Oceanography of the Beaufort Gyre state and problems

Oceanography of the Beaufort Gyre: state and problems A. Proshutinsky, Woods Hole Oceanographic Institution • Oceanographic conditions of the Beaufort Gyre (BG) are regulated by the BG system (atmosphere, sea ice, and ocean) mechanisms and interactions and will be discussed in the context of the entire Beaufort Gyre system variability. • The major goal of this talk is to show a long-term observational program specifically designed for the Barrow Cabled Observatory (BCO) will contribute to our understanding and prediction of state and variability of the Beaufort Gyre (BG) system, its regulating mechanisms, and impact on Arctic climate. Science and Education Opportunities for an Arctic Cabled Seafloor Observatory An NSF-Supported Community Meeting, Barrow, Alaska 7 – 8 February, 2005

Beaufort Gyre region:

BG in the Arctic climate system Aagaard and Carmack, 1994. BG

Arctic Ocean: vertical stratification

Kara Sea 1– Beaufort Gyre Siberia Laptev Sea Barents Sea 2– Transpolar Drift 2 3 3 – West Greenland current Barrow and Barrow Canyon 1 Greenland Al a sk a Baffin Bay Toporkov, 1970.

Coupling Diagram of the Beaufort Gyre System: Each component of the system stores and exchanges mass and energy differently during different climate regimes. Quantifying and describing the state and variability of these components and their coupling is essential to understand the state and fate of present day Arctic climate. Atmosphere Sea Ice Ocean Mixed Layer Pacific Halocline Atlantic Layer Deep Waters

SOURCES OF INFORMATION: 1. Environmental Working Group (EWG) Atlas of the Arctic Ocean, 1997, 1998 (water temperature and salinity for 1950 s, 1960 s, 1970 s, 1980 s) 2. 1990 -present hydrographic surveys in the Beaufort Sea (submarines, icebreakers, buoys, airborne expeditions, drifting stations) 3. International Arctic Buoy Program (IABP): (sea level pressure, 2 -m air temperature, ice drift vectors for 1979 -present) 4. NCAR/NCEP reanalysis project (6 -hourly SLP and SAT, 1948 present) 5. Satellite based sea ice concentration, drift, surface temperature and other products (1978 -present) 6. Atlases and reference books

Characteristics of the Beaufort Gyre Climate System • Atmospheric system: • Atmospheric system of the BG is regulated by the Arctic Oscillation processes. The origin of these processes is debatable and is beyond our discussion here. In normal oscillating arctic climate conditions the atmospheric part of the BG is responsible for: • Forcing dynamics of anticyclonic and cyclonic circulation regimes (dynamics of AO). • Establishing positive anomalies of air temperature during high AO and negative anomalies during low AO. • Producing positive anomalies of precipitation during high AO and negative during low AO. • Variability of other atmospheric parameters (cloudiness, solar radiation, humidity, wind speed) that change from regime to regime accordingly.

ATMOSPHERE and ICE DRIFT A. Winter SLP and wind C. Winter buoy drift B. Summer SLP and wind D. Summer buoy drift Over the Beaufort Gyre, large-scale atmospheric circulation changes from season to season and alternates between cyclonic (summer) and anticyclonic circulation (winter conditions). High atmospheric pressure prevails over the Beaufort Gyre in winter and low pressure dominates in summer

Seasonal variability of SLP: Solid – Anticyclonic circulation regime Dotted – Cyclonic circulation regime

Seasonal variability of surface winds: Solid – Anticyclonic circulation regime Dotted – Cyclonic circulation regime

ATMOSPHERE and ICE DRIFT A. Winter SLP and wind B. Summer SLP and wind Figure shows that the sea ice drifts anticyclonically in both winter and summer. C. Winter buoy drift D. Summer buoy drift This is because sea ice is driven by winds and ocean currents and in the annual ice drift, the ocean currents dominate wind-driven circulation.

Hydrographic station locations (blue dots) in the 1950 s and 1960 s

Hydrographic station locations (blue dots) in the 1970 s and 1980 s

WATER TEMPERATURE: 5 meters 1950 s 1970 s 1960 s 1980 s Source: EWG, 1997, 1998

WATER TEMPERATURE: 250 M 1950 s 1970 s 1960 s 1980 s Source: EWG, 1997, 1998

WATER TEMPERATURE: 500 M 1950 s 1970 s 1960 s Atlantic water with temperatures higher than 0 C occupies water layer from 300400 to ~1, 000 -1, 500 m in the Canadian Basin 1980 s Source: EWG Atlas, 1997, 1998.

WATER SALINITY: 5 M 1950 s 1960 s Arctic surface waters occupy 30 -50 meter layer with water temperatures at freezing point and relatively low salinities 1970 s 1980 s

WATER SALINITY: 150 M

Salinity distribution in the upper 200 -meter layer Alaska Beaufort Sea Beaufort Gyre Chukchi Sea Ea Se st-S ib a eri a n Laptev Sea Kara Sea Greenland Barents Sea

Top: Left: water salinity (S) at 10 m Right: Salinity section Bottom: Left: water salinity (S) at 100 m Right: Dynamic topography Data source: EWG Atlas, 1997, 1998

Beaufort Gyre mechanism of fresh water accumulation and release Wind cyclonic or anticyclonic Ice Convergence or divergence Ice and water convergence, Fresh water accumulation due to Ekman pumping and sea ice accumulation due to ridging and cooling Beaufort Gyre Fresh water accumulation or release Downwelling in the center and upwelling along continental slope

From Proshutinsky and Johnson, 1997

Parameter Anomaly ACCR Atmospheric vorticity over polar cap N P SLP over the Beaufort Gyre P N Surface wind circulation A C Surface wind speed P N Cloudiness N P Precipitation N P Air temperature N P Sea ice extent P N Sea ice thickness P N Sea ice drift A C Duration of ice melt N P Ocean surface circulation A C Ocean surface water temperature N P N – negative anomaly Ocean surface water salinity P N P – positive anomaly Ocean heat content N P A – anticyclonic (clockwise) Ocean freshwater content P N C – cyclonic (counterclockwise) Storm activity N P River discharge P N Permafrost temperature N P Interpretation of observed and simulated anomalies of environmental parameters for: Ø ACCR -Anticyclonic Circulation Regime, and Ø CCR - Cyclonic Circulation Regime in the Canadian Basin and the Beaufort Gyre.

• Oceanic system: • The oceanic portion of the Beaufort Gyre climate system: • Stabilizes the anticyclonic circulation of sea ice and upper ocean; • Accumulates and releases liquid fresh water and sea ice from the BG; • Governs the ventilation of the ocean in coastal polynyas and openings along shelf-break; • Regulates the circulation and fractional redistribution of the summer and winter Pacific waters; • Determines the pathways of fresh water export from the Arctic to the North Atlantic; • WE ASSUME THAT BARROW CANYON CAN BE USED TO DETECT CHANGES IN THE BG SYSTEN BECAUSE IT AMPLIFIES DYNAMYCS OF THE OCEANIC PORTION OF THE BG

Sea Ice System • • • Sea ice is an intermediate link between the atmosphere and ocean and is a product of interactions between the two. The sea ice system in the BG system is responsible for: Regulating momentum and heat transfer between the atmosphere and ocean. Accumulating and releasing fresh water or salt during meltingfreezing cycle. Redistributing fresh water sources by incorporating first year ice from the marginal seas into the convergent BG circulation, holding it there and transforming it into ridged and thick multiyear ice. Memorizing the previous year’s conditions, buffering variations and reducing abrupt changes. Protecting the ocean from overcooling or overheating (the latter is extremely important for polar biology). Sea ice plays an important role in the storage and redistribution of energy in arctic climate (Overland Turet, 1994).

Surface Water: • Along with sea ice, the surface water is the most active oceanic part of the BG. It is assumed that the surface water follows sea ice drift however its circulation patterns have not been measured directly. • It is important to investigate the processes and mechanisms of heat transformation and variability of FW in the upper layer for a better understanding of the FW role in stabilizing the BG system. • Recent changes in surface water structure were reported by Macdonald et al. (2002). The unusually fresh surface layer and thin ice observed in the Canada Basin interior appear to be manifestations of a complex interaction between wind fields, runoff and ice.

Pacific Water: - The circulation of Pacific water may be coherent with the surface currents but its pathways are not known from direct observations. Recently the vertical structure of this layer and its properties have been revised by Shimada et al. , (2001) and Steele et al. , (2004) where the presence of two types of summer Pacific halocline water and one type of winter Pacific halocline water in the BG were reported. - According to EWG analysis, the total thickness of the Pacific layer in the BG is approximately 150 m. This thickness is subject to temporal variability (Mc. Laughlin et al. , 2003) depending on wind stresses and circulation modes (Proshutinsky et al. , 2002). - It is important to investigate the variability of the different Pacific-origin water components, their circulation patterns and their role in stabilizing or destabilizing the BG climatic flywheel.

Atlantic Water: • The circulation pattern of this water is probably better known, but the role that atmospheric forcing plays in the propagation and transformation of Atlantic-origin waters is poorly understood. • The cyclonic pattern of this water propagation along the continental slope, proposed by Rudels et al. (1994) is supported by some numerical models (Holland, Karcher, Holloway, AOMIP, pers. com. ). However other models (Häkkinen, Maslowski, Zhang, AOMIP, pers. com. ) show anticyclonic rotation of this “wheel”.

Models with cyclonic circulation of Atlantic water MOM high resolution MOM low resolution Global, OPA POM

Models with anticyclonic circulation of Atlantic layer MOM high resolution MOM Finite elements

Atlantic Water: • Mc. Lauglin et al. , (2004) showed that Atlantic water as much as 0. 5 C warmer than the historical record were observed in the eastern Canada Basin. These observations signaled that warm-anomaly Fram Strait waters, first observed upstream in the Nansen Basin in 1990, had arrived in the Canada Basin and BG and confirm the cyclonic circulation scheme. • The collected data show that the Atlantic Waters are in transition and less dense than in previous decades. The impetus for such change requires further investigation.

Deep Water: • There are several hypotheses for the origin of the deep water in the Canada Basin (Timmermans et al. , 2003). • One hypothesis is that deep-water renewal is episodic. Another hypothesis is that the deep water is derived from continuous renewal by shelf water. It has been suggested that brine release on Arctic continental shelves is partly responsible for the formation of water that ventilates the cold Arctic halocline in the upper 200 m. Further, if the salinity of the shelf water in the Arctic increases, then water that presently maintains the halocline can become sufficiently dense to sink into the deep basins. • Presumably these processes were not important in the past but under new climatic conditions their role could be enhanced. This is because the reduction of sea ice extent and the enhanced formation of sea ice in winter as a result may lead to a larger volume of dense water formation (c. f. Mc. Laughlin et al. , 2003), under warmer climate conditions.

BGOS and BSFCO The Beaufort Gyre Observing System (BGOS) is operational since August 2003. The BGOS project is supported by NSF and current support covers 2005 -2008 (including International Polar Year 2007/2008). White starts – CTD stations; Yellow circles – moorings; red triangles – Icetethered profilers (drifting buoys) Mooring equipped with MMP profiler, ULS, ADCP, sediment trap, and bottom pressure recorder (bottom tide gauge) Beaufort Sea floor cable observatory (BGFO) location

Freshwater content (meters) and station locations in 1950 s and 1960 s

Freshwater content (meters) and station locations in 1970 s and 1980 s