Abstract
The distribution and inter-annual variation of nutrients (N, P, Si) and dissolved/particulate organic carbon were investigated in the equatorial thermocline ridge (<TEX>$7^{\circ}{\sim}11.5^{\circ}N$</TEX>, <TEX>$131.5^{\circ}W$</TEX>) of the northeast Pacific. From the Oceanic Nino Index and Multivariate ENSO Index provided by NOAA, normal condition was observed in July 2003 and August 2005 on the aspect of global climate/ocean change. However, La Ni<TEX>$\~{n}$</TEX>a and El Ni<TEX>$\~{n}$</TEX>o episodes occurred in July 2007 and August 2009, respectively. Thermocline ridge in the study area was located at <TEX>$9^{\circ}N$</TEX> in July 2003, <TEX>$8^{\circ}N$</TEX> in August 2005, <TEX>$10^{\circ}N$</TEX> in July 2007, and <TEX>$10.5^{\circ}N$</TEX> in August 2009 under the influence of global climate/ocean change and surface current system (North Equatorial Counter Current and North Equatorial Current) of the northeast Pacific. Maximum depth integrated values (DIV) of nutrients in the upper layer (0~100 m depth range) were shown in July 2007 (mean 21.12 gN/<TEX>$m^2$</TEX>, 4.27 gP/<TEX>$m^2$</TEX>, 33.72 gSi/<TEX>$m^2$</TEX>) and higher variability of DIV in the equatorial thermocline ridge was observed at <TEX>$10^{\circ}N$</TEX> during the study periods. Also, maximum concentration of dissolved organic carbon (DOC) in the upper 50 m depth layer was observed in July 2007 (mean <TEX>$107.48{\pm}14.58\;{\mu}M$</TEX>), and particulate organic carbon (POC, mean <TEX>$9.42{\pm}3.02\;{\mu}M$</TEX>) was similar to that of DOC. Nutrient concentration in the surface layer increased with effect of upwelling phenomenon in the equatorial thermocline ridge and La Ni<TEX>$\~{n}$</TEX>a episode, which had formed in the central Pacific. This process also resulted in the increasing of organic carbon concentration (DOC and POC) in the surface layer. From these results, it is suggested that spatial and temporal variation of chemical and biological factors were generated by physical processes in the equatorial thermocline ridge.
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