Kelly Kenison Falkner

Connections among ice, runoff and atmospheric forcing in the Beaufort Gyre

During SHEBA, thin ice and freshening of the Arctic Ocean surface in the Beaufort Sea led to speculation that perennial sea ice was disappearing [McPhee et al., 1998]. Since 1987, we have collected salinity, δ18O and Ba profiles near the initial SHEBA site and, in 1997, we ran a section out to SHEBA. Resolving fresh water into runoff and ice melt, we found a large background of Mackenzie River water with exceptional amounts in 1997 explaining much of the freshening at SHEBA. Ice melt went through a dramatic 4–6 m jump in the early 1990s coinciding with the atmospheric pressure field and sea-ice circulation becoming more cyclonic. The increase in sea-ice melt appears to be a thermal and mechanical response to a circulation regime shift. Should atmospheric circulation revert to the more anticyclonic mode, ice conditions can also be expected to revert although not necessarily to previous conditions.

Tracer?derived freshwater composition of the Siberian continental shelf and slope following the extreme Arctic summer of 2007

We investigate the freshwater composition of the shelf and slope of the Arctic Ocean north of the New Siberian Islands using geochemical tracer data (? 18O, Ba, and PO*4) collected following the extreme summer of 2007. We find that the anomalous wind patterns that partly explained the sea ice minimum at this time also led to significant quantities of Pacific?derived surface water in the westernmost part of the Makarov Basin. We also find larger quantities of meteoric water near Lomonosov Ridge than were found in 1995. Dissolved barium is depleted in the upper layers in one region of our study area, probably as a result of biological activity in open waters. Increasingly ice?free conditions compromise the quantitative use of barium as a tracer of river water in the Arctic Ocean.

Wind-driven transport pathways for Eurasian Arctic river discharge

Distributions of temperature, salinity, and barium in near-surface waters (depth ≤ 50 m) of the Laptev Sea and adjacent areas of the Arctic Ocean are presented for the summers of 1993, 1995, and 1996. The tracer data indicate that while fluvial discharge was largely confined to the shelf region of the Laptev Sea in the summer of 1993, surface waters containing a significant fluvial component extended beyond the shelf break and over the slope and basin areas north of the Laptev Sea in the summers of 1995 and 1996. These distributions of fluvial discharge are consistent with local winds and suggest two principal pathways by which river waters can enter the central Arctic basins from the Laptev Sea. When southerly to southeasterly wind conditions prevail, river waters are transported northward beyond the shelf break and over the slope and adjacent basin areas. These waters can then enter the interior Arctic Ocean via upper layer flow in the vicinity of the Lomonosov Ridge. Under other wind conditions, river waters are steered primarily along the inner Laptev shelf and into the East Siberian Sea as part of the predominantly eastward coastal current system. These waters then appear to cross the shelf and enter the interior Arctic Ocean via upper layer flow aligned roughly along the Mendeleyev Ridge. The extent to which either pathway is favored in a given year is largely determined by local wind patterns during the summer months, when fluvial discharge is greatest and shelf waters are at the lowest salinity of their annual cycle.

Ocean circulation and properties in Petermann Fjord, Greenland

The floating ice shelf of Petermann glacier interacts directly with the ocean and isthought to lose at least 80% of its mass through basal melting. Based on three opportunisticocean surveys in Petermann Fjord we describe the basic oceanography: the circulationat the fjord mouth, the hydrographic structure beneath the ice shelf, the oceanic heatdelivered to the under‐ice cavity, and the fate of the resulting melt water. The 1100 m deepfjord is separated from neighboring Hall Basin by a sill between 350 and 450 m deep.Fjord bottom waters are renewed by episodic spillover at the sill of Atlantic water from theArctic. Glacial melt water appears on the northeast side of the fjord at depths between200 m and that of the glacier’s grounding line (about 500 m). The fjord circulation isfundamentally three‐dimensional; satellite imagery and geostrophic calculations suggest acyclonic gyre within the fjord mouth, with outflow on the northeast side. Tidal flowsare similar in magnitude to the geostrophic flow. The oceanic heat flux into the fjordappears more than sufficient to account for the observed rate of basal melting. Cold,low‐salinity water originating in the surface layer of Nares Strait in winter intrudes farunder the ice. This may limit basal melting to the inland half of the shelf. The melt rate andlong‐term stability of Petermann ice shelf may depend on regional sea ice cover andfjord geometry, in addition to the supply of oceanic heat entering the fjord.

High‐resolution measurements of dissolved organic carbon in the Arctic Ocean by in situ fiber‐optic spectrometry

Here we report results from an extensive survey of dissolved organic carbon (DOC) in the Arctic Ocean, which was achieved by means of a high-resolution, in situ UV fluorometer deployed on a nuclear submarine. Based on a strong linear correlation observed between fluorescence (320 nm excitation, 420 nm emission) and organic carbon concentrations determined directly by high-temperature combustion, a continuous record of DOC was produced at a keel depth of 58 m along a 2900-km transect north of the Beaufort, Chukchi, East Siberian and Laptev seas. The DOC record, combined with other physical and chemical measurements, identifies areas where river waters cross the shelves and enter the circulation of the Arctic interior. Fluvial sources were found to account for 12-56% of the total DOC in parts of the upper Makarov and Amundsen basins.

An Observational Estimate of Volume and Freshwater Flux Leaving the Arctic Ocean through Nares Strait

Abstract The Arctic Ocean is an important link in the global hydrological cycle, storing freshwater and releasing it to the North Atlantic Ocean in a variable fashion as pack ice and freshened seawater. An unknown fraction of this return flow passes through Nares Strait between northern Canada and Greenland. Surveys of ocean current and salinity in Nares Strait were completed in the summer of 2003. High-resolution data acquired by ship-based acoustic Doppler current profiler and via hydrographic casts revealed subtidal volume and freshwater fluxes of 0.8 ± 0.3 Sv and –25 ± 12 mSv (Sv = 103 mSv = 106 m3 s−1), respectively. The observations resolved the dominant spatial scale of variability, the internal Rossby radius of deformation (LD ∼9 km), and revealed a complex, yet coherent along-channel flow with a Rossby number of about 0.13, close to geostrophic balance. Approximately one-third of the total volume flux was associated with across-channel slope of the sea surface and two-thirds (68%) with across-cha...

North Pole Environmental Observatory delivers early results

Scientists have argued for a number of years that the Arctic may be a sensitive indicator of global change, but prior to the 1990s, conditions there were believed to be largely static. This has changed in the last 10 years. Decadal-scale changes have occurred in the atmosphere, in the ocean, and on land [Serreze et al., 2000]. Surface atmospheric pressure has shown a declining trend over the Arctic, resulting in a clockwise spin-up of the atmospheric polar vortex. In the 1990s, the Arctic Ocean circulation took on a more cyclonic character, and the temperature of Atlantic water in the Arctic Ocean was found to be the highest in 50 years of observation [Morison et al., 2000]. Sea-ice thickness over much of the Arctic decreased 43% in 1958–1976 and 1993–1997 [Rothrock et al., 1999].

Spatial continuity of measured seawater and tracer fluxes through Nares Strait, a dynamically wide channel bordering the Canadian Archipelago

Freshwater delivered as precipitation and runoff to the North Pacific and Arctic oceans returns to the Atlantic principally via the Canadian polar shelf and Fram Strait. It is conveyed as ice or freshened seawater. Here we use detailed ship-based measurements to calculate a snap-shot of volume, freshwater, and tracer fluxes through Nares Strait, a 500-km long waterway separating Greenland and Ellesmere Island. We use quasi-synoptic observations of current by ship-mounted acoustic Doppler current profiler (ADCP), of salinity and temperature by CTD probe and of dissolved nutrients by rosette bottle sampler on four cross-sections between 82 and 78N latitude. Data were collected during the first half of August 2003. We partition the fluxes into components derived from Pacific and Atlantic inflows into the Arctic Ocean. During the time of the survey, there was a net southward 0.91 0.10 Sv (10 m s) flux of volume and a net southward 31 4 10 Sv (977 127 km y) flux of freshwater relative to a salinity of 34.8. Much of the volume flux was carried within a strong (40 cm s), narrow (10 km) subsurface jet hugging the western (Ellesmere Island) side of the strait. The presence of this jet in four sections spanning the 500-km length of the strait is evidence of a buoyant boundary current through the strait. The jet was coincident with elevated concentrations of phosphate (1.0 mmol m) and silicate (11 mmol m) which both indicate a Pacific Ocean source. We interpreted the ratio of dissolved total inorganic nitrogen to phosphate in terms of fractional dilution of Atlantic by Pacific waters. About 0.43 0.10 Sv (39%) of the southward flow was of Pacific origin. These results are a snapshot during the summer of 2003 following a prolonged period of northward directed wind stress when ice cover was mobile. Although long-term mean values are likely different, we determined that the major fraction of the through-flow is carried by a jet of scale determined by the internal Rossby radius (5-10 km).

Sources and fate of freshwater exported in the East Greenland Current

Monitoring the sources and fate of freshwater in the East Greenland Current (EGC) is important, as this water has the potential to suppress deep convection in the Nordic and Labrador Seas if the outflow of freshwater from the Arctic Ocean increases in response to climate change. Here, hydrographic, oxygen isotope ratio and dissolved barium concentration sections across Denmark Strait collected in 1998 and 1999 are used to determine the freshwater composition of the EGC at these times. Comparison of meltwater fluxes at Denmark Strait and Fram Strait indicates a net melting of sea ice into the EGC between these two locations, with a significant proportion of sea ice drifting into the Nordic Seas or on to the East Greenland Shelf. We conclude that the phase of freshwater exiting the Arctic Ocean through Fram Strait is important in determining its possible impact on deep water formation in the Nordic and Labrador Seas.

Context for the Recent Massive Petermann Glacier Calving Event

On 4 August 2010, about one fifth of the floating ice tongue of Petermann Glacier (also known as Petermann Gletscher ) in northwestern Greenland calved (Figure 1). The resulting ice island had an area approximately 4 times that of Manhattan Island (about 253±17 square kilometers). The ice island garnered much attention from the media, politicians, and the public, who raised concerns about downstream implications for shipping, offshore oil and gas operations, and possible connections to Arctic and global warming. Does this event signal a change in the glaciers dynamics? Or can it be characterized as part of the glaciers natural variability? Understanding the known historical context of this event allows scientists and the public to judge its significance.