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<p>The distribution and dynamics of dissolved organic carbon (DOC) and dissolved combined neutral sugars (DCNS) were studied across an increasing oligotrophic gradient (18 to 22<span class="inline-formula">^∘</span>&thinsp;S latitude) in the tropical South Pacific Ocean, spanning from the Melanesian Archipelago (MA) area to the western part of the South Pacific gyre (WGY), in austral summer as a part of the OUTPACE project. Our results show that DOC and DCNS concentrations exhibited no statistical differences between the MA and WGY areas (0–200&thinsp;m: 47–81&thinsp;<span class="inline-formula">µ</span>M&thinsp;C for DOC and 0.2-4.2&thinsp;<span class="inline-formula">µ</span>M&thinsp;C for DCNS). However, due to a deepening of the euphotic zone, a deeper penetration of DOC was noticeable at 150&thinsp;m of depth at the WGY area. Excess DOC (DOC<span class="inline-formula">_EX</span>) was determined as the difference between surface and deep-sea DOC values, and euphotic zone integrated stocks of both DOC and DOC<span class="inline-formula">_EX</span> were higher in the WGY than the MA area. Considering DOC<span class="inline-formula">_EX</span> as representative of semi-labile DOC (DOC<span class="inline-formula">_SL</span>), its residence time was calculated as the ratio of DOC<span class="inline-formula">_SL</span> to bacterial carbon demand (BCD). This residence time was <span class="inline-formula">176±43</span> days (<span class="inline-formula"><i>n</i>=3</span>) in the WGY area, about 3 times longer than in the MA area (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M11" display="inline" overflow="scroll" dspmath="mathml"><mrow><msub><mi>T</mi><mi mathvariant="normal">r</mi></msub><mo>=</mo><mn mathvariant="normal">51</mn><mo>±</mo><mn mathvariant="normal">13</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="59pt" height="12pt" class="svg-formula" dspmath="mathimg" md5hash="1f1229457353a2de9b9b4ab9265d8598"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-16-105-2019-ie00001.svg" width="59pt" height="12pt" src="bg-16-105-2019-ie00001.png"/></svg:svg></span></span> days, <span class="inline-formula"><i>n</i>=8</span>), suggesting an accumulation of semi-labile dissolved organic matter (DOM) in the surface waters of WGY. Average epipelagic (0–200&thinsp;m) DCNS yields (DCNS&thinsp;<span class="inline-formula">×</span>&thinsp;DOC<span class="inline-formula">⁻¹</span>) based on volumetric data were roughly similar in both areas, accounting for <span class="inline-formula">∼2.8</span>&thinsp;% of DOC. DCNS exhibited a longer residence time in WGY (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M16" display="inline" overflow="scroll" dspmath="mathml"><mrow><msub><mi>T</mi><mi mathvariant="normal">r</mi></msub><mo>=</mo><mn mathvariant="normal">91</mn><mo>±</mo><mn mathvariant="normal">41</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="59pt" height="12pt" class="svg-formula" dspmath="mathimg" md5hash="f17dc1a9c613f69ead3c360780a5771c"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-16-105-2019-ie00002.svg" width="59pt" height="12pt" src="bg-16-105-2019-ie00002.png"/></svg:svg></span></span> days, <span class="inline-formula"><i>n</i>=3</span>) than in MA (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M18" display="inline" overflow="scroll" dspmath="mathml"><mrow><msub><mi>T</mi><mi mathvariant="normal">r</mi></msub><mo>=</mo><mn mathvariant="normal">31</mn><mo>±</mo><mn mathvariant="normal">10</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="59pt" height="12pt" class="svg-formula" dspmath="mathimg" md5hash="027f5be64f6d4c7ff36441bfd093e774"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-16-105-2019-ie00003.svg" width="59pt" height="12pt" src="bg-16-105-2019-ie00003.png"/></svg:svg></span></span> days, <span class="inline-formula"><i>n</i>=8</span>), further suggesting that this DCNS pool persists longer in the surface waters of the WGY. The accumulation of DOC<span class="inline-formula">_EX</span> in the surface waters of WGY is probably due to very slow bacterial degradation due to nutrient and/or energy limitation of heterotrophic prokaryotes, indicating that biologically produced DOC can be stored in the euphotic layer of the South Pacific gyre for a long period.</p>