1 / 19

Bering Strait Mooring Array: Volume, Heat, and Freshwater Fluxes

This summary provides an overview of the Bering Strait mooring array, including volume, heat, and freshwater fluxes. It discusses the revisions made to the flux estimates, the use of modeling to estimate fluxes, and the interannual variability observed in volume transport. The summary also highlights the impact of winds and pressure differences on volume transport and the changes in freshwater and heat transport over time.

angeld
Download Presentation

Bering Strait Mooring Array: Volume, Heat, and Freshwater Fluxes

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. A summary of the Bering Strait mooring array – volume, heat and freshwater fluxes Jonathan Whitefield, Tom Weingartner (UAF) Rebecca Woodgate (UW) Thanks to: Jim Johnson, Dave Leech, Seth Danielson, Kay Runciman, Wendy Ermold, Mike Schmidt, and the scientists and crews of the Alpha Helix, Laurier, Sever, Lavrentiev and Khromov Funding from: NSF-OPP (IPY and AON projects) and NOAA

  2. Location of moorings • Revising the Bering Strait fluxes • Modelling the Bering Strait fluxes • Mooring time series • Volume • Freshwater • Heat • Bering Strait Influence • The future of the Bering Strait moorings…

  3. Moorings • Moorings deployed in the Bering Strait almost continuously since 1990. • IPY and RUSALCAincreased the number to 7 in the Strait since 2007, and another ~60km to the north – A3. • Is A3 a true representation of flow in Bering Strait? • Does it truly account for the ACC? Bering Strait summer SST image (MODIS) showing main moorings () and NCEP wind grid points (X)

  4. Revising the Bering Strait fluxes • Early measurements (1960s and 70s) used arbitrary inferred summer salinity measurements, and estimated volume transport. • Woodgate et al. (2005) use the RUSALCA mooring data to show that the assumed salinity of 32.5 is suitable for an estimate of mean Bering Strait salinity • However, CTD sections and near-shore RUSALCA moorings (A4) showed that temperature, salinity and velocity are not constant across the Strait.

  5. Revising the Bering Strait fluxes • Estimates from instantaneous observations (velocity of ~1 m s-1 and salinity of ~30) suggest ACC adds 0.2 Sv and 220 – 450 km3 yr-1. • Comparable to Yukon River input. • Historical estimates also do not account for stratification and ice transport.

  6. Revising the Bering Strait fluxes • Ice thickness inferred from ADCP records (Travers, UW MS thesis). • Mean ice thickness ~1.4m • Sea ice transports ~140 ± 40 km3 yr-1 of fresh water. • Aagaard and Carmack (1989) underestimated Bering Strait fluxes by 800 – 1000 km3yr-1.

  7. Modelling the Bering Strait fluxes • Use of a high resolution (~16km) global model provides estimates with similar resolution as the mooring array, but does not have any “gaps” in time or space.

  8. Modelling the Bering Strait fluxes • Using a transect across the Bering Strait equivalent to mooring positions, the model estimates: • mean volume transport of 1.1 Sv (increase of 25%) • mean heat transport of 4.2 x 1020 J yr-1 (increase of ~80%) • mean freshwater transport of 2700 km3 yr-1 (increase of ~60%) • These increases are comparable to those suggested by Woodgate et al. (2005, 2006). Whitefield et al., in prep

  9. Volume transport • Every year since 2005, volume transport measured at A3 exceeds the climatological value of 0.8 Sv. • Transport in 2011 is >50% greater than 2001. • However, there appears to be large interannual variability in volume transport, with periods (e.g. 1999 to 2002) with significant negative trends as well. Transport from A3 (blue) and A2 (cyan), including adjustments from 2007-2009 ADCP data for 6-12m changes in instrument depth (black)

  10. Volume transport • Transport solely due to winds always negative (i.e. southwards) • Pressure difference between Pacific and Arctic is main driver with local (and remote) forcing determining magnitude • Short term variability can be ± 4 Sv from the climatology Left: transport from NCEP winds (colours correspond to different grid points, black is mean) Right: transport due to pressure head over weekly (green) or annual (black) scale. Red lines show best fit for 2001 - 2011

  11. Freshwater transport • During RUSALCA period, heat and FW fluxes depend strongly on volume flux changes. • FW flux increased by ~1000km3 yr-1 between 2001 and 2011. • Twice the decadal variability in net precipitation (~ 500km3, Serreze et al, 2006) or Russian Rivers (~400km3, Shiklomanov and Lammers, 2009) Annual FW flux at A3 (blue) and including an estimated 800 – 1000 km3 from ACC and stratification (red)

  12. Heat transport • Annual mean temperature recorded by near-bottom CTDs show warm and cold periods. 2007 and 2011 are warmest on record. • SST from satellite similar to near-bottom A4 (i.e. ACC extends through entire water column), and is cooler in 2008-2011 (larger influence from Bering Sea waters?) • However, due to large variability of volume flux, heat flux in 2011 is 66% greater than 2001, equivalent to enough heat to melt 106 km2 of 1m thick sea ice. Annual mean near-bottom temperature from A3 (blue) and A2 (cyan) moorings, and NOAA SST product (red)

  13. Heat transport • Annual mean temperature recorded by near-bottom CTDs show warm and cold periods. 2007 and 2011 are warmest on record. • SST from satellite similar to near-bottom A4 (i.e. ACC extends through entire water column), and is cooler in 2008-2011 (larger influence from Bering Sea waters?) • However, due to large variability of volume flux, heat flux in 2011 is 66% greater than 2001, equivalent to enough heat to melt 106 km2 of 1m thick sea ice. Annual mean heat fluxes from A3 data (blue) and including a correction for the ACC (red). Black shows heat added by 20m thick surface layer

  14. Bering Strait Influence • NARR winds over Chukchi • 2008 and 2011 have persistent NE winds • 2011 has greater wind velocity than 2008 • 2009 and 2010 and more varied in strength and direction • Expect heaviest sea ice coverage to be in 2011 2008 2009 2010 2011

  15. Bering Strait Influence • Satellite imagery shows ice present in Chukchi until mid-late July for 2008-2010 July 1 July 10 July 20 July 25 2008 2009 2010

  16. Bering Strait Influence • In 2011, there was a two-phase retreat • South to north (early May) • Off AK coast (late May) • ENTIRE SHELF ice free by mid-July 1 10 15 25 May June July

  17. Bering Strait Influence • Both mean annual volume and heat transport increase linearly from 2008 (0.9 Sv; 2 x 1020 J) to 2011 (1.1 Sv; 5 x 1020 J) • 2011 fluxes are similar magnitude to 2007 • Do Bering Strait heat fluxes exert control over ice retreat on the Chukchi Shelf? • Still inconclusive, as we only have 4 years of Chukchi data • Also cannot discount wind influence Annual mean heat fluxes from A3 data (blue) and including a correction for the ACC (red). Black shows heat added by 20m thick surface layer

  18. The future of the moorings… • Is A3 a true representation of flow in Bering Strait? • NO. It provides an estimate of the Russian channel though… • Is A1 more suitable? • Could we down-size the RUSALCA array to a 3 mooring array? • Could we use a model to supplement the observations? A1 

  19. The future of the moorings… • Which areas could/should be observed by new moorings? • Gulf of Anadyr/Cape Navarin • Shpanberg/Anadyr Straits • Location of mooring key, as even flow through Anadyr Strait is non-uniform • North coast of Russia to capture SCC? • Transition between Bering Strait throughflow and Barrow Canyon/Hanna Shoal moorings (e.g. continuation of AIM moorings)? • Improve understanding of Bering Strait influence on Chukchi and other down-stream systems • Any way to improve shallow data collection? • ISCATs at ~18m do not resolve stratification, but shallower instruments are removed by ice.

More Related