Bridging the gaps between particulate backscattering measurements and modeled particulate organic carbon in the ocean

[摘要] Oceanic particulate organic carbon (POC) is a small butdynamic component of the global carbon cycle. Biogeochemical modelshistorically focused on reproducing the sinking flux of POC driven by largefast-sinking particles (LPOC). However, suspended and slow-sinking particles(SPOC, here  100  µ m) dominate the total POC (TPOC) stock,support a large fraction of microbial respiration, and can make sizablecontributions to vertical fluxes. Recent developments in the parameterization of POC reactivity in PISCES (Pelagic Interactions Scheme for Carbon andEcosystem Studies model; PISCESv2_RC) have improved its ability to capture POCdynamics. Here we evaluated this model by matching a global 3D simulationand 1D simulations at 50 different locations with observations made frombiogeochemical (BGC-) Argo floats and satellites. Our evaluation coversglobally representative biomes between 0 and 1000 m depth and relies on (1) a refined scheme for converting particulate backscattering at 700 nm( b bp700 ) to POC, based on biome-dependent POC  /   b bp700 ratios in thesurface layer that decrease to an asymptotic value at depth; (2) a novelapproach for matching annual time series of BGC-Argo vertical profiles toPISCES 1D simulations forced by pre-computed vertical mixing fields; and (3) a critical evaluation of the correspondence between in situ measurements ofPOC fractions, PISCES model tracers, and SPOC and LPOC estimated from highvertical resolution b bp700 profiles through a separation of the baselineand spike signals. We show that PISCES captures the major features of SPOC and LPOC across arange of spatiotemporal scales, from highly resolved profile time series tobiome-aggregated climatological profiles. Model–observation agreement isusually better in the epipelagic (0–200 m) than in the mesopelagic(200–1000 m), with SPOC showing overall higher spatiotemporal correlationand smaller deviation (typically within a factor of 1.5). Still, annual meanLPOC stocks estimated from PISCES and BGC-Argo are highly correlated acrossbiomes, especially in the epipelagic ( r =0.78 ; n =50 ). Estimates ofthe SPOC  /  TPOC fraction converge around a median of 85 % (range 66 %–92 %)globally. Distinct patterns of model–observations misfits are found insubpolar and subtropical gyres, pointing to the need to better resolve theinterplay between sinking, remineralization, and SPOC–LPOC interconversionin PISCES. Our analysis also indicates that a widely used satellitealgorithm overestimates POC severalfold at high latitudes during thewinter. The approaches proposed here can help constrain the stocks, andultimately budgets, of oceanic POC.

[学科分类] 大气科学