A reduction in marine primary productivity driven by rapid warming over the tropical Indian Ocean

Abstract

Among the tropical oceans, the western Indian Ocean hosts one of the largest concentrations of marine phytoplankton blooms in summer. Interestingly, this is also the region with the largest warming trend in sea surface temperatures in the tropics during the past century—although the contribution of such a large warming to productivity changes has remained ambiguous. Earlier studies had described the western Indian Ocean as a region with the largest increase in phytoplankton during the recent decades. On the contrary, the current study points out an alarming decrease of up to 20% in phytoplankton in this region over the past six decades. We find that these trends in chlorophyll are driven by enhanced ocean stratification due to rapid warming in the Indian Ocean, which suppresses nutrient mixing from subsurface layers. Future climate projections suggest that the Indian Ocean will continue to warm, driving this productive region into an ecological desert.

Biological production in the Indian Ocean upwelling zones –Part 1: refined estimation via the use of a variable compensation depth in ocean carbon models

“…The physical and biological processes and their variability over these key regions are inseparably tied to the strength of the monsoon winds and associated nutrient dynamics. The production and its variability over these coastal upwelling systems are a key concern for the fishing community, since they affect the day-to-day livelihood of the coastal populations (Harvell et al, 1999;Roxy et al, 2015;Praveen et al, 2016) and are important for the Indian Ocean rim countries due to their developing country status.…”

“…The major upwelling systems in the Indian Ocean are (1) the western Arabian Sea (WAS; Ryther and Menzel, 1965;Sarma, 2004;Wiggert et al, 2005Wiggert et al, , 2006Murtugudde et al, 2007;McCreary et al, 2009;Naqvi et al, 2010;Prasanna Kumar et al, 2010;Roxy et al, 2015), (2) the Sri Lanka Dome (SLD; Vinayachandran and Yamagata, 2008;Vinayachandran et al, 2004), (3) the Java and Sumatra coasts (SC; Susanto et al, 2001;Osawa and Julimantoro, 2010;Xing et al, 2012) and (4) the Seychelles-Chagos thermocline ridge (SCTR; Dilmahamod et al, 2016, Fig. 1).…”

Physical control of interannual variations of the winter chlorophyll bloom in the northern Arabian Sea

“…However, the shortness and discontinuity of the data call into question the reliability of these results (Beaulieu et al, 2013). Recent studies based on longer datasets (Roxy et al, 2015(Roxy et al, , 2016 rather point towards a reduction of the summer monsoon winds and an AS summer bloom reduction due to enhanced upper-ocean stratification in response to climate change. Climate change projections from coupled experiments however exhibit a large range of responses in terms of changes in the southwest monsoon (e.g.…”

Implication of our technological species being first and early

“…One imaginable (if oversimplified) example of a biosphere extinction scenario is the depletion of atmospheric oxygen caused by the loss of photosynthesis in ocean phytoplankton and rain forests, possibly accelerated by rising global temperatures. Such a process may already be in progress (Boyce et al 2010;Roxy et al 2016). The (complete) extinction of aerobic life would reset the evolutionary clock back to the time photosynthetic oxygen first appeared in the atmosphere &2.5 Gyr ago, leaving insufficient time for the evolution of another technological species.…”