Scope of activities

The overall goal of this team is to analyze processes of freshwater (FW) propagation and accumulation in the Arctic gyres: The anticyclonic Beaufort Gyre and cyclonic gyres in the subpolar North Atlantic (Labrador, Irminger, Greenland, Iceland seas). The motivation for this study is to investigate the role of FW on the Arctic climate.

Beaufort Gyre – Sub-polar Gyres: Proshutinsky and Johnson (1997) have shown that the Arctic ocean wind-driven ice drift and water circulation alternate every 5–7 years having cyclonic and anticyclonic circulation regimes with decadal scale period. Proshutinsky et al. (2002) suggested that freshwater and heat exchange between the Beaufort and sub-polar gyre climate systems drive these oscillations. Dukhovskoy et al. (2004, 2006a,b) corroborated this hypothesis employing a relatively simple multi-box model of the Arctic-subarctic climate system. Later, observations have shown that the decadal variability of arctic circulation regimes, well observed in 1946-1996, was interrupted after approximately 2003, and an anticyclonic circulation regime that started in the Arctic in 1997 has been observed until present, lasting at least 19 years instead of the expected 5-7 years. Employing a multi-box model, Proshutinsky et al. (2015) have explained this by increased freshwater fluxes from Greenland and speculated that processes of global warming can result in Arctic cooling. These hypotheses will be tested under this FAMOS-2 theme employing high resolution models able to resolve eddies and narrow boundary currents in order correctly simulate gyres’ dynamics and fresh water and heat fluxes regulating arctic climate circulation regimes.

Freshwater fluxes: The Arctic Ocean and the Greenland Ice Sheet are two sources of FW that potentially may impact the thermohaline circulation in the North Atlantic and influence the climate in the region. The Beaufort Gyre FW has been accumulated in the Arctic Ocean since 1997 driven by persistent anticyclonic regime. Accelerating since the early 1990s, the Greenland Ice Sheet mass loss exerts a significant impact on thermohaline processes in the sub-Arctic seas. It has been hypothesized that the surplus Greenland FW can spread and accumulate in the sub-Arctic seas influencing convective processes there. However, it is unknown by what mechanisms, at what rate, and on what time scales the meltwater propagates into the convective sites of the interior sub-Arctic seas (Greenland, Iceland, Irminger, Labrador seas).

These hypotheses described above have been investigated conducting observations (Beaufort Gyre Exploration study www.whoi.edu/beaufortgyre with it Beaufort Gyre Observing System (BGOS) and numerical modeling to better understand causes and mechanisms of freshwater accumulation and releases in the Beaufort Gyre region. In order to investigate the fate, pathways, and propagation rate of Greenland freshwater in the sub-Arctic seas, numerical experiments using a passive tracer to track the spreading of Greenland freshwater are conducted as a part of the Forum for Arctic Ocean Modeling and Observational Synthesis (FAMOS) effort.

The BGOS observations address the following questions:

  • What is the origin of the salinity minimum in the BG? 
  • How does salinity or FWC in the region change in time? 
  • What are the driving forces of BG water and sea-ice circulation, and what is the state and how stable is the BG system? 

  • How does the BG system change from season to season and from year to year and decade to decade under changing climate? 

  • What is the role of the BG system in Arctic climate variability?

The numerical experiments address the following questions:

  •        What is the influence of Greenland FW on ocean processes in the Arctic / subpolar North Atlantic compared to other FW sources? 
  •        What are the pathways and propagation time scales of Greenland FW in the North Atlantic?
  •        How does Greenland FW propagate into the convective sites in the North Atlantic?  
  •        What is the FW residence time in the seas?
  •        Can freshening of the upper ocean cause substantial changes in the air-sea heat fluxes large enough to impact the Arctic climate?
  •        How does the Greenland FW flux compare to the GSA events (in terms of temporal scales, fate of FW and its impact on ocean processes)?
  •        How is FW propagation simulated in different models? What are the causes of discrepancies in numerical simulations of FW propagation in the region? 

Results from the numerical experiments will provide information necessary for assessing possible consequences of the Beaufort Gyre FW release when the anticyclonic circulation switches to the cyclonic. 


Team leaders

Andrey Proshutinsky
WHOI

Dmitry Dukhovskoy
Center for Ocean-Atmospheric Prediction Studies

Paul Myers
University of Alberta

Wilbert Weijer
Los Alamos National Laboratory


Accomplishments

  • D.S. Dukhovskoy, P.G. Myers, G. Platov, M.-L. Timmermans, B. Curry, A. Proshutinsky, J.L. Bamber, E. Chassignet, X. Hu, C.M. Lee, R. Somavilla, 2016. Greenland freshwater pathways in the sub-Arctic Seas from model experiments with passive tracers. J. Geophys. Res. - FAMOS special issue, doi:10.1002/2015JC011290 
  • Proshutinsky A., R. Krishfield, M-L. Timmermans, W. Williams, S. Zimmerman, M. Yamamoto-Kawai, E. Golubeva, G. Platov, E. Watanabe, D. Dukhovskoy, J. Yang, J. Toole, J. Marshall, J. Scott, G. Manucharayn, T. Armitage and R. Kwok. Causes and consequences of the Beaufort Gyre region freshwater content changes in 2003-2016 (in preparation).

  • Bamber J.L., A. Proshutinsky,  D.S. Dukhovskoy. Land ice freshwater budget of the Arctic and North Atlantic Oceans. Part II: Oceanographic impacts and interpretation (in preparation).

In FAMOS Phase 1, three modeling groups (FSU, U. Alberta, ICMMG) performed numerical experiments with passive tracers for 14 years of integration. Model output fields were compared with observations. Similar work was done for simulations of freshwater accumulation in the Beaufort Gyre region by project participants from Russia (Golubeva and Platov), Japan (Watanabe) and FSU (Dukhovskoy).

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Questions?

Contact Andrey Proshutinsky, Senior Scientist, Woods Hole Oceanographic Institution at aproshutinsky@whoi.edu.