近岸抬升對臺灣東部黑潮生態系的影響

Effects of nearshore uplift on Kuroshio ecosystem of eastern Taiwan

呂俊逸(Lu Chun-Yi)

指導教授 ： 陳仲吉

國立臺灣師範大學/理學院/生命科學系/碩士(2019年)

https://doi.org/10.6345/NTNU201900423

摘要

黑潮是北太平洋之西方邊界流，除經由底層向上擴散外，其近岸抬升為淺層無機營養鹽的另一來源，故抬升的強弱可能影響此海域生態系之生地化反應。本研究利用OKTV計畫於2012年9月至2014年9月間，沿著臺灣東部23.75oN的黑潮測線，量測並探討黑潮近岸抬升的原因與其對黑潮生態系的影響。結果顯示，黑潮的流速、厚度、寬度及通量變化相當大，但其抬升強度主要與黑潮通量和其最快流速發生的深度和位置呈現顯著正相關，主因可能與局部通量改變使得渦度發生變化，為使渦度守恆，進而造成等密度線往近岸抬升之現象有關。另外黑潮表層100公尺以淺之無機營養鹽、葉綠素甲平均濃度亦與抬升強度呈現顯著正相關；雖然顆粒性有機碳濃度與抬升強度間並無相關，但其與葉綠素甲濃度有顯著正相關。而黑潮表層100公尺以淺，其超微型浮游植物組成主要以原核綠球藻(Prochlorococcus；Pro)為主，其次為聚球藻(Synechococcus；Syn)，再者為真核超微型浮游植物(Picoeukaryotes；PiEu)。就超微型浮游植物的豐度和組成差異以及異營性細菌的豐度變化與無機營養鹽濃度的關係而言，其中只有真核超微型浮游植物的平均豐度與硝酸鹽濃度呈現顯著正相關；而聚球藻在總水層(100公尺以淺)、表層(5公尺)和中層(50公尺)之組成比例〔Syn /(Syn+Pro+PiEu)〕則與N/P比值呈現顯著正相關，這種組成比例的改變可能與N/P比值的改變造成其潛在捕食者的豐度變化有關；但原核綠球藻的組成比例與N/P比值卻呈現顯著負相關，其組成比例的改變可能與其和聚球藻的交互作用有關。此外，異營性細菌的豐度亦與N/P比值呈現顯著負相關，且與原核綠球藻的平均豐度呈顯著正相關。若以海平面高度的變化作為間接證據，結果顯示此海域N/P比值的變化與海平面高度有顯著關聯，故此結果建議此海域N/P比值的變化應與黑潮東側的中尺度渦流(Mesoscale Eddy)有關。浮游生物的豐度與組成是影響大洋生態系變化的關鍵因素，研究結果建議此海域浮游生物的豐度與組成變化，可能受到黑潮近岸抬升強度的影響。此外，黑潮東側的中尺度渦流亦可能影響本海域生態系，值得後續研究。

關鍵字

黑潮 ； 近岸抬升 ； 無機營養鹽 ； N/P比值 ； 超微型浮游生物 ； 中尺度渦流

並列摘要

Kuroshio is the western boundary current of the North Pacific Ocean. Apart from the upward diffusion through the bottom layer, its nearshore uplift is another source of surface inorganic nutrients. Therefore, the uplift intensity may affect the biogeochemical response of the Kuroshio ecosystem. To explore the impact of the Kuroshio nearshore uplift on the ecosystem, hydrographic data along the transect line at 23.75oN of the OKTV program were measured between September 2012 to September 2014. The results show that the flow rate, thickness, width and fluxes of the Kuroshio varied temporally. The nearshore uplift intensity is significantly related to the fluxes and distance of the fastest velocity of the Kuroshio. This may be due to that its fluxes change locally in the upper layer, which causes vorticity imbalance. To maintain vorticity balance, the isopycnic lines steepen and uplift to the nearshore. The significant positive linear relationships are also observed between the uplift intensity and averaged values of inorganic nutrients or chlorophyll a over the 100m of water column. No significant pattern was evidenced between particulate organic carbon concentration and uplift intensity, but it is significantly positive correlated with chlorophyll a concentration. The major component of picophytoplankton is Prochlorococcus(Pro) and followed by Synechococcus (Syn) and Picoeukaryotes (PiEu) in the surface 100m of water column. Among all, only the average abundance of Picoeukaryotes is significantly correlated with nitrate concentration. Surprisingly, the abundance ratio of Synechococcus to (Syn+Pro+PiEu) in whole water column(above 100m)、surface(5m) and middle(50m) layers are positively related with the N/P molar ratio. This may be associated with the abundance of its potential predators which varied with the N/P molar ratio. The opposite trend is however found between the ratio of Prochlorococcus /(Syn+Pro+ PiEu) to the N/P ratio. The inverse trends between Prochlorococcus and Synechococcus to the N/P molar ratio may cause by interaction between these two picophytoplankton. Furthermore, the abundance of heterotrophic bacteria are negatively and positively related to the N/P ratio and the abundance of Prochlorococcus, respectively. The variant of the N/P ratio may be associated with the changing of the sea level height caused by mesoscale eddy on the eastern boundary of the Kuroshio. Overall, the results suggest that the nearshore uplift of the Kuroshio has significant effect on its pelagic ecosystem. In addition, the mesoscale eddy on the eastern boundary of the Kuroshio may also affect this ecosystem, and which is worthy of further study.

並列關鍵字

Kuroshio ； nearshore uplift ； inorganic nutrients ； N/P ratio ； picoplankton ； mesoscale eddy

參考文獻

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二、英文文獻

Agawin, N. S., Duarte, C., Agustí, S., & Vaqué, D. (2004). Effect of N:P ratios on response of Mediterranean picophytoplankton to experimental nutrient inputs. Aquatic Microbial Ecology, 34, 57-67.