Orbital forcing regulated Arabian Sea denitrification during the late Pleistocene
Abstract
To limit global warming to within 2�C, it is essential to understand the contribution of non-carbon dioxide greenhouse gases. Nitrous oxide (N2O), a potent greenhouse gas, has played a significant role in the recent climate change. Therefore, understanding its long-term evolution is crucial to develop effective mitigation strategies. In this study, we reconstruct the long-term history of the Arabian Sea denitrification, a major natural source of atmospheric N2O, using a marine sediment core SSD004 GC11 from the southern Arabian Sea, spanning the last 167,000 years. To trace the past denitrification history, we analysed the nitrogen isotopic composition (?15N), an indicator of denitrification and total nitrogen content (TN). Our results show a strong coupling between primary productivity and denitrification during warm intervals, however, this relationship weakens during cold intervals, despite productivity being sustained by winter monsoon-driven vertical mixing. We integrated the newly generated ?15N record with previously published records to construct a basin-wide Arabian Sea denitrification stack. The spectral analysis reveals dominant periodicity synchronous with Earth's orbital parameters, particularly obliquity and precession. Notably, obliquity signal is stronger in the southern Arabian Sea, while precession signal dominates the northern records. A cross-wavelet analysis of our core ?15N record, the Arabian Sea ?15N stack, and atmospheric N2O concentration shows a significant influence of obliquity-driven processes on regional denitrification and atmospheric N2O levels. These findings highlight the pivotal role of orbital forcing in regulating nitrogen cycling in the Arabian Sea and its broader impact on greenhouse gas dynamics.
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