臺灣東部海域深海水團之溫鹽性質與來源探討

Abstract

本研究旨在探討臺灣東部海域1000公尺深以下之深層水性質暨其來源和水團組成。本研究先使用「黑潮流量及其變化觀測計畫」下黑潮觀測航次所得之CTD資料，以溫鹽度的斜率變化界定深層水團的密度邊界，接著使用美國國家海洋資料中心的CTD、ARGO水文資料以及科技部海洋學門資料庫的船測CTD資料，整理出包含整個菲律賓海海域東經118°~150°，北緯4°~40°，每0.5°×0.5°為一網格，最大深度為2000公尺深平面網格的三維資料。然後，利用前一階段溫鹽斜率分析所得之密度區間，於設定之密度區間內進行均方根分析，以求鄰近深層海水與台灣東部海域深層海水性質之相似度，再計算位渦度、水層厚和斜壓地轉流場以追溯台灣東部海域深層水之可能路徑。最後，使用由花蓮東方的測線資料，帶入文獻中此地區可能之中、深層水來源水型，使用水團分析方法以求得台灣東部測線斷面上深層水的水團組合成分。 斜率分析研究結果顯示，台灣東部海域之深層水可以分成密度區間為1027.4~1027.5 kg m-3的「深海水第一層」，鹽度34.487~34.551、溫度3.764~2.700℃，以及密度區間為1027.6~1027.65 kg m-3的「深海水第二層」，鹽度34.578~34.610、溫度2.349~2.040℃。均方根分析的研究結果顯示，深海水第一層其鹽度性質與相同緯度海域相似，橫跨整個菲律賓海域，深海水第二層則是與其同緯度以上之菲律賓海北方海域相似。至於位渦度、水層厚以及斜壓地轉流場的計算結果則表示深海水第一層之深海水可能是由近北緯24°之深海通道進入菲律賓海盆，碰到琉球島弧後南下進入花東海盆而形成，深海水第二層也顯示了與深海水第一層類似的流況。水團分析的結果顯示，深海水第一層的水團組成為繞極深層水略等於太平洋中層水的比例，而深海水第二層則為繞極深層水大於太平洋中層水的情形。

The purpose of this study is to quantify the sources and routes of deep water mass east of Taiwan. A hydrographic data set, which ranges from 118°E to 150°E and from 4°N to 40°N with maximum depth 2000 m is obtained from Argo and CTD data over the past 20 years. This study adopts root mean square method to investigate the similarity of water masses east of Taiwan. The potential vorticity, water layer thickness and baroclinic geostrophic velocity calculating are also used to trace the deep water route in the Philippine Sea Basin. Finally, this study applies the water mass components analysis with North Pacific Intermediate Water and Circumpolar Deep Water, these two different water masses characters in the CTD datasets east of Taiwan to determine the water mass composition. The deep water east of Taiwan is defined as 'Layer 1 Deep Water' and 'Layer 2 Deep Water'. The former has a density range from 1027.4 kg m-3 to 1027.5 kg m-3, salinity range from 34.487 to 34.551 and temperature range from 3.764℃ to 2.701℃. The latter has a density range from 1027.6 kg m-3 to 1027.65 kg m-3, salinity range from 34.578 to 34.610 and temperature range from 2.349℃ to 2.040℃. The results of root mean square analysis show the water with similar salinity is zonally distributed in Layer 1 and is in northern half of Philippine Basin in Layer 2. Results from potential vorticity, water layer thickness and baroclinic geostrophic velocity indicate that the deep water east of Taiwan in Layer 1 most likely comes from the Pacific through the Philippine Sea till the Ryukyu Island Arc at 24°N. When the water impinges to the Ryukyu Island Arc, it is separated as two flows toward the north and the south. The southward-moving water goes into the Huatung Basin forming a cyclonic circulation and then leave the Huatung Basin to east of Luzon Island. The deep water east of Taiwan in Layer 2 shows a similar flow pattern as that in Layer 1. The deep water east of Taiwan in Layer 1 consists of Circumpolar Deep Water and North Pacific Intermediate Water but with more Circumpolar Deep Water than North Pacific Intermediate Water in Layer 2.