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Title: Projected decreases in future marine export production: the role of the carbon flux through the upper ocean ecosystem

Here, accurate projections of marine particle export production (EP) are crucial for predicting the response of the marine carbon cycle to climate change, yet models show a wide range in both global EP and their responses to climate change. This is, in part, due to EP being the net result of a series of processes, starting with net primary production (NPP) in the sunlit upper ocean, followed by the formation of particulate organic matter and the subsequent sinking and remineralisation of these particles, with each of these processes responding differently to changes in environmental conditions. Here, we compare future projections in EP over the 21st century, generated by four marine ecosystem models under the high emission scenario Representative Concentration Pathways (RCP) 8.5 of the Intergovernmental Panel on Climate Change (IPCC), and determine the processes driving these changes. The models simulate small to modest decreases in global EP between -1 and -12%. Models differ greatly with regard to the drivers causing these changes. Among them, the formation of particles is the most uncertain process with models not agreeing on either magnitude or the direction of change. The removal of the sinking particles by remineralisation is simulated to increase in the lowmore » and intermediate latitudes in three models, driven by either warming-induced increases in remineralisation or slower particle sinking, and show insignificant changes in the remaining model. Changes in ecosystem structure, particularly the relative role of diatoms matters as well, as diatoms produce larger and denser particles that sink faster and are partly protected from remineralisation. Also this controlling factor is afflicted with high uncertainties, particularly since the models differ already substantially with regard to both the initial (present-day) distribution of diatoms (between 11–94% in the Southern Ocean) and the diatom contribution to particle formation (0.6–3.8 times higher than their contribution to biomass). As a consequence, changes in diatom concentration are a strong driver for EP changes in some models but of low significance in others. Observational and experimental constraints on ecosystem structure and how the fixed carbon is routed through the ecosystem to produce export production are urgently needed in order to improve current generation ecosystem models and their ability to project future changes.« less
Authors:
 [1] ;  [2] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6] ;  [7] ;  [6] ;  [5] ;  [8] ;  [7]
  1. ETH Zurich, Zurich (Switzerland); Princeton Univ., Princeton, NJ (United States)
  2. ETH Zurich, Zurich (Switzerland)
  3. Lab. de Physique des Oceans, Plouzane (France)
  4. Lab des sciences du climat et de l'environnement (LSCE), Gif-sur-Yvette (France)
  5. Woods Hole Oceanographic Institution, Woods Hole, MA (United States)
  6. National Oceanic and Atmospheric Administration/Geophysical Fluid Dynamics Lab., Princeton, NJ (United States)
  7. Helmholtz Centre for Polar and Marine Research, Bremerhaven (Germany)
  8. CNRM, Toulouse (France)
Publication Date:
Type:
Accepted Manuscript
Journal Name:
Biogeosciences (Online)
Additional Journal Information:
Journal Name: Biogeosciences (Online); Journal Volume: 13; Journal Issue: 13; Journal ID: ISSN 1726-4189
Publisher:
European Geosciences Union
Research Org:
ETH Zurich, Zurich (Switzerland). Environmental Physics, Institute of Biogeochemistry and Pollutant Dynamics
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; 54 ENVIRONMENTAL SCIENCES
OSTI Identifier:
1375424