SHALLOW SHELF UPWELLING DYNAMICS AND COOL WATER MIXING BETWEEN TWO DIFFERENT REGION THROUGH KARIMATA STRAITS M. F. Akhir, P.H. Kok, Z. Zainol Institute of Oceanography and Environment, Universiti Malaysia Terengganu 2015 Aquatic Science Meeting, Granada, Spain 26 Feb 2015 Institute of Oceanography & Environment 2015 Aquatic Science Meeting

South China Sea Throughflow Qu et. al, 2006 Institute of Oceanography & Environment 2015 Aquatic Science Meeting

Upwelling Area: Western Boundary of South China Sea Vietnam Malaysia Observe the thermal front and it associated upwelling front. Institute of Oceanography & Environment 2015 Aquatic Science Meeting

Upwelling system Institute of Oceanography & Environment 2015 Aquatic Science Meeting

Upwelling Area: Western Boundary of South China Sea Vietnam Malaysia Observe the thermal front and it associated upwelling front. Institute of Oceanography & Environment 2015 Aquatic Science Meeting

Cruise data, 2011-1013 a) Thermocline uplifting b) June/July 2011 c) October 2012 Note The data of T1, T2 (27th June 2012 – 1st July 2012) , T5 and T6 (3rd – 6th July 2013) are collected during southwest monsoon. T1 and T2 Uplifting of thermocline is observed, until the subsurface at depth ~15m - ~20m. T5 and T6 Uplifted of thermocline of 30°C is observed, the location is fairly consistent with the location of cooler water band. Isotherm uplifting is a typical sign of upwelling; the uplifted isotherm is caused by the upwelling movement (Jing et al., 2009; Jing et al., 2011). The isotherm of T1 and T2 is only uplifted until the subsurface. Literature stated high atmospheric heat flux (Su & Pohlmann, 2009) and wind variation might restrict the (Kämpf, 2004) upwelled water from reaching the surface. In fact, the on board ship wind data (not shown) showed the wind direction is inconsistent, which probably caused the water does not reaching the surface. Low salinity coastal front prevent water from reaching the surface (figure on next page). T3 and T4 No thermocline uplifting is observed, thermocline is located deeper, well-mixed. The wind during October is basically stronger in SCS, it creates turbulence in sea water and break the stratification layer, result in well-mixed water column, restricted the uplifted of isotherm (Marghany et al., 1996). Northeast monsoon characteristics. e) f) June/July 2013 Institute of Oceanography & Environment 2015 Aquatic Science Meeting

January: The maximum intensity of southward western boundary current is developed, causing the maximum advection of cold water from north to south, forming SST front at around ~103°E and 104°E. Institute of Oceanography & Environment 2015 Aquatic Science Meeting

Halocline Lifting Halocline Lifting a) b) The influence of strong low-salinity coastal water (32.2-32.8 psu) can be seen between 15-20 m (Figures 2c and 2d). This coastal stratification is believed to have prevented the upwelling from reaching the surface. Institute of Oceanography & Environment 2015 Aquatic Science Meeting

ROMS Model Current Circulation (July) Temperature The upwelling and advection from south happen spontaneously? From Figure 3 (MODIS-Terra SST) and Figure 6, show that cooler SST is not continuous, it is isolated and stretches from 1.5-6°N. Current Circulation (July) Temperature Institute of Oceanography & Environment 2015 Aquatic Science Meeting

Temperature and Vertical Velocity Institute of Oceanography & Environment 2015 Aquatic Science Meeting

Positive wind stress curl = Upwelling Formula: 𝑐𝑢𝑟𝑙 𝜏 = 𝜕𝜏 𝑦 𝜕 𝑥 − 𝜕𝜏 𝑥 𝜕 𝑦 Where 𝜏 𝑥 and 𝜏 𝑦 represents the meridional and zonal components of wind stress. 𝜏 𝑥 and 𝜏 𝑦 can be calculated by following equations: 𝜏 𝑥 = 𝜌 𝑎 𝐶 𝑑 𝑊 𝑚𝑎𝑔 𝑈 𝜏 𝑦 = 𝜌 𝑎 𝐶 𝑑 𝑊 𝑚𝑎𝑔 𝑉 Where, density of air, 𝜌 𝑎 =1.22 𝑘𝑔 𝑚 −3 , dimensionless drag coefficient, 𝐶 𝑑 =2.6× 10 −3 , magnitude of wind speed, 𝑊 𝑚𝑎𝑔 , meridional wind speed, 𝑈, and zonal wind speed, 𝑉. In this paper, slightly higher drag coefficient is applied to roughly compensate for the underestimate of the wind stress caused by using mean data in the nonlinear calculation in above equations as described by Bakun & Nelson (1977). Unit: Nm-3 The wind stress curl is increase from June to August and reach maximum in August before it decrease in September. The increase and decrease of wind stress curl fairly consistent with the increase and decrease of width of upwelling band. Enriquez & Friehe (1995), wind stress curl wider the upwelling front offshore, which coincide with our finding where the width of cold water band is in good relation with positive wind stress curl. Wind stress curl (Nm-3 ) calculated from ECMWF wind field from June to September Institute of Oceanography & Environment 2015 Aquatic Science Meeting

Upwelling index Institute of Oceanography & Environment 2015 Aquatic Science Meeting

MODIS and ECMWF wind stress,a) Jun, b) July c) August, d) Sept Cooler water band form parallel with east coast of PM along 104°E (Upwelling condition). Southwest monsoon wind, almost parallel to east coast of PM, according to ekman transport, the water is deflected right, away from the coast, upwelling condition. Start appear in June, July and August, the band width increased, more predominant at center near 3-4°N, before decaying in December. Stretched from southernmost tip of PM until 6°N, very close top coast, except in the north near Terengganu 6°N. At north, the cool water band is bending away from the coast of PM, influence by current at the northern part, which carry the water away from the coast. From July until September, northward advection water from the south is observed. The width of cool water band is increase from July until August and decrease in September. The width of cold water band is influence by the strength of positive wind stress curl and well as the strength of current that advect cold water from south to north, located at Kalimantan coast. The current increase it intensity from July until August and weaken in September. The stronger the positive wind stress curl, the bigger the upwelling band. The stronger the current flow from south to north, the stronger of advection, increase the width of cool water band. At east coast of PM, local influence (upwelling) and advection from south are happen spontaneous. MODIS and ECMWF wind stress,a) Jun, b) July c) August, d) Sept Institute of Oceanography & Environment 2015 Aquatic Science Meeting

Southwest monsoon averaged (2003 - 2013) latitudinal Ekman transport, integrated Ekman pumping and total transport (unit: m3 s-1 per meter of coast). Institute of Oceanography & Environment 2015 Aquatic Science Meeting

Upwelling or Advection ? At south Advection is found. Current: Prove of advection and influence the width of cool water band. August: The month where the biggest upwelling band is found. In August, the intensity of current that advect the cold water from Kalimata coast to east coast of PM is strongest, creating the biggest upwelling band. At North Bending of cool water band away from the east coast of PM is found. Influence by the current at north part of east coast of PM that bring away the water. Upwelling or Advection ? Institute of Oceanography & Environment 2015 Aquatic Science Meeting

Monthly climatological zonal wind. Strong zonal wind stress in the Java Sea drive current into SCS during August (southwest monsoon) Institute of Oceanography & Environment 2015 Aquatic Science Meeting Susanto et. al. 2006

a) b) Current circulation during a)northeast monsoon and b)southwest monsoon. Institute of Oceanography & Environment 2015 Aquatic Science Meeting

Institute of Oceanography & Environment 2015 Aquatic Science Meeting

Conclusion Local upwelling present along the east coast of Peninsular Malaysia with influence of cool advection water starting in August. Wind driven current circulation advect cooler and high productivity water (possibly from localize upwelling in Java sea) into the SCS. At south Advection is found. Current: Prove of advection and influence the width of cool water band. August: The month where the biggest upwelling band is found. In August, the intensity of current that advect the cold water from Kalimata coast to east coast of PM is strongest, creating the biggest upwelling band. At North Bending of cool water band away from the east coast of PM is found. Influence by the current at north part of east coast of PM that bring away the water. Institute of Oceanography & Environment 2015 Aquatic Science Meeting

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