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Advanced Taiwan Ocean Prediction System

May/9/2017: Prof. Chung-Wen (June), Chang’s Speech:

Title: The biological response to MJO forcing over the MC region

 

Abstract:

Approximately half of the global primary production is carried out by oceanic phytoplankton. In most of the world ocean, productivity is enhanced in regions of upwelling of cold, nutrient-rich, bottom water in the euphotic zone; thus, local oceanography and phytoplankton productivity are tightly linked (e.g. Probyn et al., 1994; Lutjeharms and De Ruijter, 1996; Thompson et al., 2009, 2011). Many times, terrestrial nutrient inputs from local river systems also play a role in influencing nutrient supply; however, the contributions from river discharge to primary production are mostly limited to coastal regions as these nutrients would be mostly consumed in the coastal waters before reaching the larger area of the open ocean.

Located within the climatological Indo-Pacific warm pool, the Maritime Continent (MC) produces one of the most biological diversity over the world both over land and ocean. It is the distinct geophysical feature of broken islands, shallow seas, the elevated terrain of high mountains and short basin rivers in the MC region that complicate the interactive processes of the atmosphere, ocean, and land, critical for controlling the local variability of MC from weather to biological system. From November to February, the oceans in MC region are in weak Ekman-downwelling phase, which limiting the nutrient availability essential for Chlorophyll production; yet strong MJO (Madden-Julian Oscillation, 1972) events can bring up significant chlorophyll blooms in the open oceans such as the Banda Sea and the Bismarck Sea.  In contrast to most literature conceives wind-induced vertical mixing associated with the MJO as the main mechanism that controls the nutrient availability for the biological response in the Banda Sea, we find that the upstream weathering over the lands is the key factor for the nutrients supply in the open ocean.  Here, we use statistical methods to analyze the chlorophyll distribution in the MC region during strong MJO events with satellite-derived observations and the atmosphere and ocean reanalysis products CFSR.  We found that the nutrient availability in the Banda Sea comes from the river/coastal discharges associated with heavy MJO rainfalls on Kalimantan/Borneo island several MJO phases earlier.  The MJO-driven anomalous eastward surface current then transports the upstream nutrient load from Kalimantan Strait via the Java Sea into the Banda Sea, giving the chlorophyll growth in the Banda Sea a few weeks later.

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