How Monsoon and Salty Sea Water Affect Plankton in the Bay of Bengal

Jim Crocker
10th March, 2024

Image Source: Natural Science News, 2024

Key Findings

In the Bay of Bengal, tiny organisms called planktic foraminifera are found in high numbers, which helps bury carbon deep in the ocean
These organisms thrive in warm, salty waters, especially where river input and ocean upwelling provide ample food
Monsoon patterns, water temperature, and salinity all influence where these carbon-storing organisms are most abundant

The ocean plays a crucial role in regulating Earth's climate, acting as a sink for carbon dioxide (CO2), a major greenhouse gas. One of the lesser-known but significant participants in this process are tiny marine organisms called planktic foraminifera. These single-celled creatures, with their calcium carbonate shells, help sequester CO2 by trapping it in their shells, which eventually settle on the ocean floor, storing carbon for millions of years. Understanding their abundance and diversity is vital for predicting how climate change might affect this natural carbon sequestration process. In recent research by the National Institute of Oceanography^[1], scientists have discovered an exceptionally high abundance of planktic foraminifera in the southwestern Bay of Bengal, which suggests a significant carbon burial in this region. This discovery is particularly important because it provides a baseline for how these organisms distribute themselves in relation to environmental factors such as temperature, salinity, and food availability. The study found that the Cauvery River basin, with its biannual productivity and warm, saline waters, hosts a remarkably high number of planktic foraminifera. The species Globigerinita glutinata was the most abundant, followed by Globigerinoides ruber and Globigerina bulloides. Interestingly, G. bulloides thrives on the shelf where upwelling is more frequent, bringing nutrients up from the deep and promoting growth. The researchers also noted patterns in species distribution in relation to the ocean's thermocline, which is the layer in the water column that marks a rapid change in temperature with depth. The relative abundance of Globorotalia menardii, for instance, increased with higher salinity in the thermocline, but decreased with warmer thermocline temperatures. Similarly, Neogloboquadrina dutertrei and Globoquadrina conglomerata were found to prefer cooler temperatures and higher salinities in both the mixed layer and the thermocline. Moreover, the study suggests that the monsoon plays a significant role in influencing the distribution of these organisms. For example, Globigerina falconensis was more plentiful in the southernmost transect, an area impacted by intense winter monsoon precipitation. This indicates that monsoon-associated processes, along with temperature and salinity, are key factors in determining where planktic foraminifera populations thrive. These findings are not just relevant for understanding current populations but also for predicting future changes. As the study points out, shifts in water influx from the southeastern Arabian Sea could impact the planktic foraminiferal community and, consequently, the carbon burial in the southwestern Bay of Bengal. Incorporating prior research, such as the study of the Bay of Bengal and Arabian Sea oxygen deficient zones^[2], we can appreciate the complex interplay between ocean chemistry and foraminiferal populations. The absence of denitrification in the Bay of Bengal, as opposed to the Arabian Sea, supports different benthic fauna and, by extension, could influence the overlying planktic foraminiferal communities and their role in carbon sequestration. Furthermore, the synthesis of planktonic foraminifera census counts in surface sediment samples^[3] provides a valuable context for understanding the baseline distributions and how they may shift due to climate change. The automated and objective data treatment pipeline established in this earlier study ensures that the present findings are based on harmonized and reliable data. Additionally, the study of cyclonic eddies in the southwestern Bay of Bengal^[4] sheds light on the physical processes that can enhance biological productivity, ultimately affecting foraminiferal abundance and carbon burial. The eddies, driven by wind stress and Ekman pumping, bring nutrient-rich waters to the surface, setting the stage for higher biological production and, consequently, a greater presence of planktic foraminifera. Overall, the National Institute of Oceanography's study not only expands our understanding of how regional oceanographic processes influence planktic foraminiferal populations but also underscores the importance of monitoring these organisms as indicators of the ocean's health and its ability to sequester carbon amidst the challenges of global warming.

Ecology Marine Biology

References

Main Study

1) Intrusion of Arabian Sea high salinity water and monsoon-associated processes modulate planktic foraminiferal abundance and carbon burial in the southwestern Bay of Bengal.

Published 9th March, 2024

https://doi.org/10.1007/s11356-024-32685-4

Related Studies

2) Lack of denitrification causes a difference in benthic foraminifera living in the oxygen deficient zones of the Bay of Bengal and the Arabian Sea.

https://doi.org/10.1016/j.marpolbul.2020.110992

3) ForCenS, a curated database of planktonic foraminifera census counts in marine surface sediment samples.

https://doi.org/10.1038/sdata.2017.109

4) Response of micro- and mesozooplankton in the southwestern Bay of Bengal to a cyclonic eddy during the winter monsoon, 2005.

https://doi.org/10.1007/s10661-015-4609-0

Key Findings

References

Main Study

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