北南海浮游植物生物量(葉綠素-a)之多時間尺度變化分析

Multi-scale temporal variation in phytoplankton biomass (chlorophyll-a) in the northern South China Sea

侯力慈(Li-Tzu Hou)

指導教授 ： 柯佳吟

國立臺灣大學/生命科學院/漁業科學研究所/碩士(2019年)

https://doi.org/10.6342/NTU201902998

摘要

浮游植物是海洋生態系統的主要生產者，並在食物鏈中扮演重要的角色。它的豐度和分布與水溫、營養鹽、光和浮游動物的掠食有關，且亦受季節、天氣和混合層深度（Mixed layer depth，簡稱MLD）影響。本研究整理南海北部的南海時間序列測站（SEATS，116°E和18°N）在1999-2019年間收集到的30次航次資料，進行水層中葉綠素-a（Chlorophyll-a，簡稱Chl-a）濃度的“日變化”、“季節變化”及“超過十年變化”的多時間尺度分析。結果顯示在“日變化”中，Chl-a濃度在白天逐漸增加至傍晚時最高，隨後減少至黎明前最低，在冬季時，最大值與最小值差可達2倍；Chl-a濃度與混合層深度（Mixed layer depth，簡稱MLD）或海表溫度在“日變化”中沒有顯著相關性。在“季節變化”分析中，冬季（十二月和一月）的MLD較深使得Chl-a濃度均勻分布於表層且高於其他月份；此外，航次間的表層Chl-a濃度與有光層積分Chl-a濃度值分別與海表溫度和MLD有顯著相關。在“超過十年變化”的長時間尺度上，隨著海表溫度的上升（冬季: 0.05 ℃ /年; 其他月份: 0.06 ℃ /年），混合層深度亦隨之變淺（冬季: -0.80 m /年; 其他月份: -0.52 m /年），這使得SEATS 測站浮游植物生長所需的底層營養鹽輸入程度變小，最終造成有光層積分Chl-a濃度下降（冬季: -0.73 mg m-2 /年; 其他月份: -0.49 mg m-2/年）。結果表示，由於採樣的時間點可能造成Chl-a濃度的差異，在進行浮游植物濃度變化及初級生產力研究時，需考量短時間的日夜波動。而在二十年變化的分析中，本研究發現隨著海平面水溫升高及混合層深度變淺，表水10米水深的Chl-a濃度及100米有光層Chl-a濃度積分值逐年降低，可能造成南海北部生態與資源的變動。

關鍵字

浮游植物 ； 葉綠素-a ； 表水水溫 ； 混合層深度 ； 南海時間序列測站

並列摘要

Phytoplankton are major primary producers in marine ecosystems and can directly impact higher trophic levels. The abundance and distribution of phytoplankton are known to be related to water temperature, nutrient, light, and zooplankton grazing. Therefore, the phytoplankton dynamic is often linked to seasonal variations and mixed-layer depth (MLD). This study compiled and analyzed in situ fluorescence and chlorophyll-a (Chl-a) concentration data at the SouthEast Asia Time-series Study (SEATS, 116°E and 18°N) station in the northern South China Sea, to understand the phytoplankton dynamics in different time scales, diurnal, seasonal, and decadal scales. In situ Chl-a concentrations and water temperature were collected for 30 cruises throughout 1999 and 2019 at the SEATS station, and the euphotic depth integrated Chl-a concentrations were analyzed and compared with sea surface temperature (SST) and MLD. In the diurnal scale, the results showed the Chl-a concentrations increased during the day, decreased during the night time, and the variations could be as high as two-fold. In the seasonal scale, the Chl-a concentrations, SST and MLD showed two distinct patterns: the cold seasons (December and January) with low SST, deep MLD, and high Chl-a concentrations; the warm seasons (March to November) with high SST, shallow MLD, and low Chl-a concentrations. Seasonal Chl-a concentrations, SST and MLD also showed correlations. In the decadal scale, the 20-year data showed an increase in SST (cold season: 0.05 ℃/ year; warm season: 0.06 ℃/ year), a decrease in MLD (cold season: -0.80 m/ year; warm season: -0.52 m/ year), and a decrease in depth integrated Chl-a concentrations (cold season: -0.73 mg m-2/ year; warm season: -0.49 mg m-2/ year) at the SEATS station. The results suggest that, in short-term study, it is important to consider the diel fluctuations when conducting field sampling for phytoplankton and primary productivity studies; in the 20-year analysis, the increase of SST and the shallowing of MLD led to the decrease in Chl-a concentrations, and which may impact the ecology and resources in the northern South China Sea.

並列關鍵字

phytoplankton ； chlorophyll-a ； sea surface temperature ； mixed layer depth ； the SouthEast Asia Time Series (SEATS) Station

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