南海深層210Pb與210Po放射核種的沉降通量時序變化

Temporal Variation of Sinking Fluxes of 210Pb and 210Po in the Deep Basin of the South China Sea

陳彥君(Yen-Chun Chen)

指導教授 ： 魏慶琳

國立臺灣大學/理學院/海洋研究所/碩士(2016年)

https://doi.org/10.6342/NTU201601999

摘要

本研究於2013年9月到2015年5月，在南海SEATS時序測站 (116º00ºE, 18º00ºN) 施放兩組錨碇式沉降顆粒收集器，以量測水深 2000 公尺及3500 公尺的210Pb (FPb-210) 和210Po (FPo-210) 通量時序變化。
總顆粒通量 (FMass) 在水深2000公尺變化範圍介於27.0到447.2 mg m-2d-1之間，FMass (3500m) 介於30.8到528.4 mg m-2d-1之間，呈現夏低冬高的現象，顯示南海表層顆粒產生量受到季風的影響；FPb-210 (2000m) 為7.6 ~ 48.41 dpm m-2d-1，FPb-210 (3500m) 為6.93 ~ 98.47 dpm m-2d-1，210Pb的通量變化明顯受控於FMass； FPo-210在2000公尺及3500公尺分別為3.5 ~ 233.1 dpm m-2d-1以及24.8 ~ 427.9 dpm m-2d-1，與文獻報導之2008-2009年觀測結果相似。
過去科學家認為沉降顆粒樣品可能因物質再溶解而影響元素垂直通量的準確度，為確認此效應對於FPo-210量測上造成的影響，本研究分析沉降顆粒採樣杯中上層填充液 (supernatant) 的210Po濃度，結果顯示填充液中210Po總活度佔沉降顆粒中210Po的極少量 (<1%)，顯示沉降顆粒無210Po再溶解現象，因此無須考量再溶解效應修正通量。
本研究整理過去210Pb和210Po於南海水體中的活度分布以及沉降顆粒收集器量測的結果，綜合討論210Pb和210Po於南海的收支情況。由於西菲律賓海水與南海水交換以及兩海域之間的210Pb活度差異，對210Pb收支造成明顯影響，有明顯的邊緣清除現象明顯；而210Po活度在兩海域之間的活度並無明顯差異，因此西菲律賓海水的輸入，不會對210Po於南海的收支平衡有所影響。

關鍵字

南海時序測站 ； 顆粒體 ； 210Pb通量 ； 210Po通量 ； 邊緣清除現象

並列摘要

Vertical fluxes of total mass (Fmass), 210Pb (FPb-210) and 210Po (FPo-210) were determined by sediment traps deployed at two depths, 2000 m and 3500 m, at SEATS (South East Asian Time-series Study,116º00 º E,18 º 00 º N) in the northern South China Sea (SCS) during September 2013 - May 2015.
The Fmass varied seasonally, ranging from 27.0 to 447.2 mg m-2d-1 and from 30.8 to 528.4 mg m-2d-1 at 2000 m and 3500 m, respectively. The FPb-210 ranged from 7.7 to 48.4 dpm m-2d-1 and from 7.0 to 98.5 dpm m-2d-1 at the two depths, respectively. Noticeable correlation between the Fmass and the FPb-210 was found, indicating the dominant role of particle settling in the 210Pb removal from the water column of the SCS. The FPo-210 ranged from 3.5 to 233.1 dpm m-2d-1 and from 24.8 to 427.9 dpm m-2d-1 at 2000 m and 3500 m, respectively. Similar to the findings of literature data in 2008 and 2009, both the FPb-210 and the FPo-210 tend to increase with depth.
Concerns were raised regarding the effect of particle decomposition on the solubilization of elements into dissolved phase in sediment traps during sample storage. The effect of 210Po regeneration and its influence on the accuracy of the determination of the FPo-210 were evaluated. Based on the 210Po concentration in the supernatant of the sampling cups, it is found that the 210Po was less than 1% of the total activity in the particles, implying that the effect of re-solubilization is minimal and no correction was needed for the FPo-210 determination.
Based on the literature data of vertical profiles and the fluxes determined by this study, the budgets of 210Pb and 210Po in South China Sea basin were summarized. Due to the evident difference of the 210Pb activity in the Western Philippine Sea and the South China Sea, boundary scavenging plays an important role on 210Pb cycling in the SCS basin. On the contrary, less effect of water exchange between the two oceans was found for 210Po cycling in the SCS.

並列關鍵字

SEATS ； particle ； 210Pb flux ； 210Po flux ； boundary scavenging

參考文獻

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