The impact of sedimentary alkalinity release on the water column CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; system in the North Sea

H Brenner,U Braeckman,F J R Meysman,M Le Guitton

doi:10.5194/bg-13-841-2016

The impact of sedimentary alkalinity release on the water column CO&lt;sub&gt;2&lt;/sub&gt; system in the North Sea

H Brenner, U Braeckman + Show 2 more

Open Access

https://doi.org/10.5194/bg-13-841-2016

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Abstract

Abstract. It has been previously proposed that alkalinity release from sediments can play an important role in the carbonate dynamics on continental shelves, lowering the pCO2 of seawater and hence increasing the CO2 uptake from the atmosphere. To test this hypothesis, sedimentary alkalinity generation was quantified within cohesive and permeable sediments across the North Sea during two cruises in September 2011 (basin-wide) and June 2012 (Dutch coastal zone). Benthic fluxes of oxygen (O2), alkalinity (AT) and dissolved inorganic carbon (DIC) were determined using shipboard closed sediment incubations. Our results show that sediments can form an important source of alkalinity for the overlying water, particularly in the shallow southern North Sea, where high AT and DIC fluxes were recorded in near-shore sediments of the Belgian, Dutch and German coastal zone. In contrast, fluxes of AT and DIC are substantially lower in the deeper, seasonally stratified, northern part of the North Sea. Based on the data collected, we performed a model analysis to constrain the main pathways of alkalinity generation in the sediment, and to quantify how sedimentary alkalinity drives atmospheric CO2 uptake in the southern North Sea. Overall, our results show that sedimentary alkalinity generation should be regarded as a key component in the CO2 dynamics of shallow coastal systems.

Highlights

Coastal seas play a crucial role in the global carbon cycle by connecting the terrestrial, oceanic and atmospheric reservoirs (Regnier et al, 2013)
Depth profiles generally show a decline of pH in all profiled cores, which can be attributed to the release of CO2 resulting from organic matter degradation
The cores from the northern North Sea (NNS) and Skagerrak and the Norwegian Trench (SKNT) were typically characterized by a sub-surface minimum in pH, while the depths of these pH minima matched the corresponding oxygen penetration depth (OPD)

Summary

Introduction

Coastal seas play a crucial role in the global carbon cycle by connecting the terrestrial, oceanic and atmospheric reservoirs (Regnier et al, 2013). High nutrient inputs from land fuel intense primary production and stimulate atmospheric CO2 uptake, while respiration of organic matter exported from terrestrial ecosystems stimulates the release of CO2 in coastal areas (Bozec et al, 2006; Jönsson et al, 2011; Schiettecatte et al, 2007). In addition to these biological sinks and sources, the effect of temperature on the CO2 solubility controls the magnitude and direction of the CO2 exchange between coastal waters and the atmosphere (Kitidis et al, 2012; Borges and Frankignoulle, 2003). The question remains which particular drivers are governing the CO2 dynamics in a given coastal system (Borges and Frankignoulle, 2003)

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