No abstract

During Marine Science Summer Course 2017, a continuous 24-h conductivity-temperature-depth (CTD) “yoyo” measurement has been carried out at the entrance of Padangbai Lombok Strait to investigate seawater properties variations on semidiurnal tidal-scale which is dominant in the strait. The SBE CTD 19 plus is equipped with optional sensors such as pH, turbidity and chlorophyll-a derived-fluoro. During 24-h field observation, 15 CTD casts from sea surface to about 60 m depth have been acquired. It is shown that observed seawater properties fluctuate strongly four times a day, following semidiurnal-tide period with two flood-tide and two ebb-tide conditions. During flood-tide, water mass is derived from open strait with colder, saltier, denser and low dissolved oxygen characteristics. In contrast, during ebb-tide, local water mass is recirculated back from the inner bay to the open strait. It is interesting to note that fluctuation of chlorophyll-a indicates a diurnal signal. In addition, fluctuation of pH, turbidity and dissolved oxygen showed a weak semidiurnal signal.

<strong>Vertical mixing in the northern Maluku Sea and Talaud Waters in February 2021. </strong>The spatial variability of water mass mixing in the northern Maluku Sea and Talaud waters are presented based on the results of Eastern Indonesia Expedition (EIT) 2021 using RV Baruna Jaya VIII-LIPI. The turbulent kinetic energy dissipation rate was obtained using the Kunze-Williams-Briscoe (KWB) Method calculated from CTD (Conductivity, Temperature, Depth) and LADCP (Lowered Acoustic Doppler Current Profiler) datasets. We found the dissipation rate in the core layer of North Pacific Subtropical Water (NPSW) and North Pacific Intermediate Water (NPIW) are in the order of 10^-6 W/kg and 10^-8 W/kg, respectively. The KWB Method used in this study is also proven comparable with the Thorpe Method.

<p><em>The secondary entry portal of the Indonesian Throughflow (ITF) from the Pacific to Indian Oceans is considered to be via the Halmahera Sea (HS). However, few ITF studies have been done within the passage. This motivated the Internal Tides and Mixing in the Indonesian Througflow (INDOMIX) program to conduct direct measurements of currents and its variability across the eastern path of the ITF. This study focused on the intra-seasonal variability of near-bottom current in HS (129°E, 0°S), its origin and correlation with surface zonal winds and sea surface height over the equatorial Pacific Ocean. The result showed a strong northwestward mean flow with velocity exceeding 40 cm/s, which represented the current-following topography with the northwest orientation. Meridional current component was much stronger than the zonal component. The energy of power spectral density (PSD) of the current peaked on 14-days and 27-days periods. The first period was presumably related to the tidal oscillation, but the latter may be associated with surface winds perturbation. Furthermore, cross-PSD revealed a significant coherency between the observed currents and the surface zonal winds in the central equatorial Pacific zonal winds (180°E-160°W), which corroborates westward propagation of intra-seasonal sea surface height signals along the 5°S with its mean phase speeds of 50 cm/s, depicting the low-latitude westward Rossby waves on intra-seasonal band.</em></p> <p><em> </em></p> <strong><em>Keywords</em></strong><em>: current, equatorial Pacific Ocean,  zonal winds, sea surface height, Halmahera Sea</em>

This study investigates the coherency of volume transport between Halmahera throughflow and current major system in the western equatorial Pacific Ocean (Mindanao Current – MC, New Guinea Coastal/Under Current – NGCC/NGCUC, and North Equatorial Counter Current – NECC). The validated daily ocean general circulation model datasets of INDESO (2010-2014) were used in this study. The results showed that the estimated average transport volume was 25.6 Sv flowing southward through MC, 34.5 Sv flowing eastward through NECC, 18.3 Sv flowing northwestward through NGCC/NGCUC, and 2.5 Sv flowing southward through the Halmahera Sea. The variability of volume transport was dominated by intraseasonal, semiannual, and annual time-scales. The increased transport of NECC corresponded to the intensification of MC and NGCC/NGCUC transports. NGCC/ NGCUC significantly controlled the South Pacific water inflow into the Halmahera Sea because of the positively high correlation between NGCC/NGCUC transport and Halmahera throughflow transport.