東海陸棚內水團時空消長：比例、收支與意涵

Abstract

過往研究已得知東海陸棚生地化與營養鹽分布與關聯，但各水團對於其兩者時空過程影響及貢獻則不甚清楚。為此，本研究利用2003~2010年間航次實測與流量資料探討水團物理場的上（混合層）、下（次表層）兩層之季節變化。首先依據流量平衡的方法，利用HYCOM( HYbrid Coordinate Ocean Model)與其他水量資料計算流量收支；另外再利用東海七個不同月份航次與PN-Line四個航次的觀測資料，估算四季混合層與次表層的台灣海峽水(鹽度34以下)與黑潮水(鹽度34.4以上)兩者的比例。研究結果顯示，東海陸棚內混合層呈現夏淺（平均～20公尺）冬深（～100公尺）之季節變動。整層的流量收支結果指出台灣海峽(Taiwan Strait; TS)、陸棚邊緣(Shelf Break; SB)與對馬海峽(Tsushima/Korea Strait; TKS)是東海陸棚區的主要流量通道，此結果與前人研究類似；對馬海峽流量於秋季最大2.95 Sv (上1.80 Sv、下1.16 Sv)，冬季最小2.19 Sv (上1.49 Sv、下0.70 Sv)；台灣海峽流量亦是夏多（2.46 Sv, 上1.07Sv、下1.39Sv)，冬少0.44 Sv；陸棚邊緣淨流量冬高夏低 （夏～0.38 Sv，上 -0.40 Sv、下0.78 Sv；冬1.75 Sv，上1.05 Sv、下0.70 Sv)。水團比例的結果指出，夏季時整體含有48%台灣海峽水、52%黑潮水（其上層92%台灣海峽水、8%黑潮水；下層32%台灣海峽水、68%黑潮水）；冬季時整體含有27%台灣海峽水、73%黑潮水（上層含有32%台灣海峽水、68%黑潮水；下層含有1%台灣海峽水、99%黑潮水）。由此可知，夏季時東海陸棚混合層內大部份都是台灣海峽水，並且會從陸棚邊緣向外離開陸棚，唯有秋冬時黑潮水才會從陸棚邊緣進入混合層。此結果若配合各水團營養鹽資料可進一步探討東海生地化動態過程變化。

The distribution and correlation between the biogeochemistry and nutrients in the East China Sea (ECS) had been investigated. However, the influence and contribution of the water masses on the two spatiotemporal dynamics are still unclear. Here we explore the seasonal changes of the physics fields related to the proportions of water masses and budgets in the upper (mixed layer, ML) and lower (subsurface, SL) layers via cruise observations and modelled data from 2003 to 2010, respectively. The results generated from the HYCOM (Hybrid Coordinate Ocean Model) for whole water-column budget firstly show that Taiwan Strait (TS), Shelf Break (SB), and Tsushima/Korea Strait (TKS) as the major volume transports in the ECS shelf are in agreement with those from previous studies. The volume transports of TKS and TS are then high in autumn (Total, 2.95 Sv, i.e. ML 1.80 and SL 1.16) and summer (2.46 Sv, ML 1.07 and SL 1.39) and low in winter (TKS, 2.19 Sv (ML 1.49 and SL 0.70); TS, 0.44 Sv). By contrast, water transport for SB seasonally varied with a winter maximum (1.75 Sv, ML 1.05 and SL 0.70) and a summer minimum (0.38 Sv, ML -0.40 and SL 0.78 Sv). Further, the results collected by the LORECS cruises from 7 different months and PN-line for 4 seasonal data show that in summer the proportion of the whole water-mass is composed of 48% Taiwan Strait Water (TSW; Salinity < 34) and 52% Kuroshio Water (KW; Salinity > 34.4) (its ML: 92% TSW and 8% KW; SL: 32% TSW and 68% KW). In winter, the ECS shelf is composed of 27% TSW and 73% KW (ML: 32% TSW and 68% KW; SL 1% TSW and 99% KW). Overall, the ML (~20 m) of ECS shelf in summer consists mostly of TSW which flows through SB out of the ECS shelf. Only in autumn/winter, the KW flows through SB into the ML. The dynamic biogeochemistry of the ECS and nutrient supplies can be further explored.