Sources of particulate organic matter in the Chukchi and Siberian shelves: clues from carbon and nitrogen isotopes
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Sources of particulate organic matter in the Chukchi and Siberian shelves: clues from carbon and nitrogen isotopes Renming Jia1, Xinyue Mu1, Min Chen1*, Jing Zhu1, Bo Wang1, Xiaopeng Li1, A S Astakhov2, Minfang Zheng1, Yusheng Qiu1 1 College of Ocean and Earth Sciences, Xiamen University, Xiamen 361005, China 2 V.I. Il’ichev Pacific Oceanological Institute, Far Eastern Branch, Russian Academy of Sciences, Vladivostok 690041,
Russia Received 17 July 2019; accepted 6 November 2019 © Chinese Society for Oceanography and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract
The stable isotopic composition (δ13C and δ15N) and carbon/nitrogen ratio (C/N) of particulate organic matter (POM) in the Chukchi and East Siberian shelves from July to September, 2016 were measured to evaluate the spatial variability and origin of POM. The δ13CPOC values were in the range of −29.5‰ to −17.5‰ with an average of −25.9‰±2.0‰, and the δ15NPN values ranged from 3.9‰ to 13.1‰ with an average of 8.0‰±1.6‰. The C/N ratios in the East Siberian shelf were generally higher than those in the Chukchi shelf, while the δ13C and δ15N values were just the opposite. Abnormally low C/N ratios (10‰) values were observed in the Wrangel Island polynya, which was attributed to the early bloom of small phytoplankton. The contributions of terrestrial POM, bloom-produced POM and non-bloom marine POM were estimated using a three end-member mixing model. The spatial distribution of terrestrial POM showed a high fraction in the East Siberian shelf and decreased eastward, indicating the influence of Russian rivers. The distribution of non-bloom marine POM showed a high fraction in the Chukchi shelf with the highest fraction occurring in the Bering Strait and decreased westward, suggesting the stimulation of biological production by the Pacific inflow in the Chukchi shelf. The fractions of bloom-produced POM were highest in the winter polynya and gradually decreased toward the periphery. A negative relationship between the bloom-produced POM and the sea ice meltwater inventory was observed, indicating that the net sea ice loss promotes early bloom in the polynya. Given the high fraction of bloom-produced POM, the early bloom of phytoplankton in the polynyas may play an important role on marine production and POM export in the Arctic shelves. Key words: particulate organic matter, carbon isotope, nitrogen isotope, Chukchi Shelf, East Siberian Shelf, polynya Citation: Jia Renming, Mu Xinyue, Chen Min, Zhu Jing, Wang Bo, Li Xiaopeng, Astakhov A S, Zheng Minfang, Qiu Yusheng. 2020. Sources of particulate organic matter in the Chukchi and Siberian shelves: clues from carbon and nitrogen isotopes. Acta Oceanologica Sinica, 39(9): 96–108, doi: 10.1007/s13131-020-1650-9
1 Introduction As one of the most sensitive regions to global climate change, the Arctic Ocean is the freshest ocean with a large amount of freshwater input (Aagaard and Carmack, 1989). The intensified hydrologic cycles throughout the Arctic (Rawlins et al., 2010) have led to a decadal
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