scholarly journals An Observational Perspective of Sea Surface Salinity in the Southwestern Indian Ocean and Its Role in the South Asia Summer Monsoon

2018 ◽  
Vol 10 (12) ◽  
pp. 1930 ◽  
Author(s):  
Xu Yuan ◽  
Mhd. Salama ◽  
Zhongbo Su
Keyword(s):  
Indian Ocean ◽  
Summer Monsoon ◽  
Asian Summer Monsoon ◽  
Sea Surface ◽  
Sea Surface Salinity ◽  
South Asian Summer Monsoon ◽  
The South ◽  
Surface Salinity ◽  
The Indian Ocean ◽  
Southwestern Indian Ocean

The seasonal variability of sea surface salinity anomalies (SSSAs) in the Indian Ocean is investigated for its role in the South Asian Summer Monsoon. We have observed an elongated spatial-feature of the positive SSSAs in the southwestern Indian Ocean before the onset of the South Asian Summer Monsoon (SASM) by using both the Aquarius satellite and the Argo float datasets. The maximum variable areas of SSSAs in the Indian Ocean are along (60 ° E–80 ° E) and symmetrical to the equator, divided into the southern and northern parts. Further, we have found that the annual variability of SSSAs changes earlier than that of sea surface temperature anomalies (SSTAs) in the corresponding areas, due to the change of wind stress and freshwater flux. The change of barrier layer thickness (BLT) anomalies is in phase with that of SSSAs in the southwestern Indian Ocean, which helps to sustain the warming water by prohibiting upwelling. Due to the time delay of SSSAs change between the northern and southern parts, SSSAs, therefore, take part in the seasonal process of the SASM via promoting the SSTAs gradient for the cross-equator currents.

Assessing Sea Surface Salinity Derived by Aquarius in the Indian Ocean

2014 ◽  
Vol 11 (4) ◽  
pp. 719-722 ◽  
Author(s):  
Smitha Ratheesh ◽  
Rashmi Sharma ◽  
Rajesh Sikhakolli ◽  
Raj Kumar ◽  
Sujit Basu
Keyword(s):  
Indian Ocean ◽  
Sea Surface ◽  
Sea Surface Salinity ◽  
Surface Salinity ◽  
The Indian Ocean

Meridional Distribution of Surface CO2 along 67°E of the Indian Ocean

2020 ◽  
Author(s):  
Dong-Jin Kang ◽  
Sang-Hwa Choi ◽  
Daeyeon Kim ◽  
Gyeong-Mok Lee
Keyword(s):  
Indian Ocean ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Sea Surface ◽  
Sea Surface Salinity ◽  
Surface Seawater ◽  
Surface Salinity ◽  
The North ◽  
The Indian Ocean ◽  
North And South

<p>Surface seawater carbon dioxide was observed from 3 °S to 27 °S along 67 °E of the Indian Ocean in April 2018 and 2019. Partial pressure of CO<sub>2</sub>(pCO<sub>2</sub>) in the surface seawater and the atmosphere were observed every two minutes using an underway CO2 measurement system (General Oceanics Model 8050) installed on R/V Isabu. Surface water temperature and salinity were measured as well. The pCO<sub>2</sub> was measured using Li-7000 NDIR. Standard gases were measured every 8 hours in five classes with concentrations of 0 µatm, 202 µatm, 350 µatm, 447 µatm, and 359.87 µatm. The fCO<sub>2</sub> of atmosphere remained nearly constant at 387 ± 2 µatm, but the surface seawater fCO<sub>2</sub> peaked at about 3 °S and tended to decrease toward the north and south. The distribution of fCO<sub>2</sub> in surface seawater according to latitude tends to be very similar to that of sea surface temperature. In order to investigate the factors that control the distribution of fCO<sub>2</sub> in surface seawater, we analyzed the sea surface temperature, sea surface salinity, and other factors. The effects of salinity are insignificant, and the surface fCO<sub>2</sub> distribution is mainly controlled by sea surface temperature and other factors that can be represented mainly by biological activity and mixing.</p>

scholarly journals Salinity changes in the Agulhas leakage area recorded by stable hydrogen isotopes of C<sub>37</sub> alkenones during Termination I and II

2014 ◽  
Vol 10 (1) ◽  
pp. 251-260 ◽  
Author(s):  
S. Kasper ◽  
M. T. J. van der Meer ◽  
A. Mets ◽  
R. Zahn ◽  
J. S. Sinninghe Damsté ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Saline Water ◽  
Planktonic Foraminifera ◽  
Sea Surface ◽  
Sea Surface Salinity ◽  
Surface Salinity ◽  
Agulhas Current ◽  
Salinity Changes ◽  
Leakage Area ◽  
The Indian Ocean

Abstract. At the southern tip of Africa, the Agulhas Current reflects back into the Indian Ocean causing so-called "Agulhas rings" to spin off and release relatively warm and saline water into the South Atlantic Ocean. Previous reconstructions of the dynamics of the Agulhas Current, based on paleo-sea surface temperature and sea surface salinity proxies, inferred that Agulhas leakage from the Indian Ocean to the South Atlantic was reduced during glacial stages as a consequence of shifted wind fields and a northwards migration of the subtropical front. Subsequently, this might have led to a buildup of warm saline water in the southern Indian Ocean. To investigate this latter hypothesis, we reconstructed sea surface salinity changes using alkenone δD, and paleo-sea surface temperature using TEXH86 and UK'37, from two sediment cores (MD02-2594, MD96-2080) located in the Agulhas leakage area during Termination I and II. Both UK'37 and TEXH86 temperature reconstructions indicate an abrupt warming during the glacial terminations, while a shift to more negative δDalkenone values of approximately 14‰ during glacial Termination I and II is also observed. Approximately half of the isotopic shift can be attributed to the change in global ice volume, while the residual isotopic shift is attributed to changes in salinity, suggesting relatively high salinities at the core sites during glacials, with subsequent freshening during glacial terminations. Approximate estimations suggest that δDalkenone represents a salinity change of ca. 1.7–1.9 during Termination I and Termination II. These estimations are in good agreement with the proposed changes in salinity derived from previously reported combined planktonic Foraminifera δ18O values and Mg/Ca-based temperature reconstructions. Our results confirm that the δD of alkenones is a potentially suitable tool to reconstruct salinity changes independent of planktonic Foraminifera δ18O.

scholarly journals Satellite and Argo Observed Surface Salinity Variations in the Tropical Indian Ocean and Their Association with the Indian Ocean Dipole Mode

2015 ◽  
Vol 28 (2) ◽  
pp. 695-713 ◽  
Author(s):  
Yan Du ◽  
Yuhong Zhang
Keyword(s):  
Indian Ocean ◽  
Ocean Circulation ◽  
Indian Ocean Dipole ◽  
Coastal Upwelling ◽  
Tropical Indian Ocean ◽  
Sea Surface Salinity ◽  
The South ◽  
Surface Salinity ◽  
Indian Ocean Dipole Mode ◽  
The Indian Ocean

Abstract This study investigates sea surface salinity (SSS) variations in the tropical Indian Ocean (IO) using the Aquarius/Satelite de Aplicaciones Cientificas-D (SAC-D) and the Soil Moisture and Ocean Salinity (SMOS) satellite data and the Argo observations during July 2010–July 2014. Compared to the Argo observations, the satellite datasets generally provide SSS maps with higher space–time resolution, particularly in the regions where Argo floats are sparse. Both Aquarius and SMOS well captured the SSS variations associated with the Indian Ocean dipole (IOD) mode. Significant SSS changes occurred in the central equatorial IO, along the Java–Sumatra coast, and south of the equatorial IO, due to ocean circulation variations. During the negative IOD events in 2010, 2013, and 2014, westerly wind anomalies strengthened along the equator, weakening coastal upwelling off Java and Sumatra and decreasing SSS. South of the equatorial IO, an anomalous cyclonic gyre changed the tropical circulation, which favored the eastward high-salinity tongue along the equator and the westward low-saline tongue in the south. An upwelling Rossby wave favored the increase of SSS farther to the south. During the positive IOD events in 2011 and 2012, the above-mentioned processes reversed, although the decrease of SSS was weaker in magnitude.

scholarly journals Salinity changes in the Agulhas leakage area recorded by stable hydrogen isotopes of C<sub>37</sub> alkenones during Termination I and II

2013 ◽  
Vol 9 (3) ◽  
pp. 3209-3238 ◽  
Author(s):  
S. Kasper ◽  
M. T. J. van der Meer ◽  
A. Mets ◽  
R. Zahn ◽  
J. S. Sinninghe Damsté ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Saline Water ◽  
Planktonic Foraminifera ◽  
Sea Surface ◽  
Sea Surface Salinity ◽  
Surface Salinity ◽  
Agulhas Current ◽  
Salinity Changes ◽  
Temperature Reconstructions ◽  
The Indian Ocean

Abstract. At the southern tip of the African shelf, the Agulhas Current reflects back into the Indian Ocean causing so called "Agulhas rings" to spin off and release relatively warm and saline water into the South Atlantic Ocean. Previous reconstructions of the dynamics of the Agulhas current, based on paleo sea surface temperature and sea surface salinity proxies, inferred that Agulhas leakage from the Indian Ocean to the South Atlantic is reduced as a consequence of changes in wind fields related to a northwards migration of ice masses and the subtropical front during glacial stages. Subsequently, this might have led to a build-up of warm saline water in the southern Indian Ocean. To investigate this latter hypothesis, we reconstructed sea surface salinity changes using alkenone δ D, and paleo sea surface temperature using TEXH86 and UK'37, from two sediment cores (MD02-2594, MD96-2080) located in the Agulhas leakage area during Termination I and II. Both UK'37 and TEXH86 temperature reconstructions infer an abrupt warming during the glacial terminations, which is different from the gradual warming trend previously reconstructed based on Mg/Ca ratios of Globigerina bulloides. These differences in temperature reconstructions might be related to differences in the growth season or depth habitat between organisms. A shift to more negative δ Dalkenone values of approximately 14‰ during glacial Termination I and approximately 13‰ during Termination II is also observed. Approximately half of these shifts can be attributed to the change in global ice volume, while the residual isotopic shift is attributed to changes in salinity, suggesting relatively high salinities at the core sites during glacials, with subsequent freshening during glacial terminations. Approximate estimations suggest that δ Dalkenone represents a salinity change of ca. 1.7–2 during Termination I and ca. 1.5–1.7 during Termination II. These estimations are in good agreement with the proposed changes in salinity derived from previously reported combined planktonic foraminifera δ18O values and Mg/Ca-based temperature reconstructions. Our results show that the δ D of alkenones is a potentially suitable tool to reconstruct salinity changes independent of planktonic foraminifera δ18O.

scholarly journals Three types of positive Indian Ocean dipoles and their relationships with the South Asian summer monsoon

2021 ◽  
pp. 1-67
Author(s):  
Jilan Jiang ◽  
Yimin Liu ◽  
Jiangyu Mao ◽  
Jianping Li ◽  
Shuwen Zhao ◽  
...  
Keyword(s):  
Indian Ocean ◽  
South Asian ◽  
Summer Monsoon ◽  
Asian Summer Monsoon ◽  
South Asian Summer Monsoon ◽  
The South ◽  
Mature Phase ◽  
Asian Summer ◽  
Type C ◽  
Southeasterly Wind

AbstractThe relationship between the Indian Ocean dipole (IOD) and the South Asian summer monsoon (SASM), which remains a subject of controversy, was investigated using data analyses and numerical experiments. We categorized IOD events according to their sea surface temperature anomaly (SSTA) pattern: Type-W and Type-E are associated with stronger SSTA amplitudes in the western and eastern poles of the IOD, respectively, while Type-C has comparable SSTA amplitudes in both poles during boreal autumn. Type-W is associated with a weak SASM from May to summer, which contributes to substantial warming of the western pole in autumn; the east–west SST gradient linked to the warming of the western pole causes weak southeasterly wind anomalies off Sumatra and feeble and cold SSTAs in the eastern pole during the mature phase. Type-E is associated with a strong SASM and feeble warming of the western pole; interaction between the strong SASM and cold SSTAs in the eastern pole in summer results in strong southeasterly wind anomalies off Sumatra and substantial cooling of the eastern pole during the mature phase. For Type-C, warming of the western pole and cooling of the eastern pole develop synchronously without apparent SASM anomalies, and reach comparable intensities during the mature phase. Observations and numerical simulation results both indicate the role of disparate SASM anomalies in modulating SSTA patterns during the development of positive IODs. Warming of the tropical Indian Ocean becomes established in the winter and spring following Type-W and Type-C IODs, but not following Type-E events.

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