Argo profiles variability of barrier layer in the tropical Indian Ocean and its relationship with the Indian Ocean Dipole

Qiu, Yun; Cai, Wenju; Li, Li; Guo, Xiaogang

doi:10.1029/2012gl051441

Cited by 46 publications

(84 citation statements)

References 31 publications

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“…(GeoB 10013-1 and 10018-1). This pattern supports previous findings that the low-salinity tongue off western Sumatra (and thus,  18 O SW ), particularly in the fore-arc basins of Mentawai, Nias and Simeulue, ''is linked to the freshwater input in the near-surface layer from rainfall and river runoff'' 43 rather than ocean advection. Sprintall et al 44 and Janowiak and Xie 45 also stated that the freshwater pool located on the equator off the west Sumatra coast is related to a regional maximum in precipitation, as well as contribution from river runoff.…”

Section: Modern Climate Of the Study Areasupporting

confidence: 90%

North Atlantic forcing of tropical Indian Ocean climate

Mohtadi

Prange

Oppo

et al. 2014

Nature

245

228

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The response of the tropical climate in the Indian Ocean realm to abrupt climate change events in the North Atlantic Ocean is contentious. Repositioning of the intertropical convergence zone is thought to have been responsible for changes in tropical hydroclimate during North Atlantic cold spells 1-5 , but the dearth of high-resolution records outside the monsoon realm in the Indian Ocean precludes a full understanding of this remote relationship and its underlying mechanisms. Here we show that slowdowns of the Atlantic meridional overturning circulation during Heinrich stadials and the Younger Dryas stadial affected the tropical Indian Ocean hydroclimate through changes to the Hadley circulation including a southward shift in the rising branch (the intertropical convergence zone) and an overall weakening over the southern Indian Ocean. Our results are based on new, high-resolution sea surface temperature and seawater oxygen isotope records of well dated sedimentary archives from the tropical eastern Indian Ocean for the past 45,000 years, combined with climate model simulations of Atlantic circulation slowdown under Marine Isotope Stages 2 and 3 boundary conditions. Similar conditions in the east and west of the basin rule out a zonal dipole structure as the dominant forcing of the tropical Indian Ocean hydroclimate of millennial-scale events. Results from our simulations and proxy data suggest dry conditions in the northern Indian Ocean realm and wet and warm conditions in the southern realm during North Atlantic cold spells.In the North Atlantic, the most recent glacial and deglacial periods are characterized by a series of abrupt and severe cold snaps of millennial duration associated with either iceberg instabilities and surges (Heinrich events) or freshwater input from the Arctic Ocean 6 (the Younger Dryas). These abrupt events are of particular interest because they were rapidly communicated through the ocean by a slowdown, or potentially a shutdown, of the Atlantic meridional overturning circulation 7 (AMOC) and through the atmospheric circulation 8 causing climate anomalies worldwide. Climate archives document a significant tropical hydrologic response to these events. Dry Younger Dryas and Heinrich stadials have been reported from various marine and terrestrial archives across the tropical Indian Ocean 4,9-14 .However, a few records suggest wet Younger Dryas or Heinrich stadials over northeast Australia 15 , southern Indonesia 5,16 and southeast Africa 12,17 . Although there seems to be strong evidence that the intertropical convergence zone (ITCZ) moved southwards in the tropical Atlantic 2 , a wide range of mechanisms have been offered to explain the connection between the cooling of the North Atlantic and tropical Indian Ocean hydroclimates: a weakening of the rainfall system in response to regional sea surface cooling 13,14 ; and changes in the monsoon intensity 4,10,16 associated with a southward shift in the mean 1 or winter 4,5,15 position of the ITCZ or in the position of oceanic fronts 18 .How...

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Section: Modern Climate Of the Study Areasupporting

confidence: 90%

North Atlantic forcing of tropical Indian Ocean climate

Mohtadi

Prange

Oppo

et al. 2014

Nature

245

228

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“…The region we studied is characterized by intense convective precipitation, where a fresher water cap and salinity stratified barrier layer commonly exist (e.g., Masson et al 2004;Qu and Meyers 2005). A few studies revealed that the barrier layer is important to the heat exchange between the mixed layer and thermocline, thus having impact on the evolution of the IOD (e.g., Du et al 2005;Du and Xie 2008;Qiu et al 2012), like its role in the ENSO dynamics (e.g., Delcroix and McPhaden 2002;Qu et al 2014). This work suggests there was a feedback between low-salinity water, thin mixed layer, and SST increase.…”

Section: Summary and Discussionmentioning

confidence: 99%

“…6b,c). Recent studies suggested that the 2010 event might be the most significant negative IOD event in the recent decade (e.g., Qiu et al 2012). Two weak positive IOD events occurred successively in 2011 and 2012, reflected in SSS.…”

Section: A Sss Variation In the Equatorial Regionmentioning

confidence: 99%

“…The differences between SMOS and Argo SSS showed significant changes after February 2011, reduced from ,20.6 psu in September-November 2010 to about 20.1 psu afterward. The time series of rainfall suggests that the largest differences in September-November 2010 might be associated with the negative IOD event in 2010, when warmer SST and enhanced deep convection induced much heavier rainfall (Qiu et al 2012). We will come back to this point in the following sections.…”

Section: B Satellite Versus Argo Sssmentioning

confidence: 99%

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

Zhang

2015

Journal of Climate

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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.

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“…The BL forms a barrier to the entrainment and turbulent mixing of cold thermocline water into the mixed layer and inhibits the momentum of downward mixing Delecluse 1998a, 1998b). The formation mechanisms and seasonal variations of the BLs differ from region to region (Sato et al 2004(Sato et al , 2006, and they are deeply involved in the Indian Ocean Dipole (IOD; Saji et al 1999) (Masson et al 2004;Qiu et al 2012) and ENSO (Ando and McPhaden 1997;Maes et al 2002Maes et al , 2005Maes et al 2006). Previous studies have noted that the BL shows various responses to atmospheric forcing associated with westerly wind bursts and the continuous precipitation of the Madden-Julian oscillation (MJO; Madden and Julian 1971) (Cronin and McPhaden 2002;DeMott et al 2015;Drushka et al 2014).…”

Section: Introductionmentioning

confidence: 99%

Drastic thickening of the barrier layer off the western coast of Sumatra due to the Madden-Julian oscillation passage during the Pre-Years of the Maritime Continent campaign

Moteki

Katsumata

Yoneyama

et al. 2018

Prog Earth Planet Sci

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The drastic thickening of the barrier layer in the marginal sea off the western coast of Sumatra during the passage of the Madden-Julian oscillation (MJO) observed during December 2015 is investigated. Before the MJO arrival, the halocline above a depth of 20 m was very strong, and the barrier layer thickness was 5-10 m based on R/V Mirai observations. During the MJO forcing of 13-16 December, the isothermal layer drastically deepened from 20 to 100 m. Meanwhile, the mixed layer deepening lagged behind the isothermal layer deepening by 1 day, and the barrier layer underwent dramatic thickening to 60 m within 24 h. An evaluation of the vertical salinity gradient tendency showed that the dramatic thickening of the barrier layer was due to the vertical oceanic mixing by the atmospheric MJO forcing and the vertical stretching by the oceanic downwelling coastal Kelvin wave intruding from the open ocean. In addition, an evaluation of the vertical temperature gradient tendency showed that the temperature inversion in the barrier layer formed by losing heat to the atmosphere due to the MJO forcing and downward advection of the temperature gradient due to the downwelling Kelvin wave resulting in the dramatic isothermal layer deepening. One of the important factors in the drastic barrier layer thickening was the atmospheric external forcing and the oceanic internal wave being in phase. The downwelling oceanic Kelvin wave continuously lowered the thermocline from the middle of November to the end of December, and the salinity stratification in the vicinity of the thermocline was continuously mitigated by the vertical stretching. Under such conditions, the MJO forcing caused vertical mixing of the freshwater with strong salinity stratification and temperature stratification near the surface. The combination of the two distinct processes caused the drastic thickening of the barrier layer, and the barrier layer thickness reached a maximum of 85 m 5 days after the MJO arrival.

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Argo profiles variability of barrier layer in the tropical Indian Ocean and its relationship with the Indian Ocean Dipole

Cited by 46 publications

References 31 publications

North Atlantic forcing of tropical Indian Ocean climate

North Atlantic forcing of tropical Indian Ocean climate

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

Drastic thickening of the barrier layer off the western coast of Sumatra due to the Madden-Julian oscillation passage during the Pre-Years of the Maritime Continent campaign

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