Temporal and spatial trends in marine carbon isotopes in the Arctic Ocean and implications for food web studies.

Camille De La Vega,Rachel M Jeffreys,Raja Ganeshram,Claire Mahaffey,Robyn Tuerena

doi:10.1111/gcb.14832

Camille De La Vega, Rachel M Jeffreys + Show 3 more

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https://doi.org/10.1111/gcb.14832

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Abstract

The Arctic is undergoing unprecedented environmental change. Rapid warming, decline in sea ice extent, increase in riverine input, ocean acidification and changes in primary productivity are creating a crucible for multiple concurrent environmental stressors, with unknown consequences for the entire arctic ecosystem. Here, we synthesized 30 years of data on the stable carbon isotope (δ13C) signatures in dissolved inorganic carbon (δ13C‐DIC; 1977–2014), marine and riverine particulate organic carbon (δ13C‐POC; 1986–2013) and tissues of marine mammals in the Arctic. δ13C values in consumers can change as a result of environmentally driven variation in the δ13C values at the base of the food web or alteration in the trophic structure, thus providing a method to assess the sensitivity of food webs to environmental change. Our synthesis reveals a spatially heterogeneous and temporally evolving δ13C baseline, with spatial gradients in the δ13C‐POC values between arctic shelves and arctic basins likely driven by differences in productivity and riverine and coastal influence. We report a decline in δ13C‐DIC values (−0.011‰ per year) in the Arctic, reflecting increasing anthropogenic carbon dioxide (CO2) in the Arctic Ocean (i.e. Suess effect), which is larger than predicted. The larger decline in δ13C‐POC values and δ13C in arctic marine mammals reflects the anthropogenic CO2 signal as well as the influence of a changing arctic environment. Combining the influence of changing sea ice conditions and isotopic fractionation by phytoplankton, we explain the decadal decline in δ13C‐POC values in the Arctic Ocean and partially explain the δ13C values in marine mammals with consideration of time‐varying integration of δ13C values. The response of the arctic ecosystem to ongoing environmental change is stronger than we would predict theoretically, which has tremendous implications for the study of food webs in the rapidly changing Arctic Ocean.

Highlights

The 13C depletion in δ13C‐POCwater values observed in the interior shelves, Svalbard fjords, Hudson Bay and Canadian archipelago compared to other arctic shelf regions likely reflects the contribution of 13C‐depleted terrestrially derived particulate organic carbon (POC) (Boutton, 1991) from rivers, coastal erosion and glacial streams
The combined effect of a decline in ice algae (0.06 ± 0.15‰ per year, this study), increase in fractionation factor (0.045‰ per year, Young et al, 2013) and Suess effect could potentially cause the δ13C‐POC values to decrease by 0.116 ± 0.15‰ per year, which is of the same order of magnitude as the observed annual decrease in δ13C‐POCwater values in the whole Arctic (0.149 ± 0.028‰ per year) and in the Beaufort
The Atlantic and Pacific Oceans (Graham et al, 2010; McMahon et al, 2013b), this study provides a first view of δ13C‐POC values or carbon isoscape of the Arctic Ocean

Summary

Introduction

The main objective of this study was to quantify how regional differences and temporal trends in the arctic environment have altered the δ13C values in DIC and POC, representing the base of the food web We analysed the δ13C‐POCwater, δ13C‐POCice, δ13C‐DIC and δ13C‐ CO2 values in 17 marine arctic regions (Figure 1; Table 1).

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