Effect of terrestrial organic matter on ocean acidification and CO2 flux in an Arctic shelf sea

David W Capelle,Zou Zou A Kuzyk,Tim Papakyriakou,Céline Guéguen,Lisa A Miller,Robie W Macdonald

doi:10.1016/j.pocean.2020.102319

David W Capelle, Zou Zou A Kuzyk + Show 4 more

Open Access

https://doi.org/10.1016/j.pocean.2020.102319

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Abstract

Recent research has focused on the changing ability of oceans to absorb atmospheric CO2 and the consequences for ocean acidification, with Arctic shelf seas being among the most sensitive regions. Hudson Bay is a large shelf sea in northern Canada whose location at the margin of the cryosphere places it in the vanguard of global climate change. Here, we develop a four-compartment box-model and carbon budget using published and recently collected measurements to estimate carbon inputs, transformations, and losses within Hudson Bay. We estimate the annual effects of terrestrial carbon remineralization on aragonite saturation (ΩAr, a proxy for ocean acidification) and on the partial pressure of CO2 (pCO2, a proxy for air-sea CO2 flux) within each compartment, as well as the effects of marine primary production, marine organic carbon remineralization, and terrestrial calcium carbonate dissolution. We find that the remineralization of terrestrial dissolved organic carbon is the main driver of CO2 accumulation and aragonite under-saturation in coastal surface waters, but this is largely offset by marine primary production. Below the surface mixed layer, marine organic carbon remineralization is the largest contributor to CO2 accumulation and aragonite under-saturation, and is partially offset by terrestrial CaCO3 dissolution. Overall, the annual delivery and processing of carbon reduces ΩAr of water flowing through HB by up to 0.17 units and raises pCO2 by up to 165 µatm. The similarities between Hudson Bay and other Arctic shelf seas suggest these areas are also significantly influenced by terrestrial carbon inputs and transformation.

Highlights

Oceans have slowed the accumulation of CO2 in the atmosphere by absorbing an estimated 30% of the total anthropogenic CO2 emissions since 1750 (Ciais et al, 2013)
Significant advances have been made in understanding specific aspects of the Hudson Bay system (HB) carbon cycle during the last 15 years (ArcticNet research program), including marine primary production, organic carbon delivery and burial, CO2 flux, and aragonite-saturation, but these findings have not, to date, been integrated into an overall picture of carbon cycling in Hudson Bay and its implications for ocean acidification (OA) and CO2 flux
From our budget (Figs. 3–5), we infer that the remineralization of POCterr, DOCterr, and POCmar contribute to ocean acidification and CO2 flux in HB, while export production and PICterr dissolution offset these effects to some extent

Summary

Introduction

Oceans have slowed the accumulation of CO2 in the atmosphere by absorbing an estimated 30% of the total anthropogenic CO2 emissions since 1750 (Ciais et al, 2013). Freshwater dominated, high latitude, northern shelf seas are relatively prone to OA and CO2 outgassing (AMAP, 2017; Granskog et al, 2009; Guéguen et al, 2011; Mundy et al, 2010), due in part to the remineralization of terrestrial organic carbon (OCterr) supplied by rivers and coastal erosion. In the Arctic-outflow shelf sea Hudson Bay, in northern Canada (Fig. 1), strong links between CaCO3 saturation (a measure of the tendency for CaCO3 to dissolve; Azetsu-Scott et al, 2014), CO2 air-sea flux (Else et al, 2008a, 2008b), and freshwater abundance have prompted speculation that CO2 flux and OA are influenced by terrestrial carbon delivery and remineralization. It is the sum total and balance of these changes that will determine the effects of ocean acidification and future air-sea CO2 exchanges in these high-latitude northern seas

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Conclusion