Temporal variability of the anthropogenic CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; storage in the Irminger Sea

F F Pérez,M Vázquez-Rodríguez,H Mercier,X A Padín,E Louarn,A F Ríos

doi:10.5194/bg-5-1669-2008

Abstract

Abstract. The anthropogenic CO2 (Cant) estimates from cruises spanning more than two decades (1981–2006) in the Irminger Sea area of the North Atlantic Subpolar Gyre reveal a large variability in the Cant storage rates. During the early 1990's, the Cant storage rates (2.3±0.6 mol C m−2 yr−1) doubled the average rate for 1981–2006 (1.1±0.1 mol C m−2 yr−1), whilst a remarkable drop to almost half that average followed from 1997 onwards. The Cant storage evolution runs parallel to chlorofluorocarbon-12 inventories and is in good agreement with Cant uptake rates of increase calculated from sea surface pCO2 measurements. The contribution of the Labrador Seawater to the total inventory of Cant in the Irminger basin dropped from 66% in the early 1990s to 49% in the early 2000s. The North Atlantic Oscillation shift from a positive to a negative phase in 1996 led to a reduction of air-sea heat loss in the Labrador Sea. The consequent convection weakening accompanied by an increase in stratification has lowered the efficiency of the northern North Atlantic CO2 sink.

Highlights

The ocean is a CO2 sink that during the 1990s has removed 2.2±0.4 Pg C yr−1 from the atmosphere out of the total 8.0±0.5 Pg yr−1 of anthropogenic carbon (Cant) emitted to the atmosphere directly from human activities (Canadell et al, 2007)
In order to evaluate and interpret the variations of Cant rates of storage we have focused on six water masses delimited by the density intervals established following K’07 and Y’08, namely: from the upper 100 m to σθ =27.68 kg m−3 we find the sub-surface layer; The upper LSW (uLSW) is found between 27.68
We found that the largest temporal variability of AOU and %Csaantt is in the cLSW layer, where both variables are highly correlated (R2=0.94)

Summary

Introduction

The ocean is a CO2 sink that during the 1990s has removed 2.2±0.4 Pg C yr−1 from the atmosphere out of the total 8.0±0.5 Pg yr−1 of anthropogenic carbon (Cant) emitted to the atmosphere directly from human activities (Canadell et al, 2007). During the early 1990’s, the strongly positive NAO index forced an impressive and exceptional convection activity down to more than 2000 m (Dickson et al, 1996; Lazier et al, 2002; Hakkinen et al, 2004; Y’08) This resulted in the formation of the thickest layer of cLSW observed in the past 60 years (Curry et al, 1998). Decadal time series of layer thicknesses of both LSW types corroborate that, far from exceptional, uLSW is an important product of the convection activity in the Labrador Sea (K’06) These time series show that the strong formation processes of cLSW in the early 1990’s are the exceptional events.

Dataset and method

Results

Discussion