Arctic Ocean Fresh Water Observational and Model Results A.Proshutinsky, Collaborators: R. Krishfield, M-L. Timmermans, J. Toole, Woods Hole Oceanographic Institution E. Carmack, F. Mclaughlin, Institute of Ocean Sciences, Canada M. Itoh, K. Shimada JAMSTEC, Japan 12 th AOMIP workshop Woods Hole Oceanographic Institution, Woods Hole, Massachusetts January14 th, 2009

Climatology of freshwater content in the Arctic Basin (shown in colors). Solid lines depict mean salinity at 50m. Freshwater content is calculated relative to salinity 34.8 based on data from EWG (1997, 1998) annually averaged for all decades. The Beaufort Gyre region is bounded by thick blue lines.

FWC (in m) in the Arctic Ocean based on EWG Atlas [1997, 1998] for 1950s, 1960s, 1970s, and 1980s in winter. The BG region is bounded by thick blue lines. Numbers in upper right corner show FWC in the entire region (in km3).

The composition of the Beaufort Gyre Observing System (BGOS) by year. Large yellow circles show mooring locations (A, B, C, and D indicated in 2005); small white circles show locations of CTD stations and white crosses depict locations of XCTD castings; and red triangles with gray lines depict ice beacon and ITP deployment locations with their trajectories;. Background colors show bathymetry from the International Bathymetric Chart of the Arctic Ocean (IBCAO, Jacobson et al., 2000).

Drift trajectories (colored lines) of ITPs which data are used in this study. The end location of each ITP is marked by a white triangle which includes the ITP number. Also shown are the BGOS mooring locations (filled yellow circles with mooring letter identifiers), and bathymetric contours from the IBCAO. More detailed plots of each ITP drift and data are available at the ITP website (

Decadal FWC distributions. Colors and contours show BG FWC (in m) relative to salinity Numbers in bottom left corners of each panel show regional summer FWC volume (in km3) for each decade. Data for are from summer EWG gridded fields. Black dots show locations of stations with CTD data used for analysis. The 1990 and 2000 data are discussed in the text.

Late summer FWC distribution characteristics. Colors and contours show BG FWC (in m) relative to salinity Numbers in bottom left corners of each panel show regional summer FWC volume (in km3) for each year. Black dots show locations of stations with CTD data used for analysis. Bottom panel shows FWC trends calculated based on CTD station data and then interpolated/extrapolated over the entire grid.

FWC time series (in m) from MMPs and time series of sea ice draft (in m) from ULSs (bottom panel) from BGOS moorings for Dotted lines show FWC trends. Ice draft trends are also shown in the bottom panel as dashed black lines.

Anomalies of means FWC time- series for moorings A, B, C and D. Top panel shows liquid water (solid) and sea ice (dashed) FWC anomalies. Middle panel shows the total FWC (ice and water), and bottom panel shows the liquid FWC changes due to Ekman pumping.

Conceptual mechanisms of freshwater accumulation and release in the BG during a seasonal cycle. Freshwater content in summer and winter is shown in meters (isolines) calculated relative to salinity 34.8.

Sea ice and wind seasonal and annual (bottom) motion curls (x1E3) in the BG region. Yellow bars show parameters for cyclonic and red bars for anticyclonic circulation regimes (see Proshutinsky and Johnson [1997] circulation regime definition). Under cyclonic circulation when wind and ice move counterclockwise, the ice and surface water diverge and Ekman pumping results in the fresh water release from the BG region. Under anticyclonic circulation regime when wind and sea ice move clockwise, the ice and surface water converges and Ekman pumping leads to the accumulation of fresh water in the region in the fresh water release from the BG region.

Conclusions Our 1990-present analysis indicates major shifts in the amount and distribution of the Arctic Ocean fresh-water content (FWC) when compared with climatology of s. There has been substantial freshening in the Canada Basin, while FWC has decreased in the Eurasian Basin. The total BG fresh water storage did not change significantly from decade to decade in the s period. However, the 1990s conditions differ significantly from the pre-1990s climatology: the center of the FWC maximum shifted to the southeast and appeared to contract in area relative to climatology. In spite of this areal reduction, the spatially-integrated BG FWC increased by approximately 2,000 km3 relative to climatology, while lateral gradients of dynamic height increased. In addition to a spin-up of the BG, the baroclinic part of the Transpolar Drift current intensified and shifted toward Canada suggesting that the freshwater flux has been intensified as well and will continue delivering the fresh water to the North Atlantic at rates higher than at climatologically mean conditions.

Conclusions The fresh water field in the Arctic is in transition; the system is not presently in steady state (a balance between FWC accumulation and release) in spite of more than 10 years of the prevailing atmospheric anticyclonic circulation regime ( ). There are strong FWC positive trends in in BG the region suggesting the future large changes in the FW flux to the North Atlantic.

AOMIP FWC coordinated study This research will attempt to answer the fundamental questions: How does fresh water enter the Arctic Ocean system? How does it move about including undergoing phase changes? How does it finally exit the system?

1. We have to evaluate how well models can reproduce pan-Arctic freshwater and heat budgets by comparison of model outputs with budgets of Serreze et al. (2006, 2007). We anticipate that most (but perhaps not all) models will achieve freshwater and heat balance in the upper layers including the Atlantic water layer after several decades. How these balances are actually achieved will provide insight into model physics. AOMIP FWC coordinated study

2. How well the models can reproduce the basic water mass structure of the Arctic Ocean? For example, our comparison of modeled late winter sea surface salinity within the Beaufort Gyre from an early AOMIP study (Steele et al., 2001). indicates a salty bias in this variable which had not been clearly shown until then. Addressing causes of this bias, Zhang and Steele (2007) show how the magnitude of numerical vertical mixing can affect salinity structure within the Beaufort Gyre. AOMIP FWC coordinated study

3. How do models reproduce transformations of sea ice in the arctic ocean and processes of fresh water accumulation and release? AOMIP FWC coordinated study

4. It is important to reconstruct fresh water distribution in the Arctic Ocean, its variability, storage dynamics 5. and determine causes of change, and rates of it transport to the North Atlantic via Canadian and Fram Straits. 6. Recommendation about the mostly effective observational system are also planned to be provided AOMIP FWC coordinated study

Close collaboration between AOMIP and ASOF (Arctic Subarctic Ocean Fluxes) is needed. The Observational domain of ASOF and the model focus domain of AOMIP fit ideally. The observational database would need considerable effort. AOMIP FWC coordinated study

How to do this? Different groups will do this analysis differently. 1.MIT will carry out two 12-year model runs forced by conditions corresponding to low and high AO indices. This analysis is timely considering the growing body of literature attributing changes in the Arctic to the NAO and its projected intensification in response to rising levels of greenhouse gases (Dickson et al. 2000; Morison et al. 2000; Peterson et al. 2005; Stephenson et al. 2006). 2.The NPS group will lead an effort to test the importance of model resolution on accurately resolving the exchange of water between the Arctic and the Pacific and North Atlantic. Coarse models do not to resolve some straits, although they have been shown to be important for obtaining a decent representation of the MOC (Wadley and Bigg, 2002). We will address this idea by (i) closing the Canadian Archipelago and/or Bering Strait, and examine the response of the Arctic freshwater budget, and (ii) run models with specified observed current measurements. For the latter, we will run models for two cases with idealized/constant parameters and with observed water temperature, salinity and transport. 3. It is also important to investigate 1.Other AOMIP groups interested in these activities will repeat these experiments with their models or will be involved in data analysis.