Interior Arctic Ocean Research Articles

Reduced sea ice concentrations in the Arctic Ocean during the last interglacial period revealed by sediment cores off northern Greenland

We present a record encompassing marine isotope stages 7‐1 from a hitherto unexplored and heavily ice‐covered area of the Arctic Ocean, the Lomonosov Ridge off the northern Greenland‐Canada continental margin, using nannofossil and benthic foraminifera stratigraphy. Planktic foraminifera assemblages are used as a key paleoceanographic proxy, and a surprisingly large variability is found for an interior Arctic Ocean site. Abundant small (63–125 μm) subpolar Turborotalita quinqueloba occur in two sections, possibly representing substages 5e (last interglacial) and 5a (warm interstadial). However, the present‐day circulation pattern and the very distant location of high productive regions cannot explain such high abundances of subpolar specimens in the interior, perennially sea ice–covered Arctic Ocean. Hence our proxy record indicates that last interglacial sea ice concentrations were reduced off some areas of northern Greenland‐Canada. Whether this was part of a larger regional pattern or it represents the influence of polynya areas with locally increased productivity remains to be solved. With respect to glacial conditions, increased ice‐rafted debris (IRD) deposition in the area appears to be associated with glacial stages 6, 4, and late 3. Stage 2 sediments (including the Last Glacial Maximum) are condensed with a sparse IRD content only.

Circulation on the north central Chukchi Sea shelf

Abstract Mooring and shipboard data collected between 1992 and 1995 delineate the circulation over the north central Chukchi shelf. Previous studies indicated that Pacific waters crossed the Chukchi shelf through Herald Valley (in the west) and Barrow Canyon (in the east). We find a third branch (through the Central Channel) onto the outer shelf. The Central Channel transport varies seasonally in phase with Bering Strait transport, and is ∼0.2 Sv on average, although some of this might include water entrained from the outflow through Herald Valley. A portion of the Central Channel outflow moves eastward and converges with the Alaskan Coastal Current at the head of Barrow Canyon. The remainder appears to continue northeastward over the central outer shelf toward the shelfbreak, joined by outflow from Herald Valley. The mean flow opposes the prevailing winds and is primarily forced by the sea-level slope between the Pacific and Arctic oceans. Current variations are mainly wind forced, but baroclinic forcing, associated with upstream dense-water formation in coastal polynyas might occasionally be important. Winter water-mass modification depends crucially on the fall and winter winds, which control seasonal ice development. An extensive fall ice cover delays cooling, limits new ice formation, and results in little salinization. In such years, Bering shelf waters cross the Chukchi shelf with little modification. In contrast, extensive open water in fall leads to early and rapid cooling, and if accompanied by vigorous ice production within coastal polynyas, results in the production of high-salinity (>33) shelf waters. Such interannual variability likely affects slope processes and the transport of Pacific waters into the Arctic Ocean interior.

Drifting Arctic sea ice archives changes in ocean surface conditions

δ18O profiles in drifting Arctic sea ice are coupled with back trajectories of ice drift and an ice growth model to reconstruct the surface hydrography of the Arctic Ocean interior. The results compare well with δ18O values obtained by traditional oceanographic methods and known water mass distributions. Analysis of the stable isotopic composition of sea ice floes sampled at strategic and relatively accessible locations, e.g., Fram Strait, could aid in mapping spatial and temporal variations in Arctic Ocean surface waters.

Arctic warming through the Fram Strait: Oceanic heat transport from 3 years of measurements

We present estimates of volume and heat transport through Fram Strait for the period 1997 to 2000 from data of moored instruments. The annual mean volume transports at 78°55′N were between 9 2 and 10 1 Sv northward and 13 2 and 12 1 Sv southward with a net transport between 4 2 and 2 2 Sv to the south. The temperature of the northward flow of Atlantic Water had a strong seasonality with a minimum in winter. Nevertheless, the northward heat transport was highest in winter caused by the winter maximum of northward volume transport. Between 1997 and 1999, the annual mean net heat transport across 78°55′N increased from 16 12 to 41 5 TW. This resulted from a very strong increase in heat transport in the West Spitsbergen Current (mean annual values from 28 5 to 44 6 TW and to 46 5 TW in 99/00) which was not compensated by an equivalent signal in the southward flow. The heat transport to the south remained constant within error limitations. Only half of the heat flux increase in the West Spitsbergen Current was due to a higher temperature; half of it was due to a stronger flow. A similar increase as observed between 1997 and 2000 would have been sufficient to explain the warming of intermediate layers in the Eurasian Arctic observed in the early 1990s. Consequently, we suggest that a warming signal from the late 1990s is presently spreading in the interior 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.

Some thoughts on the freezing and melting of sea ice and their effects on the ocean

The high-latitude freezing and melting cycle can variously result in haline convection, freshwater capping or freshwater injection into the interior ocean. An example of the latter process is a secondary salinity minimum near 800 m-depth within the Arctic Ocean that results from the transformation on the Barents Sea shelf of Atlantic water from the Norwegian Sea and its subsequent intrusion into the Arctic Ocean. About one-third of the freshening on the shelf of that initially saline water appears to result from ice melt, although the actual sea ice flux is small, only about 0.005 Sv. A curious feature of this process is that water distilled at the surface of the Arctic Ocean by freezing ends up at mid-depth in the same ocean. This is a consequence of the ice being exported southward onto the shelf, melted, and then entrained into the northward Barents Sea throughflow that subsequently sinks into the Arctic Ocean. Prolonged reduction in sea ice in the region and in the concomitant freshwater injection would likely result in a warmer and more saline interior Arctic Ocean below 800 m.

234Th/238U disequilibrium in the central Arctic Ocean: implications for particulate organic carbon export

234Th (t1/2 = 24.1 days) was used as a tracer to investigate scavenging and particle export in the upper ocean along a transect from the Chukchi Sea to the North Pole during the 1994 Arctic Ocean Section (August–September). Large volume water samples (200–6001) were collected using in situ pumps for the determination of dissolved and particulate 234Th activity and POC and PON concentrations. The lowest total 234Th/238U activity ratio (0.14) was observed in the Chukchi Sea, consistent with enhanced scavenging in these particle-rich shelf waters. 234Th/238U disequilibrium in the interior Arctic is attributed to local biological production and the associated particle export. Estimates of the export flux of POC and PON from the upper 20–30 m were made using the 234Th, POC and PON results. POC export ranged from 38 mmol C m−2 d−1 on the Chukchi Shelf to 0.3–7 mmol C m−2 d−1 (mean=3±2 mmol C m−2 d−1) within the ice-covered interior Arctic Ocean. PON export ranged from 4.8 mmol N m−2 d−1 on the Chukchi Shelf to 0.05-1.1 mmol N m−2 d−1 (mean = 0.36 ±0.39 mmol N m−2 d−1) in the central Arctic Ocean.

Chemical interactions and sediments of the western Canadian arctic shelf

The Canadian Beaufort Shelf is the largest continental shelf on the North American side of the Arctic and is the most brackish of all Arctic shelves. Chemical data both site-specific and from the Arctic Ocean interior are reviewed for evidence of chemical processes which occur at the shelf-seabed/water interface. The important material sources to this region include the Mackenzie River, shore erosion, primary production, and long-range atmospheric transport. The latter source appears to be important for chlorinated organics. For the past two decades hydrocarbon exploration has had a local impact around drill-sites where cuttings and drill muds have been discharged. The chemical environment of the Canadian Beaufort Shelf nearshore is exceedingly dynamic due to processes mediated by ice (scour, brine drainage, water disposition) and winds (sediment resuspension and upwelling). Storms from the northwest in late summer, when there is open water, have the potential to resuspend bottom sediments in the nearshore (less than about 20 m water depth) bringing about the transport of detritus and remineralized material. Future research on seabed chemical interactions should focus on the measurement of seasonal fluxes of materials to and from the seabed, the sources of carbon to the shelf, denitrification in sediments, the response of the nearshore to late summer storms and the role of Arctic shelf sediments to the budget of chlorinated organic contaminants.