Diazotrophy as a key driver of the response of marine net primary productivity to climate change

[摘要] The impact of anthropogenic climate change on marine net primaryproduction (NPP) is a reason for concern because changing NPP will havewidespread consequences for marine ecosystems and their associated services.Projections by the current generation of Earth system models have suggesteddecreases in global NPP in response to future climate change, albeit withvery large uncertainties. Here, we make use of two versions of the InstitutPierre-Simon Laplace Climate Model (IPSL-CM) that simulate divergent NPPresponses to similar high-emission scenarios in the 21st century andidentify nitrogen fixation as the main driver of these divergent NPPresponses. Differences in the way N fixation is parameterised in the marinebiogeochemical component PISCES (Pelagic Interactions Scheme for Carbon and Ecosystem Studies) of the IPSL-CM versions lead to N-fixation ratesthat are either stable or double over the course of the 21st century,resulting in decreasing or increasing global NPP, respectively. Anevaluation of these two model versions does not help constrain future NPPprojection uncertainties. However, the use of a more comprehensive versionof PISCES, with variable nitrogen-to-phosphorus ratios as well as a revisedparameterisation of the temperature sensitivity of N fixation, suggests onlymoderate changes in globally averaged N fixation in the 21st century. Thisleads to decreasing global NPP, in line with the model-mean changes of arecent multi-model intercomparison. Lastly, despite contrasting trends inNPP, all our model versions simulate similar and significant reductions inplanktonic biomass. This suggests that projected plankton biomass may be amore robust indicator than NPP of the potential impact of anthropogenicclimate change on marine ecosystems across models.

[学科分类] 大气科学