2009年夏季東海表水元素汞海氣交換通量與分布

Abstract

本研究主要探討2009 年夏季東海海域表水之元素汞的分佈及海氣交換通量。於2009 年6 月28 日~7 月13 日利用海研一號執行航次（OR1-905），在東海海域進行採樣。航行中進行汞物種的量測，項目如下：大氣中氣態元素汞（GEM）、表水中的氣態元素汞（DEM）、及活性汞（RM）、總汞（TM）、溶解性總汞（DTM）。本研究海域內汞物種的平均濃度及變化範圍分別為：GEM之平均濃度為6.5±1.2 ng/m3（n=957），DEM為150.3±109.9 fM（35.4-592.5 fM , n=31）、RM為1.7±0.7 pM（0.3-3.2 pM , n=31）、TM為26.7±22.1 pM（6.6-87.3 pM , n=31）、DTM為23.5±21.5 pM（4.3-81.2 pM , n=31）。研究發現GEM的濃度受到區域的影響，而有近岸濃度高、遠洋低的分布，本研究利用NOAA之氣團回推圖（HYSPLIT）推測當地氣團來源，研究發現GEM濃度分布可能是受到當地氣團來源影響。表水中的汞物種（DEM、RM、TM 與 DTM）皆有相似的趨勢，大致成西高東低的分布，在長江口測站達到最高值，在黑潮流經的東海西部邊緣，則是濃度最低。本研究利用測得的大氣元素汞濃度、DEM濃度、月平均衛星風場等資料估算東海陸棚各水團海氣交換的通量值分別為沿岸湧升流區域為4.1 nmolm-2day-1、長江沖淡水區域為1.2 nmol m-2day-1、台灣暖流水及陸棚混和水區域為0.9 nmol m-2day-1、黑潮區域為0.3 nmol m-2day-1。結果顯示，整個陸棚邊源都呈現強烈的source的現象，最後估算出整個東海元素汞海氣交換通量為0.98 nmol m-2day-1，其數值與同緯度之汙染影響大的邊緣海相似。

The distribution and air-sea exchange flux of Hg0 were determined in the surface water of the East China Sea ( ECS) by the cruise OR1-905 between June 29 and 13 July, 2009. Different Hg species, such as: gaseous elemental mercury ( GEM ), dissolved elemental mercury ( DEM )、reactive mercury ( RM )、total mercury ( TM ), and dissolved total mercury ( DTM ) were also measured. The average concentrations of GEM, DEM, RM, TM and DTM in surface seawater were 6.5± 1.2 ng/m3(n = 956), 150.3± 109.9 fM (35.4- 592.5 fM, n=31) , 1.7± 0.7pM (0.3- 3.2 pM, n = 31), 26.7± 22.1 pM (6.6- 87.3 pM, n = 31) and 23.5± 21.5 pM (4.3- 81.2pM , n=31), respectively. Distinctive spatial variations of GEM concentrations were revealed, with generally higher concentrations near land masses (mainland China or Taiwan). Using source tracking techniques such as NOAA-HYSPLIT back trajectory and QSCAT wind vector, the distribution of GEM in ECS were seemingly influenced by the source of the air masses. The distribution of different Hg species (DEM、RM、TM and DTM) also had similar trends, with highest value appeared in Changjiang Diluted Water (CDW), and lowest value appeared in Kuroshio Water (KW). In area of the ECS, the air-sea exchange fluxes of Hg were estimated to be：Cold Upwelling Water (CUW) averaged 4.1 nmol m-2day-1, CDW averaged 1.2 nmol m-2day-1, Taiwan Strait Warm Water (TSWW) and Shelf Mixing Water (SMW) averaged 0.9 nmol m-2day-1, KW averaged 0.3 nmol m-2day-1. The continental shelf of ECS was a strong source (0.98 nmol m-2day-1 )for Hg0 . These fluxes assessments are comparable to other observations of polluted marginal sea at the same latitude.