S. K. Lauvset

The Nordic Seas carbon budget: Sources, sinks, and uncertainties

[1] A carbon budget for the Nordic Seas is derived by combining recent inorganic carbon data from the CARINA database with relevant volume transports. Values of organic carbon in the Nordic Seas’ water masses, the amount of carbon input from river runoff, and the removal through sediment burial are taken from the literature. The largest source of carbon to the Nordic Seas is the Atlantic Water that enters the area across the Greenland-Scotland Ridge; this is in particular true for the anthropogenic CO2. The dense overflows into the deep North Atlantic are the main sinks of carbon from the Nordic Seas. The budget show that presently 12.3 ± 1.4 Gt C yr −1 is transported into the Nordic Seas and that 12.5 ± 0.9 Gt C yr −1 is transported out, resulting in a net advective carbon transport out of the Nordic Seas of 0.17 ± 0.06 Gt C yr −1 . Taking storage into account, this implies a net air-to-sea CO2 transfer of 0.19 ± 0.06 Gt C yr −1 into the Nordic Seas. The horizontal transport of carbon through the Nordic Seas is thus approximately two orders of magnitude larger than the CO2 uptake from the atmosphere. No difference in CO2 uptake was found between 2002 and the preindustrial period, but the net advective export of carbon from the Nordic Seas is smaller at present due to the accumulation of anthropogenic CO2.

Direct measurements of CO2 flux in the Greenland Sea

[1] During summer 2006 eddy correlation CO2 fluxes were measured in the Greenland Sea using a novel system set‐up with two shrouded LICOR‐7500 detectors. One detector was used exclusively to determine, and allow the removal of, the bias on CO2 fluxes due to sensor motion. A recently published correction method for the CO2‐H2O cross‐correlation was applied to the data set. We show that even with shrouded sensors the data require significant correction due to this cross‐correlation. This correction adjusts the average CO2 flux by an order of magnitude from −6.7 × 10 −2 mol m −2 day −1 to −0.61 × 10 −2 mol m −2 day −1 , making the corrected fluxes comparable to those calculated using established parameterizations for transfer velocity. Citation: Lauvset, S. K., W. R. McGillis, L. Bariteau, C. W. Fairall, T. Johannessen, A. Olsen, and C. J. Zappa (2011), Direct measurements of CO2 flux in the Greenland Sea, Geophys. Res. Lett., 38, L12603, doi:10.1029/2011GL047722.

Constraining Projection-Based Estimates of the Future North Atlantic Carbon Uptake

AbstractThe North Atlantic is one of the major sinks for anthropogenic carbon in the global ocean. Improved understanding of the underlying mechanisms is vital for constraining future projections, which presently have high uncertainties. To identify some of the causes behind this uncertainty, this study investigates the North Atlantic’s anthropogenically altered carbon uptake and inventory, that is, changes in carbon uptake and inventory due to rising atmospheric CO2 and climate change (abbreviated as -uptake and -inventory). Focus is set on an ensemble of 11 Earth system models and their simulations of a future with high atmospheric CO2. Results show that the model spread in the -uptake originates in middle and high latitudes. Here, the annual cycle of oceanic pCO2 reveals inherent model mechanisms that are responsible for different model behavior: while it is SST-dominated for models with a low future -uptake, it is dominated by deep winter mixing and biological production for models with a high future ...

Continued warming, salinification and oxygenation of the Greenland Sea gyre

Abstract The Greenland Sea gyre is one of the few areas where the water column is ventilated through open ocean convection. This process brings both anthropogenic carbon and oxygen from the atmosphere and surface ocean into the deep ocean, and also makes the Greenland Sea gyre interesting in a global perspective. In this study, a combination of ship- and float-based observations during the period 1986–2016 are analysed. Previous studies have shown warming and salinification of the upper 2000 m until 2011. The extended data record used here shows that this is continuing until 2016. In addition, oxygen concentrations are increasing over the entire period. The changes in temperature, salinity, and especially oxygen have been more pronounced since the turn of the century. This period has also been characterised by deeper wintertime mixed-layer depths, linking the warming, salinification and oxygenation to strengthened ventilation in the Greenland Sea gyre after 2000. The results also demonstrate that the strengthened ventilation can be tied to advection of warmer and more saline surface water from the North Atlantic through the Faroe-Shetland Channel. This advection has led to more saline surface waters in the Greenland Sea gyre, which is contributing to the deeper wintertime mixed layers.

Climate response to aerosol geoengineering: a multi-method comparison.

AbstractConsidering the ambitious climate targets of the Paris Agreement to limit global warming to 2 °C, with aspirations of even 1.5 °C, questions arise on how to achieve this. Climate geoengineering has been proposed as a potential tool to minimise global harm from anthropogenic climate change. Here, an Earth System model is used to evaluate the climate response when transferring from a high CO2 forcing scenario, RCP8.5, to a middle-of-the-road forcing scenario, like RCP4.5, using aerosol geoengineering. Three different techniques are considered: stratospheric aerosol injections (SAI), marine sky brightening (MSB) and cirrus cloud thinning (CCT). The climate states appearing in the climate geoengineering cases are found to be closer to RCP4.5 than RCP8.5 and many anthropogenic global warming symptoms are alleviated. All three techniques result in comparable global mean temperature evolutions. However, there are some notable differences in other climate variables due to the nature of the forcings applie...

Can Empirical Algorithms Successfully Estimate Aragonite Saturation State in the Subpolar North Atlantic

The aragonite saturation state (ΩAr) in the subpolar North Atlantic was derived using new regional empirical algorithms. These multiple regression algorithms were developed using the bin-averaged GLODAPv2 data of commonly observed oceanographic variables (temperature (T), salinity (S), pressure (P), oxygen (O2), nitrate (NO3-), phosphate (PO4-3), silicate (Si(OH)4), and pH). Five of these variables are also frequently observed using autonomous platforms, which means they are widely available. The algorithms were validated against independent shipboard data from the OVIDE2012 cruise. It was also applied to time series observations of T, S, P and O2 from the K1 mooring (56.5°N, 52.6°W) to reconstruct for the first time the seasonal variability of ΩAr. Our study suggests: (i) linear regression algorithms based on bin-averaged carbonate system data can successfully estimate ΩAr in our study domain over the 0-3500m depth range (R2=0.985, RMSE= 0.044); (ii) that ΩAr also can be adequately estimated from solely non-carbonate observations (R2=0.969, RMSE=0.063) and autonomous sensor variables (R2=0.978, RMSE=0.053). Validation with independent OVIDE2012 data further suggests that (iii) both algorithms, non-carbonate (MEF=0.929) and autonomous sensors (MEF=0.995) have excellent predictive skill over the 0-3500 depth range; (iv) that in deep waters (>500m) observations of T, S and O2 may be sufficient predictors of ΩAr (MEF=0.913); (iv) the importance of adding pH sensors on autonomous platforms in the euphotic and remineralization zone (<500m). Reconstructed ΩAr at Irminger Sea site, and the K1 mooring in Labrador Sea show high seasonal variability at the surface due to biological drawdown of inorganic carbon during the summer, and fairly uniform ΩAr values in the water column during winter convection. Application to time series sites shows the potential for regionally tuned algorithms, but they need to be further compared against ΩAr calculated by conventional means to fully assess their validity and performance.