Abstract
Abstract. The Earth's oceans are one of the largest sinks in the Earth system for anthropogenic CO2 emissions, acting as a negative feedback on climate change. Earth system models project that climate change will lead to a weakening ocean carbon uptake rate as warm water holds less dissolved CO2 and as biological productivity declines. However, most Earth system models do not incorporate the impact of warming on bacterial remineralisation and rely on simplified representations of plankton ecology that do not resolve the potential impact of climate change on ecosystem structure or elemental stoichiometry. Here, we use a recently developed extension of the cGEnIE (carbon-centric Grid Enabled Integrated Earth system model), ecoGEnIE, featuring a trait-based scheme for plankton ecology (ECOGEM), and also incorporate cGEnIE's temperature-dependent remineralisation (TDR) scheme. This enables evaluation of the impact of both ecological dynamics and temperature-dependent remineralisation on particulate organic carbon (POC) export in response to climate change. We find that including TDR increases cumulative POC export relative to default runs due to increased nutrient recycling (+∼1.3 %), whereas ECOGEM decreases cumulative POC export by enabling a shift to smaller plankton classes (-∼0.9 %). However, interactions with carbonate chemistry cause opposite sign responses for the carbon sink in both cases: TDR leads to a smaller sink relative to default runs (-∼1.0 %), whereas ECOGEM leads to a larger sink (+∼0.2 %). Combining TDR and ECOGEM results in a net strengthening of POC export (+∼0.1 %) and a net reduction in carbon sink (-∼0.7 %) relative to default. These results illustrate the degree to which ecological dynamics and biodiversity modulate the strength of the biological pump, and demonstrate that Earth system models need to incorporate ecological complexity in order to resolve non-linear climate–biosphere feedbacks.
Highlights
Oceans absorb about a quarter of anthropogenic carbon dioxide emissions, drawing down around 2–3 PgC yr−1 in recent decades (Ciais et al, 2013; Friedlingstein et al, 2019; Gruber et al, 2019)
Our results show that the biological pump weakens by 2100 CE under most scenarios and configurations, but adding temperature-dependent remineralisation (TDR) and trait-based plankton ecology with flexible stoichiometry has strong and opposite impacts on relative biological pump strength
Under the default cGEnIE configuration (BIO+fixed profile remineralisation scheme (FPR)), anthropogenic climate change results in an overall weakening of the biological pump, with global particulate organic carbon (POC) flux falling below pre-industrial levels by 2100 CE by ∼ 6.1 % under RCP4.5 and ∼ 9.8 % under RCP8.5 (Table 2; Figs. 2 and S48 in the Supplement)
Summary
Oceans absorb about a quarter of anthropogenic carbon dioxide emissions, drawing down around 2–3 PgC yr−1 in recent decades (Ciais et al, 2013; Friedlingstein et al, 2019; Gruber et al, 2019). Most POM is remineralised to dissolved carbon and nutrients within the epipelagic mixed layer (∼ 0– 200 m), where the nutrients released are rapidly recycled into “regenerated” production (Dugdale and Goering, 1967), and in the mesopelagic zone (∼ 200–1000 m) below, but up to 4– 12 PgC yr−1 of particulate organic carbon (POC) leaves the surface ocean (Ciais et al, 2013; Dunne et al, 2007; Henson et al, 2011, 2012; Mouw et al, 2016a). Once in the poorly ventilated deep ocean, the surviving POM (most of which is subsequently remineralised) remains on centennial to millennial timescales before being eventually returned to the surface by upwelling, while a tiny fraction of mostly recalcitrant POM is buried in sediment and so sequestered on geological timescales
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call