Atlantic walrus signal latitudinal differences in the long-term decline of sea ice-derived carbon to benthic fauna in the Canadian Arctic.

Paul J Blanchfield,Thomas A Brown,David J Yurkowski,Steven H Ferguson

doi:10.1098/rspb.2020.2126

Abstract

Climate change is altering the biogeochemical and physical characteristics of the Arctic marine environment, which impacts sea ice algal and phytoplankton bloom dynamics and the vertical transport of these carbon sources to benthic communities. Little is known about whether the contribution of sea ice-derived carbon to benthic fauna and nitrogen cycling has changed over multiple decades in concert with receding sea ice. We combined compound-specific stable isotope analysis of amino acids with highly branched isoprenoid diatom lipid biomarkers using archived (1982–2016) tissue of benthivorous Atlantic walrus to examine temporal trends of sea ice-derived carbon, nitrogen isotope baseline and trophic position of Atlantic walrus at high- and mid-latitudes in the Canadian Arctic. Associated with an 18% sea ice decline in the mid-Arctic, sea ice-derived carbon contribution to Atlantic walrus decreased by 75% suggesting a strong decoupling of sea ice-benthic habitats. By contrast, a nearly exclusive amount of sea ice-derived carbon was maintained in high-Arctic Atlantic walrus (98% in 1996 and 89% in 2006) despite a similar percentage in sea ice reduction. Nitrogen isotope baseline or the trophic position of Atlantic walrus did not change over time at either location. These findings indicate latitudinal differences in the restructuring of carbon energy sources used by Atlantic walrus and their benthic prey, and in turn a change in Arctic marine ecosystem functioning between sea ice–pelagic–benthic habitats.

Highlights

Arctic marine environments are fuelled by recurrent influxes of two distinct sources of carbon that are driven by the seasonal progression of light and open water availability which varies by latitude [1]
In Foxe Basin, δ15NPhe (t5 = 0.19, p = 0.85) and trophic position (t5 = 0.63, p = 0.53) of Atlantic walrus did not change over time, whereas significant decreases occurred for sea ice-derived carbon (t8 = −4.60, p < 0.01) and δ13C of phenylalanine (δ13CPhe) (t8 = −3.80, p < 0.01; figure 3)
Using a novel biochemical coupling approach for polar environments, we identified a prominent 35-year decline (i.e. 1982–2016) in the contribution of sea ice-derived carbon to Atlantic walrus, a benthic fauna consumer, in Foxe Basin

Summary

Introduction

Arctic marine environments are fuelled by recurrent influxes of two distinct sources of carbon that are driven by the seasonal progression of light and open water availability which varies by latitude [1]. We used a novel biochemical approach by coupling source-specific highly branched isoprenoid diatom lipid biomarkers with compound-specific stable carbon and nitrogen isotope values of individual amino acids of archived walrus tissues from Jones Sound over an 11-year time period (1996– 2006) and northern Foxe Basin over a 35-year time period (1982–2016). We hypothesized that Atlantic walrus from the more-northern ice-covered waters of Jones Sound will have a higher contribution of sea ice-derived carbon in their tissues than individuals who reside in the more-southern Foxe Basin area as a result of higher summer sea ice concentrations. Brown et al [21] used highly branched isoprenoids of ringed seal (Pusa hispida) liver samples to quantify monthly changes in sea ice-derived carbon contributions to ringed seal diet Using both liver and muscle samples of Atlantic walrus allows one to measure time-integrated resource use over two different temporal scales (i.e. monthly using liver and seasonal using muscle). All statistical analyses were performed in R v. 3.6.1 [41]

Results

Findings

Discussion