Indian Ocean Dipole and El Niño/Southern Oscillation impacts on regional chlorophyll anomalies in the Indian Ocean (original) (raw)

Role of physical processes in chlorophyll distribution in the western tropical Indian Ocean

Physical control of the chlorophyll a (chl a) distribution in the western tropical Indian Ocean (WTIO, 8°N to 18°S along 65°E) was studied during the 2008 winter monsoon (WM) and the 2009 summer monsoon (SM). During both seasons, a prominent deep chlorophyll maximum (DCM, 0.3-0.5 mg m −3 ) was observed at all stations between 8°N and 10°S in the depth range of 50-75 m, but south of 10°S, this phenomenon was observed as deeper (~120 m) and relatively weak (0.15-0.3 mg m −3 ). During the SM, in addition to seasonal forcing, eddies and a freshened surface layer also played major roles in controlling the DCM and the surface chl a concentrations in the southern Arabian Sea and the equatorial Indian Ocean. During the WM, surface freshening controlled the chl a distribution in the Seychelles Chagos Thermocline Ridge (SCTR, 5°S-10°S) region by modulating the static stability and mixed layer depth. It appears that the surface freshening in this region is associated with the core of the South Equatorial Current. South of the SCTR, the chl a distribution was predominantly determined by the anti-cyclonic eddies in both seasons. The spatial patterns of the Sea Level Anomaly (SLA) followed most of the thermocline features observed during the study period.

Chlorophyll Distribution and Variability at the Surface of the Indian Ocean

Journal of Research in Environmental and Earth Sciences, 2022

Surface chlorophyll in the oceans can be a valuable tool for tracing surface water mass movement and analysing water mass mixing, important to the formation of water masses within the global oceanic circulation. It is observed differences in chlorophyll concentration in the oceanic surface layer from one oceanic region to the other. This work establishes a distribution and variability of chlorophyll in the surface layer of the tropical Indian Ocean (25°N to 30°S and 30°E to 120°E). It is based on analysis of semi-annual and annual amplitudes of chlorophyll. It is discussed the different physical processes that can be involved with the variability of chlorophyll. This analysis is strongly restricted to the available data sets. The geographical representation of the variability and distribution of the surface chlorophyll agrees well with the theoretical frame of reference.

Surface chlorophyll-a variations in the Southeastern Tropical Indian Ocean during various types of the positive Indian Ocean Dipole events

International Journal of Remote Sensing, 2019

Surface chlorophyll-a (chl-a) variation in the Southeastern Tropical Indian Ocean (SETIO) shows different patterns in response to the various types of the Indian Ocean Dipole (IOD) events. Thirteen years of remotely sensed surface chl-a data from the Moderateresolution Imaging Spectroradiometer (MODIS) were used to evaluate interannual surface chl-a variation in the SETIO. During the period of analysis (January 2003-December 2015), there were three canonical positive IOD (pIOD) and four pIOD Modoki events. It is found that the spatial patterns of surface chl-a variation were coherent with the pattern of surface wind anomaly, and the sea surface temperature anomaly (SSTA). During canonical pIOD events, high chl-a concentrations were observed in the vicinity of the Sunda Strait and along the coast of western tip of the Java Island around the Cilacap region. Meanwhile, during pIOD Modoki event, surface chl-a concentration was relatively higher and distributed wider than those observed during canonical pIOD event. The analysis shows that relatively weak upwelling event indicated by a deep isothermal layer depth (ILD) during pIOD Modoki events combined with thin barrier layer thickness (BLT) and deep mixed layer provides a favourable condition for an increase in surface chla in the SETIO region. Meanwhile, strong upwelling as indicated by shallow ILD combined with thick BLT and shallow mixed layer prevents surface chl-a to increase during canonical pIOD events.

The influence of tropical Indian Ocean warming and Indian Ocean Dipole on the surface chlorophyll concentration in the eastern Arabian Sea

Biogeosciences Discussions

This study examines the role of increased Indian Ocean warming and positive Indian Ocean Dipole (IOD) events on the surface chlorophyll concentration in the Eastern Arabian Sea (EAS) during the period 1998 to 2014. Remotely sensed surface chlorophyll concentration-during the month of October when IOD strength is maximum-at three selected areas in the EAS, viz., the central eastern Arabian Sea (CEAS, 73° E-76° E, 13° N-18° N), south eastern Arabian Sea (SEAS, 74°E-77° E, 8° N-13° N) and the southern tip of India (TIP, 74° E-78° E, 5° N-8° N) shows a steady decreasing trend, though not statistically significant. The EAS also has a higher warming trend when compared to the western basin during the study period. Our analysis has shown that in the EAS, local surface winds, remote forcing by equatorial winds and the surface and sub-surface oceanic circulation features are less (respectively more) favorable for inducing coastal upwelling during positive (respectively negative) IOD years. The Dipole Mode Index (DMI) and surface chlorophyll concentration in the EAS is significantly and negatively correlated, pointing to the fact that in the event of occurrence of frequent positive IOD years under a global warming regime, the surface chlorophyll concentration is likely to decrease during fall.

Variability of Sea Surface Temperature (SST) and Chlorophyll-A (CHL-A) Concentrations in the Eastern Indian Ocean During the Period 2002–2017

International Journal of Remote Sensing and Earth Sciences (IJReSES)

We analysed the variability of sea surface temperature (SST) and chlorophyll-a concentration (Chl-a) in the eastern Indian Ocean (EIO). We used monthly mean Chl-a and SST data with a 4-km spatial resolution derived from Level-3 Aqua Moderate-resolution Imaging Spectroradiometer (MODIS) distributed by the Asia-Pacific Data-Research Center (APDRC) for the period 2002–2017. Wavelet analysis shows the annual and interannual variability of SST and Chl-a concentration in the EIO. The annual variability of SST and Chl-a is influenced by monsoon systems. During a southeast monsoon, SST falls while Chl-a increases due to upwelling. The annual variability of SST and Chl-a is also influenced by the Indian Ocean Dipole (IOD). During positive phases of the IOD (2006, 2012 and 2015), there was more intense upwelling in the EIO caused by the negative anomaly of SST and the positive anomaly of Chl-a concentration.

A quantitative method for describing the seasonal cycles of surface chlorophyll in the Indian Ocean

Proceedings of SPIE - The International Society for Optical Engineering

The seasonal cycles of surface chlorophyll (SCHL) in the Indian Ocean (IO) are regionally described by means of 6 parameters: the timing of the bloom onset and of the bloom peak, and the integrated SCHL value in between these two extrema for both winter and summer blooms. This description, based on a climatology constructed from 7 years of SeaWiFS data, provides a regional image of the influence of the two monsoons on phytoplankton blooms. Over a large part of the basin, the seasonal cycle is characterized by two distinct growth periods, one in summer during the South West Monsoon (SWM), the other in winter during the North East Monsoon (NEM). However, in some specific areas such as the southwestern coast of India, there is no maxima during the NEM. The bloom areas during the SWM and the NEM show totally different regional patterns. Important lags in the timing of the blooms are identified, and are also associated with distinct regional patterns. The next step in the understanding o...

Surface Chlorophyll-A Variations Along the Southern Coast of Java During Two Contrasting Indian Ocean Dipole Events: 2015 and 2016

JOURNAL OF SUSTAINABILITY SCIENCE AND MANAGEMENT

Satellite-derived surface chlorophyll-a (chl-a) concentration off the southern coast of Java during the southeast monsoon season (July-September) of 2015 positive Indian Ocean Dipole (IOD) and 2016 negative IOD events was analyzed. The analysis was intended to examine how strong was the coastal upwelling, indicated by Ekman transport, during those two contrasting IOD events affecting the surface chl-a distribution. The results, however, did not reveal robust contrast patterns as was expected. Only weak coastal upwelling signals (offshore Ekman transport) were observed during the 2015 positive IOD event. This weak offshore Ekman transport combined with positive atmospheric flux prevented the exchange of cold thermocline water with the surface, resulting in weak SST cooling. The surface chl-a also only showed sporadic anomalous blooming during 2015. On the other hand, the 2016 negative IOD event has robust atmospheric and oceanic patterns. Strong onshore Ekman transport and distinct positive SST anomalies were observed. The surface chl-a patterns showing negative anomalies also clearly marked the oceanic response to those anomalously strong onshore Ekman transport. The results marked the important role of coastal upwelling for surface chl-a bloom in this area.

Does SST Explain the Seasonal Variability of Chlorophyll in the Upper Indian Ocean?

2020

Quantitative analyses of chlorophyll concentration in relation to Sea Surface Temperature (SST) can explain the spatiotemporal distribution of phytoplankton in oceans. In this study, the response of chlorophyll in the Bay of Bengal (BoB) and the Arabian Sea (AS) to seasonal SST was investigated using remotely sensed Moderate Resolution Imaging Spectroradiometer (MODIS) data. MODIS SST data were validated with in-situ data derived from the World Ocean Database. Thus, satellite-based SST estimates were more reliable for BoB than that of AS. In general, SST was comparatively high in BoB; the lowest 27.88° C recorded in January and the highest 30.33° C in April. In contrast, maximum SST in AS was 29.82° C in May and minimum 26.66° C recorded in January. The chlorophyll concentration in BoB was minimum (0.31 mg m-3) in April and maximum (0.46 mg m-3) in September. While the chlorophyllin AS was minimum (0.34 mg m-3) in April and maximum (1.18 mg m-3) in September. These results suggest a...