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

Abstract

<p><strong>Abstract.</strong> 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.</p>

Correction of inter-mission inconsistencies in merged ocean colour satellite data

“…Inter-mission inconsistencies appear as significant steps in global time series (Jackson, 2020) and seem to coincide with changes in the availability of single sensors. Similar patterns are found in numerous studies that use different merged ocean colour data sets (Kahru et al, 2012(Kahru et al, , 2015Navarro et al, 2017;Sankar et al, 2019;Kulk et al, 2020;Joseph et al, 2021) and are potentially misinterpreted as a part of natural variability. Some phenology studies that use merged ocean colour data also show patterns concurring with mission availability (Gittings et al, 2021;Staehr et al, 2022).…”

Unprecedented Surface Chlorophyll Blooms in the Southeastern Arabian Sea During an Extreme Negative Indian Ocean Dipole

“…During nIOD, Ekman suction is generally high in the SEAS (Sankar et al., 2019). Ekman vertical velocities ( W ek ; section S2) calculated from daily wind stress in the region of the eddies are shown in Figure 3g.…”

“…Seasonal evolution of chlorophyll in the Indian Ocean is often modulated by large-scale climatic events including the Indian Ocean Dipole (IOD) and El Niño (Wiggert et al, 2009). Chlorophyll anomalies during these events are associated with the basinwide variability in winds, determining the local upwelling and mixing (Chen et al, 2013;Murtugudde et al, 1999;Sankar et al, 2019;Sarma, 2006;Vidya & Kurian, 2018) or the remote forcings on thermocline (Currie et al, 2013;Girishkumar et al, 2012;Rao & Behera, 2005;Yu et al, 2005), regulating the nutrient supply to the euphotic zone. impact of negative IOD (nIOD; Vinayachandran et al, 2002) has not received enough attention.…”

“…impact of negative IOD (nIOD; Vinayachandran et al, 2002) has not received enough attention. During nIOD, the SEAS is characterized by increased Ekman suction and coastal upwelling, and shoaling of thermocline, favoring enhanced surface chlorophyll (Sankar et al, 2019). However, the positive chlorophyll anomalies during nIOD are relatively weak, compared to that during pIOD, due to the weaker influence on sea level and thermocline (Aparna et al, 2012;Parvathi et al, 2017).…”

What are the dynamics of hydrometeorological parameters on peatlands during the 2019 extreme dry season?

“…This minimal rainfall has resulted in severe drought and fires on the peatlands. This period is called the extreme dry season which occurred from July 2019 to December 2019 [7][8][9][10][11]. It is interesting to examine how the dynamics of the hydrometeorological parameters are estimated to be associated with fires on peatlands, including rainfall, groundwater levels and the number of hotspots during this period as an effort to mitigate fire disasters on peatlands.…”