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Accumulation mechanisms of trace metals into Arctic sea ice

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Title: Accumulation mechanisms of trace metals into Arctic sea ice
Other Titles: 北極海における海氷への微量金属蓄積メカニズムの解明
Authors: Evans, La Kenya Elizabeth Browse this author
Issue Date: 25-Mar-2019
Abstract: In the last 20 years the Arctic Ocean has experienced over 32% loss of summer sea ice. This loss can influence the cycling of biogeochemical materials, affecting seawater’s biology and chemistry. Sea ice is important for the supply of biogeochemical materials (trace metals, nutrients, dissolved organic matter, suspended particulate matter, etc.) to the surface waters of the polar oceans, but its role is not clear. In this study we focus on trace metals. Understanding the accumulation and release mechanisms into Arctic sea ice will clarify the geochemical behaviour of trace metals. Both dissolved (D, <0.2 μm), and labile particulate (LP, Total Dissolvable - Dissolved) Fe, Mn, and Cd were examined in sea ice and seawater collected from the Chukchi Sea, Arctic Ocean. Samples were pre-concentrated utilizing the solid-phase extraction NOBIAS Chelate PA-1 resin (Hitachi High-Technologies Corporation) and analyzed on a Graphite Furnace Atomic Absorption Spectrometer. Chukchi seawater showed high percentages for DMn (71.5%) and DCd (66.3%) with a high percentage of LPFe (94.1%). In seawater, DCd was the only metal to correlate with phosphate (R2 = 0.78) indicating a biogeochemical cycling source. Chukchi seawater concentrations of Fe and Mn may have been controlled through external sources. Sediments (shelf or river) supplied LPFe and LPMn. DFe and DMn were supplied by the Alaskan Coastal Current. Trace metal concentrations in Chukchi drifting ice were heterogeneous. Drifting ice showed high percentages for the LP fraction (99.2% Fe, 63.6% Mn and 71.2% Cd). This data indicated that, regardless of the trace metal behavior in Chukchi seawater, Chukchi drifting ice was observed to have a preference to accumulate or retain the LP trace metal fraction. To examine possible trace metal accumulation processes utilized by Arctic sea ice, the association between trace metal concentrations and ice structure were observed in floe ice. The structure of sea ice reflects the process of ice formation, which may aid in the determination of accumulation processes. An Arctic sea ice core was examined. Using photographic analysis for the percentage of pore area and δ18O analysis, sea ice structure in the core sample showed snow, granular, mixed (granular + columnar) and columnar ice. Salinity and nutrients were low, indicating brine drainage and multi-year ice. High trace metal concentrations in snow ice 4 indicated meteoric snow as a source. High concentrations of LPFe in granular ice indicated possible particulate trace metal scavenging by frazil ice. Concentrations of LPMn and LPCd were low compared to DMn and DCd in granular and snow ice. It is possible that reduction of LPFe and LPM after particle entrainment released DMn and DCd, indicating a chemical transformation process. Low dissolved and labile particulate trace metal concentrations in mixed and columnar ice indicated a release due to brine drainage. The accumulation and retention of trace metals into Arctic sea ice may be influenced by the form of sea ice. Drifting sea ice can be a long-range transporter of LP metals. Floe ice can provide both D and LP metals to the local area. Therefore, sea ice form, processes of sea ice formation, chemical transformation and brine release, are important for the accumulation, retention and release of trace metals from sea ice.
Conffering University: 北海道大学
Degree Report Number: 甲第13542号
Degree Level: 博士
Degree Discipline: 環境科学
Examination Committee Members: (主査) 准教授 西岡 純, 教授 鈴木 光次, 教授 力石 嘉人, 助教 豊田 威信, 准教授 近藤 能子(長崎大学水産学部/大学院水産・環境科学総合研究科)
Degree Affiliation: 環境科学院(地球圏科学専攻)
Type: theses (doctoral)
Appears in Collections:課程博士 (Doctorate by way of Advanced Course) > 環境科学院(Graduate School of Environmental Science)
学位論文 (Theses) > 博士 (環境科学)

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