South Pacific Intermediate Water Research Articles

Water Mass Characteristic in The Eastern Inflow Region of The Indonesian Throughflow During Leg-3 of Nusa Manggala Expedition (December 2018)

The Nusa Manggala (ENM) leg-3 expedition in 2018 was held on December 6-16 2018. The survey achieved eighteen Conductivity Temperature Depth measurement points and centered at North of West Papua and Halmahera Sea as the inflow area of eastern part of Indonesian Throughflow (ITF). The results of this study prove that Pacific Surface Water is present on the surface up to 70 m with a temperature of 26 °C - 30°C and salinity of 24 psu – 24.5 psu. Then, South Pacific Subtropical Water and South Pacific Intermediate Water are simultaneously 70 m - 250 m and 250 m - 1000 m at the northern of Halmahera Sea. They not exceed till the southern part of Halmahera Sea.

Composition of Indonesia throughflow in North Sulawesi water masses and heat content

In this research the composition of water masses in the North Sulawesi (Sangihe Talaud) waters as part of the Indonesian Throughflow is investigated and analysed by using the Optimum Multi Parameter Analysis (OMP). The data used is the World Ocean Atlas data (WOA 13) in 1° x 1° latitude longitude resolution. Main data are the salinity, temperature and pressure. The Optimum Multiparameter analysis was used to calculate the percentage of each water mass contribution in the study waters. The contributions are 20-60% at 200-500 m depth for The North Pacific Intermediate Water (NPIW), 90-100%at around 0-100 meters depth for The North Pacific Subtropical Water (NPSW),100%at 900-1500 meters depth for the South Pacific Intermediate Water (SPIW)and 80-100% at 1100-1500 meters depth for TheAntartic Intermediate Water (AAIW). Surprisingly, the South Pacific Subtropical Water (SPSW) does not have any contribution and largest heat content comes from the AAIW. Magnitudes for each heat content of water types calculated in this study for NPIW, NPSW, AAIW, SPSW, and SPIW are in the range of 1.5 × 1014∼ 1.7 × 1014 J/m2, 2 × 1012∼ 9.9 × 1012 J/m2, 2.7 × 1014∼ 3.1 × 1014 J/m2, 0 ∼ 4.3 × 1011 J/m2, and 1.8 × 1014∼ 2 × 1014 J/m2, respectively. Eventhough the AAIW has the lowest temperature range but its large contribution in the waters outnumbers the warmer water masses.

Contribution of Ekman pumping to the changes in properties and volume of the Eastern South Pacific Intermediate Water

An update on the Eastern South Pacifi c Intermediate Water (ESPIW) distribution has been possible based on ARGO (Array for Real-Time Geostrophic Oceanography) data. This study comprised over 46,000 profi les obtained during 2007-2012 from an area between the western coast of South America and 150°W, and 5° and 40°S. This information was complemented with data from the World Ocean Circulation Experiment (WOCE) P06 transects conducted in 1992 and 2010 at 32°30’S in the South Pacifi c Ocean. Based on a comparison of this update and data from 1990-2001, it was established that the ESPIW volume has increased by approximately 53%. Moreover, the area occupied by ESPIW in the 2010 WOCE P06 transect was 48% higher than in 1992. Ekman pumping velocity, calculated from the wind for the time and region of ESPIW formation, showed a signifi cant increase in Ekman pumping between 2000 and 2012. The increase in Ekman pumping from 2000 onward could explain the observed changes in ESPIW distribution (the water mass had extended zonally) and properties (salinity showed a decrease of 0.1). These changes could be explained as the consequence of atmospheric climate variability over the interior ocean.

Water mass analysis of the 2013 US GEOTRACES eastern Pacific zonal transect (GP16)

Abstract The 2013 US GEOTRACES Eastern Pacific Zonal Transect (GP16) extended from the Peruvian coast to Tahiti, along a line that fell between 10 and 15°S. This transect sampled the Peruvian oxygen deficient zone (ODZ) and the hydrothermal plume extending from the East Pacific Rise (EPR) for a variety of trace elements and isotopes (TEIs). Here we report nutrient and hydrographic measurements collected on this cruise, as well as results from an Optimum Multiparameter Analysis (OMPA) to quantify the fractional contributions of endmember water masses in each sample. The primary goals of this study were to better understand the distribution of water masses in the eastern tropical Pacific, and to help interpret TEI measurements collected on this cruise, as well as related studies carried out in the region. In the thermocline, Equatorial Subsurface Water (ESSW) dominated the low oxygen waters of the eastern tropical South Pacific, blending into Eastern South Pacific Intermediate Water (ESPIW) and South Pacific Central Water (SPCW) further west. Below the thermocline, distributions of Antarctic Intermediate Water (AAIW) and Equatorial Pacific Intermediate Water (EqPIW) were relatively homogenous along the section between 800 and 1200 m depth. Deeper in the water column, distinct water mass signatures were found on opposite sides of the EPR: southward flowing Pacific Deep Water (PDW) dominated the basin east of the EPR, while the northward flowing Antarctic Bottom Water (AABW) and Lower Circumpolar Deep Water (LCDW) had the strongest contributions on the western side of the EPR. These findings support previous studies that indicate the Peruvian ODZ is largely contained within ESSW and that the EPR plays an important role in steering water mass distributions in the deep waters of the tropical Pacific. Overall, these results agree well with previous water mass analyses in this region and are consistent with the general circulation patterns in the eastern tropical Pacific.

Changes in biological productivity and ocean-climatic fluctuations during the last ~ 1.5 kyr in the Humboldt ecosystem off northern Chile (27°S): A multiproxy approach

A sedimentary box core (BIAC072014) collected in a coastal environment in the Humboldt Current Ecosystem (HCE, Inglesa Bay, ~27°S, northern Chile) was used to reconstruct the changes in biological productivity and ocean-climate fluctuations during the last ~1.5kyr via geochemical, mineralogical and micropaleontological analyses. From ~510CE to ~930CE, “El Niño-like” conditions prevailed, while during the Medieval Climate Anomaly (MCA, ~950CE to ~1450CE), “La Niña-like” conditions predominated. This pattern might have resulted from weakening/strengthening of the Walker cell, contraction/expansion of the South Pacific Sub-tropical High (SPSH) and a predominance of warm/cold phases of the Pacific Decadal Oscillation (PDO). Between ~1820CE and the present, Inglesa Bay experienced a reduction in the Oxygen Minimum Zone (OMZ) intensity and biological productivity, an increase in the detritic input and a decrease in sea surface temperature (SST). Despite the regional intensification and secular cooling (~14°S and ~27°S) of coastal upwelling, the similarity between the reduction in biological productivity and OMZ intensity in this region and that in the central zone of Chile (~36°S) suggests that Inglesa Bay acts a transition zone in relation to the oceanographic behaviour of the HCE. The reduction in the OMZ intensity and biological productivity during the last ~200years could be explained by greater subsurface ventilation in intermediate depths due to more northward displacement of the subduction region of the Eastern South Pacific Intermediate Water (ESPIW) near ~30°S in response to the strengthening of the circulation of the Subtropical Gyre. The coastal cooling observed in the northern section of HCE during the current Warm Period suggests that it is not possible to demonstrate that El Niño-like conditions promoted the reduction in biological productivity and OMZ intensity in Inglesa Bay.

SUBTROPICAL WATER MASSES IN HALMAHERA WATERS

Research of water masses by using conductivity temperature depth (CTD), are conducted in the eastern path of the Indonesia Throughflow (ITF) in the Halmahera, Seram and Banda seas during March-April 2007 under the Expedition of Widya Nusantara (EWIN). The objective of this research is to see maximum salinity spread of South Pacific Subtropical Water (SPSW) water masses enter the eastern Indonesia Waters. The temperature and salinity profiles show the presence of the presence of SPSW have been very much confined to the Halmahera Sea only. Little of this water masses have been detected in the eastern Seram Sea, but none in Banda Sea. Early data of Arlindo Mixing (ARMIX) experiment in southeast monsoon 1993 indicated that this water masses SPSW may entered the southern most part of the Moluccas Sea. Type of South Pacific Subtropical Water (SPSW) water masses appears in the Halmahera Sea at an average depth of 200m and the dominant flows between Halmahera and Obi Islands (Moluccas Sea continues to the east). Type of South Pacific Intermediate Water (SPIW) water mass appeared on average Halmahera Sea at a depth of 750m and the dominant flows between Halmahera and Obi Islands (Moluccas Sea continues to the east). Type of North Pacific Subtropical Water (NPSW) water masses at an average depth of ~ 150m found in the northern part of Halmahera, the dominant flow to the Celebes Sea, Makassar Strait, Flores Sea and partly flows into Lombok Straits. Type of minimum salinity water mass of North Pacific Intermediate Water (NPIW) obtained at an average depth of ~ 400m dominant flow towards the Celebes Sea, Makassar Strait and Flores Sea.Keywords: maximum salinity, SPSW, Halmahera, Seram, and Banda Seas

SUBTROPICAL WATER MASSES IN HALMAHERA WATERS

<p>Research of water masses by using conductivity temperature depth (CTD), are conducted in the eastern path of the Indonesia Throughflow (ITF) in the Halmahera, Seram and Banda seas during March-April 2007 under the Expedition of Widya Nusantara (EWIN). The objective of this research is to see maximum salinity spread of South Pacific Subtropical Water (SPSW) water masses enter the eastern Indonesia Waters. The temperature and salinity profiles show the presence of the presence of SPSW have been very much confined to the Halmahera Sea only. Little of this water masses have been detected in the eastern Seram Sea, but none in Banda Sea. Early data of Arlindo Mixing (ARMIX) experiment in southeast monsoon 1993 indicated that this water masses SPSW may entered the southern most part of the Moluccas Sea. Type of South Pacific Subtropical Water (SPSW) water masses appears in the Halmahera Sea at an average depth of 200m and the dominant flows between Halmahera and Obi Islands (Moluccas Sea continues to the east). Type of South Pacific Intermediate Water (SPIW) water mass appeared on average Halmahera Sea at a depth of 750m and the dominant flows between Halmahera and Obi Islands (Moluccas Sea continues to the east). Type of North Pacific Subtropical Water (NPSW) water masses at an average depth of ~ 150m found in the northern part of Halmahera, the dominant flow to the Celebes Sea, Makassar Strait, Flores Sea and partly flows into Lombok Straits. Type of minimum salinity water mass of North Pacific Intermediate Water (NPIW) obtained at an average depth of ~ 400m dominant flow towards the Celebes Sea, Makassar Strait and Flores Sea.</p><p>Keywords: maximum salinity, SPSW, Halmahera, Seram, and Banda Seas</p>

South Pacific intermediate water oxygen depletion at the onset of the Paleocene-Eocene thermal maximum as depicted in New Zealand margin sections

[1] Extreme global warming and massive input of 13C-depleted carbon into the exogenic carbon cycle characterize the Paleocene-Eocene thermal maximum (PETM) circa 55.5 Ma. Previous work indicates that dissolved O2 concentrations dropped in some regions of the ocean during this event, but spatial, temporal, and causal relationships between warming, carbon input, and O2 deficiency remain elusive. We present lithologic, carbon isotopic, and trace fossil results from outcrops in New Zealand that clarify this issue. Sections exposed at Mead and Dee Streams in eastern Marlborough, South Island, contain expanded sedimentary intervals that were deposited before, during, and after the PETM on an upper continental slope. The PETM in these intervals is characterized by enhanced siliciclastic deposition, a hallmark negative carbon isotope excursion, and a loss of bioturbation. Importantly, however, the latter only occurs during the prominent drop in δ13C and not during its recovery. Our results suggest that South Pacific intermediate waters became hypoxic coincident to carbon injection at the start of the PETM. While higher sea surface temperatures throughout the PETM would have decreased the dissolved oxygen content of sinking surface waters, we argue here that oxygen depletion was driven by some combination of elevated temperature, water column stratification, and intermediate water methane oxidation.

Vertical and horizontal extension of the oxygen minimum zone in the eastern South Pacific Ocean

Recent hydrographic measurements within the eastern South Pacific (1999–2001) were combined with vertically high-resolution data from the World Ocean Circulation Experiment, high-resolution profiles and bottle casts from the World Ocean Database 2001, and the World Ocean Atlas 2001 in order to evaluate the vertical and horizontal extension of the oxygen minimum zone ( 600 m) off Peru between 5 and 13°S and to about 1000 km offshore. Its upper boundary is shallowest (<150 m) off Peru, shoaling towards the coast and extending well into the euphotic zone in some places. Offshore, the thickness and meridional extent of the oxygen minimum zone decrease until it finally vanishes at 140°W between 2° and 8°S. Moving southward along the coast of South America, the zonal extension of the oxygen minimum zone gradually diminishes from 3000 km (15°S) to 1200 km (20°S) and then to 25 km (30°S); only a thin band is detected at ∼37°S off Concepcion, Chile. Simultaneously, the oxygen minimum zone's maximum thickness decreases from 300 m (20°S) to less than 50 m (south of 30°S). The spatial distribution of Ekman suction velocity and oxygen minimum zone thickness correlate well, especially in the core. Off Chile, the eastern South Pacific Intermediate Water mass introduces increased vertical stability into the upper water column, complicating ventilation of the oxygen minimum zone from above. In addition, oxygen-enriched Antarctic Intermediate Water clashes with the oxygen minimum zone at around 30°S, causing a pronounced sub-surface oxygen front. The new estimates of vertical and horizontal oxygen minimum zone distribution in the eastern South Pacific complement the global quantification of naturally hypoxic continental margins by Helly and Levin [2004. Global distribution of naturally occurring marine hypoxia on continental margins. Deep-Sea Research I 51, 1159–1168] and provide new baseline data useful for studies on the role of oxygen in the degradation of organic matter in the water column and the related implications for biogeochemical cycles. Coastal upwelling zones along the eastern Pacific combine with general circulation to provide a mechanism that allows renewal of upper Pacific Deep Water, the most oxygen-poor and oldest water mass of the world oceans.

Characteristics and formation of Eastern South Pacific Intermediate Water

Newly gathered hydrographic data from the Eastern South Pacific is combined with other high‐quality data (mainly WOCE) to reassess the properties and boundaries of the Eastern South Pacific Intermediate Water (ESPIW); to date the ESPIW has been only poorly described. The ESPIW core is found off central and northern Chile, between the coast and 90°W and 20–38°S. Located at 50–400 m of depth, its temperature varies between 11–13°C, salinity ranges from 34.1–34.3, and its sigma‐t lies between 25.75–26.25 kgm−3. ESPIW spreads with the subtropical gyre circulation and can be traced to at least 150°W. Formed through the process of subduction southeastward of the wind‐driven gyre circulation, the ESPIW communicates surface properties of the waters off central Chile to tropical latitudes.