) Model and Experiments CCSM2 CCSM3 • CAM2 with T42 horizontally and 26 levels vertically • POP with 1 degree horizontally and 40 levels vertically • CSIM4 • CLM2 • Present day Experiments: 1. Three control runs: one with an open (OBS); Two with closed Bering Strait (CBS, LGM); 2. Three hosing runs with 1 Sv additional fresh water flux uniformly added into the North Atlantic between 50 and 70oN for 100 years, then this flux is switched off.

  5. Lowpass filtered THC and MHT index Control mean THC: 16 Sv OBS 18 Sv CBS 17 Sv LGM Control mean MHT: 0.85 PW OBS 0.95 PW CBS 1.16 PW LGM PW≡1015W THC declines similarly during hosing and the first 50 years after that. However, the recovery of the THC is delayed by about a century in the CBS run than in the OBS run, and delayed further in the LGM run.

  6. OBS LGM CBS OBS LGM CBS

  7. Freshwater transport is defined as: where Vfwdenotes the freshwater transport, vis the meridional velocity, s is the salinity, and s0 is the reference salinity (34.7 psu), dxdz denotes zonal and vertical integration. Note: The cumulative freshwater transport discussed later is normalized by the total additional freshwater input in the North Atlantic during the hosing.

  8. Variations of the Bering Strait Transports

  9. Cumulative freshwater and sea ice export FW, ice transports normalized by total additional FW input

  10. Cumulative freshwater anomalies between 35 and 80oN

  11. Conclusion • THC responses similarly during the hosing and the 50-yr right after that, then the THC recovers earlier in the OBS run than in the CBS and LGM runs, which is associated to the FW export at BS. • This implies that the BS can stabilize the THC and global climate on multi-century timescale.

  12. Changes of the THC (MOC) in the IPCC AR4 models

  13. Theoretical Studies of the Bering Strait and THC De Boer and Nof (2004a, b) indicate that without NADW formation, the 4 Sv of upper ocean water forced into the Atlantic by strong Southern Ocean winds will exit to the Pacific through the open Bering Strait, instead of returning to the Southern Oceans via the lower branch of the THC as NADW under present conditions. This implies that any strong freshwater flux into the North Atlantic would be quickly flushed out of there into the North Pacific by that 4 Sv upper Southern Ocean water. Consequently, the THC would be re-established fairly quickly.

  14. In the CBS run, the Atlantic salinity anomaly is stronger and the Pacific is saltier due to reduced precipitation associated to the colder climate induced by a weaker THC. In the OBS run, the Pacific surface water is fresher and the salinity anomaly in the Atlantic is weaker relative to the CBS run due to the export of FW at Bering Strait to Pacific.

  15. In the OBS run, the stronger cooling in the North Pacific is resulted from the export of the Arctic water and sea ice via Bering Strait. The decrease of the temperature anomaly in the North Atlantic is quicker in the OBS run than in the CBS run associated to the quicker recovery of the THC.

  16. Surface temperature and precipitation anomaly

More Related