Projected decreases in future marine export production: the role of the carbon flux through the upper ocean ecosystem
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 p...
Main Authors: | , , , , , , , , , , , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2016-07-01
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Series: | Biogeosciences |
Online Access: | http://www.biogeosciences.net/13/4023/2016/bg-13-4023-2016.pdf |
Summary: | 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 low
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. |
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ISSN: | 1726-4170 1726-4189 |