E. Peter Jones

Distribution of Atlantic and Pacific waters in the upper Arctic Ocean: Implications for circulation

The Atlantic and Pacific oceans provide source waters for the Arctic Ocean that can be distinguished by their differing nitrate and phosphate concentration relationships. Using these relationships, we estimate the amount of Atlantic and Pacific waters in the surface layer (top 30 m) of the Arctic Ocean. Atlantic source water is dominant in most of the Eurasian Basin and is present in significant amounts in the Makarov Basin north of the East Siberian Sea. Pacific source water is dominant in most of the Canadian Basin and is present in significant amounts in the Amundsen Basin north of Greenland. We deduce circulation patterns from the distributions of Atlantic and Pacific source waters in the surface layer of the Arctic Ocean and conclude that the flow within the surface layer differs from ice drift along the North American and European boundaries of the Polar Basin.

Changes in temperature and tracer distributions within the Arctic Ocean: results from the 1994 Arctic Ocean section

Abstract Major changes in temperature and tracer properties within the Arctic Ocean are evident in a comparison of data obtained during the 1994 Arctic Ocean Section to earlier measurements. (1) Anomalously warm and well-ventilated waters are now found in the Nansen, Amundsen and Makarov basins, with the largest temperature differences, as much as 1 °C, in the core of the Atlantic layer (200–400 m). Thus thermohaline transition appears to follow from two distinct mechanisms: narrow (order 100 km), topographically-steered cyclonic flows that rapidly carry new water around the perimeters of the basins; and multiple intrusions, 40–60 m thick, which extend laterally into the basin interiors. (2) Altered nutrient distributions that within the halocline distinguish water masses of Pacific and Atlantic origins likewise point to a basin-wide redistribution of properties. (3) Distributions of CFCs associated with inflows from adjacent shelf regions and from the Atlantic demonstrate recent ventilation to depths exceeding 1800 m. (4) Concentrations of the pesticide HCH in the surface and halocline layers are supersaturated with respect to present atmospheric concentrations and show that the ice-capped Arctic Ocean is now a source to the global atmosphere of this contaminant. (5) The radionuclide 129I is now widespread throughout the Arctic Ocean. Although the current level of 129I level poses no significant radiological threat, its rapid arrival and wide distribution illustrate the speed and extent to which waterborne contaminants are dispersed within the Arctic Ocean on pathways along which other contaminants can travel from western European or Russian sources.

Tracing the flow of North Atlantic Deep Water using chlorofluorocarbons

Chlorofluorocarbon (CFC) and hydrographic data collected in the North Atlantic in the late 1980s and early 1990s are used to confirm and add to earlier work on the large-scale circulation pathways and timescales for the spreading of North Atlantic Deep Water (NADW) components and how these components relate to the hydrographic structure. Throughout the western North Atlantic, high CFC concentrations are coincident with newly formed NADW components of Upper Labrador Sea Water (ULSW), Classical Labrador Sea Water (CLSW), and Overflow Waters (OW). ULSW is marked by a CFC maximum throughout the western subtropical and tropical Atlantic, and CLSW is marked by a CFC maximum north of 38°N in data collected in 1990–1992. Iceland-Scotland Overflow Water (ISOW) splits into two branches in the eastern basin, with one branch entering the western basin where it mixes with Denmark Strait Overflow Water (DSOW) and the densest branch flows southward along the bottom in the eastern basin. DSOW contributes the largest portion of the CFC signal in OW. It is estimated that these NADW components are at 60–75% equilibrium with the CFC concentration in the atmosphere at the time of formation. The large-scale data set confirms that NADW spreads southward by complex pathways involving advection in the Deep Western Boundary Current (DWBC), recirculation in deep gyres, and mixing. Maps of the CFC distribution show that properties within the gyres are relatively homogeneous, particularly for OW, and there is a profound change at the gyre boundaries. The density of the core of ULSW increases in the equatorward direction because of entrainment by overlying northward flowing Upper Circumpolar Water and at the equator, ULSW has the same density as CLSW in the subtropics but is warmer and saltier. The density of OW decreases between the subpolar region and the subtropics. This is caused by the least dense part of OW exiting the subpolar region in the DWBC, while the densest component recirculates in the subpolar basins. Some variability is observed in OW density in the subtropics and tropics because of variability in mixing with Antarctic Bottom Water and changes in the subtropics that are probably related to the transport of different vintages of DSOW. Ages derived from CFC ratios show that the NADW components of northern origin spread throughout the western North Atlantic within 25–30 years. This corresponds to a spreading rate of 1–2 cm s−1 and is comparable to the time a climate anomaly introduced into the subpolar North Atlantic will take to penetrate the entire western North Atlantic Ocean.

Circulation in the Arctic Ocean

Much information on processes and circulation within the Arctic Ocean has emerged from measurements made on icebreaker expeditions during the past decade. This article offers a perspective based on these measurements, summarizing new ideas regarding how water masses are formed and how they circulate. Best understood at present is the circulation of the Atlantic Layer and mid-depth waters, to depths of about 1700 m, which move in cyclonic gyres in the four major basins of the Arctic Ocean. New ideas on halocline formation and circulation are directly relevant to concerns regarding changes in ice thickness. The circulation of the halocline water in part mimics that of the underlying Atlantic Layer. A number of large eddies contributing to water mass transport have been observed. The circulation of freshwater from the Pacific Ocean and from river runoff has been better delineated. Circulation within the surface layer resembles the circulation of ice, but is different in several respects. Least understood is the circulation of the deepest waters, though some information is available. Recent observed changes in the surface waters and warm Atlantic Layer have been correlated with the North Atlantic Oscillation. While these changes are dramatic, the qualitative circulation pattern may not have been altered significantly.

Ventilation of the Arctic Ocean cold halocline: rates of diapycnal and isopycnal transport, oxygen utilization and primary production inferred using chlorofluoromethane distributions

Abstract A highly simplified model of the Arctic Ocean cold halocline, incorporating parameterizations of both along-isopycnal and diapycnal transport, has been developed and constrained by observed profiles of temperature, salinity and chlorofluoromethanes (CFMs). The bulk vertical eddy diffusivity is estimated to be ∼ 2 × 10 −6 m 2 s −1 . The model shows that by ignoring diapycnal mixing processes, the lateral exchange timescales derived from purely lateral tracer models can be significantly biased. The model, and two simpler, purely lateral models, are applied to the dissolved oxygen profile in order to calculate apparent oxygen utilization rates (AOUR). All of the models give similar values for the depth-integrated AOUR. The rates of oxygen utilization are too high to be sustained by primary production in the central Arctic Ocean, and they must therefore be balanced by production over the Arctic Ocean continental shelves. AOUR-based estimates of total shelf production range from 18 to 64 g C m −2 y −1 , and are consistent with estimates based on sparse 14 C production measurements.

Ventilation of the Arctic Ocean : Mean ages and inventories of anthropogenic CO2 and CFC-11

The Arctic Ocean constitutes a large body of water that is still relatively poorly surveyed because of logistical difficulties, although the importance of the Arctic Ocean for global circulation and climate is widely recognized. For instance, the concentration and inventory of anthropogenic CO2 (C ant) in the Arctic Ocean are not properly known despite its relatively large volume of well-ventilated waters. In this work, we have synthesized available transient tracer measurements (e.g., CFCs and SF6) made during more than two decades by the authors. The tracer data are used to estimate the ventilation of the Arctic Ocean, to infer deep-water pathways, and to estimate the Arctic Ocean inventory of C ant. For these calculations, we used the transit time distribution (TTD) concept that makes tracer measurements collected over several decades comparable with each other. The bottom water in the Arctic Ocean has CFC values close to the detection limit, with somewhat higher values in the Eurasian Basin. The ventilation time for the intermediate water column is shorter in the Eurasian Basin (∼200 years) than in the Canadian Basin (∼300 years). We calculate the Arctic Ocean C ant inventory range to be 2.5 to 3.3 Pg-C, normalized to 2005, i.e., ∼2% of the global ocean C ant inventory despite being composed of only ∼1% of the global ocean volume. In a similar fashion, we use the TTD field to calculate the Arctic Ocean inventory of CFC-11 to be 26.2 ± 2.6 × 106 moles for year 1994, which is ∼5% of the global ocean CFC-11 inventory

Nutrient regeneration in cold, high salinity bottom water of the Arctic shelves

Abstract Nutrient regeneration in cold, high salinity bottom water has been studied in Storfjorden, southern Svalbard. This bottom water was a mixture of Atlantic water with brine produced by sea ice during its formation and aging. The concentrations of nutrients, oxygen and total carbonate in this high salinity water are used to estimate the decay rates of organic matter at the sediment-water interface in a cold water environment. The relative regeneration rates of the constituents from the soft parts of organic matter are found to be in good agreement with the literature values. Silicate from the hard parts is concluded to have a higher rate of regeneration relative to the other nutrients in cold water than in warm water. The regeneration rates are used to estimate the time required for the production of the organic decay components contributing to the nutrient maximum in the upper halocline of the Canada Basin in the Arctic Ocean, in order to estimate the residence time of this water. The estimated residence times given by the different components are approximately 10 years.

Eddies of newly formed upper Labrador Sea water

A new type of submesoscale eddy has been observed south of the Labrador Sea during late winter, embedded in equatorward flow along the western boundary. The eddy radius is 20 km, with a weak dynamic signature (swirl speed of 0.5 cm/s). The center of the eddy is characterized by weak stratification, elevated concentrations of oxygen and anthropogenic tracers, and low tracer ages, all indicative of newly ventilated water. Strong lateral intrusions distort the shape of the feature. The water mass contained in the eddy is not classical Labrador Sea water (from the central Labrador Sea) but is significantly fresher and hence lighter. It is of the correct density to be the source of the high-chlorofluorocarbon layer of the shallow deep western boundary current observed further south and hence is termed upper Labrador Sea water. Using a combination of hydrographic data sets along the western boundary to implement a simple lateral diffusion model, it is shown that such eddies decay of the order of several months and are difficult to observe equatorward of the Grand Banks of Newfoundland. This is in contrast to deeper lenses of classical Labrador Sea water which persist further equatorward. Tracer-derived ages of the upper Labrador Sea water eddy range from 3 to 5 years, much older than the lifetime deduced from their lateral diffusion. A simple convection model of tracer age shows that this age discrepancy is caused by gas exchange being unable to maintain equilibrium between the deep convecting mixed layer and the atmosphere during formation.

Northern hudson bay and foxe basin: Water masses, circulation and productivity

Abstract Total alkalinity and total carbonate determinations together with salinity and temperature are used to characterize water masses in Foxe Basin, Hudson Bay and Hudson Strait. From these measurements, we are able to infer the amounts of fresh water from river runoff and from sea‐ice meltwater. The average ice cover is estimated to be 1.9 m, and the residence time of river runoff in Hudson Bay is 3—4 years. Estimates of biological productivity were made by “correcting” total carbonate measurements for effects of biological processes, giving a value of 24 gC m a for new production.

Anthropogenic carbon dioxide in the Arctic Ocean - inventory and sinks

An inventory and sequestering rate of anthropogenic carbon dioxide CTanthro in the Arctic Ocean, calculated by a plume-entrainment model, are presented. The plume is initiated by a fraction rj leaving the shelf break at 200 m, followed by an entrainment of rj for every 150 m depth the plume descends. The model is constrained by the CFC-12 and carbon tetrachloride (CCl4) distributions, with the concentrations of CFC-12, CCl4, and CTanthro in the source water calculated assuming a water in 100% equilibrium with the atmosphere. The model is run from 1750 to 1991, the latter being the year in which measurements of the transient tracers in the water column of the central Arctic Ocean were made. The output from the model gives sinks of anthropogenic carbon dioxide in 1991 of 0.026±0.009 Gt C yr−1, of which 0.0194 Gt C yr−1 is in the Eurasian Basin and 0.0070 Gt C yr−1 in the Canadian Basin. This amounts to about 1% of the total oceanic uptake of anthropogenic CO2. The Arctic Ocean inventory of anthropogenic carbon dioxide in 1991 was 1.35(+0.12/−0.06) Gt C, which is about 1% of the total oceanic inventory. The sensitivity of the computed sinks and inventories to various model assumptions was estimated.