Publications

Export 6 results:
Sort by: Author Title Type [ Year  (Desc)]
2015
Brown, ZW, Casciotti KL, Pickart RS, Swift JH, Arrigo KR.  2015.  Aspects of the marine nitrogen cycle of the Chukchi Sea shelf and Canada Basin. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 118:73-87.   10.1016/j.dsr2.2015.02.009   AbstractWebsite

As a highly productive, seasonally ice-covered sea with an expansive shallow continental shelf, the Chukchi Sea fuels high rates of sedimentary denitrification. This contributes to its fixed nitrogen (N) deficit relative to phosphorus (P), which is among the largest in the global ocean, making the Chukchi Sea severely N-limited during the phytoplankton growth season. Here, we examine aspects of the N cycle on the Chukchi Sea shelf and the downstream Canada Basin using nutrients, dissolved oxygen (O-2), and the stable isotopes of nitrate (NO3-). In the northward flow path across the Chukchi shelf, bottom waters experienced strong O-2 drawdown, from which we calculated a nitrification rate of 1.3 mmol m(-2) d(-1). This nitrification was likely primarily in sediments and directly fueled sedimentary denitrification, historically measured at similar rates. We observed significant accumulations of ammonium (NH4+) in bottom waters of the Chukchi shelf (up to > 5 mu M), which were inversely correlated with delta N-15(NO3), indicating a sediment source of N-15-enriched NH4+. This is consistent with a process of coupled partial nitrification-denitrification (CPND), which imparts significant N-15 enrichment and O-18 depletion to Pacific-origin NO3-. This CPND mechanism is consistent with a significant decrease in delta O-18(NO3) relative to Bering Sea source waters, indicating that at least 58% of NO3- populating the Pacific halocline was regenerated during its transit across the North Bering and Chukchi shelves, rather than arriving preformed from the Bering Sea slope. This Pacific-origin NO3- propagates into the Canada Basin and towards the North Atlantic, being significantly N-15-enriched and O-18-depleted relative to the underlying Atlantic waters. (C) 2015 Published by Elsevier Ltd.

2008
Marnela, M, Rudels B, Olsson KA, Anderson LG, Jeansson E, Torres DJ, Messias MJ, Swift JH, Watson AJ.  2008.  Transports of Nordic Seas water masses and excess SF6 through Fram Strait to the Arctic Ocean. Progress in Oceanography. 78:1-11.   10.1016/j.pocean.2007.06.004   AbstractWebsite

To determine the exchanges between the Nordic Seas and the Arctic Ocean through Fram Strait is one of the most important aspects, and one of the major challenges, in describing the circulation in the Arctic Mediterranean Sea. Especially the northward transport of Arctic Intermediate Water (AIW) from the Nordic Seas into the Arctic Ocean is little known. In the two-ship study of the circulation in the Nordic Seas, Arctic Ocean - 2002, the Swedish icebreaker Oden operated in the ice-covered areas in and north of Fram Strait and in the western margins of Greenland and Iceland seas, while RV Knorr of Woods Hole worked in the ice free part of the Nordic Seas. Here two hydrographic sections obtained by Oden, augmented by tracer and velocity measurements with Lowered Acoustic Doppler Current Profiler (LADCP), are examined. The first section, reaching from the Svalbard shelf across the Yermak Plateau, covers the region north of Svalbard where inflow to the Arctic Ocean takes place. The second, western, section spans the outflow area extending from west of the Yermak Plateau onto the Greenland shelf. Geostrophic and LADCP derived velocities are both used to estimate the exchanges of water masses between the Nordic Seas and the Arctic Ocean. The geostrophic computations indicate a total flow of 3.6 Sv entering the Arctic on the eastern section. The southward flow on the western section is found to be 5.1 Sv. The total inflow to the Arctic Ocean obtained using the LADCP derived velocities is much larger, 13.6 Sv, and the southward transport on the western section is 13.7 Sv, equal to the northward transport north of Svalbard. Sulphur hexafluoricle (SF(6)) originating from a tracer release experiment in the Greenland Sea in 1996 has become a marker for the circulation of AIW. From the geostrophic velocities we obtain 0.5 Sv and from the LADCP derived velocities 2.8 Sv of AIW flowing into the Arctic. The annual transport of SF(6) into the Arctic Ocean derived from geostrophy is 5 kg/year, which is of the same magnitude as the observed total annual transport into the North Atlantic, while the LADCP measurements (19 kg/year) imply that it is substantially larger. Little SF(6) was found on the western section, confirming the dominance of the Arctic Ocean water masses and indicating that the major recirculation in Fram Strait takes place farther to the south. (C) 2008 Elsevier Ltd. All rights reserved.

2003
Jones, EP, Swift JH, Anderson LG, Lipizer M, Civitarese G, Falkner KK, Kattner G, McLaughlin F.  2003.  Tracing Pacific water in the North Atlantic Ocean. Journal of Geophysical Research-Oceans. 108   10.1029/2001jc001141   AbstractWebsite

[1] In the Arctic Ocean, Pacific source water can be distinguished from Atlantic source water by nitrate-phosphate concentration relationships, with Pacific water having higher phosphate concentrations relative to those of nitrate. Furthermore, Pacific water, originally from the inflow through Bering Strait, is clearly recognizable in the outflows of low-salinity waters from the Arctic Ocean to the northern North Atlantic Ocean through the Canadian Arctic Archipelago and through Fram Strait. In the Canadian Arctic Archipelago, we observe that almost all of the waters flowing through Lancaster and Jones sounds, most of the water in the top 100 m in Smith Sound (containing the flow through Nares Strait), and possibly all waters in Hudson Bay contain no water of Atlantic origin. Significant amounts of Pacific water are also observed along the western coast of Baffin Bay, along the coast of Labrador, and above the 200-m isobath of the Grand Banks. There is a clear signal of Pacific water flowing south through Fram Strait and along the east coast of Greenland extending at least as far south as Denmark Strait. Pacific water signature can be seen near the east coast of Greenland at 66degreesN, but not in data at 60degreesN. Temporal variability in the concentrations of Pacific water has been observed at several locations where multiple-year observations are available.

2001
Ekwurzel, B, Schlosser P, Mortlock RA, Fairbanks RG, Swift JH.  2001.  River runoff, sea ice meltwater, and Pacific water distribution and mean residence times in the Arctic Ocean. Journal of Geophysical Research-Oceans. 106:9075-9092.   10.1029/1999jc000024   AbstractWebsite

Hydrographic and tracer data collected during ARK IV/3 (FS Polarstern in 1987), ARCTIC91 (IB Oden), and AOS94 (CCGS Louis S. St-Laurent) expeditions reveal the evolution of the near-surface waters in the Arctic Ocean during the late 1980s and early 1990s. Salinity, nutrients, dissolved oxygen, and delta (18)O data are used to quantify the components of Arctic freshwater: river runoff, sea ice meltwater, and Pacific water. The calculated river runoff fractions suggest that in 1994 a large portion of water from the Pechora, Oh, Yenisey, Kotuy, and Lena Rivers did not flow off the shelf closest to their river deltas, but remained on the shelf and traveled via cyclonic circulation into the Laptev and East Siberian Seas. River runoff flowed off the shelf at the Lomonosov Ridge and most left the shelf at the Mendeleyev Ridge. ARCTIC91 and AOS94 Pacific water fraction estimates of Upper Halocline Water, the traditionally defined core of the Pacific water mass, document a decrease in extent compared to historical data. The front between Atlantic water and Pacific water shifted from the Lomonosov Ridge location in 1991 to the Mendeleyev Ridge in 1994. The relative age structure of the upper waters is described by using the (3)H-(3)He age. The mean (3)H-(3)He age measured in the halocline within the salinity surface of 33.1 +/- 0.3 is 4.3 +/- 1.7 years and that for the 34.2 +/- 0.2 salinity surface is 9.6 +/- 4.6 years. Lateral variations in the relative age structure within the halocline and Atlantic water support the well-known cyclonic boundary current circulation.

1999
Macdonald, RW, Carmack EC, McLaughlin FA, Falkner KK, Swift JH.  1999.  Connections among ice, runoff and atmospheric forcing in the Beaufort Gyre. Geophysical Research Letters. 26:2223-2226.   10.1029/1999gl900508   AbstractWebsite

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 Ei al., 1998]. Since 1987, we have collected salinity, delta(18)O 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 a! though not necessarily to previous conditions.

1994
Anderson, LG, Bjork G, Holby O, Jones EP, Kattner G, Koltermann KP, Liljeblad B, Lindegren R, Rudels B, Swift J.  1994.  Water masses and circulation in the Eurasian Basin: Results from the Oden 91 expedition. Journal of Geophysical Research-Oceans. 99:3273-3283.   10.1029/93jc02977   AbstractWebsite

The Oden 91 North Pole expedition obtained oceanographic measurements on four sections in the Nansen and Amundsen basins of the Eurasian Basin and in the Makarov Basin of the Canadian Basin, thereby proving the feasibility of carrying out a typical oceanographic program using an icebreaker in the Arctic Ocean. The data show greater spatial variability in water structure and circulation than was apparent from previous data. The results show that a clear front exists between the Eurasian and Canadian basins such that upper halocline water in the Canadian Basin is almost absent from the Eurasian Basin. The lower halocline water produced in the Barents-Kara Sea region permeates much of the Eurasian Basin and flows along the continental slope into the Canadian Basin. The deeper circulation is strongly influenced by topography. Three return flows of the Atlantic layer are identified, one over the Nansen-Gakkel Ridge, one over the Lomonosov Ridge, and a third flowing from the Canadian Basin. The slight differences observed in salinity and temperature characteristics of the deeper waters of the Nansen and Amundsen basins do not lead to an obvious explanation of their origin or flow pattern.