MODIS-based Monthly Dataset of POC Flux in the Bottom of the Global Ocean Euphotic Layer (2003-2018)

The monitoring of particulate organic carbon (POC) flux at the bottom of the euphotic layer in global ocean using remote sensing satellite data plays an important role in clarifying and evaluating the ocean carbon cycle. Based on the in situ POC flux data, this paper evaluated various estimation models. The global ocean POC flux from 2003 to 2018 was calculated using the optimal model, and its temporal and spatial variation characteristics were analyzed. In general, the annual average of global ocean POC flux is about 8.5–14.3 Gt C yr − 1 for period of 2003–2018. In the spatial dimension, the POC flux in the mid-latitude ocean (30–60°) is higher than that in the low-latitude (0–30°). The POC flux in Continental Margins with water depth less than 2000 m accounted for 30% of global ocean, which should receive more attention in global carbon cycle research. In the time dimension, the global POC flux decreases year by year generally, but the POC flux abnormally decreases during El Niño and increases during La Niña. In addition, due to global warming, sea ice melting, and bipolar sea area expansion, POC flux in high-latitude oceans (60–90°) is increasing year by year.

Download Full-text

The Relationship between POC Export Efficiency and Primary Production: Opposite on the Shelf and Basin of the Northern South China Sea

Sustainability ◽

10.3390/su10103634 ◽

2018 ◽

Vol 10 (10) ◽

pp. 3634 ◽

Cited By ~ 5

Author(s):

Teng Li ◽

Yan Bai ◽

Xianqiang He ◽

Xiaoyan Chen ◽

Chen-Tung Chen ◽

...

Keyword(s):

Organic Carbon ◽

South China Sea ◽

Primary Production ◽

South China ◽

Northern South China Sea ◽

Global Ocean ◽

China Sea ◽

Euphotic Layer ◽

Poc Export ◽

The Relationship

Accurate estimation of particulate organic carbon (POC) export efficiency in the euphotic layer is essential to understand the efficiency of the ocean’s biological carbon pump, but field measurements are difficult to conduct and data are sparse. In this study, we investigated the relationship between POC sinking export efficiency and ocean net primary production (NPP) in the euphotic layer of the northern South China Sea (NSCS), with the help of high spatiotemporal coverage satellite-derived NPP. Annual mean POC export efficiency in euphotic zone is 34% for the shelf areas and 24% for the basin of the NSCS in the context of satellite-derived 16-day-composited NPP. Similar to what is generally observed in the global ocean, the POC export efficiency on the shelf areas appears to be strengthened with the increase of NPP. However, in the basin areas, the opposite relationship is observed. That is, the POC export efficiency significantly decreases with the increase of NPP. Seasonal decoupling between NPP and POC export, phytoplankton size structure, grazing by zooplankton, and dissolved organic carbon export might account for the observed negative relationship between the POC export efficiency and NPP in the euphotic layer of basin region. System comparison between shelf and basin would be helpful to promote understanding of the regulation mechanism of POC export in the tropical marginal seas.

Download Full-text

Dynamics of particulate organic carbon flux in a global ocean model

Biogeosciences Discussions ◽

10.5194/bgd-10-14715-2013 ◽

2013 ◽

Vol 10 (9) ◽

pp. 14715-14767 ◽

Cited By ~ 5

Author(s):

I. D. Lima ◽

P. J. Lam ◽

S. C. Doney

Keyword(s):

Organic Carbon ◽

Particulate Organic Carbon ◽

Relative Abundance ◽

Sediment Trap ◽

Euphotic Zone ◽

Transfer Efficiency ◽

Global Ocean ◽

Biogeochemical Model ◽

Test Model ◽

Poc Flux

Abstract. The sinking of particulate organic carbon (POC) is a key component of the ocean carbon cycle and plays an important role in the global climate system. However, the processes controlling the fraction of primary production that is exported from the euphotic zone (export ratio) and how much of it survives respiration in the mesopelagic to be sequestered in the deep ocean (transfer efficiency) are not well understood. In this study, we use a three-dimensional, coupled physical-biogeochemical model (CCSM-BEC) to investigate the processes controlling the export of particulate organic matter from the euphotic zone and its flux to depth. We also compare model results with sediment trap data and other parameterizations of POC flux to depth to evaluate model skill and gain further insight into the causes of error and uncertainty in POC flux estimates. In the model, export ratios are mainly a function of diatom relative abundance and temperature while absolute fluxes and transfer efficiency are driven by mineral ballast composition of sinking material. The temperature dependence of the POC remineralization length scale is modulated by denitrification under low O2 concentrations and lithogenic (dust) fluxes. Lithogenic material is an important control of transfer efficiency in the model, but its effect is restricted to regions of strong atmospheric dust deposition. In the remaining regions, CaCO3 content of exported material is the main factor affecting transfer efficiency. The fact that mineral ballast composition is inextricably linked to plankton community structure results in correlations between export ratios and ballast minerals fluxes (opal and CaCO3), and transfer efficiency and diatom relative abundance that do not necessarily reflect ballast or direct ecosystem effects, respectively. This suggests that it might be difficult to differentiate between ecosystem and ballast effects in observations. The model's skill at reproducing sediment trap observations is equal to or better than that of other parameterizations. However, the sparseness and relatively large uncertainties of sediment trap data makes it difficult to accurately evaluate the skill of the model and other parameterizations. More POC flux observations, over a wider range of ecological regimes, are necessary to thoroughly evaluate and test model results and better understand the processes controlling POC flux to depth in the ocean.

Download Full-text

Dynamics of particulate organic carbon flux in a global ocean model

Biogeosciences ◽

10.5194/bg-11-1177-2014 ◽

2014 ◽

Vol 11 (4) ◽

pp. 1177-1198 ◽

Cited By ~ 42

Author(s):

I. D. Lima ◽

P. J. Lam ◽

S. C. Doney

Keyword(s):

Organic Carbon ◽

Particulate Organic Carbon ◽

Relative Abundance ◽

Sediment Trap ◽

Euphotic Zone ◽

Climate System ◽

Transfer Efficiency ◽

Global Ocean ◽

Test Model ◽

Poc Flux

Abstract. The sinking of particulate organic carbon (POC) is a key component of the ocean carbon cycle and plays an important role in the global climate system. However, the processes controlling the fraction of primary production that is exported from the euphotic zone (export ratio) and how much of it survives respiration in the mesopelagic to be sequestered in the deep ocean (transfer efficiency) are not well understood. In this study, we use a three-dimensional, coupled physical–biogeochemical model (CCSM–BEC; Community Climate System Model–ocean Biogeochemical Elemental Cycle) to investigate the processes controlling the export of particulate organic matter from the euphotic zone and its flux to depth. We also compare model results with sediment trap data and other parameterizations of POC flux to depth to evaluate model skill and gain further insight into the causes of error and uncertainty in POC flux estimates. In the model, export ratios are mainly a function of diatom relative abundance and temperature while absolute fluxes and transfer efficiency are driven by mineral ballast composition of sinking material. The temperature dependence of the POC remineralization length scale is modulated by denitrification under low O2 concentrations and lithogenic (dust) fluxes. Lithogenic material is an important control of transfer efficiency in the model, but its effect is restricted to regions of strong atmospheric dust deposition. In the remaining regions, CaCO3 content of exported material is the main factor affecting transfer efficiency. The fact that mineral ballast composition is inextricably linked to plankton community structure results in correlations between export ratios and ballast minerals fluxes (opal and CaCO3), and transfer efficiency and diatom relative abundance that do not necessarily reflect ballast or direct ecosystem effects, respectively. This suggests that it might be difficult to differentiate between ecosystem and ballast effects in observations. The model's skill in reproducing sediment trap observations is equal to or better than that of other parameterizations. However, the sparseness and relatively large uncertainties of sediment trap data makes it difficult to accurately evaluate the skill of the model and other parameterizations. More POC flux observations, over a wider range of ecological regimes, are necessary to thoroughly evaluate and test model results and better understand the processes controlling POC flux to depth in the ocean.

Download Full-text

On the impact of sea ice in a global ocean circulation model

Annals of Glaciology ◽

10.3189/s0260305500013884 ◽

1997 ◽

Vol 25 ◽

pp. 111-115 ◽

Cited By ~ 3

Author(s):

Achim Stössel

Keyword(s):

Southern Ocean ◽

Sea Ice ◽

Ocean Circulation ◽

General Circulation ◽

Thermohaline Circulation ◽

Circulation Model ◽

Deep Ocean ◽

Global Ocean ◽

Convective Activity ◽

The Impact

This paper investigates the long-term impact of sea ice on global climate using a global sea-ice–ocean general circulation model (OGCM). The sea-ice component involves state-of-the-art dynamics; the ocean component consists of a 3.5° × 3.5° × 11 layer primitive-equation model. Depending on the physical description of sea ice, significant changes are detected in the convective activity, in the hydrographic properties and in the thermohaline circulation of the ocean model. Most of these changes originate in the Southern Ocean, emphasizing the crucial role of sea ice in this marginally stably stratified region of the world's oceans. Specifically, if the effect of brine release is neglected, the deep layers of the Southern Ocean warm up considerably; this is associated with a weakening of the Southern Hemisphere overturning cell. The removal of the commonly used “salinity enhancement” leads to a similar effect. The deep-ocean salinity is almost unaffected in both experiments. Introducing explicit new-ice thickness growth in partially ice-covered gridcells leads to a substantial increase in convective activity, especially in the Southern Ocean, with a concomitant significant cooling and salinification of the deep ocean. Possible mechanisms for the resulting interactions between sea-ice processes and deep-ocean characteristics are suggested.

Download Full-text