Scott, David B.
Permanent URI for this collectionhttps://hdl.handle.net/10222/22121
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Item Open Access Paleo-sea ice conditions of the Amundsen Gulf, Canadian Arctic Archipelago: Implications from the foraminiferal record of the last 200 years(2008-03) Schell, Trecia M.; Moss, Tamara J.; Scott, D. B. (David Bruce); Rochon, AndreFour boxcores were collected as part of the Canadian Arctic Exchange Shelf Study (CASES) in the Amundsen Gulf at water depths of 59 m to 600 m. Data from these cores help to develop a record of changes in the oceanographic history of the area over the last 200 years, with particular reference to the indication of paleo-sea ice formation, a key element of the Arctic ecosystem. The four sites cover a range of water depths and environments to provide a basis for comparison. The benthic foraminifera of sites CA-06 (253 m water depth) and CA-18 (600 m water depth) show an increase in Arctic Surface Water associated agglutinated foraminifera over the last similar to 100 years (uppermost 8 to 16 cm). These are indicating a decrease in sea ice cover and in cold saline Arctic Bottom Water influence; these are similar to Canadian Arctic Archipelago postglacial faunas. This contrasts with abundant planktic foraminifera at the same stations, suggesting strong, oceanic Arctic surface influence (little freshwater) in the central Gulf. The foraminifera of sites 403B (59 m water depth) and 415B (56 m water depth), at the outermost edges of Amundsen Gulf, indicate that the present-day location of the winter flaw lead has been in place for at least the last 100 years, with foraminiferal faunas similar to those of the Beaufort Shelf. Additionally, station 415 is on an earlier Holocene shoreline that is covered with cobbles.Item Open Access Messinian deep-water turbidites and glacioeustatic sea-level changes in the North Atlantic: Linkage to the Mediterranean Salinity Crisis(1996-06) Zhang, JJ; Scott, D. B. (David Bruce)Our benthic foraminiferal data clearly indicate eight layers of deepwater turbidites during the Messinian (MTL 1-8) and one in the early Pliocene (PTL 1) in Ocean Drilling Program Leg 105, Site 646B. These deep-water turbidite deposits are characterized by highly concentrated agglutinated marsh benthic foraminifera (e.g., Trochammina cf. squamata, Ammotium sp. A, Miliammina furca), rounded quartz, polished thick-walled benthic foraminifera, wood fragments, plant seeds, plant fruit, and highly concentrated mica and are interbedded with sediments containing deep-water benthic faunas. We suggest these turbidites deposited during sea-level low stands (similar to 80-100 m below sea level), and their ages are tentatively correlated to 6.59, 6.22, 6.01, 5.89, 5.75, 5.7, 5.65, 5.60, and 5.55 Ma, respectively, based on the Messinian oxygen isotope enrichments at Site 552A of Deep Sea Drilling Project Leg 81. The turbidites layers during the late Messinian, coeval with frequent climate changes suggested by six oxygen enrichment excursions of Site 552A, may have been in part linked to the late Messinian evaporite deposits in the Mediterranean Basin. The most profound climate changes at 5.75 and 5.55 Ma may have been related to the Lower and Upper Evaporites in the Mediterranean Basin.Item Open Access Radiocarbon evidence for annual growth rings in the deep-sea octocoral Primnoa resedaeformis(2005) Sherwood, OA; Scott, D. B. (David Bruce); Risk, MJ; Guilderson, TPThe deep-sea gorgonian octocoral Primnoa resedaeformis is distributed throughout the Atlantic and Pacific Oceans at depths of 65 to 3200 m. It has a 2-part skeleton of calcite and gorgonin. Towards the inside of the axial skeleton gorgonin and calcite are deposited in concentric growth rings, similar to tree rings. Colonies were collected from the NE Channel (NW Atlantic Ocean, southwest of Nova Scotia, Canada) from depths of 250 to 475 m. Radiocarbon was measured in individual rings isolated from sections of each colony, after dissolution of calcite. Each Delta C-14 measurement was paired with a ring age determined by 3 amateur ring counters. The precision of ring counts averaged better than +/- 2 yr. Accurate reconstruction of 20th century bomb-radiocarbon showed that (1) the growth rings are formed annually, (2) the gorgonin is derived from surface particulate organic matter (POM) and (3) useful environmental data are recorded in the organic endoskeletons of deep-sea octocorals. These results support the use of R resedaeformis as a long-term, high resolution monitor of ocean surface conditions, particularly in temperate and boreal environments where proxy data are lacking.Item Open Access Stable isotopic composition of deep-sea gorgonian corals Primnoa spp.: a new archive of surface processes(2005) Sherwood, OA; Heikoop, JM; Scott, D. B. (David Bruce); Risk, MJ; Guilderson, TP; McKinney, RAThe deep-sea gorgonian coral Primnoa spp. live in the Atlantic and Pacific Oceans at depths of 65 to 3200 m. They have an arborescent growth form with a skeletal axis composed of annual rings made from calcite and gorgonin. Lifespans may exceed several hundreds of years. It has been suggested that isotope profiles from the gorgonin fraction of the skeleton could be used to reconstruct long-term, annual-scale variations in surface productivity. We tested assumptions about the trophic level, intra- and inter-colony isotopic reproducibility, and preservation of isotopic signatures in a suite of modern and fossil specimens. Measurements of gorgonin delta N-15 indicate that Primnoa spp. feed mainly on zooplankton and/or sinking particulate organic matter (POMsink), and not on suspended POM (POMsusp) or dissolved organic carbon (DOC). Gorgonin delta C-13 and delta N-15 in specimens from NE Pacific shelf waters, NW Atlantic slope waters, the Sea of Japan, and a South Pacific (Southern Ocean sector) seamount were strongly correlated with surface apparent oxygen utilization (AOU; the best available measure of surface productivity), demonstrating coupling between skeletal isotopic ratios and biophysical processes in surface water. Time-series isotopic profiles from different sections along the same colony, and different colonies inhabiting the same area were identical for delta C-13, while delta N-15 profiles were less reproducible. Similarity in C:N, delta C-13 and delta(15) N between modern and fossil specimens suggest that isotopic signatures are preserved over millennial timescales. These results support the use of Primnoa spp. as historical recorders of surface water processes such as biological productivity and the isotopic composition of source nutrients.Item Open Access Foraminiferal assemblage changes over the last 15,000 years on the Mackenzie-Beaufort Sea Slope and Amundsen Gulf, Canada: Implications for past sea ice conditions(2009-06) Scott, D. B. (David Bruce); Schell, Trecia; St-Onge, Guillaume; Rochon, Andre; Blasco, SteveTwo cores, one from the Beaufort Sea Slope at 1000 m water depth (core 750) and one from the Amundsen Gulf at 426 m (core 124), were collected to help determine paleo-ice cover in the Holocene and late glacial of this area. Site 750 is particularly sensitive to changes in paleo-ice cover because it rests beneath the present ice margin of the permanent Arctic ice pack. Core 124 was sampled just in front of the former glacier that moved out into the Amundsen Gulf and started to recede about 13 ka B. P. Both cores have a strong occurrence of calcareous foraminifera in the upper few centimeters, but these disappear throughout most of the Holocene, suggesting more open water in that time period than present. In the sediments representing the end of the last glacial period (dated at similar to 11,500-14,000 calibrated years B.P. (cal B.P.)) a calcareous fauna with an abundant planktic foraminiferal fauna suggests a return to almost permanent ice cover, much like the central Arctic today. Together with the foraminifera there was also abundant ice-rafted debris (IRD) in both cores between 12,000 cal B.P. and similar to 14,000 cal B.P., but those units are of different ages between cores, suggesting different events. The IRD in both cores appears to have the same magnetic and chemical signals, but their origins cannot be determined exactly until clay mineralogy is completed. There is abundant organic debris in both cores below the IRD units: the organics in core 750 are very diffuse and not visually identifiable, but the organic material in core 124 is clearly identifiable with terrestrial root fragments; these are (14)C dated at over 37,000 years B.P. This is a marine unit as it also has glacial front foraminifera in the sediment with the organic debris that must have been originating from subglacial streams. The seismic and multibeam data both indicate glaciers did not cross the core 124 site.