Surface pH Record (1990–2013) of the Arabian Sea From Boron Isotopes of Lakshadweep Corals—Trend, Variability, and Control

Tarique, M and Rahaman, W and Fousiya, AA and Lathika, N and Thamban, M and Achyuthan, H and Misra, S (2021) Surface pH Record (1990–2013) of the Arabian Sea From Boron Isotopes of Lakshadweep Corals—Trend, Variability, and Control. In: Journal of Geophysical Research: Biogeosciences, 126 (7).

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Abstract

Atmospheric CO2 rise in post-industrial era has resulted in decline in surface ocean pH, commonly known as “ocean acidification (OA),” which has become a threat to marine calcifiers. Instrumental records of ocean pH and its reconstruction utilizing boron isotope (δ11B) composition of corals demonstrate a long-term OA trend characterized by large spatio-temporal variability in both Pacific and Atlantic oceans. However, no such record exists to elucidate long-term OA trend of the Indian Ocean. We report the first sub-annually resolved pH record (1990–2013) from the Arabian Sea based on δ11B measurements on Porites coral from Lakshadweep coral reefs. This pH record is characterized by large variability ranging from 7.93 to 8.65 with no long-term discernable trend. The long-term declining trend expected from the ∼50 ppm increase in atmospheric CO2 during the coral growth interval appears to be obscured by large surface pH variability in the Arabian Sea. Our investigation reveals that physical oceanographic processes for example, upwelling, downwelling and convective mixing modulated by El Niño-Southern Oscillation (ENSO) largely control surface pH variability and masked expected long-term OA trend resulting from anthropogenic CO2 rise. Combining the model-based predictions of increase in frequency and amplitude of ENSO events in a future warming scenario and the observed ENSO dependency of surface water pH, we predict more frequent and large pH variability (“pH extremes”) in this region. Such pH extremes and their occurrences might be critical for the resilience and adaptability of corals and other calcifiers in Arabian Sea and other similar oceanic settings elsewhere.

Item Type:	Journal Article
Publication:	Journal of Geophysical Research: Biogeosciences
Publisher:	John Wiley and Sons Inc
Additional Information:	The copyright for this article belongs to John Wiley and Sons Inc.
Keywords:	anthropogenic effect; boron isotope; climate modeling; coral; downwelling; El Nino-Southern Oscillation; global warming; long-term change; ocean acidification; pH; trend analysis, Arabian Sea; India; Indian Ocean; Indian Ocean; Lakshadweep; Pacific Ocean, Anthozoa; Porites; Porites porites; Porites porites porites
Department/Centre:	Division of Mechanical Sciences > Centre for Earth Sciences
Date Deposited:	21 Feb 2023 03:11
Last Modified:	21 Feb 2023 03:11
URI:	https://eprints.iisc.ac.in/id/eprint/80509

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