Papers by William Smethie
... AABW into a cyclonic gyre in the eastern portion of the basin and a western boundary current ... more ... AABW into a cyclonic gyre in the eastern portion of the basin and a western boundary current which carries a detectable CFC singal as far ... of 46.07 [sigma][sub 4], which is the upper bound of the water entering the Argentine Basin from the Weddell Sea (Reid, Deep-Sea Res ...
Geophysical Research Letters, Mar 24, 2007
Measurements of chlorofluorocarbon inventories during 1997-2003 allow the detection and quantific... more Measurements of chlorofluorocarbon inventories during 1997-2003 allow the detection and quantification of significant changes in the formation rates of two modes of Labrador Sea Water (LSW): Upper (ULSW) and deep LSW, both here defined in fixed density intervals. Both modes contribute to the cold limb of the Meridional Overturning Circulation. Results reveal that the lighter ULSW formed since the mid-1990s has started to replace the large pool of the deep LSW stored in the western North Atlantic. Formation of deep LSW was absent in 1997-2003. Formation of ULSW compensated for this absence during 1998/99 (7.9 Sv), but afterwards significantly declined to 2.5 Sv. The decrease of the overall LSW formation throughout 1997-2003 correlates with a declining eastward baroclinic mass transport between the centers of the subpolar and subtropical gyres since 1997, a warming of LSW, and a gradually decreasing North Atlantic Oscillation index after 1999.
Progress in Oceanography, 2019
This study evaluates the trends in anthropogenic carbon (C ant) in the different sub-basins of th... more This study evaluates the trends in anthropogenic carbon (C ant) in the different sub-basins of the Arctic Ocean between 1987 and 2015. Data were extracted from the GLODAPv2 data product as well as two GEOTRACERS cruises in the Arctic Ocean from 2015 and C ant was evaluated using the transient time distribution (TTD) approach. In the Nansen and Amundsen sub-basins, the C ant trend in the Atlantic Waters (AW, depths: 200-500 m) and dense AW (dAW, depths: 500-800 m) is about +0.7 µmol kg −1 yr −1. As we move into the Makarov and West Canadian sub-basins, the C ant trend in the AW and dAW is smaller. The upper Polar Deep Water (uPDW, depths: 800-1600 m) has a C ant trend of about +0.4-0.5 µmol kg −1 yr −1 in the Nansen, Amundsen and West Canadian sub-basins. The trend is smallest in the South Canadian sub-basin, with a value of about +0.2 µmol kg −1 yr −1. Ventilation primarily governs C ant trends while the influence of the Revelle factor plays a secondary role. The increase in the C ant column inventory is estimated to be 0.7-1.0 mol C m −2 yr −1 in the Nansen, Amundsen and Makarov sub-basins. By extrapolating the results from our defined sub-basins to the full Arctic Ocean, we estimate an C ant accumulation of 25 Tg C yr −1 in the Arctic Ocean and an inventory of about 3.6-3.
Deep Sea Research Part A. Oceanographic Research Papers, 1986
ABSTRACT
Deep Sea Research Part A. Oceanographic Research Papers, 1988
During July-August of 1984, the polar research vessel R.V. Polarstern occupied sections of oceano... more During July-August of 1984, the polar research vessel R.V. Polarstern occupied sections of oceanographic stations in and north of Fram Strait and across the Greenland Sea (Boreas Basin) south of Fram Strait. The temperature, salinity and chlorofluoromethane (CFM) data for the Polarstern stations within the Eurasian Basin reveal two deep-water masses, Eurasian Basin Bottom Water (EBBW) which lies below the ~2 = 37.46 density surface and Eurasian Basin Deep Water (EBDW) which lies above this surface. The depth of this surface is close to the 2600 m sill depth of Fram Strait. The CFM, temperature and salinity distributions suggest that EBBW is partially composed of dense, high salinity shelf water advected into the deep Eurasian Basin, where it probably circulates around the basin in a deep cyclonic boundary current. An upper limit of about 0.1 Sv was estimated from the CFM data for the transport of pure high salinity shelf water into the Eurasian Basin below 3000 m. These data together with data collected on previous cruises to the Norwegian and Greenland seas reveal that EBDW exchanges with water masses south of Fram Strait, first flowing through Fram Strait in a narrow (<10 km) deep boundary current, then mixing with Greenland Sea Deep Water in the periphery of the Greenland Gyre to form new Norwegian Sea Deep Water (NSDW). Some of this new NSDW flows southeastward into the Norwegian Sea and a mixture of old and new NSDW flows northward on the eastern side of Fram Strait, returning to the Eurasian Basin. We estimate the volume transport of EBDW southward through Fram Strait to be 0.80-0.93 Sv. Volume transports between the deep Greenland and deep Norwegian seas and between the surface and deep Greenland Sea were also estimated with respective values of 0.80-0.93 Sv and 0.50-0.52 Sv.
Ventilation and water mass ages CFC-11 data show higher concentrations in the Amundsen Basin than... more Ventilation and water mass ages CFC-11 data show higher concentrations in the Amundsen Basin than in the Nansen-or Makarov Basin, indicating younger water mass ages implying more recent ventilation. We think this is controlling the Th and Pa profiles in the Amundsen Basin: Water with Atlantic origin flows through the Siberian shelves and is entering the Amundsen Basin after undergoing scavenging history at the shelves and slopes. This change is carried downwards by reversible scavenging. The Makarov Basin water is older than that of the Eurasian Basins. Therefore, Th and Pa can accumulate accordingly. BREMERHAVEN Am Handelshafen 12 27570 Bremerhaven Telefon +49(471)4831-1565 www.awi.de/
Water samples for CFC and SF6 measurements were collected using a CTD/rosette sampling system. Th... more Water samples for CFC and SF6 measurements were collected using a CTD/rosette sampling system. The CFC/SF6 sample was the first sample drawn from the rosette bottle. The samples were collected in 250 cc glass stoppered bottles through a PVC tube connected to the rosette bottle drain valve. Bubbles were cleared from the tube with water flowing and the tube was inserted to the bottom of the 250 cc glass bottle. The glass bottle was placed in a wide mouth plastic jar that extended above the opening of the glass bottle. The overflow water collected in the jar, filling and overflowing the jar and covering the glass bottle opening. The flow continued for 3 overflow volumes of the glass bottle (750 cc) and the glass stopper was then inserted underwater preventing air from being trapped in the sample. The bottle was then placed upside down in the jar, the jar was capped and the sample stored at 2°C in a refrigerator to prevent degassing. At the end of the cruise, the samples were packed in insulated boxes with cold packs to maintain the 2°C temperature and shipped by air freight to Lamont-Doherty Earth Observatory. The measurements were carried out at Lamont using a dual purge and trap system interfaced to a dual ECD (electron capture detector) HP6890 gas chromatograph. When a water sample is introduced into the system, it is split into two aliquots, a 20 cc aliquot for CFC measurement and a 180 cc aliquot for SF6 measurement. The aliquots are transferred to appropriately sized sparging chambers and stripped with ultra high purity nitrogen, which transports the extracted gases to cold traps (Unibeads-2s for CFCs, Carboxan-1000 for SF6) cooled to -80°C. The traps are then heated to 110°C for CFCs and 165°C for SF6 and flushed into the gas chromatograph where CFCs are separated with a Porasil-B pre-column and a Carbograph 1AC main column and SF6 is separated with a pre-column and main column of Molecular Sieve 5A. The gases are detected by the ECDs. The ECDs are calibrated by running gas standards with known concentrations [...]
Geophysical Research Letters
Anthropogenic‐induced variations of the Atlantic Meridional Overturning Circulation (AMOC) and th... more Anthropogenic‐induced variations of the Atlantic Meridional Overturning Circulation (AMOC) and the associated Deep‐Water Formation (DWF) are a major concern. Using measurements of triple oxygen isotopes in the deep North Atlantic, we present novel evidence for a dramatic decadal to centennial shift in ocean conditions at the source region of DWF. These measurements suggest a recent decrease in the percentage of photosynthetic O2 derived from the source regions of AMOC in the Nordic Seas compared to the Little Ice Age. 1‐D model simulations suggest that a reduction in photosynthetic O2 production can explain the observed decrease. Alternatively, it may indicate a substantial decrease in sea‐ice cover and thus increased air‐sea gas exchange, bringing the isotopic composition of O2 closer to equilibrium with the atmosphere. Our novel data can serve as a benchmark for climate models.
Deep Sea Research Part A. Oceanographic Research Papers, 1991
Chlorofluorocarbon (CFC)-I2 and-11 (CF:CI? and CFCI3) measurements were made in seawater on the R... more Chlorofluorocarbon (CFC)-I2 and-11 (CF:CI? and CFCI3) measurements were made in seawater on the Ross Sea continental shelf and adjacent slope region in 1984. Concentrations of CFC-12 and CFC-I 1 in Ross Sea continental shelf water averaged nearly half that of saturated surface water. Circumpolar Deep Water within 50 km of the Ross Sea continental shelf also contained measureable CFC-12 and CFC-11, but an order of magnitude less than shelf waters. CFC-12 and CFC-I 1 concentrations in the deep water overlying the continental slope increased with depth, indicating recent ventilation and bottom water formation near the continental shelf. Several water masses on the continental shelf that are commonly distinguished on the basis of temperature and salinity characteristics also varied in CFC content, and thus in their modes and rates of ventilation and renewal. A time-dependent model reproducing the 1984 sub-surface shelf water CFC concentrations demonstrates the relative importance of mixed layer entrainment, gas exchange through leads in the winter sea ice field, and mixing with source waters derived from the Circumpolar Deep W;iter. Model results show that mixed layer entrainment at the beginning of winter is the dominant process ventilating sub-surface shelf water in the eastern Ross Sea. while western shelf waters also reqt,irc signific.'mt gas exchange during winter. Shelf water residence times can only be constrained by the model :rod available data to < lO years, but most probable values arc ~2.5 years in the eastern Ross Sea and ~4 years in the western Ross Sea. CFC concentr.'ttions in water which has circulated beneath and has been moditicd by the Ross Ice Shelf indicate that the transformation time from tligh Salinity Shelf Water to Ice Shelf Water can be as short as 3.5 years. With reasonable oxygen consumption and nutrient regeneration rates, the balance of ventilation anti mixing processes that reproduce observed shelf water CFC-12 concentrations also c:m account fl~r observed oxygen anti nitrate levels, if the western surface waters are undersaturated by ~ I11% at entrainment.
AGU Fall Meeting Abstracts, Dec 1, 2009
Although remote sensing technology provides measurement capability for a number of water properti... more Although remote sensing technology provides measurement capability for a number of water properties, there are important substances for which this technology does not currently exist and the only way to measure these substances is to collect water samples and return the samples to the lab. In the Arctic Ocean water samples are difficult to obtain from ships because of the extensive ice cover and thick pressure ridges. However, the ice provides a landing platform for aircraft, which can rapidly cover long distances. Aircraft have been used for sampling the Arctic Ocean for the past half-century using bottles and internally recording CTDs attached to a cable and lowered through leads or holes drilled in the ice. The routine CTD/rosette technology used for sampling from ships measures profiles of temperature, salinity, oxygen as well as other substances in situ, displays the data in real time for choosing depths to obtain water samples and the water samples are then collected with the rosette. These systems are too heavy and bulky to deploy from aircraft. We have developed a lightweight modular CTD/rosette system that is deployed through a 12-inch diameter hole drilled in the ice. The modules are connected together physically and electrically with the water bottle modules, which contain four 4-liter bottles each, stacked on top of the CTD module. The CTD traces are displayed on a laptop computer and the bottles are tripped using modified Seabird controllers and a melt-lanyard tripping mechanism. We have used this system for several years with Twin Otter fixed wing aircraft as part of the Switchyard Project, sampling a line of stations annually in the heavily ice covered region between Alert and the North Pole. Casts are carried out in a tent connected to the airplane using a lightweight winch mounted in the airplane. At the completion of a cast, the water modules are placed in a cooler with bags of snow to provide thermal stability at about 0°C and the end caps clamped shut. The modules are returned to the base camp where a variety of water samples are drawn and processed. We routinely measure samples for salinity, oxygen, nutrients, tritium, helium isotopes, CFCs, SF6, oxygen isotopes, barium and I-129, but the rosette sampler can be used for a wide range of substances. The water temperature of each bottle is measured when the oxygen sample is drawn and the average warming during the 6 - 10 hour transit time back to the base camp and during the sampling process is 2.5°C. There is no evidence in the gas samples of degassing or contamination with air and all samples are of very high quality. Vertical profiles will be presented to demonstrate data quality.
ABSTRACT A gas tight, small diameter, lightweight rosette, supporting equipment and an effective ... more ABSTRACT A gas tight, small diameter, lightweight rosette, supporting equipment and an effective operational protocol has been developed for aircraft supported sampling of sea water across the Lincoln Sea. The system incorporates a commercial off the shelf CTD electronics (SBE19+ sensor package and SBE33 deck unit) to provide real-time measurement data at the surface. We designed and developed modular water sample units and custom electronics to decode the bottle firing commands and close the sample bottles. For a typical station, we land a ski-equipped deHaviland Twin Otter (DHC-6) aircraft on a suitable piece of sea-ice, drill a 12&quot; diameter hole through the ice next to the cargo door and set up a tent to provide a reasonable working environment over the hole. A small winch with 0.1&quot; diameter single conductor cable is mounted in the aircraft by the cargo door and a tripod supports a sheave above the hole. The CTD module is connected to the end of the wire and the water sampling modules are stacked on top as the system is lowered. For most stations, three sample modules are used to provide 12 four (4) liter sample bottles. Data collected during the down-cast is used to formulate the sampling plan which is executed on the up-cast. The system is powered by a 3,700 Watt, 120VAC gasoline generator. After collection, the sample modules are stored in passively temperature stabilized ice chests during the flight back to the logistics facility at Alert where a broad range of samples are drawn and stored for future analysis. The transport mechanism has a good track record of maintaining water samples within about two degrees of the original collection temperature which minimizes out-gassing. The system has been successfully deployed during a field program each spring starting in 2004 along a transect between the north end of Ellesmere Island (Alert, Nunavut) and the North Pole. During the eight field programs we have taken 48 stations with twelve bottles at most stations (eight at some shallow stations) and with a miss-fire rate within two percent of those achieved with traditional over-the-side CTD/rosette systems.
Elsevier eBooks, Aug 1, 2018
AGU Spring Meeting Abstracts, May 1, 2004
ABSTRACT Each polar region has similarities but for the most part they are very different from ea... more ABSTRACT Each polar region has similarities but for the most part they are very different from each other. The differences are mainly a consequence of land/ocean configuration and contrasting hydrological states. While the Arctic seems to be warming, Antarctica, with the important exception of the Antarctic Peninsula, is cooling. The engagement of the two Polar Regions in the present climate system and their response and feedback to changes of the global climate and global carbon cycle is of fundamental scientific concern and high societal importance. Climate models indicate that the polar regions will bear the brunt of enhanced greenhouse global warming, and that the influence of polar climate change will spread to lower latitudes through its effect on sea level, Earth&#39;s albedo, and the ocean circulation. Recent observations lend support to some of these model-simulated trends. However, climate models do not include many of the physical or biogeochemical processes likely to be important for high latitude climate, nor do they resolve the small spatial scales characteristic of these processes. Our first priority should be to improve the observational grid required for to improve the models. The IPY offers the possibility of an international coordinated multidisciplinary effort, with consistent standards of measurements and observational design spanning both Polar Regions. We suggest the deployment of an array of sensors, much of which, due to the challenging environment conditions, will involve innovative technological systems. All climate elements will have to be covered in a unified program, including atmosphere, ocean, ice and land. For example, one can envision a series, perhaps of order ten per polar region, of heavily instrumented transects radiating from the both poles, spanning the continents, their margins and oceanic realm, to perhaps 60o latitude. Data will be gathered from the heights of the atmosphere to the depths of the ocean, with particular focus on the surface interface. Embedded in these spokes may be more focused objectives, perhaps targeting interaction between climate system elements. As with the IGY, a legacy will be established, a path will be created building the temporal dimension of research, with at least parts of the IPY observational grid extending into the future.
The EGU General Assembly, 2008
NCEI Accession 0116408 includes chemical, discrete sample, physical and profile data collected fr... more NCEI Accession 0116408 includes chemical, discrete sample, physical and profile data collected from POLARSTERN in the Arctic Ocean, Kara Sea and Laptev (or Nordenskjold) Sea from 1995-07-07 to 1995-09-20. These data include AMMONIUM (NH4), CHLOROFLUOROCARBON-11 (CFC-11), CHLOROFLUOROCARBON-113 (CFC-113), CHLOROFLUOROCARBON-12 (CFC-12), DISSOLVED OXYGEN, HYDROSTATIC PRESSURE, NITRATE, NITRITE, Potential temperature (theta), RADIUM ISOTOPES, SALINITY, TOTAL ALKALINITY (TA), WATER TEMPERATURE, pH, phosphate and silicate. The instruments used to collect these data include CTD and bottle. These data were collected by Leif Anderson of Gothenburg University; Department of Analytical and Marine Chemistry as part of the CARINA_06AQ19950707 data set. CDIAC associated the following cruise ID(s) with this data set: ARK-XI/1 and CARINA_06AQ19950707 The CARINA (CARbon dioxide IN the Atlantic Ocean) data synthesis project is an international collaborative effort of the EU IP CARBOOCEAN, and U.S. p...
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Papers by William Smethie