OS33C-01 13:40h
The deep waters of the Arctic Ocean: Recent observations and variability
Hydrographic observations from four icebreaker expeditions to the Arctic Ocean between 1991 and 2001 show evidence of changes in the deep waters of the Arctic Ocean. The deepest waters show 300-1000 m thick homogenous bottom layers, characterized by slightly warmer temperatures compared to ambient, overlying water masses, indicating that they may have formed by convection induced by geothermal heat supplied from Earth's interior. The layers are present in the central parts of the deep basins, away from continental slopes and ocean ridges. The observations also suggest relatively large changes in the deep waters of the Amundsen Basin between 1991 and 2001, with warmer water being present in 2001 over the entire deep-water column.
OS33C-02 INVITED 13:55h
The North Pole Mooring: A Window on the Arctic Ocean
We have maintained an instrumented mooring over the abyssal floor of the Arctic Ocean, about 30 n. mi. from the Pole, since April 2001. The mooring is re-deployed annually and extends to within 50 m of the surface, its instruments measuring temperature and salinity, water and ice velocity, and ice thickness. We find multi-year cooling and freshening trends both in the Atlantic layer and in the deep water. The observed Atlantic layer cooling represents a reversal of the dramatic and widely cited mid-depth warming that began about 15 years ago. The velocity records show numerous eddies in the upper ocean, generally anticyclonic, but there are also eddies that reach much deeper, including a strong five-month event the second year, during which the mooring was drawn down over 60 m. That eddy, which was anomalously warm, saline, and dense in the upper ocean, but warm, fresh, and of relatively low density in the deep water, may have extended to the ocean floor at 4300 m. Overall, the moored record suggests considerable variability in the interior ocean, away from the boundaries along which changes have been presumed to propagate. This variability extends downward at least into the upper deep waters.
OS33C-03 14:30h
Role of oceanic heat flux in the central Arctic Ocean
Recent oceanographic conditions in the eastern Arctic Ocean show remarkable surface salinization and Atlantic water warming compared with conditions prior to 1990s (e.g., Morison et al., 2002). Such a condition might cause an increase in upward oceanic heat flux, but this has not previously been investigated experimentally. Using the ice-drifting buoy data at the North Pole Environmental Observatory, we examine oceanic heat flux under the multiyear ice in the central Arctic Ocean. Upper ocean current and hydrographic data obtained from JAMSTEC Compact Arctic Drifter (J-CAD) buoys are used to estimate oceanic heat flux through seasonal pycnocline (25-50m) and the cold halocline (80-120m). We find that summer ice-melt water completely prevents oceanic heat flux through seasonal pycnocline. This supports the previous result (McPhee et al., 2003) that nearly all of the heat flux to the ice is derived from insolation during summer. In winter, upward heat flux at 25-50m depth is estimated as 2-3 [W/m2] over the basin. On the other hand, upward heat flux through the cold halocline is estimated at 2-4 [W/m2] all through the year. This suggests that heat from the Atlantic water, which passes through the cold halocline, would reach the multiyear ice only in winter.
OS33C-04 14:45h
Change in Beaufort Sea Ice in the 1990s: A Perspective Based on Thickness
A 12-year series of ice-draft measurements by sonar in the eastern Beaufort Sea provides opportunity to examine the impact of the warm 1990s in this area. The results are perhaps surprisingly. The average thickness of ice has changed little. The average ice coverage has changed little, although the coverage by old ice has increased slightly. The year 1998 stands out clearly as an anomaly. There is a large variation in average ice draft throughout the year which is driven by seasonally varying ice drift as well as by the annual cycle of freezing and melting. Inter-annual variation in average ice draft is also large, forced primarily by the impact of changes in average wind on ice circulation. However, year-to-year variation in storminess also appears important, through its impact on the flaw lead and on ridging along the coastal margin. The negligible trend in the average draft of the predominately first-year pack of this area is consistent with data for coastal sea ice over a wide area across northern Eurasia and North America, which span a half century. The trend may also be consistent with recent change in the thickness of pack ice in the central Arctic Ocean, when first-year and multi-year ice are examined separately.
OS33C-05 INVITED 15:00h
Large-Scale Variability in the Nordic Seas: Natural Variability or Climate Change?
From the 1960s to the 1990s the North-Atlantic sector experienced a large-scale change in the atmospheric circulation, going from extraordinary weak westerlies in the '60s to the strongest westerlies ever observed in the '90s. Accompanying this low frequency shift in the atmospheric forcing, astonishingly large changes have been taken place in the Nordic Seas ocean climate. We here review some of the recent findings, including the warming and narrowing of the inflowing Atlantic Water, the freshening of the intermediate water, the weakening of the convection in the Greenland Sea, the warming of the deep waters, and the possible reduction of the overflow waters feeding the Atlantic meridional overturning circulation. These changes, many unprecedented in historical records, are observed in a period with increasing levels of atmospheric CO2. According to most climate models, the result of the greenhouse gas forcing will be much higher air temperatures and increased precipitation over the northern high latitudes, a thinner and smaller ice cover, a more shallow oceanic convection, and finally a reduced overflow and a weakening of the overturning circulation. With all the evidence at hand, it is tempting to ask; are we witnessing the first of many inevitable man-made changes in the Nordic Seas climate?
OS33C-06 INVITED 15:20h
Sources to the East Greenland Current and its Contribution to the Denmark Strait Overflow
The mixing of surface, intermediate and deep waters, with emphasis on the intermediate layer, along the East Greenland Current, from the northern Fram Strait to south of Denmark Strait, is evaluated applying optimum multiparameter (OMP) analysis. The data consist of 14 parameters and were collected in May 2002, using the icebreaker Oden, along 7 sections crossing the Greenland continental margin. The water masses included in the OMP analysis comprise those exiting the Arctic Ocean, the West Spitsbergen Current (WSC) and those formed in the Greenland and Iceland Seas. The waters that overflow the Denmark Strait can be divided into a deeper higher density layer and one that lay on top of this. The high-density water is a mixture of waters having their origin in the Arctic Ocean and Greenland Sea while the water on top of this also has a significant contribution from the WSC.