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2009
Codispoti, LA, Flagg CN, Swift JH.  2009.  Hydrographic conditions during the 2004 SBI process experiments. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 56:1144-1163.   10.1016/j.dsr2.2008.10.013   AbstractWebsite

Western Arctic Shelf-Basin Interactions (SBI) process experiment cruises were conducted during spring and summer in 2002 and 2004. A comparison of the 2004 data with the results from 2002 reveals several similarities but also some distinct differences. Similarities included the following: (1) Dissolved inorganic nitrogen (DIN) (ammonium+nitrate+nitrite) limited phytoplankton growth in both years, suggesting that the fixed-N transport through Bering Strait is a major control on biological productivity. (2) The head of Barrow Canyon was a region of enhanced biological production. (3) Plume-like nutrient maxima and N** minima (a signal of sedimentary denitrification) extending from the shelf into the interior were common except at our easternmost section where the nearshore end of these features intersected the slope. (4) Particularly during summer, oxygen supersaturations were common in or just above the shallow nitracline. (5) Surface waters at our deepest stations were already depleted in nitrate, ammonium and urea during our springtime observations. A major difference between the 2 years was the greater influence of warm, relatively low-nutrient Alaska Coastal Water (ACW) during 2004 entering the region via Bering Strait. This increased inflow of ACW may have reduced photic zone nutrient concentrations. The differences in water temperature and nutrients were most pronounced in the upper similar to 100 db, and the increased influence of warm water in 2004 relative to 2002 was most evident in our East Barrow (EB) section. Although the EB data were collected on essentially the same year-days (29 July-4 August 2002 vs. 29 July-6 August 2004), the surface layers were up to 5 degrees warmer in 2004. While the stronger inflow of ACW in 2004 may have reduced the autochthonous nutrient supply, rates of primary production, bacterial production, and particulate organic carbon export were higher in 2004. This conundrum might be explained by differences in the availability of light. Although, springtime ice thicknesses were greater in 2004 than in 2002, snow cover was significantly less and may have more than compensated for the modest differences in ice thickness vis a vis light penetration. In addition, there was a rapid and extensive retreat of the ice cover in summer 2004. Increased light penetration in 2004 may have allowed phytoplankton to increase utilization of nutrients in the shallow nitracline. In addition, more light combined with warmer temperatures could enhance that fraction of primary production supported by nutrient recycling. Enhanced subsurface primary production during summer 2004 is suggested not only by the results of incubation experiments but by more extreme dissolved oxygen supersaturations in the vicinity of the nitracline. We cannot, however, ignore aliasing that might arise from somewhat different station distributions and timing. It is also possible that the rapid ice retreat and warmer temperatures lead to an acceleration in the seasonal progression of biological processes such that the summer 2004 SBI Process Cruise (HLY 04-03) experiment was observing a state that might have existed a few weeks after completion of the 2002 summer cruise (HLY 02-03). Despite these complications, there is little doubt that biological conditions at the ensemble of hydrographic stations occupied in 2004 during the SBI Process Cruises differed significantly from those at the stations occupied in 2002. (c) 2008 Published by Elsevier Ltd.

2005
Falkner, KK, Steele M, Woodgate RA, Swift JH, Aagaard K, Morison J.  2005.  Dissolved oxygen extrema in the Arctic Ocean halocline from the North Pole to the Lincoln Sea. Deep-Sea Research Part I-Oceanographic Research Papers. 52:1138-1154.   10.1016/j.dsr.2005.01.007   AbstractWebsite

Dissolved oxygen (02) profiling by new generation sensors was conducted in the Arctic Ocean via aircraft during May 2003 as part of the North Pole Environmental Observatory (NPEO) and Freshwater Switchyard (SWYD) projects. At stations extending from the North Pole to the shelf off Ellesmere Island, such profiles display what appear to be various 02 maxima (with concentrations 70% of saturation or less) over depths of 70-110 m in the halocline, corresponding to salinity and temperature ranges of 33.3-33.9 and -1.7 to -1.5 degrees C. The features appear to be widely distributed: Similar features based on bottle data were recently reported for a subset of the 1997-1998 SHEBA stations in the southern Canada Basin and in recent Beaufort Sea sensor profiles. Oxygen sensor data from August 2002 Chukchi Borderlands (CBC) and 1994 Arctic Ocean Section (AOS) projects suggest that such features arise from interleaving of shelf-derived, O(2)-depleted waters. This generates apparent oxygen maxima in Arctic Basin profiles that would otherwise trend more smoothly from near-saturation at the surface to lower concentrations at depth. For example, in the Eurasian Basin, relatively low O(2) concentrations are observed at salinities of about 34.2 and 34.7. The less saline variant is identified as part of the lower halocline, a layer originally identified by a Eurasian Basin minimum in "NO," which, in the Canadian Basin, is reinforced by additional inputs. The more saline and thus denser variant appears to arise from transformations of Atlantic source waters over the Barents and/or Kara shelves. Additional low-oxygen waters are generated in the vicinity of the Chukchi Borderlands, from Pacific shelf water outflows that interleave with Eurasian waters that flow over the Lomonosov Ridge into the Makarov Basin and then into the Canada Basin. One such input is associated with the well-known silicate maximum that historically has been associated with a salinity of approximate to 33.1. Above that (32 < S < 33), there is a layer moderately elevated in temperature (summer Bering Sea water) that we show is also O(2)-depleted. We propose that these low O(2) waters influence the NPEO and SWYD profiles to varying extents in a manner reflective of the large-scale circulation. The patterns of halocline circulation we infer from the intrusive features defy a simple boundary-following cyclonic flow. These results demonstrate the value of the improved resolution made feasible with continuous O(2) Profiling. In the drive to better understand variability and change in the Arctic Ocean, deployment of appropriately calibrated CTD-O(2) packages offers the promise of important new insights into circulation and ecosystem function. (c) 2005 Elsevier Ltd. All rights reserved.

Codispoti, LA, Flagg C, Kelly V, Swift JH.  2005.  Hydrographic conditions during the 2002 SBI process experiments. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 52:3199-3226.   10.1016/j.dsr2.2005.10.007   AbstractWebsite

A review of the hydrographic data from the 2002 Western Arctic Shelf-Basin Interactions (SBI) Process Cruises permits the following conclusions. (1) Temperature-salinity relationships were similar to canonical descriptions, but at five stations in the outer shelf/slope region, warm/high-salinity Atlantic Layer Water appeared to have risen, displaced the lower halocline, and mixed with shelf/upper halocline water. (2) Primary production in the SBI study region was strongly influenced by the advection of dissolved inorganic nitrogen (DIN) entering via Bering Strait. This import of DIN (ammonium + nitrate + nitrite) is modified by local processes, but without the Bering Strait inflow, biological productivity in the SBI region would be much lower. (3) In comparison to the inflowing Atlantic waters, DIN+ urea/phosphate and DIN + urea/silicate ratios in the Pacific waters that dominated the upper similar to 150 m of the water column were low. They were also low relative to Redfield uptake ratios for phytoplankton. (4) Microbial processes continue to destroy DIN in significant quantities as the Pacific waters transit the SBI region. (5) Nitrate and ammonium were the principal contributors to DIN. Nitrite concentrations were always < 0.4 mu M. With a few exceptions urea concentrations were < 0.5 mu M. (6) Moderate concentrations of DIN occurred in surface layers over the shelf in spring, but surface concentrations in the adjacent basin were low, suggesting that basin productivity is low. (7) In summer, DIN depletion in the surface layers was widespread, but a nutricline below similar to 15m contained chlorophyll and dissolved oxygen maxima. production in this layer. (8) A comparison of nutrient and dissolved oxygen concentrations in Suggesting net primary abyssal waters of the Canada Basin with conditions in Fram Strait suggests that the deep metabolism in the SBI region is exceedingly low compared to typical deep-ocean values. (9) The low abyssal metabolism and phosphate-silicate relationships suggest that the maxima in biogenic solutes (ammonium, silicate, etc.) that appear to originate on the shelf and penetrate the interior at halocline depths are not accompanied by comparable concentrations of labile organic matter. Thus. the moderate to high primary production over the shelf and slope supported by the import of DIN from Bering Strait is largelv regenerated over the shelf. (10) Our easternmost section (east of Pt. Barrow) displayed nutrient maxima at depths of similar to 100m as did our three sections to the west, but in this section these signals were not connected to the shelf, and were most likely advected by an eastward shelf-break jet. (c) 2005 Elsevier Ltd. All rights reserved.

2003
Anderson, LG, Jones EP, Swift JH.  2003.  Export production in the central Arctic Ocean evaluated from phosphate deficits. Journal of Geophysical Research-Oceans. 108   10.1029/2001jc001057   AbstractWebsite

[1] Primary productivity in the central Arctic Ocean has recently been reported as being much higher than earlier thought. If a significant fraction of this primary production were exported from the immediate surface region, present estimates of the carbon budget for the Arctic Ocean would have to be reassessed. Using the deficit of phosphate in the central Arctic Ocean, we show that the export production is very low, on an average less than 0.5 gC m(-2) yr(-1). This is at least an order of magnitude lower than the total production as measured or estimated from oxygen data, thus indicating extensive recycling of nutrients in the upper waters of the central Arctic Ocean and very little export production.