INSIGHTS ON CROSS SHELF TRANSPORT IN THE ARCTIC DERIVED FROM BARIUM DISTRIBUTIONS
Kelly Kenison Falkner*
Oregon State University, Corvallis, Oregon
1. INTRODUCTION
Since 1992, our laboratory group has been exploring the application of geochemical tracers to circulation in the Arctic. Early in our program, we discovered that the element barium (Ba) appeared to offer a way to distinguish between North American and Eurasian river inputs. This is not possible with other river water tracers, such as oxygen isotopes and normalized alkalinity, that have been applied in the Arctic. In addition, Ba can be used to delineate the extent of the so-called upper halocline, a subsurface water layer with a prominent dissolved silicate maximum centered around a salinity of about 33.1, primarily in the Canada Basin.
In 1993, we began a program to obtain seawater and river samples from throughout the Arctic for dissolved Ba analyses by high precision (2 %) isotope dilution-inductively coupled plasma quadrupole mass spectrometry in our laboratory at OSU. We are not aware of any previous efforts to characterize this element in the Arctic. To date, we have analyzed over 8000 samples collected from a range of platforms including ice breaker and ice-strengthened surface vessels, nuclear submarine and through-ice operations supported by aircraft and snowmobile. Sample coverage includes freshwater endmembers, through the estuaries and into the marginal seas of all major rivers emptying into the Arctic, the Bering Sea and Strait, Chukchi and Barents regions, the Canadian Archipelago and throughout the Arctic interior. This work was made possible by the generous efforts of many people on our behalf for which we are grateful.What follows is a summary of our findings to date, some of which have already appeared in the publications indicated.
2. SOURCES
From data available to now, it can be concluded that near surface Atlantic waters enter with the lowest Ba contents of all Arctic source waters (Y48 nM) (Guay and Falkner, 1998a). This source does not show spatial or temporal variability within the precision of the measurements. Concentrations are consistent with previous reports by others of Ba contents for the North Atlantic and Greenland, Norwegian and Iceland Seas (Chan et al. , 1977).
Of the major rivers which empty directly into the Arctic, the Mackenzie (endmember 400-500 nM) appears to be at least 4-fold more concentrated in Ba than other Eurasian rivers (Guay and Falkner, 1998b). This is a function of different drainage basin lithologies and elevations. In addition, the Mackenzie carries at least a 10 fold higher suspended sediment load than the Eurasian rivers. As occurs at lower latitudes, dissolved riverine Ba inputs are augmented in the estuay where suspended riverine clays desorb Ba in exchange for the more abundant cations of seawater (Guay and Falkner, 1998b). It is noted that while their Ba contents are less than the Mackenzie s, Eurasian rivers are measurably enriched with respect to the shelf seawaters into which they enter. In the seasonally productive marginal seas of the Arctic, some riverine Ba can be removed from the surface in association with biological activities. Such removal appears to be minimal under the ice cover and so signals penetrating under the ice tend to be preserved.
It is cautioned that our conclusions for the riverine sources of Ba to the Arctic are based on two summer sampling periods for the major Eurasian rivers and single summer and winter samplings of the Mackenzie. Hazardous conditions prevent us from obtaining data during the interesting period of spring break-up. It would be valuable to determine the Ba flux during this period of high suspended sediment
* Corresponding author address Kelly Kenison Falkner, 104 Ocean Admin Bldg, College of Oceanic & Atmospheric Sci., Oregon State Univ., Corvallis, OR 97331-5503; e-mail: kfalkner@oce.orst.edu
