Percampuran vertikal di Perairan Laut Maluku dan Talaud pada bulan Februari 2021

<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.

Analysis of Characteristics and Turbulent Mixing of Seawater Mass in Lombok Strait

The Lombok Strait, as one of the outlet straits, is part of the ITF route, which is directly adjacent to the Indian Ocean. There is a sill in the Lombok Strait, which is a place for internal wave generation. Leg-1 data from the Japan Agency for Marine-Earth Science and Technology in collaboration with the Agency for the Assessment and Application of Technology which is part of the Tropical Ocean Climate Study Expedition including CTD Yoyo and ADCP taken using ship vehicles R/V Kaiyo. CTD Snapshot from PUSHIDROSAL using the KRI Spica 934 vehicle part of the Opssurta Baruna Jaya 2 Expedition. Determination of seawater mass stratification with the criteria for the thermocline layer is ≥ 0.05 °C.m-1. Four types of water masses were identified, Java Sea, mixed seawater mass (Java Sea - ITF) which occurred diapycnal mixing, North Pacific Subtropical Water (NPSW) and North Pacific Intermediate Water (NPIW). The seawater mass stratification in the Lombok Strait based on temperature, salinity and density which are seen to follow the internal tidal pattern. The average values for energy dissipation and vertical diffusivity for each layer and replication were 5.73 x 10-7 W.Kg-1 and 3.67 x 10-2 m2.s-1 for CTD Yoyo and 2.25 x 10-6 W.Kg-1 and 7.38 x 10-2 m2.s-1 for CTD Snapshot. The value obtained is greater than the open ocean and straits in other studies. The high shear value confirms this in the thermocline layer. The Richardson gradient value> 0.25 is relatively constant in the thermocline layer.

Vertical turbulent nitrate flux from direct measurements in the western subarctic and subtropical gyres of the North Pacific

Vertical turbulent nitrate fluxes were estimated in the western North Pacific from direct measurements of vertical turbulent mixing and vertically continuous nitrate profiles during the summer of 2008. We made three north–south transects that covered the area from the subarctic to the subtropics including a section along the Emperor Sea Mounts. Subsurface fluxes generally showed an increasing trend with increasing vertical gradient of nitrate from oligotrophic subtropical to non-oligotrophic subarctic waters. Enhanced fluxes [O(10−6) mmol m−2 s−1] due to elevated mixing [vertical diffusivity: O(10−5) m2 s−1] were observed, especially over the Emperor Sea Mounts. It is suggested that the internal tide generated by the topography enhanced the vertical mixing. In other subarctic areas, the fluxes were estimated as O(10−7) mmol m−2 s−1. The same order of fluxes was also found in the frontal area between the subarctic and subtropical gyres, the Kuroshio–Oyashio Transition Area. Enhancement of fluxes in the frontal area, including the Kuroshio Extension, was also observed at mid-depth regions, and their vertical divergence suggested nitrate transport from North Pacific Intermediate Water to lighter densities. In the frontal areas, the enhancement of turbulence is caused by the surface wind rather than the internal tide. In contrast, in the subtropical regions, subsurface fluxes were estimated as O(10−8) mmol m−2 s−1 owing to the small nitrate gradient even where diffusivity was enhanced. In these regions, enhancement of diffusivity, including that at mid-depths, corresponded to the elevation of the internal-tide dissipation, in addition to that of surface turbulence.

Evolution and Structure of the Kuroshio Extension Front in Spring 2019

Satellite data products and high-resolution in situ observations were combined to investigate the evolution and structure of the Kuroshio Extension Front in Spring 2019. The former reveals the variation of the front is influenced by the northward movement of the Kuroshio Extension through transporting warm and saline water to a cold and brackish water region. The latter indicates steep upward slopes of the isopycnals, tilting northward in the frontal zone, as well as several ~300 m thick blobs of North Pacific Intermediate Water between 26.25 and 26.75 kg/m3, where conspicuous thermohaline intrusions occur. Further analysis indicates these thermohaline intrusions prefer to alternate salt fingering and diffusive convection interfaces, and are affected by strong shears.

The long-term variation of the Intermediate Water in the Philippines Sea

&lt;p&gt;The dimensional and temporal distribution of Antarctic Intermediate Water (AAIW) and North Pacific Intermediate Water (NPIW) in the Philippines Sea were explored using Argo profiles. As the salinity minimum of intermediate water from mid-high latitude of the southern and northern hemisphere of the Pacific Ocean, the properties of AAIW and NPIW merges at about 10&amp;#176;N with different properties in the Philippine Sea. The core of AAIW is located below 600dbar with potential density of 27&amp;#8804;&amp;#963;&lt;sub&gt;&amp;#952;&lt;/sub&gt;&amp;#8804;27.3 kg m&lt;sup&gt;-3&lt;/sup&gt; and salinity of 34.5&amp;#8804;S&amp;#8804;34.55 psu. The core of NPIW is located between 300-700dbar with potential density of 26.2&amp;#8804;&amp;#963;&lt;sub&gt;&amp;#952;&lt;/sub&gt;&amp;#8804;27 kg m&lt;sup&gt;-3&lt;/sup&gt; and salinity of 34&amp;#8804;S&amp;#8804;34.4 psu. The volume of AAIW and NPIW during January 2004 to December 2017 is negative correlated. &amp;#160;The time series of AAIW and NPIW is dominated by semi-annual signals. The variations of AAIW and NPIW was mainly affected by volume transport through 130&amp;#176;E section by North Equatorial Current (NEC) and North Equatorial Undercurrent (NEUC).&lt;/p&gt;

A modelling perspective of North Pacific Intermediate water in the future

&lt;p&gt;North Pacific Intermediate water (NPIW) is a dominant water mass controlling ~400-1200m depth North Pacific Ocean, characterized by its low salinities and relatively lower temperatures. In the modern climate, the interplay between NPIW-related physical and biogeochemical processes among seasons determines annual-mean budget and efficiency of carbon sink into the North Pacific Ocean. Thus, to understand the NPIW physics is key to project roles of the North Pacific Ocean in changing Earth climate and carbon systems in the future. In this study, we provide a modelling view of the NPIW history since Yr 1850 (historical experiment) and its projection to near future (IPCC-defined RCP 4.2 and 8.5 experiments until Yr 2100), using new-generation Alfred Wegener Institute Earth System Model (AWI-ESM). Our results suggest an important role of regional hydroclimate feedback over the NW Pacific and Sea of Okhotsk in determining the NPIW from recent past to near future.&lt;/p&gt;

Persistent millennial-scale links between North Pacific intermediate-water ventilation and North Atlantic Climate during the deglaciation and last glaciation

&lt;p&gt;The deep ocean carbon cycle, especially carbon sequestration and outgassing, is one of the mechanisms to explain variations in atmospheric CO&lt;sub&gt;2&lt;/sub&gt; concentrations on millennial and orbital timescales. However, the potential role of subtropical North Pacific subsurface waters in modulating atmospheric CO&lt;sub&gt;2&lt;/sub&gt; levels on millennial timescales is poorly constrained. Here, we investigate a suite of geochemical proxies in a sediment core from the northern and middle Okinawa Trough to understand variations in intermediate-water ventilation of the subtropical North Pacific over the last 50,000 years (50 ka). Our results suggest that enhanced mid-depth western subtropical North Pacific (WSTNP) sedimentary oxygenation occurred during cold intervals during the last deglaciation and last glaciation, while oxygenation decreased during the B&amp;#246;lling-Aller&amp;#246;d (B/A) and warm interstadials. The enhanced oxygenation during cold spells is linked to the intensified North Pacific Intermediate Water (NPIW), while interglacial increase after 8.5 ka is linked to an intensification of the Kuroshio Current due to strengthened northeast trade winds over the tropics. The enhanced formation of NPIW during Heinrich Stadials was likely driven by the perturbation of sea ice formation and sea surface salinity oscillations in high-latitude North Pacific. The diminished sedimentary oxygenation during the B/A and interstadials due to decreased NPIW formation and enhanced export production, indicates an expansion of oxygen minimum zone in the North Pacific and enhanced CO&lt;sub&gt;2&lt;/sub&gt; sequestration at mid-depth waters. We attribute the millennial-scale changes to intensified NPIW and enhanced abyss flushing during deglacial cold and warm intervals, respectively, closely related to variations in North Atlantic Deep Water formation. Out study extends the millennial-scale links between ventilation in the subtropical North Pacific Ocean and the Atlantic Climate into the last glaciations, highlighting the key roles of Atlantic Meridional Overturning Circulation in regulating the North Pacific environment at millennial timescales. Note: Financial support was provided by the National Program on Global Change and Air-Sea Interaction (GASI-GEOGE-04) and by the National Natural Science Foundation of China (Grant Nos.: 41876065, 41476056, and U1606401).&lt;/p&gt;

Subthermocline eddies in the Philippine Sea in 2017 to 2018

&lt;p&gt;In the tropical western Pacific, both of the North and South Equatorial Currents terminate with meeting oceanic continents and form the Equatorial Counter Currents and the Low Latitude Western Boundary Currents (LLWBC). There is the undercurrents that flow opposite direction below the surface currents. The North Equatorial Undercurrents flow eastward having four zonal axis which is related with the LLWBC. Below the southward flowing Mindanao Currents branched from the North Equatorial Currents, there is Mindanao Undercurrents which flow northward that is thought to be a continuation of the New Guinea Coastal Undercurrents passed through the equator. In addition to these complex current systems in the Philippine Sea, eddies exists below the thermocline. Long term current mooring data showed signals of existence of the subthermocline eddies (SE). It is inferred that the SEs are formed by the interaction between the surface currents and the undercurrents and the bottom topography. Although the SE plays an important role in the heat exchange and the intermediate water mixing, it is difficult to observe and there is still much to be revealed. This study was conducted using the CMEMS (COPERNICUS Marine and Environment Monitoring Service) gridded objective analysis fields of temperature and salinity which are produced using profiles from the in-situ real time database of the global in-situ center. The gridded data was rearranged into isopycnal surfaces and analyzed for the distribution and movement of SE. The distributions of the isopycnal layer thicknesses were presented based on the core density of the North Pacific Intermediate Water and Antarctic Intermediate Water and compared to the previous studies.&lt;/p&gt;