title: Rising atmospheric CO2leads to large impact of biology on Southern Ocean CO2uptake via changes of the Revelle factor.
abstract: The Southern Ocean is a key region for global carbon uptake and is characterized by a strong seasonality with the annual CO2uptake being mediated by biological carbon drawdown in summer. Here we show that the contribution of biology to CO2uptake will become even more important until 2100. This is the case even if biological production remains unaltered and can be explained by the decreasing buffer capacity of the ocean as its carbon content increases. The same amount of biological carbon drawdown leads to a more than twice as large reduction in CO2(aq)concentration and hence to a larger CO2gradient between ocean and atmosphere that drives the gas exchange. While the winter uptake south of 44°S changes little, the summer uptake increases largely and is responsible for the annual mean response. The combination of decreasing buffer capacity and strong seasonality of biological carbon drawdown introduces a strong and increasing seasonality in the anthropogenic carbon uptake.
  
  
  CONCLUSIONS
  Decrease of buffer capacity leads to stronger summer CO2uptake in the futureBiology will contribute more to future CO2uptake in Southern OceanSeasonality affects anthropogenic carbon uptake strongly.
authors.affiliation: Alfred Wegener Institut Helmholtz Zentrum für Polar- und Meeresforschung Bremerhaven, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Hauck
authors.affiliation: Alfred Wegener Institut Helmholtz Zentrum für Polar- und Meeresforschung Bremerhaven, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Völker
keywords: anthropogenic carbon; biological carbon draw down; buffer capacity; feedback process; ocean CO2 sink; ocean acidification