Surface chlorophyll blooms in the Southern Bay of Bengal during the extreme positive Indian Ocean dipole

AbstractThe 2019 positive Indian Ocean Dipole (IOD) event in the boreal autumn was the most serious IOD event of the century with reports of significant sea surface temperature (SST) changes in the east and west equatorial Indian Ocean. Observations of the Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the Suomi National Polar-orbiting Partnership (SNPP) between 2012 and 2020 are used to study the significant biological dipole response that occurred in the equatorial Indian Ocean following the 2019 positive IOD event. For the first time, we propose, identify, characterize, and quantify the biological IOD. The 2019 positive IOD event led to anomalous biological activity in both the east IOD zone and west IOD zone. The average chlorophyll-a (Chl-a) concentration reached over ~ 0.5 mg m−3 in 2019 in comparison to the climatology Chl-a of ~ 0.3 mg m−3 in the east IOD zone. In the west IOD zone, the biological activity was significantly depressed. The depressed Chl-a lasted until May 2020. The anomalous ocean biological activity in the east IOD zone was attributed to the advection of the higher-nutrient surface water due to enhanced upwelling. On the other hand, the dampened ocean biological activity in the west IOD zone was attributed to the stronger convergence of the surface waters than that in a normal year.

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Impact of the Strong Downwelling (Upwelling) on Small Pelagic Fish Production during the 2016 (2019) Negative (Positive) Indian Ocean Dipole Events in the Eastern Indian Ocean off Java

Climate ◽

10.3390/cli9020029 ◽

2021 ◽

Vol 9 (2) ◽

pp. 29

Author(s):

Jonson Lumban-Gaol ◽

Eko Siswanto ◽

Kedarnath Mahapatra ◽

Nyoman Metta Nyanakumara Natih ◽

I Wayan Nurjaya ◽

...

Keyword(s):

Indian Ocean ◽

Indian Ocean Dipole ◽

Pelagic Fish ◽

Eastern Indian Ocean ◽

Fish Production ◽

Small Pelagic Fish ◽

Field Surveys ◽

Chl A ◽

Positive Indian Ocean Dipole ◽

The Impact

Although researchers have investigated the impact of Indian Ocean Dipole (IOD) phases on human lives, only a few have examined such impacts on fisheries. In this study, we analyzed the influence of negative (positive) IOD phases on chlorophyll a (Chl-a) concentrations as an indicator of phytoplankton biomass and small pelagic fish production in the eastern Indian Ocean (EIO) off Java. We also conducted field surveys in the EIO off Palabuhanratu Bay at the peak (October) and the end (December) of the 2019 positive IOD phase. Our findings show that the Chl-a concentration had a strong and robust association with the 2016 (2019) negative (positive) IOD phases. The negative (positive) anomalous Chl-a concentration in the EIO off Java associated with the negative (positive) IOD phase induced strong downwelling (upwelling), leading to the preponderant decrease (increase) in small pelagic fish production in the EIO off Java.

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Two-year consecutive concurrences of positive Indian Ocean Dipole and Central Pacific El Niño preconditioned the 2019/2020 Australian “black summer” bushfires

Geoscience Letters ◽

10.1186/s40562-020-00168-2 ◽

2020 ◽

Vol 7 (1) ◽

Author(s):

Guojian Wang ◽

Wenju Cai

Keyword(s):

Indian Ocean ◽

El Niño ◽

Indian Ocean Dipole ◽

El Nino ◽

Greenhouse Warming ◽

Central Pacific ◽

Central Pacific El Niño ◽

Positive Indian Ocean Dipole ◽

The Future ◽

Rainfall Anomalies

Abstract The 2019/20 Australian black summer bushfires were particularly severe in many respects, including its early commencement, large spatial coverage, and large number of burning days, preceded by record dry and hot anomalies. Determining whether greenhouse warming has played a role is an important issue. Here, we examine known modes of tropical climate variability that contribute to droughts in Australia to provide a gauge. We find that a two-year consecutive concurrence of the 2018 and 2019 positive Indian Ocean Dipole and the 2018 and 2019 Central Pacific El Niño, with the former affecting Southeast Australia, and the latter influencing eastern and northeastern Australia, may explain many characteristics of the fires. Such consecutive events occurred only once in the observations since 1911. Using two generations of state-of-the-art climate models under historical and a business-as-usual emission scenario, we show that the frequency of such consecutive concurrences increases slightly, but rainfall anomalies during such events are stronger in the future climate, and there are drying trends across Australia. The impact of the stronger rainfall anomalies during such events under drying trends is likely to be exacerbated by greenhouse warming-induced rise in temperatures, making such events in the future even more extreme.

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Stabilised frequency of extreme positive Indian Ocean Dipole under 1.5 °C warming

Nature Communications ◽

10.1038/s41467-018-03789-6 ◽

2018 ◽

Vol 9 (1) ◽

Cited By ~ 15

Author(s):

Wenju Cai ◽

Guojian Wang ◽

Bolan Gan ◽

Lixin Wu ◽

Agus Santoso ◽

...

Keyword(s):

Indian Ocean ◽

Indian Ocean Dipole ◽

Positive Indian Ocean Dipole

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Coastal upwelling events along the southern coast of Java during the 2008 positive Indian Ocean Dipole

Journal of Oceanography ◽

10.1007/s10872-018-0475-z ◽

2018 ◽

Vol 74 (5) ◽

pp. 499-508 ◽

Cited By ~ 1

Author(s):

T. Horii ◽

I. Ueki ◽

K. Ando

Keyword(s):

Indian Ocean ◽

Indian Ocean Dipole ◽

Coastal Upwelling ◽

Southern Coast ◽

Positive Indian Ocean Dipole

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Seasonal Responses of Precipitation in China to El Niño and Positive Indian Ocean Dipole Modes

Atmosphere ◽

10.3390/atmos10070372 ◽

2019 ◽

Vol 10 (7) ◽

pp. 372 ◽

Cited By ~ 4

Author(s):

Chunxiang Li ◽

Tianbao Zhao

Keyword(s):

Indian Ocean ◽

El Niño ◽

Indian Ocean Dipole ◽

North China ◽

El Nino ◽

Southern Oscillation ◽

Southern China ◽

Northwestern China ◽

Positive Indian Ocean Dipole ◽

Seasonal Responses

Using composite, regular, and partial regression analyses in the six consecutive seasons from spring of the El Niño–Southern Oscillation (ENSO)-/Indian Ocean Dipole (IOD)-developing year through summer following the ENSO/IOD mature phase, the individual and combined impacts of El Niño and positive Indian Ocean Dipole (pIOD) on the evolution of precipitation in China are diagnosed for the period 1950–2013. It is shown that the seasonal responses of precipitation in China to El Niño and pIOD events, and their relationship with the large-scale atmospheric circulations, differ from one season to another. For the pure El Niño years, there is a seasonal reversal of precipitation over southeastern and northwestern China, with deficient precipitation occurring in these two regions before the onset of anomalous wet conditions in the developing autumn. Meanwhile, North China tends to be drier than normal in the developing seasons, but wetter than normal in the decaying seasons. For the pure pIOD events, southern China suffers a precipitation deficit (surplus) in the developing spring (summer and autumn). Furthermore, both North China and northwestern China experience excessive precipitation in the developing autumn and decaying summer. In addition, there is reduced precipitation in northeastern China during both the developing and decaying summers, whereas increased precipitation occurs in the developing autumn and decaying winter. For the combined years, southern China experiences enhanced moisture supply and suffers from increased precipitation from the developing summer through the subsequent spring, but reduced precipitation in the developing spring and decaying summer. Similar to the pure El Niño, northwestern (North) China becomes wetter than normal after the developing summer (autumn) in the combined years. In general, the ENSO/IOD-related precipitation variability could be explained by the associated anomaly circulations.

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Positive Indian Ocean Dipole events prevent anoxia off the west coast of India

Biogeosciences ◽

10.5194/bg-14-1541-2017 ◽

2017 ◽

Vol 14 (6) ◽

pp. 1541-1559 ◽

Cited By ~ 14

Author(s):

Parvathi Vallivattathillam ◽

Suresh Iyyappan ◽

Matthieu Lengaigne ◽

Christian Ethé ◽

Jérôme Vialard ◽

...

Keyword(s):

Indian Ocean ◽

West Coast ◽

Indian Ocean Dipole ◽

Boreal Summer ◽

Low Oxygen ◽

The West ◽

Easterly Wind ◽

West Coast Of India ◽

Positive Indian Ocean Dipole ◽

Subsurface Waters

Abstract. The seasonal upwelling along the west coast of India (WCI) brings nutrient-rich, oxygen-poor subsurface waters to the continental shelf, favoring very low oxygen concentrations in the surface waters during late boreal summer and fall. This yearly-recurring coastal hypoxia is more severe during some years, leading to coastal anoxia that has strong impacts on the living resources. In the present study, we analyze a 1/4° resolution coupled physical–biogeochemical regional oceanic simulation over the 1960–2012 period to investigate the physical processes influencing the oxycline interannual variability off the WCI, that being a proxy for the variability on the shelf in our model. Our analysis indicates a tight relationship between the oxycline and thermocline variations in this region on both seasonal and interannual timescales, thereby revealing a strong physical control of the oxycline variability. As in observations, our model exhibits a shallow oxycline and thermocline during fall that combines with interannual variations to create a window of opportunity for coastal anoxic events. We further demonstrate that the boreal fall oxycline fluctuations off the WCI are strongly related to the Indian Ocean Dipole (IOD), with an asymmetric influence of its positive and negative phases. Positive IODs are associated with easterly wind anomalies near the southern tip of India. These winds force downwelling coastal Kelvin waves that propagate along the WCI and deepen the thermocline and oxycline there, thus preventing the occurrence of coastal anoxia. On the other hand, negative IODs are associated with WCI thermocline and oxycline anomalies of opposite sign but of smaller amplitude, so that the negative or neutral IOD phases are necessary but not the sufficient condition for coastal anoxia. As the IODs generally start developing in summer, these findings suggest some predictability to the occurrence of coastal anoxia off the WCI a couple of months ahead.

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