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 (106 m3 s-1) flux of volume and a net southward 31±4 10-3 Sv (977±127 km3 y-1) flux of freshwater relative to a salinity of 34.8. Much of the volume flux was carried within a strong (40 cm s-1), 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-3) and silicate (11 mmol m-3) 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)

An investigation of the marine geochemistry of gold

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1989.Vita.Includes bibliographical references (leaves 94-101).by Kelly Kenison Falkner.Ph.D

Sea ice melt and meteoric water distributions in Nares Strait, Baffin Bay, and the Canadian Arctic Archipelago

Sea ice melt (SIM), meteoric water (river runoff net precipitation), and Pacific seawater contributions to the upper waters of the Canadian Arctic Archipelago (CAA), Nares Strait, and Baffin Bay during late summer 1997 and 2003 are estimated from salinity, δ18O, and nutrient data. Salinity-δ18O relationships within the study area suggest that the CAA inherits a net sea-ice formation (brine) signal from the Arctic Ocean. Inherited brine complicates the estimation of local contributions from sea ice melt and glacial runoff, especially where a significant component of the surface water derives from Arctic outflow. Our data are characterized by two linear relationships between salinity and δ18O, reflecting: (1) the mixing of deeper Atlantic seawater with brine-enriched halocline water of shelf origin and (2) mixing of halocline water with shallower waters freshened by meteoric water and local SIM. Inventories of Pacific water, meteoric water, net SIM, and local SIM were computed over the upper 150 m of the water column. Positive local SIM fractions were ubiquitous during late summer, with the largest inventories (\u3e1 m) found on the eastern sides of Baffin Bay, Kennedy Channel, and Davis Strait. In the CAA and Baffin Bay, freshwater inventories were dominated by contributions from meteoric and Pacific water, with little input from local SIM. In Smith Sound, where comparable data were collected in 1997 and 2003, meteoric water inventories of 8–10 m were similar for both years, whereas the Pacific water inventory was substantially lower in 2003 (\u3c80 m) than in 1997 (\u3e100 m), implying that the export of meteoric water from the Arctic Ocean is decoupled from Pacific water outflow

Oxygen isotope ratio, barium and salinity in waters around the North American coast from the Pacific to the Atlantic: Implications for freshwater sources to the Arctic throughflow

In 2002, oxygen isotope ratios of water (H218O/H216O), dissolved barium, and salinity were measured in surface waters around northern North America to identify freshwater sources and to provide a large-scale background for interpretation of regional inputs and processes. Oxygen isotope ratios showed that precipitation, river runoff, and sea ice meltwater were all significant contributors to the freshwater carried by the coastal component of the Arctic throughflow. Precipitation and runoff contributed \u3c40% and \u3e60%, respectively, to the freshwater found in surface waters along the Pacific coast. Sea ice meltwater contributed up to 65% to waters residing near the Mackenzie River and in the Canadian Arctic Archipelago. The salinity-barium relationship, after being corrected for dilution by sea ice meltwater, indicated that freshwater from the Mackenzie River flowed eastward into Amundsen Gulf. It did not, however, continue eastward through Dolphin Union Strait and Coronation Gulf in 2002. In the eastern part of the Canadian Arctic Archipelago, Baffin Bay and the Labrador Sea, barium concentrations in surface waters were low, the result of biological activity and/or local freshwater inputs with low barium concentrations

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

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 (L[subscript]D ~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-channel slope of isopycnal surfaces. During the period of observation, sustained wind from the southwest weakened the average down-channel flow at the surface. The speed of tidal currents exceeded subtidal components by a factor of 2. Tidal signals were resolved and removed from the observations here using two independent methods resolving horizontal and vertical variability of tidal properties, respectively. Tidal current predictions from a barotropic model agreed well with depth-averaged observations in both amplitude and phase. However, because estimates of freshwater flux require accurate surface currents (and salinity), a least squares fitting procedure using velocity data was judged more reliable, since it permits quantification of vertical tidal current variations

Hydrographic Changes in Nares Strait (Canadian Arctic Archipelago) in Recent Decades Based on δ18O Profiles of Bivalve Shells

Nares Strait is one of three main passages of the Canadian Archipelago that channel relatively fresh seawater from the Arctic Ocean through Baffin Bay to the Labrador Sea. Oxygen isotopic profiles along the growth axis of bivalve shells, collected live over the 5 – 30 m depth range from the Greenland and Ellesmere Island sides of the strait, were used to reconstruct changes in the hydrography of the region over the past century. The variability in oxygen isotope ratios is mainly attributed to variations in salinity and suggests that the northern end of Nares Strait has been experiencing an increase in freshwater runoff since the mid 1980s. The recent changes are most pronounced at the northern end of the strait and diminish toward the south, a pattern consistent with proximity to the apparently freshening Arctic Ocean source in the north and mixing with Baffin Bay waters as the water progresses southward. This increasing freshwater signal may reflect changes in circulation and ice formation that favor an increased flow of relatively fresh waters from the Arctic Ocean into Nares Strait.Le détroit de Nares est l’un des trois principaux passages de l’archipel canadien qui canalise de l’eau de mer relativement fraîche de l’océan Arctique jusqu’à la mer du Labrador en passant par la baie de Baffin. Les profils de la composition isotopique de l’oxygène le long de l’axe de développement des coquillages bivalves recueillis en vie à une profondeur variant entre 5 à 30 m des côtés du détroit à la hauteur du Groenland et de l’île d’Ellesmere ont servi à reconstruire les changements ayant caractérisé l’hydrographie de la région au cours du dernier siècle. La variabilité en matière de ratio d’isotope de l’oxygène est principalement attribuable aux variations de salinité, ce qui laisse entendre que l’extrémité nord du détroit de Nares connaît une augmentation de l’écoulement d’eau douce depuis le milieu des années 1980. Les changements récents sont plus prononcés à l’extrémité nord du détroit et diminuent en arrivant vers le sud, ce qui constitue une tendance conforme à la proximité de la source de l’océan Arctique en dessalure apparente dans le nord et qui se mélange avec les eaux de la baie de Baffin au fur et à mesure que l’eau progresse vers le sud. Cette augmentation de la présence d’eau douce peut être le reflet de changements en matière de circulation et de formation de la glace qui favorisent un écoulement accru d’eaux relativement douces en provenance de l’océan Arctique et se jettent dans le détroit de Nares

Quantitative considerations of dissolved barium as a tracer in the Arctic Ocean

Dissolved barium (Ba) was measured along transects across Fram and Denmark Straits as part of the 1998 ARK-XIV/2 Polarstern expedition. Results are combined with other available tracer observations to analyze water mass composition at Fram Strait. A combination of Pacific water and Eurasian river runoff dominated (>80% and >10% of the total mass, respectively) the upper East Greenland Current (EGC), while the remainder of the section was dominated by North Atlantic water. A much smaller contribution of Pacific water to the EGC (≈50%) at Fram Strait in 1987 suggests that this component can be quite variable in time. North American river water was not detectable at Fram Strait in 1998. Presumably, the Eurasian river water we observed at Fram Strait transited eastward along shelf within the Arctic, mixed with Pacific water in the vicinity of the East Siberian Sea, and was borne by the transpolar drift across the Arctic Ocean. In the absence of significant net ice formation along the way such a pathway can be expected to produce more pronounced freshening of the EGC than when Eurasian river water mixes more directly off shelf into salty Atlantic waters and Pacific water is diverted largely through the Canadian archipelago. Existing measurements at the main Arctic gateways were used to construct a Ba budget for the Arctic Ocean under conditions of simultaneous mass, heat, and salt conservation. This preliminary budget is statistically consistent with the steady state hypothesis. On the Arctic basin scale, Ba appears to be conservative.Keywords: dissolved barium, tracer, Arctic OceanKeywords: dissolved barium, tracer, Arctic Ocea

Relaxation of central Arctic Ocean hydrography to pre-1990s climatology

Upper ocean hydrography in the central Arctic Ocean has relaxed since 2000 to near-climatological conditions that pertained before the dramatic changes of the 1990s. The behavior of the anomalies of temperature and salinity in the central Arctic Ocean follow a first-order linear response to the AO with time constant of 5 years and a delay of 3 years.Keywords: climate change, Arctic oceanograph

Temporal variability of Cd, Pb, and Pb, isotope deposition in central Greenland snow

We present a decade-long (1981–1990) high-resolution (subseasonal) record of Pb and Cd concentrations and Pb isotopic composition in a series of 119 snow samples from a 6-m snow pit at Summit, Greenland. Both metals show order of magnitude seasonal variability, with maxima in spring of every year, coinciding with sulfate peaks. These short-term features complicate attempts to quantify secular decadal-scale trends associated with anthropogenic source changes (e.g., phasing out of leaded gasoline). A small (<50%) decrease during the decade is estimated for Pb, but no significant trend is observed for Cd. Mean concentrations for the snow pit (Pb = 216, Cd = 11 pmol kg¯¹) are indistinguishable from mean values for nearly continuous samples of the 1–6 m section of a firn core drilled 1 km away, suggesting freedom from contamination artifact. An evaluation of potential sources confirms that Pb and Cd are dominated by anthropogenic inputs. Isotopic ratios (²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁷Pb) determined on a subset of snow pit samples of varying ages within the decade indicate that springtime Pb concentration maxima are consistent with a mixture of eastern European, former Soviet Union, and western European sources, while seasonal Pb minima, especially from the early portion of the decade, plot along a different mixing line, suggesting a mixture of U.S. and European sources. The combination of Pb concentration and isotopic composition are consistent with an estimated decrease in U.S. Pb contributions of about twofold over the decade, which predicts a decadal concentration decrease in the snow of ~30%. However, the secular trends in both concentration and isotopes are barely detectable against seasonal and interannual variability. The evidence for seasonally distinct source regions may be useful for interpretation of high-resolution records of other chemical species in Greenland snow and ice. Analyses of two deep core sections dated at 1699–1700 and 1780–1788, compared to the snow pit data, indicate that both Pb and Cd deposition in central Greenland roughly doubled during the eighteenth century, then doubled again by the 1980s.Keywords: snow, Greenland, lead, pollution, cadmium, trace metal

Atlantic water circulation over the Mendeleev Ridge and Chikchi Borderland from thermohaline intrusions and water mass properties

Hydrographic and tracer data from 2002 illustrate Atlantic water pathways and variability in the Mendeleev Ridge and Chukchi Borderland (CBLMR) region of the Arctic Ocean. Thermohaline double diffusive intrusions (zigzags) dominate both the Fram Strait (FSBW) and Barents Sea Branch Waters (BSBW) in the region. We show that details of the zigzags’ temperature-salinity structure partially describe the water masses forming the intrusions. Furthermore, as confirmed by chemical tracers, the zigzags’ peaks contain the least altered water, allowing assessment of the temporal history of the Atlantic waters. Whilst the FSBW shows the 1990s warming and then a slight cooling, the BSBW has continuously cooled and freshened over a similar time period. The newest boundary current waters are found west of the Mendeleev Ridge in 2002. Additionally, we show the zigzag structures can fingerprint various water masses, including the boundary current. Using this, tracer data and the advection of the 1990s warming, we conclude the strongly topographically steered boundary current, order 50 km wide and found between the 1500 m and 2500 m isobaths, crosses the Mendeleev Ridge north of 80°N, loops south around the Chukchi Abyssal Plain and north around the Chukchi Rise, with the 1990s warming having reached the northern (but not the southern) Northwind Ridge by 2002. Pacific waters influence the Atlantic layers near the shelf and over the Chukchi Rise. The Northwind Abyssal Plain is comparatively stagnant, being ventilated only slowly from the north. There is no evidence of significant boundary current flow through the Chukchi Gap.Keywords: Arctic circulation, Arctic Ocean Boundary Current, double diffusive intrusions, Arctic change, Atlantic water circulationKeywords: Arctic circulation, Arctic Ocean Boundary Current, double diffusive intrusions, Arctic change, Atlantic water circulatio